Leptin regulated insulin secretion via stimulating IRS2-associated phosphoinositide 3-kinase activity in the isolated rat pancreatic islets

Abstract

To investigate the molecular mechanism of leptin regulating insulin secretion through determining the regulation of insulin secretion and the insulin receptor substrate (IRS)-2-associated phosphoinositide 3-kinase (PI3K) activity by leptin in the isolated rat pancreatic islets, pancreatic islets were isolated from male SD rats by the collagenase method. The purified islets were incubated with leptin 2 nmol/L for 1 h in the presence of 5.6 mmol/L or 11.1 mmol/L glucose. Insulin release was measured using radioimmunoassay. IRS-2-associated activity of PI3K was determined by immunoprecipitate assay and Western blot. The results showed that in the presence of 5.6 mmol/L glucose, leptin had no significant effect on both insulin secretion and IRS-2-associated PI3K activity, but in the presence of 11.1 mmol/L glucose, insulin release was significantly inhibited after the islets were exposed to leptin for 1 h (P<0.01). PI3K inhibitor wortmannin blocked the inhibitory regulation of leptin on insulin release (P<0.05). Western Blot assay revealed that 2 nmol/L leptin could significantly increase the IRS-2-associated activity of PI3K by 51.5% (P<0.05) in the presence of 11.1 mmol/L glucose. It was concluded that Leptin could significantly inhibit insulin secretion in the presence of 11.1 mmol/L glucose by stimulating IRS-2-associated activity of PI3K, which might be the molecular mechanism of leptin regulating insulin secretion.

Keywords

leptin / insulin secretion / phosphoinositide 3-kinase / signal transduction

References

[1] FriedmanJ M, HalaasJ L. Leptin and the regulation of body weight in mammals. Nature, 1998, 359: 763-763

[2] SeufertJ, KiefferT J, LeechC A, et al.. Leptin suppression of insulin secretion and gene expression in human pancreatic islets: implications for the development of adipogenic diabetes mellitus. J Clin Endocrinol Metab, 1999, 84: 670-670

[3] Leclercq-MeyerV, MalaisseW J. Failure of human and mouse leptin to affect insulin, glucagon and somatostatin secretion by the perfused rat pancreas at physiological glucose concentration. Mol Cell Endocrinol, 1998, 141: 111-111

[4] KiefferT J, HabenerJ F. The adipoinsular axis: effects of leptin on pancreatic beta-cells. Am J Physiol Endocrinol Metab, 2000, 278: E1-E1

[5] MortizW, LeechC A, FerrerJ, et al.. Regulated expresesion of adenosine triphosphate-sensitive potassium channel subunits in pancreatic beta-cells. Endocrinology, 2001, 142: 129-129

[6] HarveyJ, HardyS C, IrvingA J, et al.. Leptin activation of ATP-sensitive K⁺ (KATP) channels in rat CRI-G1 insulinoma cells involves disruption of the actin cytoskeleton. J Physiol, 2000, 527(Pt 1): 95-95

[7] HarveyJ, McKayN G, WalkerK S, et al.. Essential role of phosphoinositide 3-kinase in leptin-induced KATP channel activation in the rat CRI-G1 insulinoma cell line. J Biol Chem, 2000, 275: 4660-4660

[8] Yuan L, An H X, Deng X Let al. Regulation of leptin on insulin secretion and sulfonulurea receptor 1 transcription level in isolated rat pancreatic islets. Chin Med J, 2003, 16: In press.

[9] HadariY R, TzaharE, NadivO, et al.. Insulin and insulinomimetic agents induce activation of phosphatidylinositol 3-kinase upon its association with p85 (IRS-1) in intact rat livers. J Biol Chem, 1992, 267(17): 483-483

[10] IhleJ N. Cytokine receptor signaling. Nature, 1995, 377: 591-591

[11] BertiL, KellererM, CappE, et al.. Leptin stimulates glucose transport and glycogen synthesis in C²C¹² myotubes: evidence for a P13-kinase mediated effect. Diabetologia, 1997, 40: 606-606

[12] KimY B, UotaniS, PierrozD D, et al.. In vivo administration of leptin activates signal transduction directly in insulin-sensitive tissues; overlapping but distinct pathways from insulin. Endocrinology, 2000, 141: 2328-2328

[13] ShepherdP R, WithersD J, SiddleK. Phosphoinositide 3-kinase: the key switch, mechanism in insulin signaling. Biochem J, 1998, 333(Pt 3): 471-471