Examination of Bovine Red Blood Cell Death in Vitro in Response to Pathophysiologic Proapoptotic Stimuli

Background : Interspecies variations in mammalian red blood cells (RBCs) are observed in circulating RBC lifespan, cell size, fluidity, aggregation, water permeability, metabolism, lipid composition, and the overall proteome. Bovine RBC cell membrane is deficient in phosphatidylcholine and exhibits anomalies in the arrangement of phosphatidylethanolamine within the lipid bilayer. However, like human RBCs, virtually all the aminophospholipid phosphatidylserine (PS) is found within the cytoplasmic side of the cell membrane of intact circulating bovine RBCs. During apoptotic cell death of human and murine RBCs, PS translocates to the outer leaflet of the cell membrane via Ca 2+ -dependent and -independent signaling mechanisms. However, little is known about this process in bovine RBCs. Methods : Using cytofluorometry analyses, we characterized and compared the cell death responses in bovine and human RBCs in vitro exposed to various pathophysiologic cell stressors. Results : Ionic stress, by ionophore treatment, and oxidative stress enhanced cytoplasmic Ca 2+ levels and cell membrane PS expression in both bovine and human RBCs. Fever-grade hyperthermia and energy starvation promoted Ca 2+ influx and elevated reactive oxygen species levels in both human and bovine RBCs. However, bovine RBCs displayed minimal increases in PS expression elicited by hyperthermia, energy starvation, and extracellular hypertonicity as compared to human RBCs. In response to decreased extracellular osmolality, bovine RBCs exhibited significantly enhanced fragility as compared to human RBCs. Conclusions : Bovine RBCs display differential cell death patterns as compared to human RBCs, only partly explained by increased Ca 2+ influx and oxidative stress. Premature removal of circulating RBCs could potentially contribute to the pathogenesis of anemia in cattle caused by a wide range of factors such as systemic diseases, parasitic infections, and nutritional deficiencies.