Cryptic domains of tenascin-C differentially control fibronectin fibrillogenesis

A single chain variable fragment antibody (Tn 64) cognate to fibronectin type III repeats promotes corneal wound healing by inhibiting fibrosis

Corneal wound healing requires epithelial reorganization and stromal extracellular matrix (ECM) remodeling, with ECM proteins such as Tenascin C (TnC) regulating and maintaining corneal homeostasis. The N-terminal globular domain and C-terminal fibrinogen-related domains of TnC are separated by epidermal growth factor (EGF)-like repeats, and upto fifteen fibronectin type III domains (Tn fn). Overexpression of Tn fn 1-5 and its splice variants occurs in varied pathologies. We have previously used Tn64 (a single chain variable fragment antibody cognate to Tn fn 1-5) to establish roles of Tn fn 1-5 in fibrotic pathologies such as rheumatoid arthritis and posterior capsular opacification. Here, we show that Tn64 binds to Tn fn repeats 3-5 (which constitute the major site for binding of soluble fibronectin within TnC). Unlike other Tn fn domains, Tn fn 3-5 displays no inhibition of fibronectin matrix assembly. Rather, the Tn fn 3-5 construct is pro-fibrotic and elicits increased expression of fibronectin. We examined corneal epithelial as well as stromal wound healing through Tn64 binding to Tn fn 3-5, using a human corneal epithelial cell (HCEC) line, primary cultures of human corneal fibroblasts (HCFs), and an ex-vivo corneal organ culture model. Tn64 enhanced proliferation and adhesion of corneal epithelial cells, while inhibiting the migration of corneal fibroblasts and myofibroblasts. Tn64 appears to attenuate inflammation through downregulation of TNF-α, prevent corneal fibrosis by limiting fibronectin polymerization, and promote regeneration of corneal epithelia and stroma, suggesting that it could be developed as a therapeutic agent for effective anti-fibrotic corneal wound healing.

Extracellular matrix complexity in biomarker studies: a novel assay detecting total serum tenascin-C reveals different distribution to isoform-specific assays

Serum biomarkers are the gold standard in non-invasive disease diagnosis and have tremendous potential as prognostic and theranostic tools for patient stratification. Circulating levels of extracellular matrix molecules are gaining traction as an easily accessible means to assess tissue pathology. However, matrix molecules are large, multimodular proteins that are subject to a vast array of post-transcriptional and post-translational modifications. These modifications often occur in a tissue- and/or disease-specific manner, generating hundreds of different variants, each with distinct biological roles. Whilst this complexity can offer unique insight into disease processes, it also has the potential to confound biomarker studies. Tenascin-C is a pro-inflammatory matrix protein expressed at low levels in most healthy tissues but elevated in, and associated with the pathogenesis of, a wide range of autoimmune diseases, fibrosis, and cancer. Analysis of circulating tenascin-C has been widely explored as a disease biomarker. Hundreds of different tenascin-C isoforms can be generated by alternative splicing, and this protein is also modified by glycosylation and citrullination. Current enzyme-linked immunosorbent assays (ELISA) are used to measure serum tenascin-C using antibodies, recognising sites within domains that are alternatively spliced. These studies, therefore, report only levels of specific isoforms that contain these domains, and studies on the detection of total tenascin-C are lacking. As such, circulating tenascin-C levels may be underestimated and/or biologically relevant isoforms overlooked. We developed a highly specific and sensitive ELISA measuring total tenascin-C down to 0.78ng/ml, using antibodies that recognise sites in constitutively expressed domains. In cohorts of people with different inflammatory and musculoskeletal diseases, levels of splice-specific tenascin-C variants were lower than and distributed differently from total tenascin-C. Neither total nor splice-specific tenascin-C levels correlated with the presence of autoantibodies to citrullinated tenascin-C in rheumatoid arthritis (RA) patients. Elevated tenascin-C was not restricted to any one disease and levels were heterogeneous amongst patients with the same disease. These data confirm that its upregulation is not disease-specific, instead suggest that different molecular endotypes or disease stages exist in which pathology is associated with, or independent of, tenascin-C. This immunoassay provides a novel tool for the detection of total tenascin-C that is critical for further biomarker studies. Differences between the distribution of tenascin-C variants and total tenascin-C have implications for the interpretation of studies using isoform-targeted assays. These data highlight the importance of assay design for the detection of multimodular matrix molecules and reveal that there is still much to learn about the intriguingly complex biological roles of distinct matrix proteoforms.

Extracellular matrix remodeling in tumor progression and immune escape: from mechanisms to treatments

The malignant tumor is a multi-etiological, systemic and complex disease characterized by uncontrolled cell proliferation and distant metastasis. Anticancer treatments including adjuvant therapies and targeted therapies are effective in eliminating cancer cells but in a limited number of patients. Increasing evidence suggests that the extracellular matrix (ECM) plays an important role in tumor development through changes in macromolecule components, degradation enzymes and stiffness. These variations are under the control of cellular components in tumor tissue via the aberrant activation of signaling pathways, the interaction of the ECM components to multiple surface receptors, and mechanical impact. Additionally, the ECM shaped by cancer regulates immune cells which results in an immune suppressive microenvironment and hinders the efficacy of immunotherapies. Thus, the ECM acts as a barrier to protect cancer from treatments and supports tumor progression. Nevertheless, the profound regulatory network of the ECM remodeling hampers the design of individualized antitumor treatment. Here, we elaborate on the composition of the malignant ECM, and discuss the specific mechanisms of the ECM remodeling. Precisely, we highlight the impact of the ECM remodeling on tumor development, including proliferation, anoikis, metastasis, angiogenesis, lymphangiogenesis, and immune escape. Finally, we emphasize ECM "normalization" as a potential strategy for anti-malignant treatment.

Unraveling reno-protective effects of SGLT2 inhibition in human proximal tubular cells

Large clinical trials demonstrated that SGLT2 inhibitors (SGLT2i) slow the progression of kidney function decline in type 2 diabetes. Because the underlying molecular mechanisms are largely unknown, we studied the effects of SGLT2i on gene expression in two human proximal tubular (PT) cell lines under normoglycemic conditions, utilizing two SGLT2i, namely empagliflocin and canagliflocin. Genome-wide expression analysis did not reveal substantial differences between these two SGLT2i. Microarray hybridization analysis identified 94 genes that were both upregulated by TGF-β1 and downregulated by either of the two SGLT2i in HK-2 and RPTEC/TERT1 (renal proximal tubular epithelial cells/telomerase reverse transcriptase 1) cells. Extracellular matrix organization showed the highest significance in pathway enrichment analysis. Differential gene expression of three annotated genes of interest within this pathway was verified on mRNA level in both cell lines. Whereas TGF-β1 induced mRNA expression of thrombospondin 1 (THBS1; 4.3-fold), tenascin C (TNC; 8-fold), and platelet-derived growth factor subunit B (PDGF-B; 4.2-fold), SGLT2i downregulated basal mRNA expression of THBS1 (0.2-fold), TNC (0.5 fold), and PDGF-B (0.6-fold). Administration of SGLT2i in the presence of TGF-β1 resulted in a significant inhibition of TGF-β1-induced THBS1 and TNC mRNA expression and TGF-β1-induced THBS1, TNC, and PDGF-BB protein expression. We conclude that SGLT2i block basal and TGF-β1-induced expression of key mediators of renal fibrosis and kidney disease progression in two independent human PT cell lines.

Mapping the recognition domains of pneumococcal fibronectin-binding proteins PavA and PavB demonstrates a common pattern of molecular interactions with fibronectin type III repeats

Colonization of mucosal respiratory surfaces is a prerequisite for the human pathobiont Streptococcus pneumoniae (the pneumococcus) to cause severe invasive infections. The arsenal of pneumococcal adhesins interacts with a multitude of extracellular matrix proteins. A paradigm for pneumococci is their interaction with the adhesive glycoprotein fibronectin, which facilitates bacterial adherence to host cells. Here, we deciphered the molecular interaction between fibronectin and pneumococcal fibronectin-binding proteins (FnBPs) PavA and PavB respectively. We show in adherence and binding studies that the pneumococcal interaction with fibronectin is a non-human specific trait. PavA and PavB target at least 13 out of 15 type III fibronectin domains as demonstrated in ligand overlay assays, surface plasmon resonance studies and SPOT peptide arrays. Strikingly, both pneumococcal FnBPs recognize similar peptides in targeted type III repeats. Structural comparisons revealed that the targeted type III repeat epitopes cluster on the inner strands of both β-sheets forming the fibronectin domains. Importantly, synthetic peptides of FnIII¹ , FnIII⁵ or FnIII¹⁵ bind directly to FnBPs PavA and PavB respectively. In conclusion, our study suggests a common pattern of molecular interactions between pneumococcal FnBPs and fibronectin. The specific epitopes recognized in this study can potentially be tested as antimicrobial targets in further scientific endeavours.

Soft-Mechanochemistry: Mechanochemistry Inspired by Nature

Cells and bacteria use mechanotransduction processes to transform a mechanical force into a chemical/biochemical response. The area of chemistry where chemical reactions are induced by mechanical forces is called mechanochemistry. Over the last few years, chemists developed force-induced reactions affecting covalent bonds in molecules under tension which requires high energy input and/or high intensity forces. In contrast, in nature, mechanotransduction processes take place with forces of much weaker intensity and much less demanding energy. They are mainly based on protein conformational changes or changes in supramacromolecular architectures. Mechanochemistry based on such low-energy-demanding processes and which does not affect chemical bonds can be called soft-mechanochemistry. In this feature article, we first discuss some examples of soft-mechanochemistry processes encountered in nature, in particular, cryptic sites, allowing us to define more precisely the concepts underlying soft-mechanochemistry. A series of examples, developed over the past few years, of chemomechanoresponsive systems based on soft-mechanochemistry principles are given. We describe, in particular, cryptic site surfaces, enzymatically active films whose activity can be modulated by stretching and films where stretching induces changes in their fluorescence properties. Finally, we give our view of the future of soft-mechanochemistry.

Tenascin-C: Form versus function

Tenascin-C is a large, multimodular, extracellular matrix glycoprotein that exhibits a very restricted pattern of expression but an enormously diverse range of functions. Here, we discuss the importance of deciphering the expression pattern of, and effects mediated by, different forms of this molecule in order to fully understand tenascin-C biology. We focus on both post transcriptional and post translational events such as splicing, glycosylation, assembly into a 3D matrix and proteolytic cleavage, highlighting how these modifications are key to defining tenascin-C function.

The co-expression of MMP-9 and Tenascin-C is significantly associated with the progression and prognosis of pancreatic cancer

BACKGROUND

Matrix metalloproteinase-9 (MMP-9) and Tenascin-C (TN-C) have been shown to be involved in the metastasis of many tumors. The purpose of this study was to determine the relationship between the co-expression of these two molecules and the clinical prognosis of pancreatic cancer.

METHODS

We investigated the expression of TN-C and MMP-9 in 103 pancreatic cancer tissues by immunohistochemistry and used statistical analyses to investigate the correlations of individual expression or co-expression of these two molecules with clinicopathological parameters and survival of pancreatic cancer.

RESULTS

The expression of MMP-9 and TN-C were increased in pancreatic cancer. The co-expression of MMP-9 and TN-C was also detected. The expression of MMP-9 and TN-C were correlated with vascular invasion, lymph node invasion, liver metastases and TNM stage. The co-expression of MMP-9 and TN-C was significantly related to the pancreatic cancer metastases. The individual overexpression of MMP-9 or TN-C significantly decreased the overall survival rates. The co-expression of MMP-9 and TN-C had the lowest overall survival rates. The co-expression of MMP-9 and TN-C was an independent predictor of survival for pancreatic cancer patients.

CONCLUSIONS

Co-expression of MMP-9 and TN-C was associated with poorer prognosis and was found to be an independent predictor of survival.

Different forms of tenascin-C with tenascin-R regulate neural differentiation in bone marrow-derived human mesenchymal stem cells

Mesenchymal stem cells (MSCs) are currently thought to transdifferentiate into neural lineages under specific microenvironments. Studies have reported that the tenascin family members, tenascin-C (TnC) and tenascin-R (TnR), regulate differentiation and migration, in addition to neurite outgrowth and survival in numerous types of neurons and mesenchymal progenitor cells. However, the mechanisms by which TnC and TnR affect neuronal differentiation are not well understood. In this study, we hypothesized that different forms of tenascin might regulate the neural transdifferentiation of human bone marrow-derived mesenchymal stem cells. Human MSCs were cultured in media incorporated with soluble tenascins, or on precoated tenascins. In a qualitative polymerase chain reaction analysis, adding a soluble TnC and TnR mixture to the medium significantly enhanced the expression of neuronal and glial markers, whereas no synaptic markers were expressed. Conversely, in groups of cells treated with coated TnC, hMSCs showed neurite outgrowth and synaptic marker expression. After being treated with coated TnR, hMSCs exhibited neuronal differentiation; however, it inhibited neurite outgrowth and synaptic marker expression. A combination of TnC and TnR significantly promoted hMSC differentiation in neurons or oligodendrocytes, induced neurite formation, and inhibited differentiation into astrocytes. Furthermore, the effect of the tenascin mixture showed dose-dependent effects, and a mixture ratio of 1:1 to 1:2 (TnC:TnR) provided the most obvious differentiation of neurons and oligodendrocytes. In a functional blocking study, integrin α7 and α9β1-blocking antibodies inhibited, respectively, 80% and 20% of mRNA expression by hMSCs in the coated tenascin mixture. In summary, the coated combination of TnC and TnR appeared to regulate neural differentiation signaling through integrin α7 and α9β1 in bone marrow-derived hMSCs. Our findings demonstrate novel mechanisms by which tenascin regulates neural differentiation, and enable the use of cell therapy to treat neurodegenerative diseases.

Tenascin-C and carcinoma cell invasion in oral and urinary bladder cancer

Carcinoma invasion is a complex process regulated by genetic and epigenetic factors as well. A relevant supportive condition for cancer cell migration is the reorganization of the extracellular matrix (ECM), which is realized in an orchestrated multicellular manner including carcinoma cells and stromal fibroblasts. An important key player in the process of ECM reorganization is Tenascin-C (Tn-C). The molecule occurs as different isoforms generated by alternative splicing and de novo glycosylation. Large variants of Tn-C are abundantly re-expressed in the invasive front of many carcinoma types. A special role for initiating migration and accompanied epithelial to mesenchymal transition has been suggested. Here, we review the current knowledge concerning the tumor biological importance of Tn-C, the synthesis and alternative splicing during the invasive process in general, and give an overview on the impact of Tn-C in urothelial carcinoma of the urinary bladder (UBC) and oral squamous cell carcinoma (OSCC).

Iron chelator alleviates tubulointerstitial fibrosis in diabetic nephropathy rats by inhibiting the expression of tenascinC and other correlation factors

Tubulointerstitial fibrosis is the final common pathway to diabetic nephropathy. However, only a few drugs are responsible for this pathologic process. We investigated the possible effect of deferiprone (iron chelator) treatment on experimental diabetic nephropathy (DN) rats, as well as the mechanisms involved in this process. Diabetic nephropathy was induced in rats by feeding on high-carbohydrate-fat food and injecting streptozotocin. After 20 weeks of deferiprone treatment, tubulointerstitial morphology was detected by staining with hematoxylin-eosin and Masson's trichrome. Tubulointerstitial fibrosis was measured using the point-counting technique. Biochemical parameters including fasting glucose, insulin resistance (IR), serum iron, ferritin, transferrin saturation (TS), and urinary albumin/creatinine ratio (UA/C) were detected in diabetic nephropathy models. Semiquantitative RT-PCR, western blot, and immunohistochemistry were utilized for evaluating mRNA and protein levels of tenascin C, fibronectin 1 (Fn1), TGF-β1, and collagen IV in nephridial tissue, respectively. Malonialdehyde (MDA) and superoxide dismutase (SOD) were determined by pyrogallol and thiobarbituric acid method. Tubulointerstitial fibrosis was significantly ameliorated after deferiprone treatment, and both mRNA and protein expressions of profibrotic factors were inhibited in treatment groups. Meanwhile, high levels of serum iron, ferritin, TS, and UA/C were observed in DN rats. These factors were down-regulated by deferiprone treatment. Furthermore, deferiprone effectively relieved serum IR and regulated oxidative stress process. Our results demonstrated the anti-fibrosis potential and renoprotective effects of deferiprone for diabetic nephropathy, and this process was partially mediated by tenascin C blocking.

The effects of tenascin C knockdown on trabecular meshwork outflow resistance

PURPOSE

Tenascin C (TNC) is a matricellular glycoprotein whose expression in adult tissue is indicative of tissue remodeling. The purpose of the current study was to determine the localization of TNC in trabecular meshwork (TM) tissue and to analyze the effects of TNC on intraocular pressure (IOP).

METHODS

Human TM frontal sections were immunostained with anti-TNC and imaged by confocal microscopy. TNC mRNA and protein levels were quantitated in anterior segments perfused at physiological and elevated pressure. Short, hairpin RNA (shRNA) silencing lentivirus targeting full-length TNC (shTNC) was applied to anterior segment perfusion organ cultures. The IOPs and central corneal thickness (CCT) of wild-type, TNC(-/-), and tenascin X (TNX(-/-)) knockout mice were measured.

RESULTS

TNC was distributed in the juxtacanalicular (JCT) region of adult human TM, predominantly in the basement membrane underlying the inner wall of Schlemm's canal. Application of shTNC lentivirus to human and porcine anterior segments in perfusion culture did not significantly affect outflow rate. Although TNC was upregulated in response to pressure, there was no difference in outflow rate when shTNC-silenced anterior segments were subjected to elevated pressure. Furthermore, IOPs and CCTs were not significantly different between TNC(-/-) or TNX(-/-) and wild-type mice.

CONCLUSIONS

TNC does not appear to contribute directly to outflow resistance. However, TNC immunolocalization in the JCT of adult human eyes suggests that certain areas of the TM are being continuously remodeled with or without an IOP increase.

Cleavage of extracellular matrix in periodontitis: gingipains differentially affect cell adhesion activities of fibronectin and tenascin-C

Gingipains are cysteine proteases that represent major virulence factors of the periodontopathogenic bacterium Porphyromonas gingivalis. Gingipains are reported to degrade extracellular matrix (ECM) of periodontal tissues, leading to tissue destruction and apoptosis. The exact mechanism is not known, however. Fibronectin and tenascin-C are pericellular ECM glycoproteins present in periodontal tissues. Whereas fibronectin mediates fibroblast adhesion, tenascin-C binds to fibronectin and inhibits its cell-spreading activity. Using purified proteins in vitro, we asked whether fibronectin and tenascin-C are cleaved by gingipains at clinically relevant concentrations, and how fragmentation by the bacterial proteases affects their biological activity in cell adhesion. Fibronectin was cleaved into distinct fragments by all three gingipains; however, only arginine-specific HRgpA and RgpB but not lysine-specific Kgp destroyed its cell-spreading activity. This result was confirmed with recombinant cell-binding domain of fibronectin. Of the two major tenascin-C splice variants, the large but not the small was a substrate for gingipains, indicating that cleavage occurred primarily in the alternatively spliced domain. Surprisingly, cleavage of large tenascin-C variant by all three gingipains generated fragments with increased anti-adhesive activity towards intact fibronectin. Fibronectin and tenascin-C fragments were detected in gingival crevicular fluid of a subset of periodontitis patients. We conclude that cleavage by gingipains directly affects the biological activity of both fibronectin and tenascin-C in a manner that might lead to increased cell detachment and loss during periodontal disease.

Matrikines and the lungs

The extracellular matrix is a complex network of fibrous and nonfibrous molecules that not only provide structure to the lung but also interact with and regulate the behaviour of the cells which it surrounds. Recently it has been recognised that components of the extracellular matrix proteins are released, often through the action of endogenous proteases, and these fragments are termed matrikines. Matrikines have biological activities, independent of their role within the extracellular matrix structure, which may play important roles in the lung in health and disease pathology. Integrins are the primary cell surface receptors, characterised to date, which are used by the matrikines to exert their effects on cells. However, evidence is emerging for the need for co-factors and other receptors for the matrikines to exert their effects on cells. The potential for matrikines, and peptides derived from these extracellular matrix protein fragments, as therapeutic agents has recently been recognised. The natural role of these matrikines (including inhibitors of angiogenesis and possibly inflammation) make them ideal targets to mimic as therapies. A number of these peptides have been taken forward into clinical trials. The focus of this review will be to summarise our current understanding of the role, and potential for highly relevant actions, of matrikines in lung health and disease.

Plasma and cellular fibronectin: distinct and independent functions during tissue repair

Fibronectin (FN) is a ubiquitous extracellular matrix (ECM) glycoprotein that plays vital roles during tissue repair. The plasma form of FN circulates in the blood, and upon tissue injury, is incorporated into fibrin clots to exert effects on platelet function and to mediate hemostasis. Cellular FN is then synthesized and assembled by cells as they migrate into the clot to reconstitute damaged tissue. The assembly of FN into a complex three-dimensional matrix during physiological repair plays a key role not only as a structural scaffold, but also as a regulator of cell function during this stage of tissue repair. FN fibrillogenesis is a complex, stepwise process that is strictly regulated by a multitude of factors. During fibrosis, there is excessive deposition of ECM, of which FN is one of the major components. Aberrant FN-matrix assembly is a major contributing factor to the switch from normal tissue repair to misregulated fibrosis. Understanding the mechanisms involved in FN assembly and how these interplay with cellular, fibrotic and immune responses may reveal targets for the future development of therapies to regulate aberrant tissue-repair processes.

Advances in tenascin-C biology

Tenascin-C is an extracellular matrix glycoprotein that is specifically and transiently expressed upon tissue injury. Upon tissue damage, tenascin-C plays a multitude of different roles that mediate both inflammatory and fibrotic processes to enable effective tissue repair. In the last decade, emerging evidence has demonstrated a vital role for tenascin-C in cardiac and arterial injury, tumor angiogenesis and metastasis, as well as in modulating stem cell behavior. Here we highlight the molecular mechanisms by which tenascin-C mediates these effects and discuss the implications of mis-regulated tenascin-C expression in driving disease pathology.

Identification of novel and distinct binding sites within tenascin-C for soluble and fibrillar fibronectin

Interactions between fibronectin and tenascin-C within the extracellular matrix provide specific environmental cues that dictate tissue structure and cell function. The major binding site for fibronectin lies within the fibronectin type III-like repeats (TNfn) of tenascin-C. Here, we systematically screened TNfn domains for their ability to bind to both soluble and fibrillar fibronectin. All TNfn domains containing the TNfn3 module interact with soluble fibronectin. However, TNfn domains bind differentially to fibrillar fibronectin. This distinct binding pattern is dictated by the fibrillar conformation of FN. TNfn1-3, but not TNfn3-5, binds to immature fibronectin fibrils, and additional TNfn domains are required for binding to mature fibrils. Multiple binding sites for distinct regions of fibronectin exist within tenascin-C. TNfn domains comprise a binding site for the N-terminal 70-kDa domain of fibronectin that is freely available and a binding site for the central binding domain of fibronectin that is cryptic in full-length tenascin-C. The 70-kDa and central binding domain regions are key for fibronectin matrix assembly; accordingly, binding of several TNfn domains to these regions inhibits fibronectin fibrillogenesis. These data highlight the complexity of protein-protein binding, the importance of protein conformation on these interactions, and the implications for the physiological assembly of complex three-dimensional matrices.