Transforming growth factor（TGF）-β superfamily signaling pathways not only regulate numerous physiological processes such as embryonic development, angiogenesis and wound healing, but also play an important role in the regulation of cell proliferation, differentiation, maturation and programmed cell death. In addition, signaling by TGF-β superfamily also regulates chondrogenesis and cartilage development. Smad protein mediate signal transduction induced by the TGF-β superfamily members by transmitting the signals from the cell surface to the nucleus. In this review, we focus on the classification of Smad, the mechanism of the transduction of TGF-β superfamily signals by Smad, the mechanism of the Smad signaling regulates the chondrogenesis and the negative regulation of Smad signaling.
