The cardiac microenvironment is continuously exposed to multiple forms of mechanical stress. These include dynamic stimuli such as cyclic strain and shear stress^[26]. In addition, cells experience forces transmitted through cell-cell interactions as well as mechanical cues derived from the ECM, including stiffness, topography, and geometric confinement. These ECM-derived cues are generally considered static biomechanical properties^[26-28]. Together, these mechanical stimuli drive functional changes in multiple cardiac cell types, including cardiomyocytes, endothelial cells, fibroblasts, and immune cells [Figure 1].

Among the dynamic stimuli, cyclic strain is a mechanical force generated by the heartbeat. During myocardial contraction and chamber filling, cardiac tissues undergo repetitive stretching. Experimental data indicate that physiological valvular tissues typically experience approximately 10% cyclic strain, whereas pathological conditions such as valvular disease or abnormal hemodynamic loading, including hypertension, HF, and pressure overload, can increase strain levels toward ~20%^[29].

Another important mechanical stimulus in the cardiovascular system is wall shear stress, which arises from blood flow acting on the vascular endothelium. In coronary arteries, shear stress varies throughout the cardiac cycle and contributes to endothelial homeostasis. Physiological shear stress promotes anti-inflammatory signaling and vascular stability. In contrast, low shear stress is associated with endothelial dysfunction and initiation of atherosclerotic plaques, while abnormally high shear stress in stenotic regions may contribute to plaque destabilization and vascular remodeling^[30].

In addition to hemodynamic forces, progressive ECM remodeling during cardiac aging and fibrosis alters matrix stiffness and mechanical signaling, which in turn regulates cellular behavior. In this review, we primarily focus on ECM-derived mechanical cues and their roles in the initiation, progression, and resolution of cardiac fibrosis.

ECM stiffening is a defining biomechanical feature of cardiac fibrosis and represents a critical contextual signal that shapes cellular behavior within the myocardium. Changes in myocardial stiffness not only reflect disease severity but also actively regulate mechanoresponsive cells, including macrophages. Under physiological conditions, the stiffness of healthy myocardium typically ranges from ~10 to 15 kPa. However, during pathological remodeling, such as that induced by pressure overload, myocardial stiffness can increase significantly. In murine models subjected to transverse aortic constriction (TAC), stiffness has been shown to rise to 30-50 kPa, as measured by atomic force microscopy (AFM)^[31]. By contrast, clinical in vivo elastography and ultrasound-based assessments report increased myocardial stiffness in patients with HF, rising from approximately 4 kPa in healthy hearts to about 12 kPa in diseased myocardium^[32-34]. These differences underscore the importance of reporting measurement modality and species when comparing stiffness values across studies.

Myocardial stiffness is primarily governed by dynamic remodeling of the cardiac ECM [Figure 2]. Under physiological conditions, the ECM comprises a highly organized network of fibrillar collagens (primarily types I and III), elastin, laminin, fibronectin, proteoglycans, and glycosaminoglycans^[35]. Together, these components maintain myocardial structural integrity, elasticity, and essential cell-matrix interactions. In response to pathological stimuli, such as pressure overload, ischemic injury, or aging, the homeostatic balance between ECM synthesis and degradation is disrupted^[36]. Following MI, ECM remodeling is temporally staged, with early matrix degradation and provisional matrix formation followed by collagen accumulation and progressive stiffening during scar maturation^[37,38].

Beyond injury-induced fibrosis, inherited cardiomyopathies also exhibit prominent ECM remodeling and myocardial stiffening. For example, hypertrophic cardiomyopathy (HCM) is frequently accompanied by abnormal ECM turnover, interstitial fibrosis, and increased left ventricular stiffness, which correlates with disease severity and clinical symptoms^[39]. Notably, these fibrotic and biomechanical changes can develop in the absence of classic ischemic or pressure-overload injury, highlighting ECM remodeling as an intrinsic driver of myocardial stiffening in certain genetic heart diseases.

In ischemic cardiomyopathy (ICM), a leading cause of HF, ECM remodeling largely represents a secondary response to cardiomyocyte injury and death and is characterized by progressive accumulation of collagens, proteoglycans, glycoproteins, and regulators of ECM cross-linking, as revealed by quantitative ECM proteomics^[40]. This injury-driven ECM deposition initially serves an adaptive role in maintaining structural integrity but ultimately becomes maladaptive, forming a feed-forward loop in which increased matrix stiffness further amplifies profibrotic signaling and adverse cardiac remodeling^[20].

Aging represents a distinct and progressive driver of myocardial stiffening, characterized by cumulative collagen cross-linking and impaired matrix turnover. Alterations in the composition of specific ECM proteins are key determinants of myocardial stiffness. Among fibrillar collagens, type I and type III are the major structural proteins in the heart. Numerous studies reported an increased collagen I/III ratio across diverse cardiovascular diseases, a change that correlates with progressive myocardial stiffening and reduced tissue compliance^[41,42]. In addition to collagens, other structural ECM components (for example, fibronectin, elastin) and matricellular proteins (for example, tenascin, osteopontin, secreted protein acidic and rich in cysteine (SPARC)) play crucial roles in maintaining ECM homeostasis^[43]. Fibronectin assembly is essential for ECM organization because fibronectin fibrillogenesis is required for the proper deposition of collagen I and thrombospondin 1^[44].

Beyond structural proteins, non-structural enzymes such as matrix metalloproteinases (MMPs) play a critical role in ECM remodeling and myocardial stiffening during cardiac fibrosis. MMPs are a large family of zinc-dependent endopeptidases that degrade various ECM components, including collagens, elastin, fibronectin, laminin, and proteoglycans^[45]. To date, over 20 MMPs have been identified and are typically classified based on substrate specificity and structural domains, such as collagenases (e.g., MMP-1, MMP-8, MMP-13), gelatinases (e.g., MMP-2, MMP-9), stromelysins (e.g., MMP-3, MMP-10), and membrane-type MMPs (MT-MMPs)^[46]. In the heart, MMPs are produced by cardiac fibroblasts, macrophages, neutrophils, and endothelial cells in response to injury or stress signals. These enzymes play essential roles in ECM turnover, angiogenesis, and tissue repair following injury. However, dysregulated MMP activity is a hallmark of pathological cardiac remodeling. For instance, elevated levels of circulating MMP-9 have been demonstrated in patients with coronary artery disease (CAD)^[47]. A study using transgenic mice with macrophage-specific overexpression of MMP-9 demonstrated that elevated MMP-9 levels led to age-dependent cardiac inflammation and fibrosis^[48]. This finding was evidenced by increased expression of pro-inflammatory genes and excessive collagen deposition, ultimately resulting in myocardial stiffening and impaired cardiac function^[49].

Secreted phosphoprotein 1 (SPP1), also known as osteopontin, has emerged as a critical regulator of ECM remodeling in several cardiovascular conditions, including thrombus formation^[50], vascular disease^[10,51], and HF^[52]. Via interactions with integrins and CD44, SPP1 modulates ECM synthesis, crosslinking, and degradation, thereby influencing tissue repair and fibrotic remodeling^[53,54]. Notably, SPP1 expression is also mechanosensitive. In tumor models, elevated ECM stiffness induces SPP1 expression and secretion, thereby contributing to tumor-associated fibrosis^[55,56]. Aberrant SPP1 production is also associated with vascular stiffening and pathological calcification^[57,58]. Although direct evidence that SPP1 acts as an intrinsic ECM stiffness sensor in the cardiovascular system remains unclear, our recent data demonstrate that increasing matrix stiffness upregulates SPP1 expression and secretion in macrophages, and this in turn exacerbates vascular ECM remodeling^[10]. As the most abundant immune cell population in the heart, macrophages are essential for tissue homeostasis and for orchestrating early inflammatory responses after cardiovascular injury^[59-61]. Nonetheless, the precise mechanisms by which cardiac macrophages sense and transduce ECM-derived mechanical cues remain largely unresolved.

Progressive ECM stiffening is a hallmark of cardiac aging and fibrosis and profoundly influences the behavior of multiple cardiac cell types. For cardiomyocytes, increased ECM stiffness disrupts contractile function and calcium handling, impairs sarcomere organization, and promotes pathological hypertrophy. Cardiomyocytes cultured on stiff substrates exhibit altered mechanotransduction signaling and reduced contractile efficiency, suggesting that pathological stiffening of the myocardium can directly contribute to impaired cardiac performance and HF progression^[62,63].

Endothelial cells also respond dynamically to changes in matrix stiffness. Increased substrate stiffness enhances endothelial proliferation, migration, and cytoskeletal remodeling via mechanosensitive signaling pathways. These stiffness-dependent endothelial responses may contribute to vascular remodeling and impaired endothelial barrier function, thereby influencing myocardial perfusion and inflammatory signaling during cardiac disease^[64].

Cardiac fibroblasts are the primary ECM-producing cells in the heart and are highly responsive to mechanical cues. Elevated matrix stiffness promotes fibroblast activation into myofibroblasts, characterized by increased proliferation, upregulation of α-smooth muscle actin (α-SMA), and excessive collagen synthesis. This stiffness-driven fibroblast activation establishes a positive feedback loop: ECM deposition raises tissue stiffness, which in turn further exacerbates myocardial fibrosis and structural remodeling^[43,65,66].

By comparison, the mechanosensitivity of immune cells, particularly macrophages, in the cardiac microenvironment is less well characterized. In multiple noncardiac tissues, macrophages and other immune cells respond to matrix stiffness by altering polarization, migration, and inflammatory signaling, but evidence from the heart remains limited^[6]. Understanding how immune cells, particularly macrophages, sense and respond to ECM stiffening may provide new insights into the regulation of inflammation and fibrosis in the diseased heart^[62].

Cardiac aging and age-associated fibrosis are accompanied by profound remodeling of the cardiac immune microenvironment, with macrophages forming a highly heterogeneous and functionally diverse population. Under steady-state conditions, the adult heart is predominantly populated by embryonically derived CCR2^- resident macrophages that maintain tissue homeostasis. In contrast, aging and chronic cardiac stress increase the proportion of monocyte-derived CCR2⁺ macrophages that display pro-inflammatory and profibrotic phenotypes^[67]. Single-cell transcriptomic and lineage-tracing studies reveal that aging is associated with shifts in cardiac macrophage composition, including reduced self-renewal capacity, impaired efferocytosis, and upregulation of inflammatory and ECM-related gene programs^[68].

Fibrotic remodeling of the aged heart is closely linked to the expansion of distinct macrophage subsets that express profibrotic mediators, SPP1, transforming growth factor-beta (TGF-β), and matrix-remodeling enzymes, and that spatially colocalize with activated fibroblasts within fibrotic niches^[67]. Collectively, these findings indicate that cardiac macrophages do not constitute a uniform population during aging. Rather, they adopt diverse, context-dependent states that integrate inflammatory signaling, fibrotic remodeling, and tissue-specific cues, thereby shaping disease progression in the cardiac microenvironment.

Disease etiology further shapes macrophage heterogeneity in the fibrotic heart. Integrated single-cell transcriptomic analysis across distinct cardiac conditions—MI, ICM, dilated cardiomyopathy (DCM), and heart failure (HF)^[69,70]—has demonstrated that pathological environments differentially regulate macrophage gene programs. In DCM and MI, multiple macrophage clusters exhibit robust profibrotic signatures characterized by secretion of ECM-related mediators such as Fibronectin 1 (FN1), SPP1, and Thrombospondin-1 (THBS1)^[69,71], promoting widespread macrophage-fibroblast communication. By contrast, in ICM and HF, profibrotic activity is often confined to a smaller subset of macrophage clusters, producing a more localized fibrotic phenotype^[72]. Despite these disease-specific differences, all conditions converge on enhanced ECM remodeling and activation of ECM-receptor signaling pathways, suggesting a shared fibrotic microenvironment that engages common cellular sensing mechanisms.

Importantly, the relationship between ECM remodeling and macrophage activation is bidirectional. Increasing ECM stiffness can directly modulate macrophage mechanosensing and drive functional reprogramming^[73,74], while activated macrophages in turn promote ECM deposition, cross-linking, and fibroblast activation through inflammatory cytokines and matricellular signals^[75,76]. These reciprocal interactions form a feed-forward loop that amplifies myocardial stiffening and fibrotic remodeling [Figure 3]. The specific mechanobiological pathways by which macrophages interpret these environmental cues are discussed in subsequent sections.

Much of the mechanistic evidence for integrin-mediated macrophage mechanotransduction has been derived from non-cardiac disease models or in vitro systems that control matrix stiffness. For instance, Chen et al.^[92] demonstrated that low matrix stiffness drives bone marrow-derived macrophages (BMDMs) towards a classically activated M1 phenotype, characterized by high levels of CD86 and reactive oxygen species (ROS), whereas intermediate stiffness favors an M2-like phenotype expressing CD206. Loss of integrin function reduced macrophage sensitivity to ECM stiffness, altered M2 polarization, and decreased expression of downstream effectors such as Hypoxia-inducible factor-1 alpha (HIF-1α) and lysyl oxidase-like 2 (LOXL2)^[93]. Although these findings are made primarily from tumor models and hydrogel systems, they support a stiffness-dependent integrin-macrophage regulatory axis.

Studies directly addressing this pathway in cardiac disease are still limited. Cardiovascular research, however, provides supporting evidence that integrins mediate macrophage-ECM interactions in fibrosis. For example, Shimojo et al.^[94] reported that integrin αVβ3 senses the ECM protein Tenascin-C and activates the Nuclear factor kappa B (NF-κB)/Interleukin-6 (IL-6) axis, thereby exacerbating cardiac fibrosis. Together, these findings suggest that integrin-dependent mechanotransduction helps shape macrophage behavior within the fibrotic heart microenvironment.

Although studies specifically addressing YAP-mediated mechanotransduction in cardiac macrophages remain limited, the mechanisms by which YAP responds to mechanical cues have been well characterized in vitro. In cultured macrophages, YAP activity is dynamically regulated by substrate stiffness, with dephosphorylation and enhanced nuclear translocation observed on stiffer matrices^[102]. Activation of the YAP pathway modulates macrophage activation programs: it increases expression of pro-inflammatory cytokines (such as IL-6, IL-1β, and IL-12β) and can regulate anti-inflammatory markers (such as Arg178), thereby reprogramming macrophage functional states^[25,108-110]. On rigid substrates, including glass or fibrotic ECM, macrophages exhibit enhanced F-actin polymerization and increased traction forces, which promote YAP nuclear localization and transcriptional activation. Consistently, Meli et al.^[111] demonstrated that macrophages cultured on soft fibrin hydrogels display reduced YAP nuclear translocation and attenuated pro-inflammatory cytokine expression upon lipopolysaccharide (LPS) stimulation, whereas stiffer matrices enhanced YAP-dependent transcription and amplified inflammatory responses. These effects were abolished by cytochalasin D, an inhibitor of actin polymerization^[111] , highlighting the critical role of cytoskeletal remodeling in YAP-mediated mechanotransduction.

To date, most studies of YAP-mediated mechanotransduction in cardiac macrophages have examined inflammatory activation. However, other fundamental macrophage functions—such as migration and phagocytosis, which are essential for responding to cardiac injury and driving fibrotic progression—remain poorly understood in relation to YAP signaling. While direct evidence from the heart is limited, findings from other ECM-rich environments provide indirect mechanistic insights. For example, in the bone microenvironment, YAP-dependent mechanosensing regulates actin cytoskeletal integrity and is required for the formation of podosomes and sealing zones in osteoclasts, structures that are essential for osteoclastogenesis^[112]. By analogy, similar cytoskeletal control mechanisms may operate in macrophages within fibrotic cardiac tissue. Taken together, available evidence supports the concept that YAP/TAZ-mediated mechanotransduction links increased ECM stiffness to sustained inflammation and fibrosis in the heart.

Emerging in vivo studies suggest that macrophage-specific deletion or knockdown of Piezo1 can attenuate cardiac inflammation and ameliorate myocardial injury in inflammatory cardiac conditions^[125], highlighting that suppressing Piezo1 signaling is protective in the heart. However, whether these cardioprotective effects are directly mediated by altered mechanical sensing by cardiac macrophages remains insufficiently explored. Furthermore, mechanistic insights linking Piezo1 to macrophage mechanotransduction within the cardiac microenvironment remain limited.

Accumulating in vitro studies have extensively characterized Piezo1 as a central mechanosensor governing macrophage responses to extracellular mechanical cues. Among the classical immune functions of macrophages, Piezo1 has been widely recognized as a key regulator of polarization in response to matrix stiffness. Atcha et al.^[126] demonstrated that ECM stiffening promotes Piezo1 activation, evidenced by increased Piezo1 expression and intracellular Ca²⁺ influx. Activation of Piezo1 augmented the proinflammatory M1 polarization of macrophages on stiff hydrogels, marked by increased inducible nitric oxide synthase (iNOS) expression and NF-κB signaling, while simultaneously suppressing M2 polarization, as indicated by downregulated Arg1 levels. Moreover, Piezo1 has been shown to be essential for durotaxis—the migration of cells along stiffness gradients-in various non-immune cell types^[127-129]. Whether Piezo1-mediated mechanical sensing also guides the transition from circulating monocytes to CCR2⁺ cardiac-infiltrating macrophages under fibrotic conditions represents an important area for future investigation.

In myeloid lineages, Notch2 is the predominant receptor and plays a crucial role in regulating monocyte fate and tissue-resident macrophage composition^[137]. In a mouse model of lung injury and fibrosis, antibody-mediated blockade of Notch2 attenuated fibrotic progression by modulating the population of MoMFs characterized by high expression of fibrotic markers such as Spp1, cluster of differentiation 9 (Cd9), glycoprotein non-metastatic melanoma protein B (Gpnmb), and fatty acid binding protein 5 (Fabp5)^[138]. These findings suggest that Notch signaling may serve as an upstream regulator of profibrotic pathways in infiltrating macrophages. Although Notch can respond to fibrotic environmental cues surrounding macrophages, it remains unclear whether it directly senses ECM stiffness. Nevertheless, current evidence in vitro indicates that Notch interacts with classical mechanosensors in macrophages, such as Piezo1^[122] and YAP^[139], supporting its role in mechanotransduction.

Current experimental models investigating macrophage mechanosensing in fibrosis predominantly rely on stiffness-tunable hydrogels, such as polyacrylamide gel^[24], alginate^[140], or gelatin-based matrices^[141], to mimic ECM mechanics. While these reductionist systems have provided important mechanistic insights, several limitations become apparent when they are applied to the cardiac context. First, most mechanistic insights into macrophage responses to matrix stiffness are derived from tumor models or non-cardiac fibrotic tissues, whereas studies focusing specifically on cardiac macrophages remain relatively limited. Given that different organs exhibit distinct stiffness profiles^[142], macrophage mechanotransduction is likely shaped by tissue-specific microenvironments.

Indeed, hydrogel-based studies have shown that macrophages exposed to stiffened substrates resembling the aging cardiac matrix adopt pro-inflammatory phenotypes, underscoring the relevance of mechanical cues in the aging heart^[74]. In addition to matrix stiffness, recent studies have shown that cardiac macrophages can directly sense mechanical stretch through stretch-activated ion channels, such as Piezo1, highlighting stretch as another physiologically relevant mechanical cue in the myocardium^[143]. Nevertheless, current studies largely examine individual mechanical parameters separately. Although composite mechanical models integrating multiple cues, such as cyclic stretch and matrix stiffness, have been developed to study cardiomyocyte-fibroblast interactions^[144], their application to cardiac macrophages remains limited. This highlights the need for more physiologically relevant experimental models. Such models are required to better recapitulate the complex mechanical landscape of the cardiac microenvironment.

Looking ahead, AFM provides a powerful approach to quantify the mechanical properties of the cardiac microenvironment under distinct physiological and pathological conditions^[145]. AFM-based measurements have enabled high-resolution mapping of myocardial stiffness across different disease contexts and anatomical regions, revealing pronounced mechanical heterogeneity within the fibrotic heart^[146]. For example, AFM analyses in MI models have demonstrated region-specific increases in tissue stiffness spanning several hundred kilopascals^[147], underscoring the spatial complexity of myocardial mechanics under pathological conditions. Such AFM-derived stiffness profiles may serve as an important reference for calibrating in vitro mechanical models, thereby improving their physiological relevance.

In parallel, organoid-based platforms represent a promising in vitro strategy to recapitulate the complex cellular and mechanical features of the cardiac microenvironment. Emerging studies in non-cardiac organoid systems, including liver and intestinal organoids, have demonstrated that hydrogel stiffness and viscoelasticity function as instructive biomechanical cues regulating tissue organization, cell fate decisions, and inflammatory responses^[148,149]. By contrast, despite rapid advances in cardiac organoid technologies, systematic incorporation of tunable mechanical properties into human cardiac organoids remains limited. Notably, recent human heart-macrophage assembloid models have begun to recapitulate immune-cardiac interactions in a three-dimensional context, and single-cell transcriptomic analyses have revealed that macrophages within these assembloids exhibit profibrotic transcriptional signatures, including high expression of SPP1, suggesting their potential role in ECM remodeling^[150]. Together, the integration of AFM-guided mechanical calibration with advanced cardiac organoid and assembloid systems may offer a powerful framework to investigate macrophage mechanotransduction in a cardiac-specific and physiologically relevant manner.

Two main therapeutic strategies have been proposed to modulate cell mechanotransduction: one targets intracellular mechanosensitive molecules, and the other focuses on remodeling the ECM [Table 1].

Most current approaches are based on cancer studies, where immune mechanosensing is modified to enhance immune cell function. For example, Mout et al.^[130] designed multivalent soluble agonists targeting Notch, a well-established mechanosensor involved in T cell development and activation^{[130,131,169-171]}, to deliver mechanical force and promote Notch signaling in scalable T cell differentiation platforms. Another team developed an antibody targeting discoidin domain receptor 1 (DDR1), a mechanosensor that we^[172,173] and others^[174] have found to sense ECM stiffness independently of its classical ligand in the vascular wall. In breast cancer models, the DDR1 antibody blocked the interaction between DDR1 and its canonical ligand, collagen, thereby altering collagen fiber alignment and enhancing immune cell infiltration^[175]. Another strategy involves targeting the intracellular cytoskeleton, a core component of mechanotransduction. For example, inhibiting ras homolog family member A (RhoA), a small Rho GTPase that regulates cytoskeleton dynamics^[176], has been shown to improve the regenerative capacity of aged hematopoietic stem cells and to correct lympho/myeloid skewing in vivo^[177].

In the context of fibrosis, targeting macrophage-specific mechanotransduction is an emerging direction. Chen et al.^[178] reported that inhibition of FAK-mediated signaling in macrophages attenuated scar formation in multiple fibrotic models. Although cardiac fibrosis represents the terminal stage of many heart diseases, limited studies have directly explored macrophage-specific mechanical signaling in this process. Cho et al.^[31] found that targeting Src, an upstream mechanosensitive kinase regulating YAP/TAZ signaling in cardiac fibroblasts, reduced cardiac fibrosis. Given the pivotal macrophage-fibroblast crosstalk in fibrosis progression, this study highlights the feasibility of modulating macrophage mechanotransduction as a therapeutic strategy. Furthermore, since macrophages are essential players in inflammation and immune activation in infectious diseases, strategies targeting macrophage-ECM interactions have shown promise in mitigating infection-related cardiac fibrosis, such as human immunodeficiency virus (HIV)-associated cardiovascular events^[179,180]. For instance, the anti-α4 integrin antibody natalizumab was found to reduce macrophage infiltration and fibrosis in the left ventricle of simian immunodeficiency virus macaque 251 strain (SIVmac251)-infected rhesus macaques, a model of HIV-induced heart disease^[151].

Among the mechanosensors, integrins are the most widely targeted, likely due to their accessibility on the cell surface and responsiveness to molecular blockade^[181]. The first integrin-targeting drug approved for clinical use was Abciximab, an αIIbβ3 antagonist approved in 1994 for coronary artery disease, highlighting the cardiovascular relevance of integrin inhibition^[153]. Efalizumab, an αL integrin inhibitor approved in 2003 for treating plaque psoriasis, was withdrawn in 2009 because of serious adverse effects^[154,155]. In 2004, natalizumab, a broad-spectrum α4 integrin inhibitor, was approved for multiple sclerosis^[152]. Since then, several subtype-specific integrin inhibitors have reached the clinic: vedolizumab (α4β7) for inflammatory bowel disease (approved in 2014) and lifitegrast (αLβ2) for dry eye disease (approved in 2016)^[156,157]. Carotegrast (AJM300), the first oral integrin inhibitor, was approved in 2022 for the treatment of active ulcerative colitis^[158]. Together, these advances reflect renewed momentum in integrin-targeted therapy development.

In addition to integrins, other mechanosensitive pathways have been explored. Verteporfin, an inhibitor of YAP signaling, is an approved small-molecule photosensitizer for neovascular macular degeneration^[182]. Several other agents are under clinical investigation. For example, Defactinib (VS-6063), a FAK inhibitor from Verastem Oncology, is in phase II trials for pancreatic cancer due to its anti-fibrotic properties (NCT02758587). Rho-associated coiled-coil containing protein kinase (ROCK) is a key mechanotransducer that controls cytoskeletal tension via myosin activation^[183]. Among its isoforms, ROCK2 has attracted particular attention; with the selective inhibitor, KD025 has completed phase II clinical trials for lung fibrosis (NCT02688647). Notch, functioning both as a mechanosensitive receptor and a transcriptional regulator, represents a particularly promising therapeutic target. The pan-Notch pathway inhibitor CB-103 is currently under clinical evaluation for the treatment of solid tumors^[164].

Despite these developments, no drugs have yet entered clinical trials specifically targeting macrophage mechanotransduction in cardiovascular disease. Although the peptide inhibitor of Piezo1, GsMTx4, has demonstrated cardioprotective effects in preclinical HF models^[165], its clinical utility remains to be validated. Importantly, recent studies suggest potential in this direction: Cho et al.^[31] reported that suppressing stromal mechanosensing reduced cardiac fibrosis, while Chen et al.^[178] demonstrated that targeting circulating mechanoresponsive monocytes and macrophages alleviated fibrosis in a humanized scarring model. Together, these findings support further exploration of macrophage-targeted mechanotherapies in cardiac fibrosis.

In addition to cellular targets, normalizing the ECM has emerged as a promising therapeutic strategy, particularly in the context of tumor immunotherapy. For instance, studies have shown that chimeric antigen receptor T (CAR-T) cells expanded on softened Matrigel exhibited enhanced stemness and increased cytotoxicity against solid tumors compared with cells cultured on conventional plastic surfaces^[184]. This supports the notion that ECM softening can enhance immune cell function and suggests a broader role for matrix modulation in regulating macrophage behavior.

Among the contributors to ECM stiffening, members of the lysyl oxidase (LOX) family, including LOX, LOXL1, and LOXL2, are key drivers of collagen crosslinking during fibrosis^[185-187]. β-Aminopropionitrile (BAPN), a well-known pan-LOX inhibitor, disrupts collagen crosslinking and thus softens the ECM. In animal studies, BAPN has been shown to reduce skin fibrosis and improve scar appearance^[188]. It also appears to modulate macrophage polarization, shifting the balance between M1 and M2 phenotypes^[189]. In cardiovascular studies, BAPN reduced myocardial fibrosis and altered macrophage populations in models of age-related cardiac fibrosis, suggesting potential utility in cardiac fibrosis therapy^[190]. However, BAPN has not progressed to current clinical studies. Only two early studies, conducted before the 1980s, evaluated its ability to inhibit collagen crosslinking in patients with scleroderma and urethral strictures^[191,192]. The lack of clinical development is primarily due to its in vivo toxicity^[193]. In animal models, BAPN induces lathyrism—characterized by extensive connective tissue damage and development of abdominal aortic aneurysm (AAA)^[194,195]. Another pan-LOX inhibitor, PXS-5505, has shown promising effects in treating myelofibrosis and thrombocythemia, which are associated with elevated cardiovascular risk due to chronic inflammation, abnormal platelet activity, and a prothrombotic state^[196].

Among LOX family members, LOXL2 has been the most frequently targeted in cardiovascular research. Elevated levels of circulating LOXL2 have been detected in patients with HF^[197]. A small-molecule LOXL2 inhibitor, SNT-5382, has been shown to reduce fibrosis and improve cardiac function in a mouse model of MI, with phase I trials demonstrating good safety^[166]. Another LOXL2 inhibitor, the monoclonal antibody Simtuzumab, has been tested in clinical trials for fibrotic diseases such as liver and lung fibrosis (e.g., NCT01707472, NCT01672853), but its efficacy in cardiac fibrosis remains unclear.

Beyond the LOX family, other ECM-modulating strategies are being explored. For example, targeting hyaluronan synthesis using the natural inhibitor ethyl-3,4-dihydroxybenzoate has shown efficacy in preclinical models of breast cancer^[168]. MMP-9, a MMP that degrades ECM components such as collagen and gelatin, has also been investigated. Monoclonal antibodies targeting MMP-9 have entered clinical trials for fibrotic diseases, chronic obstructive pulmonary disease (COPD), and solid tumors (e.g., NCT02077465, NCT02545504). Although numerous studies have shown that plasma MMP-9 levels correlate with the extent of myocardial remodeling and the progression of HF^[198], therapeutic strategies targeting MMP-9 remain largely restricted to animal models rather than clinical studies in cardiac disease. The difficulty in clinically translating MMP-9-targeted therapies may be partially attributed to the dual, stage-dependent roles of MMP-9 in cardiac disease. In early stages of tissue injury, MMP-9 contributes to ECM degradation, immune cell infiltration, and clearance of damaged matrix, facilitating tissue repair. Specifically, elevated MMP-9 expression in macrophages has been shown to improve ventricular function following MI by modulating inflammatory and fibrotic responses during the early stages of tissue repair^[199]. In this context, MMP-9 facilitates ECM degradation, promotes immune cell infiltration, and clearance of damaged tissue, collectively supporting tissue recovery. However, sustained or excessive MMP-9 activity may exert detrimental effects by promoting the release and activation of profibrotic cytokines, particularly TGF-β^[200]. Elevated TGF-β levels enhance crosstalk between macrophages and fibroblasts, stimulating fibroblast activation and excessive collagen production^[201]. This profibrotic cascade contributes to maladaptive ECM remodeling, progressive fibrosis, and ultimately HF. These contrasting roles highlight the stage-dependent duality of MMPs in cardiac disease. While transient activation may be beneficial during early repair phases, chronic overexpression can drive pathological remodeling, suggesting that selective or temporally controlled modulation, rather than broad-spectrum inhibition, may offer a more effective and safer approach for treating fibrosis-related cardiac conditions.

In summary, although many ECM-targeting approaches were initially developed for cancer and fibrotic disorders, the shared mechanisms of ECM remodeling across organ systems suggest strong translational potential for treating cardiac fibrosis and HF. Continued preclinical validation and the development of targeted delivery strategies will be essential to overcome systemic toxicity and to optimize therapeutic efficacy in cardiovascular settings.