Heparan sulfate is necessary for the early formation of nascent fibronectin and collagen I fibrils at matrix assembly sites

Unexpected Remyelination in the Absence of Matrix Metalloproteinase 7

In multiple sclerosis (MS), an influx of immune cells into the central nervous system leads to focal demyelinating lesions in the brain, optic nerve, and spinal cord. As MS progresses, remyelination increasingly fails, leaving neuronal axons vulnerable to degeneration and resulting in permanent neurological disability. In chronic MS lesions, the aberrant accumulation of extracellular matrix (ECM) molecules, including fibronectin and hyaluronan, impairs oligodendrocyte progenitor cell differentiation, contributing to remyelination failure. Removing inhibitory ECM is therefore a therapeutic target to stimulate remyelination in MS. Intriguingly, the expression of the fibronectin-degrading enzyme matrix metalloproteinase 7 (MMP7) is decreased in chronic MS lesions compared to control white matter. Therefore, we examined the role of MMP7 upon cuprizone-induced demyelination, hypothesizing that the lack of MMP7 would lead to impaired breakdown of its ECM substrates, including fibronectin, and diminished remyelination. Unexpectedly, remyelination proceeded efficiently in the absence of MMP7. In the remyelination phase, the lack of MMP7 did not lead to the accumulation of fibronectin or of laminin, another MMP7 substrate. Moreover, in the setting of chronic demyelination, levels of fibronectin were actually lower in MMP7-/- mice, while levels of hyaluronan, which is not a known MMP7 substrate, were also lower. Overall, these results indicate that MMP7 is not essential for remyelination in the cuprizone model and point to an unexpected complexity in how MMP7 deficiency influences fibronectin and hyaluronan levels in chronic demyelination.

Fibronectin matrix assembly at a glance

The organization and mechanics of extracellular matrix (ECM) protein polymers determine tissue structure and function. Secreted ECM components are assembled into polymers via a cell-mediated process. The specific mechanisms that cells use for assembly are crucial for generating tissue-appropriate matrices. Fibronectin (FN) is a ubiquitous and abundant ECM protein that is assembled into a fibrillar matrix by a receptor-mediated process, and the FN matrix provides a foundation for incorporation of many other proteins into the ECM. In this Cell Science at a Glance article and the accompanying poster, we describe the domain organization of FN and the events that initiate and propagate a stable insoluble network of FN fibrils. We also discuss intracellular pathways that regulate FN assembly and the impact of changes in assembly on disease progression.

Multi-omics analyses of early-onset familial Alzheimer's disease and Sanfilippo syndrome zebrafish models reveal commonalities in disease mechanisms

Sanfilippo syndrome (mucopolysaccharidosis type III, MPSIII) causes childhood dementia, while Alzheimer's disease is the most common type of adult-onset dementia. There is no cure for either of these diseases, and therapeutic options are extremely limited. Increasing evidence suggests commonalities in the pathogenesis of these diseases. However, a direct molecular-level comparison of these diseases has never been performed. Here, we exploited the power of zebrafish reproduction (large families of siblings from single mating events raised together in consistent environments) to conduct sensitive, internally controlled, comparative transcriptome and proteome analyses of zebrafish models of early-onset familial Alzheimer's disease (EOfAD, psen1Q96_K97del/+) and MPSIIIB (nagluA603fs/A603fs) within single families. We examined larval zebrafish (7 days post fertilisation), representing early disease stages. We also examined the brains of 6-month-old zebrafish, which are approximately equivalent to young adults in humans. We identified substantially more differentially expressed genes and pathways in MPS III zebrafish than in EOfAD-like zebrafish. This is consistent with MPS III being a rapidly progressing and earlier onset form of dementia. Similar changes in expression were detected between the two disease models in gene sets representing extracellular matrix receptor interactions in larvae, and the ribosome and lysosome pathways in 6-month-old adult brains. Cell type-specific changes were detected in MPSIIIB brains at 6 months of age, likely reflecting significant disturbances of oligodendrocyte, neural stem cell, and inflammatory cell functions and/or numbers. Our 'omics analyses have illuminated similar disease pathways between EOfAD and MPS III indicating where efforts to find mutually effective therapeutic strategies can be targeted.

Enhancing intrinsic TGF-β signaling via heparan sulfate glycosaminoglycan regulation to promote mesenchymal stem cell capabilities and chondrogenesis for cartilage repair

Osteoarthritis burdens patients due to the limited regenerative capacity of chondrocytes. Traditional cartilage repair often falls short, necessitating innovative approaches. Mesenchymal stem cells (MSCs) show promise for regeneration. Heparan sulfate glycosaminoglycans (HS-GAGs) regulate cellular functions, making them a target for cartilage repair. This study highlights how Heparinase III (HepIII) cleaves intact HS-GAGs in bone marrow-derived MSCs (BM-MSCs), enhancing their capabilities and specifically promoting chondrogenesis. HepIII-treated BM-MSCs cultured in a hanging drop device for three days, significantly increased cell number and aggregation into a cell sphere with early chondrogenesis. HepIII promoted BM-MSCs toward chondrogenesis, increasing type II collagen, intact HS-GAGs, and sulfated GAG content, while upregulating chondrogenic and heparan sulfate proteoglycan genes. Treatment with the TGF-β inhibitor (SB-431542) in HepIII-treated BM-MSCs demonstrated enhanced intrinsic transforming growth factor-β (TGF-β) signaling and fibronectin expression. This approach also boosted BM-MSC self-renewal, immunosuppressive potential, and modified acetylated histone signatures, offering a cost-effective strategy for cartilage repair by addressing inflammation, metabolic changes, and the high costs of traditional TGF-β methods. From the results, HepIII-treated BM-MSCs show potential for use in combination with other biopolymers as injectable gels to improve cartilage repair in osteoarthritis patients in the near future.

Mechanisms of assembly and remodelling of the extracellular matrix

The extracellular matrix (ECM) is the complex meshwork of proteins and glycans that forms the scaffold that surrounds and supports cells. It exerts key roles in all aspects of metazoan physiology, from conferring physical and mechanical properties on tissues and organs to modulating cellular processes such as proliferation, differentiation and migration. Understanding the mechanisms that orchestrate the assembly of the ECM scaffold is thus crucial to understand ECM functions in health and disease. This Review discusses novel insights into the compositional diversity of matrisome components and the mechanisms that lead to tissue-specific assemblies and architectures tailored to support specific functions. The Review then highlights recently discovered mechanisms, including post-translational modifications and metabolic pathways such as amino acid availability and the circadian clock, that modulate ECM secretion, assembly and remodelling in homeostasis and human diseases. Last, the Review explores the potential of 'matritherapies', that is, strategies to normalize ECM composition and architecture to achieve a therapeutic benefit.

Detection of PatIent-Level distances from single cell genomics and pathomics data with Optimal Transport (PILOT)

Although clinical applications represent the next challenge in single-cell genomics and digital pathology, we still lack computational methods to analyze single-cell or pathomics data to find sample-level trajectories or clusters associated with diseases. This remains challenging as single-cell/pathomics data are multi-scale, i.e., a sample is represented by clusters of cells/structures, and samples cannot be easily compared with each other. Here we propose PatIent Level analysis with Optimal Transport (PILOT). PILOT uses optimal transport to compute the Wasserstein distance between two individual single-cell samples. This allows us to perform unsupervised analysis at the sample level and uncover trajectories or cellular clusters associated with disease progression. We evaluate PILOT and competing approaches in single-cell genomics or pathomics studies involving various human diseases with up to 600 samples/patients and millions of cells or tissue structures. Our results demonstrate that PILOT detects disease-associated samples from large and complex single-cell or pathomics data. Moreover, PILOT provides a statistical approach to find changes in cell populations, gene expression, and tissue structures related to the trajectories or clusters supporting interpretation of predictions.

Heparin-collagen I bilayers stimulate FAK/ERK½ signaling via α2β1 integrin to support the growth and anti-inflammatory potency of mesenchymal stromal cells

Understanding mesenchymal stromal cells (MSCs) growth mechanisms in response to surface chemistries is essential to optimize culture methods for high-quality and robust cell yields in cell manufacturing applications. Heparin (HEP) and collagen 1 (COL) substrates have been reported to enhance cell adhesion, growth, viability, and secretory potential in MSCs. However, the biomolecular mechanisms underlying the benefits of combined HEP/COL substrates are unknown. This work used HEP/COL bilayered surfaces to investigate the role of integrin-HEP interactions in the advantages of MSC culture. The layer-by-layer approach (LbL) was used to create HEP/COL bilayers, which were made up of stacks of 8 and 9 layers that combined HEP and COL in an alternate arrangement. Surface spectroscopic investigations and laser scanning microscopy evaluations verified the biochemical fingerprint of each component and a total stacked bilayer thickness of roughly 150 nm. Cell growth and apoptosis in response to IC50 and IC75 levels of BTT-3033 and Cilengitide, α2β1 and αvβ3 integrin inhibitors respectively, were evaluated on HEP/COL coated surfaces using two bone marrow-derived MSC donors. While integrin activity did not affect cell growth rates, it significantly affected cell adhesion and apoptosis on HEP/COL surfaces. HEP-ending HEP/COL surfaces significantly increased FAK-ERK½ phosphorylation and endogenous cell COL deposition compared to COL, COL-ending HEP/COL and uncoated surfaces. BTT-3033 but not Cilengitide treatment markedly affected FAK-ERK½ activity levels on HEP-ending HEP/COL surfaces supporting a major role for α2β1 activity. BTT-3033 treatment on HEP-ending bilayers reduced MSC-mediated macrophage inhibitory activity and altered the cytokine profile of co-cultures. Overall, this study supports a novel role for HEP in regulating the survival and potency of MSCs via enhancing the α2β1-FAK-ERK½ signaling mechanism.

Direct antitumoral effects of sulfated fucans isolated from echinoderms: a possible role of neuropilin-1/β1 integrin endocytosis and focal adhesion kinase degradation

Hypercoagulability, a major complication of metastatic cancers, has usually been treated with heparins from natural sources, or with their synthetic derivatives, which are under intense investigation in clinical oncology. However, the use of heparin has been challenging for patients with risk of severe bleeding. While the systemic administration of heparins, in preclinical models, has shown primarily attenuating effects on metastasis, their direct effect on established solid tumors has generated contradictory outcomes. We investigated the direct antitumoral properties of two sulfated fucans isolated from marine echinoderms, FucSulf1 and FucSulf2, which exhibit anticoagulant activity with mild hemorrhagic potential. Unlike heparin, sulfated fucans significantly inhibited tumor cell proliferation (by ~30-50%), and inhibited tumor migration and invasion in vitro. We found that FucSulf1 and FucSulf2 interacted with fibronectin as efficiently as heparin, leading to loss of prostate cancer and melanoma cell spreading. The sulfated fucans increased the endocytosis of β1 integrin and neuropilin-1 chains, two cell receptors implicated in fibronectin-dependent adhesion. The treatment of cancer cells with both sulfated fucans, but not with heparin, also triggered intracellular focal adhesion kinase (FAK) degradation, with a consequent overall decrease in activated focal adhesion kinase levels. Finally, only sulfated fucans inhibited the growth of B16-F10 melanoma cells implanted in the dermis of syngeneic C57/BL6 mice. FucSulf1 and FucSulf2 arise from this study as candidates for the design of possible alternatives to long-term treatments of cancer patients with heparins, with the advantage of also controlling local growth and invasion of malignant cells.

Sulfated motifs in heparan sulfate inhibit Streptococcus pneumoniae adhesion onto fibronectin and attenuate corneal infection

A large number of bacterial pathogens bind to host extracellular matrix (ECM) components. For example, many Gram-negative and Gram-positive pathogens express binding proteins for fibronectin (FN) on their cell surface. Mutagenesis studies of bacterial FN-binding proteins have demonstrated their importance in pathogenesis in preclinical animal models. However, means to draw on these findings to design therapeutic approaches that specifically target FN-bacteria interactions have not been successful because bacterial pathogens can elaborate several FN-binding proteins and also because FN is an essential protein and likely a nondruggable target. Here we report that select heparan compounds potently inhibit Streptococcus pneumoniae infection of injured corneas in mice. Using intact heparan sulfate (HS) and heparin (HP), heparinase-digested fragments of HS, HP oligosaccharides, and chemically or chemoenzymatically modified heparan compounds, we found that inhibition of S. pneumoniae corneal infection by heparan compounds is not mediated by simple charge effects but by a selective sulfate group. Removal of 2-O-sulfates significantly inhibited the ability of HP to inhibit S. pneumoniae corneal infection, whereas the addition of 2-O-sulfates to heparosan (H) significantly increased H's ability to inhibit bacterial corneal infection. Proximity ligation assays indicated that S. pneumoniae attaches directly to FN fibrils in the corneal epithelial ECM and that HS and HP specifically inhibit this binding interaction in a 2-O-sulfate-dependent manner. These data suggest that heparan compounds containing 2-O-sulfate groups protect against S. pneumoniae corneal infection by inhibiting bacterial attachment to FN fibrils in the subepithelial ECM of injured corneas. Moreover, 2-O-sulfated heparan compounds significantly inhibited corneal infection in immunocompromised hosts, by a clinical keratitis isolate of S. pneumoniae, and also when topically administered in a therapeutic manner. These findings suggest that the administration of nonanticoagulant 2-O-sulfated heparan compounds may represent a plausible approach to the treatment of S. pneumoniae keratitis.

Nucleation of fibronectin fibril assembly requires binding between heparin and the 13th type III module of fibronectin

Fibronectin (FN), a critical component of the extracellular matrix, is assembled into fibrils through a cell-mediated process. Heparan sulfate (HS) binds to the III13 module of FN, and fibroblasts lacking this glycosaminoglycan exhibit reduced FN fibril assembly. To determine if HS depends on III13 to control FN assembly, we deleted both III13 alleles in NIH 3T3 cells using the CRISPR-Cas9 system. ΔIII13 cells assembled fewer FN matrix fibrils and less DOC-insoluble FN matrix than wildtype cells. Little if any mutant FN matrix was assembled when purified ΔIII13 FN was provided to Chinese hamster ovary (CHO) cells, showing that lack of III13 caused the deficiency in assembly by ΔIII13 cells. Addition of heparin promoted the assembly of wildtype FN by CHO cells, but it had no effect on the assembly of ΔIII13 FN. Furthermore, heparin binding stabilized the folded conformation of III13 and prevented it from self-associating with increasing temperature suggesting that stabilization by HS/heparin binding might regulate interactions between III13 and other FN modules. This effect would be particularly important at matrix assembly sites where our data show that ΔIII13 cells require both exogenous wildtype FN and heparin in the culture medium to maximize assembly site formation. Our results show that heparin-promoted growth of fibril nucleation sites is dependent on III13. We conclude that HS/heparin binds to III13 to promote and control the nucleation and development of FN fibrils.

A single-cell transcriptional atlas reveals resident progenitor cell niche functions in TMJ disc development and injury

The biological characteristics of the temporomandibular joint disc involve complex cellular network in cell identity and extracellular matrix composition to modulate jaw function. The lack of a detailed characterization of the network severely limits the development of targeted therapies for temporomandibular joint-related diseases. Here we profiled single-cell transcriptomes of disc cells from mice at different postnatal stages, finding that the fibroblast population could be divided into chondrogenic and non-chondrogenic clusters. We also find that the resident mural cell population is the source of disc progenitors, characterized by ubiquitously active expression of the NOTCH3 and THY1 pathways. Lineage tracing reveals that Myh11⁺ mural cells coordinate angiogenesis during disc injury but lost their progenitor characteristics and ultimately become Sfrp2⁺ non-chondrogenic fibroblasts instead of Chad⁺ chondrogenic fibroblasts. Overall, we reveal multiple insights into the coordinated development of disc cells and are the first to describe the resident mural cell progenitor during disc injury.

A high-impact FN1 variant correlates with fibronectin-mediated glomerulopathy via decreased binding to collagen type IV

The glomerular basement membrane (GBM) consists of laminins, collagen IV, nidogens, and fibronectin and is essential for filtration barrier integrity in the kidney. Critically, structural and functional abnormalities in the GBM are involved in chronic kidney disease (CKD) occurrence and development. Fibronectin is encoded by FN1 and is essential for podocyte-podocyte and podocyte-matrix interactions. However, disrupted or disordered fibronectin occurs in many kidney diseases. In this study, we identified a novel mutation (c.3415G>A) in FN1 that causes glomerular fibronectin-specific deposition in a gain-of-function manner, that may be associated with thin basement membrane nephropathy (TBMN) and expand the spectrum of phenotypes seen in glomerulopathy with fibronectin deposits (GFND). Our studies confirmed this variant increased fibronectin's ability to bind to integrin, thereby maintaining podocyte adhesion. Also, we hypothesised that TBMN arose as the fibronectin variant exhibited a decreased capacity to bind COL4A3/4. Our study is the first to identify and link this novel pathogenic mutation (c.3415G>A) in FN1 to GFND as well as TBMN, which may broaden the phenotype and mutation spectrums of the FN1 gene. We believe our data will positively impact genetic counselling and prenatal diagnostics for GFND with TBMN and other associated conditions that may be commonly benign conditions in humans, and may not require proteinuria-lowering treatments or renal biopsy.