MMP13 and osteoarthritis: The genes enriched in the osteoarthritis pathway include the upregulation of various matrix degradation enzymes, such as Adamts4, Adamts5, Mmp9, and Mmp13, and the downregulation of cartilage-related genes, such as collagen type II alpha 1 chain Col2a1, frizzled-related protein (Frzb), Indian hedgehog (Ihh), and Sox9 (Supplemental File, osteoarthritis pathway sheet).