Circulating MicroRNAs Associated with Intensive Lifestyle Intervention and Metformin in the Diabetes Prevention Program Cohort Project summary Type 2 diabetes is priority for both public health and precision medicine. The etiology of type 2 diabetes is complex and both genetic and lifestyle/environmental factors contribute to risk. Current approaches to risk prediction and risk reduction are limited because they fail to account for the interactions between biological and lifestyle risk factors. MicroRNAs regulate expression of genes in response to lifestyle factors and capture the combined effects of genetic predisposition and the environment. Extracellular circulating microRNAs, which are readily detectable in blood, are emerging as useful indicators of disease etiology and show changes in response to the environment and behaviors. Our own prior studies and others have provided preliminary information about microRNAs as predictive biomarkers for incident type 2 diabetes and responses to risk reduction interventions. We showed that circulating microRNAs are associated with risk for type 2 diabetes, response to an insulin sensitizing pharmacologic agent, and lifestyle interventions (e.g., yoga, physical activity). Prior studies have been primarily cross-sectional in nature and were not powered to evaluate clusters of microRNAs as predictive markers. This study will determine whether microRNAs predict incident type 2 diabetes and whether there are interactions with risk reduction interventions. We will measure microRNAs in a subset of plasma samples banked at the NIDDK biorespository from participants in the completed NIH-funded Diabetes Prevention Program (DPP) trial that tested the effect of metformin, intensive lifestyle intervention, and placebo on risk for type 2 diabetes. This trial showed intensive lifestyle intervention decreased incidence of type 2 diabetes by 58% and metformin by 31% compared to placebo. The existing phenotypic data and biologic specimens from the DPP trial provide an exceptional opportunity to evaluate the relationships between longitudinal changes in both microRNAs and risk for type 2 diabetes in an extremely well characterized sample of individuals who underwent interventions that decreased incidence of type 2 diabetes. Circulating microRNAs will be measured using a flow cytometry- based direct detection assay that is compatible with heparin, the anticoagulant used for sample collection in the DPP trial. This study will be the first to evaluate, in a large, rigorously conducted clinical trial, microRNAs, singularly and as clusters, as predictors of type 2 diabetes and interactions with risk reduction interventions. This will also be the first study to model longitudinal trajectories of microRNAs and fasting blood glucose over time. This knowledge will improve our understanding of inter-individual variability in risk prediction, optimization of risk reduction interventions, and mechanisms for type 2 diabetes and responses to risk reduction interventions.