PROJECT SUMMARY Coronary Microvascular Disease (CMVD), defined as disease of the coronary pre-arterioles, arterioles, and capillaries, accounts for 30-50% of the burden of Ischemic Heart Disease (IHD). However, little is known about the pathogenesis and there are no targeted therapies. Friend of Gata 2 (FOG2) is a cardiomyocyte transcriptional co-regulator which is crucial for both the development and maintenance of the coronary microvasculature. FOG2 promotes expression of angiogenic genes and inhibits expression of anti-angiogenic genes, however, there are two predominant isoforms of FOG2, and the mechanism by which FOG2 promotes an angiogenic program is not known. Our central hypothesis that cardiomyocyte FOG2S is the isoform which regulates a pro-angiogenic gene program to support coronary microvasculature, via interactions with HIF1a. Our objectives in this proposal are to define the structure-function relationship of FOG2 isoforms and HIF1a and establish the paracrine effects of cardiomyocyte FOG2 and FOG2S on heterotypic vascular cells phenotypes, as outlined in the following two aims. In Aim 1, we will determine the structure-function relationship between FOG2 and HIF1a using co-immunoprecipitations studies and luciferase constructs for angiogenic gene promoters. We will also establish the genome-wide cistrome of FOG2 isoforms. In Aim 2, we will determine the paracrine effects of cardiomyocyte FOG2S on vascular cells in vivo and in vitro. First we use a new isoform-specific inducible knockdown model we have developed to define the role of FOG2S in maintaining the coronary microcirculation in vivo. We then establish the ability of cardiomyocyte FOG2S, as opposed to FOG2, to regulate endothelial and smooth muscle cell proliferation, migration, and angiogenic potential. Our studies will provide novel insight into mechanisms of coronary microvascular homeostasis. The proposal's outcomes will fill a critical gap in understanding the molecular factors maintaining the coronary microvasculature and shed light on mechanisms relevant to a significant portion of IHD.