Type III Transforming Growth Factor-β Receptor RNA Interference Enhances Transforming Growth Factor β3-Induced Chondrogenesis Signaling in Human Mesenchymal Stem Cells

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