Regulation of GSK3β by Ser³⁸⁹ Phosphorylation During Neural Development

GSK3β is a constitutively active kinase that promotes cell death, which requires strict regulatory mechanisms. Although Akt-mediated phosphorylation at Ser⁹ is the default mechanism to inactivate GSK3β, phosphorylation of GSK3β at Ser³⁸⁹ by p38 MAPK has emerged as an alternative inhibitory pathway that provides cell protection and repair in response to DNA damage. Phosphorylation of Ser³⁸⁹ GSK3β has been detected in adult brain, where it has been related to neuronal survival and behavior. However, the use of this pathway to regulate GSK3β in the neonatal developing brain is unknown. In this study, we show that phosphorylation of GSK3β at Ser³⁸⁹ in the brain is developmentally regulated, with the highest levels corresponding to the first 2 weeks of age. Moreover, we found that the phosphorylation of GSK3β at Ser³⁸⁹ is the preferential mechanism for inactivating brain GSK3β in 2-week-old mice. Importantly, we show that phospho-Ser³⁸⁹ GSK3β expression is predominant in neuronal cell cultures from neonatal brain relative to other cell populations. However, phospho-Ser³⁸⁹ GSK3β is triggered by DNA double-strand breaks in all developing neural cell types examined. Thus, the phosphorylation of GSK3β on Ser³⁸⁹ could be a central regulatory mechanism to restrain GSK3β during neurogenesis early in life.