Regional quantification of cartilage type II collagen and aggrecan messenger RNA in joints with early experimental osteoarthritis

OBJECTIVE: Accurate assessment of chondrocyte metabolism is a potentially valuable indicator of cartilage health in osteoarthritis (OA). This study was conducted to explore the anabolic metabolism of chondrocytes early in the natural history of an experimental canine model of OA. METHODS: Competitive reverse transcription-polymerase chain reaction was used to calculate the copy number of type II collagen and the messenger RNA (mRNA) levels of aggrecan core protein in articular cartilage samples obtained from different regions of the femorotibial joint 12 and 39 weeks after cruciate transection. RESULTS: Gene expression of both type II collagen and aggrecan in cartilage samples obtained from experimental joints at both intervals after surgery was elevated significantly compared with that in samples from contralateral control joints. The number of mRNA copies per microgram of DNA of aggrecan exceeded that of type II collagen in control cartilage, but the copy number of type II collagen mRNA exceeded that of aggrecan in OA cartilage. Thus, the ratio of type II collagen-to-aggrecan mRNA copy number (normalized to DNA) was shown to be characteristically altered in cartilage with experimental OA. CONCLUSION: Accurate assessment of multiple gene products in small samples of cartilage taken from focal areas of a joint can be used diagnostically for monitoring chondrocyte metabolism and possibly for staging at least the early phases of this joint disease.