Type VI collagen induces cardiac myofibroblast differentiation: implications for postinfarction remodeling. (33/145)

Cardiac fibroblast (CF) proliferation and differentiation into hypersecretory myofibroblasts can lead to excessive extracellular matrix (ECM) production and cardiac fibrosis. In turn, the ECM produced can potentially activate CFs via distinct feedback mechanisms. To assess how specific ECM components influence CF activation, isolated CFs were plated on specific collagen substrates (type I, III, and VI collagens) before functional assays were carried out. The type VI collagen substrate potently induced myofibroblast differentiation but had little effect on CF proliferation. Conversely, the type I and III collagen substrates did not affect differentiation but caused significant induction of proliferation (type I, 240.7 +/- 10.3%, and type III, 271.7 +/- 21.8% of basal). Type I collagen activated ERK1/2, whereas type III collagen did not. Treatment of CFs with angiotensin II, a potent mitogen of CFs, enhanced the growth observed on types I and III collagen but not on the type VI collagen substrate. Using an in vivo model of myocardial infarction (MI), we measured changes in type VI collagen expression and myofibroblast differentiation after post-MI remodeling. Concurrent elevations in type VI collagen and myofibroblast content were evident in the infarcted myocardium 20-wk post-MI. Overall, types I and III collagen stimulate CF proliferation, whereas type VI collagen plays a potentially novel role in cardiac remodeling through facilitation of myofibroblast differentiation.  (+info)

Decorin and biglycan expression is differentially altered in several muscular dystrophies. (34/145)

Biglycan and decorin are small extracellular proteoglycans that interact with cytokines, whose activity they may modulate, and with matrix proteins, particularly collagens. To better understand their role in muscle fibrosis, we investigated expression of decorin and biglycan transcripts and protein in muscle of several forms of muscular dystrophy, and also expression of perlecan, an extracellular proteoglycan unrelated to collagen deposition. In Duchenne muscular dystrophy (DMD) and LAMA2-mutated congenital muscular dystrophy (MDC1A) we also quantitated transcript levels of the profibrotic cytokine TGF-beta1. We examined muscle biopsies from nine DMD patients, aged 2-8 years; 14 BMD (Becker muscular dystrophy) patients (nine aged 1-5 years; five aged 30-37 years); four MDC1A patients (aged 2-7 years); six dysferlin-deficient patients (aged 19-53 years) with mutation ascertained in two, and normal expression of proteins related to limb girdle muscular dystrophies in the others; 10 sarcoglycan-deficient patients: seven with alpha-sarcoglycan mutation, two with beta-sarcoglycan mutation and one with gamma-sarcoglycan mutation (five aged 8-15 years; five aged 26-43 years); and nine children (aged 1-6 years) and 12 adults (aged 16-61 years) suspected of neuromuscular disease, but who had normal muscle on biopsy. Biglycan mRNA levels varied in DMD and MDC1A depending on the quantitation method, but were upregulated in BMD, sarcoglycanopathies and dysferlinopathy. Decorin mRNA was significantly downregulated in DMD and MDC1A, whereas TGF-beta1 was significantly upregulated. Decorin mRNA was normal in paediatric BMD, but upregulated in adult BMD, sarcoglycanopathies and dysferlinopathy. Perlecan transcript levels were similar to those of age-matched controls in all disease groups. By immunohistochemistry, decorin and biglycan were mainly localized in muscle connective tissue; their presence increased in relation to increased fibrosis in all dystrophic muscle. By visual inspection, decorin bands on immunoblot did not differ from those of age-matched controls in all patient groups. However, when the intensity of the bands was quantitated against vimentin and normalized against sarcomeric actin, in DMD and MDC1A the ratio of band intensities was significantly lower than in age-matched controls. Variations in the transcript and protein levels of these proteoglycans in different muscular dystrophies probably reflect the variable disruption of extracellular matrix organization that occurs in these diseases. The significantly lowered decorin levels in DMD and MDC1A may be related to the increased TGF-beta1 levels, suggesting a therapeutic role of decorin in these severe dystrophies.  (+info)

Distribution of type VI collagen in the cartilaginous tissue of the proximal tibia in the domestic cat. (35/145)

To investigate the distribution of the early stage chondrocytes during the formation and closure of epiphyseal growth plate (EGP) of the domestic cat, we examined the EGP of proximal tibiae by immunohistochemistry for type VI collagen. In the epiphyseal cartilage without the secondary ossification center (SOC) and EGP in newborn cats aged 1 and 10 days, type VI collagen-positive chondrocytes were located around the cartilage canals and articular surface. In the epiphyseal cartilage with the SOC and EGP in young cats aged 1 to 3 months, type VI collagen-positive chondrocytes were located in the upper resting zone of the EGP, and then increased throughout the resting zone along with maturation. In the adult cats with the partially closed EGP, type VI collagen-positive chondrocytes were distributed throughout the remaining EGP. These findings indicate that the early stage chondrocytes characterized with type VI collagen are continuously located in the EGP during maturation. In addition, the increase of the early stage chondrocytes and the decrease of the reserve chondrocytes in the EGP along with maturation may cause the cessation of the longitudinal growth of the EGP, and finally bring about the EGP closure.  (+info)

Ullrich congenital muscular dystrophy and Bethlem myopathy: clinical and genetic heterogeneity. (36/145)

Ullrich congenital muscular dystrophy (UCMD), due to mutations in the collagen VI genes, is an autosomal recessive form of CMD, commonly associated with distal joints hyperlaxity and severe course. A mild or moderate involvement can be occasionally observed. OBJECTIVE: To evaluate the clinical picture of CMD patients with Ullrich phenotype who presented decreased or absent collagen VI immunoreactivity on muscular biopsy. RESULTS: Among 60 patients with CMD, two had no expression of collagen V and their clinical involvement was essentially different: the first (3 years of follow-up) has mild motor difficulty; the second (8 years of follow-up) never acquired walking and depends on ventilatory support. A molecular study, performed by Pan et al. at the Thomas Jefferson University, demonstrated in the first a known mutation of Bethlem myopathy in COL6A1 and in the second the first dominantly acting mutation in UCMD and the first in COL6A1, previously associated only to Bethlem myopathy, with benign course and dominant inheritance. CONCLUSION: Bethlem myopathy should be considered in the differential diagnosis of UCMD, even in patients without fingers contractures; overlap between Ullrich and Bethlem phenotypes can be supposed.  (+info)

A landscape effect in tenosynovial giant-cell tumor from activation of CSF1 expression by a translocation in a minority of tumor cells. (37/145)

Tenosynovial giant-cell tumor (TGCT) and pigmented villonodular synovitis (PVNS) are related conditions with features of both reactive inflammatory disorders and clonal neoplastic proliferations. Chromosomal translocations involving chromosome 1p13 have been reported in both TGCT and PVNS. We confirm that translocations involving 1p13 are present in a majority of cases of TGCT and PVNS and show that CSF1 is the gene at the chromosome 1p13 breakpoint. In some cases of both TGCT and PVNS, CSF1 is fused to COL6A3 (2q35). The CSF1 translocations result in overexpression of CSF1. In cases of TGCT and PVNS carrying this translocation, it is present in a minority of the intratumoral cells, leading to CSF1 expression only in these cells, whereas the majority of cells express CSF1R but not CSF1, suggesting a tumor-landscaping effect with aberrant CSF1 expression in the neoplastic cells, leading to the abnormal accumulation of nonneoplastic cells that form a tumorous mass.  (+info)

Beta ig-h3 interacts directly with biglycan and decorin, promotes collagen VI aggregation, and participates in ternary complexing with these macromolecules. (38/145)

Recombinant human beta ig-h3 was found to bind 125I-labeled small leucine-rich proteoglycans (SLRPs), biglycan, and decorin, in co-immunoprecipitation experiments. In each instance the binding could be blocked by an excess of the unlabeled proteoglycan, confirming the specificity of the interaction. Scatchard analysis showed that biglycan bound beta ig-h3 more avidly than decorin with Kd values estimated as 5.88 x 10(-8) and 1.02 x 10(-7) M, respectively. In reciprocal blocking experiments both proteoglycans inhibited the others binding to beta ig-h3 indicating that they may share the same binding site or that the two binding sites are in close proximity on the beta ig-h3 molecule. Since beta ig-h3 and the SLRPs are known to be associated with the amino-terminal region of collagen VI in tissue microfibrils, the effects of including collagen VI in the incubations were investigated. Co-immunoprecipitation of 125I-labeled biglycan incubated with equimolar mixtures of beta ig-h3 and pepsin-collagen VI was increased 6-fold over beta ig-h3 alone and 3-fold over collagen VI alone. Similar increases were also observed for decorin. The findings indicate that beta ig-h3 participates in a ternary complex with collagen VI and SLRPs. Static light scattering techniques were used to show that beta ig-h3 rapidly forms very high molecular weight complexes with both native and pepsin-collagen VI, either alone or with the SLRPs. Indeed beta ig-h3 was shown to form a complex with collagen VI and biglycan, which appeared to be much more extensive than that formed by beta ig-h3 with collagen VI and decorin or those formed between the collagen and beta ig-h3, biglycan, or decorin alone. Biglycan core protein was shown to inhibit the extent of complexing of beta ig-h3 with native and pepsin-collagen VI suggesting that the glycosaminoglycan side chains of the proteoglycan were important for the formation of the large ternary complexes. Further studies showed that the direct interaction between beta ig-h3 and biglycan and between biglycan and collagen VI were also important for the formation of these complexes. The globular domains of collagen VI also appeared to have an influence on the interaction of the three components. Overall the results indicate that beta ig-h3 can differentially modulate the aggregation of collagen VI with biglycan and decorin. Thus this interplay is likely to be important in tissues such as cornea where such complexes are considered to occur.  (+info)

The C5 domain of the collagen VI alpha3(VI) chain is critical for extracellular microfibril formation and is present in the extracellular matrix of cultured cells. (39/145)

Collagen VI, a microfibrillar protein found in virtually all connective tissues, is composed of three distinct subunits, alpha1(VI), alpha2(VI), and alpha3(VI), which associate intracellularly to form triple helical heterotrimeric monomers then dimers and tetramers. The secreted tetramers associate end-to-end to form beaded microfibrils. Although the basic steps in assembly and the structure of the tetramers and microfibrils are well defined, details of the interacting protein domains involved in assembly are still poorly understood. To explore the role of the C-terminal globular regions in assembly, alpha3(VI) cDNA expression constructs with C-terminal truncations were stably transfected into SaOS-2 cells. Control alpha3(VI) N6-C5 chains with an intact C-terminal globular region (subdomains C1-C5), and truncated alpha3(VI) N6-C1, N6-C2, N6-C3, and N6-C4 chains, all associated with endogenous alpha1(VI) and alpha2(VI) to form collagen VI monomers, dimers and tetramers, which were secreted. These data demonstrate that subdomains C2-C5 are not required for monomer, dimer or tetramer assembly, and suggest that the important chain selection interactions involve the C1 subdomains. In contrast to tetramers containing control alpha3(VI) N6-C5 chains, tetramers containing truncated alpha3(VI) chains were unable to associate efficiently end-to-end in the medium and did not form a significant extracellular matrix, demonstrating that the alpha3(VI) C5 domain plays a crucial role in collagen VI microfibril assembly. The alpha3(VI) C5 domain is present in the extracellular matrix of SaOS-2 N6-C5 expressing cells and fibroblasts demonstrating that processing of the C-terminal region of the alpha3(VI) chain is not essential for microfibril formation.  (+info)

Zonal variations in the three-dimensional morphology of the chondron measured in situ using confocal microscopy. (40/145)

OBJECTIVE: Chondrocytes in articular cartilage are surrounded by a narrow pericellular matrix (PCM), which together with the enclosed cell(s) are termed the "chondron". Although the precise function of this tissue region is unknown, previous studies provide indirect evidence that the PCM plays an important role in governing the local mechanical environment of chondrocytes. In particular, theoretical models of the chondron under mechanical loading suggest that the shape, size, and biomechanical properties of the PCM significantly influence the stress-strain and fluid flow environment of the cell. The goal of this study was to quantify the three-dimensional morphology of chondron in situ using en bloc immunolabeling of type VI collagen coupled with fluorescence confocal microscopy. METHODS: Three-dimensional reconstructions of intact, fluorescently labeled chondrons were made from stacks of confocal images recorded in situ from the superficial, middle, and deep zones of porcine articular cartilage of the medial femoral condyle. RESULTS: Significant variations in the shape, size, and orientation of chondrocytes and chondrons were observed with depth from the tissue surface, revealing flattened discoidal chondrons in the superficial zone, rounded chondrons in the middle zone, and elongated, multicellular chondrons in the deep zone. CONCLUSIONS: The shape and orientation of the chondron appear to reflect the local collagen architecture of the interterritorial matrix, which varies significantly with depth. Quantitative measurements of morphology of the chondron and its variation with site, disease, or aging may provide new insights into the influence of this structure on physiology and the pathology of articular cartilage.  (+info)