Effects of mechanical stress on expression of differentiated phenotypes of chondrocytes

In the patients with dislocated hip arthropathy, cartilage gene expression was confirmed in weight-bearing inner layer tissues of the joint capsule. Because these inner layer tissues of the joint capsule formed joint-like structures with the femoral head for a long period, cartilaginous genes may have been expressed in the weight-bearing inner surface of the joint capsule. There was a difference in expression of the genes between weight-bearing and non-weight-bearing parts. From a quantitative comparison between GAPDH and aggrecan gene expression, aggrecan gene expression was 30-fold higher in the weight-bearing part than in the non-weight-bearing part. Aggrecan gene expression was not detected in outer layer tissues of the joint capsule. Type II collagen and TGF-beta genes were also detected, and both genes showed differences in expression between the weight-bearing and non-weight-bearing parts like the aggrecan gene. This may have been because mechanical stress caused cartilaginous differentiation in undifferentiated mesenchymal tissues in the inner layer of the joint capsule. Cell differentiation and proliferation caused by mechanical stress are indicate key role to osteoarticular tissues, and it is considered important for orthopedic treatment to evaluate the process in detail.