Requirement of 5-HT2CRs in POMC and SIM1 neurons to Regulate Energy Homeostasis

描述(申请人提供)：5-羟色胺(5-HT)和相关的激动剂被很好地描述为作用于下丘脑弓状核和室旁核(ARH和PVH)中其受体(5HT2CR)的2C亚型，以抑制食物摄取和发挥减肥作用。相反，这种作用所需的ARH和PVH中5-羟色胺和相关激动剂的特定神经元靶点还没有很好的定义。最近的工作是选择性地将5HT2CR的表达恢复到ARH内的前阿片黑素皮质素(POMC)神经元，发现这个独特的神经元亚群是一个很有可能成为靶点的亚群。这一观点是基于有证据表明，选择性地重新激活POMC神经元中的5HT2CRs可以拯救5HT2CR缺失小鼠的肥大和肥胖表型。本申请的初步数据还强调，PVH中的SIM1神经元共表达5HT2CRs，可能是5-羟色胺和相关激动剂靶向的一种神经元。目前的建议旨在测试5-羟色胺及其相关激动剂是否需要在ARH和PVH的POMC和SIM1神经元上分别表达5HT2CR，以维持正常体重并发挥减肥作用。这将通过将POMC或SIM1神经元内源性5HT2CR选择性缺失的基因工程小鼠模型与能量稳态的综合分析以及5-羟色胺激动剂间氯苯基哌嗪(MCPP)和D-芬氟拉明(d-Fen)的管理相结合来实现。在POMC或SIM1神经元中使用cre-lox技术选择性缺失5HT2CRs的小鼠模型为评估这些通路的生理相关性和需求提供了一个强大而独特的模型。分析这些小鼠表型的综合方法将包括对小鼠模型的组织学验证，以及对大脑发育和神经存活的评估。代谢笼研究也将在喂食食物和高脂肪饮食的小鼠身上进行，以评估食物的摄入量、能量消耗和体力活动。综上所述，这些方法将提供对5-羟色胺和相关激动剂在中枢神经系统的影响的机械性洞察。预期的结果是，5-羟色胺及其相关激动剂将需要POMC和SIM1神经元维持正常体重动态平衡，并完全介导mCPP和d-Fen的减肥作用。这些发现将提高我们对身体如何控制能量动态平衡的理解，并可能提供新的治疗靶点。 与公共健康相关：5-羟色胺(5-羟色胺)和相关的药理激动剂通过激活下丘脑弓状核和室旁核(ARH和PVH)中的2C亚型的5-羟色胺受体(5HT2CR)来抑制食物摄取和减轻体重。本实验的目的是确定5-羟色胺及其相关激动剂是否需要在ARH中的前阿片黑素皮质素(POMC)神经元和/或PVH中的SIM1神经元中表达5HT2CR来发挥减肥作用。拟议中的研究将提高我们对5-羟色胺如何作用于大脑特定神经元以控制能量动态平衡的理解，并可能确定对抗肥胖的新治疗靶点。

DESCRIPTION (provided by applicant): Serotonin (5-HT) and related agonists are well characterized to act upon the 2C isoform of its receptor (5HT2CR) in the arcuate and paraventricular nuclei of the hypothalamus (ARH and PVH) to suppress food intake and exert anti-obesity effects. The specific neuronal targets of 5-HT and related agonists in the ARH and PVH required for such effects are, in contrast, not well defined. Recent work in which 5HT2CR expression was selectively restored to pro-opiomelanocortin (POMC) neurons within the ARH identifies that this distinct neuronal sub-set is a strong candidate to be a target. This notion is based on evidence that selective re- activation of 5HT2CRs in POMC neurons rescues the hyperphagic and obese phenotype of 5HT2CR-null mice. Preliminary data in this application also highlights that simple-minded 1 (SIM1) neurons in the PVH co-express 5HT2CRs and may be one type of neuron targeted by 5-HT and related agonists. The current proposal aims to test whether 5-HT and related agonists require 5HT2CR expression in POMC and SIM1 neurons in the ARH and PVH, respectively, to maintain normal body weight and to exert anti-obesity effects. This will be accomplished by combining genetically engineered mouse models in which endogenous 5HT2CR are selectively deleted in either POMC or SIM1 neurons with comprehensive analyses of energy homeostasis and administration of 5-HT agonists m-chloro-phenylpiperazine (mCPP) and D-fenfluramine (d-Fen). The proposed mouse models in which 5HT2CRs will be selectively deleted using cre-lox techniques in either POMC or SIM1 neurons provide a powerful and unique model to assess the physiological relevance and requirement for these pathways. The comprehensive approach to analyze the phenotype of these mice will include histological validation of the mouse model as well as assessments of brain development and neural survival. Metabolic cages studies will also be performed in mice fed chow and high-fat diet to assess food intake, energy expenditure, and physical activity. Taken together, these approaches will provide mechanistic insight into the effects of 5-HT and related agonists in the CNS. The expected findings are that 5-HT and related agonist will require POMC and SIM1 neurons to maintain normal body weight homeostasis and to fully mediate the anti- obesity effects of mCPP and d-Fen. These findings would improve our understanding about how the body controls energy homeostasis and potentially offer new therapeutic targets. PUBLIC HEALTH RELEVANCE: Serotonin (5-HT) and related pharmacological agonists suppress food intake and reduce body weight by activating the 2C isoform of the 5-HT receptor (5HT2CR) in the arcuate and paraventricular nuclei of the hypothalamus (ARH and PVH). The objective of the proposed experiments is to determine whether 5-HT and related agonists require 5HT2CR expression in proopiomelanocortin (POMC) neurons in the ARH and/or simple-minded 1 (SIM1) neurons in the PVH to exert anti-obesity effects. The proposed studies will improve our understanding about how 5-HT acts in specialized neurons of the brain to control energy homeostasis and may identify novel therapeutic targets to combat obesity.