Neural and molecular mechanisms of glucosensation mediating food choice behavior

描述（由申请人提供）：部分由于肥胖和糖尿病的全球发病率上升，调节进食行为的分子机制受到了广泛关注。然而，尽管我们对食物摄入和新陈代谢如何协调的理解有了巨大的增长，但对进食背后的神经回路和基因却知之甚少。此外，来自代谢（补充能量）和享乐（奖励）喂养回路的信号如何整合以调节食物摄入和食物选择仍然不清楚。虽然已经从哺乳动物模式生物中学到了很多，但由于在这些模型中进行遗传筛选的困难，很少有涉及摄食行为和能量稳态的基因被鉴定出来。因此，使用遗传上适合的模式生物，如果蝇，提供了一个理想的策略，以补充哺乳动物的研究。在我的博士后研究期间，我开发了一种研究果蝇食物选择行为的方法，并发现果蝇具有一种独立于味道检测食物营养价值的机制。具体来说，食物匮乏的苍蝇更喜欢高热量的糖，而不是零热量的甜味剂。通过遗传和行为筛选，我确定了一个保守的基因，这是苍蝇进行代谢性进食选择所必需的。该基因是果蝇钠-葡萄糖转运蛋白（dSGLT）的候选基因，在果蝇脑中的一小部分神经元中表达。我的假设是，dSGLT通过监测血液中的葡萄糖水平来调节食物选择。事实上，在哺乳动物下丘脑中表达的该基因的同源物被认为通过影响神经元的兴奋性在响应葡萄糖水平变化中发挥积极作用，但它们在进食中的作用尚不清楚。由于下丘脑中葡萄糖神经感知的缺陷已被证明在肥胖症的发展中起作用，并导致2型糖尿病，因此更好地理解摄食和代谢基础上的葡萄糖感觉的分子机制至关重要。在该提案中，我提出了一个集中的策略来表征果蝇候选dSGLT在葡萄糖感觉和行为中的功能。我将确定dSGLT是否是一种葡萄糖传感器，以及它如何赋予表达它的神经元葡萄糖传感特性。我将分析表达该基因的神经回路是否是必要的， 足够的代谢糖的选择，以及这些神经元中葡萄糖感觉的动力学如何调节食物选择行为。最后，我将进行两个有针对性的遗传筛选：一个是识别dSGLT神经元中参与葡萄糖传感下游的其他基因，另一个是识别SGLT神经元下游的神经肽和神经肽回路，这些神经肽和神经肽回路介导最终调节食物选择的效应机制。这些研究将提供深入了解葡萄糖感觉的分子机制及其在摄食中的作用。他们还将为哺乳动物研究人员提供保守的基因，作为分子和神经化学标记物，用于未来的葡萄糖感觉，喂养和疾病的研究。

DESCRIPTION (provided by applicant): Due in part to the rise in the worldwide incidence of obesity and diabetes, the molecular mechanisms regulating feeding behavior have received much attention. However, despite the tremendous increases in our understanding of how food intake and metabolism are coordinated, very little is known about the neural circuits and genes underlying feeding. Furthermore, how signals from both metabolic (to replenish energy) and hedonic (for reward) feeding circuits are integrated to regulate food intake and food choice remain unclear. While much has been learned from mammalian model organisms, very few genes involved in feeding behavior and energy homeostasis have been identified because of the difficulty in performing genetic screens in these models. Thus, using a genetically amenable model organism such as the fruit fly provides an ideal strategy to complement mammalian research. During my postdoctoral studies I developed an assay to study food choice behavior in Drosophila and found that flies are equipped with a mechanism to detect the nutritional value of food independently of taste. Specifically, food-deprived flies prefer calorie-rich sugars to zero-calorie sweeteners. Through genetic and behavioral screens, I identified a conserved gene that is required for flies to make metabolic feeding choices. This gene, a candidate Drosophila Sodium-Glucose-Transporter (dSGLT) is expressed in a small subset neurons in the fly brain. My hypothesis is that dSGLT regulates food choice by monitoring glucose levels in the blood. Indeed, homologues of this gene expressed in the mammalian hypothalamus are thought to play an active role in responding to changing glucose levels by affecting the excitability of neurons, but their role in feeding is not known. As defects in neural sensing of glucose in the hypothalamus have been shown to play a role in the development of obesity and contribute to type-2 diabetes, it is of the utmost importance to better understand the molecular mechanism of glucosensation underlying feeding and metabolism. In this proposal I present a focused strategy to characterize the function of the fly candidate dSGLT in glucose-sensation and behavior. I will determine if dSGLT is a glucose sensor and how it confers glucosensing properties to the neurons that express it. I will analyze if the neural circuit expressing this gene is necessary and sufficient for the choice for metabolizable sugars, and how the dynamics of glucosensation in these neurons modulate food choice behavior. Finally, I will conduct two targeted genetic screens: one to identify other genes involved downstream of glucosensing in dSGLT neurons and the other to identify the neuropeptides and neuropeptide circuits downstream of SGLT neurons that mediate the effector mechanisms ultimately regulating food choice. These studies will provide insights into the molecular mechanisms of glucosensation and its role in feeding. They will also provide mammalian researchers with conserved genes to use as molecular and neurochemical markers in future studies of glucosensation, feeding, and disease.