Nicotinamide nucleotide transhydrogenase regulates redox balance in atherosclerosis

动脉粥样硬化是血管壁的一种进行性慢性炎症性疾病，在整个疾病发展过程中受氧化应激调节。内皮功能障碍是动脉粥样硬化发展的关键启动步骤，越来越多的证据表明线粒体活性氧（ROS）是内皮功能障碍和血管炎症的重要因素。烟酰胺核苷酸转氢酶（NNT）作为一种重要的酶在线粒体NADPH水平的调节中逐渐出现，它可以通过调节线粒体氧化还原张力（ROS产生和去除的平衡）对许多代谢途径产生重大影响。我们的初步数据支持这一概念，并表明C57Bl/6J （6J）细胞中NNT的缺失导致了不同的线粒体生物能量谱和促氧化线粒体表型，其特征是超氧化物产生增加和谷胱甘肽过氧化物酶活性降低。有趣的是，我们发现与C57Bl/6N （6N）相比，6J动物更容易受到高脂肪饮食诱导的斑块形成的影响。在两种动物中，斑块的形成是由血浆脂质的增加引起的。然而，线粒体靶向超氧化物歧化酶模拟物MitoTEMPO对6N和6J动物的血脂和斑块形成有明显的影响。MitoTEMPO治疗降低了6N动物的血脂，但没有降低6J动物的血脂，令人惊讶的是，它加剧了6J动物的斑块形成，这表明线粒体活性氧的产生在这些动物动脉粥样硬化的发展中起着关键作用。基于这些发现，我们提出NNT活性的丧失有助于促进线粒体氧化表型，通过增强线粒体ROS的产生、内皮功能障碍和血管炎症来加剧动脉粥样硬化的进展。为了验证这一假设，研究人员提出将确定i) NNT是否抑制线粒体ROS产生并保持人血管内皮细胞正常的内皮•NO功能；ii) NNT表达的减少是否会增加线粒体ROS的产生并刺激Nox活性，从而导致内皮功能障碍；iii)内皮细胞NNT是否对高脂饮食小鼠的线粒体氧化还原张力和血管功能起到关键调节作用。拟议研究的数据将确定NNT是线粒体功能和ROS产生的主要调节因子，其缺失通过促进内皮功能障碍和血管炎症，导致斑块发展增加，从而加剧动脉粥样硬化的发展。

Atherosclerosis, a progressive chronic inflammatory disease of the vessel wall, is regulated by oxidant stress throughout the course of disease development. Endothelial dysfunction is a critical, initiating step in the development of atherosclerosis and increasing evidence implicates mitochondrial reactive oxygen species (ROS) as an important contributor to endothelial dysfunction and vascular inflammation. Nicotinamide nucleotide transhydrogenase (NNT) is emerging as an important enzyme in the regulation of mitochondrial NADPH levels which can have a significant impact on a number of metabolic pathways through the regulation of mitochondrial redox tone (balance of ROS production and removal). Our preliminary data supports this concept and indicates that that the absence of NNT in C57Bl/6J (6J) cells led to distinct mitochondrial bioenergetic profiles and a pro-oxidative mitochondrial phenotype characterized by increased superoxide production and reduced glutathione peroxidase activity. Interestingly, we found that 6J animals are more susceptible to high fat diet induced plaque formation compared to C57Bl/6N (6N). Plaque formation was driven by increased plasma lipids in both animals. However, treatment with the mitochondria targeted superoxide dismutase mimetic MitoTEMPO had distinct effects on serum lipids and plaque formation in the 6N and 6J animals. MitoTEMPO treatment reduced plasma lipids in the 6N animals but not the 6J, and surprisingly, exacerbated plaque formation in the 6J animals, demonstrating a critical role for the production of mitochondrial reactive oxygen species in the development of atherosclerosis in these animals. Building upon these findings, we propose that the loss of NNT activity contributes to a pro-oxidative mitochondrial phenotype that exacerbates the progression of atheroscelrosis by enhancing mitochondrial ROS production, endothelial dysfunction, and vascular inflammation. To test this hypothesis, studies are proposed that will determine i) if NNT inhibits mitochondrial ROS production and preserves normal endothelial •NO function in human vascular endothelial cells; ii) if reduced NNT expression will increase mitochondrial ROS production and stimulate Nox activity that contributes to endothelial dysfunction; and iii) if endothelial NNT critically regulates mitochondrial redox tone and vascular function in mice treated with high fat diet. Data from the proposed studies will identify NNT as a master regulator of mitochondrial function and ROS production whose absence exacerbates the development of atherosclerosis by promoting endothelial dysfunction and vascular inflammation, leading to increased plaque development.