MEF2C is a new regulator of the human articular chondrocyte phenotype
MEF2C plays a role in diverse tissues, most notably heart, brain, eyes and developing bones. Here we report for the first time that MEF2C is present and active in the permanent articular cartilage in humans which lines and protects our joints throughout life. We show that MEF2C directly targets cartilage master regulator gene SOX9, and SOX9, in turn, regulates MEF2C in a novel positive feedback loop maintaining high expression levels of both transcription factors, and consequently stabilising the articular chondrocyte phenotype and helping prevent hypertrophy and subsequent calcification and vascularisation. We propose that MEF2C and SOX9 may show similar cooperative activity in other tissues, and across a range of adult murine tissues we found co-expression of both transcription factors in cartilage, trachea, brain, eyes and heart. Strikingly, all of these tissues are prone to calcification and further study of MEF2C/SOX9 cooperativity in these organs will be revealing.