PROJECT SUMMARY/ABSTRACT My long-term professional goal is to become a successful, independent scientist with a research program focused on the integrative physiological response of exercise to identify potential therapeutic targets for the treatment and/or prevention of metabolic disease. Hepatic steatosis, the excessive storage of fat in the liver, has become the most common cause of chronic liver disease worldwide. Exercise can treat and/or prevent steatosis independent of weight status; however, mechanisms remain unclear. In rodents, genetic overexpression of cholesterol 7 α-hydroxylase (CYP7a1), the rate limiting enzyme for bile acid (BA) synthesis, protects against diet-induced steatosis and chronic exercise produces a similar phenotype. CYP7a1 is regulated by numerous mechanisms during both postprandial, and fasting conditions. During postprandial conditions, induction of CYP7a1 and subsequent BA synthesis increases via insulin-specific inactivation of forkhead box transcription factor 1 (FoxO1); whereas under fasting conditions, CYP7a1 transcription is regulated by nuclear localization of transcription factor EB (TFEB). Importantly, exercise enhances and/or restores hepatic insulin action and increases nuclear localization of TFEB in skeletal muscle. However, it remains unknown if exercise contributes to elevated and/or improved BA synthesis through these mechanisms. My overall hypothesis is that exercise protects against diet-induced hepatic steatosis, in part, through enhanced transcriptional regulation of CYP7a1 allowing for increased BA synthesis and fecal BA excretion, which pulls hepatic acetyl-CoA away from de novo lipogenesis to act as an energetic siphon during chronic nutrient excess (i.e., obesity). I will test this overall hypothesis by investigating the impact of exercise on BA metabolism, in diet-induced obese mice. In Aim 1, I will determine whether enhanced hepatic-insulin action induced by acute exercise will increase postprandial induction of CYP7a1 transcription and subsequent BA synthesis. In Aim 2, I will investigate if nuclear translocation of TFEB and TFEB induced transcription of CYP7a1 plays a critical role in the long term effects of exercise to upregulate hepatic BA metabolism and divert excess acetyl-CoA away from de novo lipogenesis and toward BA synthesis and excretion. These studies will contribute to the identification of mechanisms by which exercise protects against hepatic steatosis through a novel pathway while also providing an excellent foundation of training in liver and integrative metabolism.