Elucidating the Role of Endothelial NAD Metabolism in Atherosclerosis

项目摘要 在美国，即使在积极的临床治疗背景下，动脉粥样硬化仍然是导致死亡的主要原因。 以及公共卫生努力降低高脂血症等危险因素。因此，非常需要更好的 了解动脉粥样硬化发病机制，以开发新的治疗策略 循环风险因素的下游。动脉粥样硬化的发病机制始于动脉的内皮层 壁：内皮细胞功能障碍（ECD）和EC炎症先于动脉粥样硬化斑块形成， 与不良心血管事件相关。ECD和EC炎症均随年龄增长而增加，年龄是一个重要因素。 动脉粥样硬化的主要不可改变的危险因素。重要的是，烟酰胺的沉默调节蛋白（SIRT）家族的活化 腺嘌呤二核苷酸（NAD+）依赖性脱乙酰酶，特别是SIRT 1，已被报道减缓多种 与年龄相关的表型特别是，我们的实验室和其他实验室已经表明，内皮细胞NAD+的水平 随着年龄的增长而减少，SIRT 1的内皮特异性过表达足以减缓ECD， 动脉粥样硬化的进展。此外，在老年小鼠中口服给予NAD+前体增加了 主动脉SIRT 1表达和活性，并减少ECD，表明增加NAD+可用性可以促进 老年EC中的SIRT 1活性。因此，NAD+平衡的丧失似乎是动脉粥样硬化形成的中心，但知之甚少 EC是如何维持NAD稳态的活体小鼠中NAD+前体的定量通量分析具有 最近发现，肝源性烟酰胺（NAM）是主要的循环NAD+前体， 组织中这表明，NAM磷酸核糖基转移酶（NAMPT），催化第一个和第二个磷酸核糖基转移酶。 NAM合成NAD+的限速步骤，对于产生内皮NAD+和维持内皮细胞的功能至关重要。 NAD+依赖性酶的活性。因此，我假设内皮NAMPT是细胞自主的， 需要产生NAD+和维持内皮SIRT 1活性，并且内皮NAMPT 过表达将防止动脉粥样硬化的进展。为了验证这个假设，我们有 产生内皮特异性功能获得（GOF）和功能丧失（LOF）NAMPT小鼠模型。在Aim中 1，我将使用培养的初级动脉EC和稳定同位素碳示踪结合定量通量分析 以计算NAMPT NAD+产生和SIRT 1 NAD+消耗的速率。我还将确定NAMPT是否 SIRT 1脱乙酰活性需要NAMPT活性，如果NAMPT活化足以维持SIRT 1活性， 在氧化应激下。在目标2中，我将测试NAMPT GOF或口服NAD+补充剂是否足以减缓 动脉粥样硬化的进展，以及NAMPT LOF是否加速动脉粥样硬化。最终，这项工作将改善 了解EC NAD+代谢及其在维持SIRT 1活性中的作用，并告知NAMPT激活 和/或NAD+补充可能是减少动脉粥样硬化负担的治疗途径 独立于循环危险因素如高脂血症。

Project Summary Atherosclerosis remains a leading cause of death in the United States, even in the context of aggressive clinical and public health efforts to lower risk factors such as hyperlipidemia. Thus, there is a significant need for better mechanistic understanding of atherosclerosis pathogenesis in order to develop novel therapeutic strategies downstream of circulating risk factors. Atherosclerosis pathogenesis begins in the endothelial layer of the arterial wall: endothelial cell dysfunction (ECD) and EC inflammation precede atherosclerotic plaque formation and are associated with adverse cardiovascular events. Both ECD and EC inflammation increase with age, and age is a major non-modifiable risk factor for atherosclerosis. Importantly, activation of sirtuin (SIRT) family of nicotinamide adenine dinucleotide (NAD+) - dependent deacetylases, particularly SIRT1, has been reported to slow a variety of age-associated phenotypes. In particular, our lab and others have shown that levels of endothelial NAD+ decrease with age, and that endothelial-specific overexpression of SIRT1 is sufficient to slow ECD and progression of atherosclerosis. Furthermore, oral administration of NAD+ precursors in aged mice increases aortic SIRT1 expression and activity, and reduces ECD, suggesting that increasing NAD+ availability can promote SIRT1 activity in aged ECs. Loss of NAD+ balance thus appears to be central to atherogenesis, but little is known about how ECs maintain NAD homeostasis. Quantitative flux analysis of NAD+ precursors in live mice has recently uncovered that liver-derived nicotinamide (NAM) is the main circulating NAD+ precursor that reaches tissues. This suggests that the enzyme NAM phosphoribosyltransferase (NAMPT), which catalyzes the first and rate-limiting step in NAD+ synthesis from NAM, is critical for producing endothelial NAD+ and maintaining the activity of NAD+ - dependent enzymes. Thus, I hypothesize that endothelial NAMPT is cell-autonomously required to produce NAD+ and maintain endothelial SIRT1 activity, and that endothelial NAMPT overexpression will protect against progression of atherosclerosis. To test this hypothesis, we have generated endothelial-specific gain-of-function (GOF) and loss-of-function (LOF) NAMPT mouse models. In Aim 1, I will use cultured primary arterial ECs and stable isotope carbon tracing coupled with quantitative flux analysis to calculate rates of NAMPT NAD+ production and SIRT1 NAD+ consumption. I will also determine if NAMPT activity is required for SIRT1 deacetylation activity, and if NAMPT activation is sufficient to maintain SIRT1 activity upon oxidative stress. In Aim 2, I will test if NAMPT GOF or oral NAD+ supplementation is sufficient to slow progression of atherosclerosis, and if NAMPT LOF accelerates atherosclerosis. Ultimately, this work will improve understanding of EC NAD+ metabolism and its role in maintaining SIRT1 activity, and inform if NAMPT activation and/or NAD+ replenishment could be a therapeutic avenue for reducing the burden of atherosclerosis independently of circulating risk factors such as hyperlipidemia.