We have recently discovered that hemoglobin ? is enriched in myoendothelial junctions, the anatomical location where endothelial cells and smooth muscle cells make contact in the resistance arteries. This was a significant finding because it demonstrated that hemoglobin ? had an important and active role outside of erythrocytes. This protein is one of only a few truly polarized proteins to be localized to endothelial-derived myoendothelial junctions, and the siRNA-induced decrease in the amount of the protein significantly altered arterial reactivity, including constriction to phenylephrine and dilation to acetylcholine. The mechanism we derived was based on evidence indicating that monomeric hemoglobin ? is a potent scavenger of nitric oxide, and that endothelial nitric oxide synthase (eNOS) and hemoglobin ? were found to be in a macromolecular complex. Based on this work, as well as a plethora of strong preliminary data, we hypothesize that hemoglobin ? at the myoendothelial junction is a novel regulator of nitric oxide signaling which can impact blood pressure regulation. We will test this hypothesis using two specific aims: 1.) investigate the effects of endothelial hemoglobin a gene ablation/over-expression on arterial function and 2.) elucidate how AHSP and eNOS regulate hemoglobin ? expression and dioxygenase activity at the MEJ.
These aims will be elucidated using studies focused first on a floxed hemoglobin ? mouse as well as a hemoglobin a over-expressing mouse to determine the effects of deletion/over-expression of this protein in endothelium on arterial reactivity, whole tissue blood flow, peripheral resistance and blood pressure. In addition, a human model of the disease alpha thalassemia where 2 alleles of hemoglobin a are deleted will be used to study the effects of this genome-wide heterozygous deletion on the vasculature. Next we will investigate how the hemoglobin ? chaperone hemoglobin ? stabilizing protein (AHSP) may traffic hemoglobin ? to the myoendothelial junction or act directly as a regulator of the hemoglobin ? redox state, altering the ability of nitric oxide to bind. The sum of this proposal unites and builds on the dat obtained from our previous R01 by allowing us for the first time to ask the direct question as to the function of the myoendothelial junction in intact animals. Indeed, we believe part of the answers could provide the basis for a completely new understanding of blood pressure control by the peripheral vasculature, as well as the derivation of unexplored pharmacological targets for control of hypertension.

Public Health Relevance

We recently demonstrated that hemoglobin a was found in the arteries that regulate blood pressure but not in the larger conduit arteries. This protein, lon thought to have been confined to red blood cells, was found in aterial walls at anatomical structures termed myoendothelial junctions. Our work has demonstrated this protein has a fundamental role regulating how an artery constricts or dilates. Because of this, we believe that hemoglobin a may be important for regulation of blood pressure. We have therefor sought to test this idea by trying to determine how the protein moves to myoendothelial junctions, how to disrupt activity of hemoglobin a, and the effects of excessive/deletion of hemoglobin a from arteries. We believe this work will provide a framework for determining the role it may play in blood pressure and lead to a novel pharmacological target.

National Institute of Health (NIH)
National Heart, Lung, and Blood Institute (NHLBI)
Research Project (R01)
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Vascular Cell and Molecular Biology Study Section (VCMB)
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Gao, Yunling
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University of Virginia
Schools of Medicine
United States
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Billaud, Marie; Lohman, Alexander W; Johnstone, Scott R et al. (2014) Regulation of cellular communication by signaling microdomains in the blood vessel wall. Pharmacol Rev 66:513-69
Butcher, Joshua T; Johnson, Tyler; Beers, Jody et al. (2014) Hemoglobin ? in the blood vessel wall. Free Radic Biol Med 73:136-42
Lohman, Alexander W; Isakson, Brant E (2014) Differentiating connexin hemichannels and pannexin channels in cellular ATP release. FEBS Lett 588:1379-88
Straub, Adam C; Butcher, Joshua T; Billaud, Marie et al. (2014) Hemoglobin ?/eNOS coupling at myoendothelial junctions is required for nitric oxide scavenging during vasoconstriction. Arterioscler Thromb Vasc Biol 34:2594-600
Isakson, Brant E; Thompson, Roger J (2014) Pannexin-1 as a potentiator of ligand-gated receptor signaling. Channels (Austin) 8:118-23
Straub, Adam C; Zeigler, Angela C; Isakson, Brant E (2014) The myoendothelial junction: connections that deliver the message. Physiology (Bethesda) 29:242-9
Billaud, Marie; Johnstone, Scott R; Isakson, Brant E (2012) Loss of compliance in small arteries, but not in conduit arteries, after 6 weeks exposure to high fat diet. J Cardiovasc Transl Res 5:256-63
Billaud, Marie; Lohman, Alexander W; Straub, Adam C et al. (2012) Characterization of the thoracodorsal artery: morphology and reactivity. Microcirculation 19:360-72
Heberlein, Katherine R; Han, Jenny; Straub, Adam C et al. (2012) A novel mRNA binding protein complex promotes localized plasminogen activator inhibitor-1 accumulation at the myoendothelial junction. Arterioscler Thromb Vasc Biol 32:1271-9
Straub, Adam C; Billaud, Marie; Johnstone, Scott R et al. (2011) Compartmentalized connexin 43 s-nitrosylation/denitrosylation regulates heterocellular communication in the vessel wall. Arterioscler Thromb Vasc Biol 31:399-407

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