Both p110a and p110b Isoforms of Phosphatidylinositol 3-OH-Kinase are Required for Insulin Signalling in the Hypothalamus

• Published in: Journal of neuroendocrinology Vol. 22; no. 6; pp. 534 - 542
• Main Authors: Tups, A, Anderson, G M, Rizwan, M, Augustine, R A, Chaussade, C, Shepherd, PR, Grattan, DR
• Format: Journal Article
• Language: English
• Published: 01-06-2010
• ISSN: 0953-8194
• DOI: 10.1111/j.1365-2826.2010.01975.x

Both insulin and leptin action in the brain are considered to involve activation of phosphoinositide 3-kinase (PI3K), although the roles of different PI3K isoforms in insulin signalling in the hypothalamus are unknown. In the present study, we characterised the roles of these isoforms in hypothalamic insulin and leptin signalling and investigated the cross-talk of both hormones. To evaluate PI3K levels in the hypothalamus, PI3K was immunoprecipitated using an antibody directed against the p85 subunit, and then total PI3K activity was measured in the presence of novel isoform-selective pharmacological inhibitors of each isoform of PI3K. Subsequently, these inhibitors were administered into the lateral ventricle of male Sprague-Dawley rats, followed by vehicle, insulin, leptin or both hormones 45 min later. PI3K activity was determined by immunohistochemical detection of phosphorylated AKT (S473). In a separate study, the effects of the inhibitors on the anorexigenic action of insulin and leptin were determined. Hypothalamic insulin signalling was specifically mediated by the combined actions of the class Ia isoforms p110a and p110b. Total hypothalamic PI3K activity was inhibited 65% by a p110a inhibitor, and 35% by a p110b inhibitor, with a combination of inhibitors being equally effective as the broad-spectrum PI3K inhibitor wortmannin. Individual i.c.v. administration of p110a and p110b inhibitors partly prevented insulin-induced phosphorylated AKT (S473) in the arcuate nucleus, whereas simultaneous application completely blocked insulin action. Unlike insulin, leptin did not induce phosphorylated AKT in the hypothalamus, as detected by immunohistochemistry, and the anorectic effects of leptin were not affected by pre-treatment with a combination of p110a and p110b inhibitors. The enhanced anorectic effect of a combined i.c.v. application of both insulin and leptin could be prevented by pre-treatment with the combination of p110a and p110b inhibitors. The data suggest that p110a and p110b isoforms of PI3K are necessary to mediate insulin action in the hypothalamus. The role of PI3K in leptin action is less clear, but it may be involved by means of an insulin-dependent sensitisation of leptin action.