Altered Glut4, <scp>IRAP</scp> , and Brain Insulin Signaling in a Mouse Model of Epilepsy and Contributions to Glucose Transport in Neurons and Astrocytes

There is evidence that glucose transport is impaired between seizures, which can promote seizure generation. In addition to glucose transporters Glut1 and Glut3, Glut4 is also found in the brain. Glut4 translocation is regulated by insulin signaling in peripheral tissues and insulin-regulated aminopeptidase (IRAP), but remains poorly understood in the brain. This study aimed to characterize the expression of Glut1, Glut3, Glut4, and key regulators of Glut4 trafficking in the chronic stage of the mouse pilocarpine epilepsy model. Roles of Glut4 and IRAP in glucose uptake were investigated in cultured neurons versus astrocytes. Western blot, RT-qPCR, and immunohistochemistry were used to investigate the expression of Glut1, Glut3, Glut4, IRAP, and insulin signaling genes in the chronic stage of the mouse pilocarpine model in the hippocampus and cortex between seizures. Contributions of Glut4 and IRAP to ³H-2-deoxyglucose uptake were quantified in primary mouse neurons and astrocytes. In the hippocampus during the chronic stage of the model, Glut1 and IRAP expression was unaltered, Glut3 decreased, but Glut4 2.5-fold increased with Glut4 and IRAP being specifically upregulated in GFAP⁺ astrocytes. Insulin signaling appeared altered, with reduced expression of key pathway genes and changed phospho-Akt^Ser473 and -AMPKα^Thr172 levels. Although systemically injected insulin did not activate brain insulin signaling, insulin and neurotransmitters stimulated glucose transport into cultured neurons and astrocytes by 15%-50%. This was largely mediated by Glut4, despite its relatively low expression in these cells. Notably, in neurons but not in astrocytes, IRAP inhibitors further enhanced this stimulated transport by an additional 15% via Glut4-mediated uptake. This is the first report showing increased astrocytic Glut4 expression in a rodent epilepsy model. Along with the finding of significant contributions of Glut4 and IRAP to glucose uptake in neurons, our work points to IRAP inhibitors as new pharmacological approaches improving neuronal energy supply to prevent seizure generation in epilepsy.