The objective of this proposal is to identify the signaling and molecular mechanisms whereby prolonged exposure to elevated fatty acids affects preproinsulin gene transcription, a phenomenon that contributes to the inexorable deterioration of beta-cell function in type 2 diabetes. Previously, we have demonstrated that palmitate inhibits insulin gene expression at the transcriptional level via ceramide synthesis in isolated islets.
Specific Aim 1 : To identify the signaling pathways mediating palmitate inhibition of insulin gene transcription in isolated islets and insulin-secreting cells. We will assess the involvement of the MAPK and PI3 kinase pathways by measuring kinase activity and phosphorylation state in response to glucose and palmitate. We will attempt to modulate palmitate-inhibition of transcription factor activity and insulin gene transcription by using pharmacological inhibitors and adenovirus-mediated overexpression of kinase isoforms.
Specific Aim 2 : To determine the mechanisms whereby palmitate inhibits expression of MafA and nuclear localization of PDX-1 in isolated islets and insulin-secreting cells. We will ascertain whether palmitate affects MafA expression at the transcriptional or post-transcriptional level by measuring mRNA stability and using promoter-reporter constructs;determine whether palmitate affects PX-1 nuclear localization by immunohistochemistry;and examine binding of MafA and PDX-1 to the endogenous insulin gene promoter by chromatin immunoprecipitation assays.
Specific Aim 3 : To ascertain whether combined hyperlipidemia and hyperglycemia affect insulin gene transcription in islets from chronically infused rats and high-fat fed mice. We will ascertain whether expression and binding activity of PDX-1 and MafA;activity of the insulin gene promoter;and insulin mRNA levels are affected in islets isolated from 1) Wistar rats following a 24- and 72-h infusion of glucose and fatty acids, alone or in combination; and 2) high-fat fed C57BI/6J mice. This project has the potential to uncover the cellular and molecular mechanisms by which excessive levels of fatty acids adversely affect pancreatic beta-cell function and thereby contribute to the deterioration of glucose homeostasis during the course of type 2 dabetes. It will provide new therapeutic targets aimed at preserving insulin secretion in type 2 diabetes, a devastating disease that affects more than 18 million Americans.
|Ghislain, Julien; FontÃ©s, Ghislaine; Tremblay, Caroline et al. (2016) Dual-Reporter Î²-Cell-Specific Male Transgenic Rats for the Analysis of Î²-Cell Functional Mass and Enrichment by Flow Cytometry. Endocrinology 157:1299-306|
|Koppe, Laetitia; Nyam, Elsa; Vivot, Kevin et al. (2016) Urea impairs Î² cell glycolysis and insulin secretion in chronic kidney disease. J Clin Invest 126:3598-612|
|FontÃ©s, Ghislaine; Ghislain, Julien; Benterki, Isma et al. (2015) The Î”F508 Mutation in the Cystic Fibrosis Transmembrane Conductance Regulator Is Associated With Progressive Insulin Resistance and Decreased Functional Î²-Cell Mass in Mice. Diabetes 64:4112-22|
|Mosser, Rockann E; Maulis, Matthew F; MoullÃ©, Valentine S et al. (2015) High-fat diet-induced Î²-cell proliferation occurs prior to insulin resistance in C57Bl/6J male mice. Am J Physiol Endocrinol Metab 308:E573-82|
|Semache, Meriem; Ghislain, Julien; Zarrouki, Bader et al. (2014) Pancreatic and duodenal homeobox-1 nuclear localization is regulated by glucose in dispersed rat islets but not in insulin-secreting cell lines. Islets 6:e982376|
|Zarrouki, Bader; Benterki, Isma; Fontes, Ghislaine et al. (2014) Epidermal growth factor receptor signaling promotes pancreatic *-cell proliferation in response to nutrient excess in rats through mTOR and FOXM1. Diabetes 63:982-93|
|Kilic, Gamze; Alvarez-Mercado, Ana I; Zarrouki, Bader et al. (2014) The islet estrogen receptor-Î± is induced by hyperglycemia and protects against oxidative stress-induced insulin-deficient diabetes. PLoS One 9:e87941|
|Fergusson, Grace; Ethier, MÃ©lanie; GuÃ©vremont, MÃ©lanie et al. (2014) Defective insulin secretory response to intravenous glucose in C57Bl/6J compared to C57Bl/6N mice. Mol Metab 3:848-54|
|d'Assignies, Gaspard; FontÃ©s, Ghislaine; Kauffmann, Claude et al. (2013) Early detection of liver steatosis by magnetic resonance imaging in rats infused with glucose and intralipid solutions and correlation to insulin levels. Metabolism 62:1850-7|
|Fergusson, Grace; Ethier, MÃ©lanie; Zarrouki, Bader et al. (2013) A model of chronic nutrient infusion in the rat. J Vis Exp :|
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