Properties and Functions of Myochondrocytes and Myochondroblasts in Different Human Cartilage Tissues-An Overview.

A subset of chondrocytes in various human cartilage tissues, including neoplastic, regenerative, and normal cartilage, expresses α-smooth muscle actin (α-SMA), a protein typically found in smooth muscle cells. These α-SMA-containing chondrocytes, termed myochondrocytes and myochondroblasts, may play important roles in cartilage physiology, regeneration, and structural integrity, particularly in auricular and articular cartilage. This review synthesizes current knowledge regarding the terminology, distribution, and biological significance of these cells across normal, osteoarthritic, transplanted, and neoplastic cartilage. We summarize key findings from immunohistochemical studies using markers such as S-100, α-SMA, and SOX9, along with ultrastructural confirmation of myofilament bundles via electron microscopy. Current evidence suggests that myochondrocytes exhibit enhanced regenerative potential and contribute to matrix remodeling. Furthermore, their presence reflects the inherent cellular heterogeneity of cartilage, potentially arising from transdifferentiation processes involving fibroblasts, mesenchymal stem cells, or chondroblasts. Finally, TGF-β1 and PDGF-BB are identified as a critical modulator of α-SMA expression and chondrocyte phenotype. A deeper understanding of nature and function of myochondrocytes and myochondroblasts may improve interpretations of cartilage pathology and inform strategies for tissue engineering and cartilage repair. This review highlights the need for further investigation into the molecular regulation and functional roles of these cells in both physiological and pathological contexts.