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]. The gene discussed is MMP13; the disease is arthritic joint disease.