Transforming growth factor-1 stimulates mesenchymal stem cell proliferation by altering cell cycle through FAK-Akt-mTOR pathway

Background: Mesenchymal stem cells (MSCs) are promising for cell therapy and regenerative medicine. An increased need for expanding of MSCs under serum-free condition to achieve a sufficient quantity for therapeutic applications is inevitable. Transforming growth factor-1 (TGF-1) is widely used for expanding clinical-grade MSCs in vitro. This work focuses on the influence of TGF-1 on proliferation in rat bone marrow-derived MSCs (BMSCs) and the underlying mechanism.Materials and Methods: BMSCs were isolated and cultured with or without TGF-1 in a serum-free medium and Cell Counting Kit-8 assay was used to detect BMSCs proliferation. Cell cycle transition was also analyzed. Further, the expression levels of cyclin D1, phosphorylated focal adhesion kinase, and downstream effectors in Akt-mTOR-S6K1 signaling pathway were examined by western blotting.Results and Conclusion: TGF-1 triggered proliferation via accelerating G1/S cell cycle transition in BMSCs. The addition of TGF-1 can activate Akt-mTOR-S6K1 pathway. Additionally, FAK was found to be involved in the process. Upon adding the FAK inhibitor, both the activation of Akt-mTOR-S6K1 and TGF-1-induced cell proliferation were abrogated. Together, an insight understanding of how TGF-1 influences BMSCs proliferation is achieved. This study provides a possible strategy of supplementing TGF-1 in serum-free medium for in vitro expansion, which eventually would advance the production of clinical-grade MSCs for regenerative medicine.