Heme-induced metabolic stress drives ferroptosis in sickle cell disease

(请保存在Word中，不要保存为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患者存在糖酵解、三羧酸(TCA)循环、核苷酸分解代谢和谷胱甘肽代谢等代谢产物的异常代谢谱。由于这些代谢产物对低氧反应至关重要，导致红细胞镰状，介导炎症反应，并激活氧化应激反应，因此有理由表征这些异常代谢程序促进SCD疾病进展和严重程度的机制。 通过代谢产物谱分析，我们证明溶血中过量的血红素暴露会损害三氯乙酸循环活性，导致2-羟基戊二酸(2OG)的累积水平，这些水平将外流到L-2-羟基戊二酸(L2HG)。累积的2OG和L2HG通过调节依赖于2OG的组蛋白去甲基酶的活性而显示出表观遗传修饰功能，并诱导组蛋白超甲基化。这些异常的表观遗传改变抑制了参与血红素/铁代谢和铁性下垂反应的基因的表达，并导致铁依赖的程序性细胞死亡。过量的血红素也被发现诱导核因子红系2相关因子2(NRF2)的表达，NRF2是氧化应激反应的主要调节因子。在SCD小鼠模型中，NRF2消融增加了L2HG水平和组蛋白甲基化，以影响参与氧化和铁下垂应激反应的基因的表达。根据这些初步发现，我们假设Nrf2/氯化血红素/L2HG信号介导了一种整合的代谢、表观遗传和铁下垂反应程序来调节SCD的严重程度。我们将通过两个具体目标来检验这一假设。目的1.验证一种假说，即在红细胞生成过程中，血红素同时影响代谢和铁链调节通路，从而驱动铁链下垂。目的2.通过调节Nrf2/氯化血红素/L2HG信号通路在临床前SCD动物模型中的治疗潜力。研究结果将表明，Nrf2/氯化血红素/L2HG信号整合了代谢、表观遗传和铁上链程序来调节SCD疾病的严重程度。这种信号将被用于治疗SCD。

(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.