Endothelial HIF-2 α regulates murine pathological angiogenesis and revascularization processes

Localized tissue hypoxia is a consequence of vascular compromise or rapid cellular proliferation and is a potent inducer of compensatory angiogenesis. The oxygen-responsive transcriptional regulator hypoxia-inducible factor 2 α (HIF-2 α) is highly expressed in vascular ECs and, along with HIF-1 α, activates expression of target genes whose products modulate vascular functions and angiogenesis. However, the mechanisms by which HIF-2 α regulates EC function and tissue perfusion under physiological and pathological conditions are poorly understood. Using mice in which Hif2a was specifically deleted in ECs, we demonstrate here that HIF-2 α expression is required for angiogenic responses during hindlimb ischemia and for the growth of autochthonous skin tumors. EC-specific Hif2a deletion resulted in increased vessel formation in both models; however, these vessels failed to undergo proper arteriogenesis, resulting in poor perfusion. Analysis of cultured HIF-2 α - deficient ECs revealed cell-autonomous increases in migration, invasion, and morphogenetic activity, which correlated with HIF-2 α -dependent expression of specific angiogenic factors, including delta-like ligand 4 (Dll4), a Notch ligand, and angiopoietin 2. By stimulating Dll4 signaling in cultured ECs or restoring Dll4 expression in ischemic muscle tissue, we rescued most of the HIF-2 α -dependent EC phenotypes in vitro and in vivo, emphasizing the critical role of Dll4/Notch signaling as a downstream target of HIF-2 α in ECs. These results indicate that HIF-1 α and HIF-2 α fulfill complementary, but largely nonoverlapping, essential functions in pathophysiological angiogenesis.
Introduction The therapeutic manipulation of angiogenesis holds great promise for treating diverse pathological conditions, including cancer, macular degeneration, atherosclerosis, and peripheral arterial disease (PAD) (1), (2). However, the ability to [...]