The effect of short-term fasting on the insulin signaling in the rat hypothalamus

Abstract

The aim: Our previous study1 showed that short-term fasting increased insulin expression in hypothalamus. The aim of the follow up study was to investigate the effect of short-term food deprivation on the insulin signaling pathways in the same brain region. Therefore, we analyzed expression of IRS1, IRS2, PI3K, AKT, ERK and theirs phosphorylated forms in the rat hypothalamus. Methods: Two months old male Wistar rats were exposed to six-hour fasting beginning at 6 pm. Controls (C) had free access to food and were sacrificed simultaneously with the fasting counterparts. Western blot was used to determine the levels of the examined proteins in both the cytosolic fraction and total protein isolate. Results: The amounts of IRS1, IRS2, and their phosphorylated forms (pIRS1-Tyr612, pIRS2-Ser731) were not altered after six-hour fasting, nor was that of PI3K-p85. Fasting did not change the levels of AKT1/2/3 and phospho-AKT1/2/3-Ser473 either. ERK1/2 and phospho-ERK1/2-Thr202/Tyr204 levels were also not significantly different between control and experimental rats when measured in the total protein isolate. However, fasting upregulated the levels of phosho-ERK1/2 in the cytosolic protein fraction. Conclusion: Although hypothalamic insulin content was increased after short-term fasting, no differences in PI3K/AKT signaling pathway activation were observed. However, results indicate that locally produced insulin may potentially be involved in the activation of MAPK signaling pathway.