PI3K-dependent inactivation of FoxO transcription factors in a hippocampal model of oxidative stress

Abstract

We have previously demonstrated the alteration of cell viability, morphology and lipid peroxidation as well as the activation of PI3K/Akt/GSK3ß pathway in a model of iron-induced neurodegeneration. The exposure of a mouse hippocampal neuronal 2+ cell line (HT22) to different concentrations of Fe (25-200 μM) for 2+ 24 h led us to define a mild oxidative injury status (25-50 μM Fe ). The aim of this work was to investigate the involvement of FoxO transcription factors, known downstream effectors of PI3K, during iron-triggered mild oxidative stress. Under this experimental condition, reactive oxygen species measured by fluorescence microscopy increased with small changes in cell viability, and SOD1 levels decreased whereas catalase levels showed no changes with respect to controls. The localization of phosphorylated and non-phosphorylated FoxO3a was studied in nuclear and cytosolic fractions. Levels of phospho-FoxO3a (the inactive form) increased in the cytosolic fraction of cells treated with iron in a PI3K- dependent manner. Consistent with this, total FoxO3a content decreased in the nuclear fraction. FoxO1 phosphorylation also increased in the cytosolic fraction. Our results show that iron- induced neurotoxicity activates PI3K/Akt/GSK3ß promoting FoxO3a/FoxO1 phosphorylation, their inactivation and their cytosolic localization under mild oxidative injury in hippocampal neurons