Enhanced proliferation of bone marrow mesenchymal stem cells by co-culture with TM4 mouse Sertoli cells: involvement of the EGF/PI3K/AKT pathway.

Bone marrow mesenchymal stem cells (BM-MSCs) are considered as a promising option in the field of regenerative medicine and tissue engineering. However, little is known about how TM4 mouse Sertoli cells, which are known to enhance stem cells proliferation in co-culture, may influence the proliferation of BM-MSCs and which signaling pathways are involved in. To address these questions, an in vitro transwell system was used. We found that TM4 cells could produce soluble factors which enhanced the growth of BM-MSCs without inhibiting the multipotency. Furthermore, cell cycle analysis showed that co-culture with the TM4 cells accelerated the progress of BM-MSCs from the G1 to the S phase. The expression of the phospho-akt, mdm2, as well as pho-CDC2, and cyclin D1 were markedly upregulated in co-cultured BM-MSCs. The observed promoting effect was significantly inhibited by the administration of the PI3K/AKT inhibitor, LY294002. Among the various growth factors produced by TM4 cells, the epithelial growth factor (EGF) stimulated the proliferation of the BM-MSCs more significantly compared with the other growth factors examined in this study. Neutralization of EGF via a blocking antibody significantly limited the promoting growth effect in BM-MSCs. These results suggest that TM4 cells provide a favorable in vitro environment for BM-MSCs growth and imply the involvement of the EGF/PI3K/AKT pathway.