Understanding the roles of cardiac NAD pools and therapeutic effects of precursor supplements in heart failure

了解心脏NAD+池的作用及前体补充剂的治疗作用 心力衰竭 我们正在探索一种假设，即烟酰胺腺嘌呤二核苷酸(NAD+)的代谢可以作为靶点 以提高人类心脏衰竭的功能能力。NAD+是一种普遍存在的分子，作为一种 细胞内数百种酶的氧化还原辅因子或底物。它来自饮食中的色氨酸， 烟酸、烟酰胺或合成中间体，但心脏中的大部分合成是通过烟酰胺。 NAD+浓度在衰竭的人类心脏和一些心力衰竭的啮齿动物模型中下降。高剂量的 包括烟酰胺核苷(NR)和烟酰胺单核苷酸(NMN)在内的前体具有治疗作用 对啮齿动物模型的影响。然而，使用的剂量超过了人类可以容忍的剂量，并有可能导致 与人类相关的剂量的影响仍不确定。我们的初步和公布的结果表明， 在啮齿动物模型中可能需要剂量的NR和NMN，因为这两个分子都被广泛代谢 口服时在肠道和肝脏中，只有一小部分完好无损地到达循环。在……里面 相比之下，静脉注射允许更高比例的剂量到达心脏等器官。 除了有关剂量的问题外，保护机制仍不清楚。据推测， 涉及心脏NAD+水平，但全身补充研究保留了其他 组织起到保护作用，例如通过降低血压。我们呈现的是一只带有 心肌细胞特异性NAD+丢失损害心功能并提出一种新模型的产生 特异性检测线粒体NAD+在心肌细胞内的作用。这将通过以下方式实现 靶向SLC25A51，我们最近发现它是线粒体NAD+转运蛋白。我们提出三个建议 具体目标：目标1)测试心脏特异性NAD+消耗是否足以概括代谢 和心力衰竭的电学后果，目的2)测试替代分娩途径是否可以使心脏 NAD+将通过与人类相关的低剂量在小鼠中拯救，并目的3)测试是否改变线粒体 NAD+足以自行调节心脏功能或改变对诱发性心力衰竭的易感性。我们的 利用AAV靶向SLC25A51在心脏中表达的方法将是第一次对 这种改变线粒体NAD+池的蛋白质已经在体内进行了尝试。总而言之，这些研究将 揭示NAD+代谢如何影响心脏生理的基本细节，并将有助于指导努力 开发治疗或预防人类患者心力衰竭的新的治疗方法。

Understanding the roles of cardiac NAD+ pools and therapeutic effects of precursor supplements in heart failure We are exploring the hypothesis that nicotinamide adenine dinucleotide (NAD+) metabolism can be targeted to improve functional capacity in failing human hearts. NAD+ is a ubiquitous molecule that is required as a redox cofactor or substrate for hundreds of enzymes within the cell. It is derived from dietary tryptophan, niacin, nicotinamide, or synthetic intermediates, but the majority of synthesis in the heart is via nicotinamide. NAD+ concentration falls in failing human hearts and in some rodent models of heart failure. High doses of precursors including nicotinamide riboside (NR) and nicotinamide mononucleotide (NMN) have therapeutic effects in rodent models. However, the doses used exceed what is tolerable in humans and the potential for effects at human-relevant doses remains uncertain. Our preliminary and published results suggest that high doses of NR and NMN may be required in rodent models because both molecules are extensively metabolized in the intestines and liver when delivered orally, with only a tiny fraction reaching the circulation intact. In contrast, intravenous delivery allows a much higher proportion of the dose to reach organs such as the heart. In addition to questions about dosing, the mechanism of protection has remained unclear. It is presumed to involve cardiac NAD+ levels, but whole-body supplementation studies leave open the possibility that other tissues mediate protection, for example through lowering blood pressure. We present a knockout mouse with cardiomyocyte-specific loss of NAD+ that impairs heart function and propose the generation of a new model to specifically test the role of mitochondrial NAD+ within the cardiomyocytes. This will be accomplished by targeting SLC25A51, which we recently identified as the mitochondrial NAD+ transporter. We propose three specific aims: Aim 1) Test whether heart-specific NAD+ depletion is sufficient to recapitulate the metabolic and electrical consequences of heart failure, Aim 2) Test whether alternate delivery routes can allow cardiac NAD+ to be rescued by low, human-relevant doses in mice, and Aim 3) Test whether altering mitochondrial NAD+ is sufficient to modulate heart function on its own or modifies susceptibility to induced heart failure. Our approach of using AAV to target SLC25A51 expression in the heart will be the first time that modulation of this protein to alter the mitochondrial NAD+ pool has been attempted in vivo. Together, these studies will reveal fundamental details of how NAD+ metabolism influences cardiac physiology, and will help guide efforts to develop novel therapeutic approaches for the treatment or prevention of heart failure in human patients.