Abstract 61: Deficiency of the RNA Editing Enzyme ADAR2 Impairs Inflammation, Neovascularization and Functional Recovery of Ischemic Tissues

Background: Adenosine deaminase acting on RNA-2 (ADAR2) enzyme catalyzes adenosine-to-inosine (A-to-I) RNA editing of mRNAs and microRNAs and controls brain development. However, the role of endothelial cell ADAR2 in vascular biology and inflammation has not been described so far. Methods and Results: ADAR2 is expressed in human and murine endothelial cells and is 2-fold induced by hypoxia or hind limb ischemia in mice (P<0.05 for all). ADAR2 deficiency resulted in 73±12% impairment of leukocyte infiltration, in 53±4% reduced neovascularization, and a 40±6% decreased blood-flow recovery of ischemic muscle tissues in a hindlimb ischemia mouse model (P<0.001 for all). Mechanistically, among the highly ADAR2-regulated transcripts was interleukin-6 signal transducer (IL6ST or gp130), the receptor of interleukin-6 (IL-6). Silencing of ADAR2 resulted in a downregulation of gp130 mRNA and protein expression in endothelial cells by 65±5% and 50±5%, respectively (P<0.001 for both). Similarly, the expression of gp130 mRNA was decreased by 50±25% (P<0.05) in murine lung endothelial cells, which derived from transgenic ADAR2-null mice. In order to investigate the physiological relevance we treated endothelial cells, which were transfected with a siRNA against ADAR2 or scrambled control, with IL-6 and sIL6Ra. Silencing of ADAR2 reduced by at least 2-fold the IL-6-mediated STAT3 phosphorylation, the mRNA expression of the IL-6-induced downstream genes MCP-1, VCAM-1 and E-selectin, and the IL-6-induced platelet and leukocyte adhesion on endothelial cells and endothelial cell network formation (P<0.05 for all). Of interest, ADAR2 regulated gp130 mRNA stability. Co-silencing of ADAR2 and Drosha completely restored the ADAR2-regulated gp130 mRNA expression indicating that ADAR2 regulates the maturation of specific miRNAs. Indeed, ADAR2 regulates by at least 2-fold the expression of 20 microRNAs, including of miR-579 and miR-320e, which are predicted to bind to the 3’-untranslated region of IL6ST mRNA. Conclusions: Taken together, ADAR2 constitutes a potential candidate for therapeutic modulation of angiogenesis and inflammation in ischemic tissues.