This grant will continue to focus on insulin secretion and the role of the pancreatic beta-cell in diabetes as it has since 1983 when it was originally funded. In the next funding period, we will attempt to understand the gene-phenotype relationships of recently identified diabetes genes, to define the mechanisms responsible for the loss of pancreatic beta-cell mass and to develop novel approaches to its preservation in diabetes. Recent genome wide association (GWA) studies have identified novel genetic variants that increase risk for Type 2 diabetes (T2DM). Although many of these variants reduce insulin levels, in most cases the mechanisms operative in the beta-cell to cause a reduction in insulin secretion remain to be worked out. We now propose to characterize, compare and contrast the physiological changes in insulin secretion in non-diabetic subjects with different genetic variants associated with T2DM. Understanding the mechanisms responsible for reduced pancreatic beta-cell mass in T2DM and developing novel scientific approaches to promoting increased pancreatic beta-cell survival is the second scientific focus of this application. We have demonstrated that deficiency of the beta-cell transcription factor Pdx1 leads to accelerated pancreatic beta-cell death due to autophagy and apoptosis. In the next funding cycle, we will continue to define the mechanisms responsible for beta-cell death in Pdx1-deficient states. There are 2 specific aims:
Specific Aim 1 : To study the clinical physiology of genetic variants associated with T2DM. We will test the hypothesis that subjects with genetic variants associated with reduced insulin secretion and increased risk for T2DM will have phenotypic abnormalities detectable even when glucose tolerance is normal and different genetic variants will lead to different clinical phenotypes. We propose to study the T2DM-associated genes KCNJ11, TCF7L2, KCNQ1, CDKAL1, IGF2BP2 and SLC30A8 since it appears that diabetes-associated variants in these genes increase T2DM risk by decreasing insulin secretion.
Specific Aim 2 : To study the mechanisms of beta-cell death due to Pdx1 deficiency and to develop novel approaches to the preservation of beta-cell mass. Our studies will identify the mechanisms responsible for the increase in beta-cell death in Pdx1 mice and will determine whether inhibiting the pathways involved will prevent the reduction of beta-cell mass, preserve beta-cell function and delay or prevent the onset of hyperglycemia. Preliminary data show that Pdx1 deficiency leads to increased expression of pro-apoptotic proteins in the pancreatic beta-cell including NIX, PUMA and BIM as well as CHOP, a mediator of apoptosis in response to ER stress. We will now explore the hypothesis that if the expression of any of these factors or Cyclophilin D, a component of the mitochondrial permeability transition pore is reduced in Pdx1 deficient MIN6 cells or Pdx1 mice, survival of beta-cells is increased, beta-cell mass preserved and hyperglycemia delayed or prevented.
The American Diabetes Association [Diabetes Care, 31:1-2, (2008)] points out that in the United States alone, greater than 17.5 million persons have been diagnosed with type 2 diabetes mellitus (T2DM) with an associated yearly economic burden exceeding $174 billion. The incidence of the disease is increasing rapidly on a worldwide basis with staggering impact on cost of healthcare and quality of life. Thus, there is an urgent need to increase our understanding of the pathogenesis of this disorder in order to develop more targeted approaches to prevention and treatment. The proposed studies will define the effects on insulin secretion of specific genes that are associated with increased T2DM risk in the population. We will also study the molecular mechanisms responsible for the death of pancreatic beta-cells in diabetes and explore novel mechanisms to preventing beta-cell loss. If successful these studies could contribute to advances that would have a positive impact on human health.
|Sun, Juan; Mao, Li-Qun; Polonsky, Kenneth S et al. (2016) Pancreatic Î²-Cell Death due to Pdx-1 Deficiency Requires Multi-BH Domain Protein Bax but Not Bak. J Biol Chem 291:13529-34|
|Ren, Decheng; Sun, Juan; Mao, Liqun et al. (2014) BH3-only molecule Bim mediates Î²-cell death in IRS2 deficiency. Diabetes 63:3378-87|
|Ren, Decheng; Sun, Juan; Wang, Changzheng et al. (2014) Role of BH3-only molecules Bim and Puma in Î²-cell death in Pdx1 deficiency. Diabetes 63:2744-50|
|Pedersen, Morten Gram; Mosekilde, Erik; Polonsky, Kenneth S et al. (2013) Complex patterns of metabolic and CaÂ²âº entrainment in pancreatic islets by oscillatory glucose. Biophys J 105:29-39|
|Klein, Samuel; Fabbrini, Elisa; Patterson, Bruce W et al. (2012) Moderate effect of duodenal-jejunal bypass surgery on glucose homeostasis in patients with type 2 diabetes. Obesity (Silver Spring) 20:1266-72|
|Reeds, Dominic N; Patterson, Bruce W; Okunade, Adewole et al. (2011) Ginseng and ginsenoside Re do not improve Î²-cell function or insulin sensitivity in overweight and obese subjects with impaired glucose tolerance or diabetes. Diabetes Care 34:1071-6|
|Villareal, Dennis T; Robertson, Heather; Bell, Graeme I et al. (2010) TCF7L2 variant rs7903146 affects the risk of type 2 diabetes by modulating incretin action. Diabetes 59:479-85|
|Cheverud, James M; Fawcett, Gloria L; Jarvis, Joseph P et al. (2010) Calpain-10 is a component of the obesity-related quantitative trait locus Adip1. J Lipid Res 51:907-13|
|Wice, Burton M; Wang, Songyan; Crimmins, Dan L et al. (2010) Xenin-25 potentiates glucose-dependent insulinotropic polypeptide action via a novel cholinergic relay mechanism. J Biol Chem 285:19842-53|
|Fujimoto, Kei; Ford, Eric L; Tran, Hung et al. (2010) Loss of Nix in Pdx1-deficient mice prevents apoptotic and necrotic Î² cell death and diabetes. J Clin Invest 120:4031-9|
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