Effects of lysosomal enzymes on the type of collagen synthesized by bovine articular cartilage

The relationship between collagen metabolism and temporomandibular joint osteoarthrosis in mice

The histologic changes in the temporo mandibular joint (TMJ) and the activity of serum collagenase-like (CL) peptidase and prolyl endopeptidase (PEP) were compared in mice with spontaneous osteoarthrosis (C57 black mouse/6 Silverberg (C57BL/6S) and control mice (C57 black mouse/6N (C57BL/6N) and ddY). The onset of osteoarthrosis of the TMJ in the C57BL/6S mice was noted at 12 weeks of age. Clefting in the chondrocyte layer was noted at 24 to 36 weeks of age; chondrocyte cluster and pannus at 36 to 60 weeks of age; and clefts deep in the bone and formation of osteophytes at 72 to 96 weeks of age. CL-peptidase and PEP activity significantly higher in C57BL/6S mice than in osteoarthrosis-free C57BL/6N and ddY mice. These changes occurred at an earlier age than the histologic changes. The findings suggest that these enzymes may play a significant role in the onset of osteoarthrosis in joints.

Complete cDNA sequence of chicken vigilin, a novel protein with amplified and evolutionary conserved domains

The complete cDNA (4375 bp), coding for a new protein called vigilin, was isolated from chicken chondrocytes. The cDNA shows an open reading frame of 1270 amino acids which are organized in 14 tandemly repeated homologous domains. Each domain consists of two subdomains, one with a conserved sequence motif of 35 amino acids (subdomain A) and another one with a presumptive alpha-helical structure of 21-33 amino acids (subdomain B). 149 amino acids at the N-terminus and 71 amino acids at the C-terminus of vigilin do not show the characteristic domain structure. No sequence characteristic of a signal peptide has been found, which argues for an intracellular localisation of vigilin. Vigilin is highly expressed in freshly isolated chicken chondrocytes but little in chondrocytes after prolonged time in culture. Vigilin mRNA exists in two size species, 4.4 kb and 6.5 kb in length due to the usage of different polyadenylation sites. Comparison of the vigilin sequence with data bases showed a remarkable similarity to protein HX from Saccharomyces cerevisiae [Delahodde, A., Becam, A. M., Perea, J. & Jacq, C. (1986) Nucleic Acids Res. 14, 9213-9214]. The yeast protein consists of eight homologous domains with 11 conserved amino acid residues within a set of 35 amino acids. The N-terminal and C-terminal regions of vigilin and protein HX do not reveal any sequence similarity. These results, together with the demonstration of the characteristic vigilin sequence motif in a human cDNA clone, suggest that the repeats represent evolutionary conserved autonomous domains within a family of proteins found in yeast, chicken and man.

Identification of collagen type I and type II in chondroid tissue

This paper deals with investigations concerning the matrix of chondroid tissue. Among the 73 human fetus or child mandibles and the 42 cat mandibles we have studied histologically and microradiographically, 8 human and 3 cat mandibles were used to determine the collagen composition in chondroid tissue matrix, and 10 cat mandibles were analyzed in order to have an ultrastructural approach to chondroid tissue. Both in human and cat mandibles, types I and II collagen were identified by indirect immunofluorescence and immunoperoxidase techniques. Electron microscopic analysis shows large collagen fibrils which correspond to type I collagen, and smaller collagen fibrils, principally located at the periphery of the chondroid cells. From our investigations, chondroid tissue should be considered as being different from both bone and cartilage, although it is not a transitional tissue, since no transformation of chondroid tissue into bone is observed; it should be classified as an intermediate tissue between cartilage and bone because of its morphological characteristics.

Type II collagen-induced arthritis. A morphologic and biochemical study of articular cartilage

Articular cartilage was obtained from type II collagen-induced arthritic rat joints. Transmission electron microscopy showed a gradual degeneration of chondrocytes, disorganization of the collagenous extracellular matrix, and formation of microscars. Biochemical analyses indicated that type II collagen was the only collagen present and that it was normal in regard to hydroxylation of lysine and glycosylation of hydroxylysine. Analyses of the proteoglycan in the extracellular matrix revealed a 50% loss of chondroitin sulfate and keratan sulfate.

Change in the expression of collagen genes in dividing and nondividing chondrocytes

Chondrocytes were isolated from the sterna of 17-day-old chick embryos by enzyme digestion. Rapid proliferation of chondrocytes was achieved in the presence of chick serum (10%, v/v). Addition of either hydroxyurea (10(-3) M) or cytosine arabinoside (10 microgram/ml) to the culture medium was used to arrest growth of cells. Under both conditions, however, a rather fast switch of synthesis from type II to type I collagen was observed. This suggests that the loss of the differentiated state of chondrocytes in culture is not necessarily bound to mitosis.

The proliferation of chondrocytes and pannus in adjuvant arthritis

Cell proliferation in the pannus formation of adjuvant arthritis was studied by autoradiography. It was found that after day 9 an increased cell proliferation starts in the joint capsule recessus and synovial villi on the injected side. From these proliferating cells a pannus, which during the first phase frequently consists only of few cell layers, extends over the cartilage surface. With advancing disease the thickness of the pannus increases and further centripetal growth may cause the entire cartilage surface to be covered. This proliferating pannus tissue may invade the cartilage and destroy it. Since in this area of destruction labelled cells are frequently present, it may be assumed that proliferating cells with a high enzyme content are particularly responsible for the immediate degradation of cartilage. No involvement of chondrocytes in pannus formation was confirmed by the methods employed. There was neither increased proliferation of surface chondrocytes nor increased proliferation of chondrocytes in the depth of cartilage.

Biochemical characteristics and biological significance of the genetically-distinct collagens

In recent years it has become evident that genetic polymorphism is dramatically expressed in the structural protein, collagen. Current information on the biochemical properties, biosynthesis, and tissue distribution of Type I, II, and III collagens is summarized with special reference to possible unique functional roles fulfilled by each of these collagens.

Immunohistological study on collagen in cartilage-bone metamorphosis and degenerative osteoarthrosis

Synthesis of collagen by chondrocytes was studied by immunofluorescence using antibodies specific for type I, II and III collagen. The following tissues and culture conditions were chosen for this immunohistological study: normal articular cartilage, epiphyseal growth cartilage, cartilage undergoing osteoarthrotic degeneration, suspension culture and monolayer culture. While type II collagen is the unique collagen all over hyaline cartilage, type I collagen is produced by hypertrophic chondrocytes in the growth plate. In addition, chondrocytes in osteoarthrotic areas of articular cartilage synthesize type I collagen. Under in vitro culture conditions, chondrocytes initially product type II collagen and synthesize later on type I collagen. The change of synthesis from type II to type I collagen is more rapid in monolayer than in suspension culture. It is concluded that the presence of matrix compounds and the cellmatrix interaction as well are necessary to maintain synthesis of type II collagen in chondrocytes. Alterations in the cell-matrix interactions are shown to occur in the hypertrophic zone of the epiphyseal growth plate, in cartilage undergoing osteoarthrotic degeneration as well as in chondrocytes grown in culture. Thus, change in the control of gene activity may subsequently lead to change in collagen synthesis. It is possible that the synthesis of type I collagen, which cannot fulfil the physiological function of a structural element in cartilageneous tissue, is a crucial factor in the process of osteoarthrosis.

Characterization of collagen and its precursors synthesized by rabbit-articular-cartilage cells in various culture systems

Rabbit articular cartilage synthesizes type II collagen, comprised of alpha1(II) chains, in vivo or in vitro. Chondrocytes from the same tissue have the ability to produce type I chollagen with the chain composition 2alpha(I)-alpha2 or type II collagen, depending upon the culture systems in which they are maintained. Type I collagen and its precursors have been identified in the medium of monolayer cultures. Upon transfer from monolayer to suspension cultures, the cells synthesize type II collagen in the medium devoid of CaCl2 and type I collagen and its precursors in the complete medium.

Hemodynamically-induced increase in soluble collagen in the anastomosed veins of experimental arteriovenous fistulae

External jugular veins that had been subjected to the hemodynamic stresses produced by experimental arteriovenous anastomosis developed 2% increased total protein contents and 17% increased collagen contents. When the stressed veins were homogenized and extracted with saline solutions, statistically significant increases in the saline-soluble proteins and in the saline-soluble collagen (87% and 267%, respectively) were observed. Increased amounts of low molecular weight peptides were found in the extracts. A fraction of these peptides could be degraded by Clostridium collagenase. The saline extract also contained proteins which resembled by their amino-acid composition the acidic structural proteins of the connective tissues. Additonally, in 3 dogs so tested, changes were found in the hydroxylation and glycosylation of lysine from gelatin extracts as well as in the lysine and desmosine contents of the insoluble elastin fractions. This is the first demonstration of a hemodynamically induced increase in the saline solubility of connective tissue proteins in the absence of dietary manipulations.

Changes in type of collagen synthesized as clones of chick chondrocytes grow and eventually lose division capacity

Clones of embryonic chick chondrocytes have been isolated and collagen biosynthesis has been followed as the clones grow and eventually lose division capacity. Analysis of collagen type at each successive subculture until the time of cellular senescence has shown that a change in synthesis occurs from the cartilage-specific Type II collagen (chain composition [alpha1(II)]3) to a mixture of Type I collagen (chain composition [alpha1(I)2alpha2) and the Type I trimer (chain composition[alpha1(I)]3). The results demonstrate unequivocally that the expression of the chick chondrocyte phenotype is unstable in vitro, and that previous experiments with mass cultures of chondrocytes cannot be accounted for by overgrowth of fibroblasts. Since similar morphological changes and a similar "switching" in collagen biosynthesis have been observed after growth of chondrocytes for a few days in 5-bromo-2'-deoxyuridine, it is proposed that growth in this analog accelerates those changes that eventually lead to cellular senescence.

Metabolic changes in rabbit articular cartilage due to inflammation

The effect of inflammation on the articular cartilage of rabbit knee joints were studied. The inflammation was induced by intraarticular injections of corton oil or rabbit peritoneal leukocyte lysates. An increase in the activities of various lysosomal enzymes was observed in the synovial fluid as well as in the cartilage of the inflamed joints. Loss of proteoglycans, increased rate of degradation of collagen and proteoglycans, and increased rate of their synthesis were evident in the treated cartilage. The rate of uptake of 3H-thymidine was also increased. A significant change was observed in the type of collagen synthesized by these explants in vitro. In addition to synthesizing their characteristics Type II collagen, the cartilage explants from the treated joints synthesized Type I collagen.

Defects in the biochemistry of collagen in diseases of connective tissue

The collagens are the major structural glycoproteins of connective tissues. A unique primary structure and a multiplicity of post-translational modification reactions are required for normal fibrillogenesis. The post-translational modifications include hydroxylation of prolyl and lysyl residues, glycosylation, folding of the molecule into triple-helical conformation, proteolytic conversion of precursor procollagen to collagen, and oxidative deamination of certain lysyl and hydroxylysyl residues. Any defect in the normal mechanisms responsible for the synthesis and secretion of collagen molecules or the deposition of these molecules into extracellular fibers could result in abnormal fibrillogenesis; such defects could result in a connective tissue disease. Recently, defects in the regulation of the types of collagen synthesized and in the enzymes involved in the post-translational modifications have been found in heritable diseases of connective tissue. Thus far, the primary heritable disorders of collagen metabolism in man include lysyl hydroxylase deficiency in Ehlers-Danlos syndrome type VI, p-collagen peptidase deficency in Ehlers-Danlos syndrome type VII, decreased synthesis of type III collagen in Ehlers-Danlos syndrome type IV, lysyl oxidase deficency in S-linked cutis laxa and Ehlers-Danlos syndrome type V, and decreased synthesis of type I collagen in osteogenesis imperfecta.

Electron microscopic studies on the uptake of colloidal thorium dioxide particles by isolated fetal guinea-pig chondrocytes and the distribution of labeled lysosomes in cartilage formed by transplanted chondrocytes

Chondrocytes isolated from fetal, guinea-pig epiphyses were grown in monolayer culture, exposed to thorium dioxide particles, and studied ultrastructurally after varying intervals. The exogenous marker was ingested by endocytosis and subsequently accumulated in lysosomes. After intramuscular injection into young guinea pigs, the thorium dioxide-labeled chondrocytes formed a typical hyaline cartilage. This consisted mainly of rounded or polygonal cells with large, eccentrically located nuclei. The cytoplasm showed an extensive granular endoplasmic reticulum and a well-developed Golgi complex, suggesting active synthesis and secretion of matrix components. Among the other cytoplasmic organelles, lysosomes containing variable amounts of marker particles were observed. After 2-3 weeks the transplants whowed signs of cellular degeneration and disintergration. During these processes, lysosomes remained structurally intact and, furthermore, retained the incorporated marker. Thus, thorium dioxide-labeled bodies were found in former chondrocyte lucunae and in the intercellular substance proper. In the latter location labeled bodies could be observed in close proximity to early mineral deposits. These results are discussed with special special reference to the cellular origin and lysosomal nature of matrix vesicles in calcifying cartilages.

Differences in collagen metabolism between normal and osteoarthritic human articular cartilage

Normal human articular cartilage synthesizes only one type of a chain, which exhibits the chromatographic behavior of the alpha(l)(II) chains described for chick and bovine cartilage. Osteoarthritic cartilage, on the other hand, synthesizes in addition a collagen containing alpha(2) chains and beta components. The different structural features of the two types of collagen may account for some of the functional defects of osteoarthritic cartilage.