Beta-arrestin Regulation of Ghrelin Signaling in Modulating Addictive Behavior

描述(由申请人提供)：在美国，超过2000万人使用非法药物对经济和医疗资源的分配都产生了负面影响。滥用药物会干扰大脑的多巴胺奖励系统，导致一种模型，在该模型中，吸毒和寻找毒品的行为被认为是中枢神经系统的病理。从疾病的角度来看，药物滥用可以通过寻求将多巴胺信号恢复正常的药物疗法来治疗。调节食物摄入的内源性激素Ghrelin似乎是中枢神经系统多巴胺信号的最强调节器之一，因此Ghrelin受体可能是对抗成瘾行为的主要靶点。与典型的G蛋白偶联受体(GPCRs)一样，GHSR1a ghrelin受体通过两条途径传递信号，一条由G蛋白调节，另一条由Arrestin(？arr)蛋白调节。因此，每个信号臂都是经典配体或新发现的功能选择性偏向配体进行药理调节的潜在靶点。然而，GHSR1a介导对滥用药物的反应的信号事件以及ARR的相对贡献，可能对多巴胺能回路可塑性的调节具有重要作用，目前还没有很详细的信息。我们的NIDA(国家药物滥用研究所)赞助的P30中心有一个项目，用于识别和表征有助于理解和治疗药物滥用的小分子GPCR配体。我们认为，GHSR1a是治疗成瘾的一个杰出的药理靶点，ARR信号将在调节多巴胺能信号方面发挥重要作用。为了验证我们的假设，我们有两个具体的目标：1.使用模型细胞系统来表征GHSR1a信号转导通路。我们将(A)确定ARR和G蛋白对GHSR1a转运和信号转导的贡献，(B)修改GHSR1a和ARRs之间相互作用的分子决定因素，(C)评估ARR和G蛋白信号偏向，以及(D)建立高通量和二级筛选来识别ARR/G蛋白偏向的配体；2.使用动物模型确定ARR在GHSR1a介导的行为中的作用。我们将在野生型和arr2基因敲除(Arr2KO)小鼠中建立，药物抑制和/或激活GHSR1a会改变对可卡因的行为反应，同时确定arr2在这些反应中的作用。这些从基础研究角度的研究将评估Ghrelin受体对奖赏寻求行为调控的重要性；在细胞和动物模型中提供一个框架，用于研究经典的Ghrelin受体配体以及识别和表征功能选择性的配体。这些研究还将为未来与ARR1KO小鼠和多巴胺受体亚型KO小鼠的比较研究提供一个范例。总之，我们从临床角度的研究为快速、安全地开发Ghrelin信号以减少药物使用和药物寻找行为奠定了重要的基础。

DESCRIPTION (provided by applicant): The use of illicit drugs by over twenty millions individuals in the United States negatively impacts both the economy and allocation of medical resources. Drugs of abuse can interfere with the brain's dopamine reward system, leading to a model in which drug taking and drug seeking behaviors are considered pathologies of the central nervous system. When viewed in the perspective of a disease, drug abuse becomes treatable with pharmacological therapies that seek to restore dopamine signaling to normal. The endogenous hormone ghrelin, which regulates food intake, appears to be one of the strongest modulators of CNS dopamine signaling underlying reward, and thus ghrelin receptors may be prime targets for antagonizing addictive behaviors. The GHSR1a ghrelin receptor, like typical G protein coupled receptors (GPCRs), signals through two pathways, one regulated by G-proteins and the other by ¿-arrestin (¿arr) proteins. Each signaling arm is thus a potential target for pharmacological regulation by either classical ligands or the newly recognized class of functionally selective biased ligands. However, the signaling events by which GHSR1a mediates the response to drugs of abuse and the relative contribution of ¿arr, which may be important to the modulation of dopaminergic circuit plasticity, have not been well detailed. Our NIDA (National Institute on Drug Abuse) sponsored P30 Center has a program in place to identify and characterize small molecule GPCR ligands useful for understanding and treating drug abuse. We believe the GHSR1a presents an outstanding pharmacological target for treating addiction and that ¿arr signaling will play an important role in modulating dopaminergic signaling to this end. To test our hypotheses we have two specific aims: 1. Characterize GHSR1a signal transduction pathways using a model cell system. We will (a) determine the contribution ¿arr versus G protein to GHSR1a trafficking and signaling, (b) modify molecular determinants underlying the interaction between GHSR1a and ¿arrs, (c) evaluate ¿arr versus G protein signaling bias and (d) establish a high throughput and secondary screens to identify ¿arr/G protein biased ligands; 2. Determine the role of ¿arrs in GHSR1a-mediated behaviors using an animal model. We will establish in wild-type and ¿arr2 knockout (¿arr2KO) mice that pharmacological suppression and/or activation of GHSR1a produces a change in the behavioral responses to cocaine while determining the role of ¿arr2 in these responses. These studies from a basic research perspective will assess the importance of ¿arrs to ghrelin receptor regulation of reward seeking behavior; providing in cell and animal models a framework for investigating classical ghrelin receptor ligands as well as identifying and characterizing functionally selective ones. These studies will also provide a paradigm for future comparative investigations with ¿arr1KO mice and dopamine receptor subtype KO mice. Altogether, our studies from a clinical perspective lay crucial groundwork for the expeditious and safe pharmacological exploitation of ghrelin signaling to reduce drug use and drug-seeking behaviors.