Linking red blood cell functional phenotypes to environmental tolerance in high-altitude adapted deer mice

Oxygen (O 2 ) is essential for vertebrate life, and complex cardio-respiratory systems have evolved to transport the gas from the environment to each individual cell. Even short disruptions of this O 2 flux can have deleterious effects that are linked to numerous disease states. Animals that have adapted to hypoxic environments, such as deer mice ( Peromyscus maniculatus) native to high altitude, can provide valuable insight into naturally evolved solutions to O 2 deprivation. Previous work has shown that high-altitude deer mice have evolved a higher hemoglobin O 2 affnity and other coordinated changes across the O 2 transport cascade that enable higher metabolic rates in hypoxia. Red blood cells (RBC) are the functional unit of O 2 and carbon dioxide transport in the blood and play central roles in matching O 2 supply and demand in the microcirculation by releasing signaling molecules such as ATP and gasotransmitters; but how these cellular mechanisms respond to hypoxic environments has not been studied. We hypothesized that high-altitude adaptation in deer mice has improved the function of RBCs for cardiovascular gas transport in hypoxia. Lab-raised breeding colonies of deer-mice were established from wild mice caught at low altitude (~400 m in the Great Plains of Nebraska) and at high altitude (~4300 m in the Rocky Mountains of Colorado). Using a common-garden experimental design, third-generation deer mice from high- and low-altitude populations were acclimated to warm normoxia (21°C, 21 kPa O 2 ) or cold hypobaric hypoxia (5°C, 12 kPa O 2 ) for 8 weeks. Blood samples were collected for measurements of hematocrit, hemoglobin concentration, RBC volume, plasma erythropoietin concentration, RBC contents of membrane transport and channel proteins (anion exchanger, aquaporin 1 and rhesus associated glycoprotein) by immunocytochemistry and western blotting, and carbonic anhydrase activity using biochemical techniques. The release of ATP from RBCs was measured in tonometers at decreasing levels of O 2 by luminometry, and the vascular sensitivity to ATP was determined by wire myography on second-order mesenteric arteries. Finally, bone marrow samples were collected from the femurs to measure gene expression levels in the erythropoietic tissue. Our experimental design allowed us to examine the interactive effects of cold hypoxic environments on RBC phenotype, by untangling environmentally-induced plasticity from the signatures of adaptation that are unique to high-altitude natives. This work is providing a better understanding of how RBC function participates in matching cardiovascular O 2 supply and demand in extreme hypoxia, which has important applications in animal and human health. This work was supported by a NSERC Canada Banting Postdoctoral Fellowship to TSH and a Discovery Grant to GRS. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.