Regulation of morphine tolerance by alternative Splicing

吗啡在慢性疼痛治疗中的应用由于耐受性的迅速发展而受到限制。与吗啡的镇痛作用相反，吗啡引起的瘙痒不会产生耐受性。吗啡的镇痛特性是由mu-阿片受体（MOR1）介导的，而吗啡引起的瘙痒是由c端剪接变体MOR1D介导的。我们之前的工作已经确定，高效激动剂如芬太尼或舒芬太尼刺激grk2 /3依赖性的苏氨酸370 （T370）、丝氨酸375 （S375）、苏氨酸（T376）和苏氨酸（T379）在MOR1受体的c端磷酸化，而吗啡诱导选择性和grk5依赖性的S375磷酸化，而不会引起受体的快速内吞。相反，吗啡促进MOR1D受体的磷酸化和内化。我们还表明，体内对高效受体激动剂的耐受性比吗啡耐受性发展得慢得多。研究拨款提案的具体目标是:1)确定吗啡公差在小说MOR1D敲鼠标,2)来阐明的磷酸化和内化MOR1D受体在体内和体外,3)检查机制的阿片类药物依赖MOR1D敲在老鼠(增益函数模型)和S375A敲在老鼠(损失函数模型),4)研究阿片受体的角色内化和脱敏病理性疼痛。这些研究将为内源性mu-阿片受体的激动剂选择性调节及其功能后果提供新的见解。

The utility of morphine in the treatment of chronic pain is limited by the rapid development of tolerance. In contrast to its analgesic effects, tolerance does not develop to morphine-induced itch. Whereas the analgesic properties of morphine are mediated by the mu-opioid receptor (MOR1), morphine-induced itch is mediated by the C-terminal splice variant MOR1D. Our previous work has established that, high-efficacy agonists such as fentanyl or sufentanil stimulate a GRK2/3-dependent phosphorylation of threonin 370 (T370), serin 375 (S375), threonin (T376) und threonin (T379) within the C-terminus of the MOR1 receptor, while morphine induces a selective and GRK5-dependent S375 phosphorylation without causing a rapid endocytosis of the receptor. In contrast, morphine promotes a robust phosphorylation and internalization of the MOR1D receptor. We have also shown that in vivo tolerance to high-efficacy agonists develops at a much slower rate than morphine tolerance. The specific aims of the research grant proposal are: 1) to determine morphine tolerance in a novel MOR1D knock in mouse, 2) to elucidate the phosphorylation and internalization of the MOR1D receptor in vivo and in vitro, 3) to examine the mechanisms of opioid dependence in MOR1D knock in mice (gain of function model) and in S375A knock in mice (loss of function model), 4) to examine the role of opioid receptor internalization and desensitization in pathological pain. These studies will provide novel insights into the agonist-selective regulation of endogenous mu-opioid receptors and its functional consequences.