Collagen II

Collagen II is the major collagen synthesized by chondrocytes and a core structural component of articular cartilage, vitreous humour, inner ear, and nucleus pulposus^[1]. Mechanistically, COL2A1 suppresses articular chondrocyte hypertrophy and osteoarthritis progression by promoting integrin β1-SMAD1 interaction and regulating BMP-SMAD1 signaling^[2]. In disease models, COL2A1 loss accelerates chondrocyte hypertrophy, while degenerative human articular cartilage shows reduced COL2A1 with increased hypertrophic markers and BMP-SMAD1 activity^[2]. Type II collagen degradation can also expose a cryptic peptide sequence that induces collagenase activity, MMP-13, and chondrocyte hypertrophy in articular cartilage explants^[3]. Compared with type X collagen, which marks hypertrophic chondrocytes in osteoarthritis, collagen II better reflects the stable hyaline cartilage phenotype^[4]. Compared with collagen I devices, collagen II biomaterials more directly match cartilage extracellular matrix composition and support cartilage engineering research^[5]. For experimental applications, collagen II scaffolds help maintain or rejuvenate hyaline chondrocyte phenotype through Wnt-related mechanisms, supporting use in cartilage tissue engineering models^[6].