Medical Student Research Fellowship for Summer 2009
Mentor: Joyce J. Repa
Room number: Y6.322C
Mail Code: 9077
Phone number: 214-648-9431
Project title: The role of the Vitamin D Receptor in the endocrine pancreas.
Human subjects IRB approved project number (where applicable): N/A
Animal subjects IRB approved project number (where applicable): 0986-07-02-1
Project Type: animal-based research and basic research
Brief Description of Project:
Recent epidemiologic evidence suggests that Vitamin D deficiency is strongly correlated with the incidence of type 2 diabetes mellitus ((1-3)). Recently, the Repa lab has identified the Vitamin D Receptor (VDR) as the most abundant ligand-binding nuclear hormone receptor present in the mouse pancreatic islet (and also evident in human islets (4)). In addition, preincubation of mouse islets with vitamin D enhances glucose-stimulated insulin secretion from islets of wildtype, but not Vdr-/-, mice.
To identify molecular mechanisms linking VDR activity and islet function, the Repa group performed global gene expression profiling by microarray analysis (5). Human pancreatic islets were obtained from a cadaveric donor and cultured for 16h in the presence of 20 nM Vit D or vehicle (DMSO), total RNA was isolated and microarray analysis was performed using the Human Affymetrix U133 Plus 2.0 array platform. Comparative gene expression (cut-off 2.0) and statistical evaluation (t-test, p <0.05) done using GeneSifter software revealed that Vit D exposure resulted in increased mRNA levels for 942 genes and decreased expression of 1085 genes. To confirm and extend these findings, similar experiments were performed using isolated islets from wildtype and Vdr-knockout mice, exposed to Vit D3 (16h, 20 nM) or vehicle, and assessed using the Illumina Mouse-6 V2 BeadChip microarray platform. Gene pattern analysis revealed that 202 genes were selectively upregulated in the wildtype islet by Vit D3 with no change in RNA level in the Vdr-/- islet. Cumulatively, these studies identify Vit D-mediated regulation of genes involved in calcium signaling, immune system processes and cell adhesion.
The goal of this summer research project is to focus on a gene identified by these microarray analyses of both human and mouse islets (CaV2.3, a prominent calcium channel of the beta-cell involved in insulin release) and define the molecular mechanism that links Vit D activity with the transcriptional regulation of CaV2.3. We will define VDR-binding sites in the promoter of the CaV2.3 gene and use cell reporter assays, gel-shift assays, and chromatin-immunoprecipitation to define the VDR-mediated regulation of this gene.
1. Mattila C, Knekt P, Mannisto S, Rissanen H, Laaksonen MA, Montonen J, Reunanen A 2007 Serum 25-hydroxyvitamin D concentration and subsequent risk of type 2 diabetes. Diabetes Care 30:2569-2570
2. Forouhi NG, Luan J, Cooper AD, Boucher BJ, Wareham NJ 2008 Baseline serum 25-hydroxy vitamin D is predictive of future glycaemic status and insulin resistance: The MRC Ely prospective study 1990-2000. Diabetes on-line June 30
3. Holick MF 2007 Vitamin D deficiency. New Engl J Med 357:266-281
4. Chuang J-C, Cha J-Y, Garmey JC, Mirmira RG, Repa JJ 2008 Nuclear hormone receptor expression in the endocrine pancreas. Mol Endocrinol 22:2353-2363
5. Kjalarsdottir L, Chuang J-C, Repa JJ 2009 Vitamin D-regulated gene expression in the endocrine pancreas. ADA abstract for the 69th scientific session, June 5-9, 2009.
Previous Research Activities or Publications with Medical Students:
Summer 2002. Vinu George Ipe, MSTP student summer rotation.
Summer 2005. Isaac See, UTSW Medical Student participant in Clinical and Basic Research Training for Medical Students program (T35 DK066141-03, McPhaul, M. director). His abstract was selected for presentation at the 44th Medical Student Forum. [summer 2008 - residency in Internal Medicine - UTSW].
Summer 2006. Niti Chokshi, Texas A&M Medical Student participant in T35 program described above.