Insulin sensitivity/resistance and insulin secretion have received much attention in the study of metabolic disorders (such as diabetes, obesity, the metabolic syndrome, and polycystic ovary syndrome) that predispose to cardiovascular disease, while insulin clearance has been largely overlooked. Insulin clearance is a highly heritable trait. Preliminary data show that haplotypes in the genes for adenosine monophosphate deaminase (AMPD1 and AMPD2) and the AMP-activated protein kinase (AMPK) 12 subunit are associated with variation in the metabolic clearance rate of insulin (MCRI). Thus, the hypothesis underlying this proposal is that genes involved in the interconversion of adenine nucleotides (AMP, ADP, ATP) and cellular response to these molecules (AMPK system) are determinants of insulin clearance. This application proposes further research elucidating the role of these and related genes in insulin clearance, using both a biologic candidate gene approach as well as positional candidate genes identified by whole-genome linkage scans.
In Aim 1, 1536 single nucleotide polymorphisms (SNPs) in ~100 genes (high-priority based on function) related to adenine nucleotide metabolism and the AMPK system will be genotyped in the first half (Set 1) of the Mexican- American Coronary Artery Disease (MACAD) cohort;these SNPs and derived haplotypes will be analyzed for association with MCRI. The top 25 genes showing association with MCRI will then be genotyped (384 SNPs) and tested for association with MCRI in MACAD Set 2 (second half of that cohort). Only genes associated with MCRI in both Sets will be evaluated in Aim 3.
In Aim 2, whole genome linkage scans for MCRI will be carried out in two Hispanic cohorts (MACAD, and the Mexican-American hypertension (MA-HTN) cohort). Positional candidate genes (50-70 genes anticipated) under peaks (LOD >1.4) found in both cohorts and under the most significant (LOD>2) peaks in either cohort will be analyzed for association with MCRI in MACAD.
In Aim 3, the genes identified in Aims 1 and 2 as associated with MCRI will be tested for association in the MA-HTN cohort, as a final confirmation.
In Aim 4, the genes with confirmed association will then be sequenced (in subjects of divergent genotype and phenotype) to identify potential functional variants. Variants identified by sequencing will be evaluated for association with MCRI in the combined MACAD and MA-HTN cohort. This proposal is unique in its exploration of insulin clearance, an understudied trait that is highly heritable. Also innovative is the focus on genes related to adenine nucleotides and cellular energy state. The study will examine these genes in multiple Hispanic populations, allowing for verification/replication of positive genetic associations, and benefits from the fact that both cohorts have already been recruited and have undergone detailed physiologic phenotyping of whole-body insulin clearance by the euglycemic-hyperinsulinemic clamp. The novel phenotype and genes considered are likely to lead to new insights in insulin metabolism. Project Narrative: The goal of this proposal is to discover genes that influence the body's ability to eliminate insulin. Abnormal levels of insulin are characteristic of several metabolic disorders, such as diabetes, obesity, the metabolic syndrome, and polycystic ovary syndrome, all of which are risk factors for cardiovascular disease. An understanding of the genes underlying insulin removal may lead to improvements in prevention and treatment of these disorders.
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