Targeting NAD Metabolism to Improve Glucose Homeostasis in Obesity and Aging

摘要 针对NOT-AG-20-034：“针对NIH赠款的以阿尔茨海默氏症为重点的行政补充， 不专注于阿尔茨海默病”，我们建议利用最先进的非侵入性成像技术 宾夕法尼亚大学开发的技术，以跟踪脑中烟酰胺腺嘌呤二核苷酸（NAD）的变化 在阿尔茨海默病（AD）的充分表征的5XFAD小鼠模型中， 没有补充的NAD前体。这些实验将测试大脑NAD的变化 浓度预测或与活动物的认知缺陷相关。关键是，基于MRI的成像 所采用的技术易于转化为人类受试者。拟议的研究属于范围 目标2：“确定NAD损害的下游机制 限制和补充前体恢复”，并将增加大量的工作价值， 阿尔茨海默病正在成为NAD代谢可能产生影响的关键领域。 在过去的7年里，多项研究表明，在啮齿动物模型中， 在用烟酰胺核苷（NR）或烟酰胺单核苷酸肽补充动物后的AD。 然而，现有的数据不足以决定性地确定补充是否是有效的。 增加受影响大脑区域的NAD含量，无论NAD水平的变化是否先于认知效应， 或者它们是否与个体动物的认知功能相关。在某些情况下，NAD 从死后的大脑样本中提取和测量，但这不是一个理想的方法，因为它不能 纵向进行，不能区分神经元NAD浓度的变化， 神经元密度，并且不能用于人类（由于明显的原因，在活的患者中，而且在术后， 尸体样本，几乎总是收集得太慢，无法保存代谢物）。MRI解决了所有 这些问题，并将使我们能够澄清NAD代谢的相关性，在啮齿动物使用的技术 可以很容易地转化为人类患者。在拟议的研究中，我们将纵向跟踪 未治疗或给予NR的5XFAD小鼠队列中的认知功能和脑NAD水平 饮用水脑NAD水平将与基于MRI的谷氨酸浓度测量值重叠 （“GluCEST”），其最近已被验证为突触密度的标志物。在9个月大的时候， 将处死队列，以进行AD相关病理学和生物化学的组织学评估。 代谢物浓度的测定。这些实验将推进父母的核心目标 奖，了解在何处以及何时NAD代谢是重要的，并将测试一个假设，可以 导致迫切需要的AD生物标志物，甚至是延迟进展的治疗方法。

Abstract In response to NOT-AG-20-034: “Alzheimer's-focused administrative supplements for NIH grants that are not focused on Alzheimer's disease”, we propose to take advantage of state-of-the art noninvasive imaging techniques developed at Penn in order to follow changes in brain nicotinamide adenine dinucleotide (NAD) levels over time in the well-characterized 5XFAD mouse model of Alzheimer's disease (AD) with and without a supplemental NAD precursor. These experiments will test whether changes in brain NAD concentration anticipate or correlate with cognitive deficits in live animals. Critically, the MRI-based imaging techniques employed are readily translatable to human subjects. The proposed studies fall within the scope of Aim 2 of the parent award: “Determine the downstream mechanisms that are compromised by NAD limitation and restored by supplemental precursors,” and will add substantial value to the work, as Alzheimer's disease is emerging as a key area in which NAD metabolism may have an impact. Over the past 7 years, multiple studies have demonstrated improvements in cognition in rodent models of AD after supplementing animals with either nicotinamide riboside (NR) or nicotinamide mononucleotide. However, the available data are insufficient to determine conclusively whether supplementation is increasing NAD content in affected brain regions, whether changes in NAD levels precede cognitive effects, or whether they correlate with cognitive function on an individual animal basis. In a few cases, NAD was extracted and measured from post-mortem brain samples, but this is not an ideal approach as it cannot be performed longitudinally, cannot distinguish changes in neuronal NAD concentration from changes in neuronal density, and cannot be used in humans (for obvious reasons in living patients, but also in post- mortem samples, which are almost always collected too slowly to preserve metabolites). MRI solves all of these problems and will allow us to clarify the relevance of NAD metabolism in rodents using a technique that can be readily translated to human patients. In the proposed studies, we will longitudinally follow cognition function and brain NAD levels in cohorts of 5XFAD mice that are untreated or given NR in the drinking water. Brain NAD levels will be overlaid with an MRI-based measure of glutamate concentration (“GluCEST”), which has been recently validated as a marker of synaptic density. At 9 months of age, the cohorts will be sacrificed for histological assessments of AD-related pathology and biochemical determination of metabolite concentrations. These experiments will advance the core goals of the parent award, to understand where and when NAD metabolism is important, and will test a hypothesis that could lead to desperately needed biomarkers for AD, or even a therapeutic approach to delay progression.