Comodulation of NO-Dependent Vasodilation by Erythroid Band 3 and Hemoglobin: A GP.Mur Athlete Study

Abstract

GP.Mur, a red blood cell (RBC) hybrid protein encoded by glycophorin B-A-B, increases expression of erythroid band 3 (Anion Exchanger-1, SLC4A1). GP.Mur is extremely rare but has a prevalence of 1–10% in regions of Southeast Asia. We unexpectedly found slightly higher blood pressure (BP) among healthy Taiwanese adults with GP.Mur. Since band 3 has been suggested to interact with hemoglobin (Hb) to modulate nitric oxide (NO)-dependent hypoxic vasodilation during the respiratory cycle, we hypothesized that GP.Mur red cells could exert differentiable effects on vascular tone. Here we recruited GP.Mur-positive and GP.Mur-negative elite male college athletes, as well as age-matched, GP.Mur-negative non-athletes, for NO-dependent flow-mediated dilation (FMD) and NO-independent dilation (NID). The subjects were also tested for plasma nitrite and nitrate before and after arterial occlusion in FMD. GP.Mur+ and non-GP.Mur athletes exhibited similar heart rates and blood pressure, but GP.Mur+ athletes showed significantly lower FMD (4.8 ± 2.4%) than non-GP.Mur athletes (6.5 ± 2.1%). NO-independent vasodilation was not affected by GP.Mur. As Hb controls intravascular NO bioavailability, we examined the effect of Hb on limiting FMD and found it to be significantly stronger in GP.Mur+ subjects. Biochemically, plasma nitrite levels were directly proportional to individual band 3 expression on the red cell membrane. The increase of plasma nitrite triggered by arterial occlusion also showed small dependency on band 3 levels in non-GP.Mur subjects. By the GP.Mur comparative study, we unveiled comodulation of NO-dependent vasodilation by band 3 and Hb, and verified the long-pending role of erythroid band 3 in this process.

Erythroid anion transport, nitric oxide, and blood pressure

“…From a seminal study on Andean high-altitude dwellers with excessive erythrocytosis (EE), a significantly inverse correlation was found between Hb and NO-dependent vasodilation (%FMD) in EE patients ( Tremblay et al, 2019 ). In these GP.Mur+ athletes, we also observed a significantly inverse correlation between Hb and %FMD ( Figure 1B : the correlation is shown as the solid line); this correlation was not found in the control athletes ( Figure 1B : shown as a dotted line as the correlation was not statistically significant) ( Hsu et al, 2021 ). A closer comparison between Tremblay’s and our data revealed a key difference: Hb in the highlanders with EE was abnormally high (20–27 g/dL), and that for the male college athletes in this study with or without GP.Mur was all within the normal range for men (12.5–17 g/dL).…”

“…Ultrasound was used to track vasodilation or the degree of increase in the brachial arterial diameter of each subject during a period of stimulation and recovery (FMD was stimulated by 5-minute vasoconstriction and NID by sublingual nitroglycerin). While NID in GP.Mur+ and the control athletes was not different, FMD measured in the GP.Mur+ athletes was significantly lower than FMD measured in the control athletes (4.6% ± 2.3% [GP.Mur] versus 6.3% ± 2.4% [control]) ( Hsu et al, 2021 ).…”

“…Compared to the controls, the blood pressure in the GP.Mur+ men was ∼60% more dependent on individual Hb levels. The positive correlation between Hb and BP could be caused by the following: (1) more circulating RBCs (as shown with an abnormally higher RBC count and Hb concentrations in high-altitude EE) increase blood viscosity and intravascular pressure ( Tremblay et al, 2019 ), and (2) Hb scavenges intravascular NO species more effectively (as shown with a stronger Hb–FMD correlation and stronger Hb–BP correlation found in GP.Mur+ carriers) ( Figure 1B, C ) ( Hsu et al, 2021 ; Chen et al, 2022 ). Since Hb is enclosed inside the RBC membrane, the second scenario points to the fact that GP.Mur/increased AE1 activities on the RBC membrane could promote Hb scavenging of NO species during blood circulation.…”

“…(B, C) Previous studies on healthy people showed that GPMur/increased AE1 imposes higher sensitivities of FMD and SBP to Hb levels. (B) The Hb–FMD correlation for GP.Mur+ male athletes ( R ∼ 0.53) was replotted using the published data ( Hsu et al, 2021 ). (C) The Hb–SBP correlations for GP.Mur+ men ( R ∼ 0.44) and for control men ( R ∼ 0.37) were replotted using the published data collected at the MMH health check-up center in Eastern Taiwan ( Chen et al, 2022 ).…”

A Balance between Transmembrane-Mediated ER/Golgi Retention and Forward Trafficking Signals in Glycophorin-Anion Exchanger-1 Interaction

“…AE1 is a versatile and functionally important protein that facilitates major physiologic functions (blood CO 2 metabolism and acid-base homeostasis), RBC structural stability, as well as red cell processing of nitric oxide (NO) [ 20 , 21 , 51 , 52 , 53 , 54 , 55 , 56 ]. Glycophorin A, glycophorin B and variants, such as GP.Mur, are involved in AE1 complex formation and surface expression to different extents [ 54 ].…”