PROJECT SUMMARY The current pandemic of obesity and insulin resistance across the lifespan presents an immense public health challenge. Human observational studies and fecal transplantation studies in animal models (both largely focused on adults) have found an interconnection among obesity, insulin resistance, and the microbiota. Because epidemiology points to childhood origins for the genesis of obesity, there is a critical need to understand the mechanisms of pediatric obesity and to develop tools for its prediction, prevention, and treatment. Children with severe obesity mimic adult phenotypes in their development of metabolic and cardiovascular risk, and yet are at the earliest stages of disease with fewer and less severe co-morbid conditions. Thus children with obesity present a unique opportunity and an ideal population in which to garner deeper insights into the obesity-associated microbiome. To enable such insights, the objective of this proposal is to establish a comprehensive research resource to define mechanisms underlying microbial regulation of host metabolism in adolescents with obesity (ages 12-18 yrs) before and after weight loss intervention. The proposed research leverages Duke’s unique and well-established intervention program for pediatric obesity and insulin resistance. Our prior studies have applied metabolomic technology to reveal that blood metabolites such as branched chain amino acids (BCAA) are negatively associated with insulin sensitivity following adult weight loss interventions, and we have used gnotobiotic mice to demonstrate their positive association with microbiota-mediated weight gain. Our preliminary studies indicate that BCAA and related metabolites are also associated with insulin resistance and weight gain in adolescents. Our central hypothesis is that human gut bacteria control host weight gain and insulin resistance in adolescents by modifying host metabolism. This hypothesis will be tested in two specific aims: Aim 1. Develop a resource to define associations between intestinal microbiota and a severely obese population of adolescents enrolled in an outpatient weight management intervention program. Aim 2. Define the molecular mechanisms by which human intestinal bacteria regulate metabolic traits linked to pediatric obesity. Completion of this work will provide three key resources for broad use by the scientific community: (1) a clinical sample, microbiota strain, and data repository from a unique pediatric weight management intervention cohort, (2) a comprehensive suite of robust genetic, molecular profiling, and phenotyping technologies that will yield unique insights into the microbial communities that control body weight and responses to obesity intervention, and (3) insights into molecular mechanisms by which BCAA and other identified microbial products influence metabolic health during childhood and adolescence. These new resources, technologies, and mechanistic insights will have a positive imp...