Role of opioid receptor trafficking in tolerance and dependence

描述(申请人提供)：成瘾生物学中的一个基本问题是，为什么吗啡和海洛因等鸦片类生物碱类药物具有很高的耐受性和成瘾性，而阿片受体的天然多肽配体内啡肽和脑啡肽则没有。在激动剂激活后，阿片受体受到多种机制的调节。在这些调节机制中，阿片受体的快速内吞作用特别令人感兴趣，因为它受多肽激动剂和生物碱药物的不同调节。具体地说，内源性阿片肽和某些阿片类药物，如依托啡和美沙酮，可以刺激u阿片受体的快速内化。然而，吗啡强烈地激活受体信号，但不能刺激u阿片受体的快速内化。此外，在内吞作用之后，单个受体可以被区别地分类为循环内吞体内和溶酶体。这种分选机制可以通过两种对细胞信号产生相反影响的方式来促进受体的调节。首先，内吞作用可以作为受体再增敏的一种机制，将内化的受体运送到内体，在内体中以完全活跃的状态被循环到质膜。其次，快速内化可以作为受体下调的第一步，将受体运送到内小体，然后再从内小体送到溶酶体进行降解。因此，对于每个受体/配体对，必须同时评估内吞和后内吞特性。我们已经产生了突变的u阿片受体，其内吞和内吞后转运特性发生了改变。在这里，我们建议利用这些突变受体来评估改变贩运对耐受性、戒断和成瘾发展的分子和行为影响。

DESCRIPTION (provided by applicant): A fundamental question in addiction biology is why opiate alkaloid drugs such as morphine and heroin have a high liability for inducing tolerance and addiction while endorphins and enkephalins, the native peptide ligands for opioid receptors, do not. Following activation by agonists, opioid receptors are regulated by multiple mechanisms. Of these regulatory mechanisms, rapid endocytosis of opioid receptors is of particular interest because it is differentially regulated by peptide agonists and alkaloid drugs. Specifically, endogenous opioid peptides and certain opiate drugs such as etorphine and methadone stimulate the rapid internalization of mu opioid receptors. Morphine however, strongly activates receptor signaling but fails to stimulate the rapid internalization of mu opioid receptors. Furthermore, following endocytosis, individual receptors can be sorted differentially between recycling endosomes and lysosomes. This sorting mechanism can contribute to receptor regulation in two ways that have opposing effects on cell signaling. First, endocytosis can serve as a mechanism for receptor resensitization by delivering internalized receptors to endosomes from where they are recycled to the plasma membrane in a fully active state. Second, rapid internalization can serve as a first step toward receptor downregulation by delivering the receptors to endosomes from which they are sent to lysosomes for degradation. Hence for each receptor/ligand pair, one must evaluate both the endocytic and post-endocytic properties. We have generated mutant mu opioid receptors with altered endocytic and post- endocytic trafficking properties. Here we propose to utilize these mutant receptors to assess the molecular and behavioral effects of altered trafficking on the development of tolerance, withdrawal, and addiction.