Disturbances of metabolism, often linked to mitochondrial function, have a major impact on disease risk and healthspan among human populations. Type 2 diabetes mellitus, non-alcoholic fatty liver disease, hypertension, hyperlipidemia, and cardiovascular diseases are all linked to major changes in metabolic and mitochondrial function. A complex set of genetic and environmental factors-including diet-underlie individual differences in the risk and severity of metabolic syndrome. This project is focused on the complex gene-by- environmental interactions (GXE) that contribute to mitochondrial and metabolic syndrome, and that reduce healthy lifespan. We use a new integrative systems genetics approach to study effects of a high fat Western diet. This work relies on a large family of isogenic and genetically diverse murine lines-including F1 hybrids- that serve as a translational and mechanistic bridge between reductionist and integrative approaches. Identical cohorts will be studied as a function of age on markedly different diets. In Aim 1, we study lifespan using BXD strains and non-inbred but isogenic F1 cohorts of females under high and low fat diets. We map and quantify novel GXE-type modifier loci, candidate genes, and molecular networks that modulate healthspan and longevity. In Aim 2 we generate deep molecular, mitochondrial, and metabolic biomarker data as a function of age and diet. We expect that gene variants and diet will be causally linked to mitochondrial function and to metabolism in key organs and tissues. In Aim 3 we model complex and integrative molecular and cellular networks that define differences in vitality and healthspan. We use sophisticated bioinformatic and statistical frameworks (eQTL analysis, ANOVA, and structural equation modeling). Finally, in Aim 4 we validate and translate networks involved in metabolism, mitochondria, and healthspan. We test candidate genes using gain- and loss-of-function strategies in C. elegans. We evaluate translational relevance of candidate genes and biomarkers by testing for associations in a remarkably well studied cohort of 161,000 postmenopausal women (Women's Health Initiative data sets). The WHI is an ideal translation companion to test effects of diet. This project will (1) identify high impact variants and molecular/metabolic networks involved in metabolic diseases and healthspan, and (2) provide an experimental and predictive systems biology framework that links genotype and environmental factors to disease risk in human populations.