Role of Carnitine Acetyltransferase in Mitochondrial and Metabolic Function

 描述(由申请人提供)：我们在线粒体功能、能量平衡和代谢组学领域的工作使我们发现心脏代谢不良结果与组织/血液中酰肉碱结合物水平之间存在显著的相关性。这些代谢物来源于燃料分解代谢的酰基辅酶A中间产物，并允许线粒体输出多余的碳。我们的工作模型将酰肉碱定位为线粒体应激的生物标记物和缓解压力的工具。为了验证这一假说，我们一直在研究肉碱乙酰转移酶(CrAT)的代谢和生理意义，CrAT是一种线粒体基质酶，用于将乙酰辅酶A和其他短链酰辅酶A物种转化为膜上的酰基肉碱。在前一个资金周期中，我们确定CrAT的酰基缓冲能力对于正常的燃料选择、血糖控制和运动耐量是必要的。我们最令人兴奋和潜在的重要发现之一是，基因消融小鼠骨骼肌中的CrAT会增加组织中乙酰辅酶A的浓度，并加剧饮食诱导的线粒体蛋白质的乙酰化。赖氨酸乙酰化(ACK)是一种可逆的翻译后蛋白质修饰(PTM)，两个碳乙酰基共价结合到赖氨酸残基的e-氨基上。这种PTM主要存在于线粒体蛋白上，过量的ACK与缺乏sirtuin 3(Sirtuin 3)的小鼠的代谢性疾病有关，sirtuin 3(Sirtuin 3)是线粒体定位的主要去乙酰基酶，可以从特定赖氨酸残基中去除乙酰基。我们的初步数据表明，当乙酰辅酶A的线粒体库扩大时，ACK可以非酶的方式发生。该项目应用最先进的蛋白质组学和代谢组学方法来验证我们的假设，即CrAT和SIRT3协同发挥功能以对抗线粒体碳应激，并且这些酶功能的共存不足有助于代谢疾病背景下的代谢失调。由于CrAT和SIRT3依赖于必需的微量营养素底物L-肉碱和烟酰胺的可用性，我们还将确定同时针对这两个系统的新组合营养策略在应用于肥胖啮齿动物时是否具有相加或协同的代谢益处。

 DESCRIPTION (provided by applicant): Our work in the area of mitochondrial function, energy homeostasis and metabolomics has led us to discover a remarkably strong association between adverse cardiometabolic outcomes and tissue/blood levels of acylcarnitine conjugates. These metabolites derive from acyl-CoA intermediates of fuel catabolism and permit mitochondrial export of excess carbons. Our working model positions acylcarnitines as biomarkers of mitochondrial stress and vehicles of stress relief. To test this hypothesis we have been studying the metabolic and physiological importance of carnitine acetyltransferase (CrAT), the mitochondrial matrix enzyme that converts acetyl-CoA and other short chain acyl-CoA species to their membrane permeant acylcarnitine counterparts. During the previous funding cycle we determined that the acyl group buffering capacity of CrAT is necessary for normal fuel selection, glucose control and exercise tolerance. One of the most exciting and potentially important discoveries we made is that genetic ablation of CrAT in mouse skeletal muscle increases tissue concentrations of acetyl-CoA and exacerbates diet-induced acetylation of mitochondrial proteins. Lysine acetylation (AcK) is reversible post-translational protein modification (PTM) in which a two carbon acetyl group is covalently bound to the e-amino group of a lysine residue. This PTM is found prominently on mitochondrial proteins and excessive AcK has been linked to metabolic disease in mice lacking sirtuin 3 (SIRT3), the principal mitochondrial-localized deacetylase enzyme that removes acetyl groups from specific lysine residues. Our preliminary data suggest AcK can occur non- enzymatically when the mitochondrial pool of acetyl-CoA expands. The proposed project applies state-of-the-art proteomics and metabolomics approaches to test our hypothesis that CrAT and SIRT3 function cooperatively to oppose mitochondrial carbon stress, and that coexisting insufficiencies in the function of these enzymes contribute to metabolic dysregulation in the context of metabolic disease. Because CrAT and SIRT3 depend on availability of essential micronutrient substrates, L-carnitine and nicotinamide, we will also determine whether a new combinatorial nutraceutical strategy that targets the two systems simultaneously might confer additive or perhaps synergetic metabolic benefits when administered to obese rodents.