Cell-specific Modulation of Feeding Behavior by Serotonin 2C Receptor RNA Processing

5-羟色胺受体的2C亚型（5HT2C）与许多人类精神和行为障碍有关。然而，该受体最具特征的功能涉及由弓状核中产生前阿黑皮素（POMC）的神经元中的5HT 2C受体表达介导的厌食反应 调节进食行为和能量平衡。编码5HT2C的转录本 受体可以通过RNA加工事件进行差异修饰，包括选择性剪接和腺苷- 去肌苷（A-to-I）编辑。5HT2C转录物可以经历多达五次A-to-I编辑事件，以生成多达 24种蛋白质同种型在G蛋白偶联功效和组成性活性方面不同，而选择性剪接 可以产生受体的截短形式（5HT 2C-tr），其通过异源二聚化和将全长受体隔离在内质网内来降低受体信号传导。因此， 5HT2C RNA可能代表了一种重要的调节机制，通过这种机制，神经元可以通过改变在神经元中表达的功能不同的5HT2C同种型的身份来调节它们对变化的细胞外信号的反应性。 特定的神经元细胞类型。不幸的是，在许多大脑区域和内部的异质表达， 不同的神经元群体阻碍了理解5HT2C RNA加工如何促进特定回路或行为的调节的努力。拟议研究的长期目标 是为了定义调节5HT2C表达和信号传导的细胞机制，以及5HT2C加工和摄食相关病理之间的可能关系。最近的研究发现， 5HT2C受体表达和5HT2C介导的行为在小鼠模型和诊断为 Prader-Willi综合征（PWS）。此外，突变小鼠仅被工程化以表达完全编辑的5HT2C。 受体同种型表现出PWS的表型特征，包括不能茁壮成长和断奶后摄食过多。因此，RNA编辑和剪接对摄食行为具有显著影响，表明5HT2C转录物的不适当加工可能是摄食和代谢紊乱的一个促成因素。在本申请中，可以在POMC中诱导5HT2C-tr表达的突变小鼠系 将表征神经元以评估5HT2C-tr调节对体内5HT2C信号传导的功能重要性。 为了评估操纵5HT2C RNA加工是否代表一种生理机制， 神经元依赖的喂养信号被调制，三个不同的模型系统将被用来检查 饮食、运动和药物操作对POMC神经元中5HT 2C RNA加工的影响。最后， 我们将测试特定的、编辑过的5HT2C受体亚型拯救摄食过多、成熟期发作的能力。 当仅在POMC中诱导表达时，肥胖和II型糖尿病与5HT2C-无效表型相关 神经元预期所提出的研究将提供关键的见解，人类的分子病因学 与进食和能量平衡改变有关的疾病。

The 2C-subtype of serotonin receptor (5HT2C) has been implicated in numerous human psychiatric and behavioral disorders. The best-characterized function for this receptor however, involves an anorectic response mediated by 5HT2C receptor expression in pro-opiomelanocortin (POMC)-producing neurons in the arcuate nucleus of the hypothalamus to modulate feeding behavior and energy homeostasis. Transcripts encoding the 5HT2C receptor can be modified differentially by RNA processing events that include alternative splicing and adenosine- to-inosine (A-to-I) editing. 5HT2C transcripts can undergo up to five A-to-I editing events to generate as many as 24 protein isoforms that differ in G-protein coupling efficacy and constitutive activity, while alternative splicing can produce a truncated version of the receptor (5HT2C-tr) which decreases receptor signaling by heterodimerization and sequestration of the full-length receptor within the endoplasmic reticulum. Thus, the processing of 5HT2C RNAs may represent a critical regulatory mechanism by which neurons can modulate their responsiveness to changing extracellular signals by altering the identity of functionally distinct 5HT2C isoforms expressed in specific neuronal cell types. Unfortunately, heterogeneous expression in many brain regions and within different neuronal populations has hampered efforts to understand how 5HT2C RNA processing contributes to the modulation of specific circuits or behaviors. The long-term objectives of the proposed research are to define the cellular mechanisms that regulate 5HT2C expression and signaling, as well as possible relationships between 5HT2C processing and feeding-related pathologies. Recent studies have identified alterations in both 5HT2C receptor expression and 5HT2C-mediated behaviors in mouse models and patients diagnosed with Prader-Willi Syndrome (PWS). Furthermore, mutant mice engineered solely to express the fully edited 5HT2C receptor isoform exhibit phenotypic characteristics of PWS including a failure to thrive and post-weaning hyperphagia. Thus, RNA editing and splicing have dramatic consequences on feeding behavior suggesting that improper processing of 5HT2C transcripts may represent a contributing factor to disorders of feeding and metabolism. In the current application, mutant mouse lines in which expression of the 5HT2C-tr can be induced in POMC neurons will be characterized to assess the functional importance of 5HT2C-tr modulation for 5HT2C signaling in vivo. To assess whether manipulation of 5HT2C RNA processing represents a physiological mechanism by which neuron-dependent feeding signals are modulated, three distinct model systems will be used to examine the effects of diet, exercise and pharmacologic manipulation on 5HT2C RNA processing in POMC neurons. Finally, we will test the ability of specific, edited isoforms of the 5HT2C receptor to rescue the hyperphagia, maturity-onset obesity and type II diabetes associated with the 5HT2C-null phenotype when inducibly expressed solely in POMC neurons. It is anticipated that the proposed studies will provide critical insights into molecular etiology of human disorders associated with alterations in feeding and energy homeostasis.