MMP9 and rheumatoid arthritis: Participates in chondrocyte biology; specific processes in which the enzyme is involved are apoptosis of hypertrophic chondrocytes present in utero, bone development (e.g., by being highly active to angiogenesis in the growth plate), strength and toughness of bone, as well as the regulation of gene pathways responsible for osteoclastogenesis). In turn, MMP-9 overexpression contributes to sinonasal osteitis, rheumatoid arthritis, and degenerated lumbar disk tissues.