Pathogenic Role of IL-18 in Sickle Cell Cardiomyopathy and Inducible Ventricular Tachycardia

摘要：镰状细胞病患者表现为心血管症状和猝死。 是导致过早死亡的首要原因。不幸的是，这些因素导致了平均水平的停滞。 这些患者的预期寿命(在第四个十年)在过去20年里，又一次深刻的健康 在非裔美国人(AA)中观察到的差异。尽管扩展了对定义特征的理解 包括全身血管闭塞发作和溶血，缺乏联系心脏的信息。 从病理学到过早死亡。使用系统生物学方法，我们已经产生了非常新颖的 一种以前未被识别的人镰状心肌病的特征信息，其定义为 心肌纤维化、舒张期功能障碍、复极延长和诱发性室性心动过速 “人性化”的镰刀鼠模型。这些研究进一步证明了循环显著上调。 IL18基因表达是一种已建立的炎症体和促纤维化介质，由游离血红素上调，在 镰刀状心肌病。此外，暴露于IL-18是诱发镰刀鼠室性心动过速的关键因素。 初步数据进一步表明，心肌钾通道的表达和活性降低 (KCND2/KCND3)，可延长复极，使IL-18介导的急剧增加 NADPH氧化酶4(NOX4)的表达，后者是活性氧合物种(ROS)的关键来源，以及 诱导心脏细胞凋亡。我们进一步表明，长期抑制IL-18可减少心脏细胞凋亡， 镰刀形小鼠心肌IL-18受体(IL-18R)减少和心肌IL-18R减少，纤维化和改善舒张期功能 NOX4表达。最后，我们的基因组研究确定了与以下基因相关的新的多态 IL18表达增强和校正QT间期延长是室性心动过速的危险因素。因此， 通过三个特定的目标(SA)，R01将询问IL-18/IL-18- 18R/NOX4信号严重下调KCND2和KCND3功能并促进心肌 纤维化持续激活，加重镰状心肌病和室性心动过速发展。SA#1将 在单核细胞系中从功能上验证血红素介导的包括SNPs在内的IL18启动子调控。SA#2 将定义IL-18/IL-18R/NOX4信号如何急剧下调KCND2/KCND3功能，从而导致 长时间的复极和慢性，会导致心肌细胞凋亡和纤维化。SA#3将定义 预防镰状细胞相关诱导性室性心动过速策略的疗效。从以下方面获得的知识 该R01将直接转化为未来评估心脏性猝死风险的临床生物标记物研究 突出那些溶血负荷、致病性IL18 SNP和循环IL-18水平较高的患者 理论上有更高的室性心动过速风险。此外，这些数据将测试有效和新颖的个性化治疗方法 一种鲜为人知的致命的镰状细胞病表现。

ABSTRACT: Individuals with sickle cell disease exhibit cardiovascular manifestations and sudden death as the top causes of premature death. These factors, unfortunately, contribute to the plateauing of the average life expectancy of these patients (in the 4th decade) over the past two decades, yet another profound health disparity observed in African Americans (AAs). Despite expanded understanding of the defining features including systemic vaso-occlusive episodes and hemolysis, there is a paucity of information linking cardiac pathology to premature death. Using system biology approaches, we have generated highly novel information characterizing a previously unrecognized human sickle cardiomyopathy defined by myocardial fibrosis, diastolic dysfunction, prolonged repolarization, and inducible ventricular tachycardia (VT) in the “humanized” sickle mouse model. These studies further demonstrated significant upregulation of circulating IL18 gene expression, an established inflammasome and pro-fibrotic mediator upregulated by free heme, in sickle cardiomyopathy. Additionally, exposure to IL-18 was a key factor in inducing VT in sickle mice. Preliminary data further link decreased expression and activity of cardiac potassium channels (KCND2/KCND3) in sickle mice, which can prolong repolarization, to acute increases in IL-18-mediated NADPH oxidase 4 (Nox4) expression, the latter a key source of reactive oxygenation species (ROS) and induction of cardiac apoptosis. We have further shown that chronic IL-18 inhibition reduces cardiac apoptosis, fibrosis and improves diastolic function in sickle mice coupled with reduced cardiac IL-18 receptor (IL-18R) and Nox4 expression. Finally, our genomic studies have identified novel polymorphisms (SNPs) associated with enhanced IL18 expression and prolonged corrected QT (QTc) interval, an established risk factor for VT. Thus, via three specific aims (SAs), this R01 will interrogate the mechanistic basis for the hypothesis that IL-18/IL- 18R/Nox4 signaling critically downregulates KCND2 and KCND3 function acutely and promotes myocardial fibrosis with sustained activation, exacerbating sickle cardiomyopathy and VT development. SA #1 will functionally validate heme-mediated IL18 promoter regulation including SNPs in a monocyte cell line. SA #2 will define how IL-18/IL-18R/Nox4 signaling acutely downregulates KCND2/KCND3 function leading to prolonged repolarization and chronically, results in cardiac apoptosis and fibrosis. SA #3 will define the therapeutic efficacy of strategies to prevent sickle cell-associated inducible VT. The knowledge gained from this R01 will directly translate into future clinical biomarker studies evaluating risk of sudden cardiac death highlighting those patients with a higher hemolytic burden, pathogenic IL18 SNPs, and circulating IL-18 levels with theoretically higher VT risk. Additionally, the data will test for effective and novel personalized therapies in a poorly recognized and fatal manifestation of sickle cell disease.