Inactivation of glycogen synthase kinase-3α is required for mitochondria-mediated apoptotic germ cell phagocytosis in Sertoli cells.

The rapid and efficient clearance of apoptotic germ cells (GCs) by Sertoli cells (SCs) is important for spermatogenesis. High mitochondrial activity in phagocytes is critical for continued clearance of apoptotic cells. However, the underlying molecular mechanism is poorly understood. Glycogen synthase kinase-3 alpha (GSK3 alpha) is a protein kinase that participates in the regulation of mitochondrial activity. Immunohistochemistry evidenced the predominant presence of the Ser21 phosphorylation GSK3 alpha (inactivation) signal in SCs. Heat shock-induced apoptosis of GCs and dephosphorylation of GSK3 alpha in SCs is a perfect model to investigate the role of GSK3 alpha in phagocytic action. The number of apoptotic GCs was significantly lower in GSK3 alpha inhibitor pre-treated mice with HS compared to normal control. In vitro phagocytosis assays shown that the phagocytic activity in GSK3 alpha activated SCs was downregulated, while GSK3 alpha inhibitor supplementation restored this process. Moreover, GSK3 alpha activation participates in the alteration of the mitochondrial ultrastructure and activity. In particular, GSK3 alpha activation inhibits mitochondrial fission via phosphorylation of dynamin related protein 1 at Ser637. Changes of mitochondrial activity resulted in the accumulation of lipid droplets and the alteration of metabolism pattern in SCs. In summary, our results demonstrate that inactivation of GSK3 alpha is required for mitochondria-mediated apoptotic GCs phagocytosis in SCs.