P21-activated protein kinase-1 (Pak1) plays a role in insulin secretion and GLP-1 production. Pak1-/- mice were found to carry a defect in pyruvate tolerance test (IPPTT), leading us to speculate whether Pak1 represses hepatic gluconeogenesis. We show here that the defect in IPPTT became more severe in aged Pak1-/- mice. In primary hepatocytes, IPA3, a potent inhibitor of group I Paks, reduced basal glucose production, attenuated forskolin- or glucagon-stimulated glucose production, and attenuated the stimulation of forskolin on the expression of Pck1 and G6pc. In addition, the capacity of primary hepatocytes isolated from Pak1-/- mice in glucose production at the basal level is significantly lower than that of... More
P21-activated protein kinase-1 (Pak1) plays a role in insulin secretion and GLP-1 production. Pak1-/- mice were found to carry a defect in pyruvate tolerance test (IPPTT), leading us to speculate whether Pak1 represses hepatic gluconeogenesis. We show here that the defect in IPPTT became more severe in aged Pak1-/- mice. In primary hepatocytes, IPA3, a potent inhibitor of group I Paks, reduced basal glucose production, attenuated forskolin- or glucagon-stimulated glucose production, and attenuated the stimulation of forskolin on the expression of Pck1 and G6pc. In addition, the capacity of primary hepatocytes isolated from Pak1-/- mice in glucose production at the basal level is significantly lower than that of the control littermates. These in vitro observations imply that the direct effect of Paks in hepatocytes is the stimulation of gluconeogenesis, and that the impairment in IPPTT in Pak1-/- mice is due to the lack of Pak1 elsewhere. Consecutive i.p. injection of forskolin for two weeks increased gut proglucagon expression, associated with improved IPPTT in aged Pak1-/- mice and wild-type controls. In addition, administration of the DPP-IV inhibitor sitagliptin for 1 wk reversed the defect in IPPTT in aged Pak1-/- mice, associated with increased plasma GLP-1 levels. Our observations indicate a potential role of Pak1 in the gut-pancreas-liver axis in controlling glucose disposal, and affirmed the therapeutic application of GLP-1 and DPP-IV inhibitors in attenuating hepatic gluconeogenesis.
