Articular cartilage and changes in arthritis - An introduction: Cell biology of osteoarthritis

The reaction patterns of chondrocytes in osteoarthritis can be summarized i n five categories: (1) proliferation and cell death (apoptosis); changes in (2) synthetic activity and (3) degradation; (4) phenotypic modulation of t he articular chondrocytes; and (5) formation of osteophytes, In osteoarthri tis, the primary responses are reinitiation of synthesis of cartilage macro molecules, the initiation of synthesis of types IIA and III procollagens as markers of a more primitive phenotype, and synthesis of active proteolytic enzymes. Reversion to a fibroblast-like phenotype, known as 'dedifferentia tion', does not appear to be an important component. Proliferation plays a role in forming characteristic chondrocyte clusters near the surface, while apoptosis probably occurs primarily in the calcified cartilage.