Hemoglobin βCys93 is essential for cardiovascular function and integrated response to hypoxia

Area of Science:

• Physiology
• Biochemistry
• Cardiovascular Science

Background:

• Hemoglobin (Hb) is crucial for oxygen delivery in vertebrates.
• A conserved cysteine residue (βCys93) in Hb's β-chain is implicated in S-nitrosothiol (SNO)-mediated hypoxic vasodilation by red blood cells (RBCs).
• The precise physiological role of βCys93 and RBC-mediated vasodilation remains incompletely understood.

Purpose of the Study:

• To investigate the physiological significance of the conserved βCys93 residue in hemoglobin.
• To elucidate the molecular basis of hypoxic vasodilation and blood flow autoregulation.
• To determine the necessity of βCys93-derived S-nitrosothiol (SNO) bioactivity for cardiovascular function and adaptation to hypoxia.

Main Methods:

• Generation and analysis of mice with a βCys93Ala mutation in hemoglobin.
• Assessment of peripheral blood flow and tissue oxygenation under normoxic and hypoxic conditions.
• Evaluation of cardiac function, fetal viability, and survival rates in mutant mice.

Main Results:

• Mice with the βCys93Ala mutation exhibited impaired hypoxic vasodilation and reduced blood flow autoregulation.
• Mutant animals showed decreased baseline peripheral blood flow and tissue oxygenation, with excessive decline during hypoxia.
• βCys93Ala mutation led to myocardial ischemia under normoxia, acute cardiac decompensation, and increased mortality during hypoxia, along with diminished fetal viability.

Conclusions:

• βCys93-derived SNO bioactivity is essential for maintaining tissue oxygenation within the respiratory cycle.
• This bioactivity is critical for normal cardiovascular function and the circulatory system's adaptation to hypoxic stress.
• The study clarifies the molecular mechanism underlying blood flow autoregulation and the vital role of RBCs in oxygen homeostasis.