TYPE-X COLLAGEN-SYNTHESIS IN HUMAN OSTEOARTHRITIC CARTILAGE - INDICATION OF CHONDROCYTE HYPERTROPHY

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 H-3-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.