Genetic and functional studies of novel type 2 diabetes susceptibility genes

Lead Research Organisation: Imperial College London
Department Name: School of Public Health

Abstract

Diabetes is a complex metabolic disease, with both genetic and environmental causes, in which the body?s ability to maintain normal blood glucose levels is compromised. In recent years, diabetes has developed into a global health problem of epidemic proportions, consuming as much as 10 % of the health care budgets of many westernised countries. Increases in blood glucose concentrations have very serious health implications, and can lead to blindness, heart disease, kidney malfunction and nerve damage. There are two main clinical subtypes of diabetes: type 1 diabetes is characterised by the destruction of the insulin-secreting pancreatic cells that regulate blood glucose levels; and type 2 diabetes (T2D) is characterised by insulin resistance and dysfunctional insulin secretion. Of the two subtypes, T2D is by far the predominant form of diabetes, accounting for up to 90% of the total diabetes prevalence.

Our research is focussed on the identification of the genes that predispose an individual to develop T2D and on elucidating the molecular mechanisms by which the products of these T2D ?susceptibility genes? influence an individual?s risk of T2D. We have recently completed the first ever genetic scan of all 46 human chromosomes for T2D susceptibility genes (the results of this research will be published in a top journal, Nature, later in 2007). Our results confirmed a previously known susceptibility gene on chromosome 10 (called TCF7L2) and identified novel T2D susceptibility genes, including a zinc transporter gene called ZnT-8. Zinc is very important for regulating the pancreatic secretion of the hormone insulin that acts to control blood glucose levels.

The proposed project aims to follow up on our genetic scan by: a) carrying out an exhaustive genetic analysis of these novel genetic loci in the European population and b) elucidating the molecular mechanisms by which the key genes, TCF7L2 and ZnT-8, contribute to T2D risk.

Technical Summary

Type 2 diabetes is a major and growing health problem with both genetic and environmental causes. Together with our collaborators at McGill University, Montreal, Canada, we have performed, in a French population, the first published genome wide association (GWA) scan for T2D genes (Sladek et al., Nature, 2007, in press). Our results replicated the established strong association with the TCF7L2 SNP rs7903146 (p=1.51 x 10-34) and confirmed associations for eight SNPs in four novel T2D susceptibility loci.

This project aims to carry out exhaustive fine mapping of these 4 loci (and additional loci ones likely to appear from ongoing WGA studies) in the European population and to elucidate the molecular mechanisms by which the transcription factor TCF7L2 and the Zinc transporter ZnT-8 contribute to T2D risk.

We have three specific aims:

Aim 1: We will undertake fine mapping of the novel susceptibility loci in order to identify the putative aetiological variants that are responsible for the association signals. We shall genotype the entire catalogue of common SNPs at all four loci in our extensive French case-control samples. T2D-associated SNPs will be subjected to large scale replication and prospective cohort studies.

Aim 2: TCF7L2 is a transcription factor targeted by the Wnt signalling pathway, important for pancreatic development. We seek to determine the following: what is the impact of TCF7L2 silencing on glucose- and other nutrient-stimulated insulin secretion, beta-cell proliferation/survival, and the expression of key beta-cell genes? What is the impact of TCF7L2 over-expression on beta-cell secretory function, proliferation/apoptosis, and beta-cell gene expression? How does the TCF7L2 rs7903146 polymorphism affect mRNA stability, splicing and transcriptional activity? What is the phenotype of knock-in mice bearing the at-risk rs7903146 allele?

Aim 3. Apart from rs7903146 in TCF7L2, the strongest WGA signal was provided by the coding SNP rs13266634, a R325W variant in SLC30A8 (ZnT-8), a beta-cell restricted vesicular zinc transporter. We will firstly examine the importance of ZnT-8 for normal beta cell glucose metabolism, basal and stimulated insulin secretion as well as beta-cell growth and survival. We will then determine the effect of the R325W variant on ZnT-8 activity and function, in terms of protein stability, sub-cellular localisation, and zinc uptake into insulin vesicles.

We believe that this integrated genetic and functional approach to the study of novel T2D susceptibility loci should bring new insights to the molecular determinants of this disease, opening new avenues for predicting and treating diabetes and its complications.

Publications

10 25 50
 
Description AMPK in central control of hepatic glucose production 
Organisation University of Toronto
Country Canada 
Sector Academic/University 
PI Contribution Generation and use of adenoviral constructs
Impact Publication in Diabetes 2010 (x2)
Start Year 2008
 
Description Conditional knockout mice 
Organisation Cochin Institute
Country France 
Sector Academic/University 
PI Contribution Generation of tissue specifi KO mice
Impact Publication in Diabetologia, 2010 (Sun et al)
 
Description D Bosco (Université de Genève) 
Organisation University of Geneva
Department Faculty of Diabetes
Country Switzerland 
Sector Academic/University 
PI Contribution Experiments for publications
Collaborator Contribution Experiments for publications
Impact Sorcin links pancreatic ß cell lipotoxicity to ER Ca2+ stores - Marmugi A et al - PMID: 26822088 Hypoxia lowers SLC30A8/ZnT8 expression and free cytosolic Zn2+ in pancreatic beta cells. Gerber PA et al PMID: 24865615 Incretin-modulated beta cell energetics in intact islets of Langerhans. Hodson DJ et al - PMID: 24766140 ADCY5 couples glucose to insulin secretion in human islets. Hodson DJ et al PMID: 24740569 Lipotoxicity disrupts incretin-regulated human ß cell connectivity. Hodson DJ et al - PMID: 24018562
Start Year 2013
 
Description Denton 
Organisation University of Bristol
Country United Kingdom 
Sector Academic/University 
PI Contribution Experiments for publications
Collaborator Contribution Experiments for publications
Impact manuscript (in press) Denton RM et al Biochem J 2016
Start Year 2014
 
Description Denton 
Organisation University of Pisa
Country Italy 
Sector Academic/University 
PI Contribution Experiments for publications
Collaborator Contribution Experiments for publications
Impact Sorcin links pancreatic ß cell lipotoxicity to ER Ca2+ stores - Marmugi A et al - PMID: 26822088 Hypoxia lowers SLC30A8/ZnT8 expression and free cytosolic Zn2+ in pancreatic beta cells. Gerber PA et al PMID: 24865615 Incretin-modulated beta cell energetics in intact islets of Langerhans. Hodson DJ et al - PMID: 24766140 ADCY5 couples glucose to insulin secretion in human islets. Hodson DJ et al PMID: 24740569 Lipotoxicity disrupts incretin-regulated human ß cell connectivity. Hodson DJ et al - PMID: 24018562
Start Year 2014
 
Description Generator of b-cell specfic knock-out mice for PASK 
Organisation AstraZeneca
Country United Kingdom 
Sector Private 
PI Contribution Design of PASK flox'd mice
Impact None as yet
Start Year 2009
 
Description Gerald Gradwohl (IGBMC) 
Organisation Institute of Genetics and Molecular and Cellular Biology (IGBMC)
Country France 
Sector Academic/University 
PI Contribution Experiments for publications
Collaborator Contribution Experiments for publications
Impact Piccard et al - http://www.ncbi.nlm.nih.gov/pubmed/25497096
Start Year 2015
 
Description James Shapiro (Alberta) 
Organisation University of Alberta
Country Canada 
Sector Academic/University 
PI Contribution Experiments for publications
Collaborator Contribution Experiments for publications
Impact ADCY5 couples glucose to insulin secretion in human islets. Hodson DJ et al PMID: 24740569 Sorcin links pancreatic ß cell lipotoxicity to ER Ca2+ stores - Marmugi A et al - PMID: 26822088
Start Year 2014
 
Description Lorenzo Piemouti (Milan) 
Organisation University of Milan
Country Italy 
Sector Academic/University 
PI Contribution Experiments for publications
Collaborator Contribution Experiments for publications
Impact ADCY5 couples glucose to insulin secretion in human islets. Hodson DJ et al - PMID: 24740569 Sorcin links pancreatic ß cell lipotoxicity to ER Ca2+ stores. Marmugi A et al - PMID: 26822088
Start Year 2014
 
Description Piero Marchetti (Pisa) 
Organisation University of Pisa
Country Italy 
Sector Academic/University 
PI Contribution experiments for publications
Collaborator Contribution experiments for publications
Impact Sorcin links pancreatic ß cell lipotoxicity to ER Ca2+ stores - Marmugi A et al - PMID: 26822088 Hypoxia lowers SLC30A8/ZnT8 expression and free cytosolic Zn2+ in pancreatic beta cells. Gerber PA et al PMID: 24865615 Incretin-modulated beta cell energetics in intact islets of Langerhans. Hodson DJ et al - PMID: 24766140 ADCY5 couples glucose to insulin secretion in human islets. Hodson DJ et al PMID: 24740569 Lipotoxicity disrupts incretin-regulated human ß cell connectivity. Hodson DJ et al - PMID: 24018562
Start Year 2014
 
Description Role of AMPK in counter regulation 
Organisation Yale University
Country United States 
Sector Academic/University 
PI Contribution Provision of adenoviral constructs
Impact None as yet
Start Year 2008
 
Description Sekler 
Organisation Ben-Gurion University of the Negev
Country Israel 
Sector Academic/University 
PI Contribution Experiments for research paper
Collaborator Contribution Experiments for research paper
Impact Publication Pancreatic beta-cell Na+ channels control global Ca2+ signaling and oxidative metabolism by inducing Na+ and Ca2+ responses that are propagated into mitochondria. DOI - 10.1096/fj.13-248161
Start Year 2013
 
Description Yuval Dor (Israel) 
Organisation Open University of Israel
Country Israel 
Sector Academic/University 
PI Contribution Experiments for publications
Collaborator Contribution Experiments for publications
Impact LKB1 and AMPK differentially regulate pancreatic ß-cell identity - Kone M1 et al - FASEB J. 2014 Nov;28(11):4972-85. doi: 10.1096/fj.14-257667. Epub 2014 Jul 28. Loss of Liver Kinase B1 (LKB1) in Beta Cells Enhances Glucose-stimulated Insulin Secretion Despite Profound Mitochondrial Defects. Swisa A1et al - J Biol Chem. 2015 Aug 21;290(34):20934-46. doi: 10.1074/jbc.M115.639237. Epub 2015 Jul 2.
Start Year 2014