Role of opioid receptor trafficking in tolerance and dependence

描述（由申请人提供）：成瘾生物学的一个基本问题是，为什么阿片生物碱类药物如吗啡和海洛因有很高的诱导耐受性和成瘾的倾向，而内啡肽和脑啡肽，阿片受体的天然肽配体，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特别令人感兴趣，因为它受到肽激动剂和生物碱药物的不同调节。具体来说，内源性阿片肽和某些阿片药物如埃托啡和美沙酮刺激mu阿片受体的快速内化。然而，吗啡强烈激活受体信号，但不能刺激mu阿片受体的快速内化。此外，在内吞作用之后，单个受体可以在循环内体和溶酶体之间进行不同的分类。这种分选机制可以通过两种方式促进受体调节，这两种方式对细胞信号传导有相反的影响。首先，内吞作用可以作为受体再敏化的一种机制，通过将内化的受体传递到核内体，在核内体中，它们在完全活跃的状态下再循环到质膜。其次，快速内化可以作为受体下调的第一步，通过将受体传递到核内体，然后将它们送到溶酶体进行降解。因此，对于每个受体/配体对，必须评估内吞和后内吞性质。我们已经产生了改变了内吞和内吞后运输特性的突变型mu阿片受体。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.