Reexpression of type IIA procollagen by adult articular chondrocytes in osteoarthritic cartilage

Objective. To test for the reexpression of the chondroprogenitor splice var iant of the gene COL2A1, type IIA procollagen (containing a cysteine-rich N H2 propeptide), in adult articular chondrocytes in osteoarthritic (OA) join t disease, Methods. In situ hybridization and immunohistochemical localization were pe rformed on normal and OA articular cartilage specimens. The presence of typ e IIA procollagen messenger RNA (mRNA) expression was confirmed by Northern blot analysis. Results, In normal articular cartilage, no expression of mRNA or presence o f type IIA procollagen was found. In OA articular cartilage, focally intens e staining for type IIA protein was detected. Consistent with this, chondro cytes, particularly in the middle zones of articular cartilage, expressed t ype IIA procollagen mRNA. OA repair cartilage typically showed a broad zone of cells expressing type IIA mRNA and protein. Conclusion. Type IIA procollagen is reexpressed by adult articular chondroc ytes in OA cartilage degeneration, indicating the potential reversion of th e cells to a chondroprogenitor cellular phenotype, The absence of type IIA mRNA and protein in normal adult articular cartilage and its onset in the d iseased state suggests type IIA procollagen as a marker of OA.