HIF-2α-Haploinsufficient mice have blunted retinal neovascularization due to impaired expression of a proangiogenic gene battery

PURPOSE. To characterize the effect of HIF-2 alpha haploinsufficiency on retinal neovascularization and angiogenic signaling in neonatal mice. METHODS. Retinal samples were obtained from HIF-2 alpha-haploinsufficient (Epas1(+/-)) and wild-type (Epas1(+/+)) neonatal mice subjected to an oxygen-induced retinopathy (OIR) protocol. Histologic and molecular studies were performed immediately, 12 hours, or 5 days after initiation of the hypoxia phase of the OIR protocol. Molecular profiling was performed in mouse brain endothelial cells maintained in normoxia or hypoxia. Transfection studies assessed the response of isolated promoter regions from proangiogenic genes to HIF-1 alpha or -2 alpha overexpression. RESULTS. Epas1(+/-) mice exhibited no significant differences in retinal vasculature during normal development but had reduced retinal neovascularization in an OIR protocol. Multiple proangiogenic factors were induced during the hypoxia phase in Epas1(+/+) OIR retinal samples, whereas Epas1(+/-) OIR retinal samples had absent or blunted induction of these same factors. Several, but not all, proangiogenic factors were induced in mouse brain endothelial cells after hypoxia. In transfection assays, most proangiogenic promoter regions were preferentially activated by HIF-2 alpha relative to HIF-1 alpha. CONCLUSIONS. HIF-2 alpha deficiency results in reduced neovascularization and blunted inducibility of multiple proangiogenic factors in the retinas of mice with OIR. The authors propose that HIF-2 alpha is a master regulator of proangiogenic factors in retinal vascular endothelial cells, the predominant cell type of the retina in which HIF-2 alpha is expressed. Future studies will address whether the molecular and functional roles for HIF-2 alpha identified from these studies can be generalized to other pathophysiological states involving neovascularization.