Mitochondrial Retention and Autophagy Dysregulation Drive Oxidative Stress in Sickle Cell Disease Erythrocytes.

Abstract

Sickle cell disease (SCD) is an inherited blood disorder caused by a mutation in the beta-globin gene, leading to hemoglobin polymerization under low oxygen conditions. This results in sickle-shaped red blood cells (Erythrocytes), hemolysis, severe acute and chronic pain, and shortened erythrocyte lifespan. The severity of disease in SCD is linked to the type of hemoglobin mutation, with HbSS causing more frequent and severe than HbSC. We previously identified mitochondrial retention and excessive reactive oxygen species (ROS) production in SCD erythrocytes. Here, we report that SCD patients with the HbSS exhibit significantly higher erythrocyte mitochondrial retention and ROS levels than those with the HbSC. Mitochondrial retention positively correlates with serum bilirubin and LDH, particularly in hydroxyurea-naïve patients. Gene expression analysis using a human autophagy array revealed upregulation of SNCA, GABARAP, GABRAPL2, MAP1LC3B, and CTSB in erythrocyte precursor cells from SCD patients experiencing severe pain. Immunoblot analyses further confirmed accumulation of GABARAP, GABARAPL1, GABARAPL2, cathepsin B, and synuclein-alpha in circulating erythrocytes and plasma from SCD patients compared to controls. Our findings suggest a potential link between dysregulated autophagy proteins and erythrocyte mitochondrial retention in SCD patients, opening new avenues for therapeutic interventions targeting these proteins to mitigate SCD pathogenesis. TEASER ABSTRACT: Sickle cell disease (SCD) causes painful crises due to hemoglobin mutations, with HbSS patients experiencing more severe symptoms than HbSC. We show that HbSS erythrocytes retain more mitochondria and produce higher ROS levels, correlating with bilirubin and LDH, especially in hydroxyurea-naïve individuals. Autophagy-related genes and proteins SNCA, GABARAPs, CTSB are upregulated in erythrocyte precursors and plasma of SCD patients with severe pain. These findings suggest a potential link between dysregulated autophagy proteins and mitochondrial retention in SCD patients, opening new avenues for therapeutic interventions.