Decreased insulin action, impaired insulin secretion and increased adiposity are important risk factors for development of type 2 diabetes. These risk factors are present even when individuals have both normal fasting and two hour glucose concentrations indicating a very early role for decreased insulin secretion in the development of type 2 diabetes. As adipose and muscle tissue have effects on insulin action and secretion, we examined RNA expression in both tissues to find associations with insulin action and secretion. We found that a number of genes demonstrate bimodal expression in muscle tissue. One of these genes (ACTN3) was modestly associated with insulin action. Another bimodally expressed gene, HLA DRB1 was associated with a single nucleotide polymorphism linked presence of HLA DRB1 haplotype. Moreover, presence of HLA DRB1 was found to be protective for diabetes and associated with increased insulin secretion as measured by the intravenous and oral glucose tolerance tests. We are continuing to investigate expression data in muscle and adipose tissue and their associations with prediabetic phenotypes. We are continuing to investigate additional factors which control insulin secretion and insulin action. Individuals who are undergoing bariatric surgery using the following techniques: Roux-en-Y gastric bypass, laporoscopic band, or gastric sleeve will undergo measures of insulin action, insulin secretion and meal tests prior to and one month following the surgery. This study will investigate how by-pass of the duodenum and specific areas of the stomach influence insulin action and secretion, as well as their affect on insulin, c-peptide and gastrointestinal hormones during meal tests performed prior to and following the surgery. Adiposity is also a pro-inflammatory state and such inflammation may affect insulin action directly. We have previously investigated the role of recently identified adipose tissue macrophages and their associations with obesity and insulin action. Adipose tissue macrophages increased with adiposity, and were negatively associated with insulin action, although not independent of adiposity. However, markers of macrophage activation in adipose tissue (specifically plasminogen activator inhibitor-1 (PAI-1) were associated worsening insulin action independent of body fat, indicating a role for macrophage activation in insulin resistance. We have also found that adipose tissue macrophage content is negatively associated with HDL-cholesterol providing a mechanism for a link between increased adiposity and cardiovascular disease. Previous predictors of weight gain based on this study have included, higher respiratory quotient, higher insulin mediated glucose uptake, lower free T3, and relatively lower energy expenditure. As variability in energy expenditure remains a potential mediator of weight change we have continued to evaluate factors related to metabolic rate. We investigated the association of plasma and cerebrospinal fluid (CSF) endocannabinoids and related acylethanolamides with energy expenditure. We found that the CSF endocannabinoid, 2-arachidonoylglycerol (2-AG), is higher in American Indians, and that CSF oleoylethanolamide was associated with energy expenditure. As these are derivatives of fatty acids, we are continuing to investigate the role of fatty acid derivatives in food intake, insulin action and energy expenditure.
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