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

了解心脏NAD+池的作用和前体补充剂的治疗作用， 心力衰竭 我们正在探索的假设，烟酰胺腺嘌呤二核苷酸（NAD+）代谢可以针对 来改善衰竭心脏的功能NAD+是一种普遍存在的分子， 氧化还原辅因子或细胞内数百种酶的底物。它来源于膳食色氨酸， 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+浓度福尔斯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）和烟酰胺单核苷酸肽（NMN）的前体具有治疗作用， 在啮齿动物模型中的作用。然而，使用的剂量超过了人类可耐受的剂量， 在人类相关剂量下的影响仍然不确定。我们的初步和发表的结果表明，高 在啮齿动物模型中可能需要NR和NMN剂量，因为这两种分子都被广泛代谢 当口服时，在肠道和肝脏中，只有一小部分完整地到达循环。在 相比之下，静脉内递送允许更高比例的剂量到达器官，例如心脏。 除了剂量问题外，保护机制仍不清楚。据推测， 涉及心脏NAD+水平，但全身补充研究留下了其他可能性， 组织介导保护，例如通过降低血压。我们给一只敲除小鼠 心肌细胞特异性NAD+损失损害心脏功能，并提出了一种新的模型的产生 以专门测试线粒体NAD+在心肌细胞中的作用。这将通过 靶向SLC25A51，我们最近确定为线粒体NAD+转运蛋白。我们提出了三 1）测试心脏特异性NAD+消耗是否足以概括代谢性NAD+消耗。 目的2）测试替代递送途径是否可以允许心脏起搏， 在小鼠中通过低的人类相关剂量拯救NAD+，目的3）测试是否改变线粒体 NAD+本身足以调节心脏功能或改变对诱导心力衰竭的易感性。我们 使用AAV靶向心脏中的SLC 25A51表达的方法将是第一次调节 已经尝试在体内使用这种蛋白质来改变线粒体NAD+库。这些研究将 揭示NAD+代谢如何影响心脏生理学的基本细节，并将有助于指导工作， 开发用于治疗或预防人类患者心力衰竭的新治疗方法。

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.