Similar to endochondral ossification, articular cartilage is also an avascular tissue and predominantly expresses Sox9 and type II collagen in normal circumstances but upregulates Runx2, HIF2, MMP13 and type X collagen as cartilage degenerates and osteoarthritis develops, in a pattern inverse to Sox9 and type II collagen expression43. Here, MMP13 is linked to osteoarthritis.