Summary: In hearts, Endothelial cells (EC), closely surround cardiomyocytes (CM) and this intricate anatomical arrangement of cardiomyocytes within the capillary network not only allows for physiological transport but also for local communication between endothelial cells and cardiomyocytes during development and in both physiological and pathophysiological conditions. Acute myocardial infarction (MI) inflicts massive injury to the coronary microcirculation leading to vascular disintegration and capillary rarefication in the infarct region. Accumulating evidence suggests that the ongoing molecular conversation between EC and CM is highly relevant to the post-infarct angiogenesis and progression of myocardial injury and repair processes. Similarly, bone- marrow derived endothelial precursor cells (BM-EPC) have been shown to facilitate post-MI neovascularization. Following MI, efficient perfusion provided by micro vessels is required to prevent further cardiomyocyte death, which contributes to infarct expansion, left ventricular dilation, and adverse cardiac remodeling. Few studies have investigated whether and how communicative signals produced by stressed CM impact local EC and distant BM-EPC biology and angiogenic functions following myocardial injury. Particularly, whether extracellular vesicles or exosomes (EV/Exo) secreted from stressed CMs communicate with and modulate EC/EPC biology and angiogenesis during ischemic injury and the molecular cargo from stressed CM-exosomes that may alter EC function remains largely unexplored. The scientific premise of proposed studies is based on our exciting preliminary data that demonstrates that circulating exosomes from plasma of mice shortly after MI are highly enriched in two cardiomyocyte derived microRNAs (Myo-miR208 and Myo-miR499) and that post-MI circulating exosomes from stressed CM transfer these myomiRs not only locally to cardiac endothelial cells but also distantly to BM-EPCs. These CM communicative signals induce EC and EPC dysfunction downstream of these myo- miRs. Overall, this project will test the central hypothesis that ‘cardiomyocyte exosome-mediated delivery of MyomiRs 208 and 499 to EC and EPCs negatively alters their biology and inhibits post-MI neovascularization leading to adverse cardiac remodeling and that inhibition of myomiRs208/499 will improve post-MI angiogenesis and cardiac functions’. We will test this hypothesis by conducting experiments organized under following specific aims: 1) To establish the inhibitory effect of cardiomyocyte exosome-delivered myo-miRs 208a-3p and 499-5p on post-MI angiogenesis and cardiac functions; 2) To elucidate the downstream targets and molecular mechanisms of myo-miRs 208a-3p and 499-5p mediated endothelial cell dysfunction; and 3) To determine the differential therapeutic efficacy of post-MI and non-injured mouse bone marrow derived EPCs and their exosomes on post-MI cardiac repair. We believe that proposed studies will not only enhance new...