In support of this conclusion, Xu et al. found that exogenous addition of SPP1, especially phosphorylated SPP1, can induce Mmp13 expression in cultured human chondrocytes while Attur et al. found that mouse articular chondrocytes lacking Postn exhibited reduced Mmp13 expression in an arthritis model [56, 57]. This evidence concerns the gene MMP13 and Arthritis.