Mechanisms of Iron-Mediated Renal Injury in a Mouse Model of Sickle Cell Disease

Mohammad O. Sako¹, Margi Patel², Savannah Walker², Malgorzata Kasztan¹, ¹Division of Hematology/Oncology, Department of Pediatrics, University of Alabama at Birmingham, ²Division of Nephrology, Department of Medicine, University of Alabama at Birmingham

Sickle cell disease (SCD) is a hematologic disorder characterized by polymerization of the mutated hemoglobin S and sickling of red blood cells, leading to hemolysis, release of free heme/iron, and subsequent tissue iron accumulation. The kidney is one of the most frequently affected organs by iron overload, and chronic hemolysis is associated with chronic kidney disease severity in SCD. The potential role of iron overload in causing the observed renal injury in SCD has never been established. The goal of my study is to identify the impact of iron accumulation on the renal phenotype in SCD and how differences in mitochondrial dysfunction and/or ferroptosis may explain sex differences in kidney injury.

Using humanized SCD mice, we previously demonstrated comparable iron accumulation in the kidney of male and female mice. However, SCD males develop a more severe renal injury, evidenced by proteinuria, than females (2.2 0.2 vs. 0.9 0.1, p<0.0001). Renal iron content correlates with proteinuria in SCD males (R2=0.48, p=0.006), suggesting sex-dependent differences in iron-mediated renal injury in SCD mice. Next, I observed an abundant 4-HNE staining, a hallmark of ferroptosis, in the renal cortex of SCD males, when compared to age-matched controls. Additionally, I observed significantly lower state 3 oxygen consumption rate (108 18 vs 165 9, p=0.05), signifying lower oxidative phosphorylation capacity and complex I-dependent respiration in SCD males. In addition, there was significant reduction in state 4◦ respiration (36.4 3.4 vs. 52.8 3.4 in controls, p=0.03) indicating high proton motive force, decreased O2 flux and subsequent increased ROS production in the mitochondria in male SCD mice. I also detected decrease in maximum complex IV activity in male SCD mice (326 64 vs. 640 51 in controls, p=0.02), which represents high levels of mitochondrial ROS. Taken together, my data may suggest that iron accumulation causes kidney injury via ROS-dependent ferroptosis and mitochondrial dysfunction in SCD mice. Funding: NHLBI–R00HL144817 and ASN Norman Siegel Research Grant.