Neurochemistry/physiology of proopiomelanocortin neurons

描述（由申请人提供）：肥胖及其2型糖尿病并发症目前是全球主要的健康问题。过去十年的研究已经确定了下丘脑弓状核和孤束核（NTS）在中枢神经系统控制食欲和能量消耗中的关键作用。我们和其他人已经表明，表达阿黑皮素原（POMC）的肽能神经元，位于这两个核团内，是介导能量稳态的神经回路的关键细胞元件。黑皮质素肽，包括α、β和γ-黑素细胞刺激激素和促肾上腺皮质激素，抑制进食并增加代谢率。神经黑皮质素受体（MC 4-R和MC 3 -4）或POMC的突变导致人类和啮齿动物模型的肥胖，强调了这类神经肽递质的重要性。相比之下，POMC衍生的β-内啡肽刺激摄食并介导可口食物的行为强化特性。我们最近发现，相当大比例的POMC神经元还合成经典的快速抑制性神经递质γ-氨基丁酸（GABA），这一发现挑战了广泛持有的假设，即POMC神经元将共表达兴奋性氨基酸递质谷氨酸。GABA以前共定位在邻近人群的食欲，神经肽Y/agglutinase基因相关的转录神经元在弓状核，这通常反对POMC神经元的功能。基于这些数据和其他研究表明POMC神经元在其个体对激素和突触信号的反应中存在质的差异，我们假设POMC神经元不是同质细胞的同步群体，而是由在能量平衡中具有不同作用的亚群组成。此外，我们假设，从POMC神经元的GABA和肽调节剂的协调释放可能是其在自身受体的作用机制的一个关键方面，和其他神经元的突触前和突触后位点。因此，本项目的总体目标是进一步描绘弓状核和NTS内POMC神经元亚群的神经化学基础，并将这些亚群与它们在代谢率和食物摄入调节中的特定作用相匹配。具体目标是：1）利用新开发的具有POMC的选择性神经元缺陷的突变小鼠模型来确定不同黑皮质素受体配体在中枢神经系统能量稳态控制中的特定生理功能;（2）映射共同-GABA和POMC肽在POMC神经元的弓状核和下丘脑投射内的定位，并测试来自POMC神经元的GABA释放如何与POMC神经元的释放和黑皮质素和β-内啡肽对能量稳态的生理活性;和3）使用以下遗传技术探测弓状核和NTS的功能组织：a）通过转基因定向的毒素递送对所选POMC神经元组的细胞特异性消融;和B）聚集嵌合体分析，以并置脑内野生型和POMC缺陷型神经元的多种不同组合。这些研究的结果有望显著增加我们对体重调节所涉及的脑区和机制的基本理解，并为预防和治疗肥胖症带来新的治疗方法。

DESCRIPTION (provided by applicant): Obesity and its complications stemming from type 2 diabetes mellitus are now leading health concerns worldwide. Research in the past decade has established a critical role for the arcuate nucleus of the hypothalamus and the nucleus tractus solitarius (NTS) in the CNS control of appetite and energy expenditure. We and others have shown that peptidergic neurons expressing proopiomelanocortin (POMC), located within both of these nuclei, are key cellular elements of the neural circuits that mediate energy homeostasis. The melanocortin peptides, including alpha, beta, and gamma-melanocyte stimulating hormones and adrenocorticotrophic hormone inhibit feeding and increase metabolic rate. Mutations in either of the neural melanocortin receptors (MC4-R and MC3-4) or POMC cause obesity in humans and rodent models, emphasizing the importance of this class of neuropeptide transmitter. In contrast, POMC derived beta-endorphin stimulates feeding and mediates the behavioral reinforcing properties of palatable food. We have recently discovered that a substantial proportion of POMC neurons also synthesize the classical, fast inhibitory neurotransmitter gamma-amino butyric acid (GABA), a finding that challenges the widely held assumption that POMC neurons would coexpress the excitatory amino acid transmitter glutamate. GABA was previously co-localized in an adjacent population of orexigenic, neuropeptide Y/agouti gene-related transcript neurons in the arcuate nucleus, which generally oppose the function of POMC neurons. Based on these data and other studies showing qualitative differences among POMC neurons in their individual responses to hormonal and synaptic signals, we hypothesize that POMC neurons are not a synchronized population of homogenous cells, but instead composed of subpopulations with distinct roles in energy balance. Furthermore, we postulate that the coordinated release of GABA and peptide modulators from POMC neurons may be a key aspect of their mechanism of action at autoreceptors, and pre- and postsynaptic sites on other neurons. Therefore, the overall goal of this project is to further delineate the neurochemical basis of subpopulations of POMC neurons within the arcuate nucleus and NTS and to match these subpopulations with their specific actions in the regulation of metabolic rate and food intake. The specific aims are to: 1) Utilize a newly developed mutant mouse model with selective neuronal deficiency of POMC to determine the specific physiological functions of the different melanocortin receptor ligands in the central nervous system control of energy homeostasis; 2) Map the co-localization of GABA and POMC peptides within the arcuate nucleus and hypothalamic projections of POMC neurons and test how GABA release from POMC neurons is integrated with the release and physiological activity of melanocortins and beta-endorphin on energy homeostasis; and 3) Probe the functional organization of the arcuate nucleus and NTS using the genetic techniques of: a) Cell-specific ablation of selected groups of POMC neurons by transgene-directed toxin delivery; and b) Aggregation chimera analysis to juxtapose multiple different combinations of wild-type and POMC-deficient neurons within the brain. Results from these studies are expected to significantly increase our basic understanding of the brain areas and mechanisms involved in the regulation of body weight and lead to new therapeutic approaches for the prevention and treatment of obesity.