Heme-induced metabolic stress drives ferroptosis in sickle cell disease

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(PLEASE KEEP IN WORD, DO NOT PDF) Individuals with sickle cell disease (SCD) have severe anemia due to chronic red blood cell hemolysis and increased oxidative stress. SCD patients present abnormal metabolome profiling for metabolites involved in glycolysis, the tricarboxylic acid (TCA) cycle, nucleotide catabolism, and glutathione metabolism. As those metabolites are critical for the hypoxic response, contributing to RBC sickling, mediating inflammation, and activating oxidative stress response, it is warranted to characterize the mechanism by which those aberrant metabolic programs contribute to the SCD disease progression and severity. By metabolite profiling analysis, we demonstrate that excess heme exposure from hemolysis impairs the TCA cycle activity, leading to accumulated levels of 2-Oxoglutarate (2OG), which will outflow towards L-2-hydroxyglutarate (L2HG). The accumulated 2OG and L2HG display epigenetic modification functions through regulating the enzymatic activity of 2OG-dependent histone demethylases and induce histone hypermethylation. These aberrant epigenetic changes suppress the expression of genes involved in heme/iron metabolism and ferroptosis response and cause iron-dependent programmed cell death ferroptosis. Excess heme was also found to induce the expression of nuclear factor erythroid 2-related factor 2 (Nrf2), a master regulator of the oxidative stress response. Nrf2 ablation in SCD mouse model increased both L2HG levels and histone methylation to affect the expression of genes involved in oxidative and ferroptosis stress response. From these preliminary findings, we hypothesize that the Nrf2/hemin/L2HG signaling mediates an integrated metabolic, epigenetic, and ferroptotic response program to regulate SCD severity. We will test this hypothesis with two specific aims. Aim 1. To test the hypothesis that heme affects both metabolic and ferroptotic regulatory pathways to drive ferroptosis during erythropoiesis. Aim 2. To evaluate the therapeutic potential by modulating the Nrf2/hemin/L2HG signaling in preclinical SCD animal model. Findings from the studies will illustrate that the Nrf2/hemin/L2HG signaling integrates metabolic, epigenetic and ferroptotic programs to modulate the severity of SCD disease. Such signaling would be therapeutically exploitable for SCD treatment.