Genetic control of quantitative traits associated with the metabolic syndrome

描述(申请人提供)：最近的生化和遗传学证据有力地支持了肥胖和相关的代谢紊乱是由线粒体功能缺陷发展而来的。这些缺陷产生了由活性氧(ROS)介导的过量细胞氧化应激。一种似乎可以改善代谢紊乱结果的机制是线粒体质子泄漏，即线粒体中能量产生与呼吸作用的解偶联。据报道，解偶联蛋白(UCPs)介导的线粒体呼吸轻度解偶联可以减少动物体内脂肪储存和ROS的产生，有利于改善胰岛素敏感性。利用18个不相关的野生型黑腹果蝇近交系，我们已经证明，自然发生的遗传变异影响骨骼肌线粒体状态4呼吸速率(例如基础质子泄漏)的个体间变异性。我们还表明，骨骼肌线粒体状态4呼吸频率的变化与脂肪储存的变化呈负相关。这表明有些基因具有较高的线粒体偶联效率和较高的脂肪储存量，而另一些基因的偶联效率较低，需要更多的能量来维持线粒体的电化学梯度。这些观察提出了一个重要的问题，即为什么线粒体质子泄漏的变异(例如代谢效率低下)在自然种群中是进化保守的。我们推测，在我们的初步研究中观察到的线粒体状态4呼吸和脂肪储存之间的权衡是相互竞争的生物功能之间有限资源分配的反映。我们的假设是，虽然具有高效线粒体偶联的个体可以成功地利用他们的脂肪储存来繁殖和应对环境挑战，例如对抗感染，但那些偶联效率较低的个体将需要使用更多的能量来维持他们的线粒体电化学梯度，而牺牲了其他生物体的功能。然而，线粒体基质子泄漏可能会减少ROS的产生，从而保护细胞免受退化和衰老的影响。该项目的具体目标是：(1)进行全基因组关联扫描，以绘制影响肌肉特定线粒体生物能量学、ROS产生、能量代谢特征、食物摄入量、先天免疫反应和雌性繁殖力的自然变异的遗传变异。(2)确定幼龄果蝇(3-5日龄)线粒体生物能特性的基因共表达网络。(3)验证目标2中的分析确定的10个“中枢基因”是否负责线粒体生物能量学的协调调节，并影响整个生物体的能量动态平衡和生活史特征。(4)研究先前目标中确定的10个果蝇候选基因在人类同源基因中的遗传变异是否与人类肥胖和相关代谢结果的表型变异有关。这些研究将为线粒体偶联效率的遗传基础提供新的见解，因为它与代谢、免疫反应和生活史特征有关。 公共卫生相关性：这项拟议的研究旨在确定控制骨骼肌特定线粒体偶联效率、全身能量代谢、免疫能力和生物体生活史特征的个体间变异性的调控基因。这些遗传途径将通过整合遗传和表达网络分析在果蝇身上识别出来。利用这些信息，将进行基于人类群体的关联研究，以调查已识别的调控基因的自然变异对与代谢综合征相关的数量性状的影响。

DESCRIPTION (provided by applicant): Recent biochemical and genetic evidence provides strong support that obesity and related metabolic disorders develop from defects in mitochondrial function. These defects produce excess cellular oxidative stress mediated by reactive oxygen species (ROS). One mechanism that appears to improve outcomes in metabolic disorders is mitochondrial proton leak, i.e., the uncoupling of energy production from respiration in the mitochondria. Mild uncoupling in mitochondrial respiration mediated by uncoupling proteins (UCPs) has been reported to decrease fat storage and ROS production in animals and favorably modifies insulin sensitivity. Using 18 unrelated wild-type inbred lines of D. melanogaster, we have shown that naturally occurring genetic variation affects inter-individual variability in mitochondrial state 4 respiration rates (e.g. basal proton leak) in skeletal muscles. We have also shown that variation in mitochondrial state 4 respiration rates in skeletal muscles is negatively correlated with variation in fat storage. This implies that some genotypes have higher mitochondrial coupling efficiency and store higher quantities of fat while other genotypes have lower coupling efficiency and require more energy for maintaining their mitochondrial electrochemical gradient. These observations raise the important question of why variation in mitochondrial proton leak (e.g. metabolic inefficiency) is evolutionary conserved in natural populations. We speculate that the trade-off between mitochondrial state 4 respiration and fat storage observed in our preliminary studies is a reflection of the allocation of finite resources between competing organismal functions. Our hypothesis is that while individuals with efficient mitochondrial coupling can successfully use their fat storage for reproduction and for coping with environmental challenges, such as fighting infection, those with less coupling efficiency will need to use more energy for maintaining their mitochondrial electrochemical gradient at the expense of other organismal functions. However, mitochondrial basal proton leak may decrease ROS generation and, therefore, protect against cellular degeneration and aging. The Specific Aims of this project are to: (1) Perform a genome-wide association scan to map genetic variants affecting naturally occurring variation in muscle-specific mitochondrial bioenergetics, ROS production, energy metabolism traits, food intake, innate immune response, and female fecundity. (2) Determine the gene co-expression network regulating mitochondrial bioenergetic traits in young flies (3-5 days old). (3) Verify whether 10 of the "hub genes" identified by the analyses performed in Aim 2 are responsible for the coordinated regulation of mitochondrial bioenergetics and also impact whole-organism energy homeostasis and life-history traits. (4) Investigate whether genetic variants in human orthologs of the 10 Drosophila candidate genes identified in the previous aims are associated with phenotypic variation in human obesity and related metabolic outcomes. These studies will provide new insights into the genetic basis of mitochondrial coupling efficiency as it relates to metabolic, immune response and life-history traits. PUBLIC HEALTH RELEVANCE: The proposed study has been designed to identify the regulatory genes that control inter-individual variability in skeletal muscle-specific mitochondrial coupling efficiency, whole-body energy metabolism, immunocompetence, and organismal life-history traits. These genetic pathways will be identified by integrating genetic and expression network analysis in Drosophila melanogaster. Using this information, human population-based association studies will be performed to investigate the effect of natural variation in the identified regulatory genes on quantitative traits associated with the metabolic syndrome.