An important role of endothelial hairy‐related transcription factors in mouse vascular development

Abstract

The Hairy-related transcription factor family of Notch- and ALK1-downstream transcriptional repressors, called Hrt/Hey/Hesr/Chf/Herp/Gridlock, has complementary and indispensable functions for vascular development. While mouse embryos null for either Hrt1/Hey1 or Hrt2/Hey2 did not show early vascular phenotypes, Hrt1/Hey1; Hrt2/Hey2 double null mice (H1(ko) /H2(ko) ) showed embryonic lethality with severe impairment of vascular morphogenesis. It remained unclear, however, whether Hrt/Hey functions are required in endothelial cells or vascular smooth muscle cells. In this study, we demonstrate that mice with endothelial-specific deletion of Hrt2/Hey2 combined with global Hrt1/Hey1 deletion (H1(ko) /H2(eko) ) show abnormal vascular morphogenesis and embryonic lethality. Their defects were characterized by the failure of vascular network formation in the yolk sac, abnormalities of embryonic vascular structures and impaired smooth muscle cell recruitment, and were virtually identical to the H1(ko) /H2(ko) phenotypes. Among signaling molecules implicated in vascular development, Robo4 expression was significantly increased and activation of Src family kinases was suppressed in endothelial cells of H1(ko) /H2(eko) embryos. The present study indicates an important role of Hrt1/Hey1 and Hrt2/Hey2 in endothelial cells during early vascular development, and further suggests involvement of Robo4 and Src family kinases in the mechanisms of embryonic vascular defects caused by the Hrt/Hey deficiency.

Transcription factors regulating vasculogenesis and angiogenesis

“…242,243 Loss of HEY1/HEY2 resulted in both reduced Ephb2 and Jag1 expression and increased Robo4 and Flk1 expression. [242][243][244] However, there are currently few wellcharacterized direct endothelial targets of HEY1/2 described in the literature, and it is unclear to what extent the phenotype in the compound Hey1/2 null mice can be attributed to vascular versus cardiac defects. [242][243][244] 9 | HLX HLX1 is a homeobox TF with a currently undefined DNA binding motif expressed in hemato-endothelial progenitors from E7.75 (Table 2).…”

Blood flow diverts extracellular vesicles from endothelial degradative compartments to promote angiogenesis

“…Whether this transfer results from direct signaling from endosome membranes or from cytoplasmic cargo release remains to be deciphered. Among the genes upregulated by tEVs in flow-stimulated endothelial cells, we found several pro-angiogenic transcription factors, such as ID1, ID2, ID3, Hey1, Hey2, MAFB, Runx1 and HES1 (Benezra et al, 2001; Fischer et al, 2004; Morioka et al, 2014; Kitagawa et al, 2013). We further identified genes that are involved in two pro-angiogenic signaling pathways, Notch (HEY1, HEY2, HES1, JAG1) and TGFß (Smad6, Smad7, Bambi, PMEPA1, Nog) (Fig.4a, right).…”

Blood flow diverts extracellular vesicles from endothelial degradative compartments to promote angiogenesis

“…Indeed, different sets of genes are transcriptionally impacted by tEVs when endothelial cells are cultured in static or low flow (Fig 4A, right). Among the genes upregulated by tEVs in flow‐stimulated endothelial cells, we found several pro‐angiogenic transcription factors, such as ID1, ID2, ID3, Hey1, Hey2, MAFB, Runx1 and HES1 (Benezra et al , 2001; Fischer et al , 2004; Kitagawa et al , 2013; Morioka et al , 2014). We further identified genes that are involved in two pro‐angiogenic signaling pathways, the Notch (HEY1, HEY2, HES1, JAG1) and the TGFß (Smad6, Smad7, Bambi, PMEPA1, Nog) pathways (Fig 4A, right).…”