056 Activation of Sterol Regulatory Element‐Binding Proteins ((SREBPs) is Critical in IL‐8‐Induced Angigiogenesi

Angiogenesis is an essential process during wound healing. The chemokine IL-8 is a well-known inflammatory and angiogenic factor. We found that IL-8 stimulates activation of SREBPs, molecules that are critical for cholesterol and fatty acid metabolism, and that this activation is markedly increased during IL-8-induced angiogenesis. Two important processes in the early stages of angiogenesis are increase in proliferation and migration of endothelial cells. Therefore, we tested whether IL-8 stimulates these processes in a SREBP-dependent manner both in vivo and in culture. Our data show that IL-8 stimulates SREBP-1 and -2 gene expression which leads to an increase in both the precursor and the mature forms of these proteins in human microvascular endothelial cells (hMVEC). In addition, several genes downstream of SREBPs are also up-regulated by IL-8 stimulation, in particular 3-hydroxy -3-methylglutaryl coenzyme A reductase (HMGCA). Furthermore, SREBP-1 was abundant in the neovasculature of wound healing skin, and this expression could be suppressed by local application of antibodies to IL-8 or to its receptors, CXCR1 and CXCR2. To test whether SREBP activation is critical for the proliferation and migration of endothelial cells induced by IL-8 during angiogenesis, we used either RNA interference (RNAi) to inhibit the SREBP cleavage-activating protein (SCAP) that escorts SREBPs from the ER to the Golgi for maturation (activation), or treated endothelial cells with 25-hydroxycholesterol (25-HC), an inhibitor of SREBP activation. Both SCAP RNAi and 25-HC significantly inhibited IL-8-induced SREBP activation during endothelial cell migration and proliferation indicating that SREBPs are critical components of the signaling pathways leading to IL8-induced angiogenesis. In addition, in the chick chorioallantoic membrane (CAM) model, 25-HC markedly inhibited both developmental- and IL-8-induced angiogenesis in 7-day and 10-day CAMs, respectively. In conclusion, our results indicate a novel regulatory mechanism for IL-8-induced angiogenesis that is mediated by SREBPs.