Chondrocyte

Chondrocyte is the only cell type found in mature cartilage. It originates from mesenchymal progenitor cells that differentiate into chondroblasts, which secrete extracellular matrix and become embedded in lacunae as chondrocytes. Chondrocytes reside within the cartilaginous matrix of all three cartilage types: hyaline, elastic, and fibrocartilage, which is avascular and relies on diffusion for nutrients and waste removal.

The primary role of chondrocytes is to maintain the cartilaginous extracellular matrix. They synthesize collagen type II, aggrecan and other proteoglycans, non-collagenous proteins, and enzymes involved in matrix remodeling. In response to mechanical load and biochemical signals, chondrocytes regulate matrix turnover through expression of matrix metalloproteinases and tissue inhibitors of metalloproteinases. Pericellular and territorial matrices around lacunae influence nutrient exchange and mechanotransduction.

During development, chondrocytes participate in endochondral ossification, where immature chondrocytes in growth plates undergo hypertrophy before being replaced by bone. Regulatory pathways include Sox9, which promotes chondrogenesis, and signaling interactions involving Indian hedgehog (Ihh) and parathyroid hormone-related protein (PTHrP) that coordinate growth plate activity and chondrocyte maturation. Runx2 contributes to hypertrophic differentiation.

Clinical relevance includes cartilage-related diseases such as chondrosarcoma, a cancer of chondrocytes, and osteoarthritis, which features cartilage degradation and altered chondrocyte function. Chondrocytes are central to cartilage repair and tissue engineering, where strategies aim to enhance chondrogenesis and restore functional matrix in damaged tissue.