Collagen IV, encoded by genes COL4A1/COL4A2, is a major component of the basement membrane, a specialised extracellular matrix (ECM) structure. Mutations in these genes cause a genetic form of cerebral small vessel disease (cSVD), a leading cause of stroke and dementia. White matter abnormalities are a hallmark of cSVD and are closely linked to cognitive decline and dementia. While white matter defects occur in patients with COL4A1/2 mutations, they remain understudied and their mechanisms are unclear. To address these knowledge gaps, we combined magnetic resonance diffusion tensor imaging, pathology, ultrastructural investigations, behaviour and proteomic analysis of white matter in an established mouse model of cSVD due to a Col4a1 mutation (Col4a1+/Svc). The studies revealed that Col4a1+/Svc mice have reduced myelinating oligodendrocyte pools, axonal myelination defects, and altered white matter structural integrity as well as cognitive impairments. Proteomic analysis of isolated white matter from Col4a1+/Svc mice identified extensive changes to ECM and basement membrane composition. Furthermore, this provided evidence for altered endoplasmic reticulum (ER) biology including ER stress. To determine if white matter defects can be attenuated by targeting protein folding in the ER by promoting collagen IV secretion, we treated mice with the FDA-approved chemical chaperone 4-phenylbutyric acid. This revealed increased myelinating oligodendrocytes and improved axon-glial integrity in Col4a1+/Svc mice. These data provide novel insight into the pathomolecular mechanisms of collagen IV mutations in white matter abnormalities in cSVD and identify a modifiable pathway as a putative therapeutic target.
Andrew Leask and Asma Fadl interviewed Neha Dinesh, recipient of the American Society for Matrix Biology (ASMB) Founders Award at the ASMB meeting at Baltimore, November 2025.
Heart failure (HF) is often accompanied by cardiac fibrosis, a pathological process defined by excessive deposition of extracellular matrix (ECM) and predominantly mediated by cardiac fibroblasts. The accumulation of ECM leads to myocardial remodeling and stiffening, impairing cardiac function and exacerbating the risk of cardiac arrhythmia. Cartilage intermediate layer protein (CILP) is a matricellular protein that has recently been associated with cardiac fibrosis and identified in cardiac fibroblasts. While CILP is known to respond to mechanical stress and modulates ECM synthesis in cartilage, its function, regulation, and mechanism of action in cardiac tissue remain poorly understood. Both in cardiac fibroblasts and chondrocytes, the well-known profibrotic transforming growth factor beta (TGF-β) promotes CILP expression. However, the existing literature leads to a contradiction in its function: while some evidence indicates a protective role by inhibiting TGF-β signaling in the heart, others have shown a pathogenic role, where CILP promotes fibrosis. Additionally, studies have reported increased circulating CILP levels in patients with cardiovascular or cardiometabolic disorders, suggesting potential as a biomarker of HF. Nevertheless, these human association data do not clarify whether CILP is protective or pathogenic. This review summarizes the existing knowledge about CILP in cardiac tissue, explores its connections with distinct cardiac fibroblast subpopulations and evaluates its potential as biomarker and therapeutic target in cardiac fibrosis.
The cell surface glycocalyx is a pericellular matrix that surrounds all cells, including macrophages, and regulates their function and interaction with the environment. The glycocalyx is composed of a range of glycans and glyco-proteins and its shedding into the blood is observed in, and is used as a marker of, a variety of inflammatory conditions such as viral infections. However, little is known about the signals and locations that regulate glycocalyx formation and heterogeneity across macrophage subsets. We now report that mouse lung macrophages express a glycocalyx that is dependent on their anatomical location and the mediators driving their differentiation from monocytes. Furthermore, during inflammatory conditions, caused by viral infection, the macrophage glycocalyx is remodelled in complex ways. Overall, our study provides a novel pathway involved in macrophage glycocalyx formation at rest and during inflammatory responses at mucosal tissue sties. This impacts our emerging understanding of the glycocalyx on immune cells beyond the classical paradigm of glycocalyx regulation of endothelial and vascular function.
Laminins initiate basement membrane (BM) assembly by adhering to cells, establishing cytoskeletal links through integrin and dystroglycan receptors, and by polymerizing to form a sheet-like provisional matrix that recruits other BM components to complete assembly. Laminin polymerization is mediated by the LN domain tips of the three short arms that bind together to form "polymer nodes" connecting adjacent laminins. The first step of this assembly is the low affinity binding of a β-LN domain to a γ-LN domain, followed by a higher affinity binding of an α-LN domain to the β-γ complex. Negative staining, mutagenesis, and cryo-electron microscopic studies have revealed the polymer node is organized as a triskelion connected by "toe-to heel" LN interactions. A related structure using toe-to-heel LN interactions is seen in the polymer inhibiting complex formed when netrin-4 binds to laminin γ1. LAMA2-deficient related dystrophy, affecting muscle, peripheral nerve and brain, results from nonsense, missense, and deletion mutations of the LAMA2 gene. A clinical subset is caused by in-frame mutations in the α2-LN domain that prevent polymerization. A dystrophic mouse model (dy2J/dy2J) was used to develop a method of disease amelioration by expressing laminin-binding proteins that bear a functional α1-LN domain to enable polymerization. A model for the more common severe dystrophy (dy3K/dy3K), in which α2-laminins are replaced by α4-laminins, benefits from double expression of laminin-binding proteins that enable polymerization and that bind to dystroglycan. Such approaches, using adeno-associated virus (AAV) delivery of genes encoding these proteins, hold promise in the development of treatments for the human condition.
Intracerebral hemorrhage (ICH) causes high rates of mortality and long-term disability, but there are no effective treatments currently. Two key pathologies of ICH are blood-brain barrier (BBB) damage and white matter injury. Previous studies show that oligodendrocytes (OLs) regulate BBB integrity and (re)myelination via the extracellular matrix (ECM). The receptors that mediate these functions, however, remain incompletely understood. Here, we investigated the function of OL-derived integrin-β1 under both homeostatic and ICH conditions using conditional knockout mice. The mutant mice were grossly normal with intact BBB and OL maturation/myelination under homeostatic conditions. After ICH, however, these mutants exhibited exacerbated brain injury, including larger hematoma volume, elevated brain edema, aggravated axonal injury, enhanced BBB damage, compromised OL differentiation/maturation, impaired remyelination, and worsened neurological dysfunction. Subsequent studies revealed that the enhanced BBB injury was mediated by both paracellular and transcellular mechanisms and associated with pericyte defects. These findings demonstrate that OL-derived integrin-β1 is dispensable under homeostatic conditions but strictly required for BBB repair and remyelination following hemorrhagic stroke.
Secreted Protein Acidic and Rich in Cysteine (SPARC), also known as osteonectin or BM-40, is a prototypical matricellular protein that regulates the dynamic interplay between cells and the extracellular matrix (ECM). Unlike structural ECM components that primarily provide mechanical support, SPARC functions as a regulatory molecule that modulates cell-matrix communication, collagen fibrillogenesis, and tissue remodeling. In musculoskeletal tissues -including bone, cartilage, skeletal muscle, tendons, and intervertebral discs - SPARC plays essential roles in organizing ECM architecture, maintaining mechanical integrity, and coordinating adaptive responses to mechanical loading. Emerging evidence indicates that SPARC also acts beyond classical ECM regulation by linking ECM organization to intracellular signaling and metabolic pathways. In this review, we summarize the structural features and biological functions of SPARC, with particular emphasis on its roles in skeletal and connective tissues. We discuss its contribution to ECM assembly and cell-matrix interactions across diverse tissue environments. Finally, we highlight emerging concepts linking SPARC to tissue degeneration, inflammation, and aging, and explore its potential as a biomarker and therapeutic target in musculoskeletal disease.
The blood-brain barrier (BBB) is an elegant structure composed of brain endothelial cells, pericytes, astrocyte endfeet, and non-cellular components—the glycocalyx and basal lamina (BL). By actively regulating molecular and cellular exchanges between the blood and the brain, the BBB maintains CNS homeostasis under physiological conditions. BBB disruption drives secondary brain injury after stroke and correlates with stroke outcomes. In Alzheimer’s disease (AD), BBB breakdown is an early pathology and plays an important role in cognitive impairment. Previous studies mainly concentrate on how different cellular components of the BBB regulate its integrity in physiological and pathological conditions, leaving the glycocalyx and BL understudied. In this review, we elucidate glycocalyx and BL changes in neurological disorders and discuss the functional significance of these alterations. Specifically, the structure/composition of the glycocalyx and BL as well as the mechanical properties, turnover and assembly of the BL are described first. Next, we summarize how the glycocalyx and BL as well as the major constituents of the BL change in stroke and AD. The functional significance of these alterations is also discussed. Last, we review key questions that need to be answered and future directions in the field.
Excessive deposition of extracellular matrix (ECM) following laminectomy contributes to epidural scar formation, which is associated with postoperative lumbodorsal pain. This study aimed to investigate the role and mechanisms of the ECM glycoprotein tenascin-C (TNC) in epidural scar formation using a murine laminectomy model. TNC was significantly increased in the epidural scarring tissues from the patients recovered after spine operation. As similar, the epidural scar was enriched with TNC in a mouse model of laminectomy. TNC promoted the activation of fibroblasts. In addition to the membrane receptor Toll-like receptor 4 (TLR4), TNC directly bind with Caveolin-1 via its EGFL domain. Mechanistically, TNC/Caveolin-1 suppressed transforming growth factor-β receptor I (TβRI) activity, thereby enhancing fibronectin synthesis in fibroblasts. In the mouse model of epidural fibrosis, TNC-knockout (TNC-KO) significantly reduced epidural scar formation accompanied by decreased collagen deposition and fibronectin (Fn) content within scar tissue. In conclusion, our findings highlight TNC as a critical mediator of epidural fibrosis, and anti-TNC therapeutics may represent a promising strategy to mitigate postoperative epidural scarring.
Testican-2 (SPOCK2) is a secreted, extracellular matrix-associated proteoglycan that modulates cell-matrix interactions, extracellular proteolysis, and tissue-specific signaling across multiple organs. Beyond its initial characterization in the central nervous system, subsequent studies have established roles in the lung, pancreas, bone, and kidney, where testican-2 regulates tissue remodeling and extracellular matrix dynamics under both physiological and disease conditions. Mechanistic, genetic, and proteomic studies highlight its dual role as a biomarker and functional modulator, with kidney disease emerging as a clinically relevant context. However, upstream regulators, cell-type-specific functions, context-dependent effects, and the structural basis underlying its domain-specific interactions remain to be fully defined. This review synthesizes current evidence on testican-2 biology across tissues and disease settings, highlighting emerging themes and unresolved questions. A clearer understanding of its regulation and function will help refine its value as a biomarker and potential therapeutic target.
Tendon injuries account for considerable and escalating clinical burden. After injury, tendons heal poorly with persistent fibrovascular scar. Unlike healthy tendon which is type I collagen (COL1)-rich and highly-aligned, fibrovascular scar is type III collagen (COL3)-rich and disorganized; this compositional and organizational change has been implicated in the functional deficits resulting from tendon injury. Accordingly, COL3 is historically considered a primary driver of poor tendon healing. Given compelling evidence of COL3’s role in regulating matrix structure and cell behavior, we sought to define the role of COL3 in driving physiologic/pathologic tendon healing through regulation of all phases of healing. Leveraging a mouse model of global, inducible Col3a1 knockdown, we reduced Col3a1 expression at the time of patellar tendon injury and investigated extracellular matrix, cellular, and mechanical changes at 1-, 3-, and 6-weeks post-injury. Based on data from other tissues, we hypothesized that COL3 loss would exacerbate poor tendon healing, with temporally-distinct contributions to tendon healing outcomes resulting from COL3’s critical regulation of matrix organization, cell phenotype and activities, and tissue mechanics. Unexpectedly, reduction of COL3 in young adult mice did not change collagen architecture and had few, nuanced impacts on cell behavior and tissue mechanics throughout healing. These findings challenge the conventional paradigm that COL3 drives poor tendon healing outcomes and emphasize the need to identify matrix and cell mechanisms contributing to poor tendon healing. Understanding COL3’s role in other injury models and lifespan contexts, including tendon development and aging, will provide more insight into its regulatory and therapeutic potential.
Jamuar syndrome (Developmental and Epileptic Encephalopathy 84, OMIM# 618792) is a rare autosomal recessive congenital disorder of glycosylation (CDG), caused by variations in the gene encoding UDP-glucose dehydrogenase (UGDH). Although a number of UGDH variants have been functionally characterized, there is an incomplete catalogue of variants and their impacts on development. Here, we present functional data characterizing new missense variants from three unrelated individuals who were D379N homozygous, Y356D homozygous, and compound heterozygous A436G/R442W, respectively. UGDH activity was low to undetectable in patient-derived fibroblasts bearing either UGDH D379N or UGDH A436G/R442W, relative to WT fibroblasts, despite robust UGDH expression in both. Measurement of nucleotide sugar levels revealed a significant decrease in the UGDH product, UDP-glucuronate, and consequent reductions in hyaluronan production, Notch1 levels, and rate of O-and N-linked glycan synthesis, consistent with loss of UGDH activity. These features support the designation of UGDH D379N and UGDH A436G as causative variants in Jamuar Syndrome. We expressed and purified UGDH D379N, A436G, R442W, R443H, and Y356D variants to examine underlying molecular mechanisms. Kinetic properties and structural stability assays selectively revealed significant changes in conformational dynamics that manifested strong effects on endogenous inhibitor binding and product inhibition. The results suggest that alterations to the C-terminal domain impact activity of UGDH in cells by impairing its cofactor exchange rate and diminishing quaternary association. These effects would be maximized at developmental milestones in which hypoxia drives morphological change, since NADH accumulation would then decrease glycosaminoglycan production, with profound developmental consequences.
Tissue remodeling critically depends on fibroblasts and macrophages, but the timely and coordinated induction of phenotypes that promote remodeling-associated extracellular matrix (ECM) and interstitial collagen degradation is poorly understood. Here, we exploit the potency of activated dermal fibroblasts and macrophage plasticity to study cell-cell interplay. We identify fibroblasts as vigorous stimulators of co-cultured macrophages' differentiation towards a collagen-clearing phenotype. Fibroblasts secrete several soluble factors with macrophage recruitment and stimulation potential, including M-CSF, CXCL-1, CCL2, IL-6, and TIMP-1. IL-6-driven upregulation of Mannose Receptor (MR, CD206), an endocytic collagen-clearance receptor, is identified as a key macrophage effector-response. Mouse dermal in situ collagen turnover models demonstrate that macrophage MR-dependent collagen-uptake constitutes a recruitable pathway that can readily facilitate collagen degradation and links IL-6 macrophage-stimulation to the process. Importantly, a novel fibroblast depleter system reveals that fibroblasts dictate macrophage differentiation and collagen-clearance in vivo. Our study establishes activated fibroblasts as critical orchestrators of macrophage functions with potential impact on physiological tissue remodeling and fibrosis.
To understand the physiological significance of the interaction between Cathepsin K (CtsK) and heparan sulfate (HS) in bone resorption, we manipulated HS-CtsK interaction genetically by mutating three basic residues of CtsK responsible for binding HS. This knockin strain (CtskAAA) expresses an HS-binding deficient CtsK variant. In contrast to CtsK-KO mice, which display profound osteopetrosis, under C57BL/6 background CtskAAA/AAA mice display an osteoporotic phenotype due to enhanced bone resorption by the mutant osteoclasts. This phenotype is consistent with our finding that HS inhibits the collagenase activity of CtsK, suggesting that HS functions as a restraining mechanism to dampen CtsK activity. Surprisingly, under 129S1 background, CtskAAA/AAA mice display increased bone mass due to reduced bone resorptive activity of the mutant osteoclasts, opposite to the phenotype found under C57BL/6 background. This phenotype appears to reflect another biochemical property of HS-CtsK interaction, where HS can stabilize CtsK and extend its half-life. Combined, our data provide strong genetic evidence that CtsK-HS interaction is required for normal osteoclast activity in bone homeostasis through two mechanisms. Endogenous HS likely functions as a buffering agent to prevent excessive resorption and promote sustained resorption, and the balance point of the buffering can be greatly affected by genetic backgrounds.
Inadequate collagen deposition is at the core of various pathologies, including non-healing wounds, fibrotic diseases, and tumour progression. It is therefore paramount to fully understand how central effectors affect collagen synthesis and turnover. Here, we will focus on two interconnected physiological effectors, vitamin C (ascorbic acid) and hypoxia (low oxygen levels), which both regulate collagen abundance and organisation. Ascorbic acid (AA) is known to act as a cofactor for collagen-modifying enzymes (collagen prolyl and lysyl hydroxylases) and is vital for collagen thermal stability, proper folding, and fibrillogenesis. Similarly, hypoxia has a strong impact on collagen synthesis, primarily through the stabilisation and activation of the hypoxia-inducible factors (HIFs), which, in turn, upregulate the expression of a range of collagen-modifying enzymes, including the collagen prolyl and lysyl hydroxylases. The consequence of both pathways is an enhanced collagen production, stability, maturation and cross-linking. Since AA and hypoxia both act on collagen hydroxylases, although by different mechanisms, i.e. AA increases the enzymatic activity whereas HIF increases the enzyme production, one can expect a possible synergistic effect of both factors. However, a more complex interplay exists between oxygen levels, AA and collagen as HIF affects AA intracellular uptake via the upregulation of one of its transporters while AA promotes HIF hydroxylation, thus reducing its stability and activity. A comprehensive understanding of this bidirectional control and the feedback loops between hypoxia, AA, and collagen is therefore critical to better tackle pathologies linked to abnormal collagen synthesis.
Extracellular matrix (ECM) remodeling is essential for adaptation to changing mechanical demands, yet the mechanisms linking altered strain to functional outcomes remain poorly understood. This study aimed to define molecular and cellular programs driving the adaptation of tendon to increased (exercise) and decreased (disuse) strain. Male murine flexor tendon explants were cultured in incubator-housed tensile bioreactors and subjected to step changes in cyclic strain. After acclimation at 1% cyclic strain, exercise tendons experienced a step increase to 5% cyclic strain, while disuse tendons underwent stress deprivation. Increased strain produced significant mechanical adaptations, including increased elastic modulus and failure stress. Multiscale analyses of matrix organization, tissue composition, protein synthesis, signaling factors, and proteolytic activity revealed the mechanisms underlying these adaptations. Exercise-induced functional improvements were linked to an anabolic remodeling program characterized by TGF-β and IL-6 signaling, small leucine-rich proteoglycan expression, MMP suppression, and enhanced collagen alignment. These findings indicate that regulators of matrix organization and turnover, beyond synthesis alone, are critical for functional adaptation. In contrast, mechanical unloading reduced collagen synthesis and promoted an MMP-dominant, catabolic phenotype favoring matrix breakdown. This study provides a comprehensive characterization of ECM remodeling, linking defined mechanical perturbations to molecular regulation and emergent structure-function relationships. These findings identify targetable mediators of adaptive remodeling and establish a framework for future studies of maladaptive ECM changes in aging, injury, and disease.
