Action of rheumatoid synovial collagenase on cartilage collagen. Different susceptibilities of cartilage and tendon collagen to collagenase attack.

The action of purified rheumatoid synovial collagenase on purified cartilage collagen, alpha-1(II)-3, in solution at 25 degrees C has been characterised. The enzyme attacked cartilage collagen in solution producing a 58% reduction in specific viscosity and resulting in the appearance of two reaction products which represented approximately three-quarter and one-quarter fragments of the intact molecule as shown by disc electrophoresis in polyacrylamide gels containing sodium dodecyl sulphate. The alpha-chain fragments which comprised each of these components corresponded to molecular weights of approximately 74000 and 21000. Electron microscopy of segment-long-spacing crystallites of the reaction products revealed three-quarter (TC-a) and one-quarter (TC-b) length fragments, and permitted accurate localization of the cleavage locus between bands 41 and 42 (I-41). This cleavage site and the formation of TC-a and TC-b reaction products are very similar to those found for type-I collagen substrates. Cartilage collagen in solution was found to be more resistant to collagenase attack than tendon collagen, the rate of cartilage collagen degradation being six times slower than that for tendon collagen, as judged by viscometry. The mid-point melting temperatures (T-m) for lathyritic cartilage and tendon collagen were 40.5 and 41.5 degrees C, and for the collagenase-produced reaction products 38.5 and 37.5 degrees C, respectively. The significance of these findings is discussed in relation to the structure of type I and II collagens.     

Occurrence of collagen and proteoglycan forms of type IX collagen in chick embryo cartilage. Production and characterization of a collagen form-specific antibody.

Type IX collagen from chick embryonic cartilage is a proteoglycan bearing a single chondroitin sulfate chain covalently linked to the alpha 2(IX) polypeptide chain. We have isolated type IX collagen metabolically labeled with [3H]proline using an antibody to type IX collagen and have found that the molecule is synthesized in two forms, a collagen form (COLIX) and a proteoglycan form (PGIX). In cultured chondrocytes, the two forms of type IX collagen showed a different ability to be deposited in the matrix. We have suggested the possibility that both forms may arise from an alternative substitution of a chondroitin sulfate chain to the NC3 domain of the alpha 2(IX) chain. Based on the reported amino acid sequence at the NC3 domain of alpha 2(IX), we have synthesized undecapeptides containing the sequence around the glycosaminoglycan attachment site of the alpha 2(IX) chain. Antibody against the peptide, which was raised in rabbit, only recognized COLIX and made it possible to distinguish COLIX from PGIX. Evidence shows that this could be due to a difference in antigenicity of the NC3 domain of the alpha 2(IX) chain between COLIX and PGIX caused by the substitution of a chondroitin sulfate chain to the serine residue in this domain. Therefore, this antibody may be useful as a probe for studies on the functions of glycosaminoglycan substitution in type IX collagen.     

Isolation of bovine type X collagen and immunolocalization in growth-plate cartilage.

The accessibility of the cysteine residues of actin from rabbit muscles to the thiol-targeted reagent 7-dimethylamino-4-methyl-(N-maleimidyl)coumarin (DACM) was investigated. Under conditions where the actin is in the unpolymerized form (G-actin), the most reactive thiol group was Cys-257, suggesting that it was located on the surface of the actin molecule. The selective modification of Cys-374 for this reagent as reported by Sutoh [(1982) Biochemistry 21, 3654-3661] was not observed. Cys-10, Cys-217 and Cys-374 were much less reactive and only gradually became extensively modified when the concentration of DACM approached 5 molar equivalents of actin. Presumably these thiol groups were located further inward away from the surface or situated in a different environment that rendered them less reactive. On the other hand, Cys-285 was completely inaccessible and presumably was buried. The lack of preferential labelling of Cys-374 by DACM is incompatible with the finding with iodoacetic acid as the reagent as reported by Elzinga & Collins [(1975) J. Biol. Chem. 250, 5897-5905]. This discrepancy, however, might well be due to the different reagents employed. The DACM-G-actin largely retained its competence for polymerization. Upon polymerization of G-actin, practically all the thiol groups became inaccessible to DACM, suggesting that a drastic change occurred in the conformation of actin units in the transition of monomers to filamentous actin.     

Ablation of collagen IX and COMP disrupts epiphyseal cartilage architecture.

Chondrodysplasias are a genetically heterogeneous group of skeletal disorders. Mutations in genes coding for cartilage oligomeric matrix protein (COMP), collagen IX and matrilin-3 have been described to cause the autosomal dominantly inherited form of multiple epiphyseal dysplasia (MED). Even though there is clear evidence that these cartilage matrix proteins interact with each other, their exact functions in matrix organisation and bone development still need to be elucidated. We generated a mouse model lacking both collagen IX and COMP to study the potential complementary role of these proteins in skeletal development. Mice deficient in both proteins exhibit shortened and widened long bones as well as an altered bone structure. They display severe growth plate abnormalities with large hypocellular areas in the central parts of the tibia. In addition, chondrocytes in the proliferative and hypertrophic zones do not show their typical columnar arrangement. These phenotypical traits were not observed in mice deficient only in COMP, while mice lacking only collagen IX showed similar growth plate disturbances and shorter and wider tibiae. The contribution of COMP to the phenotype of mice deficient in both collagen IX and COMP appears minor, even though clear differences in the deposition of matrilin-3 were detected.     

Silver staining of collagen fibrils in cartilage

Summary Direct visualization of individual collagen fibrils by light microscopy in human cartilage was achieved by applying a periodic acid-silver methenamine stain on plastic sections. Collagen fibrils, 100 nm in diameter or thicker, were delineated individually by light microscopy and were easily traced for a length beyond 100m. Thinner fibrils not readily visible optically were identified if arranged in compact bundles as occurring in the superficial zone of articular cartilage.     

Modulation of collagen synthesis in normal and osteoarthritic cartilage

In osteoarthritic cartilage, chondrocytes are able to present heterogeneous cellular reactions with expression and synthesis of the (pro)collagen types characteristic of prechondrocytes (type IIA), hypertrophic chondrocytes (type X), as well as differentiated (types IIB, IX, XI, VI) and dedifferentiated (types I, III) chondrocytes. The expression of type IIA procollagen in human osteoarthritic cartilage support the assumption that OA chondrocytes reverse their phenotype towards a chondroprogenitor phenotype. Recently, we have shown that dedifferentiation of mouse chondrocytes induced by subculture was associated with the alternative splicing of type II procollagen pre-mRNA with a switch from the IIB to the IIA form. In this context, we demonstrated that BMP-2 favours expression of type IIB whereas TGF-beta1 potentiates expression of type IIA induced by subculture. These data reveal the specific capability of BMP-2 to reverse the program of chondrocyte dedifferentiation. This interesting feature needs to be tested with human chondrocytes since cell amplification is required for the currently used autologous chondrocyte transplantation.     

Localization of collagen X in human fetal and juvenile articular cartilage and bone.

The tissue localization was analysed of collagen X during human fetal and juvenile articular cartilage-bone metamorphosis. This unique collagen type was found in the hypertrophic cartilage zone peri- and extracellularly and in cartilage residues within bone trabeculae. In addition, occasionally a slight intracellular staining reaction was found in prehypertrophic proliferating chondrocytes and in chondrocytes surrounding vascular channels. A slight staining was also seen in the zone of periosteal ossification and occasionally at the transition zone of the perichondrium to resting cartilage. Our data provide evidence that the appearance of collagen X is mainly associated with cartilage hypertrophy, analogous to the reported tissue distribution of this collagen type in animals. In addition, we observed an increased and often "spotty" distribution of collagen X with increasing cartilage "degeneration" associated with the closure of the growth plate. In basal hypertrophic cartilage areas, a co-distribution of collagens II and X was found with very little and "spotty" collagen III. In juvenile cartilage areas around single hypertrophic chondrocytes, co-localization of collagens X and I was also detected.     

Peptides of type II collagen can induce the cleavage of type II collagen and aggrecan in articular cartilage.

The objective of this study was to determine whether a fragment(s) of type II collagen can induce cartilage degradation. Fragments generated by cyanogen bromide (CB) cleavage of purified bovine type II collagen were separated by HPLC. These fragments together with selected overlapping synthetic peptides were first analysed for their capacity to induce cleavage of type II collagen by collagenases in chondrocyte and explant cultures of healthy adult bovine articular cartilage. Collagen cleavage was measured by immunoassay and degradation of proteoglycan (mainly aggrecan) was determined by analysis of cleavage products of core protein by Western blotting. Gene expression of matrix metalloproteinases MMP-13 and MMP-1 was measured using Real-time PCR. Induction of denaturation of type II collagen in situ in cartilage matrix with exposure of the CB domain was identified with a polyclonal and monoclonal antibodies that only react with this domain in denatured but not native type II collagen. As well as the mixture of CB fragments and peptide CB12, a single synthetic peptide CB12-II (residues 195-218), but not synthetic peptide CB12-IV (residues 231-254), potently and consistently induced in explant cultures at 10 microM and 25 microM, in a time, cell and dose dependent manner, collagenase-induced cleavage of type II collagen accompanied by upregulation of MMP-13 expression but not MMP-1. In isolated chondrocyte cultures CB12-II induced very limited upregulation of MMP-13 as well as MMP-1 expression. Although this was accompanied by concomitant induction of cleavage of type II collagen by collagenases, this was not associated by aggrecan cleavage. Peptide CB12-IV, which had no effect on collagen cleavage, clearly induced aggrecanase specific cleavage of the core protein of this proteoglycan. Thus these events involving matrix molecule cleavage can importantly occur independently of each other, contrary to popular belief. Denaturation of type II collagen with exposure of the CB12-II domain was also shown to be much increased in osteoarthritic human cartilage compared to non-arthritic cartilage. These observations reveal that peptides of type II collagen, to which there is increased exposure in osteoarthritic cartilage, can when present in sufficient concentration induce cleavage of type II collagen (CB12-II) and aggrecan (CB12-IV) accompanied by increased expression of collagenases. Such increased concentrations of denatured collagen are present in adult and osteoarthritic cartilages and the exposure of chondrocytes to the sequences they encode, either in soluble or more likely insoluble form, may therefore play a role in the excessive resorption of matrix molecules that is seen in arthritis and development.     

Abnormal collagen fibrils in cartilage of matrilin-1/matrilin-3-deficient mice

Matrilins are oligomeric extracellular matrix adaptor proteins mediating interactions between collagen fibrils and other matrix constituents. All four matrilins are expressed in cartilage and mutations in the human gene encoding matrilin-3 (MATN3) are associated with different forms of chondrodysplasia. Surprisingly, however, Matn3-null as well as Matn1- and Matn2-null mice do not show an overt skeletal phenotype, suggesting a dominant negative pathomechanism for the human disorders and redundancy/compensation among the family members in the knock-out situation. Here, we show that mice lacking both matrilin-1 and matrilin-3 develop an apparently normal skeleton, but exhibit biochemical and ultrastructural abnormalities of the knee joint cartilage. At the protein level, an altered SDS-PAGE band pattern and a clear up-regulation of the homotrimeric form of matrilin-4 were evident in newborn Matn1/Matn3 and Matn1 knock-out mice, but not in Matn3-null mice. The ultrastructure of the cartilage matrix after conventional chemical fixation was grossly normal; however, electron microscopy of high pressure frozen and freeze-substituted samples, revealed two consistent observations: 1) moderately increased collagen fibril diameters throughout the epiphysis and the growth plate in both single and double mutants; and 2) increased collagen volume density in Matn1(-/-)/Matn3(-/-) and Matn3(-/-) mice. Taken together, our results demonstrate that matrilin-1 and matrilin-3 modulate collagen fibrillogenesis in cartilage and provide evidence that biochemical compensation might exist between matrilins.     

Characterization of collagen types XII and XIV from fetal bovine cartilage.

The structurally related type XII-like collagen molecules TL-A and TL-B were recently identified in fetal bovine epiphyseal cartilage and subsequently shown to be collagen types XII and XIV, respectively. By indirect immunofluorescent staining of cartilage using monoclonal antibodies to the NC3 domains of each molecule, it was shown that type XII collagen was present predominantly around cartilage canals, the articular surface, subperichondrial margins, and the perichondrium, was less so in the remaining cartilage matrix, and was absent from the growth plate region. In the permanent cartilage of trachea, type XII stained somewhat more intensely in the margins beneath the loose connective tissue. Type XIV collagen localized more uniformly throughout the articular cartilage and was also absent from the growth plate region, whereas in tracheal cartilage, its distribution was similar to type XII. We have characterized the structure of these cartilage molecules and compared them with those from fetal bovine skin. Extraction of cartilage with 1 M NaCl and differential NaCl precipitation yields a fraction enriched for these two collagens. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting with monoclonal antibodies to the large amino-terminal non-triple-helical domain, NC3, revealed the presence in cartilage of two forms of type XII collagen: type XIIB, the molecule previously identified in chick and bovine tissues, and type XIIA, a much larger form equivalent to the molecule recently identified in WISH-transformed epithelial cell culture medium (Lunstrum, G. P., McDonough, A. M., Marinkovich, M. P., Keene, D. R., Morris, N. P., and Burgeson, R. E. (1992) J. Biol. Chem. 267, 20087-20092). Digestion with bacterial collagenase shows that the increased mass is present in the NC3A domain. Additional purification by velocity sedimentation and observation of rotary-shadowed images demonstrates molecules with extended non-triple-helical arms approximately 80 nm in length analogous to the WISH cell molecules. Electrophoretic mobilities of bands corresponding to type XIIA, but not type XIIB, are sensitive to chondroitinase ABC, indicating that type XIIA is a chondroitin sulfate proteoglycan and that modification occurs predominantly within the NC3A domain distal to NC3B. Neither type XIIB from skin nor type XIIA from WISH cells are chondroitinase-sensitive. By similar analysis, a portion of the type XIV collagen chains in cartilage was also sensitive to chondroitinase digestion. Chondroitin sulfate is apparently not located on its NC3 domain. As in skin, collagen types XII and XIV have subtly different distributions within cartilage and type XII may have a tissue-specific structure.     

Biochemical and ultrastructural studies of collagen and proteochondroitin sulfate in normal and nanomelic cartilage.

Biochemical and ultrastructural analysis of the sternal cartilage of chick embryos homozygous for the autosomal recessive gene nanomelia suggest that the mutant cells are functional chondrocytes in all respects except in proteochondroitin sulfate synthesis. Proteochondroitin sulfate synthesized by normal and mutant sterna in vitro was chromatographed on 1% agarose. Two distinct fractions of proteochondroitin sulfate were resolved from both normal and mutant cartilage. In normal cartilage, the major fraction represents approximately 90% of the total material, and in the mutant, this fraction is reduced to 10%, while the second fraction remains unchanged. It is suggested that at the onset of chondrogenesis in the mutant, an augmentation in the syntheis of the major fraction does not occur.Collagen synthesis in the mutant cartilage was analyzed by hydroxyproline determination, carboxymethylcellulose chromatography, and amino acid analysis to determine the percentage hydroxylation of lysine residues. By these procedures, collagen synthesis in the mutant was found to be both quantitatively and qualitatively similar to normal.Ultrastructural studies on the mutant sterna revealed that while the mutant chondrocytes were normal in appearance, the amount of extracellular matrix was decreased. In conjunction with this decrease, there is a severe reduction in the number of proteochondroitin sulfate matrix granules. No differences were observed in the collagen fibrils.     

Rice bifunctional alpha-amylase/subtilisin inhibitor: cloning and characterization of the recombinant inhibitor expressed in Escherichia coli

The complete nucleotide sequences of the cDNA and its gene that encode a bifunctional alpha-amylase/subtilisin inhibitor of rice (Oryza sativa L.) (RASI) were analyzed. RASI cDNA (939 bp) encoded a 200-residue polypeptide with a molecular mass of 21,417 Da, including a signal peptide of 22 amino acids. Sequence comparison and phylogenetic analysis showed that RASI is closely related to alpha-amylase/subtilisin inhibitors from barley and wheat. RASI was found to be expressed only in seeds, suggesting that it has a seed-specific function. A coding region of RASI cDNA without the signal peptide was introduced into Escherichia coli and was expressed as a His-tagged protein. Recombinant RASI was purified to homogeneity in a single step by Ni-chelating affinity column chromatography and characterized to elucidate the target enzyme. The recombinant inhibitor had strong inhibitory activity toward subtilisin, with an equimolar relationship, comparable with that of native RASI, and weak inhibitory activity toward some microbial alpha-amylases, but not toward animal or insect alpha-amylases. These results suggest that RASI might function in the defense of the seed against microorganisms.     

Biosynthesis of collagen and other matrix proteins by articular cartilage in experimental osteoarthrosis.

Osteoarthrosis was induced in one knee joint of dogs by an established surgical procedure. Changes in the articular cartilage in the biosynthesis of collagen and other proteins were sought by radiochemical labelling in vivo, with the following findings. (1) Collagen synthesis was stimulated in all cartilage surfaces of the experimental joints at 2, 8 and 24 weeks after surgery. Systemic labelling with [3H]proline showed that over 10 times more collagen was being deposited per dry weight of experimental cartilage compared with control cartilage in the unoperated knee. (2) Type-II collagen was the radiolabelled product in all samples of experimental cartilage ranging in quality from undamaged to overtly fibrillated, and was the only collagen detected chemically in the matrix of osteoarthrotic cartilage from either dog or human joints. (3) Hydroxylysine glycosylation was examined in the newly synthesized cartilage collagen by labelling dog joints in vivo with [3H]lysine. In experimental knees the new collagen was less glycosylated than in controls. However, no difference in glycosylation of the total collagen in the tissues was observed by chemical analysis. (4) Over half the protein-bound tritium was extracted by 4 M-guanidinium chloride from control cartilage labelled with [3H]proline, compared with one-quarter or less from experimental cartilage. Two-thirds of the extracted tritium separated in the upper fraction on density-gradient centrifugation in CsCl under associative conditions. Much of this ran with a single protein band on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis under reducing conditions. The identity of this protein was unknown, although it resembled serum albumin in mobility afte disulphide-bond cleavage.