Accelerated Development of Aging-Associated and Instability-Induced Osteoarthritis in Osteopontin-Deficient Mice

Objective. To investigate the role of osteopontin (OPN) in the development of osteoarthritis (OA) under in vivo and in vitro conditions. Methods. Both instability-induced and aging-associated OA models were generated using OPN-deficient (OPN-/-) and control wild-type (WT) mice. An in vitro cartilage degradation model was also used, to evaluate the effect of OPN on proteoglycan loss from joint cartilage. Results. OPN deficiency exacerbated both aging-associated and instability-induced OA. Both structural changes and an increased loss of proteoglycan from cartilage tissue were augmented in the absence of OPN. OPN deficiency also led to the induction of matrix metalloproteinase 13 (MMP-13), which degrades a major component of the cartilage matrix protein type II collagen. Both the loss of proteoglycan and the induction of the collagen-degrading enzyme MMP-13 facilitated the development of OA. Conclusion. OPN plays a pivotal role in the progression of both instability-induced and aging-associated spontaneous OA. OPN is a critical intrinsic regulator of cartilage degradation via its effects on MMP-13 expression and proteoglycan loss.