Akt regulates Sox10 expression to control oligodendrocyte differentiation via phosphorylating FoxO1

Sox10 is a well-known factor to control oligodendrocyte (OL) differentiation and its expression is regulated by Olig2. As an important protein kinase, Akt has been implicated in diseases with white matter (WM) abnormalities. To study whether and how Akt may regulate OL development, we generated OL lineage cells-specific Akt1/Akt2/Akt3 triple conditional knockout (Akt cTKO) mice. Both male and female mice were used. These mutants exhibit complete loss of mature OLs and unchanged apoptotic cell death in the central nervous system. We show that deletion of Akt three isoforms causes down-regulation of Sox10 and decreased levels of phosphorylated FoxO1 (pFoxO1) in the brain. In vitro analysis reveals that expression of FoxO1 with mutations on phosphorylation sites for Akt significantly represses the Sox10 promoter activity, suggesting that phosphorylation of FoxO1 by Akt is important for Sox10 expression. We further demonstrate that mutant FoxO1 without Akt phosphorylation epitopes is enriched in the Sox10 promoter. Together, this study identifies a novel FoxO1 phosphorylation-dependent mechanism for Sox10 expression and OL differentiation. SIGNIFICANCE STATEMENT Dysfunction of Akt is associated with white matter diseases including the agenesis of the corpus callosum. However, it remains unknown whether Akt plays an important role in oligodendrocyte differentiation. To address this question, we generated oligodendrocyte lineage cells-specific Akt1/Akt2/Akt3 triple conditional knockout mice. Akt mutants exhibit deficient white matter development, loss of mature oligodendrocytes, absence of myelination and unchanged apoptotic cell death in the central nervous system. We demonstrate that deletion of Akt three isoforms leads to down-regulation of Sox10, and that phosphorylation of FoxO1 by Akt is critical for Sox10 expression. Together, these findings reveal a novel mechanism to regulate Sox10 expression. This study may provide insights on molecular mechanisms for neurodevelopmental diseases caused by dysfunctions of protein kinases.