ENDOPLASMIC RETICULUM STRESS RESPONSE IN HUMAN TYPE 2 DIABETES

点击翻译按钮获取中文摘要

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Type 2 diabetes (T2DM) is a common, inherited disease that appears to result from a large number of common DNA sequence variants. Despite extensive investigation, the early pathological events in humans remain uncertain. Recent animal data suggest that a pathway common to all cells and all organisms, the endoplasmic reticulum stress response (ERSR) is activated in adipocytes and hepatocytes with obesity, and likely in pancreatic $-cells, but no human data are available. We will combine human physiological and molecular studies with a genomics approach to identify sequence variants in the extensive transcription cascade that is initiated with the response to unfolded proteins and may lead to protein degradation, altered transcription, and cellular apoptosis. We hypothesize that 1) ERSR is activated in subcutaneous adipose tissue from both glucose tolerant obese individuals and individuals with impaired glucose tolerance relative to nonobese, healthy, glucose tolerant individuals, that these pathways are downregulated by thiazolidinediones in adipocytes, and that common cis-acting DNA sequence variants alter the expression of key ERSR genes and increase susceptibility to T2DM. To test these hypotheses we propose four Specific Objectives, of which only the first is proposed at present for IRB and GCRC approval. We will test 40 individuals in each of 3 groups (normoglycemic, lean controls; obese, normoglycemic individuals, and individuals with impaired glucose tolerance) in two ethnic groups, African American and Caucasian. We will characterize insulin sensitivity using the intravenous glucose tolerance test and Minimal Model, and will obtain adipose and muscle by needle biopsy. W e will determine ERSR by measuring transcription and phosphorylation of key ERSR genes. In subsequent aims, to be performed using tissues gathered in this an other ongoing studies, we will measure the change in transcription of the most significant genes in adipose and muscle before and after treatment with pioglitazone, and we will use a novel approach to identify cis-acting sequence variants in ERSR genes by testing adipose, muscle, and epstein-bar virus transformed lymphocytes for evidence of an imbalance in mRNA levels. Finally, we will examine each gene which shows evidence for altered transcription or RNA stability by searching for additional coding or regulatory sequence variants, establishing the associations between these variants in a population (haplotype structure), and testing those variants that identify these haplotypes for an association with T2DM, insulin resistance, and disordered insulin secretion. Only studies of Aim 1 are proposed at the present time, and will seek to collect pilot data that may be used to prepare an application to NIH to provide adequate funding to perform the proposed studies. This work will eventually identify potential genetic variants that might provide drug targets or a means to identify individuals who would benefit from drugs aimed at altering ERSR gene transcription. This work thus has the potential to have a direct impact on the prevention and care of T2DM and metabolic syndrome.