Many inflammatory diseases that are responsible for a majority of deaths are still uncurable, in part as the underpinning pathomechanisms and how to combat them is still poorly understood. Tissue-resident macrophages play pivotal roles in the maintenance of tissue homeostasis, but if they gradually convert to proinflammatory phenotypes, or if blood-born proinflammatory macrophages persist long-term after activation, they contribute to chronic inflammation and fibrosis. While biochemical factors and how they regulate the inflammatory transcriptional response of macrophages have been at the forefront of research to identify targets for therapeutic interventions, evidence is increasing that physical factors also tune the macrophage phenotype. Recently, several mechanisms have emerged as to how physical factors impact the mechanobiology of macrophages, from the nuclear translocation of transcription factors to epigenetic modifications, perhaps even DNA methylation. Insight into the mechanobiology of macrophages and associated epigenetic modifications will deliver novel therapeutic options going forward, particularly in the context of increased inflammation with advancing age and age-related diseases. We review here how biophysical factors can co-regulate pro-inflammatory gene expression and epigenetic modifications and identify knowledge gaps that require urgent attention if this therapeutic potential is to be realized.

Despite the significant progress made in medicine, we still struggle today with treating many long term, progressive diseases that are typically accompanied by chronic inflammatory processes. As the clinical focus historically has been on organ-specific diseases, medicine was compartmentalized along organ-specific divisions, which presents challenges to recognizing generic pathogenic mechanisms. Even though organ-specific cell niches have distinct biochemical and biophysical characteristics, inflammatory processes are at the core of many chronic diseases and common pathomechanisms are now emerging. The importance of understanding the role of biomechanical signals in the inflammatory status of cells, including macrophages and fibroblasts, is exemplified by the impact of inflammation in human ageing and age-related disease. Advancing age is accompanied by an increase in systemic inflammation, termed inflammageing,1 which predisposes to several age-related diseases with an inflammatory component, including cardiovascular disease, non-healing post injury, Alzheimer's disease, and cancer.2 

The term “inflammation” refers to a cascade of events that often starts with an infectious challenge or a sterile injury that activates immune cells, notably macrophages, to produce a range of soluble mediators (cytokines) that mediate the immune system response. Eventually, this inflammatory response is actively terminated to ensure homeostasis and the healing of tissue, i.e., “resolution of inflammation.”3 Lipopolysaccharides (LPS) are frequently used as immune cell activators for in vitro cell culture experiments, as they mimic the interaction of immune cells, including macrophages, with the cell wall of gram-negative bacteria. Macrophages, the major cellular drivers of the inflammatory process, originate from two distinct lineages:4,5 tissue resident macrophages are seeded into organ tissues during early embryonic development and self-maintain locally throughout adult life with minimal contribution from circulating monocytes, whereas blood monocyte-derived macrophages home to sites of injury or infection to respond to the challenge. These are short-lived cells and originate from adult hematopoietic stem cells. Macrophages play pivotal roles in the maintenance of tissue homeostasis achieved through their differentiation into two broad phenotypes, M1 pro-inflammatory macrophages and M2 macrophages, which have a more anti-inflammatory function. While there is a broad spectrum of intermediate states between M1 and M2,6,7 the graded balance of these main phenotypes influences the chronicity and outcomes of the inflammatory response.7 For example, if macrophages persist in a pro-inflammatory M1 phenotype, they can contribute to chronic inflammation and fibrosis;8,9 in contrast through their functions in the clearance of apoptotic cells and cellular debris and secretion of anti-inflammatory cytokines, the M2 macrophages contribute to the resolution of inflammation to reestablish tissue homeostasis.10 In addition to macrophages that display the M1 or M2 phenotype, also a variety of organ-specific subsets exists.11 

While niche-specific transcriptomic and epigenetic profiles as well as secretome are well documented for multiple tissues and various physiological contexts, cell phenotypes are also determined by a range of biophysical factors and stimuli.12–20 Micro- and nanofabricated materials and devices have allowed researchers to probe how cell behavior and function depend on the physical properties of their microenvironment, including flow, stiffness of the microenvironment, extracellular matrix (ECM) tethering to the substrate, the ECM viscoelastic properties, topography, and spatial confinement as well as tensile or compressive forces12–46 [Fig. 1(a)]. The role of the tissue microenvironment is well recognized in mechanobiology and is particularly well studied for mesenchymal cells, as physical cell-cell communication and between cells and their extracellular niche environments are also crucial to direct cell fate.15,20–28,30,32,34,36,39–42,47–51 Cells sense mechanical properties of their environment by pulling on it or pushing against it. Much progress has been made in the molecular understanding of how mechanical stimuli are sensed and transduced by mesenchymal cells into biochemical signals (mechanotransduction), which then regulates gene transcription processes and subsequently cell phenotype.30,32,34,36,39–42

FIG. 1.

Multifactorial tissue specific physical properties and selected bioengineering tools to elicit their respective roles on regulating cell signaling and function. (a) The stiffness is different for different organs. Organ cartoons reproduced with permission from Jain et al., Annu. Rev. Biomed. Eng. 21, 267–297 (2019). Copyright 2019 Annual Reviews, Inc. (b) Microfabricated cell niches to probe cell behavior under controlled conditions to recreate selected physical properties of cell-niches. Cartoons adapted and modified from Refs. 12, 33, 46, and 74. Reproduced with permission from N. Jain and V. Vogel, Nat. Mater. 17, 1134–1144 (2018). Copyright 2018 Springer Nature Limited. Reproduced with permission from Elacqua et al., PLoS One 13, e0195664 (2018). Copyright 2018 Authors, licensed under a Creative Commons Attribution (CC BY) license. Reproduced with permission from N. J. Walters and E. Gentleman, Acta Biomater. 11, 3–16 (2015). Copyright 2015 Authors, licensed under a Creative Commons Attribution (CC BY) license.

FIG. 1.

Multifactorial tissue specific physical properties and selected bioengineering tools to elicit their respective roles on regulating cell signaling and function. (a) The stiffness is different for different organs. Organ cartoons reproduced with permission from Jain et al., Annu. Rev. Biomed. Eng. 21, 267–297 (2019). Copyright 2019 Annual Reviews, Inc. (b) Microfabricated cell niches to probe cell behavior under controlled conditions to recreate selected physical properties of cell-niches. Cartoons adapted and modified from Refs. 12, 33, 46, and 74. Reproduced with permission from N. Jain and V. Vogel, Nat. Mater. 17, 1134–1144 (2018). Copyright 2018 Springer Nature Limited. Reproduced with permission from Elacqua et al., PLoS One 13, e0195664 (2018). Copyright 2018 Authors, licensed under a Creative Commons Attribution (CC BY) license. Reproduced with permission from N. J. Walters and E. Gentleman, Acta Biomater. 11, 3–16 (2015). Copyright 2015 Authors, licensed under a Creative Commons Attribution (CC BY) license.

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In contrast, current research in immune cell biology is still dominated by a cell centric view, rather than taking a more holistic view that considers how cells react to both biochemical and biophysical microenvironmental factors. With respect to immune cells, T cell activation is affected by substrate stiffness37,43 and nanoporous substrates,29 and macrophage phenotype is greatly impacted by a multitude of different physical factors14,33 (as discussed in detail below in Secs. II–V). Far less is known about the mechanobiology of other immune cells, including B cells38,52 and dendritic cells.31,35 What has been revealed is that various mechanotransduction-induced signaling pathways trigger the translocation of transcription factors from the cytoplasm to the nucleus,53–56 including myocardin related transcription factor-A (MRTF-A), which is released from actin upon stress fiber assembly and yes-associated protein (YAP)/TAZ whose dephosphorylation is induced in response to the opening of mechanosensitive ion channels, including piezo channels.57–63 Beyond regulating the transcription of genes, nuclear translocation of transcription factors also triggers various epigenetic modifications as reviewed further below.

Despite this rapid emergence of mechanobiology and the study of underpinning mechanisms, knowledge gaps exist as to how these mechanisms relate to chronic inflammatory diseases and, in particular, the relevance to inflammatory macrophages. How to intervene to reestablish homeostasis after infection, injury or pathological tissue transformation is still one of the biggest challenges of regenerative medicine. As the field of immunology has only recently started to appreciate the impact of physical factors on macrophage phenotype regulation, a review of the literature is provided here to summarize what is known of how biophysical factors can regulate inflammatory gene expression and macrophage polarization in the context of inflammation and disease, and what research questions require urgent attention. Current evidence highlights already how the changing landscape of biomechanical signals during inflammation directs several inflammatory biochemical intermediates in response to pro-inflammatory activation, which then converge onto transcriptional and epigenetic modifications (histone modifications and DNA methylation) and changes in the chromosome landscape as reviewed here. As such these changes could be either modulated by altering the biophysical properties of the microenvironment or be targeted by specific drugs modulating mechanosensitive signals. Since these nuclear events and epigenetic modifications have previously been shown in other cell types to be dependent on the nucleoskeleton or nuclear meshwork, the data taken together also suggest the existence of an unknown and yet to be explored role of the nuclear meshwork in driving inflammatory activation of macrophages, which requires urgent attention. Even though recent reviews have individually provided a glimpse onto these regulatory events,14,33,64 a comprehensive review is missing in the field.

Organ-specific cell niches are complex and comprise many cell types, all in close proximity to each other. Each organ is characterized by organ-specific cell types that are supported and surrounded by stromal cells common to most organs, including fibroblasts as well as immune cells that have sentinel functions in sensing injury and infection. This latter group includes primarily tissue resident macrophages and macrophages derived from activated, homed-in circulating macrophages. Other common cellular tissue residents can include adipocytes as active endocrine producers, as well as perivascular mesenchymal stem and endothelial cells. These cell societies communicate with each other biochemically and physically. They respond to global metabolite composition65 as well as to localized autocrine and paracrine signaling to which all cell types contribute. Most importantly in the context of this review, macrophages can sense physical cues in their environment, including soft or more rigid substrates66–70 or microstructured environments,12,13,71,72 or cyclic strain,73 and respond in a mechanosensitive manner [Fig. 1(b)].

Cell niches are not only characterized by the resident cells but also have characteristic ECM compositions, assembled into complex meshworks of nanofibrils that are undergoing constant remodeling by the synergistic actions of various cell types. Some of these cells synthesize the ECM or its components, while they themselves or others contribute by secreting cross-linking and proteolytic enzymes.75,76 Although most of the complex organ-specific niches serve highly specialized functions, inflammatory processes or pathologies of different organ types are likely based on common principles and shared mechanisms. As the complex secretome of macrophages is shifting in response to external stimuli, the intercellular niche communication is tuned bidirectionally. The secretome of macrophages exposed to calcium oxalate crystals, for example, is shifted toward proteins involved mainly in “inflammatory response” and “fibroblast activation” and activates the expression of alpha Smooth Muscle Actin (a-SMA) in renal fibroblasts.77 Vice versa, the secretome of preconditioned mesenchymal stem cells drives polarization and reprogramming of M2a macrophages toward an interleukin (IL)-10-producing phenotype, thus improving their regenerative and immunomodulatory capacities78 and in cancer. The tumor microenvironment is rich in crosslinked collagen79 and other ECM components, creating niches for tumor-promoting macrophages.80,81 This bidirectional communication can also explain pharmacological side effects or be exploited therapeutically. Naïve, M1, and M2 macrophages are affected by the antipsychotic drug Olanzapine, known to cause metabolic side effects by promoting obesity and diabetes, as the macrophage-derived secretome is sufficient to confer olanzapine-mediated insulin resistance in human adipocytes.82 Macrophages thereby play key roles in shaping healthy cell niches, as well as the tumor microenvironment, tumor immunity, and the response to immunotherapy.4,83 Fibrotic pathologies84,85 and ageing86,87 are also associated with major changes in the ECM composition and crosslinking, which alters the physical properties of the cell niches, to which the cells respond in a negative feedback loop. This ultimately leads to a loss of organ function. Indeed, the “big five” contributors to fibrotic pathologies of a range of organs have been proposed to include: macrophages, myofibroblasts, matrix, mechanics, and miscommunication.88 Yet, how the synergy of physical and biochemical stimuli together orchestrate cell niche functions is not fully understood. This is particularly striking when we consider that the failure of proinflammatory macrophages to revert to anti-inflammatory macrophages is associated with the onset of fibrotic diseases.88,89

More than a century ago, it was first reported that brain-resident macrophages, i.e., microglia, have a characteristic morphology defined by a small cell body with fine ramified processes [Fig. 2(a), left].90 The first hand-drawn images of resting and activated microglia were sketched by Merzbacher in 1909, which interestingly suggested significant changes in microglia morphology upon inflammatory activation.90 The LPS-activated microglia were found to be rounder and flatter with a pancake-like morphology [Fig. 2(a), right].90 These hand-drawn sketches also suggested an increased spreading area upon pro-inflammatory activation with LPS. In the absence of bioengineering tools and techniques at that time it was not possible to deduce any potential regulatory and functional link between changes in microglia morphology and their inflammatory state. It took the scientific community more than a century to finally establish these links.

FIG. 2.

Macrophage activation leads to changes in cellular morphology, actin polymerization, and nuclear translocation of transcription factors: (a) early hand-drawn sketches of unactivated microglia (left) and activated microglia (right) show characteristic ramified and flat morphology, respectively (permissions are not needed).90 (b) Representative images of (i) control (M0), (ii) LPS-treated (M1), and (iii) IL-4/IL-13-treated (M2) bone marrow derived macrophages (BMDMs) stained for F-actin (green).12 (c) Cell spreading area vs total F-actin content in LPS-treated BMDMs.12 (d) Time course changes in cell spreading areas, nuclear levels of MRTF-A and F/G-actin ratios in LPS-treated BMDMs for different periods of time.12 Data adapted and modified from Ref. 12. Reproduced with permission from N. Jain and V. Vogel, Nat. Mater. 17, 1134–1144 (2018). Copyright 2018 Springer Nature Limited.

FIG. 2.

Macrophage activation leads to changes in cellular morphology, actin polymerization, and nuclear translocation of transcription factors: (a) early hand-drawn sketches of unactivated microglia (left) and activated microglia (right) show characteristic ramified and flat morphology, respectively (permissions are not needed).90 (b) Representative images of (i) control (M0), (ii) LPS-treated (M1), and (iii) IL-4/IL-13-treated (M2) bone marrow derived macrophages (BMDMs) stained for F-actin (green).12 (c) Cell spreading area vs total F-actin content in LPS-treated BMDMs.12 (d) Time course changes in cell spreading areas, nuclear levels of MRTF-A and F/G-actin ratios in LPS-treated BMDMs for different periods of time.12 Data adapted and modified from Ref. 12. Reproduced with permission from N. Jain and V. Vogel, Nat. Mater. 17, 1134–1144 (2018). Copyright 2018 Springer Nature Limited.

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As for tissue resident macrophages, also the pro-inflammatory activation of bone marrow derived macrophages (BMDMs) with LPS leads to major morphological changes: with a delay of a few hours, the cell spreading area increases significantly and the macrophages transition from an elongated to a more rounded cell shape [Fig. 2(b)],12 which is concomitant with enhanced actin polymerization [Fig. 2(c)]. Interestingly, removal of LPS restores the resting morphology, although over a longer timescale, further confirming a functional link between macrophage morphology and pro-inflammatory phenotype.12 In contrast, pro-healing, anti-inflammatory differentiation of macrophages to an M2 phenotype, using interleukin (IL)-4/IL-13, results in elongated morphologies13 [Fig. 2(b)]. Elongation factor, defined as the length of the longest axis divided by the length of the shortest axis across the cell nucleus, increases more than threefold in M2 macrophages.

With the advent of bioengineering tools and techniques, we can now address in detail the key question: Does macrophage activation first lead to a change of gene expression profile which is then followed by a change in cell morphology, or vice versa? Recent data show that certain cell morphologies, as imposed by spatial constraints, can help in stabilizing macrophage phenotype. To ask whether staging a fully fledged inflammatory response requires actin polymerization, bioengineered tools were used to spatially confine macrophages on micropatterned adhesive islands of defined sizes and shapes. For example, the production of inflammatory cytokines including IL-6 and tumor necrosis factor-alpha (TNF-α) was greatly reduced when the spreading of BMDMs was restricted by culturing them on adhesive islands of appropriate size, in hemispherical pores, or in a close-packed cell layer.12 This shows nicely that imposing spatial confinement can indeed modulate the pro-inflammatory response of macrophages. Importantly, using fibronectin coated stripes or nanofibers that can cause cell elongation, it has been shown that BMDMs can be polarized toward the M2 phenotype without any additional stimulation with IL-4/IL-13.13,82,83 Furthermore, by confining macrophages in 2D and 3D substrates, our lab has shown that the expression of pro-inflammatory secondary response genes (IL-6, iNOS, CXCL9), necessary for prolonging the process of inflammation, is dependent on macrophage spreading.12 Moreover, these spatial constraints can dampen or synergize with chemical stimulants to decrease or increase the inflammatory phenotype of macrophages. These data suggest that morphological cues may be used to complement or dampen the effects of cytokines or other pro-inflammatory factors already present in the cell microenvironment.

These findings are significant, as tissue resident macrophages are found in a range of tissue-specific sizes and shapes, surrounded by niches with tissue-specific characteristics including stiffness, ECM composition, fiber density, and fiber tension.91 While M1 macrophages greatly increase in circularity and cell area upon activation in vitro,12 M2 macrophages elongate with little change in the cell spreading area.12,13 Such changes may have relevance to disease pathogenesis, for example, macrophage elongation is also seen in certain disease states such as atherosclerosis.92,93 In addition to topographical cues, physiological levels of interstitial flow are also able to stabilize the M2-like phenotype.94 Also substrate stiffness tunes M2 activation, whereby cells on softer substrates show enhanced M2-like phenotypes as regulated by RhoGTPase signaling.68 While many other effects have described how physical factors impact macrophage behavior and phenotype,14,33,95,96 our emphasis here is to ask how selected physical factors impact the cytokine gene transcription machinery of macrophages. For example, what is the impact of environmentally imposed elongation on the M1 phenotype? One report suggested that enforcing cell elongation has only a limited effect on the M1 response,12 whereas another report suggests that elongation protects macrophages from M1 polarization by inflammatory stimuli.13 These differential findings clearly suggest the need for further research.

Changes in cellular morphology are coupled with a reorganization of the cytoskeleton. As the first fragile contacts, i.e., focal adhesions, become mechanically reinforced, assembly of a mature cytoskeleton progresses rapidly, guided by the spatial locations of the point of contact to the extracellular matrix. Major insights into these processes were gained via research on mesenchymal cells through the micro- and nanofabrication of adhesive contacts. These studies illustrated how the cytoskeletal filaments are bundled along with the primary directions of force transmission through the cell, as imposed by the spatial presentation of environmental anchor points.42,97–99 Microcontact printing of adhesive islands revealed that changes in fibroblast cell morphology are associated with the reorganization of the cytoskeletal architecture.100,101 For example, a triangular fibroblast shows triangular pockets of polymerized F-actin around the nucleus whereas a circular cell shows circular rings of F-actin around the nucleus.100 However, establishing such connections in macrophages is more difficult as macrophages do not have actomyosin fibers. The majority of studies have largely focused on quantifying the levels of F-actin and myosin-II contractility during macrophage activation [Fig. 2(c)]. An increase in the cell spreading area during pro-inflammatory activation of macrophages is coupled with a significant increase in actin polymerization and formation of actin microfilaments (F-actin) within 3–6 h post-LPS treatment [Fig. 2(c)].12 Monomeric actin (G-actin) constitutes about 60% of cellular actin prior to LPS stimulation, which increases the F/G actin ratio and, thus, shifts the balance toward actin polymerization [Fig. 2(c)].12 These increased polymerized actin levels go along with increases of the cell size; thus, spatial confinement of macrophages restricts their spreading and reduces actin polymerization.12 

Initiating actin polymerization involves the phosphorylation of paxillin on tyrosine 118 and Neural Wiskott-Aldrich syndrome protein (N-WASP) on serine 484/485, two actin-regulatory proteins important for actin polymerization and reorganization.102 Importantly, an increase in actin-polymerization is necessary to elicit the pro-inflammatory response of macrophages. The depolymerization of actin, using pharmacological inhibitors like latrunculin-A, results in a significant decrease in the expression of pro-inflammatory genes and cytokines and is also coupled with a significant decrease in the cell spreading area.12 Similar experiments using cytochalasin-D and other drugs targeting actin polymerization and pathways have established that the actin cytoskeleton is a key mediator in the process of macrophage proinflammatory activation.103–105 Given the mechanosensitive nature of actin and the importance of actin polymerization in regulating the staged response of macrophages, it should be noted that the levels of p-myosin light chain upon LPS stimulation, i.e., a measure of cell contractility, remained unchanged during macrophage pro-inflammatory activation.12 Even though the total cellular contractility was found to be similar, traction force microscopy (TFM) suggested higher traction forces in M1 macrophages upon LPS/interferon (IFN) γ stimulation, as compared to M0 mouse BMDMs.106 It should be noted that in human BMDMs, an opposite effect was found using TFM, i.e., that M1 macrophages generate significantly less force than M0 or M2 macrophages,107 suggesting that a careful and detailed analysis of macrophage contractility as a function of stimulants and substrate properties needs to be performed. Also, the details of how mechanical forces and spatial cues reinforce and reorganize the cytoskeleton in macrophages have still not been fully characterized.

Actin polymerization has been shown to drive macrophage pro-inflammatory activation by regulating the nuclear-to-cytoplasmic shuttling of critical transcription factors.12,108 The transcription factor MRTF-A binds to G-actin in the cytoplasm, and the onset of actin polymerization leads to its release and results in its nuclear translocation. Upon complexation with the serum response factor (SRF), the complex drives the expression of various genes,109 yet the role of the MRTF-A-SRF complex has only recently been probed during macrophage activation12,110 (Fig. 3). Using MRTF-A knockout (KO) or SRF-KO BMDMs revealed that the MRTF-A-SRF complex positively drives the expression of critical pro-inflammatory genes like IL-6 and Nos2 (Ref. 12) (Fig. 3). Mechanistically, the regulation is mediated via recruitment of the nuclear factor κB (NF-κB), another critical transcription factor110 in the promoter region of pro-inflammatory genes, which requires MRTF-A. Another, central mechano-sensitive transcription factor complex, yes-associated protein (YAP), has recently been shown to promote the pro-inflammatory response by increasing IL6 expression (Fig. 3), while concomitantly decreasing pro-healing, anti-inflammatory responses by decreasing arginase-I expression.108 LPS activation of macrophages leads to a higher accumulation of YAP in the nucleus, which depends on actin polymerization, and depolymerization of actin inhibits nuclear translocation of YAP, thereby reducing the secretion of pro-inflammatory cytokines like TNF-α108 (Fig. 3). Again, this influence was independent of myosin-II phosphorylation. Vice versa, genetic deletion of YAP/TAZ leads to impaired pro-inflammatory activation of macrophages. It is also important to note that unlike in fibroblasts, nuclear translocation of NF-κB is not sensitive to changes in macrophage spreading, suggesting cell-specific mechanosensitivity of certain classes of transcription factors.12,100

FIG. 3.

Mechano-regulation of the pro-inflammatory transcription in macrophages: Chemical and metabolic signaling pathways implicated in M1 macrophage polarization. An initial stimulus leads to the activation and nuclear translocation of sequence-specific transcription factors that eventually mediate changes in the transcriptional output. Note that conventional signaling diagrams do not consider the possibility that some of the signaling processes are mechanoregulated. Various signaling steps were recently described to be regulated by cellular sensing of physical factors which we marked here in red. This includes recently uncovered mechanosensitive transcription factors like MRTF-A and YAP, and how they are under the regulation of integrins and piezo channels. Abbreviations—CSF: colony-stimulating factor; GM-CSF: granulocyte macrophage colony-stimulating factor; IFN: interferon; IL: interleukin; IRF: interferon-regulatory factor; JAK: Janus kinase; MSK: mitogen- and stress-activated kinase; NF-κB: nuclear factor κB; Nos2: nitric oxide synthase 2; STAT: signal transducer and activator of transcription; TLR4: toll-like receptor 4; MRTF-A: myocardin related transcription factor-A; YAP: yes-associated protein 1. Cartoon adapted and modified from.111 Permission obtained from T. Lawrence and G. Natoli, Nat. Rev. Immunol. 11, 750–761 (2011). Copyright 2011 Springer Nature Limited.

FIG. 3.

Mechano-regulation of the pro-inflammatory transcription in macrophages: Chemical and metabolic signaling pathways implicated in M1 macrophage polarization. An initial stimulus leads to the activation and nuclear translocation of sequence-specific transcription factors that eventually mediate changes in the transcriptional output. Note that conventional signaling diagrams do not consider the possibility that some of the signaling processes are mechanoregulated. Various signaling steps were recently described to be regulated by cellular sensing of physical factors which we marked here in red. This includes recently uncovered mechanosensitive transcription factors like MRTF-A and YAP, and how they are under the regulation of integrins and piezo channels. Abbreviations—CSF: colony-stimulating factor; GM-CSF: granulocyte macrophage colony-stimulating factor; IFN: interferon; IL: interleukin; IRF: interferon-regulatory factor; JAK: Janus kinase; MSK: mitogen- and stress-activated kinase; NF-κB: nuclear factor κB; Nos2: nitric oxide synthase 2; STAT: signal transducer and activator of transcription; TLR4: toll-like receptor 4; MRTF-A: myocardin related transcription factor-A; YAP: yes-associated protein 1. Cartoon adapted and modified from.111 Permission obtained from T. Lawrence and G. Natoli, Nat. Rev. Immunol. 11, 750–761 (2011). Copyright 2011 Springer Nature Limited.

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While the activity of most of these transcription factors during pro-inflammatory activation was characterized downstream of toll-like receptor 4 (TLR4) signaling, the major receptor that mediates LPS signaling,111 there is growing evidence that other surface molecules,112 mainly integrins113 and ion-channels like piezo-1,114 co-regulate the activity of these mechanosensitive transcription factors like MRTF-A and YAP (Fig. 3). As the piezo channel opening is regulated by membrane tension, which will change as cells bind and pull on their environment. It is expected that blocking integrin signaling decreases LPS induced production of TNF-α as well.113 Piezo1 activity promotes Interferon-γ and LPS-induced inflammatory and suppresses IL-4 and IL-13-induced healing responses,114 illustrating membrane-mediated crosstalk between these different membrane receptors, i.e., TLR4, integrins, and ion-channels.113,115 How the crosstalk between these receptors and transcription factors are regulated by the physical properties of macrophage niches in different tissue environments is unclear (Fig. 3), and understanding this will help in probing whether the physical properties of these niches tune macrophage differentiation and stabilize tissue-resident macrophage phenotypes.

Contrary to pro-inflammatory macrophage activation, the organization and levels of actin polymerization during pro-healing M2 macrophage activation are still not well characterized. Even though certain reports suggest that inhibiting actin polymerization and myosin contractility significantly reduce M2 activation, without altering their cell elongation,13 the specific role of the cytoskeleton during M2 activation needs further clarification.

As cytoskeletal components mechanically couple the cell adhesions of the plasma membrane to the cell nucleus, the nucleus can get mechanically strained leading or at least contributing to its remodeling. In fibroblast and epithelial cells, highly tensed actin stress fibers, called the actin-cap,116–118 span the cell nucleus and compress it,99,117 which has a profound impact on the architecture of the nuclear lamina119 and the nucleus117 [Fig. 4(a)]. This is largely mediated via force transmission from extracellular anchor points via the cytoskeletal filaments, including intermediate filaments, to the nucleus, where Linker of Nucleoskeleton and Cytoskeleton (LINC) complexes couple the cytoskeletal filaments to the nuclear lamina [Fig. 4(b)].120 These LINC proteins establish a direct physical linkage from the cytoskeleton via the nuclear lamina to chromatin and, thus, play a pivotal role in nuclear mechanosensing [Fig. 4(b)].120,121 The inner nuclear membrane is thereby linked to the nuclear lamina via a meshwork of type V intermediate filaments, the nuclear lamins, and associated proteins.122 The nuclear lamina interacts with chromatin and tethers heterochromatin to the nuclear periphery. The term “heterochromatin” was coined by Emil Heitz to distinguish regions that remained strongly stained throughout the cell cycle from those that became invisible during interphase.123 Heterochromatin is associated with a dense chromatin structure, where genes are thought to be inaccessible to transcriptional factors necessary for gene activation. The main mammalian lamins are lamin-A and C (also called lamin-A/C) and the evolutionarily older lamins B1 and B2.122 Cryo-electron tomography insights into the molecular arrangement of the nuclear lamina reveal a fiber-like morphology of lamin networks decorated with globules, forming filaments that are packaged into a 14 nm thick layer (the lamina).124–126 Disruptions of either the LINC complex or its physical coupling to the nuclear lamina or of lamin self-assembly into filaments by point mutations directly impinge on the nuclear architecture leading to multiple disease conditions collectively known as laminopathies.127 

FIG. 4.

Physical coupling of the actin cap and the cytoskeleton to the nuclear lamina via the LINC complex proteins: (a) color coded height map of actin. Blue, green, and yellow colors represent the actin structure at the basal, middle, and apical plane (paxillin in red). Middle panel: Zoom in view of actin at apical, middle, and basal plane. Right panel: 3D reconstruction of actin and nucleus. Cartoon adapted and modified from.118 Reprinted from Li et al., Biomaterials 35, 961–969 (2014). Copyright 2014 Elsevier. (b) LINC complexes consist of KASH-domain-containing nesprin isoforms on the outer nuclear membrane (ONM) that are connected to the cytoplasmic actin filaments, intermediate filaments, and microtubules. SUN proteins interact with the nuclear lamina decorating the inner nuclear membrane (INM). SUN proteins and nesprins are connected through KASH-SUN interactions in the perinuclear space. Cartoon adapted and modified.120 Reproduced with permission from Sneider et al., Cell Adhes. Migr. 13, 50–62 (2019). Copyright 2019 Authors, licensed under a Creative Commons Attribution (CC BY) license. (c) Representative image of a single BMDM, stained for F-actin and nuclei, showing the absence of a conventional actin-cap.12 Scale bars, 10 μm. Physical connections between nucleus and cytoplasm via LINC complex are not characterized in macrophages. Cartoons adapted and modified from.12 Reproduced with permission from N. Jain and V. Vogel, Nat. Mater. 17, 1134–1144 (2018). Copyright 2018 Springer Nature Limited.

FIG. 4.

Physical coupling of the actin cap and the cytoskeleton to the nuclear lamina via the LINC complex proteins: (a) color coded height map of actin. Blue, green, and yellow colors represent the actin structure at the basal, middle, and apical plane (paxillin in red). Middle panel: Zoom in view of actin at apical, middle, and basal plane. Right panel: 3D reconstruction of actin and nucleus. Cartoon adapted and modified from.118 Reprinted from Li et al., Biomaterials 35, 961–969 (2014). Copyright 2014 Elsevier. (b) LINC complexes consist of KASH-domain-containing nesprin isoforms on the outer nuclear membrane (ONM) that are connected to the cytoplasmic actin filaments, intermediate filaments, and microtubules. SUN proteins interact with the nuclear lamina decorating the inner nuclear membrane (INM). SUN proteins and nesprins are connected through KASH-SUN interactions in the perinuclear space. Cartoon adapted and modified.120 Reproduced with permission from Sneider et al., Cell Adhes. Migr. 13, 50–62 (2019). Copyright 2019 Authors, licensed under a Creative Commons Attribution (CC BY) license. (c) Representative image of a single BMDM, stained for F-actin and nuclei, showing the absence of a conventional actin-cap.12 Scale bars, 10 μm. Physical connections between nucleus and cytoplasm via LINC complex are not characterized in macrophages. Cartoons adapted and modified from.12 Reproduced with permission from N. Jain and V. Vogel, Nat. Mater. 17, 1134–1144 (2018). Copyright 2018 Springer Nature Limited.

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In contrast to mesenchymal cells, blood born cells often must crawl through tiny constrictions to reach their destiny, including transmigration through the endothelium, which requires that they undergo extreme cellular and nuclear deformations.128–130 Even though the functional and regulatory role of the LINC complex has been extensively studied for mesenchymal cells and more recently for immune cells, their potential role in regulating macrophage homeostasis vs their inflammatory or pro-healing responses are still largely unknown [Fig. 4(c)]. As the assembly of conventional actin stress fibers has so far not been described for macrophages, how they establish a physical connection between cytoskeleton and nuclear lamina is not known. As the nuclear architecture and the nuclear lamina regulates gene expression by controlling the three-dimensional organization of genes and their distal regulatory sequences,131–140 the intra-nuclear space and chromosome rearrangement during macrophage differentiation, polarization, and inflammatory activation has yet to be revealed.

As cell size and nuclear size are positively correlated, it has been shown that pro-inflammatory M1 activation of macrophages results in a significant increase in the nuclear projection area and nuclear volume.12 In contrast, during M2 activation, macrophage elongation correlates with an increased nuclear aspect ratio.12 LPS induced increases in nuclear projection area and volume are dependent on the level of polymerization of actin.12 Depolymerization of actin in LPS activated BMDMs results in a significant decrease in nuclear size.12 Lamin-A/C is abundantly expressed in most differentiated cells, but the amount of lamin-A/C varies greatly between immune cell types with macrophages and dendritic cells (another early initiator of inflammation) expressing high levels, but resting T and B cells expressing low to barely detectable amounts.141–144 Research on the role of lamin-A/C during inflammation has largely been focused on T cells, which show a significant upregulation of lamin-A/C upon activation.145 Lamin-A expression accelerates T cell receptor (TCR) clustering and leads to enhanced downstream signaling, including extracellular signal-regulated kinase 1/2 (ERK1/2) signaling as well as increased target gene expression contributing to T-cell activation.144 

Differentiation of rat and human macrophages has been shown to be accompanied by increased expression of lamin-A/C,143 which also increases during the differentiation of human peripheral blood monocytes into macrophages.146 Even though these studies have characterized the levels of lamin-A/C in different macrophage types, the central question which needs to be addressed is whether lamin-A/C expression has any potential role during macrophage inflammatory activation. A recent study from our lab suggests a potential and previously unknown role of lamin-A/C in regulating the pro-inflammatory response.147 Reanalyzing publicly available RNA-Seq data148–153 revealed that in several tissue-resident macrophages, both in mice and humans, upon LPS activation (both in vitro and in vivo), there is a significant decrease in the levels of lamin-A/C mRNA (Fig. 5). Concomitantly, the pro-inflammatory activation of BMDMs also results in a significant decrease in lamin-A/C protein levels.147 Previous studies have quantified the turnover rate of lamins in quiescent fibroblasts, revealing that around 10% of lamin-A/C is replaced within 24 h in the lamina meshwork with newly synthesized lamin-A/C proteins.154 Since a decrease in more than 50% is seen within 12–18 h of activation, lamin-A/C downregulation is an active process, which is due to lamin-A/C phosphorylation followed by its degradation.147 Mechanistically, lamin-A/C downregulation is necessary to drive pro-inflammatory gene expression, as inhibiting lamin-A/C degradation in BMDMs blocks pro-inflammatory gene expression (IL-6 and TNF-a) and also pro-inflammatory cytokine secretion. Regarding tissue-resident macrophages, lamin A/C ablation in immune cells results in a selective depletion of lung alveolar macrophages and a heightened susceptibility to influenza infection.155 These alveolar macrophages also display DNA damage and p53-dependent senescence, hallmarks of inflammation and ageing, further confirming a potential role of nuclear lamina in macrophage function and inflammation. Finally, the overexpression of the lamin-A mutant progerin, a truncated version of the lamin-A protein,156 which does not properly integrate into the lamina and disrupts the nuclear lamina meshwork, leads to significant disfigurement of the nucleus.156 This induces endothelial cell dysfunction, characterized by increased inflammation and oxidative stress together with persistent DNA damage, increased expression of cell cycle arrest proteins, and cellular senescence, further providing proof of lamin-A/C as inflammatory regulator.157 

FIG. 5.

Pro-inflammatory macrophage activation results in a reversible lamin-A/C downregulation: Color coded map shows the mRNA expression levels of various pro-inflammatory genes and lamin-A/C in microglia of LPS-injected mice (5 mg/kg), in LPS-treated mouse microglia, bone marrow derived macrophages (BMDMs) and in LPS treated human monocyte and alveolar macrophages. Also shown are the expression levels in the LPS treated macrophage cell line THP-1 (human). Expression data were obtained from public repositories.148–153 

FIG. 5.

Pro-inflammatory macrophage activation results in a reversible lamin-A/C downregulation: Color coded map shows the mRNA expression levels of various pro-inflammatory genes and lamin-A/C in microglia of LPS-injected mice (5 mg/kg), in LPS-treated mouse microglia, bone marrow derived macrophages (BMDMs) and in LPS treated human monocyte and alveolar macrophages. Also shown are the expression levels in the LPS treated macrophage cell line THP-1 (human). Expression data were obtained from public repositories.148–153 

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Downregulation and degradation of the nuclear lamina are thus a mechano-regulated process and depend on a variety of physical parameters, including substrate stiffness.158,159 A recent study has revealed that lamin-A/C phosphorylation and turnover depend on the rigidity of the extracellular matrix. For example, mesenchymal stem cells (MSCs) grown on soft polymeric substrates show higher lamina degradation as compared to ones on stiff substrates.158 Even though the available evidence points toward a functional role of lamin-A/C during macrophage pro-inflammatory activation (Fig. 5), a detailed understanding of how the phosphorylation and subsequent degradation of lamin-A/C might drive inflammatory gene expression is lacking. The regulation could be at multiple levels starting from transcriptional regulation. Lamin-A/C has previously been shown to alter the spatial localization and activity of critical transcription factors like NF-κB160 and MRTF-A.161,162 One potential mechanism by which lamin-/C degradation could cause changes in a pro-inflammatory genomic program is by tuning the differential nuclear-to-cytoplasmic localization of these transcription factors. Similarly, there is a strong regulatory coupling between nuclear lamina and histone modifications (as discussed below in Sec. X). Thus, whether changes in lamin-A/C levels during M1 activation drive inflammatory histone modifications and epigenetic remodelling could be another interesting question to address. This includes probing major histone modifications like H3K4me3, a histone mark that is accumulated in the promoter region of pro-inflammatory genes upon LPS activation.163 At the same time, it is also absolutely crucial to explore the role of other nuclear envelope (NE) proteins in order to develop a more complete picture of the regulatory landscape by which macrophage activation is regulated by alterations of the NE, thus tuning the balance between pro-inflammatory and pro-healing macrophages.

Expression of the pro-inflammatory secretome requires access to the corresponding genes. It is worth mentioning that the changes in accessibility of chromatin and genes, as probed using Assay for Transposase-Accessible Chromatin using sequencing (ATAC-Seq), has shown that accessibility depends on the mechanical environment and mechanical status of cells. Uniaxial cyclic stretching of MSCs, for example, induces differentiation into osteoblasts by upregulating the chromatin accessibility of genes associated with the regulation of cell morphogenesis, cell–substrate adhesion, and ossification.164 Another study has shown that stiff ECM induces a tumorigenic phenotype through changes in nuclear morphology, chromatin state, and accessibility of chromatin.165 Cells cultured in stiff matrices displayed more accessible chromatin sites, which exhibited footprints of specific protein 1 transcription factor binding, and this transcription factor acts along with the histone deacetylases 3 and 8 to regulate the induction of stiffness-mediated tumorigenicity.165 

During the past decade, genome-wide mapping methods have identified genomic regions that are in close contact with the nuclear lamina, termed lamina-associated domains (LADs).166,167 Transcriptionally inactive genes are generally positioned at the nuclear lamina and are part of these LADs;135,168 however, only ∼30% of LADs, as identified by sequencing, map to the nuclear periphery. LADs are of particular interest because most of the several thousands of genes in LADs are expressed at very low levels, thus suggesting a role in gene repression.135,168 Single-cell techniques like DamID, a method to capture contacts between DNA and a given protein of interest, have facilitated the identification of genomic regions in contact with the nuclear periphery and nuclear lamina.169 A few recent studies have shown that lamins differentially regulate distinct LADs at the nuclear periphery, which can in turn influence global 3D genome organization and gene expression.44,170 Gene activation inside LADs typically causes detachment of the entire transcription unit from the nuclear lamina, whereas inactivation of active genes can lead to increased nuclear lamina contacts.131 Lamin loss causes expansion or detachment of specific LADs in mouse embryonic stem cells (ESCs). The detached LADs disrupt interactions of both LADs and chromatin, thereby impacting genome organization and potentially genomic profiles.44 However, our understanding of LADs in macrophages is minimal. It is worth probing whether pro-inflammatory genes are part of these LADs and whether nuclear lamina degradation releases LADs in the interior of the nucleus so as to facilitate the expression of pro-inflammatory genes, which are otherwise silent and/or lowly expressed in resting macrophages.

Nuclear lamina-influenced changes in gene expression are also associated with changes in gene positioning. For example, knockdown of lamin A/C deregulates expression levels of genes; both KLK10 (Chr.19, LAD+) and MADH2 (Chr.18, LAD−) were significantly repressed, while BCL2L12 (Chr.19, LAD−) was de-repressed.171 These genes also reposition with respect to the nuclear envelope upon Lamin-A/C knockdown. One recent study showed the relocation of pro-inflammatory genes like TNF-α, a highly transcribed gene in LPS activated macrophages, within the nuclear space during macrophage activation.172 In contrast, the down-regulated genes did not change their position.172 A more detailed study involving several genes is required though to confirm that gene repositioning is necessary to regulate the pro-inflammatory protein expression. Whether and how nuclear lamina degradation is critical for this relocation is completely unknown.

Finally, it has been shown in several cell types that changes in the nuclear lamina and in lamin-A/C aid the repositioning of chromosomes due to altered interactions between chromosomes and the inner nuclear membrane. Three-dimensional DNA-immunoFISH revealed that the repositioning of chromosomal regions to the nuclear lamina is dependent on breakdown and reformation of the nuclear envelope during mitosis. During mitosis, chromosome movement correlates with reduced lamin association with the nuclear rim.173 This requires phosphorylation of lamin at sites analogous to those that open lamina network crosslinks in mitosis.173 Failure to remodel the lamina results in delayed meiotic entry, altered chromatin organization, and slowed chromosome movement.173 Nuclear lamina disruption in Drosophila S2 cells also leads to chromatin compaction and repositioning from the nuclear envelope.174 Additionally, the downregulation of lamin-A/C results in increased nuclear dynamics, thereby enabling relative displacement of chromosomes within the nucleus, leading to the formation of new chromosome surroundings and interactions. Even though similar processes are expected to regulate macrophage phenotypes, whether chromosome repositioning takes place during macrophage inflammatory activation and regulates their response remains unknown. Whether the phosphorylation induced degradation of the nuclear lamina during macrophage activation helps in chromosome repositioning is also not known and is worth future investigations to better characterize and fully understand the process of inflammatory activation.

Epigenetics is the study of how cells control gene activity without changing the DNA sequence.175 Epigenetic changes/modifications are modifications to DNA that regulate whether genes are turned on or off and the set of modifications that regulate the expression of genes in a cell is termed the “epigenome.” The term, “epigenetics,” was first used to refer to the complex interactions between the genome and the environment that is involved in development and differentiation in higher organisms. Conrad Waddington coined the term “epigenetic landscape” defined by the molecular mechanisms that convert the genetic information into observable traits or phenotypes.176 Epigenetic modifications are either heritable chemical or physical changes in chromatin, and the main types of epigenetic modifications include histone modifications and DNA methylation. Gene expression is also influenced epigenetically by non-coding RNAs such as microRNA (miRNAs) and long non-coding RNA (lncRNAs).177–180 Epigenetic modifications steer the response of macrophages to external physical or biochemical stimuli and include the downstream secretion of pro-inflammatory or pro-healing factors. The secretome differs significantly between M1 and M2 activated macrophages,12,181–185 and the role of mechanical forces and physical factors is still being explored. The mechano-response of immune cells, however, might not necessarily be steered by the same epigenetic modifications as described so far for mesenchymal cells, in part due to their rather different cytoskeletal architecture, a possibility we will now explore further.

The first evidence of the link between LPS stimulation and epigenetic regulation in inflammatory genes dates back to 1999, as LPS stimulation induces the cytokine IL-12p40 production in murine macrophages by rapid and specific nucleosome translocation at the promoter region.186 A nucleosome is a section of DNA that is wrapped around a core of proteins. Each nucleosome is composed of a little less than two turns of DNA wrapped around a set of eight proteins called histones, which are known as a histone octamer. Each histone octamer is composed of two copies each of the histone proteins H2A, H2B, H3, and H4. With the advent of advanced sequencing techniques, changes in epigenetic modifications, mainly histone modifications and DNA methylation during macrophage inflammatory activation, have now been extensively probed.9,182,187,188 The development of chromatin immunoprecipitation assays in conjunction with advanced sequencing technologies has allowed researchers to probe different histone modifications and map the locations of specific proteins across the genome at high resolution during macrophage activation.188,189 LPS activation is a TLR4-dependent event and results in the acetylation and methylation of histones H3 and H4.190 Trimethylation of histone 3 lysine 4 (H3K4) is associated with active gene transcription, and trimethylation of H3K9, H3K27, and H3K79 is linked to silencing of gene expression during inflammation.190 As a major role of pro-inflammatory macrophages is to sterilize wound sites through the secretion of various cytokines, trimethylation of H3K4 on pro-inflammatory cytokine gene promoters must be induced in M1 macrophages in response to TLR stimulation.

Various histone modifications in response to alterations of physical properties of the cell microenvironment have recently been reported for mesenchymal cells. Acetylation of H3 on Lysine 9 (AcH3K9), for example, depends on the cell spreading area of fibroblasts.100 Similarly, stiff polymeric matrices lead to significantly higher levels of AcH3 but decreased levels of AcH4.165 Fibroblasts cultured in grooves (10 μm in width and spacing) showed not only markedly increased global AcH3 marks, but also a significant increase in methylation (both di- and tri-methylation) of histone H3 at lysine 4 (H3K4me2 and H3K4me3, respectively) relative to flat surfaces.191 Increased levels of histone H3 acetylation have also been reported in mesenchymal stem cells cultured on elastic membranes patterned with parallel microgrooves (10 μm wide).192 Importantly, other histone modifications are also sensitive to the physical properties of the cell microenvironment. Even in primary BMDMs, confining cells in a 3D environment induces trimethylation of histone 3 at residue K4 (H3K4me3).193 Several other histone modifications have been reported to be under the regulation of physical properties of the microenvironment, such as topography, lamina flow, substrate stiffness, and 3D collagen gels, and this has been reviewed extensively.194 

In contrast, whether histone modifications induced during macrophage activation are cell niche dependent was not known until recently (Fig. 6). H3K36me2, a crucial histone modification to promote pro-inflammatory gene expression, is dependent on whether macrophages are free to spread or are spatially confined.12 Another central histone modification, AcH3 which is necessary for pro-inflammatory responses, has been shown to be dependent on the cell shape, being lower in elongated cells.106 The mechano-sensitivity of other modifications remains to be explored (Fig. 6). Even though it is well accepted that changes in cell spreading and confinement significantly alter nuclear architecture,100,101 whether the histone modifications are sensitive to these changes in the nuclear architecture has not been elucidated. Since chromatin is physically anchored to the nuclear lamina,174,195–197 it can be hypothesized that changes in the nuclear architecture and nuclear lamina could potentially drive differential histone modifications. In support of this, changes in the pattern of histone modifications in fibroblasts have been associated with mutations in A-type lamin, whereby heterochromatin markers, such as H3K9 trimethylation and heterochromatin-associated protein HP1γ, are reduced in cells with mutated lamin-A genes.198–200 In contrast, H4K20 trimethylation is increased in laminopathy fibroblasts, which have a lamin-A mutation.201 In addition, mutations in the lamin-A gene also result in a decreased level of H3K27 trimethylation on the inactive chromosome X.201 This shows that histone modifications are correlated and potentially regulated by lamin-A and nuclear lamina. Thus, we suggest a potential regulatory route by which changes in pro-inflammatory histone modifications during macrophage activation occur via mechanosensitive nuclear lamina and associated proteins.

FIG. 6.

Mechano-regulation of enzymes involved in histone modifications and DNA methylations during macrophage polarization: Cartoon shows relevant epigenetic enzymes that regulate the macrophage phenotype as summarized by their influence. As shown in the balance model, the enzymes above the arrows have been shown to have activating effects, while those under the T-shaped support stand have repressive effects on M1/M2 activation. However, their regulatory dependence on different physical factors, which are known to exist in tissues, still needs to be probed. Cartoon adapted from.190 Reproduced with permission from Chen et al., Cell Mol. Immunol. 17, 36–49 (2020). Copyright 2020 Authors, licensed under a Creative Commons Attribution (CC BY) license.

FIG. 6.

Mechano-regulation of enzymes involved in histone modifications and DNA methylations during macrophage polarization: Cartoon shows relevant epigenetic enzymes that regulate the macrophage phenotype as summarized by their influence. As shown in the balance model, the enzymes above the arrows have been shown to have activating effects, while those under the T-shaped support stand have repressive effects on M1/M2 activation. However, their regulatory dependence on different physical factors, which are known to exist in tissues, still needs to be probed. Cartoon adapted from.190 Reproduced with permission from Chen et al., Cell Mol. Immunol. 17, 36–49 (2020). Copyright 2020 Authors, licensed under a Creative Commons Attribution (CC BY) license.

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Histone modifications are largely driven by histone methyltransferases (HMTs), histone acetyltransferases (HATs), and histone deacetylases (HDACs), which have been extensively reviewed elsewhere51 (Fig. 6). Even though HATs have been shown to be involved in initiating gene expression in macrophages during inflammation, only a limited number of reports have detailed to date how HATs catalyze the expression of specific M1 or M2 macrophage associated genes.182 In contrast, several HDACs, mainly HDAC3,202,203 are known to be involved in M1 activation and play a prominent role in the regulation of immunological pathways. In response to LPS, HDAC3-deficient macrophages are unable to induce the expression of several pro-inflammatory genes including IL-6.12 Insight into whether these histone remodeling enzymes are mechano-regulated, and whether their spatial localization and activity are driven by biophysical forces, has only recently been gained. HDAC3 nuclear translocation depends on macrophage spreading, being lower in spatially confined macrophages, establishing HDAC3 as a mechano-sensitive histone modification enzyme.12 Even though HDAC3 translocation in fibroblasts is dependent on actin polymerization,100 whether a similar mechanism exists in macrophages is still not known. p300 HAT enzymatic activity is also dependent on macrophage elongation. p300 is an important HAT associated with macrophage pro-inflammatory activation.204 LPS treated BMDMs, cultured on fibronectin coated micropatterned stripes, showed a lower enzymatic activity of p300 HAT,106 establishing p300 as a mechano-responsive histone remodeling enzyme. However, such data provide only preliminary evidence that the spatial localization and activity of HDACs and HATs, and potentially of other HMTs, are driven by a diverse set of mechanical and/or biochemical signals. Altogether, this provides first insight into the biophysical control of histone modification and chromatin remodeling enzymes and thereby how physical factors can regulate gene expression during macrophage activation.

DNA methylation, together with histone modifications, can also regulate gene expression.205–207 DNA methylation, and specifically methylation of the 5-carbon of cytosine (5 mC), is the most studied and among the most significant epigenetic modification207,208 [Fig. 7(a)]. DNA hypermethylation results in gene silencing by affecting the binding of methylation-sensitive DNA binding proteins and/or by further interacting with various histone modifications and co-repressors that alter DNA accessibility to transcriptional factors.208,209 DNA methylation is catalyzed by DNA methyltransferases (DNMTs) [Fig. 7(a)], including DNMT1, DNMT3a, and DNMT3b. DNMT1, which is responsible for DNA methylation maintenance, binds to methyl groups in hemimethylated DNA strands during DNA replication, whereas de novo DNMT3a and DNMT3b add methyl groups to CpG dinucleotides of unmethylated DNA.206 DNMT1 may also have a role in de novo DNA methylation.210 Recently, more attention has been given to 5-hydroxymethylcytosine (5hmC), which is an oxidation product of 5mC, and contrary to 5mC, the presence of 5hmC has generally been associated with increased gene expression211–213 [Fig. 7(a)]. The mammalian enzymes responsible for generating these modifications are the three ten-eleven translocation (TET) dioxygenases (TET1, TET2, and TET3) that utilize the co-factors α-ketoglutarate, reduced iron, and molecular oxygen to oxidize the methyl group (demethylation) at the 5 position of 5mC.214–216 Optical mapping techniques revealed that pro-inflammatory activation of BMDMs results in a significant decrease in the levels of DNMTs, i.e., DNMT1, DNMT3a, and DNMT3b with a concomitant increase in the levels of the TET2 enzyme [Fig. 7(b)].217 

FIG. 7.

Changes in DNA Epigenetic modifications (DNA Methylation) during LPS induced pro-inflammatory macrophage activation: (a) depiction of cytosine methylation and demethylation processes. The different modified forms of cytosine (5mC, 5hmC, 5fC, and 5caC) along with the corresponding enzymes responsible for each modification are shown.217 (b) Bar graph shows the differential levels of various DNMTs, TETs, and TDG enzymes in M0 and M1 BMDMs as obtained from RNA-Seq and qPCR experiments, both performed after 6 h of LPS treatment.217 DNMTs: DNA methyltransferases; TET: ten-eleven translocation; TDG: thymine-DNA glycosylase. Data adapted from Ref. 217. Reproduced with permission from Jain et al., Epigenetics 14, 1183–1193 (2019). Copyright 2019 Taylor and Francis Group.217 

FIG. 7.

Changes in DNA Epigenetic modifications (DNA Methylation) during LPS induced pro-inflammatory macrophage activation: (a) depiction of cytosine methylation and demethylation processes. The different modified forms of cytosine (5mC, 5hmC, 5fC, and 5caC) along with the corresponding enzymes responsible for each modification are shown.217 (b) Bar graph shows the differential levels of various DNMTs, TETs, and TDG enzymes in M0 and M1 BMDMs as obtained from RNA-Seq and qPCR experiments, both performed after 6 h of LPS treatment.217 DNMTs: DNA methyltransferases; TET: ten-eleven translocation; TDG: thymine-DNA glycosylase. Data adapted from Ref. 217. Reproduced with permission from Jain et al., Epigenetics 14, 1183–1193 (2019). Copyright 2019 Taylor and Francis Group.217 

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Whether DNA methylation is a mechano-regulated process remains elusive (Fig. 6). Only recently, it has been shown for various cell types, but not yet in macrophages, that DNA methylation depends on the biophysical properties of the cellular microenvironment.194 As cells engage in reciprocal interactions with their matrix, it is not surprising that DNA methylation is sensitive to ECM stiffness with global hypermethylation under stiff ECM conditions in mouse embryonic stem cells and embryonic fibroblasts compared with soft ECM.218 Stiff ECM enhances DNA methylation of both promoters and gene bodies, especially the 5′ promoter regions of pluripotent genes.218 The enhanced DNA methylation is functionally required for the loss of pluripotent gene expression in mESCs grown on stiff ECM, allowing them to differentiate along a specific lineage.218 Moreover, the altered DNA methylation is driven by ECM-regulated nuclear transport of DNA methyltransferase three-like (DNMT3L), which is promoted by a stiff ECM.218 Finally, using gastric cancer cells, it has been shown that the stiffness of the ECM reversibly regulates the DNA methylation of the promoter region of the mechanosensitive protein YAP.219 Similarly, seminal findings have been published showing that DNA methylation and DNA methyltransferases are also sensitive to shear stress.220–222 Both in vitro and in vivo blood flow models revealed that disturbed flow, as observed during atherosclerosis and characterized by low and oscillating shear stress, induces expression of DNMT1 and thereby regulates the genome-wide DNA methylation pattern. However, whether the tissue-dependent mechanical properties of microniches as discussed above drive macrophage homeostatic function and inflammation via DNA methylation remains unknown. As cells cannot only feel the stiffness of their microenvironment but also respond to the stretch-induced switching of the functional display of ECM fibers,49 future work is also needed to elucidate how changes of the mechanobiology of ECM alter the above-mentioned dependencies.

Finally, non-coding RNAs (miRNAs and lncRNAs) are important regulators of epigenetic modifications and, thus, gene expression, and their regulatory role during macrophage polarization has only recently been explored.177–180 Even though MicroRNA-503-5p inhibits stretch-induced osteogenic cell differentiation and bone formation223 and microRNA-103a functions as a mechanosensitive microRNA to inhibit bone formation through targeting Runx2,224 it is not yet known whether they play a mechano-regulated role in macrophage activation. While the mechano-sensitivity of epigenetic modifications and microRNA has been reviewed with a focus on endothelial and mesenchymal cells,225–229 our knowledge in the context of macrophages thus remains sparse.

Physiological ageing is accompanied by a chronic, sub-clinical increase in pro-inflammatory cytokines (TNFα, IL-6) and reduced anti-inflammatory cytokines (IL-10) in the blood, termed inflammageing.230,231 This gradual progression with advancing age is a biomarker of ageing associated with an increased risk of several age-related diseases, including cardiovascular disease,232 sarcopenia,233 cancer,234 and dementia.235 Importantly, humans who reach very old age, i.e., centenarians, maintain a low inflammatory status with increased levels of anti-inflammatory cytokines, thus minimizing inflammageing.236 Understanding the causes of inflammageing enables better rational therapeutic strategies that would have broad health benefits, helping to deliver a healthy old age and prevent many age-related diseases and frailty.

While inflammageing is driven by many factors, a key contributor is the appearance of monocytes/macrophages that are in a state of low-level constitutive activation, resulting in the secretion of pro-inflammatory cytokines in the absence of infection.237 The differentiation of monocytes/macrophages to either a pro-inflammatory or more regulatory phenotypes is influenced by a variety of processes, including signals from cytokines but also in response to their physical environment as reviewed here. Research has shown that the direction of polarization can be influenced by ECM components as well as by culturing these cells on substrates of differing stiffnesses.238,239 Interestingly, the stiffness of the macrophage itself, again regulated by actin polymerization, also influences its phenotype. The mechanisms underlying the shift with age to pro-inflammatory phenotypes are poorly understood but appear to involve changes within cells and their response to microenvironmental biomechanical changes.

In a variety of cell types, there is increasing evidence that ageing is associated with changes in the mechanical properties of cells and strong correlations exist between age and cytoplasmic stiffness.240 Indeed, the mechanical stiffness of skin fibroblasts has been shown to correlate with biological age in humans.17 Ageing also influences the ability of cells to transduce biophysical changes into intracellular signals, altering the response of cells and tissues to mechanical forces.241 In the case of macrophages, the literature is focused on the response of these cells to their environment with age and little is known about age-related effects on macrophage stiffness. Recent studies have shown that culturing BMDMs from mice on substrates of increasing stiffness led to induction of a pro-inflammatory phenotype,242 confirming earlier reports of the ability of biomechanical forces to influence macrophage polarization.243 This earlier study also revealed that the mechanotransduction signal to achieve the inflammatory phenotype was mediated via transient receptor potential vanilloid 4 (TRPV4), a mechanosensitive ion channel.243 Thus, although the literature is sparse currently, there is support for the mechanical changes experienced by the macrophage in the aged environment contributing to its pro-inflammatory state and, thus, to inflammageing.

Other important contributors to inflammageing include senescent cells. These proliferatively quiescent cells are highly metabolically active, producing a complex pro-inflammatory secretome termed the senescence associated secretory phenotype (SASP).244 Senescent cells undergo profound morphological changes indicating an important role for mechanical signals in cell senescence.245 Senescent cells have increased vimentin, decreased actin, tubulin, and the focal adhesion protein paxillin.245 In the human progeria syndrome, Hutchinson–Gilford progeria syndrome increased cytoskeletal stiffness and RhoAGTPase activation in progeria cells was directly coupled with the morphological changes of cell senescence and induction of the pro-inflammatory response.246 

As stated earlier, it is now widely recognized that most age-related diseases have a strong inflammatory component. The source of this inflammation is varied ranging from increased adiposity to reduced physical inactivity but includes the increased pro-inflammatory status of macrophages and cell senescence.230,231 That both cell and tissue mechanical properties change during disease is also now being appreciated with altered stiffness of cardiac muscle influencing the pro-inflammatory phenotype of infiltrating macrophages.242 In fibrotic diseases such as Idiopathic Pulmonary Fibrosis, matrix stiffening is evident and pathogenic, whereby α6-integrin is a matrix stiffness-regulated mechanosensitive molecule, which confers an invasive fibroblast phenotype.187 In neurodegenerative diseases such as Alzheimer's disease, a pathological feature is increased neuroinflammation, mediated through central nervous system based macrophages, the microglia. These cells, like their peripheral counterparts, have an activated, pro-inflammatory phenotype in Alzheimer's disease.247 Whether this is related to alterations in the stiffness of brain regions, for example, due to the presence of misfolded proteins such as amyloid, or simply a straight immune response to these proteins is yet to be determined.

It is of uttermost importance to find cures for the many inflammatory diseases that are responsible for the majority of deaths and whose incidence increases with age. What has become evident is that an improved understanding of the role of mechanical forces in modulating the inflammatory status of cells such as macrophages and senescent stromal cells will deliver novel therapeutic options going forward. Creating new paradigms, which integrate biochemical, immunological, and mechanobiological factors, will produce significant new insights into age-related disease pathogenesis. Defining how to regenerate tissues affected by inflammatory pathologies, a major challenge in regenerative medicine, also requires mechanobiological knowledge. Since the demonstration that substrate stiffness correlates with mesenchymal stem cell differentiation fate,24 for example, many bioengineers focused on synthesizing new biomaterials that match tissue specific Young's moduli. Importantly, cells not only sense Young's modulus of their microenvironment: as they pull on the extracellular anchor points, they displace the adhesive ligands, which vice versa impacts integrin clustering and downstream mechanosensation,23,25–28,41 and at the same time stretch the ECM fibers, which can switch mechano-regulated molecular binding sites either on or off.49,248–250 As macrophages are major contributors to adverse inflammatory and fibrotic responses to implanted biomaterials,251 the development of immunomodulating biomaterials and of therapies to regenerate organs will require an improved understanding of how macrophage activation and polarization is steered by the physical properties of their niches, among all the other well described regulatory factors. Gaining a thorough understanding how physical properties of cell niches tune the pro-inflammatory response of macrophages, or if altered promote their pro-healing M2 phenotype, will thus be highly significant for many disciplines from cell biology to developmental biology. This knowledge will also impact medicine and translational approaches for novel therapies for age-related disease, as the efficacies of therapeutics are impacted by the complexity of the pathological cell niches. The identification of mechanosensitive targets in signaling cascades that regulate the pro-inflammatory or pro-healing phenotype can further be explored as new therapeutic targets.

N.J. was supported by the Institute of Inflammation and Ageing, the School of Chemical Engineering, and the Swiss National Science Foundation (SPARK CRSK-3_195952). J.M.L. was supported by the Medical Research Council Versus Arthritis Centre for Musculoskeletal Ageing Research and the National Institute for Health and Care Research (NIHR) Birmingham Biomedical Research Centre. V.V. was supported by ETH Zurich and the Swiss National Science Foundation (SNSF). The views expressed are those of the authors and not necessarily of the funding agencies, including SNSF, NIHR, National Health Service, or Department of Health and Social Care, or ETH Zurich.

The authors have no conflicts to disclose.

Ethics approval is not required.

Nikhil Jain: Conceptualization (equal); Data curation (equal); Formal analysis (equal); Funding acquisition (equal); Investigation (equal); Methodology (equal); Project administration (equal); Resources (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review and editing (equal). Janet Lord: Writing – original draft (equal); Writing – review and editing (equal). Viola Vogel: Conceptualization (equal); Data curation (equal); Formal analysis (equal); Funding acquisition (equal); Investigation (equal); Methodology (equal); Project administration (equal); Resources (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review and editing (equal).

The data that support the findings of this study are available from the corresponding authors upon reasonable request.

1.
L.
Ferrucci
and
E.
Fabbri
, “
Inflammageing: Chronic inflammation in ageing, cardiovascular disease, and frailty
,”
Nat. Rev. Cardiol.
15
,
505
522
(
2018
).
2.
G. W.
Schmid-Schonbein
, “
Analysis of inflammation
,”
Annu. Rev. Biomed. Eng.
8
,
93
131
(
2006
).
3.
G. W.
Schmid-Schonbein
, “
2008 Landis Award lecture. Inflammation and the autodigestion hypothesis
,”
Microcirculation
16
,
289
306
(
2009
).
4.
Y.
Lavin
,
A.
Mortha
,
A.
Rahman
, and
M.
Merad
, “
Regulation of macrophage development and function in peripheral tissues
,”
Nat. Rev. Immunol.
15
,
731
744
(
2015
).
5.
C.
Schulz
 et al., “
A lineage of myeloid cells independent of Myb and hematopoietic stem cells
,”
Science
336
,
86
90
(
2012
).
6.
L.
Chavez-Galan
,
M. L.
Olleros
,
D.
Vesin
, and
I.
Garcia
, “
Much more than M1 and M2 macrophages, there are also CD169(+) and TCR(+) macrophages
,”
Front. Immunol.
6
,
263
(
2015
).
7.
Y.
Yao
,
X. H.
Xu
, and
L.
Jin
, “
Macrophage polarization in physiological and pathological pregnancy
,”
Front. Immunol.
10
,
792
(
2019
).
8.
A.
Schlitzer
and
J. L.
Schultze
, “
Tissue-resident macrophages—How to humanize our knowledge
,”
Immunol. Cell Biol.
95
,
173
177
(
2017
).
9.
L. C.
Davies
and
P. R.
Taylor
, “
Tissue-resident macrophages: Then and now
,”
Immunology
144
,
541
548
(
2015
).
10.
T. A.
Wynn
,
A.
Chawla
, and
J. W.
Pollard
, “
Macrophage biology in development, homeostasis and disease
,”
Nature
496
,
445
455
(
2013
).
11.
L. C.
Davies
,
S. J.
Jenkins
,
J. E.
Allen
, and
P. R.
Taylor
, “
Tissue-resident macrophages
,”
Nat. Immunol.
14
,
986
995
(
2013
).
12.
N.
Jain
and
V.
Vogel
, “
Spatial confinement downsizes the inflammatory response of macrophages
,”
Nat. Mater.
17
,
1134
1144
(
2018
).
13.
F. Y.
McWhorter
,
T.
Wang
,
P.
Nguyen
,
T.
Chung
, and
W. F.
Liu
, “
Modulation of macrophage phenotype by cell shape
,”
Proc. Natl. Acad. Sci.
110
,
17253
17258
(
2013
).
14.
V. S.
Meli
 et al., “
Biophysical regulation of macrophages in health and disease
,”
J. Leukocyte Biol.
106
,
283
299
(
2019
).
15.
P.
Bandaru
 et al., “
Mechanical cues regulating proangiogenic potential of human mesenchymal stem cells through YAP-mediated mechanosensing
,”
Small
16
,
e2001837
(
2020
).
16.
N.
Toepfner
 et al., “
Detection of human disease conditions by single-cell morpho-rheological phenotyping of blood
,”
Elife
7
,
e29213
(
2018
).
17.
J. M.
Phillip
 et al., “
Biophysical and biomolecular determination of cellular age in humans
,”
Nat. Biomed. Eng.
1
,
0093
(
2017
).
18.
S. R.
Clippinger
 et al., “
Disrupted mechanobiology links the molecular and cellular phenotypes in familial dilated cardiomyopathy
,”
Proc. Natl. Acad. Sci.
116
,
17831
17840
(
2019
).
19.
W. F.
Liu
, “
Mechanical regulation of cellular phenotype: Implications for vascular tissue regeneration
,”
Cardiovasc. Res.
95
,
215
222
(
2012
).
20.
H.
Li
 et al., “
Biomechanical cues as master regulators of hematopoietic stem cell fate
,”
Cell Mol. Life Sci.
78
,
5881
5902
(
2021
).
21.
P.
Agarwal
and
R.
Zaidel-Bar
, “
Mechanosensing in embryogenesis
,”
Curr. Opin. Cell Biol.
68
,
1
9
(
2021
).
22.
C.
Argentati
 et al., “
Insight into mechanobiology: How stem cells feel mechanical forces and orchestrate biological functions
,”
Int. J. Mol. Sci.
20
,
5337
(
2019
).
23.
O.
Chaudhuri
,
J.
Cooper-White
,
P. A.
Janmey
,
D. J.
Mooney
, and
V. B.
Shenoy
, “
Effects of extracellular matrix viscoelasticity on cellular behaviour
,”
Nature
584
,
535
546
(
2020
).
24.
A. J.
Engler
,
S.
Sen
,
H. L.
Sweeney
, and
D. E.
Discher
, “
Matrix elasticity directs stem cell lineage specification
,”
Cell
126
,
677
689
(
2006
).
25.
A.
Kumar
,
J. K.
Placone
, and
A. J.
Engler
, “
Understanding the extracellular forces that determine cell fate and maintenance
,”
Development
144
,
4261
4270
(
2017
).
26.
J.
Li
 et al., “
Biophysical and biochemical cues of biomaterials guide mesenchymal stem cell behaviors
,”
Front. Cell Dev. Biol.
9
,
640388
(
2021
).
27.
P.
Romani
,
L.
Valcarcel-Jimenez
,
C.
Frezza
, and
S.
Dupont
, “
Crosstalk between mechanotransduction and metabolism
,”
Nat. Rev. Mol. Cell Biol.
22
,
22
38
(
2021
).
28.
B.
Trappmann
 et al., “
Extracellular-matrix tethering regulates stem-cell fate
,”
Nat. Mater.
11
,
642
649
(
2012
).
29.
M.
Aramesh
 et al., “
Nanoconfinement of microvilli alters gene expression and boosts T cell activation
,”
Proc. Natl. Acad. Sci.
118
,
e2107535118
(
2021
).
30.
K.
Burridge
,
E.
Monaghan-Benson
, and
D. M.
Graham
, “
Mechanotransduction: From the cell surface to the nucleus via RhoA
,”
Philos. Trans. R. Soc., B
374
,
20180229
(
2019
).
31.
M.
Chakraborty
 et al., “
Mechanical stiffness controls dendritic cell metabolism and function
,”
Cell Rep.
34
,
108609
(
2021
).
32.
J. D.
Humphrey
,
E. R.
Dufresne
, and
M. A.
Schwartz
, “
Mechanotransduction and extracellular matrix homeostasis
,”
Nat. Rev. Mol. Cell Biol.
15
,
802
812
(
2014
).
33.
N.
Jain
,
J.
Moeller
, and
V.
Vogel
, “
Mechanobiology of macrophages: How physical factors coregulate macrophage plasticity and phagocytosis
,”
Annu. Rev. Biomed. Eng.
21
,
267
297
(
2019
).
34.
F.
Martino
,
A. R.
Perestrelo
,
V.
Vinarsky
,
S.
Pagliari
, and
G.
Forte
, “
Cellular mechanotransduction: From tension to function
,”
Front. Physiol.
9
,
824
(
2018
).
35.
S. F. B.
Mennens
 et al., “
Substrate stiffness influences phenotype and function of human antigen-presenting dendritic cells
,”
Sci. Rep.
7
,
17511
(
2017
).
36.
P.
Niethammer
, “
Components and mechanisms of nuclear mechanotransduction
,”
Annu. Rev. Cell Dev. Biol.
37
,
233
256
(
2021
).
37.
R. S.
O'Connor
 et al., “
Substrate rigidity regulates human T cell activation and proliferation
,”
J. Immunol.
189
,
1330
1339
(
2012
).
38.
S.
Shaheen
 et al., “
Substrate stiffness governs the initiation of B cell activation by the concerted signaling of PKCβ and focal adhesion kinase
,”
Elife
6
,
e23060
(
2017
).
39.
G. V.
Shivashankar
, “
Mechanosignaling to the cell nucleus and gene regulation
,”
Annu. Rev. Biophys.
40
,
361
378
(
2011
).
40.
K. H.
Vining
and
D. J.
Mooney
, “
Mechanical forces direct stem cell behaviour in development and regeneration
,”
Nat. Rev. Mol. Cell Biol.
18
,
728
742
(
2017
).
41.
V.
Vogel
and
M.
Sheetz
, “
Local force and geometry sensing regulate cell functions
,”
Nat. Rev. Mol. Cell Biol.
7
,
265
275
(
2006
).
42.
H.
Wolfenson
,
B.
Yang
, and
M. P.
Sheetz
, “
Steps in mechanotransduction pathways that control cell morphology
,”
Annu. Rev. Physiol.
81
,
585
605
(
2019
).
43.
D. J.
Yuan
,
L.
Shi
, and
L. C.
Kam
, “
Biphasic response of T cell activation to substrate stiffness
,”
Biomaterials
273
,
120797
(
2021
).
44.
X.
Zheng
 et al., “
Lamins organize the global three-dimensional genome from the nuclear periphery
,”
Mol. Cell
71
,
802
815.e7
(
2018
).
45.
P. M.
Davidson
,
J.
Sliz
,
P.
Isermann
,
C.
Denais
, and
J.
Lammerding
, “
Design of a microfluidic device to quantify dynamic intra-nuclear deformation during cell migration through confining environments
,”
Integr. Biol.
7
,
1534
1546
(
2015
).
46.
N. J.
Walters
and
E.
Gentleman
, “
Evolving insights in cell–matrix interactions: Elucidating how non-soluble properties of the extracellular niche direct stem cell fate
,”
Acta Biomater.
11
,
3
16
(
2015
).
47.
J.
Barthes
 et al., “
Cell microenvironment engineering and monitoring for tissue engineering and regenerative medicine: The recent advances
,”
Biomed. Res. Int.
2014
,
921905
.
48.
A. W.
Holle
 et al., “
Cell-extracellular matrix mechanobiology: Forceful tools and emerging needs for basic and translational research
,”
Nano Lett.
18
,
1
8
(
2018
).
49.
V.
Vogel
, “
Unraveling the mechanobiology of extracellular matrix
,”
Annu. Rev. Physiol.
80
,
353
387
(
2018
).
50.
P.
Zhang
 et al., “
The physical microenvironment of hematopoietic stem cells and its emerging roles in engineering applications
,”
Stem Cell Res. Ther.
10
,
327
(
2019
).
51.
T.
Zhang
,
S.
Cooper
, and
N.
Brockdorff
, “
The interplay of histone modifications—Writers that read
,”
EMBO Rep.
16
,
1467
1481
(
2015
).
52.
Y.
Zeng
 et al., “
Substrate stiffness regulates B-cell activation, proliferation, class switch, and T-cell-independent antibody responses in vivo
,”
Eur. J. Immunol.
45
,
1621
1634
(
2015
).
53.
H. Q.
Le
 et al., “
Mechanical regulation of transcription controls polycomb-mediated gene silencing during lineage commitment
,”
Nat. Cell Biol.
18
,
864
875
(
2016
).
54.
P.
Speight
,
M.
Kofler
,
K.
Szaszi
, and
A.
Kapus
, “
Context-dependent switch in chemo/mechanotransduction via multilevel crosstalk among cytoskeleton-regulated MRTF and TAZ and TGFβ-regulated Smad3
,”
Nat. Commun.
7
,
11642
(
2016
).
55.
M. K.
Vartiainen
,
S.
Guettler
,
B.
Larijani
, and
R.
Treisman
, “
Nuclear actin regulates dynamic subcellular localization and activity of the SRF cofactor MAL
,”
Science
316
,
1749
1752
(
2007
).
56.
Y.
Wang
 et al., “
Visualizing the mechanical activation of Src
,”
Nature
434
,
1040
1045
(
2005
).
57.
X.
Cai
,
K. C.
Wang
, and
Z.
Meng
, “
Mechanoregulation of YAP and TAZ in cellular homeostasis and disease progression
,”
Front. Cell Dev. Biol.
9
,
673599
(
2021
).
58.
S.
Dupont
 et al., “
Role of YAP/TAZ in mechanotransduction
,”
Nature
474
,
179
183
(
2011
).
59.
A.
Totaro
 et al., “
YAP/TAZ link cell mechanics to Notch signalling to control epidermal stem cell fate
,”
Nat. Commun.
8
,
15206
(
2017
).
60.
A.
Totaro
,
T.
Panciera
, and
S.
Piccolo
, “
YAP/TAZ upstream signals and downstream responses
,”
Nat. Cell Biol.
20
,
888
899
(
2018
).
61.
O.
Dobrokhotov
,
M.
Samsonov
,
M.
Sokabe
, and
H.
Hirata
, “
Mechanoregulation and pathology of YAP/TAZ via Hippo and non-Hippo mechanisms
,”
Clin. Transl. Med.
7
,
23
(
2018
).
62.
T. P.
Driscoll
,
B. D.
Cosgrove
,
S. J.
Heo
,
Z. E.
Shurden
, and
R. L.
Mauck
, “
Cytoskeletal to nuclear strain transfer regulates YAP signaling in mesenchymal stem cells
,”
Biophys. J.
108
,
2783
2793
(
2015
).
63.
X. Z.
Fang
 et al., “
Structure, kinetic properties and biological function of mechanosensitive Piezo channels
,”
Cell Biosci.
11
,
13
(
2021
).
64.
P. K.
Veerasubramanian
,
A.
Trinh
,
N.
Akhtar
,
W. F.
Liu
, and
T. L.
Downing
, “
Biophysical and epigenetic regulation of cancer stemness, invasiveness and immune action
,”
Curr. Tissue Microenviron. Rep.
1
,
277
300
(
2020
).
65.
E.
Peranzoni
 et al., “
Role of arginine metabolism in immunity and immunopathology
,”
Immunobiology
212
,
795
812
(
2007
).
66.
K. M.
Adlerz
,
H.
Aranda-Espinoza
, and
H. N.
Hayenga
, “
Substrate elasticity regulates the behavior of human monocyte-derived macrophages
,”
Eur. Biophys. J.
45
,
301
309
(
2016
).
67.
A. K.
Blakney
,
M. D.
Swartzlander
, and
S. J.
Bryant
, “
The effects of substrate stiffness on the in vitro activation of macrophages and in vivo host response to poly(ethylene glycol)-based hydrogels
,”
J. Biomed. Mater. Res. A
100
,
1375
1386
(
2012
).
68.
E.
Gruber
,
C.
Heyward
,
J.
Cameron
, and
C.
Leifer
, “
Toll-like receptor signaling in macrophages is regulated by extracellular substrate stiffness and Rho-associated coiled-coil kinase (ROCK1/2)
,”
Int. Immunol.
30
,
267
278
(
2018
).
69.
L. E.
Hind
,
M.
Dembo
, and
D. A.
Hammer
, “
Macrophage motility is driven by frontal-towing with a force magnitude dependent on substrate stiffness
,”
Integr. Biol.
7
,
447
453
(
2015
).
70.
T.
Okamoto
 et al., “
Reduced substrate stiffness promotes M2-like macrophage activation and enhances peroxisome proliferator-activated receptor gamma expression
,”
Exp. Cell Res.
367
,
264
273
(
2018
).
71.
T. U.
Luu
,
S. C.
Gott
,
B. W.
Woo
,
M. P.
Rao
, and
W. F.
Liu
, “
Micro- and nanopatterned topographical cues for regulating macrophage cell shape and phenotype
,”
ACS Appl. Mater. Interfaces
7
,
28665
28672
(
2015
).
72.
B. D.
Ratner
, “
A pore way to heal and regenerate: 21st century thinking on biocompatibility
,”
Regener. Biomater.
3
,
107
110
(
2016
).
73.
H.
Miyazaki
and
K.
Hayashi
, “
Effects of cyclic strain on the morphology and phagocytosis of macrophages
,”
Biomed. Mater. Eng.
11
,
301
309
(
2001
).
74.
J. J.
Elacqua
,
A. L.
McGregor
, and
J.
Lammerding
, “
Automated analysis of cell migration and nuclear envelope rupture in confined environments
,”
PLoS One
13
,
e0195664
(
2018
).
75.
P.
Lu
,
K.
Takai
,
V. M.
Weaver
, and
Z.
Werb
, “
Extracellular matrix degradation and remodeling in development and disease
,”
Cold Spring Harb. Perspect. Biol.
3
,
a005058
(
2011
).
76.
M.
McMahon
,
S.
Ye
,
J.
Pedrina
,
D.
Dlugolenski
, and
J.
Stambas
, “
Extracellular matrix enzymes and immune cell biology
,”
Front. Mol. Biosci.
8
,
703868
(
2021
).
77.
S.
Yoodee
 et al., “
Effects of secretome derived from macrophages exposed to calcium oxalate crystals on renal fibroblast activation
,”
Commun. Biol.
4
,
959
(
2021
).
78.
M.
Holthaus
,
N.
Santhakumar
,
T.
Wahlers
, and
A.
Paunel-Gorgulu
, “
The secretome of preconditioned mesenchymal stem cells drives polarization and reprogramming of M2a macrophages toward an IL-10-producing phenotype
,”
Int. J. Mol. Sci.
23
,
4104
(
2022
).
79.
L.
Przybyla
,
J. M.
Muncie
, and
V. M.
Weaver
, “
Mechanical control of epithelial-to-mesenchymal transitions in development and cancer
,”
Annu. Rev. Cell Dev. Biol.
32
,
527
554
(
2016
).
80.
I.
Soncin
 et al., “
The tumour microenvironment creates a niche for the self-renewal of tumour-promoting macrophages in colon adenoma
,”
Nat. Commun.
9
,
582
(
2018
).
81.
M.
Casanova-Acebes
 et al., “
Tissue-resident macrophages provide a pro-tumorigenic niche to early NSCLC cells
,”
Nature
595
,
578
584
(
2021
).
82.
A. S.
Priya Dipta
,
M.
Shmuel
,
F.
Forno
,
J. W.
Eriksson
,
M. J.
Pereira
,
X. M.
Abalo
,
M.
Wabitsch
,
M.
Thaysen-Andersen
, and
T.
Boaz
, “
Macrophage-derived secretome is sufficient to confer olanzapine-mediated insulin resistance in human adipocytes
,”
Compr. Psychoneuroendocrinol.
7
,
100073
(
2021
).
83.
A.
Mantovani
,
F.
Marchesi
,
A.
Malesci
,
L.
Laghi
, and
P.
Allavena
, “
Tumour-associated macrophages as treatment targets in oncology
,”
Nat. Rev. Clin. Oncol.
14
,
399
416
(
2017
).
84.
K. M.
Vannella
and
T. A.
Wynn
, “
Mechanisms of organ injury and repair by macrophages
,”
Annu. Rev. Physiol.
79
,
593
617
(
2017
).
85.
Z.
Julier
,
A. J.
Park
,
P. S.
Briquez
, and
M. M.
Martino
, “
Promoting tissue regeneration by modulating the immune system
,”
Acta Biomater.
53
,
13
28
(
2017
).
86.
W.
Carver
and
E. C.
Goldsmith
, “
Regulation of tissue fibrosis by the biomechanical environment
,”
Biomed. Res. Int.
2013
,
101979
.
87.
J. W.
O'Connor
and
E. W.
Gomez
, “
Biomechanics of TGFβ-induced epithelial-mesenchymal transition: Implications for fibrosis and cancer
,”
Clin. Transl. Med.
3
,
23
(
2014
).
88.
P.
Pakshir
and
B.
Hinz
, “
The big five in fibrosis: Macrophages, myofibroblasts, matrix, mechanics, and miscommunication
,”
Matrix Biol.
68–69
,
81
93
(
2018
).
89.
T. A.
Wynn
and
K. M.
Vannella
, “
Macrophages in tissue repair, regeneration, and fibrosis
,”
Immunity
44
,
450
462
(
2016
).
90.
L.
Merzbacher
, “
Untersuchungen über die Morphologie und Biologie der Abraümzellen im Zentralnervesystem
,” Doctoral dissertation (
Fischer Verlag
,
1909
).
91.
C. M.
Fonta
 et al., “
Fibronectin fibers are highly tensed in healthy organs in contrast to tumors and virus-infected lymph nodes
,”
Matrix Biol. Plus
8
,
100046
(
2020
).
92.
G.
Chinetti-Gbaguidi
 et al., “
Human atherosclerotic plaque alternative macrophages display low cholesterol handling but high phagocytosis because of distinct activities of the PPARγ and LXRα pathways
,”
Circ. Res.
108
,
985
995
(
2011
).
93.
J. L.
Stoger
 et al., “
Distribution of macrophage polarization markers in human atherosclerosis
,”
Atherosclerosis
225
,
461
468
(
2012
).
94.
R.
Li
 et al., “
Interstitial flow promotes macrophage polarization toward an M2 phenotype
,”
Mol. Biol. Cell
29
,
1927
1940
(
2018
).
95.
Y.
Liu
and
T.
Segura
, “
Biomaterials-mediated regulation of macrophage cell fate
,”
Front. Bioeng. Biotechnol.
8
,
609297
(
2020
).
96.
S. F. B.
Mennens
,
K.
van den Dries
, and
A.
Cambi
, “
Role for mechanotransduction in macrophage and dendritic cell immunobiology
,”
Results Probl. Cell Differ.
62
,
209
242
(
2017
).
97.
D. W.
Dumbauld
 et al., “
Contractility modulates cell adhesion strengthening through focal adhesion kinase and assembly of vinculin-containing focal adhesions
,”
J. Cell Physiol.
223
,
746
756
(
2010
).
98.
K. K.
Elineni
and
N. D.
Gallant
, “
Regulation of cell adhesion strength by peripheral focal adhesion distribution
,”
Biophys. J.
101
,
2903
2911
(
2011
).
99.
J. Y.
Shiu
,
L.
Aires
,
Z.
Lin
, and
V.
Vogel
, “
Nanopillar force measurements reveal actin-cap-mediated YAP mechanotransduction
,”
Nat. Cell Biol.
20
,
262
271
(
2018
).
100.
N.
Jain
,
K. V.
Iyer
,
A.
Kumar
, and
G. V.
Shivashankar
, “
Cell geometric constraints induce modular gene-expression patterns via redistribution of HDAC3 regulated by actomyosin contractility
,”
Proc. Natl. Acad. Sci.
110
,
11349
11354
(
2013
).
101.
M.
Versaevel
,
T.
Grevesse
, and
S.
Gabriele
, “
Spatial coordination between cell and nuclear shape within micropatterned endothelial cells
,”
Nat. Commun.
3
,
671
(
2012
).
102.
G.
Kleveta
 et al., “
LPS induces phosphorylation of actin-regulatory proteins leading to actin reassembly and macrophage motility
,”
J. Cell Biochem.
113
,
80
92
(
2012
).
103.
S. M.
Eswarappa
,
V.
Pareek
, and
D.
Chakravortty
, “
Role of actin cytoskeleton in LPS-induced NF-κB activation and nitric oxide production in murine macrophages
,”
Innate Immun.
14
,
309
318
(
2008
).
104.
N.
Isowa
 et al., “
LPS-induced depolymerization of cytoskeleton and its role in TNF-α production by rat pneumocytes
,”
Am. J. Physiol.
277
,
L606
L615
(
1999
).
105.
C.
Pergola
 et al., “
Modulation of actin dynamics as potential macrophage subtype-targeting anti-tumour strategy
,”
Sci. Rep.
7
,
41434
(
2017
).
106.
P. K.
Veerasubramanian
 et al., “
A Src-H3 acetylation signaling axis integrates macrophage mechanosensation with inflammatory response
,”
Biomaterials
279
,
121236
(
2021
).
107.
L. E.
Hind
,
E. B.
Lurier
,
M.
Dembo
,
K. L.
Spiller
, and
D. A.
Hammer
, “
Effect of M1–M2 polarization on the motility and traction stresses of primary human macrophages
,”
Cell Mol. Bioeng.
9
,
455
465
(
2016
).
108.
V. S.
Meli
 et al., “
YAP-mediated mechanotransduction tunes the macrophage inflammatory response
,”
Sci. Adv.
6
,
eabb8471
(
2020
).
109.
E. N.
Olson
and
A.
Nordheim
, “
Linking actin dynamics and gene transcription to drive cellular motile functions
,”
Nat. Rev. Mol. Cell Biol.
11
,
353
365
(
2010
).
110.
L.
Yu
 et al., “
MRTF-A mediates LPS-induced pro-inflammatory transcription by interacting with the COMPASS complex
,”
J. Cell Sci.
127
,
4645
4657
(
2014
).
111.
T.
Lawrence
and
G.
Natoli
, “
Transcriptional regulation of macrophage polarization: Enabling diversity with identity
,”
Nat. Rev. Immunol.
11
,
750
761
(
2011
).
112.
D.
Fei
 et al., “
Fibronectin (FN) cooperated with TLR2/TLR4 receptor to promote innate immune responses of macrophages via binding to integrin β1
,”
Virulence
9
,
1588
1600
(
2018
).
113.
M. M.
Monick
,
L.
Powers
,
N.
Butler
,
T.
Yarovinsky
, and
G. W.
Hunninghake
, “
Interaction of matrix with integrin receptors is required for optimal LPS-induced MAP kinase activation
,”
Am. J. Physiol.
283
,
L390
402
(
2002
).
114.
H.
Atcha
 et al., “
Mechanically activated ion channel Piezo1 modulates macrophage polarization and stiffness sensing
,”
Nat. Commun.
12
,
3256
(
2021
).
115.
Z.
Chen
 et al., “
Integrin β3 modulates TLR4-mediated inflammation by regulation of CD14 expression in macrophages in septic condition
,”
Shock
53
,
335
343
(
2020
).
116.
P. M.
Davidson
and
B.
Cadot
, “
Actin on and around the nucleus
,”
Trends Cell Biol.
31
,
211
223
(
2021
).
117.
S. B.
Khatau
 et al., “
A perinuclear actin cap regulates nuclear shape
,”
Proc. Natl. Acad. Sci.
106
,
19017
19022
(
2009
).
118.
Q.
Li
,
A.
Kumar
,
E.
Makhija
, and
G. V.
Shivashankar
, “
The regulation of dynamic mechanical coupling between actin cytoskeleton and nucleus by matrix geometry
,”
Biomaterials
35
,
961
969
(
2014
).
119.
T. O.
Ihalainen
 et al., “
Differential basal-to-apical accessibility of lamin A/C epitopes in the nuclear lamina regulated by changes in cytoskeletal tension
,”
Nat. Mater.
14
,
1252
1261
(
2015
).
120.
A.
Sneider
,
J.
Hah
,
D.
Wirtz
, and
D. H.
Kim
, “
Recapitulation of molecular regulators of nuclear motion during cell migration
,”
Cell Adhes. Migr.
13
,
50
62
(
2019
).
121.
N.
Wang
,
J. D.
Tytell
, and
D. E.
Ingber
, “
Mechanotransduction at a distance: Mechanically coupling the extracellular matrix with the nucleus
,”
Nat. Rev. Mol. Cell Biol.
10
,
75
82
(
2009
).
122.
Y.
Gruenbaum
and
R.
Foisner
, “
Lamins: Nuclear intermediate filament proteins with fundamental functions in nuclear mechanics and genome regulation
,”
Annu. Rev. Biochem.
84
,
131
164
(
2015
).
123.
E.
Heitz
, “
Das Heterochromatin der Moose
,”
Jahrb. Wiss. Bot.
69
,
762
818
(
1928
).
124.
Y.
Turgay
 et al., “
The molecular architecture of lamins in somatic cells
,”
Nature
543
,
261
264
(
2017
).
125.
Y.
Turgay
and
O.
Medalia
, “
The structure of lamin filaments in somatic cells as revealed by cryo-electron tomography
,”
Nucleus
8
,
475
481
(
2017
).
126.
R.
Tenga
and
O.
Medalia
, “
Structure and unique mechanical aspects of nuclear lamin filaments
,”
Curr. Opin. Struct. Biol.
64
,
152
159
(
2020
).
127.
A.
Janin
,
D.
Bauer
,
F.
Ratti
,
G.
Millat
, and
A.
Mejat
, “
Nuclear envelopathies: A complex LINC between nuclear envelope and pathology
,”
Orphanet J. Rare Dis.
12
,
147
(
2017
).
128.
M.
Raab
 et al., “
ESCRT III repairs nuclear envelope ruptures during cell migration to limit DNA damage and cell death
,”
Science
352
,
359
362
(
2016
).
129.
H. R.
Manley
,
M. C.
Keightley
, and
G. J.
Lieschke
, “
The neutrophil nucleus: An important influence on neutrophil migration and function
,”
Front. Immunol.
9
,
2867
(
2018
).
130.
P.
Shah
 et al., “
Nuclear deformation causes DNA damage by increasing replication stress
,”
Curr. Biol.
31
,
753
765.e6
(
2021
).
131.
L.
Brueckner
 et al., “
Local rewiring of genome-nuclear lamina interactions by transcription
,”
EMBO J.
39
,
e103159
(
2020
).
132.
A.
Gonzalez-Sandoval
 et al., “
Perinuclear anchoring of H3K9-methylated chromatin stabilizes induced cell fate in C. elegans embryos
,”
Cell
163
,
1333
1347
(
2015
).
133.
T.
Isoda
 et al., “
Non-coding transcription instructs chromatin folding and compartmentalization to dictate enhancer-promoter communication and T cell fate
,”
Cell
171
,
103
119.e18
(
2017
).
134.
E.
Lund
 et al., “
Lamin A/C-promoter interactions specify chromatin state-dependent transcription outcomes
,”
Genome Res.
23
,
1580
1589
(
2013
).
135.
D.
Peric-Hupkes
 et al., “
Molecular maps of the reorganization of genome-nuclear lamina interactions during differentiation
,”
Mol. Cell
38
,
603
613
(
2010
).
136.
H.
Pickersgill
 et al., “
Characterization of the Drosophila melanogaster genome at the nuclear lamina
,”
Nat. Genet.
38
,
1005
1014
(
2006
).
137.
A.
Poleshko
 et al., “
Genome-nuclear lamina interactions regulate cardiac stem cell lineage restriction
,”
Cell
171
,
573
587
(
2017
).
138.
M. I.
Robson
 et al., “
Tissue-specific gene repositioning by muscle nuclear membrane proteins enhances repression of critical developmental genes during myogenesis
,”
Mol. Cell
62
,
834
847
(
2016
).
139.
C. L.
Smith
,
A.
Poleshko
, and
J. A.
Epstein
, “
The nuclear periphery is a scaffold for tissue-specific enhancers
,”
Nucl. Acids Res.
49
,
6181
6195
(
2021
).
140.
S.
Maharana
 et al., “
Chromosome intermingling-the physical basis of chromosome organization in differentiated cells
,”
Nucl. Acids Res.
44
,
5148
5160
(
2016
).
141.
F.
Contu
 et al., “
Distinct 3D structural patterns of lamin A/C expression in Hodgkin and Reed–Sternberg cells
,”
Cancers
10
,
286
(
2018
).
142.
R. K.
Gieseler
 et al., “
Dendritic accessory cells derived from rat bone marrow precursors under chemically defined conditions in vitro belong to the myeloid lineage
,”
Eur. J. Cell Biol.
54
,
171
181
(
1991
).
143.
R. K.
Gieseler
,
H.
Xu
,
R.
Schlemminger
, and
J. H.
Peters
, “
Serum-free differentiation of rat and human dendritic cells, accompanied by acquisition of the nuclear lamins A/C as differentiation markers
,”
Adv. Exp. Med. Biol.
329
,
287
291
(
1993
).
144.
J. M.
Gonzalez-Granado
 et al., “
Nuclear envelope lamin-A couples actin dynamics with immunological synapse architecture and T cell activation
,”
Sci. Signal
7
,
ra37
(
2014
).
145.
V.
Rocha-Perugini
and
J. M.
Gonzalez-Granado
, “
Nuclear envelope lamin-A as a coordinator of T cell activation
,”
Nucleus
5
,
396
401
(
2014
).
146.
J. H.
Peters
,
J.
Ruppert
,
R. K.
Gieseler
,
H. M.
Najar
, and
H.
Xu
, “
Differentiation of human monocytes into CD14 negative accessory cells: Do dendritic cells derive from the monocytic lineage?
,”
Pathobiology
59
,
122
126
(
1991
).
147.
J. L.
Mehl
 et al., “
Blockage of lamin-A/C loss diminishes the pro-inflammatory macrophage response
,” bioRxiv (
2022
).
148.
M. L.
Bennett
 et al., “
New tools for studying microglia in the mouse and human CNS
,”
Proc. Natl. Acad. Sci.
113
,
E1738
E1746
(
2016
).
149.
D.
Leyva-Illades
,
R. P.
Cherla
,
C. L.
Galindo
,
A. K.
Chopra
, and
V. L.
Tesh
, “
Global transcriptional response of macrophage-like THP-1 cells to Shiga toxin type 1
,”
Infect. Immun.
78
,
2454
2465
(
2010
).
150.
B.
Novakovic
 et al., “
β-glucan reverses the epigenetic state of LPS-induced immunological tolerance
,”
Cell
167
,
1354
1368.e14
(
2016
).
151.
M.
Pinilla-Vera
 et al., “
Full spectrum of LPS activation in alveolar macrophages of healthy volunteers by whole transcriptomic profiling
,”
PLoS One
11
,
e0159329
(
2016
).
152.
M.
Pulido-Salgado
,
J. M.
Vidal-Taboada
,
G. G.
Barriga
,
C.
Sola
, and
J.
Saura
, “
RNA-Seq transcriptomic profiling of primary murine microglia treated with LPS or LPS + IFNγ
,”
Sci. Rep.
8
,
16096
(
2018
).
153.
S.
Raza
 et al., “
Analysis of the transcriptional networks underpinning the activation of murine macrophages by inflammatory mediators
,”
J. Leukocyte Biol.
96
,
167
183
(
2014
).
154.
A.
Buchwalter
and
M. W.
Hetzer
, “
Nucleolar expansion and elevated protein translation in premature aging
,”
Nat. Commun.
8
,
328
(
2017
).
155.
N. S.
De Silva
 et al., “
Nuclear envelope disruption triggers hallmarks of aging in lung alveolar macrophages
,” bioRxiv (
2022
).
156.
P.
Taimen
 et al., “
A progeria mutation reveals functions for lamin A in nuclear assembly, architecture, and chromosome organization
,”
Proc. Natl. Acad. Sci.
106
,
20788
20793
(
2009
).
157.
G.
Bidault
 et al., “
Progerin expression induces inflammation, oxidative stress and senescence in human coronary endothelial cells
,”
Cells
9
,
1201
(
2020
).
158.
A.
Buxboim
 et al., “
Matrix elasticity regulates lamin-A,C phosphorylation and turnover with feedback to actomyosin
,”
Curr. Biol.
24
,
1909
1917
(
2014
).
159.
J.
Swift
and
D. E.
Discher
, “
The nuclear lamina is mechano-responsive to ECM elasticity in mature tissue
,”
J. Cell Sci.
127
,
3005
3015
(
2014
).
160.
F. G.
Osorio
 et al., “
Nuclear lamina defects cause ATM-dependent NF-κB activation and link accelerated aging to a systemic inflammatory response
,”
Genes Dev.
26
,
2311
2324
(
2012
).
161.
C. Y.
Ho
,
D. E.
Jaalouk
,
M. K.
Vartiainen
, and
J.
Lammerding
, “
Lamin A/C and emerin regulate MKL1–SRF activity by modulating actin dynamics
,”
Nature
497
,
507
511
(
2013
).
162.
S.
Talwar
,
N.
Jain
, and
G. V.
Shivashankar
, “
The regulation of gene expression during onset of differentiation by nuclear mechanical heterogeneity
,”
Biomaterials
35
,
2411
2419
(
2014
).
163.
V.
Ruenjaiman
 et al., “
Profile of histone H3 lysine 4 trimethylation and the effect of lipopolysaccharide/immune complex-activated macrophages on endotoxemia
,”
Front. Immunol.
10
,
2956
(
2019
).
164.
D.
Zhang
,
R.
Zhang
,
X.
Song
,
K. C.
Yan
, and
H.
Liang
, “
Uniaxial cyclic stretching promotes chromatin accessibility of gene loci associated with mesenchymal stem cells morphogenesis and osteogenesis
,”
Front. Cell Dev. Biol.
9
,
664545
(
2021
).
165.
R. S.
Stowers
 et al., “
Matrix stiffness induces a tumorigenic phenotype in mammary epithelium through changes in chromatin accessibility
,”
Nat. Biomed. Eng.
3
,
1009
1019
(
2019
).
166.
B.
van Steensel
and
A. S.
Belmont
, “
Lamina-associated domains: Links with chromosome architecture, heterochromatin, and gene repression
,”
Cell
169
,
780
791
(
2017
).
167.
N.
Briand
and
P.
Collas
, “
Lamina-associated domains: Peripheral matters and internal affairs
,”
Genome Biol.
21
,
85
(
2020
).
168.
C.
Leemans
 et al., “
Promoter-intrinsic and local chromatin features determine gene repression in LADs
,”
Cell
177
,
852
864.e14
(
2019
).
169.
K. L.
de Luca
and
J.
Kind
, “
Single-cell DamID to capture contacts between DNA and the nuclear lamina in individual mammalian cells
,”
Methods Mol. Biol.
2157
,
159
172
(
2021
).
170.
Y.
Kim
,
X.
Zheng
, and
Y.
Zheng
, “
Role of lamins in 3D genome organization and global gene expression
,”
Nucleus
10
,
33
41
(
2019
).
171.
D.
Ranade
,
R.
Pradhan
,
M.
Jayakrishnan
,
S.
Hegde
, and
K.
Sengupta
, “
Lamin A/C and Emerin depletion impacts chromatin organization and dynamics in the interphase nucleus
,”
BMC Mol. Cell Biol.
20
,
11
(
2019
).
172.
R.
Solinhac
 et al., “
Transcriptomic and nuclear architecture of immune cells after LPS activation
,”
Chromosoma
120
,
501
520
(
2011
).
173.
J.
Link
 et al., “
Transient and partial nuclear lamina disruption promotes chromosome movement in early meiotic prophase
,”
Dev. Cell
45
,
212
225
(
2018
).
174.
S. V.
Ulianov
 et al., “
Nuclear lamina integrity is required for proper spatial organization of chromatin in Drosophila
,”
Nat. Commun.
10
,
1176
(
2019
).
175.
B.
Weinhold
, “
Epigenetics: The science of change
,”
Environ. Health Perspect.
114
,
A160
A167
(
2006
).
176.
C. H.
Waddington
,
An Introduction to Modern Genetics
(
Routledge
,
2016
).
177.
S.
Mohapatra
,
C.
Pioppini
,
B.
Ozpolat
, and
G. A.
Calin
, “
Non-coding RNAs regulation of macrophage polarization in cancer
,”
Mol. Cancer
20
,
24
(
2021
).
178.
Y.
Jia
and
Y.
Zhou
, “
Involvement of lncRNAs and macrophages: Potential regulatory link to angiogenesis
,”
J. Immunol. Res.
2020
,
1704631
.
179.
S.
Ghafouri-Fard
 et al., “
The impact of non-coding RNAs on macrophage polarization
,”
Biomed. Pharmacother.
142
,
112112
(
2021
).
180.
P.
Jiang
and
X.
Li
, “
Regulatory mechanism of lncRNAs in M1/M2 macrophages polarization in the diseases of different etiology
,”
Front. Immunol.
13
,
835932
(
2022
).
181.
K.
Das Gupta
,
M. R.
Shakespear
,
A.
Iyer
,
D. P.
Fairlie
, and
M. J.
Sweet
, “
Histone deacetylases in monocyte/macrophage development, activation and metabolism: Refining HDAC targets for inflammatory and infectious diseases
,”
Clin. Transl. Immunol.
5
,
e62
(
2016
).
182.
T. S.
Kapellos
and
A. J.
Iqbal
, “
Epigenetic control of macrophage polarisation and soluble mediator gene expression during inflammation
,”
Mediators Inflammation
2016
,
6591703
.
183.
M. R.
Shakespear
,
M. A.
Halili
,
K. M.
Irvine
,
D. P.
Fairlie
, and
M. J.
Sweet
, “
Histone deacetylases as regulators of inflammation and immunity
,”
Trends Immunol.
32
,
335
343
(
2011
).
184.
T.
Roger
 et al., “
Histone deacetylase inhibitors impair innate immune responses to Toll-like receptor agonists and to infection
,”
Blood
117
,
1205
1217
(
2011
).
185.
H. T.
Aung
 et al., “
LPS regulates proinflammatory gene expression in macrophages by altering histone deacetylase expression
,”
FASEB J.
20
,
1315
1327
(
2006
).
186.
J. S.
Cowdery
,
N. J.
Boerth
,
L. A.
Norian
,
P. S.
Myung
, and
G. A.
Koretzky
, “
Differential regulation of the IL-12 p40 promoter and of p40 secretion by CpG DNA and lipopolysaccharide
,”
J. Immunol.
162
,
6770
6775
(
1999
).
187.
H.
Chen
 et al., “
Mechanosensing by the α6-integrin confers an invasive fibroblast phenotype and mediates lung fibrosis
,”
Nat. Commun.
7
,
12564
(
2016
).
188.
L. B.
Ivashkiv
, “
Epigenetic regulation of macrophage polarization and function
,”
Trends Immunol.
34
,
216
223
(
2013
).
189.
T.
Kuznetsova
,
K. H. M.
Prange
,
C. K.
Glass
, and
M. P. J.
de Winther
, “
Transcriptional and epigenetic regulation of macrophages in atherosclerosis
,”
Nat. Rev. Cardiol.
17
,
216
228
(
2020
).
190.
S.
Chen
,
J.
Yang
,
Y.
Wei
, and
X.
Wei
, “
Epigenetic regulation of macrophages: From homeostasis maintenance to host defense
,”
Cell Mol. Immunol.
17
,
36
49
(
2020
).
191.
T. L.
Downing
 et al., “
Biophysical regulation of epigenetic state and cell reprogramming
,”
Nat. Mater.
12
,
1154
1162
(
2013
).
192.
Y.
Li
 et al., “
Biophysical regulation of histone acetylation in mesenchymal stem cells
,”
Biophys. J.
100
,
1902
1909
(
2011
).
193.
P.
Wang
 et al., “
WDR5 modulates cell motility and morphology and controls nuclear changes induced by a 3D environment
,”
Proc. Natl. Acad. Sci.
115
,
8581
8586
(
2018
).
194.
S.
Kilian
, “
Materials control of the epigenetics underlying cell plasticity
,”
Nat. Rev. Mater.
6
,
69
83
(
2021
).
195.
R.
Czapiewski
,
M. I.
Robson
, and
E. C.
Schirmer
, “
Anchoring a leviathan: How the nuclear membrane tethers the genome
,”
Front. Genet.
7
,
82
(
2016
).
196.
D.
Bouvier
,
J.
Hubert
,
A. P.
Seve
, and
M.
Bouteille
, “
Characterization of lamina-bound chromatin in the nuclear shell isolated from HeLa cells
,”
Exp. Cell Res.
156
,
500
512
(
1985
).
197.
Y. Y.
Shevelyov
and
S. V.
Ulianov
, “
The nuclear lamina as an organizer of chromosome architecture
,”
Cells
8
,
136
(
2019
).
198.
J. C.
Harr
 et al., “
Loss of an H3K9me anchor rescues laminopathy-linked changes in nuclear organization and muscle function in an Emery–Dreifuss muscular dystrophy model
,”
Genes Dev.
34
,
560
579
(
2020
).
199.
P.
Chaturvedi
and
V. K.
Parnaik
, “
Lamin A rod domain mutants target heterochromatin protein 1alpha and beta for proteasomal degradation by activation of F-box protein, FBXW10
,”
PLoS One
5
,
e10620
(
2010
).
200.
P.
Scaffidi
and
T.
Misteli
, “
Lamin A-dependent nuclear defects in human aging
,”
Science
312
,
1059
1063
(
2006
).
201.
D. K.
Shumaker
 et al., “
Mutant nuclear lamin A leads to progressive alterations of epigenetic control in premature aging
,”
Proc. Natl. Acad. Sci.
103
,
8703
8708
(
2006
).
202.
X.
Chen
 et al., “
Requirement for the histone deacetylase Hdac3 for the inflammatory gene expression program in macrophages
,”
Proc. Natl. Acad. Sci.
109
,
E2865
E2874
(
2012
).
203.
M.
Ghiboub
 et al., “
HDAC3 mediates the inflammatory response and LPS tolerance in human monocytes and macrophages
,”
Front. Immunol.
11
,
550769
(
2020
).
204.
S.
Ghisletti
 et al., “
Identification and characterization of enhancers controlling the inflammatory gene expression program in macrophages
,”
Immunity
32
,
317
328
(
2010
).
205.
A. J.
Lea
 et al., “
Genome-wide quantification of the effects of DNA methylation on human gene regulation
,”
Elife
7
,
e37513
(
2018
).
206.
L. D.
Moore
,
T.
Le
, and
G.
Fan
, “
DNA methylation and its basic function
,”
Neuropsychopharmacology
38
,
23
38
(
2013
).
207.
A.
Bird
, “
DNA methylation patterns and epigenetic memory
,”
Genes Dev.
16
,
6
21
(
2002
).
208.
E.
Li
and
Y.
Zhang
, “
DNA methylation in mammals
,”
Cold Spring Harb. Perspect. Biol.
6
,
a019133
(
2014
).
209.
M.
Curradi
,
A.
Izzo
,
G.
Badaracco
, and
N.
Landsberger
, “
Molecular mechanisms of gene silencing mediated by DNA methylation
,”
Mol. Cell Biol.
22
,
3157
3173
(
2002
).
210.
C.
Haggerty
 et al., “
Dnmt1 has de novo activity targeted to transposable elements
,”
Nat. Struct. Mol. Biol.
28
,
594
603
(
2021
).
211.
M.
Bachman
 et al., “
5-hydroxymethylcytosine is a predominantly stable DNA modification
,”
Nat. Chem.
6
,
1049
1055
(
2014
).
212.
G.
Ficz
 et al., “
Dynamic regulation of 5-hydroxymethylcytosine in mouse ES cells and during differentiation
,”
Nature
473
,
398
402
(
2011
).
213.
I. H.
Lin
,
Y. F.
Chen
, and
M. T.
Hsu
, “
Correlated 5-hydroxymethylcytosine (5hmC) and gene expression profiles underpin gene and organ-specific epigenetic regulation in adult mouse brain and liver
,”
PLoS One
12
,
e0170779
(
2017
).
214.
C.
Dahl
,
K.
Gronbaek
, and
P.
Guldberg
, “
Advances in DNA methylation: 5-hydroxymethylcytosine revisited
,”
Clin. Chim. Acta
412
,
831
836
(
2011
).
215.
J. U.
Guo
,
Y.
Su
,
C.
Zhong
,
G. L.
Ming
, and
H.
Song
, “
Hydroxylation of 5-methylcytosine by TET1 promotes active DNA demethylation in the adult brain
,”
Cell
145
,
423
434
(
2011
).
216.
M.
Tahiliani
 et al., “
Conversion of 5-methylcytosine to 5-hydroxymethylcytosine in mammalian DNA by MLL partner TET1
,”
Science
324
,
930
935
(
2009
).
217.
N.
Jain
 et al., “
Global modulation in DNA epigenetics during pro-inflammatory macrophage activation
,”
Epigenetics
14
,
1183
1193
(
2019
).
218.
X. B.
Zhao
 et al., “
Extracellular matrix stiffness regulates DNA methylation by PKCα-dependent nuclear transport of DNMT3L
,”
Adv. Healthcare Mater.
10
,
e2100821
(
2021
).
219.
M.
Jang
 et al., “
Matrix stiffness epigenetically regulates the oncogenic activation of the Yes-associated protein in gastric cancer
,”
Nat. Biomed. Eng.
5
,
114
123
(
2021
).
220.
J.
Dunn
 et al., “
Flow-dependent epigenetic DNA methylation regulates endothelial gene expression and atherosclerosis
,”
J. Clin. Invest.
124
,
3187
3199
(
2014
).
221.
Y. Z.
Jiang
 et al., “
Hemodynamic disturbed flow induces differential DNA methylation of endothelial Kruppel-Like Factor 4 promoter in vitro and in vivo
,”
Circ. Res.
115
,
32
43
(
2014
).
222.
J.
Zhou
,
Y. S.
Li
,
K. C.
Wang
, and
S.
Chien
, “
Epigenetic mechanism in regulation of endothelial function by disturbed flow: Induction of DNA hypermethylation by DNMT1
,”
Cell Mol. Bioeng.
7
,
218
224
(
2014
).
223.
L.
Liu
 et al., “
MicroRNA-503-5p inhibits stretch-induced osteogenic differentiation and bone formation
,”
Cell Biol. Int.
41
,
112
123
(
2017
).
224.
B.
Zuo
 et al., “
microRNA-103a functions as a mechanosensitive microRNA to inhibit bone formation through targeting Runx2
,”
J. Bone Miner. Res.
30
,
330
345
(
2015
).
225.
Z.
Chen
 et al., “
Mechanosensitive miRNAs and bone formation
,”
Int. J. Mol. Sci.
18
,
1684
(
2017
).
226.
J.
Fernandez Esmerats
,
J.
Heath
, and
H.
Jo
, “
Shear-sensitive genes in aortic valve endothelium
,”
Antioxid. Redox Signaling
25
,
401
414
(
2016
).
227.
H.
Giral
,
A.
Kratzer
, and
U.
Landmesser
, “
MicroRNAs in lipid metabolism and atherosclerosis
,”
Best Pract. Res. Clin. Endocrinol. Metab.
30
,
665
676
(
2016
).
228.
D. Y.
Lee
and
J. J.
Chiu
, “
Atherosclerosis and flow: Roles of epigenetic modulation in vascular endothelium
,”
J. Biomed. Sci.
26
,
56
(
2019
).
229.
X.
Loyer
,
Z.
Mallat
,
C. M.
Boulanger
, and
A.
Tedgui
, “
MicroRNAs as therapeutic targets in atherosclerosis
,”
Expert Opin. Ther. Targets
19
,
489
496
(
2015
).
230.
C.
Franceschi
 et al., “
Inflamm-aging: An evolutionary perspective on immunosenescence
,”
Ann. N. Y. Acad. Sci.
908
,
244
254
(
2000
).
231.
C.
Franceschi
 et al., “
Inflammaging and anti-inflammaging: A systemic perspective on aging and longevity emerged from studies in humans
,”
Mech. Ageing Dev.
128
,
92
105
(
2007
).
232.
S.
Masiha
,
J.
Sundstrom
, and
L.
Lind
, “
Inflammatory markers are associated with left ventricular hypertrophy and diastolic dysfunction in a population-based sample of elderly men and women
,”
J. Hum. Hypertens.
27
,
13
17
(
2013
).
233.
P.
Soysal
 et al., “
Inflammation and frailty in the elderly: A systematic review and meta-analysis
,”
Ageing Res. Rev.
31
,
1
8
(
2016
).
234.
D.
Il'yasova
 et al., “
Circulating levels of inflammatory markers and cancer risk in the health aging and body composition cohort
,”
Cancer Epidemiol. Biomarkers Prev.
14
,
2413
2418
(
2005
).
235.
H.
Akiyama
 et al., “
Inflammation and Alzheimer's disease
,”
Neurobiol. Aging
21
,
383
421
(
2000
).
236.
D.
Monti
,
R.
Ostan
,
V.
Borelli
,
G.
Castellani
, and
C.
Franceschi
, “
Inflammaging and human longevity in the omics era
,”
Mech. Ageing Dev.
165
,
129
138
(
2017
).
237.
N. A.
Duggal
,
R. D.
Pollock
,
N. R.
Lazarus
,
S.
Harridge
, and
J. M.
Lord
, “
Major features of immunesenescence, including reduced thymic output, are ameliorated by high levels of physical activity in adulthood
,”
Aging Cell
17
,
e12750
(
2018
).
238.
M. L.
Previtera
and
A.
Sengupta
, “
Substrate stiffness regulates proinflammatory mediator production through TLR4 activity in macrophages
,”
PLoS One
10
,
e0145813
(
2015
).
239.
R.
Sridharan
,
B.
Cavanagh
,
A. R.
Cameron
,
D. J.
Kelly
, and
F. J.
O'Brien
, “
Material stiffness influences the polarization state, function and migration mode of macrophages
,”
Acta Biomater.
89
,
47
59
(
2019
).
240.
M. N.
Starodubtseva
, “
Mechanical properties of cells and ageing
,”
Ageing Res. Rev.
10
,
16
25
(
2011
).
241.
F. A.
Pelissier
 et al., “
Age-related dysfunction in mechanotransduction impairs differentiation of human mammary epithelial progenitors
,”
Cell Rep.
7
,
1926
1939
(
2014
).
242.
M.
Haschak
 et al., “
Macrophage phenotype and function are dependent upon the composition and biomechanics of the local cardiac tissue microenvironment
,”
Aging
13
,
16938
16956
(
2021
).
243.
B.
Dutta
,
R.
Goswami
, and
S. O.
Rahaman
, “
TRPV4 plays a role in matrix stiffness-induced macrophage polarization
,”
Front. Immunol.
11
,
570195
(
2020
).
244.
A.
Freund
,
A. V.
Orjalo
,
P. Y.
Desprez
, and
J.
Campisi
, “
Inflammatory networks during cellular senescence: Causes and consequences
,”
Trends Mol. Med.
16
,
238
246
(
2010
).
245.
K.
Nishio
and
A.
Inoue
, “
Senescence-associated alterations of cytoskeleton: Extraordinary production of vimentin that anchors cytoplasmic p53 in senescent human fibroblasts
,”
Histochem. Cell Biol.
123
,
263
273
(
2005
).
246.
X.
Mu
 et al., “
Cytoskeleton stiffness regulates cellular senescence and innate immune response in Hutchinson–Gilford progeria syndrome
,”
Aging Cell
19
,
e13152
(
2020
).
247.
V. H.
Perry
,
J. A.
Nicoll
, and
C.
Holmes
, “
Microglia in neurodegenerative disease
,”
Nat. Rev. Neurol.
6
,
193
201
(
2010
).
248.
A. S.
Adhikari
,
J.
Chai
, and
A. R.
Dunn
, “
Mechanical load induces a 100-fold increase in the rate of collagen proteolysis by MMP-1
,”
J. Am. Chem. Soc.
133
,
1686
1689
(
2011
).
249.
K.
Saini
,
S.
Cho
,
L. J.
Dooling
, and
D. E.
Discher
, “
Tension in fibrils suppresses their enzymatic degradation—A molecular mechanism for ‘use it or lose it’
,”
Matrix Biol.
85–86
,
34
46
(
2020
).
250.
D.
Ortiz Franyuti
,
M.
Mitsi
, and
V.
Vogel
, “
Mechanical stretching of fibronectin fibers upregulates binding of interleukin-7
,”
Nano Lett.
18
,
15
25
(
2018
).
251.
K. E.
Martin
and
A. J.
Garcia
, “
Macrophage phenotypes in tissue repair and the foreign body response: Implications for biomaterial-based regenerative medicine strategies
,”
Acta Biomater.
133
,
4
16
(
2021
).