Glucose And BCAA Metabolism in the Heart

描述（由申请人提供）：底物代谢对心脏的正常生物学和生理学至关重要。随着肥胖症和糖尿病发病率的不断上升，人们对心脏代谢，特别是缺血和衰竭心脏中的葡萄糖和脂质代谢的兴趣得到了更新和证实。大量的研究集中在葡萄糖和脂肪酸之间的底物偏好在心脏病发展中的转变。然而，心脏中其他种类底物的代谢，如氨基酸，很少被研究。最近，越来越多的证据表明，支链氨基酸的代谢在心血管和代谢性疾病的发生过程中发生了显著的改变。代谢组学技术的应用表明，血中支链氨基酸（BCAA）及相关代谢物水平与胰岛素抵抗和冠心病密切相关；与支链氨基酸相关的代谢物特征可以预测肥胖患者的干预结果，并且对治疗性干预有独特的反应。在动物研究中，补充BCAA可以促进高脂肪饮食背景下的胰岛素抵抗，但可以延长正常饮食小鼠的平均寿命，并增强心肌和骨骼肌的线粒体生物发生和功能。这些数据主要来自代谢组学和营养学研究，提出了BCAA细胞代谢及其调控机制的问题。支链氨基酸，如亮氨酸、异亮氨酸和缬氨酸，是哺乳动物必需的氨基酸。支链氨基酸的分解代谢是维持体内支链氨基酸稳态的关键步骤。线粒体定位蛋白磷酸酶2C （PP2Cm）是激活BCAA分解代谢的关键酶，其缺失导致心脏BCAA分解代谢受损，加剧了心脏对应激的反应，这表明BCAA分解代谢在心脏对应激的反应中起着重要作用。我们对心脏中BCAA分解代谢的调节知之甚少，也不知道它与其他底物代谢的关系。通过使用心脏特异性过表达胰岛素独立葡萄糖转运蛋白GLUT1 （GLUT1- tg）的小鼠模型，我们获得了令人兴奋的初步数据，证明细胞内葡萄糖增加通过转录机制下调BCAA分解代谢。这使我们假设葡萄糖和BCAA的代谢稳态是通过一个涉及Klf15和胰岛素敏感性的互惠调节回路实现的。本研究拟探讨葡萄糖与心脏BCAA代谢之间的机制联系，具体目的如下：1)验证葡萄糖通过转录因子Klf15及其靶基因调控BCAA分解代谢的假说；2)确定葡萄糖或BCAA利用改变对心脏底物代谢的整体影响，并验证BCAA分解代谢受损促进胰岛素抵抗的假设；3)验证BCAA分解代谢缺陷通过损害糖代谢和线粒体功能加速慢性应激期心力衰竭发展的假说。

DESCRIPTION (provided by applicant): Substrate metabolism is essential for the normal biology and physiology of the heart. The soaring incidence of obesity and diabetes has renewed and substantiated interest on cardiac metabolism, in particular, the glucose and lipids metabolism, in the ischemic and failing hearts. A large number of studies have focused on the shift of substrate preference between glucose and fatty acids in the development of heart diseases. However, metabolism of other classes of substrates in the heart, such as amino acids, has rarely been studied. Recently, emerging evidence suggests that the metabolism of branched-chain amino acids is significantly altered during the development of cardiovascular and metabolic diseases. Application of metabolomics technology has shown that blood levels of branched-chain amino acids (BCAA) and related metabolites are strongly associated with insulin resistance and coronary heart disease; the BCAA-related metabolites signature is predictive of intervention outcomes in patience with obesity and it is uniquely responsive to therapeutic interventions. In animal studies, BCAA supplementation promotes insulin resistance on high-fat diet background but increases average lifespan of mice on normal diet and enhances mitochondrial biogenesis and function in cardiac and skeletal muscle. These data, mostly generated by metabolomics and nutritional studies, raise the question of cellular metabolism of BCAA and its regulatory mechanisms. BCAAs, e.g. leucine, isoleucine and valine, are essential amino acids for mammals. Catabolism of BCAAs is a key step in maintaining BCAA homeostasis in the body. Impairment of BCAA catabolism in the heart due to the deletion of mitochondrial localized protein phosphatase 2C (PP2Cm), a key enzyme in activating BCAA catabolism, exacerbates cardiac responses to stress suggesting an important role of BCAA catabolism for cardiac response to stress. Little is known about the regulation of BCAA catabolism in the heart, nor of its relationship to the metabolism of other substrates. Using a mouse model with cardiac specific overexpression of insulin independent glucose transporter GLUT1 (GLUT1-TG) we have generated exciting preliminary data demonstrating that increased intracellular glucose down regulates BCAA catabolism through transcriptional mechanisms. This leads us to hypothesize that the metabolic homeostasis of glucose and BCAA is achieved via a reciprocal regulatory circuit involving Klf15 and insulin sensitivity. Here we propose to investigate the mechanistic link between glucose and BCAA metabolism in the heart through the following specific aims: 1) to test the hypothesis that glucose regulates BCAA catabolism via transcription factor Klf15 and its target genes; 2) To determine the global impact of altered glucose or BCAA utilization on cardiac substrate metabolism and to test the hypothesis that impaired BCAA catabolism promotes insulin resistance; 3) To test the hypothesis that defective BCAA catabolism accelerates the development of heart failure during chronic stress by impairing glucose metabolism and mitochondrial function.