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Abstract
Chondrogenic promotion by rhGDF5 with or without rhTGFβ3 was studied in pellet culture of human mesenchymal stem cells (HMSCs). A synergy between rhGDF5 and rhTGFβ3 was observed in promoting chondrogenesis. rhBMP2, rhBMP6, rhBMP7 and rhTGFβ1 were further tested and showed the same effect. To explore the mechanism, the expression of TGFβtype I and II receptors, ALK5, ALK2, ALK3, ALK6, TGFβRII, BMPRII, ActRII was studied. ALK6 showed increase by the rhTGFβ1 or rhTGFβ3 treatment. ALK6 protein expression also showed increase by rhTGFβ3. rhTGFβ1/rhTGFβ3 induced ALK6 up-regulation was inhibited by SD-208, a TGFβ type I receptor inhibitor. Chondrogenesis by rhTGFβ1/rhTGFβ3 or the combination between rhTGFβ1/rhTGFβ3 and rhGDF5 also was diminished by SD-208. SMAD1/5/8 phosphorylation in nascent human mesenchymal stem cells (HMSCs) was stimulated weakly by rhGDF5 but strongly by rhBMP7. The rhGDF5 stimulated SMAD1/5/8 phosphorylation was enhanced by rhTGFβ1/rhTGFβ3 but inhibited by SD-208. The rhBMP7 stimulated SMAD1/5/8 phosphorylation did not show influence by rhTGFβ3 and SD-208. Our results indicated the potential involvement of ALK6 activation by rhTGFβs in the synergy between rhTGFβs and rhBMPs.