Human chondrocyte cultures as models of cartilage-specific gene regulation

Chondrocytes comprise the single cellular component of adult hyaline cartilage and are considered to be terminally differentiated cells that maintain the cartilage matrix when turnover is low. The major components of the extracellular matrix synthesized by these specialized cells include highly crosslinked fibrils of the final synthesized and secreted triple helical type II collagen molecule that interact with other cartilage-specific collagens IX and XI, the large aggregating proteoglycan aggrecan, small proteoglycans, such as biglycan and decorin, and other specific and nonspecific matrix proteins that are expressed at defined stages during development and growth 1, 2. This matrix confers tensile strength and flexibility to articular surfaces and serves specialized functions in only a few other tissues Cultured chondrocytes have served as useful models for studying chondrocyte differentiation and the effects of cytokines and growth factors that control the maintenance or suppression of differentiated cartilage phenotype 3.