PROJECT SUMMARY/ABSTRACT More than one third of the United States population is obese, and obesity-related conditions, including heart disease and type 2 diabetes, are leading causes of preventable death. Type 2 diabetes, obesity, and their complications pose an enormous burden on our healthcare system, making it essential to develop new prevention and treatment modalities. The beiging of white adipose tissue (WAT) has emerged as a potential therapeutic tool since the induction of these cells has been postulated to contribute to non-shivering thermogenesis, thereby increasing energy expenditure and potentially inducing weight loss. One physiological means to increase beiging in human WAT may be exercise training. In rodents, recent studies from the Goodyear laboratory and other groups have demonstrated that exercise training causes beiging of WAT as indicated by an increase in expression of beige cell-specific marker genes including UCP1, the appearance of multilocular droplets, and an increase in mitochondrial function. Moreover, transplantation of subcutaneous WAT (scWAT) from trained mice into sedentary mice causes a dramatic improvement in glucose tolerance and insulin sensitivity in the recipient mice, and there is strong evidence that this effect is mediated, at least in part, by increased expression and release of exercise-induced adipokines. Whether exercise training causes beiging in human subjects is not well understood. Furthermore, whether training results in adaptations to scWAT that stimulate tissue-to-tissue communication to mediate the beneficial effects of exercise in humans has not been investigated. To address these questions, four Specific Aims have been identified: 1) To determine if exercise training causes beiging of scWAT in human subjects. These studies will be done in lean, healthy-obese, and obese subjects with type 2 diabetes; 2) To determine if exercise training alters the metabolic phenotype of scWAT from human subjects. This will include studies of mitochondrial function and glucose and fatty acid metabolism in scWAT; 3) To determine if exercise training increases the expression of novel adipokines in scWAT that function in tissue-to-tissue communication. Studies under this aim will also determine if there are increases in circulating novel adipokines and if these adipokines can increase metabolism in human muscle and fat cell lines; and 4) To identify non-biopsy biomarkers of exercise-induced beiging and metabolic changes in scWAT from human subjects. We will employ an unbiased proteomics approach to address this aim. These studies will determine if beiging of scWAT is a fundamental adaptation to exercise training in humans. The findings could lead to treatment strategies and biologics for the treatment of obesity and type 2 diabetes.