Light and electron microscopic in-situ hybridization of collagen type I and type II mRNA in the fibrocartilaginous tissue of late-stage osteoarthritis.

OBJECTIVE Biochemical analysis indicates the presence of collagen type I in fibrocartilaginous tissue of osteoarthritic cartilage, whereas normal hyaline cartilage contains only collagen type II produced by normal chondrocytes. Fibrocartilaginous tissue of late-stage osteoarthritis also exhibits irregularly shaped type 2b secretory chondrocytes as described in the literature. We have attempted to elucidate the type of cell which produces each type of collagen in late-stage osteoarthritis. DESIGN We carried out in-situ hybridization at the light and electron microscopic level on the same tissue embedded in LR-Gold applying silver enhancement for gold-coupled anti-DIG antibodies. We correlated the types of cells with the expression of transcripts for type I and type II collagen. RESULTS We found that cells resembling type 2b secretory chondrocytes of deep zones of fibrocartilaginous tissue expressed collagen type I mRNA and almost no collagen type II mRNA. The amount of collagen type I mRNA was as high as the amount produced in normal human skin fibroblasts. CONCLUSION Some of the collagen type I in osteoarthritic human cartilage of late-stage disease is produced by cells resembling type 2b secretory chondrocytes of the deep zone.