ABSTRACT Results of several preclinical studies and clinical trials suggest that cell therapy improves cardiac function after myocardial infarction; however, high variability, marginal efficacy, and our poor understanding of the mechanisms by which cell therapy works have precluded its clinical translation. One major knowledge gap is a lack of understanding of how host metabolism impinges on the efficacy of cell therapy. This is important because a pervasive feature of heart failure is insulin resistance, a condition known to affect glucose transport in the myocardium as well as the function of circulating and tissue-resident stem cells. This dysfunction is further exacerbated by frank diabetes, a condition inordinately common in HF patients. Therefore, identification of the metabolic factors that determine the efficacy of cell therapy is required to optimize cell therapy for HF patients. In this project, we will examine how diabetes affects cardiac repair induced by transplantation of cardiac mesenchymal cells (CMCs) or paracrine factors derived therefrom. Our preliminary data indicate that, in contrast to CMCs isolated from non-diabetic mice, CMCs isolated from diabetic mice fail to improve the function of the infarcted heart. The diabetic CMCs show elevated rates of glycolysis associated with expression of Pfkfb3, which in cardiac progenitor cells increases glycolysis by augmenting phosphofructokinase activity and appears to diminish their proliferation and survival. In addition, we find that these changes involve not only glycolytic mediators such as PFKFB3, but mitochondrial effectors such as sirtuin 1 (Sirt1) as well. Building on these observations, we propose to test the hypothesis that diabetes compromises the therapeutic efficacy of CMCs by chronically increasing glycolysis, which alters paracrine mechanisms that mediate cardiac repair, and that Sirt1 improves the repair capacity of CMCs by augmenting mitochondrial activity and thereby decreasing glycolysis. To test this hypothesis, we will i) determine how diabetes affects CMC-mediated myocardial repair, ii) elucidate how glycolysis affects CMC repair competence, and iii) develop strategies to improve CMC therapy in diabetes. This project will provide fundamental knowledge regarding how metabolic disease affects cell therapy and how mesenchymal cells adapt to nutrient stress. In addition, these studies will illuminate mechanisms by which metabolism regulates paracrine factor secretion, thereby generating novel biological understanding of cell-cell communication. Collectively, the knowledge garnered from this project will facilitate the optimization of cell therapy protocols and provide critical direction to ongoing clinical trials.