Major role of collagen IIB in the elevation of total type II procollagen messenger RNA in the hypertrophic phase of experimental osteoarthritis

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Abstract
Objective. To define the relative contributions of procollagen IIA and IIB messenger RNA (mRNA) in the 8‐fold elevation of total (IIA + IIB) type II procollagen mRNA in cartilage from joints with early experimental osteoarthritis (OA). Methods. Unilateral cruciate ligament transection was performed on skeletally mature animals. Total RNA was extracted from articular cartilage from control joints and from joints with experimental OA. Northern blot hybridization with oligoprobes was used to distinguish between types IIA and IIB mRNA. Results. Levels of IIA mRNA were similar in control and experimental cartilage. Type IIB mRNA accounted for the increase in total type II mRNA expression in OA joints. Conclusion. Although OA chondrocytes adapt to making immature forms of aggrecan proteoglycan, they do not revert to the prechondrocyte stage characterized by IIA mRNA expression.