Exogenous Heparan Sulfate Enhances the TGF-<i>β</i>3-Induced Chondrogenesis in Human Mesenchymal Stem Cells by Activating TGF-<i>β</i>/Smad Signaling

Heparan sulfate (HS) interacts with growth factors and has been implicated in regulating chondrogenesis. However, the effect of HS on TGF- β -mediated mesenchymal stem cell (MSC) chondrogenesis and molecular mechanisms remains unknown. In this study, we explored the effects of exogenous HS alone and in combination with TGF- β 3 on chondrogenic differentiation of human MSCs and possible signal mechanisms. The results indicated that HS alone had no obvious effects on chondrogenic differentiation of human MSCs and TGF- β /Smad2/3 signal pathways. However, the combined TGF- β 3/HS treatment resulted in a significant increase in GAG synthesis, cartilage matrix protein secretion, and cartilage-specific gene expression compared to cells treated with TGF- β 3 alone. Furthermore, HS inhibited type III TGF- β receptors (T β RIII) expression and increased TGF- β 3-mediated ratio of the type II (T β RII) to the type I (T β RI) TGF- β receptors and phosphorylation levels of Smad2/3. The inhibitor of the TGF- β /Smad signal, SB431542, not only completely inhibited HS-stimulated TGF- β 3-mediated Smad2/3 phosphorylation but also completely inhibited the effects of HS on TGF- β 3-induced chondrogenic differentiation. These results demonstrate exogenous HS enhances TGF- β 3-induced chondrogenic differentiation of human MSCs by activating TGF- β /Smad2/3 signaling.