Regulation of endothelial hemoglobin alpha expression by Kruppel-like factors

Abstract

Hemoglobin subunit alpha (HBA) expression in endothelial cells (ECs) has recently been shown to control vascular tone and function. We sought to elucidate the transcriptional regulation of HBA expression in the EC. Gain of KLF2 or KLF4 function studies led to significant induction of HBA in ECs. An opposite effect was observed in ECs isolated from animals with endothelial-specific ablation of Klf2, Klf4 or both. Promoter reporter assays demonstrated that KLF2/KLF4 transactivated the hemoglobin alpha promoter, an effect that was abrogated following mutation of all four putative KLF-binding sites. Fine promoter mutational studies localized three out of four KLF-binding sites (sites 2, 3, and 4) as critical for the transactivation of the HBA promoter by KLF2/KLF4. Chromatin immunoprecipitation studies showed that KLF4 bound to the HBA promoter in ECs. Thus, KLF2 and KLF4 serve as important regulators that promote HBA expression in the endothelium.

Heterocellular Contact Can Dictate Arterial Function

“…However, in mice with a disrupted alpha globin gene product (due to the insertion of a neomycin cassette into exon 2 of the Hba1 gene), the dependence on NO signaling is not lost: relaxation is almost completely blunted with L-NAME alone, with little additive effect from EDH inhibitors ( Figure 4I). Within the vasculature, cell-cell interactions induce protein expression to influence cellular function 23,[40][41][42][43] and our results embody this motif: alpha globin expression is induced upon heterocellular contact (EC-SMC coupling) and alters cellular function (altered mechanism of arterial relaxation). This data also fits well with previous work demonstrating alpha globin's regulation of eNOS 24,25 and suggests that alpha globin expression is important for EDH based signaling to predominate.…”

“…24,25 Its expression at the MEJ may act to finely control vasodilation by limiting the diffusion of eNOS-derived NO to the SMC. 39 Contact between ECs and SMCs is required for the expression of alpha globin in ECs 23,40 , and in the newly formed EC projections that resulted from PAI-1 treatment, alpha globin expression is significantly increased which correlated with limited dilatory effect of NO ( Figure 4H). However, in mice with a disrupted alpha globin gene product (due to the insertion of a neomycin cassette into exon 2 of the Hba1 gene), the dependence on NO signaling is not lost: relaxation is almost completely blunted with L-NAME alone, with little additive effect from EDH inhibitors ( Figure 4I).…”

Identification of the initial molecular changes in response to circulating angiogenic cells-mediated therapy in critical limb ischemia

“…Thus, an increase of HB levels could help to increase oxygen transport after the hypoxic situation induced by ischemia. Additionally, HB increase could promote vascular tone through participating in the NO transfer between ECs and vascular smooth muscle cells [48]. On the other hand, decreased levels of MB, a muscle-specific protein of oxidative metabolism, could also induce NO bioavailability [49,50].…”

Novel insights into potential therapeutic targets and biomarkers using integrated multi-omicsapproaches for dilated and ischemic cardiomyopathies

“…Similarly, Orphan nuclear receptor 4A1 (NR4A1) showed a marked upregulation in the hypertrophic state while in a healthy left ventricle it was low ( Table 1). NR4A1 has recently been described to play a role in cardiac stress responses and hypertrophic growth 103 . As a complete contrast, dilated cardiomyopathy showed a marked loss in adipocyte signatures (Table1), for example, fatty acid-binding protein 4 (FABP4) has been shown to contribute to cardiac metabolism 104,105 ; thus, observed alterations might indicate a change in the energy metabolism of the heart.…”