Role of SIRT3 in Modulation of Lipotoxicity in Liver

描述（由申请人提供）：Sirtuins是NAD+依赖性蛋白质脱乙酰酶，其介导对多种应激（包括卡路里限制和代谢应激）的适应性应答。Sirtuin 3（SIRT 3）位于线粒体基质内，在那里它调节多种代谢酶的乙酰化水平。虽然在热量限制模型中得到了很好的表征，但对Sirtuins和乙酰化在热量过量条件下的作用知之甚少。我们最近的研究结果表明，当正常小鼠喂食高脂肪饮食时，它们表现出SIRT 3活性降低，线粒体功能受损，以及肝脏中多种蛋白质（包括促凋亡酶）的过度乙酰化。此外，SIRT 3敲除小鼠具有加速衰老和癌症的迹象。了解SIRT 3在热量过剩条件下在肝脏中的生化功能和调节可能有助于解释线粒体功能降低与脂质和葡萄糖代谢紊乱之间的联系，如2型糖尿病和非酒精性脂肪肝（NAFLD）。该提议的直接目的是双重的：1）确定在高脂肪喂养期间肝SIRT 3活性的恢复是否可以减弱肥胖相关的脂肪变性或肝胰岛素抵抗的进展，和2）确定增加肝NAD+（SIRT 3活性的主要决定因素）是否将减弱肥胖相关的线粒体ROS和蛋白质乙酰化。该项目的长期目标是剖析过量营养素如何导致关键蛋白质过度乙酰化的机制，并确定SIRT 3在NAFLD和2型糖尿病易感性中的调节作用。 公共卫生相关性：非酒精性脂肪性肝病（NAFLD）是最常见的营养障碍，目前影响50%的肥胖成年人和1/3的肥胖儿童。最近的研究结果表明，Sirtuin 3（SIRT 3）可能在连接肝脏燃料代谢和线粒体健康方面发挥重要作用。这里提出的研究将调查SIRT 3作为一个有希望的目标，以防止肥胖引起的代谢并发症，包括NAFLD的作用。这些研究的结果将解决SIRT 3活性改变是否有助于肥胖诱导的肝脏脂肪变性，胰岛素抵抗和线粒体功能障碍的进展，并确定增加SIRT 3活性是否可以防止（或至少最小化）这些并发症，为开发NAFLD治疗提供有价值的信息。

DESCRIPTION (provided by applicant): Sirtuins are NAD+-dependent protein deacetylases that mediate adaptive responses to a variety of stresses, including calorie restriction and metabolic stress. Sirtuin 3 (SIRT3) is localized within the mitochondrial matrix, where it regulates acetylation levels of a diverse set of metabolic enzymes. Although well characterized in models of caloric restriction, relatively little is known about the role of Sirtuins and acetylaion under conditions of caloric excess. Our recent results show that when normal mice are fed a high fat diet they demonstrate reduced SIRT3 activity, impaired mitochondrial function, and hyperacetylation of a diverse set of proteins, including gluconeogenic enzymes, in their livers. Furthermore, SIRT3 knockout mice have signs of accelerated aging and cancer. Understanding SIRT3's biochemical function and regulation in the liver under conditions of caloric excess may potentially help explain the connection between reduced mitochondrial function and disorders of lipid and glucose metabolism, such as type 2 diabetes and nonalcoholic fatty liver disease (NAFLD). The immediate purpose of this proposal is two-fold: 1) determine if restoration of hepatic SIRT3 activity during high fat feeding can attenuate the progression of obesity- related steatosis or hepatic insulin resistance, and 2) Determine whether increasing hepatic NAD+, the major determinant of SIRT3 activity, will attenuate obesity-linked mitochondrial ROS and protein acetylation. The long-term goal of this project is to dissect the mechanisms surrounding how excess nutrients lead to hyperacetylation of key proteins and to identify a regulatory role for SIRT3 in NAFLD and susceptibility to type 2 diabetes. PUBLIC HEALTH RELEVANCE: Nonalcoholic fatty liver disease (NAFLD) is the most common nutritional disorder, currently affecting 50 percent of obese adults and 1/3 of obese children. Recent findings indicate that Sirtuin 3 (SIRT3) may play an important role linking hepatic fuel metabolism and mitochondrial health. The studies proposed here will investigate the role of SIRT3 as a promising target to protect against obesity-induced metabolic complications, including NAFLD. Findings from these studies will resolve whether altered SIRT3 activity contributes to the progression of obesity-induced liver steatosis, insulin resistance, and mitochondrial dysfunction, and determine if increasing SIRT3 activity can protect against (or at least minimize) these complications, providing valuable information for developing treatments for NAFLD.