The specific roles of miRNAs in vascular function are just beginning to be explored. Our previous work has shown that reduction of overall miRNA levels via Dicer silencing in human endothelial cells (EC) strongly regulates angiogenic gene expression and impairs aspects of in vitro angiogenesis including EC growth and morphogenesis. These in vitro experiments are supported by new exciting preliminary data in vivo data using mice conditionally lacking the rate limiting enzyme (Dicer) in miRNA synthesis in EC. Mice lacking Dicer in EC (EC specific Dicer KO) are viable but exhibit impaired post-natal angiogenic responses. In order to dissect the relationships between signal transduction, gene expression and miRNAs in EC, we show that treatment of EC with VEGF stimulates time-dependent changes in global miRNA profiles and show that components of the miRNA cluster, miR 17-92 can regulate aspects of VEGF induced cell growth and morphogenesis. In addition, we have identified a specific miRNA (miR-155) that regulates the levels of endothelial nitric oxide synthase (eNOS) in cultured EC. Thus, we hypothesize that Dicer generated endothelial miRNAs regulate the extent of angiogenesis and blood flow control in vivo by regulating mRNA levels and/or the translational stability of important proteins. We will: 1. Identify and characterize angiogenic growth factor regulated miRNAs in EC; 2. Define the roles of miR 17-92 in models of angiogenesis and 3. Define the roles of miR-155 in regulating eNOS function in vitro and in vivo. Collectively, this work will facilitate the understanding of the importance of miRNAs in EC biology and shed insights into their role as potential therapeutics targets.