G. Weseloh

OBJECTIVE: To investigate the appearance of hypertrophic chondrocytes in osteoarthritic (OA) cartilage, using type X collagen as a specific marker. METHODS: The biosynthesis of type X collagen was examined by metabolic labeling of freshly isolated articular chondrocytes with 3H-proline, immunoprecipitation, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the synthesized collagens. Extracellular deposition of types X and II collagen was analyzed immunohistochemically. RESULTS: Immunostaining revealed an irregular distribution of type X collagen, which was localized around chondrocyte clusters in fibrillated OA cartilage, but was absent from the noncalcified region of normal articular cartilage. Freshly isolated OA chondrocytes synthesized predominantly type X collagen, while control chondrocytes synthesized mostly type II collagen. CONCLUSION: Our findings indicate focal premature chondrocyte differentiation to hypertrophic cells in OA cartilage.

Normal and osteoarthritic human articular cartilage was inves- tigated by in situ hybridization for expression patterns of the fibrillar collagens type I, II, and III to evaluate phenotypic changes of articular chondrocytes related to the disease. In 11 out of 20 samples, a defined subset of chondrocytes in the su- perficial and upper middle zone of osteoarthritic cartilage showed significant levels of cytoplasmic al (III) mRNA, whereas strong signals of at (II) mRNA were found in the up- per and lower middle zone, partially overlapping with the zone of al (III) mRNA-expressing cells. The extent of type II and III collagen expression depended on the integrity of the extra- cellular matrix surrounding the chondrocytes, and the location within the articular cartilage. No atl (I) mRNA was detectable in osteoarthritic original articular cartilage. The at (I) probe did, however, reveal signals in pannuslike tissue, osteophytes, and bone cells. In normal articular cartilage, no detectable lev- els of cytoplasmic mRNA for Al (I), a2(I), or al (III) were seen. Using specific mono-and polyclonal antibodies, we found deposition of type III collagen but hardly any of type I collagen in the superficial zone of osteoarthritic cartilage that is consis- tent with the in situ hybridization results.