Regulator of G protein signaling proteins differentially control opioid analgesia

描述（由申请人提供）：G蛋白信号传导调节因子（RGS）蛋白是G蛋白偶联受体（GPCR）辅助蛋白家族，其对于细胞信号传导（包括μ阿片受体（莫尔）下游的信号传导）的时间和空间控制至关重要。RGS蛋白是GTP酶加速蛋白（GAP），其加速结合GTP的Ga的水解并促进无活性的Ga GDP的形成以关闭GPCR的信号传导。我们已经表明，RGS蛋白质用于终止莫尔信号转导至腺苷酸环化酶和MAP激酶途径。另一方面，莫尔释放细胞内钙的有效信号传导需要RGS蛋白GAP活性。因此，RGS活性控制单个细胞内信号传导途径的平衡。我们最近使用了一种新的工具来探索RGS蛋白对GPCR信号的调节：转基因敲入小鼠，其表达对RGS蛋白差距活性不敏感的Ga α蛋白。在这些小鼠中，抗伤害感受依赖于所采用的阿片样物质激动剂和疼痛测定。例如，在热板测定中，RGS调节的丧失增强吗啡，而不影响美沙酮，抗伤害感受。相反，在尾部撤回试验中，RGS活性的去除降低了吗啡和美沙酮的抗伤害感受。这表明参与这两种行为的不同神经元通路对RGS蛋白作用表现出不同的敏感性。我们建议继续探索这些小鼠，以解决一系列关于莫尔信号传导及其与抗伤害感受的关系的基本问题。例如：抗伤害性试验之间的差异是否是由于RGS作用的部位特异性差异？观察到的激动剂差异的基础是什么？这些差异是否可以用细胞信号水平的影响来解释？同样使用Galpha蛋白的其他神经递质系统的作用是什么？更多的临床相关疼痛模型也受RGS蛋白的调节吗？我们的总体概念框架如下：1）RGS活性控制GPCR信号传导到多个通路的平衡，并且这种平衡可能在疼痛中被破坏，以及2）RGS诱导的M0R介导的抗伤害感受的变化可能反映神经递质系统，特别是伤害感受素（NOP）系统之间的平衡的改变。拟议的研究将促进我们对阿片信号通路及其通过RGS蛋白的调节的理解，并在改变行为的背景下解释这些作用。这项研究的结果可能被用来开发更好的镇痛药物。

DESCRIPTION (provided by applicant): Regulators of G protein Signaling (RGS) proteins are a family of G protein-coupled receptor (GPCR) accessory proteins that are essential for the temporal and spatial control of cell signaling, including signaling downstream of the mu-opioid receptor (MOR). RGS proteins are GTPase accelerating proteins (GAPs) that accelerate the hydrolysis of Galpha bound GTP and promote the formation of inactive Galpha GDP to switch off signaling by GPCRs. We have shown that RGS proteins serve to terminate signaling of MOR to adenylate cyclase and the MAP kinase pathway. On the other hand, efficient signaling of MOR to release intracellular calcium requires RGS protein GAP activity. Thus, RGS activity controls the balance of signaling pathways within a single cell. We recently used a novel tool to explore regulation of GPCR signaling by RGS proteins: a transgenic knock-in mouse that expresses Galpha proteins that are insensitive to the GAP activity of RGS proteins. In these mice antinociception is dependent on the opioid agonist and pain assay employed. For example, in the hot-plate assay loss of RGS regulation potentiates morphine, without affecting methadone, antinociception. In contrast, in the tail-withdrawal assay removal of RGS activity decreases both morphine and methadone antinociception. This suggests the different neuronal pathways involved in these two behaviors show differential sensitivity to RGS protein action. We propose to continue our exploration of these mice to tackle a series of fundamental questions concerning MOR signaling and its relationship to antinociception. For example: Are the differences between antinociceptive tests due to site-specific variation in RGS action? What is the basis of the observed agonist differences? Can the differences be explained by effects at the level of cell signaling? What is the role of other neurotransmitter systems that also use Galpha proteins? Are more clinically-related pain models also regulated by RGS proteins? Our overall conceptual framework is as follows: 1) RGS activity controls the balance of GPCR signaling to multiple pathways and this balance may be disrupted in pain and 2) RGS-induced changes in MOR-mediated-antinociception may reflect an alteration in the balance between neurotransmitter systems, particularly the nociceptin (NOP) system. The proposed studies will advance our understanding of opioid signaling pathways and their regulation by RGS proteins and explain these actions in the context of altered behaviors. Results from this study may be exploited to develop better analgesic drugs.