Abstract 5588: Identification of Aria as a Novel Factor Regulating Endothelial Cell Apoptosis and Angiogenesis in vivo
Endothelial apoptosis is a pivotal process for angiogenesis during embryogenesis as well as postnatal life. Here, we identified a novel gene (ARIA) that regulates endothelial apoptosis and angiogenesis. ARIA was expressed in a variety of human cultured endothelial cells as well as in blood vessels of e9.5d mouse embryos. Knockdown of ARIA in HUVEC using siRNA significantly attenuated endothelial apoptosis, but not affected cell migration or proliferation. This anti-apoptotic effect by ARIA-knockdown was attributable to the enhanced expressions of inhibitor of apoptosis (cIAP)-1 and cIAP-2. cIAP-1 and cIAP-2 play as ‘guardians’ of the cell death machinery by directly binding to and neutralizing the caspases as well as by modulating the death signaling through TNF receptors. Simultaneous knockdown of cIAP-1 and cIAP-2 abolished the anti-apoptotic effect of ARIA-knockdown. On the other hand, yeast two-hybrid screening identified the 20S proteasome α subunit-7 as a binding partner of ARIA. We then found that cIAP-1 and cIAP-2 are targeted by the proteasome, and that ARIA regulates the proteasomal degradation of cIAP-1 and cIAP-2 in endothelial cells. In vivo angiogenesis was studied by Matrigel-plug assay and mouse ischemic retinopathy model, in which ARIA was knocked down by mixing siRNA in the plugs and intravitreal injection of siRNA respectively. In both the models, ARIA-knockdown significantly enhanced the in vivo angiogenesis through attenuating the endothelial apoptosis. To further study ARIA function in vivo, we have generated the ARIA knockout mice. Tumor xenograft growth was significantly enhanced in ARIA knockout mice than that in wildtype mice. The number of microvessels was significantly greater with appearance of less apoptotic endothelial cells in the tumor xenografts implanted into ARIA knockout mice than in wildtype mice. Taken together, ARIA is a novel factor regulating endothelial apoptosis as well as angiogenesis through modulating the proteasomal degradation of cIAP-1 and cIAP-2 in endothelial cells. Since ARIA is preferentially expressed in endothelial cells, ARIA is an attractive new target for pharmacotherapeutic agents to treat ischemic cardiovascular diseases.