Beta-arrestin Regulation of Ghrelin Signaling in Modulating Addictive Behavior

描述（由申请人提供）：美国有超过2000万人使用非法药物，对经济和医疗资源的分配产生负面影响。滥用药物会干扰大脑的多巴胺奖励系统，导致一种模式，在这种模式中，吸毒和寻求毒品的行为被认为是中枢神经系统的病理学。从疾病的角度来看，药物滥用是可以通过药物治疗来治疗的，药物治疗旨在使多巴胺信号恢复正常。调节食物摄入的内源性激素胃饥饿素似乎是中枢神经系统多巴胺信号潜在奖励的最强调节剂之一，因此胃饥饿素受体可能是对抗成瘾行为的主要目标。GHSR1a饥饿素受体，像典型的G蛋白偶联受体（gpcr）一样，通过两条途径发出信号，一条由G蛋白调节，另一条由ß-阻滞蛋白（ßarr）调节。因此，无论是经典配体还是新发现的一类功能选择性偏配体，每个信号臂都是药理学调控的潜在靶标。然而，GHSR1a介导药物滥用反应的信号事件和ßarr的相对贡献可能对多巴胺能回路可塑性的调节很重要，但尚未得到很好的详细说明。我们的NIDA（国家药物滥用研究所）赞助的P30中心有一个项目，用于识别和表征对理解和治疗药物滥用有用的小分子GPCR配体。我们相信GHSR1a是治疗成瘾的一个突出的药理学靶点，而ßarr信号将在调节多巴胺能信号中发挥重要作用。为了验证我们的假设，我们有两个具体的目标：1。利用模型细胞系统表征GHSR1a信号转导通路。我们将(a)确定ßarr与G蛋白对GHSR1a运输和信号传导的贡献，(b)修改GHSR1a与ßarrs之间相互作用的分子决定因素，(c)评估ßarr与G蛋白信号传导偏倚，(d)建立高通量和二级筛选来鉴定ßarr/G蛋白偏倚配体；2. 利用动物模型确定ßarrs在ghsr1a介导的行为中的作用。我们将在野生型和ßarr2敲除（ßarr2KO）小鼠中建立药物抑制和/或激活GHSR1a产生对可卡因行为反应的变化，同时确定ßarr2在这些反应中的作用。这些研究将从基础研究的角度评估ßarrs对胃饥饿素受体调节寻求奖励行为的重要性；在细胞和动物模型中提供研究经典胃饥饿素受体配体以及识别和表征功能选择性配体的框架。这些研究也将为未来ßarr1KO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，从临床角度来看，我们的研究为快速、安全地利用胃饥饿素信号来减少药物使用和寻求药物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 ß-arrestin (ßarr) 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 ßarr, 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 ßarr 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 ßarr versus G protein to GHSR1a trafficking and signaling, (b) modify molecular determinants underlying the interaction between GHSR1a and ßarrs, (c) evaluate ßarr versus G protein signaling bias and (d) establish a high throughput and secondary screens to identify ßarr/G protein biased ligands; 2. Determine the role of ßarrs in GHSR1a-mediated behaviors using an animal model. We will establish in wild-type and ßarr2 knockout (ßarr2KO) mice that pharmacological suppression and/or activation of GHSR1a produces a change in the behavioral responses to cocaine while determining the role of ßarr2 in these responses. These studies from a basic research perspective will assess the importance of ßarrs 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 ßarr1KO 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.