Transforming Growth Factor-β1 (TGF-β1) Induces Mouse Precartilaginous Stem Cell Proliferation through TGF-β Receptor II (TGFRII)-Akt-β-Catenin Signaling

Precartilaginous stem cells (PSCs) could self-renew or differentiate into chondrocytes to promote bone growth. In the current study, we aim to understand the role of transforming growth factor-β1 (TGF-β1) in precartilaginous stem cell (PSC) proliferation, and to study the underlying mechanisms. We successfully purified and primary-cultured PSCs from the neonate mice' perichondrial mesenchyme, and their phenotype was confirmed by the PSC marker fibroblast growth factor receptor-3 (FGFR-3) overexpression. We found that TGF-β1 induced Akt-glycogen synthase kinase-3β (GSK3β) phosphorylation and β-catenin nuclear translocation in the mouse PSCs, which was almost blocked by TGF-β receptor-II (TGFRII) shRNA knockdown. Further, perifosine and MK-2206, two Akt-specific inhibitors, suppressed TGF-β1-induced GSK3β phosphorylation and β-catenin nuclear translocation. Akt inhibitors, as well as β-catenin shRNA knockdown largely inhibited TGF-β1-stimulated cyclin D1/c-myc gene transcription and mouse PSC proliferation. Based on these results, we suggest that TGF-β1 induces Akt activation to promote β-catenin nuclear accumulation, which then regulates cyclin D1/c-myc gene transcription to eventually promote mouse PSC proliferation.