Mechanisms of oxygen off-loading from red blood cells in murine models of human disease

Red blood cells (RBCs) play a vital role in gas transport—carrying O2 from the alveolar air to systemic tissues, and CO2 in the opposite direction. Their task is central to many diseases of major public-health relevance, in- cluding including heart failure, pulmonary disease (including COVID-19), vascular disease, and sepsis (hy- poperfusion). An important component in the movement of these gases within the body is the transport of these gases across of the plasma membrane (PM) of the RBCs. The dogma had been that all gases cross all mem- branes merely by dissolving in and diffusing through membrane lipids. However, challenging this dogma was the discovery of the first CO2 impermeable membranes, and the first evidence that a gas (CO2) moves through a membrane protein (the water channel aquaporin 1, AQP1). In human RBCs, aquaporin-1 (AQP1) and the Rh complex (including RhAG) account for 90% of membrane CO2 permeability. Preliminary data on O2-offloading from RBCs from knockout (KO) suggests that these two channels, together, are responsible for ~55% of O2 permeability (PM,O2). The addition of the membrane-impermeant inhibitor pCMBS to RBCs from the double- knockout (dKO) mouse reduces PM,O2 by ~90%. Aging mice appear to gradually undergo a decrease in PM,O2 that does not occur in dKOs. A surprising preliminary observation is that the knockout (KO) of one or both of these channels reduces maximal O2 uptake rate (V?O2 max) without decreasing—and, in fact, often increasing—running performance. This grant has two aims. Aim 1 is to determine the extent to which channels vs. lipid composition contribute to the rate of O2 offloading (kHbO2). One approach is to study aging wild-type (WT) vs. KO mice. Another is to examine mice with RBCs genetically depleted or replete in AE1, or depleted in MCT1. The third approach is to examine mice of disease models or widely different genetic background. In each case, the investigators will examine hematology, RBC size and shape, proteomics, lipidomics, and genomics. 3D macroscopic mathemati- cal modeling will play a central role in data interpretation. Finally, the investigators will use exercise protocols to to determine V?O2 max, critical speed, exercise economy, and speed of V?O2 kinetics. They will also examine cardio- vascular and muscle parameters. In Aim 2, the goal is to elucidate the molecular mechanism of O2 movement through AQP1, RhAG, and candidate O2 channels (e.g., AE1). The investigators will use an iterative approach, the first step of which involves identifying prioritizing missense single nucleotide polymorphisms (SNPs), as well as other mutations that come forward in Aim 1. The investigators will use a novel neutral buoyance assay to measure O2 uptake into oocytes and thereby assess these mutants channels. Molecular dynamics and molecular biophysics will complete the iteration before choosing additional laboratory mutation for analysis. The proposed research will reorganize thinking about O2 carriage by blood and could lead to therapies to improve exercise in patients with diminished exercise capacity.