Protein Kinase C Regulates Self-Renewal of Mouse Spermatogonial Stem Cells

Spermatogonial stem cells (SSCs) have unique abilities to self-renew and differentiate into committed cells that can finally produce sperm. Glial cell line-derived neurotrophic factor (GDNF) has been reported as a crucial factor for SSC self-renewal. However, the intracellular mechanisms of SSC self-renewal remain unclear. To investigate these mechanisms, we assessed the effect of GDNF-related signaling pathways on SSCs using an in vitro culture system combined with a transplantation technique to confirm stem cell activity and quantify stem cell numbers. Phosphoinositide-3 kinase (PI3K), Akt, Src family kinase (SFK), and protein kinase C (PKC) are down-stream signaling pathways activated by GDNF binding to its receptors. Of these, little is known regarding the role of PKC signaling in SSC self-renewal. In this study, we compared the effects of PKC with other signaling pathways for SSC self-renewal. When SSCs were cultured with a chemical inhibitor of PKC for 8 days, self-renewal was rapidly prevented and the number of cultured cells decreased significantly. However, apoptosis analysis revealed that the number of apoptotic cells in the cells treated with PKC inhibitor was not significantly different from those in the control. In addition, no significant difference was observed in the differentiation of cells cultured in the presence of PKC inhibitor and untreated culture. Transplantation analysis showed colony formation in the recipient testis was similar for cells cultured with addition of each inhibitor compared with control, indicating that they are functionally normal. Collectively, these results demonstrate that PKC signaling is a crucial pathway for the self-renewal division of SSCs.