2012 Annual Report
1a.Objectives (from AD-416):
Elevated fat levels within skeletal muscle cells (intramyocellular lipids) are highly correlated with muscle and whole-body insulin resistance, and more prevalent in obesity. The molecular links and metabolic shifts driving this association remain open to debate, but notably, reduced muscle mitochondrial fatty acid (FA) beta-oxidation is more prevalent among insulin-resistant/diabetic persons. Therefore, discovery of biomarkers reflective of the status of an individual’s muscle FA beta-oxidation activity or capacity would have tremendous prognostic and diagnostic value in terms of diabetes. Furthermore, characterization of metabolites associated with muscle mitochondrial fat metabolism should uncover candidate signaling factors which tie FA ß-oxidation to insulin signaling. We propose to identify, for the first time, specific biomarkers of muscle FA beta-oxidation using multiple metabolomic analytical platforms to compare metabolite profiles in samples derived from biological systems displaying disparate muscle fat combustion, including: isolated mitochondrial organelles and muscle cells catabolizing FA at different rates, a UCP3 transgenic animal model, and human subjects harboring a UCP3 truncation polymorphism. Pilot validation studies will test whether plasma metabolites and/or metabolite signatures identified in cell, animal, and human studies that track muscular FA beta-oxidation can be experimentally increased in obese, insulin-resistant subjects via a diet-exercise regimen designed to improve muscle fitness and FA combustion.
1b.Approach (from AD-416):
A comprehensive analytical chemistry assay measuring >400 metabolites will be employed to test samples derived from the following project aims:
Aim 1--Identify Metabolite Biomarkers of Muscle Fat Combustion in Organelle, Cell, and Animal Models Displaying Significantly Altered Fatty Acid beta-Oxidation. We will determine how metabolite profiles shift in models displaying increased muscle beta-oxidation (uncoupling protein 3-overexpressing muscle cell line and muscle UCP3-transgenic mice), and hypothesize that profiles in UCP3-overexpressing systems will reflect increased FA beta-oxidation. Complementary studies will identify tissue-specific metabolites generated by mitochondria in the course of palmitate catabolism in vitro, comparing muscle to liver and kidney preparations.
Aim 2--Identify Metabolite Biomarkers of Muscle Fat Combustion in Humans Harboring a UCP3 Missense Polymorphic Allele. We predict that subjects with this polymorphism (that yields a truncated UCP3 and 50% decreased whole-body fat combustion) will display a distinctive plasma metabolite profile indicative of reduced muscle FA oxidation, when compared to subjects without the polymorphism.
Aim 3--Determine Whether Metabolomic Profiles Reflective of Muscle Fat Combustion Predict Metabolic Health Changes Following Diet & Exercise Intervention in Obese Subjects. We hypothesize that biomarkers reflective of normal to increased muscle beta-oxidation will be increased, and markers indicative of poor muscle fat combustion reduced, in a cohort of sedentary obese subjects undergoing a 4 month diet-exercise protocol which will increase muscle fitness and improve insulin action.
This research contributes to objectives 3 and 6 of the in-house parent project. A large number of blood plasma samples derived from obesity and diabetes models have been analyzed for hundreds of metabolites, to identify markers of metabolic health and diabetes. In addition to analysis of samples from rodent models of progression to type 2 diabetes mellitus, samples from human clinical studies have been assessed from women at-risk for diabetes and who have improved their health through exercise and diet. Current efforts are focused on determining the structures of unidentified metabolites marking poor metabolic health and that are consistently observed across all studies to date and across models. The impact of these efforts is that the metabolites identified point to a new understanding of the metabolic perturbations that lead to disease in type 2 diabetes and obesity, and illustrate that proper diet and exercise could modify metabolite patterns that reflect healthier tissues.