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

5-羟色胺受体(5HT2C)的2C亚型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弓状核中产生阿片黑素皮质素原(POMC)的神经元中5HT2C受体的表达所介导的厌食反应 调节摄食行为和能量平衡的下丘脑。编码5HT2C的转录产物 受体可以通过RNA加工事件进行差异修饰，其中包括选择性剪接和腺苷- 对肌苷(A对I)编辑。5HT2C转录可以经历最多五个A-to-I编辑事件，以生成多达 24个G蛋白偶联效率和构成活性不同的蛋白质异构体，而选择性剪接 可以产生受体的截断版本(5HT2C-TR)，它通过内质网内全长受体的异源二聚和隔离来减少受体信号。因此，处理 5HT2C RNA可能代表着一种关键的调控机制，神经元可以通过改变表达在 特定的神经细胞类型。不幸的是，在许多大脑区域和内部的异质性表达 不同的神经元群体阻碍了理解5HT2C RNA处理如何对特定电路或行为进行调节的努力。拟议研究的长期目标 是为了确定调控5HT2C表达和信号的细胞机制，以及5HT2C处理和摄食相关病理之间的可能关系。最近的研究已经确定了在 5HT2C受体的表达和5HT2C介导的行为在小鼠模型和诊断为 Prader-Willi综合征(PWS)。此外，突变小鼠只表达完全编辑的5HT2C 受体亚型表现出PWS的表型特征，包括无法生长和断奶后的吞噬功能亢进。因此，RNA编辑和剪接对摄食行为有显著的影响，这表明对5HT2C转录本的不当处理可能是导致摄食和代谢障碍的一个因素。在目前的应用中，可以在POMC中诱导表达5HT2C-TR的突变小鼠系 在活体中，神经元的特征将被用来评估5HT2C-TR调制对5HT2C信号的功能重要性。 评估5HT2C RNA加工的操纵是否代表一种生理机制，通过这种机制 神经元依赖的馈入信号是调制的，将使用三个不同的模型系统来检查 饮食、运动和药物操作对POMC神经元5HT2C RNA加工的影响最后， 我们将测试特定的、编辑过的5HT2C受体亚型的能力，以挽救过度吞噬、成熟发作 仅在POMC中诱导表达5HT2C缺失表型与肥胖和II型糖尿病相关 神经元。预计拟议的研究将为人类的分子病因学提供重要的见解。 与进食和能量动态平衡改变相关的疾病。

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.