title: Activation of cAMP signaling attenuates impaired hepatic glucose disposal in aged male p21-activated protein kinase-1 knockout mice.
abstract: p21-activated protein kinase-1 (Pak1) plays a role in insulin secretion and glucagon-like peptide-1 (GLP-1) production. Pak1(-/-) mice were found to carry a defect in ip 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, 2,2'-dihydroxy-1,1'-dinaphthyldisulfide, a potent inhibitor of group I Paks, reduced basal glucose production (GP), attenuated forskolin- or glucagon-stimulated GP, 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 GP 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 ip injection of forskolin for 2 weeks increased gut proglucagon expression, associated with improved IPPTT in aged Pak1(-/-) mice and wild-type controls. In addition, administration of the DPP-IV (dipeptidyl peptidase-4) inhibitor sitagliptin for 1 week 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.
authors.affiliation: Division of Advanced Diagnostics (Y.-t.A.C., W.I., W.S., Z.E.S., T.J.), Toronto General Research Institute, University Health Network, Toronto, Canada M5G 1L7; Department of Physiology (Y.-t.A.C., T.J.), University of Toronto, Toronto, Canada M5S 1A8; and Institute of Medical Science (W.I., T.J.), University of Toronto, Canada; and Fox Chase Cancer Center (J.C.), Philadelphia, Pennsylvania 19111.
authors.forename: Yu-Ting Alex
authors.initials: YT
authors.lastname: Chiang
authors.forename: Wilfred
authors.initials: W
authors.lastname: Ip
authors.forename: Weijuan
authors.initials: W
authors.lastname: Shao
authors.forename: Zhuolun Eric
authors.initials: ZE
authors.lastname: Song
authors.forename: Jonathan
authors.initials: J
authors.lastname: Chernoff
authors.forename: Tianru
authors.initials: T
authors.lastname: Jin
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D052216:Glucagon-Like Peptide 1 / Q000097:blood / Q000378:metabolism; D005947:Glucose / Q000378:metabolism*; D022781:Hepatocytes / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D011719:Pyrazines / Q000494:pharmacology; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction; D000068900:Sitagliptin Phosphate; D014230:Triazoles / Q000494:pharmacology; D054462:p21-Activated Kinases / Q000172:deficiency / Q000235:genetics*
chemical_list: D011719:Pyrazines; D014230:Triazoles; D005576:Colforsin; D052216:Glucagon-Like Peptide 1; D000242:Cyclic AMP; D054462:p21-Activated Kinases; D005947:Glucose; D000068900:Sitagliptin Phosphate