COL2A1 and disease of the tendon: For example, (1) Sox9, Col1a1, and Col2a1 have been shown to play important functions in cartilage development [89, 90]; (2) Mgp was found to be related to the onset of osteoarthritis during cartilage development [91]; (3) Bcl2 was a key protein of the PI3K-AKT signaling pathway, which was closely associated with chondrocyte proliferation [92]; and (4) COL5A1 polymorphism was associated with susceptibility to tendon disease [93].