Type III Transforming Growth Factor- β Receptor RNA Interference Enhances Transforming Growth Factor β 3-Induced Chondrogenesis Signaling in Human Mesenchymal Stem Cells.

The type III transforming growth factor- β (TGF- β ) receptor (T β RIII), a coreceptor of the TGF- β superfamily, is known to bind TGF- β s and regulate TGF- β signaling. However, the regulatory roles of T β RIII in TGF- β -induced mesenchymal stem cell (MSC) chondrogenesis have not been explored. The present study examined the effect of T β RIII RNA interference (RNAi) on TGF- β 3-induced human MSC (hMSC) chondrogenesis and possible signal mechanisms. A lentiviral expression vector containing T β RIII small interfering RNA (siRNA) (SiT β RIII) or a control siRNA (SiNC) gene was constructed and infected into hMSCs. The cells were cultured in chondrogenic medium containing TGF- β 3 or control medium. T β RIII RNAi significantly enhanced TGF- β 3-induced chondrogenic differentiation of hMSCs, the ratio of type II (T β RII) to type I (T β RI) TGF- β receptors, and phosphorylation levels of Smad2/3 as compared with cells infected with SiNC. An inhibitor of the TGF- β signal, SB431542, not only inhibited T β RIII RNAi-stimulated TGF- β 3-mediated Smad2/3 phosphorylation but also inhibited the effects of T β RIII RNAi on TGF- β 3-induced chondrogenic differentiation. These results demonstrate that T β RIII RNAi enhances TGF- β 3-induced chondrogenic differentiation in hMSCs by activating TGF- β /Smad2/3 signaling. The finding points to the possibility of modifying MSCs by T β RIII knockdown as a potent future strategy for cell-based cartilage tissue engineering.