Nrf2 acts cell-autonomously in endothelium to regulate tip cell formation and vascular branching.

Angiogenesis, in which new blood vessels form via endothelial cell (EC) sprouting from existing vessels, is a critical event in embryonic development and multiple disease processes. Many insights have been made into key EC receptors and ligands/growth factors that govern sprouting angiogenesis, but intracellular molecular mechanisms of this process are not well understood. NF-E2-related factor 2 (Nrf2) is a transcription factor well-known for regulating the stress response in multiple pathologic settings, but its role in development is less appreciated. Here, we show that Nrf2 is increased and activated during vascular development. Global deletion of Nrf2 resulted in reduction of vascular density as well as EC sprouting. This was also observed with specific deletion of Nrf2 in ECs, but not with deletion of Nrf2 in the surrounding nonvascular tissue. Nrf2 deletion resulted in increased delta-like ligand 4 (Dll4) expression and Notch activity in ECs. Blockade of Dll4 or Notch signaling restored the vascular phenotype in Nrf2 KOs. Constitutive activation of endothelial Nrf2 enhanced EC sprouting and vascularization by suppression of Dll4/Notch signaling in vivo and in vitro. Nrf2 activation in ECs suppressed Dll4 expression under normoxia and hypoxia and inhibited Dll4-induced Notch signaling. Activation of Nrf2 blocked VEGF induction of VEGFR2-PI3K/Akt and downregulated HIF-2α in ECs, which may serve as important mechanisms for Nrf2 inhibition of Dll4 and Notch signaling. Our data reveal a function for Nrf2 in promoting the angiogenic sprouting phenotype in vascular ECs.

Wei Y ，Gong J ，Thimmulappa RK ，Kosmider B ，Biswal S ，Duh EJ ... -  《-》

Endothelial HIF-2α 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 2α (HIF-2α) is highly expressed in vascular ECs and, along with HIF-1α, activates expression of target genes whose products modulate vascular functions and angiogenesis. However, the mechanisms by which HIF-2α 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-2α 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-2α-deficient ECs revealed cell-autonomous increases in migration, invasion, and morphogenetic activity, which correlated with HIF-2α-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-2α-dependent EC phenotypes in vitro and in vivo, emphasizing the critical role of Dll4/Notch signaling as a downstream target of HIF-2α in ECs. These results indicate that HIF-1α and HIF-2α fulfill complementary, but largely nonoverlapping, essential functions in pathophysiological angiogenesis.

Skuli N ，Majmundar AJ ，Krock BL ，Mesquita RC ，Mathew LK ，Quinn ZL ，Runge A ，Liu L ，Kim MN ，Liang J ，Schenkel S ，Yodh AG ，Keith B ，Simon MC ... -  《-》

Notch-dependent VEGFR3 upregulation allows angiogenesis without VEGF-VEGFR2 signalling.

Benedito R ，Rocha SF ，Woeste M ，Zamykal M ，Radtke F ，Casanovas O ，Duarte A ，Pytowski B ，Adams RH ... -  《-》

Semaphorin 3E-Plexin-D1 signaling regulates VEGF function in developmental angiogenesis via a feedback mechanism.

Kim J ，Oh WJ ，Gaiano N ，Yoshida Y ，Gu C ... -  《-》

Synchronization of endothelial Dll4-Notch dynamics switch blood vessels from branching to expansion.

Ubezio B ，Blanco RA ，Geudens I ，Stanchi F ，Mathivet T ，Jones ML ，Ragab A ，Bentley K ，Gerhardt H ... -  《eLife》