Localization of a binding site for the proteoglycan decorin on collagen XIV (undulin)

The Versatility of Collagen in Pharmacology: Targeting Collagen, Targeting with Collagen

Collagen, a versatile family of proteins with 28 members and 44 genes, is pivotal in maintaining tissue integrity and function. It plays a crucial role in physiological processes like wound healing, hemostasis, and pathological conditions such as fibrosis and cancer. Collagen is a target in these processes. Direct methods for collagen modulation include enzymatic breakdown and molecular binding approaches. For instance, Clostridium histolyticum collagenase is effective in treating localized fibrosis. Polypeptides like collagen-binding domains offer promising avenues for tumor-specific immunotherapy and drug delivery. Indirect targeting of collagen involves regulating cellular processes essential for its synthesis and maturation, such as translation regulation and microRNA activity. Enzymes involved in collagen modification, such as prolyl-hydroxylases or lysyl-oxidases, are also indirect therapeutic targets. From another perspective, collagen is also a natural source of drugs. Enzymatic degradation of collagen generates bioactive fragments known as matrikines and matricryptins, which exhibit diverse pharmacological activities. Overall, collagen-derived peptides present significant therapeutic potential beyond tissue repair, offering various strategies for treating fibrosis, cancer, and genetic disorders. Continued research into specific collagen targeting and the application of collagen and its derivatives may lead to the development of novel treatments for a range of pathological conditions.

Supply chain logistics - the role of the Golgi complex in extracellular matrix production and maintenance

The biomechanical and biochemical properties of connective tissues are determined by the composition and quality of their extracellular matrix. This, in turn, is highly dependent on the function and organisation of the secretory pathway. The Golgi complex plays a vital role in directing matrix output by co-ordinating the post-translational modification and proteolytic processing of matrix components prior to their secretion. These modifications have broad impacts on the secretion and subsequent assembly of matrix components, as well as their function in the extracellular environment. In this Review, we highlight the role of the Golgi in the formation of an adaptable, healthy matrix, with a focus on proteoglycan and procollagen secretion as example cargoes. We then discuss the impact of Golgi dysfunction on connective tissue in the context of human disease and ageing.

Decorin knockdown affects the gene expression profile of adhesion, growth and extracellular matrix metabolism in C-28/I2 chondrocytes

Decorin is a member of small leucine-rich proteoglycan family, which is involved in multiple biological functions mainly as a structural and signaling molecule, and disturbances in its own metabolism plays a crucial role in the pathogenesis of osteoarthropathy. In this study, we aim to further explore the biological function of decorin and their role in human chondrocyte cell line, C28/I2. Lentivirus-mediated shRNA was applied to down-regulate decorin expression in C28/I2 chondrocytes. Effect of decorin knockdown on gene expression profiles was determined by RNA sequencing followed by bioinformatics analysis. MTT, adhesion assays and flow cytometry were used to investigate the effect of decorin knockdown on cell proliferation, adhesion, and apoptosis. sGAG content in the culture medium was determined by DMMB assay. Stably transfected C28/I2 cells were seeded onto the cancellous bone matrix gelatin (BMG) to construct tissue-engineered cartilage. The histological patterns were evaluated by H&E and Toluidine blue staining. In this study, 1780 differentially expressed genes (DEGs) including 864 up-regulated and 916 down-regulated genes were identified using RNA-Seq. The reliability of the gene expression was further verified by qRT-PCR. GO and KEGG pathway enrichment analysis revealed diverse cellular processes were affected by decorin silencing such as: cell adhesion, growth, and metabolism of extracellular matrix. In addition, we confirmed that down-regulation of decorin significantly suppressed cell proliferation and adhesion and induced apoptosis. The sGAG content in the media was significantly increased after decorin silencing. Engineered articular tissues in the decorin knockdown group exhibited cartilage destruction and proteoglycan loss as evidenced by H&E and Toluidine blue stains. Overall, this combined data helps to provide a comprehensive understanding of the roles of decorin following its knockdown in C28/I2 cells.

Study of the Chronology of Expression of Ten Extracellular Matrix Molecules during the Myogenesis in Cattle to Better Understand Sensory Properties of Meat

The sensory properties of beef are known to depend on muscle fiber and intramuscular connective tissue composition (IMCT). IMCT is composed of collagens, proteoglycans and glycoproteins. The differentiation of muscle fibers has been extensively studied but there is scarcity in the data concerning IMCT differentiation. In order to be able to control muscle differentiation to improve beef quality, it is essential to understand the ontogenesis of IMCT molecules. Therefore, in this study, we investigated the chronology of appearance of 10 IMCT molecules in bovine Semitendinosus muscle using immunohistology technique at five key stages of myogenesis. Since 60 days post-conception (dpc), the whole molecules were present, but did not have their final location. It seems that they reach it at around 210 dpc. Then, the findings emphasized that since 210 dpc, the stage at which the differentiation of muscle fibers is almost complete, the differentiation of IMCT is almost completed. These data suggested that for the best controlling of the muscular differentiation to improve beef sensory quality, it would be necessary to intervene very early (before the IMCT constituents have acquired their definitive localization and the muscle fibers have finished differentiating), i.e., at the beginning of the first third of gestation.

An atlas of the aging lung mapped by single cell transcriptomics and deep tissue proteomics

Aging promotes lung function decline and susceptibility to chronic lung diseases, which are the third leading cause of death worldwide. Here, we use single cell transcriptomics and mass spectrometry-based proteomics to quantify changes in cellular activity states across 30 cell types and chart the lung proteome of young and old mice. We show that aging leads to increased transcriptional noise, indicating deregulated epigenetic control. We observe cell type-specific effects of aging, uncovering increased cholesterol biosynthesis in type-2 pneumocytes and lipofibroblasts and altered relative frequency of airway epithelial cells as hallmarks of lung aging. Proteomic profiling reveals extracellular matrix remodeling in old mice, including increased collagen IV and XVI and decreased Fraser syndrome complex proteins and collagen XIV. Computational integration of the aging proteome with the single cell transcriptomes predicts the cellular source of regulated proteins and creates an unbiased reference map of the aging lung.

Aging impacts lung functionality and makes it more susceptible to chronic diseases. Combining proteomics and single cell transcriptomics, the authors chart molecular and cellular changes in the aging mouse lung, discover aging hallmarks, and predict the cellular sources of regulated proteins.

An atlas of the aging lung mapped by single cell transcriptomics and deep tissue proteomics

Aging promotes lung function decline and susceptibility to chronic lung diseases, which are the third leading cause of death worldwide. Here, we use single cell transcriptomics and mass spectrometry-based proteomics to quantify changes in cellular activity states across 30 cell types and chart the lung proteome of young and old mice. We show that aging leads to increased transcriptional noise, indicating deregulated epigenetic control. We observe cell type-specific effects of aging, uncovering increased cholesterol biosynthesis in type-2 pneumocytes and lipofibroblasts and altered relative frequency of airway epithelial cells as hallmarks of lung aging. Proteomic profiling reveals extracellular matrix remodeling in old mice, including increased collagen IV and XVI and decreased Fraser syndrome complex proteins and collagen XIV. Computational integration of the aging proteome with the single cell transcriptomes predicts the cellular source of regulated proteins and creates an unbiased reference map of the aging lung.

Gene profile of zebrafish fin regeneration offers clues to kinetics, organization and biomechanics of basement membrane

How some animals regenerate missing body parts is not well understood. Taking advantage of the zebrafish caudal fin model, we performed a global unbiased time-course transcriptomic analysis of fin regeneration. Biostatistics analyses identified extracellular matrix (ECM) as the most enriched gene sets. Basement membranes (BMs) are specialized ECM structures that provide tissues with structural cohesion and serve as a major extracellular signaling platform. While the embryonic formation of BM has been extensively investigated, its regeneration in adults remains poorly studied. We therefore focused on BM gene expression kinetics and showed that it recapitulates many aspects of development. As such, the re-expression of the embryonic col14a1a gene indicated that col14a1a is part of the regeneration-specific program. We showed that laminins and col14a1a genes display similar kinetics and that the corresponding proteins are spatially and temporally controlled during regeneration. Analysis of our CRISPR/Cas9-mediated col14a1a knockout fish showed that collagen XIV-A contributes to timely deposition of laminins. As changes in ECM organization can affect tissue mechanical properties, we analyzed the biomechanics of col14a1a^-/- regenerative BM using atomic force microscopy (AFM). Our data revealed a thinner BM accompanied by a substantial increase of the stiffness when compared to controls. Further AFM 3D-reconstructions showed that BM is organized as a checkerboard made of alternation of soft and rigid regions that is compromised in mutants leading to a more compact structure. We conclude that collagen XIV-A transiently acts as a molecular spacer responsible for BM structure and biomechanics possibly by helping laminins integration within regenerative BM.

Odd skipped-related 1 identifies a population of embryonic fibro-adipogenic progenitors regulating myogenesis during limb development

Fibro-adipogenic progenitors (FAPs) are an interstitial cell population in adult skeletal muscle that support muscle regeneration. During development, interstitial muscle connective tissue (MCT) cells support proper muscle patterning, however the underlying molecular mechanisms are not well understood and it remains unclear whether adult FAPs and embryonic MCT cells share a common lineage. We show here that mouse embryonic limb MCT cells expressing the transcription factor Osr1, differentiate into fibrogenic and adipogenic cells in vivo and in vitro defining an embryonic FAP-like population. Genetic lineage tracing shows that developmental Osr1⁺ cells give rise to a subset of adult FAPs. Loss of Osr1 function leads to a reduction of myogenic progenitor proliferation and survival resulting in limb muscle patterning defects. Transcriptome and functional analyses reveal that Osr1⁺ cells provide a critical pro-myogenic niche via the production of MCT specific extracellular matrix components and secreted signaling factors.

Fibro-adipogenic progenitors (FAPs) form part of interstitial muscle connective tissue (MCT) in adults but the origin of this non-myogenic lineage is unclear. Here, the authors show that Odd skipped related 1 (Osr1) in mice marks embryonic MCT, giving rise to FAPs, and loss of Osr1 in the limb causes muscle defects.

Regulators of Collagen Fibrillogenesis during Molar Development in the Mouse

Development of mammalian teeth and surrounding tissues includes time-space changes in the extracellular matrix composition and organization. This requires complex control mechanisms to regulate its synthesis and remodeling. Fibril-associated collagens with interrupted triple helices (FACITs) and a group of small leucine-rich proteoglycans (SLRPs) are involved in the regulation of collagen fibrillogenesis. Recently, collagen type XII and collagen type XIV, members of the FACITs family, were found in the peridental mesenchyme contributing to alveolar bone formation. This study was designed to follow temporospatial expression of collagen types XIIa and XIVa in mouse first molar and adjacent tissues from embryonic day 13, when the alveolar bone becomes morphologically apparent around the molar tooth bud, until postnatal day 22, as the posteruption stage. The patterns of decorin, biglycan, and fibromodulin, all members of the SLRPs family and interacting with collagens XIIa and XIVa, were investigated simultaneously. The situation in the tooth was related to what happens in the alveolar bone, and both were compared to the periodontal ligament. The investigation provided a complex localization of the five antigens in soft tissues, the dental pulp, and periodontal ligaments; in the mineralized tissues, predentin/dentin and alveolar bone; and junction between soft and hard tissues. The results illustrated developmentally regulated and tissue-specific changes in the balance of the two FACITs and three SLRPs.

Systems Genetics Approach Identifies Gene Pathways and Adamts2 as Drivers of Isoproterenol-Induced Cardiac Hypertrophy and Cardiomyopathy in Mice

We previously reported a genetic analysis of heart failure traits in a population of inbred mouse strains treated with isoproterenol to mimic catecholamine-driven cardiac hypertrophy. Here, we apply a co-expression network algorithm, wMICA, to perform a systems-level analysis of left ventricular transcriptomes from these mice. We describe the features of the overall network but focus on a module identified in treated hearts that is strongly related to cardiac hypertrophy and pathological remodeling. Using the causal modeling algorithm NEO, we identified the gene Adamts2 as a putative regulator of this module and validated the predictive value of NEO using small interfering RNA-mediated knockdown in neonatal rat ventricular myocytes. Adamts2 silencing regulated the expression of the genes residing within the module and impaired isoproterenol-induced cellular hypertrophy. Our results provide a view of higher order interactions in heart failure with potential for diagnostic and therapeutic insights.

New insight of some extracellular matrix molecules in beef muscles. Relationships with sensory qualities

The aim of this study was to highlight the relationships between decorin, tenascin-X and type XIV collagen, three minor molecules of extracellular matrix (ECM), with some structural parameters of connective tissue and its content in total collagen, its cross-links (CLs) and its proteoglycans (PGs). In addition, we have evaluated impact of these minor molecules on beef quality traits. The relative abundance of these molecules was evaluated by western blot analysis in Longissimus thoracis (LT) and Biceps femoris (BF) muscles from Aberdeen Angus and Blond d'Aquitaine beef breeds. Decorin and tenascin-X were more abundant in BF than in LT (1.8 v. 0.5 arbitrary units (AU), respectively, P<0.001, and 1.0 v. 0.6 AU, P<0.05). There was no muscle effect for collagen XIV content. Decorin and tenascin-X relative abundance were positively correlated with perimysium and endomysium areas and with collagen characteristics (total, insoluble and CLs). Decorin was negatively correlated with total PG content and positively with tenascin-X. Collagen XIV was correlated with any of parameters measured. To assess the impact of decorin, tenascin-X and collagen XIV and of their ratios to total collagen and PGs on shear force and quality traits we realized, respectively, a multiple-linear regression analysis and a Pearson's correlation analysis. Decorin and tenascin-X relative abundance were, respectively, negatively and positively involved in juiciness. Decorin relative abundance was also negatively involved in abnormal flavour and positively in overall liking. The ratio of decorin to total collagen and PGs was negatively correlated to juiciness, together with collagen XIV ratio to total PGs. The ratios of decorin, tenascin-X and collagen XIV to total PGs were positively correlated to sensory tenderness, negatively to abnormal beef flavour and positively to overall liking. The ratio of decorin to total collagen was also negatively correlated to abnormal flavour and positively to overall liking while its ratio to total PGs was positively correlated to beef flavour and overall liking. Results of the present study highlighted for the first time the possible role of minor ECM molecules on beef quality traits. In addition, variations of meat texture and more generally of sensory qualities would depend not only to the quantity of total collagen and of its CLs, but also of components of ECM such as decorin, tenascin-X and collagen XIV and of their ratios to total collagen and PGs.

Identification of a DNA methylome profile of esophageal squamous cell carcinoma and potential plasma epigenetic biomarkers for early diagnosis

DNA methylation is a critical epigenetic mechanism involved in key cellular processes. Its deregulation has been linked to many human cancers including esophageal squamous cell carcinoma (ESCC). This study was designed to explore the whole methylation status of ESCC and to identify potential plasma biomarkers for early diagnosis. We used Infinium Methylation 450k array to analyze ESCC tissues (n = 4), paired normal surrounding tissues (n = 4) and normal mucosa from healthy individuals (n = 4), and combined these with gene expression data from the GEO database. One hundred and sixty eight genes had differentially methylated CpG sites in their promoter region and a gene expression pattern inverse to the direction of change in DNA methylation. These genes were involved in several cancer-related pathways. Three genes were validated in additional 42 ESCC tissues and paired normal surrounding tissues. The methylation frequency of EPB41L3, GPX3, and COL14A1 were higher in tumor tissues than in normal surrounding tissues (P<0.017). The higher methylation frequency of EPB41l3 was correlated with large tumor size (P = 0.044) and advanced pT tumor stage (P = 0.001). The higher methylation frequency of GPX3 and COL14A1 were correlated with advanced pN tumor stage (P = 0.001 and P<0.001). The methylation of EPB41L3, GPX3, and COL14A1 genes were only found in ESCC patients' plasma, but not in normal individuals upon testing 42 ESCC patients and 50 healthy individuals. Diagnostic sensitivity was increased when methylation of any of the 3 genes were counted (64.3% sensitivity and 100% specificity). These differentially methylated genes in plasma may be used as biomarkers for early diagnosis of ESCC.

Lumican binds ALK5 to promote epithelium wound healing

Lumican (Lum), a small leucine-rich proteoglycan (SLRP) family member, has multiple matricellular functions both as an extracellular matrix component and as a matrikine regulating cell proliferation, gene expression and wound healing. To date, no cell surface receptor has been identified to mediate the matrikine functions of Lum. This study aimed to identify a perspective receptor that mediates Lum effects on promoting wound healing. Transforming growth factor-β receptor 1 (ALK5) was identified as a potential Lum-interacting protein through in silico molecular docking and molecular dynamics. This finding was verified by biochemical pull-down assays. Moreover, the Lum function on wound healing was abrogated by an ALK5-specific chemical inhibitor as well as by ALK5 shRNAi. Finally, we demonstrated that eukaryote-specific post-translational modifications are not required for the wound healing activity of Lum, as recombinant GST-Lum fusion proteins purified from E. coli and a chemically synthesized LumC₁₃ peptide (the last C-terminal 13 amino acids of Lum) have similar effects on wound healing in vitro and in vivo.

The regulatory roles of small leucine-rich proteoglycans in extracellular matrix assembly

Small leucine-rich proteoglycans (SLRPs) are involved in a variety of biological and pathological processes. This review focuses on their regulatory roles in matrix assembly. SLRPs have protein cores and hypervariable glycosylation with multivalent binding abilities. During development, differential interactions of SLRPs with other molecules result in tissue-specific spatial and temporal distributions. The changing expression patterns play a critical role in the regulation of tissue-specific matrix assembly and therefore tissue function. SLRPs play significant structural roles within extracellular matrices. In addition, they play regulatory roles in collagen fibril growth, fibril organization and extracellular matrix assembly. Moreover, they are involved in mediating cell-matrix interactions. Abnormal SLRP expression and/or structures result in dysfunctional extracellular matrices and pathophysiology. Altered expression of SLRPs has been found in many disease models, and structural deficiency also causes altered matrix assembly. SLRPs regulate assembly of the extracellular matrix, which defines the microenvironment, modulating both the extracellular matrix and cellular functions, with an impact on tissue function.

Integrated proteomic, transcriptomic, and biological network analysis of breast carcinoma reveals molecular features of tumorigenesis and clinical relapse

Gene and protein expression changes observed with tumorigenesis are often interpreted independently of each other and out of context of biological networks. To address these limitations, this study examined several approaches to integrate transcriptomic and proteomic data with known protein-protein and signaling interactions in estrogen receptor positive (ER+) breast cancer tumors. An approach that built networks from differentially expressed proteins and identified among them networks enriched in differentially expressed genes yielded the greatest success. This method identified a set of genes and proteins linking pathways of cellular stress response, cancer metabolism, and tumor microenvironment. The proposed network underscores several biologically intriguing events not previously studied in the context of ER+ breast cancer, including the overexpression of p38 mitogen-activated protein kinase and the overexpression of poly(ADP-ribose) polymerase 1. A gene-based expression signature biomarker built from this network was significantly predictive of clinical relapse in multiple independent cohorts of ER+ breast cancer patients, even after correcting for standard clinicopathological variables. The results of this study demonstrate the utility and power of an integrated quantitative proteomic, transcriptomic, and network analysis approach to discover robust and clinically meaningful molecular changes in tumors.

Pathophysiological mechanisms of autosomal dominant congenital stromal corneal dystrophy: C-terminal-truncated decorin results in abnormal matrix assembly and altered expression of small leucine-rich proteoglycans

Autosomal-dominant congenital stromal corneal dystrophy (CSCD) is a human genetic disease characterized by corneal opacities beginning shortly after birth. It is linked to a frameshift mutation in decorin, resulting in a C-terminal truncation lacking 33 amino acids that includes the "ear" repeat, a feature specific for small leucine-rich proteoglycans. Our goals are to elucidate the roles of the mutant decorin in CSCD pathophysiology and to decipher the mechanism whereby mutant decorin affects matrix assembly. A novel animal model that recapitulates human CSCD was generated. This transgenic mouse model targets expression of truncated decorin to keratocytes, thereby mimicking the human frameshift mutation. Mutant mice expressed both wild-type and mutant decorin. Corneal opacities were found throughout, with increased severity toward the posterior stroma. The architecture of the lamellae was disrupted with relatively normal lamellae separated by regions of abnormal fibril organization. Within abnormal zones, the interfibrillar spacing and the fibril diameters were increased. Truncated decorin negatively affected the expression of endogenous decorin, biglycan, lumican, and keratocan and positively affected fibromodulin. Our results provide a mechanistic explanation for the generation of corneal opacities in CSCD. Thus, truncated decorin acts in a dominant-negative manner to interfere dually with matrix assembly and binding to receptor tyrosine kinases, thereby causing abnormal expression of endogenous small leucine-rich proteoglycans leading to structural abnormalities within the cornea and vision loss.

Extracellular matrix molecules: potential targets in pharmacotherapy

The extracellular matrix (ECM) consists of numerous macromolecules classified traditionally into collagens, elastin, and microfibrillar proteins, proteoglycans including hyaluronan, and noncollagenous glycoproteins. In addition to being necessary structural components, ECM molecules exhibit important functional roles in the control of key cellular events such as adhesion, migration, proliferation, differentiation, and survival. Any structural inherited or acquired defect and/or metabolic disturbance in the ECM may cause cellular and tissue alterations that can lead to the development or progression of disease. Consequently, ECM molecules are important targets for pharmacotherapy. Specific agents that prevent the excess accumulation of ECM molecules in the vascular system, liver, kidney, skin, and lung; alternatively, agents that inhibit the degradation of the ECM in degenerative diseases such as osteoarthritis would be clinically beneficial. Unfortunately, until recently, the ECM in drug discovery has been largely ignored. However, several of today's drugs that act on various primary targets affect the ECM as a byproduct of the drugs' actions, and this activity may in part be beneficial to the drugs' disease-modifying properties. In the future, agents and compounds targeting directly the ECM will significantly advance the treatment of various human diseases, even those for which efficient therapies are not yet available.

Identification of candidate tumour suppressor genes frequently methylated in renal cell carcinoma

Promoter region hyermethylation and transcriptional silencing is a frequent cause of tumour suppressor gene (TSG) inactivation in many types of human cancers. Functional epigenetic studies, in which gene expression is induced by treatment with demethylating agents, may identify novel genes with tumour-specific methylation. We used high-density gene expression microarrays in a functional epigenetic study of 11 renal cell carcinoma (RCC) cell lines. Twenty-eight genes were then selected for analysis of promoter methylation status in cell lines and primary RCC. Eight genes (BNC1, PDLIM4, RPRM, CST6, SFRP1, GREM1, COL14A1 and COL15A1) showed frequent (>30% of RCC tested) tumour-specific promoter region methylation. Hypermethylation was associated with transcriptional silencing. Re-expression of BNC1, CST6, RPRM and SFRP1 suppressed the growth of RCC cell lines and RNA interference knock-down of BNC1, SFRP1 and COL14A1 increased the growth of RCC cell lines. Methylation of BNC1 or COL14A1 was associated with a poorer prognosis independent of tumour size, stage or grade. The identification of these epigenetically inactivated candidate RCC TSGs can provide insights into renal tumourigenesis and a basis for developing novel therapies and biomarkers for prognosis and detection.

The role of small leucine-rich proteoglycans in collagen fibrillogenesis

Small leucine-rich proteoglycans/proteins (SLRPs) are associated with collagen fibril formation, and therefore important for the proper formation of extracellular matrices. SLRPs are differentially expressed in tissues and during pathological conditions, contributing to the development of connective tissue properties. The binding of SLRPs to collagens have recently been characterized, and may give some clues to the significance of these interactions. In this mini review, we summarize published work in this field, and propose several mechanisms for how SLRPs can control collagen matrix structure and function. SLRPs appear to influence collagen cross-linking patterns. We also propose that the SLRP-collagen interactions can assist in the process of juxtaposing the collagen monomers by steric hindrance or by directly connecting two collagen monomers during the fibril growth.

The matricellular functions of small leucine-rich proteoglycans (SLRPs)

The small leucine-rich proteoglycans (SLRPs) are biologically active components of the extracellular matrix (ECM), consisting of a protein core with leucine rich-repeat (LRR) motifs covalently linked to glycosaminoglycan (GAG) side chains. The diversity in composition resulting from the various combinations of protein cores substituted with one or more GAG chains along with their pericellular localization enables SLRPs to interact with a host of different cell surface receptors, cytokines, growth factors, and other ECM components, leading to modulation of cellular functions. SLRPs are capable of binding to: (i) different types of collagens, thereby regulating fibril assembly, organization, and degradation; (ii) Toll-like receptors (TLRs), complement C1q, and tumor necrosis factor-alpha (TNFalpha), regulating innate immunity and inflammation; (iii) epidermal growth factor receptor (EGF-R), insulin-like growth factor receptor (IGF-IR), and c-Met, influencing cellular proliferation, survival, adhesion, migration, tumor growth and metastasis as well as synthesis of other ECM components; (iv) low-density lipoprotein receptor-related protein (LRP-1) and TGF-beta, modulating cytokine activity and fibrogenesis; and (v) growth factors such as bone morphogenic protein (BMP-4) and Wnt-I-induced secreted protein-1 (WISP-1), controlling cell proliferation and differentiation. Thus, the ability of SLRPs, as ECM components, to directly or indirectly regulate cell-matrix crosstalk, resulting in the modulation of various biological processes, aptly qualifies these compounds as matricellular proteins.

Running GAGs: myxoid matrix in tumor pathology revisited: what's in it for the pathologist?

Ever since Virchow introduced the entity myxoma, abundant myxoid extracellular matrix (ECM) has been recognized in various reactive and neoplastic lesions. Nowadays, the term "myxoid" is commonly used in daily pathological practice. But what do today's pathologists mean by it, and what does the myxoid ECM tell the pathologist? What is known about the exact composition and function of the myxoid ECM 150 years after Virchow? Here, we give an overview of the composition and constituents of the myxoid ECM as known so far and demonstrate the heterogeneity of the myxoid ECM among different tumors. We discuss the possible role of the predominant constituents of the myxoid ECM and attempt to relate them to differences in clinical behavior. Finally, we will speculate on the potential relevance of this knowledge in daily pathological practice.

The elongated first fibronectin type III domain of collagen XIV is an inducer of quiescence and differentiation in fibroblasts and preadipocytes

Collagen XIV (CXIV) is a fibril-associated collagen that is mainly expressed in well differentiated tissues and in late embryonic development. Because CXIV is almost absent in proliferating and/or dedifferentiated tissues, a functional role in maintaining cell differentiation is suspected. We demonstrate antiproliferative, quiescence- and differentiation-inducing effects of human CXIV and its recombinant fragments on mesenchymal cells. In primary human fibroblasts, in mouse 3T3 fibroblasts and in 3T3-L1 preadipocytes, CXIV reduced de novo DNA synthesis by 75%, whereas cell numbers and viability remained unaltered. Cells showed no signs of apoptosis, and maximal proliferation was restored when serum was supplemented, thus indicating that CXIV induced reversible cellular quiescence. Exposure of fibroblasts to CXIV in vitro led to cellular bundles and clusters. CXIV also triggered trans-differentiation of 3T3-L1 preadipocytes into adipocytes, as could be shown by lipid accumulation and by expression of the glucose transporter Glut4. These effects were also observed with the amino-terminal recombinant fragment Gln(29)-Pro(154) that harbors the first fibronectin type III domain and a 39-amino-acid extension, whereas no activity was found for all other recombinant CXIV fragments. Based on these finding the development of small molecular analogs that modulate fibroblast cell growth and differentiation, e.g. in wound healing and fibrosis, seems feasible.

The collagen superfamily: from the extracellular matrix to the cell membrane

The collagen superfamily is highly complex and shows a remarkable diversity in molecular and supramolecular organization, tissue distribution and function. However, all its members share a common structural feature, the presence of at least one triple-helical domain, which corresponds to a number of (Gly-X-Y)n repeats (X being frequently proline and Y hydroxyproline) in the amino acid sequence. Several sub-families have been determined according to sequence homologies and to similarities in the structural organization and supramolecular assembly. In the present review, we focus on the newly described fibrillar collagens, fibrillar-associated collagens with interrupted triple helix, membrane collagens and multiplexins. Recent advances in the characterization of proteins containing triple-helical domains but not referred to as collagens are also discussed.

Interaction between proteoglycans and alpha-elastin in construction of extracellular matrix of human yellow ligament

One type of large proteoglycan and three types of small proteoglycans (decorin, decorin-subtype, and biglycan) were purified by chromatography, and alpha-elastin was isolated by alkali treatment from human yellow ligaments taken at the time of operation. The interaction of the proteoglycans with immobilized alpha-elastin on a sensor was analyzed by surface plasmon resonance, and we confirmed that each of the small proteoglycans exhibited a specific binding to alpha-elastin. The binding sites of small proteoglycans were contained in the protein cores. In addition, the differences in the interaction of the small proteoglycans with alpha-elastin of normal and ossified ligaments were compared. The interactions of the small proteoglycans with alpha-elastin of the ossified ligaments were lower than those with alpha-elastin of the normal ligaments. In the ossified ligaments, neodesmosine, one of the cross-linking amino acids, was significantly less than in the normal ligaments (p < .05).

Scleral structure, organisation and disease. A review

Although disease of the sclera is unusual, when it occurs it can rapidly destroy both the eye and vision. However, normally the sclera provides an opaque protective coat for the intraocular tissues and a stable support during variations in internal pressure and eye movements, which would otherwise perturb the visual process through distortion of the retina and the lens/iris diaphragm. This stability, which is vital for clear vision is made possible by the organisation and viscoelastic properties of scleral connective tissue. Microscopically, the sclera displays distinct concentric layers including, from outside, Tenon's capsule, episclera, the scleral stroma proper and lamina fusca, melding into underlying choroid. Two sites exhibit specialised structure and function: the perilimbal trabecular meshwork, through which aqueous filters into Schlemm's canal, and the lamina cribrosa, which permits axons of the optic nerve to exit the posterior sclera. Throughout, sclera is densely collagenous, the stroma consisting of fibrils with various diameters combining into either interlacing fibre bundles or defined lamellae in outer zones. Scleral fibrils are heterotypic structures made of collagen types I and III, with small amounts of types V and VI also present. Scleral elastic fibres are especially abundant in lamina fusca and trabecular meshwork. The interfibrillar matrix is occupied by small leucine-rich proteoglycans, decorin and biglycan, containing dermatan and dermatan/chondroitin sulphate glycosaminoglycans, together with the large proteoglycan, aggrecan, which also carries keratan sulphate sidechains. Decorin is closely associated with the collagen fibrils at specific binding sites situated close to the C-terminus of the collagen molecules. Proteoglycans influence hydration, solute diffusion and fluid movement through the sclera, both from the uvea and via the trabecular meshwork. As the sclera is avascular, nutrients come from the choroid and vascular plexi in Tenon's capsule and episclera, where there is an artery to artery anastomosis in which blood oscillates, rather than flows rapidly. This predisposes to the development of vasculitis causing a spectrum of inflammatory conditions of varying intensity which, in the most severe form, necrotising scleritis, may destroy all of the structural and cellular components of the sclera. Scleral cells become fibroblastic and the stroma is infiltrated with inflammatory cells dominated by macrophages and T-lymphocytes. This process resembles, and may be concurrent with, systemic disease affecting other connective tissues, particularly the synovial joints in rheumatoid arthritis. Current views support an autoimmune aetiology for scleritis. Whilst the role of immune complexes and the nature of initial pro-inflammatory antigen(s) remain unknown, the latter may reside in scleral tissue components which are released or modified by viral infection, injury or surgical trauma.

Interaction of decorin with CNBr peptides from collagens I and II. Evidence for multiple binding sites and essential lysyl residues in collagen

Decorin is a small leucine-rich chondroitin/dermatan sulfate proteoglycan reported to interact with fibrillar collagens through its protein core and to localize at d and e bands of the collagen fibril banding pattern. Using a solid-phase assay, we have determined the interaction of peptides derived by CNBr cleavage of type I and type II collagen with decorin extracted from bovine tendon and its protein core and with a recombinant decorin preparation. At least five peptides have been found to interact with all three decorin samples. The interaction of peptides with tendon decorin has a dissociation constant in the nanomolar range. The triple helical conformation of the peptide trimeric species is a necessary requisite for the binding. All positive peptides have a region within the d and e bands of collagen fibrils. Two chemical derivatives of collagens and of positive peptides were prepared by N-acetylation and N-methylation of the primary amino group of Lys/Hyl side chains. Chemical modifications performed in mild conditions do not significantly alter the thermal stability of peptide trimeric species whereas they affect the interaction with decorin: N-acetylation eliminates both the positive charge and the binding to decorin, whereas N-methylation preserves the cationic character and modulates the binding. We conclude that decorin makes contacts with multiple sites in type I collagen and probably also in type II collagen and that some collagen Lys/Hyl residues are essential for the binding.

Decorin inhibits endothelial migration and tube-like structure formation: role of thrombospondin-1

Interactions between endothelial cell receptors and the extracellular matrix (ECM) play a critical, yet poorly understood role in angiogenesis. Based on the anti-adhesive role of decorin, we hypothesized that decorin binding to ECM molecules such as thrombospondin-1 (TSP-1) plays a regulatory role in endothelial tube-like structure (TLS) formation. To test this hypothesis, endothelial cells were plated on TSP-1, decorin, or mixed substrates of TSP-1 plus decorin. TLS formation was induced by applying type I collagen on the confluent endothelial monolayer. Cartilage decorin inhibited the formation of TLSs in a concentration-dependent manner. On substrates of high decorin concentrations (2.5 and 5.0 microg/cm(2)) the reduction in TLSs was due either to a reduction in the number of adhering cells or to decreased cell migration. At low decorin concentrations (0.05 and 0.25 microg/cm(2)) the reduction in TLSs was independent of the number of attached cells. Time-lapse video microscopy revealed that decorin substrates facilitated homotypic aggregation and isolated cord formation at the expense of endothelial migration and TLS formation. Consistent with the reduced migration, endothelial cells formed fewer vinculin-positive focal adhesions and actin-stress fibers on decorin substrates. Endothelial migration and TLS formation were also significantly inhibited by skin decorin and the protein core of cartilage decorin. The inhibition of TLS formation by the protein core of cartilage decorin was potentiated by TSP-1. These findings suggest that decorin alone or in combination with TSP-1 interferes with the activation of endothelial cell receptors by ECM molecules, thus blocking intracellular signals that induce cytoskeletal reorganization, migration, and TLS formation.

Biglycan and decorin bind close to the n-terminal region of the collagen VI triple helix

The binding of native biglycan and decorin to pepsin-extracted collagen VI from human placenta was examined by solid phase assay and by measurement of surface plasmon resonance in the BIAcore(TM)2000 system. Both proteoglycans exhibited a strong affinity for collagen VI with dissociation constants (K(D)) of approximately 30 nm. Removal of the glycosaminoglycan chains by chondroitinase ABC digestion did not significantly affect binding. In coprecipitation experiments, biglycan and decorin bound to collagen VI and equally competed with the other, suggesting that biglycan and decorin bind to the same binding site on collagen VI. This was confirmed by electron microscopy after negative staining of complexes between gold-labeled proteoglycans and collagen VI, demonstrating that both biglycan and decorin bound exclusively to a domain close to the interface between the N terminus of the triple helical region and the following globular domain. In solid phase assay using recombinant collagen VI fragments, it was shown that the alpha2(VI) chain probably plays a role in the interaction.

Alternative splicing of the first F3 domain from chicken collagen XIV affects cell adhesion and heparin binding

The N terminus of chicken collagen XIV is subject to alternative splicing. The longer isoform contains a fibronectin type III (F3) domain at its N terminus, whereas the shorter isoform is lacking this domain. Alternative splicing of the F3 domain is developmentally regulated. At early embryonic stages, both isoforms are expressed, whereas after hatching only the longer isoform is expressed. When immobilized on plastic dishes, the recombinant F3 domain promotes the adhesion of mesenchymal cells. Attachment to this domain is specifically inhibited by heparin but not by other glycosaminoglycans. Molecular modeling studies illustrate that the first F3 domain harbors a positively charged groove, which may accommodate the negatively charged heparin chain. Site-directed mutagenesis of a single lysine residue within this groove abolishes the cell binding activity but does not affect the heparin binding activity. Cell binding and heparin binding are therefore two functionally distinct properties shared by the N-terminal F3 domain. When full-length collagen XIV polypeptides that either contain or lack the first F3 domain are tested on heparin-Sepharose, a pronounced difference in their relative affinity is observed. Thus, alternative splicing of the N-terminal F3 domain influences the interaction of this FACIT (fibril-associated collagens with interrupted triple helices) collagen with cells and with glycosaminoglycans.

Expression of type XIV collagen in developing chicken tendons: association with assembly and growth of collagen fibrils

Collagen fibril assembly is a multistep process involving multiple macromolecular interactions. Type XIV collagen contains multiple domains and is capable of interacting with collagen fibrils and other extracellular matrix components. During tendon development, naturally changing expression of type XIV collagen and its variants may modulate such interactions. Type XIV collagen was studied using immunochemical and molecular approaches. Western analysis demonstrated that type XIV collagen content was high between days 14 and 19, decreasing sharply at hatching. Immunoelectron microscopy demonstrated that type XIV collagen was fibril-associated, with a periodicity of 67 nm, indicating specific interactions. Decreased fibril-associated reactivity for type XIV collagen was seen at hatching, indicating a removal of collagen XIV from the fibril surface. The expression of two NC1 splice variants was analyzed. Overall, type XIV collagen mRNA decreased significantly from day 14 to hatching. The long NC1 splice variant was the predominant species at 14 days; at 19 days the two variants were expressed in lower amounts at nearly a 1:1 ratio; at hatching, both variants were expressed minimally. Changes in splice variant expression, suggest that different functional forms of type XIV collagen are present, allowing modified interactions with fibrils during development. In conclusion, type XIV collagen is fibril-associated and developmentally regulated. Modulation of expression of the NC1 splice variants may mediate the fibril interactions that allow the transition from growing fibril intermediates to mature fibrils.

Fibrogenesis and fibrolysis in collagenous colitis. Patterns of procollagen types I and IV, matrix-metalloproteinase-1 and -13, and TIMP-1 gene expression

Collagenous colitis is characterized by the deposition of a superficial subepithelial collagenous layer, the pathogenesis of which is unknown. Because the excess matrix deposition is potentially reversible, a labile imbalance between fibrogenesis and fibrolysis may be suspected. Expression of procollagen alpha1(I) and alpha1(IV), matrix-metalloproteinase (MMP)-1 and -13, and tissue inhibitor of metalloproteinase (TIMP)-1 genes was semiquantitated by in situ hybridization on serial biopsies of 12 patients with collagenous colitis and compared to controls. Collagen types I, III, IV, and VI, tenascin, undulin/collagen XIV, and alpha-actin were localized by immunohistology. The superficial collagen layer stained strongly for collagen types I, III, and VI, and particularly for tenascin, but not for undulin. Elevated procollagen alpha1(I), procollagen alpha1(IV), and TIMP-1 transcript levels were found in alpha-actin-positive cells with linear distribution underneath the superficial collagenous layer, whereas MMP-1 RNA expression was variable and restricted to cell clusters. MMP-13 expression was undetectable. The patterns of procollagen alpha1(I)- and alpha1(IV)-specific labeling, combined with an intense tenascin- but absent undulin-specific staining, indicate deposition of an immature interstitial matrix that may be susceptible to degradation. The restricted MMP-1 RNA expression, counteracted by increased TIMP-1 expression, suggests locally impaired fibrolysis as a relevant factor in the pathogenesis of collagenous colitis.

Structural analysis of the heparin-binding site of the NC1 domain of collagen XIV by CD and NMR

Type XIV collagen, a fibril-associated collagen with interrupted triple helices (FACIT), interacts with the surrounding extracellular matrix and/or with cells via its binding to glycosaminoglycans (GAGs). To further characterize such interactions in the NC1 domain of chicken collagen XIV, we identified amino acids essential for heparin binding by affinity chromatography analysis after proteolytic digestion of the synthetic peptide NC1(84-116). The 3D structure of this peptide was then obtained using circular dichroism and NMR. The NC1(84-116) peptide appeared poorly structured in water, but the stabilization of its conformation by the interaction with hydrophobic surfaces or by using cosolvents (TFE, SDS) revealed a high propensity to adopt an alpha-helical folding. A 3D structure model of NC1(84-116), calculated from NMR data recorded in a TFE/water mixture, showed that the NC1-heparin binding site forms a amphipathic alpha-helix exhibiting a twisted basic groove. It is structurally similar to the consensus spatial alpha-helix model of heparin-binding [Margalit et al. (1993) J. Biol. Chem. 268, 19228-19231], except that the GAG binding domain of NC1 may be extended over 18 residues, that is, the NC1(94-111) segment. In addition, the formation of a hydrophobic groove upon helix formation suggests the contribution of additional sequences to ensure the stability of the GAG-binding domain. Overall the NC1(84-116) model exhibits a nativelike conformation which presents suitably oriented residues for the interaction with a specific GAG.

A 16-kDa fragment of collagen type XIV is a novel neutrophil chemotactic factor purified from rat granulation tissue

A neutrophil chemotactic factor has been purified from the homogenate of rat granulation tissues. The purified chemoattractant was a basic protein with heparin-binding site and gave a single band corresponding to a molecular mass of 16 kDa on SDS-PAGE under reducing conditions. The chemoattractant was treated with lysylendopeptidase and the resulting peptides were isolated by reversed-phase HPLC. Amino acid sequences of the peptides were almost identical with the sequence of N-terminal fibronectin type III domain of human collagen type XIV, suggesting that the purified chemoattractant consists mainly of N-terminal fibronectin type III domain and the adjacent heparin-binding site of rat collagen type XIV. The 16-kDa fragment of collagen type XIV dose dependently attracted rat neutrophils and transiently increased the intracellular free Ca2+ concentration of neutrophils. The results suggest that the novel chemoattractant plays a role in neutrophil recruitment in rat inflammation.

Characterization of two LGR genes homologous to gonadotropin and thyrotropin receptors with extracellular leucine-rich repeats and a G protein-coupled, seven-transmembrane region

The receptors for LH, FSH, and TSH belong to the large G protein-coupled, seven-transmembrane (TM) protein family and are unique in having a large N-terminal extracellular (ecto-) domain containing leucine-rich repeats important for interaction with the glycoprotein ligands. We have identified two new leucine-rich repeat-containing, G protein-coupled receptors and named them as LGR4 and LGR5, respectively. The ectodomains of both receptors contain 17 leucine-rich repeats together with N- and C-terminal flanking cysteine-rich sequences, compared with 9 repeats found in known glycoprotein hormone receptors. The leucine-rich repeats in LGR4 and LGR5 are arrays of 24 amino acids showing similarity to repeats found in the acid labile subunit of the insulin-like growth factor (IGF)/IGF binding protein complexes as well as slit, decorin, and Toll proteins. The TM region and the junction between ectodomain and TM 1 are highly conserved in LGR4, LGR5, and seven other LGRs from sea anemone, fly, nematode, mollusk, and mammal, suggesting their common evolutionary origin. In contrast to the restricted tissue expression of gonadotropin and TSH receptors in gonads and thyroid, respectively, LGR4 is expressed in diverse tissues including ovary, testis, adrenal, placenta, thymus, spinal cord, and thyroid, whereas LGR5 is found in muscle, placenta, spinal cord, and brain. Hybridization analysis of genomic DNA indicated that LGR4 and LGR5 genes are conserved in mammals. Comparison of overall amino acid sequences indicated that LGR4 and LGR5 are closely related to each other but diverge, during evolution, from the homologous receptor found in snail and the mammalian glycoprotein hormone receptors. The identification and characterization of new members of the LGR subfamily of receptor genes not only allow future isolation of their ligands and understanding of their physiological roles but also reveal the evolutionary relationship of G protein-coupled receptors with leucine-rich repeats.

Location and distribution of non-collagenous matrix proteins in musculoskeletal tissues of rat

The study assessed immunohistochemically the location and distribution of various non-collagenous matrix proteins (fibronectin, laminin, tenascin-C, osteocalcin, thrombospondin-1, vitronectin and undulin) in musculoskeletal tissues of rat. Fibronectin and thrombospondin-1 were found to be ubiquitous in the studied tissues. High immunoreactivity of these proteins was found in the extracellular matrix of the anatomical sites where firm bindings are needed, i.e. between muscle fibres and fibre bundles, between the collagen fibres of a tendon and at myotendinous junctions, osteotendinous junctions and articular cartilage. Tenascin-C was found in the extracellular matrix of regions where especially high forces are transmitted from one tissue component to the other, such as myotendinous junctions and osteotendinous junctions. Laminin was demonstrated in the basement membranes of the muscle cells and capillaries of the muscle-tendon units. Osteocalcin immunoreactivity concentrated in the extracellular matrix of areas of newly formed bone tissue, i.e. in the subperiosteal and subchondral regions, osteoid tissue and mineralized fibrocartilage zone of the osteotendinous junction. Mild vitronectin activity could be seen in the extracellular matrix of the osteotendinous and myotendinous junctions, and high activity around the bone marrow cells. Undulin could be demonstrated in the extracellular matrix (i.e. on the collagen fibres) of the tendon and epimysium only. However, it was co-distributed with fibronectin and tenascin-C. Together, these findings on the normal location and distribution of these non-collagenous proteins in the musculoskeletal tissues help to form the basis of knowledge against which the location and distribution of the these proteins in various pathological processes could be compared.

Leucine-rich repeat glycoproteins of the extracellular matrix

The extracellular matrix plays an integral role in the pivotal processes of development, tissue repair, and metastasis by regulating cell proliferation, differentiation, adhesion, and migration. This review is focused on a family of related glycoproteins represented by at least one member in all specialized extracellular matrices. This family currently comprises nine members grouped together on the basis of their presence in the extracellular matrix and by virtue of a leucine-rich repeat motif that dominates the structure of the core protein. It is likely that most, if not all the members of this group exist as proteoglycans in some tissues, and thus have been termed the Small Leucine-Rich Proteoglycan family, or SLRPs. The leucine-rich repeat (LRR) is usually present in tandem array and has been described in an increasing number of proteins, giving rise to a LRR-superfamily. The LRR domain of the SLRP family is unique within the superfamily in that it is flanked by cysteine clusters, and the 24 amino acid consensus for SLRP members is x-x-I/V/L-x-x-x-x-F/P/L-x-x-L/P-x-x-L-x-x-L/I-x-L-x-x-N-x-I/L, where x is any amino acid. Enormous progress has been made in describing the membership, structure and localization of this family, and recently new insight has emerged into the putative function of these molecules not just as modulators of matrix assembly but also on their intriguing role in regulating cell growth, adhesion, and migration. Determination of membership, structure and putative function of this fascinating class of molecules is summarized in this review.

Localization of a cell adhesion site on collagen XIV (undulin)

Cell adhesion to collagen XIV is implied to be mediated by proteoglycans as cellular receptors (T. Ehnis et al., 1996, Exp. Cell Res. 229, 388-397). In order to define the cell binding region(s), fusion proteins expressed in Escherichia coli and covering the large noncollagenous domain NC3 of collagen XIV were used as substrates for the adhesion of skin fibroblasts. A prominent cell binding site could be localized in the N-terminal fibronectin type III repeat of collagen XIV and its immediate C-terminal extension. Since this region also mediates the binding of the small chondroitin/dermatan sulfate proteoglycan decorin (T. Ehnis et al., 1997, J. Biol. Chem. 272, 20414-20419), our finding could provide the molecular basis for the observation that decorin serves as inhibitor and potential modulator of cellular interactions with collagen XIV.

Complete primary structure of human collagen type XIV (undulin)

A partial cDNA sequence coding for the human extracellular matrix protein undulin has been completed. The completed sequence provides conclusive evidence for the suggested identity of undulin and collagen type XIV. Two differently sized polyproteins of 1780 and 1796 amino acids, with an overall amino acid sequence identity of 75% compared to chicken CXIV, emerge from variant 3' sequence ends encoding the C-terminal non-collagenous (NC) NC1 domain of human collagen type XIV.