Abstract 45: Critical Residues of the Hemoglobin a / Endothelial Nitric Oxide Synthase Macromolecular Complex Within Endothelial Cells Can Regulate Arterial Reactivity and Blood Pressure

Abstract

Arterial vascular reactivity is a fundamental process to the regulation of blood pressure, blood flow and oxygen delivery and is governed in part by endothelial nitric oxide (NO) synthase (eNOS). We recently demonstrated that monomeric hemoglobin α (Hb α) is 1) expressed in arterial endothelial cells, 2) enriched at the myoendothelial junction, 3) forms a complex with eNOS and 4) regulates the effect of eNOS signaling during vascular reactivity. Based on these results, we hypothesized that a macromolecular complex may form between Hb α and eNOS to regulate NO signaling. In silico modeling of potential Hb α and eNOS protein-protein interaction sites identified a discreet pocket and sequence where Hb α and eNOS may interface. Therefore, we created a TAT-linked peptide identical to the Hb α sequence (Hb α-X) along with a scrambled control (Hb α-scr). Using recombinant eNOS and Hb α protein, we demonstrate by coimmunoprecipitation a loss of protein-protein interaction in the presence of the Hb α-X peptide but not the Hb α-scr. Consistent with these results, the Hb α-X peptide incubated with thoracodorsal arteries exhibited disruption of the Hb α and eNOS complex measured by coimmunoprecpitation and by a proximity ligation technique. Next, we performed vascular reactivity studies, which resulted in significantly altered responses to both phenylephrine and acetylcholine with the Hb α-X peptide, which were reversed with a NOS inhibitor. To test the in vivo effect of these peptides on blood pressure, we administered the peptides to mice via intraperitoneal injection and performed real-time measurements using radio telemetry. Mice injected with the Hb α-X peptide showed a significant decrease in blood pressure (MAP= -10 mmHg). Collectively, these results identify a novel Hb α sequence that is critical for Hb α/eNOS interaction, control of arterial vascular reactivity and regulation of blood pressure.