Different responses of articular cartilage to strenuous running and joint immobilization.

Objective: To compare the pathological changes in cartilage derived from rats that developed osteoarthritis either by joint immobilization or by strenuous treadmill running in order to better understand their respective pathomechanism.

Method: A total of 24 male Wistar rats were randomly assigned to three groups: sedentary control (CON), immobilization (IM), and strenuous running (SR). For rats in the IM group, unilateral knee joint was immobilized in flexion. Rats in the SR group underwent treadmill running with high intensity. Eight weeks later, all animals were sacrificed. Femoral condyles were collected to take histological observation for cartilage characteristic and immunohistochemistry for collagen type II. In addition, cartilage samples were obtained to assess gene expression of aggrecan, collagen type II, biglycan, and fibromodulin by quantitative RT-PCR.

Results: Gross and histological observation showed osteoarthritic changes in groups SR and IM; however, more severe cartilage degradation was revealed in the latter. Proteoglycan and collagen II content decreased in groups SR and IM in comparison to group CON, with more loss in group IM. In group SR, mRNA levels in femoral cartilage were found to be unaltered for all the molecules measured. On the contrary, these molecules were significantly downregulated in group IM.

Conclusion: Differences in gross observation, histological characteristics, and gene expression of proteoglycans and collagen II suggest that both knee immobilization and strenuous running would lead to degenerative change of cartilage, but at different stages of the degenerative process.