Metabolic stimulation improves bioenergetics and haematologic indices of circulating erythrocytes from sickle cell mice

Abstract

Circulating mature red blood cells (RBCs) from patients and mice with sickle cell disease (SCD) abnormally retain mitochondria, a factor shown to contribute to the disease's pathobiology. To further understand the functional implications of RBC mitochondria retention in SCD, we used mitochondria inhibitors and metabolites/substrates from the tricarboxylic acid cycle, oxidative phosphorylation and glycolysis pathways (ADP, glutamate, malate, pyruvate, succinate or all metabolites combined) and examined RBC bioenergetics, reactive oxygen species (ROS) levels, calcium flux and hydration. In RBCs from sickle mice, mitochondria inhibition reduced ATP levels by 30%-60%, whereas control RBCs were unaffected. Conversely, in vitro treatment with metabolites/substrates known to stimulate mitochondria function increased RBC ATP levels and reduced RBC ROS, and these effects were notably more pronounced in sickle RBCs compared to those in control mice. In sickle RBCs, the increases in ATP and decreases in ROS were associated with greater decreases in RBC baseline calcium concentration and improvements in calcium flux. These changes also led to greater increases in RBC volume and hydration, and greater decreases in mean corpuscular haemoglobin concentration in sickle RBCs compared to control RBCs. These results propose a novel model of RBC metabolism in SCD, where retained mitochondria in circulating RBCs are functional and can significantly impact RBC bioenergetics, ATP production and RBC hydration and redox status. These in vitro findings could inform the development of in vivo strategies aimed at increasing RBC ATP, reducing RBC ROS, improving RBC hydration, which could decrease sickling and prove beneficial in SCD. KEY POINTS: Red blood cells (RBCs) from humans and mice with sickle cell disease (SCD) abnormally retain mitochondria. Mitochondria inhibitors lower ATP in circulating RBCs from sickle mice indicating that retained mitochondria contribute to ATP levels in sickle RBC. Metabolic stimulation of mitochondria function improves RBC bioenergetics, redox state and calcium flux, and increases RBC hydration. These data propose a new model of RBC metabolism in SCD, where in addition to glycolysis, retained mitochondria contribute to RBC ATP production. The effects of metabolic stimulation of RBCs resulting in improved RBC bioenergetics and hydration may prove beneficial in SCD.

Keywords: bioenergetics; calcium; haemoglobin; haemoglobinopathy; mitochondria; red blood cell; redox; sickle cell.