Smad3‐Deficient Chondrocytes Have Enhanced BMP Signaling and Accelerated Differentiation

Smad3 deficiency accelerates chondrocyte maturation and leads to osteoarthritis. Primary chondrocytes without Smad3 lack compensatory increases of TGF‐β signaling factors, but BMP‐related gene expression is increased. Smad2 or Smad3 overexpression and BMP blockade abrogate accelerated maturation in Smad3−/− chondrocytes. BMP signaling is increased in TGF‐β deficiency and is required for accelerated chondrocyte maturation.