Heme-induced metabolic stress drives ferroptosis in sickle cell disease

（请保持文字，不要PDF） 镰状细胞病（SCD）患者由于慢性红细胞溶血和氧化应激增加而患有严重贫血。SCD患者存在参与糖酵解、三羧酸（TCA）循环、核苷酸催化剂和谷胱甘肽代谢的代谢物的异常代谢组谱。由于这些代谢物对缺氧反应至关重要，有助于RBC镰状化，介导炎症和激活氧化应激反应，因此有必要表征这些异常代谢程序导致SCD疾病进展和严重程度的机制。 通过代谢物谱分析，我们证明，过量的血红素暴露于溶血损害TCA循环活性，导致2-酮戊二酸（2 OG）的积累水平，这将流向L-2-羟基戊二酸（L2 HG）。积累的2 OG和L2 HG通过调节2 OG依赖的组蛋白去甲基化酶的酶活性而显示表观遗传修饰功能，并诱导组蛋白高甲基化。这些异常的表观遗传变化抑制了血红素/铁代谢和铁凋亡反应相关基因的表达，并导致铁依赖性程序性细胞死亡铁凋亡。过量的血红素也被发现诱导核因子红细胞2相关因子2（Nrf 2），一个主调节器的氧化应激反应的表达。SCD小鼠模型中的Nrf 2消融增加了L2 HG水平和组蛋白甲基化，从而影响参与氧化和铁凋亡应激反应的基因的表达。从这些初步的发现，我们假设Nrf 2/氯化血红素/L2 HG信号介导的综合代谢，表观遗传，和铁蛋白反应程序，以调节SCD的严重程度。我们将以两个具体目标来检验这一假设。目标1.验证血红素影响红细胞生成过程中代谢和铁凋亡调节途径以驱动铁凋亡的假设。目标2.在临床前SCD动物模型中评价通过调节Nrf 2/hemin/L2 HG信号传导的治疗潜力。这些研究的结果将说明Nrf 2/氯化血红素/L2 HG信号转导整合了代谢、表观遗传和铁促凋亡程序，以调节SCD疾病的严重程度。这种信号传导将在治疗上可用于SCD治疗。

(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.