In vivo effect of opticin deficiency in cartilage in a surgically induced mouse model of osteoarthritis.

The SLRP opticin (OPTC) has been demonstrated to be produced and degraded in osteoarthritic (OA) human cartilage. Here, we investigated the in vivo effect of OPTC deficiency in OA cartilage. OA was induced in 10-week-old Optc -/- and Optc +/+ mice. Ten weeks post-surgery, cartilage was processed for histology and immunohistochemistry. SLRP expression was determined in non-operated mouse cartilage. OA Optc -/- demonstrated significant protection against cartilage degradation. Data revealed that in non-operated Optc -/- cartilage, expression of SLRPs lumican and epiphycan was up-regulated at day 3 and in 10-week-olds (p ≤ 0.039), and fibromodulin down-regulated in 10-week-olds (p = 0.001). Immunohistochemistry of OA mice showed a similar pattern. In OA Optc -/- cartilage, markers of degradation and complement factors were all down-regulated (p ≤ 0.038). In OA Optc -/- cartilage, collagen fibers were thinner and better organized (p = 0.038) than in OA Optc +/+ cartilage. The protective effect of OPTC deficiency during OA results from an overexpression of lumican and epiphycan, known to bind and protect collagen fibers, and a decrease in fibromodulin, contributing to a reduction in the complement activation/inflammatory process. This work suggests that the evaluation of the composition of the different SLRPs in OA cartilage could be applied as a new tool for OA prognosis classification.