G protein-coupled receptors and associated
The beta-cell response to metabolic stress
The beta-cell has a strong capacity to adjust to a changing metabolic environment. For example, the vast majority of people who gain weight and become resistant to the action of insulin do not develop diabetes because their beta-cells are able to compensate for insulin resistance by two mechanisms: 1- a large increase in insulin secretion; 2- cell proliferation which leads to enhanced functional beta-cell mass. In about 20% of individuals, however, these compensatory mechanisms are deficient or absent and type 2 diabetes (T2D) develops. Our laboratory tries to understand the cellular and molecular basis of these compensatory mechanisms and their failure under conditions of metabolic stress.
Historically our lab has focused on understanding the mechanisms of glucolipotoxicity, the combination of excessive levels of glucose and fatty-acids which is proposed to mediate, at least in part, the deterioration of beta-cell function and consequently glucose homeostasis (1). In vitro, we have shown that prolonged exposure of isolated islets of Langerhans to elevated levels of fatty acids and glucose impairs insulin gene expression (2; 3) via transcriptional mechanisms that involve de novo synthesis of ceramide (4; 5). Inhibition of insulin gene transcription involves reduction of MafA expression as well as exclusion of PDX-1 from the nuclear compartment (6). This transcriptional effect is mediated by the enzyme PAS kinase (7; 8). In vivo, we have shown that prolonged infusion of glucose and Intralipid in rats also leads to a decrease in insulin gene expression and nuclear exclusion of PDX-1 (9) which, in older animals, in turn impairs insulin biosynthesis and secretion (10).
We have also examined the beta-cell response to other situations or disease states. For example, we have shown that mice carrying the most frequent human mutation of the cystic fibrosis transmembrane conductance regulator (CFTR) causing cystic fibrosis do not have an intrinsic beta-cell secretory defect but develop insulin resistance and a beta-cell mass deficit with age (11). Recently, we have demonstrated that the uremic toxin urea impairs insulin secretion via excessive O-glycosylation of the glycolytic enzyme phosphofructokinase-1, a phenomenon that may explain, at least in part, the prevalence of dysregulations of glucose homeostasis in chronic kidney disease (12).
During the course of these project we have generated novel research tools, including a transgenic rat expressing a Renilla luciferase (RLuc)-enhanced yellow fluorescent protein (YFP) fusion under the control of a 9-kb genomic fragment from the rat ins2 gene (RIP7-RLuc-YFP) (13). This rat line is available from the Rat Resource and Research Center (RRRC) at http://www.rrrc.us/Strain/?x=757&log=yes.
The observation that infusion of excess nutrients in rats leads to a marked increase in beta-cell mass (10) has led us to investigate the underlying mechanism. We found that the increase in beta-cell mass in infused rats is a compensatory mechanism involving the growth factor HB-EGF, the EGF receptor, the kinase mTOR and the transcription factor FoxM1 which promote beta-cell proliferation (14). Further examination of this phenomenon revealed that excess glucose and lipids synergistically and reversibly promote beta-cell proliferation via direct action on the beta-cell (15) but also indirectly through the brain via the autonomic nervous system (16). Currently, the focus of the lab is to identify pathways that couple nutrient-induced b-cell proliferation to HB-EGF and to understand how fatty acids cooperate with glucose to promote beta-cell proliferation in rodent and human islets. To address these questions we are using state-of-the-art approaches including lipidomics, single-cell RNA-seq and flow cytometry.
This project is funded by the US National Institutes of Health (NIH), Canadian Institutes of Health Research (CIHR) and the Quebec Cardiometabolic Health, Diabetes and Obesity Research Network (CMDO).
1. Poitout V, Robertson RP: Glucolipotoxicity: fuel excess and beta-cell dysfunction. Endocr Rev 2008;29:351-366.
2. Jacqueminet S, Briaud I, Rouault C, et al.: Inhibition of insulin gene expression by long-term exposure of pancreatic beta cells to palmitate is dependent on the presence of a stimulatory glucose concentration. Metabolism 2000;49:532-536.
3. Briaud I, Harmon JS, Kelpe CL, et al.: Lipotoxicity of the pancreatic beta-cell is associated with glucose-dependent esterification of fatty acids into neutral lipids. Diabetes 2001;50:315-321.
4. Kelpe CL, Moore PC, Parazzoli SD, et al.: Palmitate inhibition of insulin gene expression is mediated at the transcriptional level via ceramide synthesis. J Biol Chem 2003;278:30015-30021.
5. Moore PC, Ugas MA, Hagman DK, et al.: Evidence against the involvement of oxidative stress in fatty acid inhibition of insulin secretion. Diabetes 2004;53:2610-2616.
6. Hagman DK, Hays LB, Parazzoli SD, et al.: Palmitate inhibits insulin gene expression by altering PDX-1 nuclear localization and reducing MafA expression in isolated rat islets of Langerhans. J Biol Chem 2005;280:32413-32418.
7. Fontes G, Semache M, Hagman DK, et al.: Involvement of Per-Arnt-Sim Kinase and extracellular-regulated kinases-1/2 in palmitate inhibition of insulin gene expression in pancreatic beta-cells. Diabetes 2009;58:2048-2058.
8. Semache M, Zarrouki B, Fontes G, et al.: Per-Arnt-Sim kinase regulates pancreatic duodenal homeobox-1 protein stability via phosphorylation of glycogen synthase kinase 3beta in pancreatic beta-cells. J Biol Chem 2013;288:24825-24833.
9. Hagman DK, Latour MG, Chakrabarti SK, et al.: Cyclical and alternating infusions of glucose and intralipid in rats inhibit insulin gene expression and Pdx-1 binding in islets. Diabetes 2008;57:424-431.
10. Fontes G, Zarrouki B, Hagman DK, et al.: Glucolipotoxicity age-dependently impairs beta cell function in rats despite a marked increase in beta cell mass. Diabetologia 2010;53:2369-2379.
11. Fontes G, Ghislain J, Benterki I, et al.: The DeltaF508 Mutation in the Cystic Fibrosis Transmembrane Conductance Regulator Is Associated With Progressive Insulin Resistance and Decreased Functional beta-Cell Mass in Mice. Diabetes 2015;64:4112-4122.
12. Koppe L, Nyam E, Vivot K, et al.: Urea impairs beta cell glycolysis and insulin secretion in chronic kidney disease. J Clin Invest 2016;126:3598-3612.
13. Ghislain J, Fontes G, Tremblay C, et al.: Dual-Reporter beta-Cell-Specific Male Transgenic Rats for the Analysis of beta-Cell Functional Mass and Enrichment by Flow Cytometry. Endocrinology 2016;157:1299-1306.
14. Zarrouki B, Benterki I, Fontes G, et al.: Epidermal growth factor receptor signaling promotes pancreatic beta-cell proliferation in response to nutrient excess in rats through mTOR and FOXM1. Diabetes 2014;63:982-993.
15. Moulle VS, Vivot K, Tremblay C, et al.: Glucose and fatty acids synergistically and reversibly promote beta cell proliferation in rats. Diabetologia 2017;60:879-888.
16. Moulle VS, Tremblay C, Castell AL, et al.: The autonomic nervous system regulates pancreatic beta-cell proliferation in adult male rats. Am J Physiol Endocrinol Metab 2019;