Red blood cell-mediated S-nitrosohemoglobin-dependent vasodilation: lessons learned from a β-globin Cys93 knock-in mouse

RT Premont, JD Reynolds, R Zhang… - Antioxidants & Redox …, 2021 - liebertpub.com
Antioxidants & Redox Signaling, 2021liebertpub.com
Significance: Red blood cell (RBC)-mediated vasodilation plays an important role in oxygen
delivery. This occurs through hemoglobin actions, at least in significant part, to convert heme-
bound nitric oxide (NO)(in tense [T]/deoxygenated-state hemoglobin) into vasodilator S-
nitrosothiol (SNO)(in relaxed [R]/oxygenated-state hemoglobin), convey SNO through the
bloodstream, and release it into tissues to increase blood flow. The coupling of hemoglobin
R/T state allostery, both to NO conversion into SNO and to SNO release (along with oxygen) …
Significance: Red blood cell (RBC)-mediated vasodilation plays an important role in oxygen delivery. This occurs through hemoglobin actions, at least in significant part, to convert heme-bound nitric oxide (NO) (in tense [T]/deoxygenated-state hemoglobin) into vasodilator S-nitrosothiol (SNO) (in relaxed [R]/oxygenated-state hemoglobin), convey SNO through the bloodstream, and release it into tissues to increase blood flow. The coupling of hemoglobin R/T state allostery, both to NO conversion into SNO and to SNO release (along with oxygen), under hypoxia supports the model of a three-gas respiratory cycle (O2/NO/CO2).
Recent Advances: Oxygenation of tissues is dependent on a single, strictly conserved Cys residue in hemoglobin (βCys93). Hemoglobin couples SNO formation/release at βCys93 to O2 binding/release at hemes (“thermodynamic linkage”). Mice bearing βCys93Ala hemoglobin that is unable to generate SNO-βCys93 establish that SNO-hemoglobin is important for R/T allostery-regulated vasodilation by RBCs that couple blood flow to tissue oxygenation.
Critical Issues: The model for RBC-mediated vasodilation originally proposed by Stamler et al. in 1996 has been largely validated: SNO-βCys93 forms in vivo, dilates blood vessels, and is hypoxia-regulated, and RBCs actuate vasodilation proportionate to hypoxia. Numerous compensations in βCys93Ala animals to alleviate tissue hypoxia (discussed herein) are predicted to preserve vasodilatory responses of RBCs but impair linkage to R/T transition in hemoglobin. This is borne out by loss of responsivity of mutant RBCs to oxygen, impaired blood flow responses to hypoxia, and tissue ischemia in βCys93-mutant animals.
Future Directions: SNO-hemoglobin mediates hypoxic vasodilation in the respiratory cycle. This fundamental physiology promises new insights in vascular diseases and blood disorders.
Mary Ann Liebert