Department of Physiology and Pharmacology, Inflammation Research Network-Snyder Institute for Chronic Diseases and Alberta Children's Hospital Research Institute, University of Calgary, 3330 Hospital Dr NW, Calgary, Alberta, T2N 4N1, Canada.
Hotchkiss Brain Institute. Cumming School of Medicine. University of Calgary, Calgary, Alberta, T2N 4N1, Canada.
Mol Brain. 2020 Apr 14;13(1):61. doi: 10.1186/s13041-020-00599-0.
Postoperative shivering and cold hypersensitivity are major side effects of acute and chronic opioid treatments respectively. TRPM8 is a cold and menthol-sensitive channel found in a subset of dorsal root ganglion (DRG) nociceptors. Deletion or inhibition of the TRPM8 channel was found to prevent the cold hyperalgesia induced by chronic administration of morphine. Here, we examined the mechanisms by which morphine was able to promote cold hypersensitivity in DRG neurons and transfected HEK cells. Mice daily injected with morphine for 5 days developed cold hyperalgesia. Treatment with morphine did not alter the expressions of cold sensitive TREK-1, TRAAK and TRPM8 in DRGs. However, TRPM8-expressing DRG neurons isolated from morphine-treated mice exhibited hyperexcitability. Sustained morphine treatment in vitro sensitized TRPM8 responsiveness to cold or menthol and reduced activation-evoked desensitization of the channel. Blocking phospholipase C (PLC) as well as protein kinase C beta (PKCβ), but not protein kinase A (PKA) or Rho-associated protein kinase (ROCK), restored channel desensitization. Identification of two PKC phosphorylation consensus sites, S1040 and S1041, in the TRPM8 and their site-directed mutation were able to prevent the MOR-induced reduction in TRPM8 desensitization. Our results show that activation of MOR by morphine 1) promotes hyperexcitability of TRPM8-expressing neurons and 2) induces a PKCβ-mediated reduction of TRPM8 desensitization. This MOR-PKCβ dependent modulation of TRPM8 may underlie the onset of cold hyperalgesia caused by repeated administration of morphine. Our findings point to TRPM8 channel and PKCβ as important targets for opioid-induced cold hypersensitivity.
术后寒战和冷超敏反应分别是急性和慢性阿片类药物治疗的主要副作用。TRPM8 是一种冷敏和薄荷醇敏感的通道，存在于背根神经节（DRG）伤害感受器的亚群中。TRPM8 通道的缺失或抑制被发现可以预防慢性给予吗啡引起的冷痛觉过敏。在这里，我们研究了吗啡促进 DRG 神经元和转染的 HEK 细胞冷超敏反应的机制。每天给小鼠注射吗啡 5 天，会引起冷痛觉过敏。吗啡治疗并未改变 DRG 中冷敏感 TREK-1、TRAAK 和 TRPM8 的表达。然而，从吗啡处理的小鼠中分离的表达 TRPM8 的 DRG 神经元表现出过度兴奋。体外持续给予吗啡处理可使 TRPM8 对冷或薄荷醇的反应性敏感，并减少通道激活引起的脱敏。阻断磷脂酶 C（PLC）以及蛋白激酶 Cβ（PKCβ），但不是蛋白激酶 A（PKA）或 Rho 相关蛋白激酶（ROCK），可恢复通道脱敏。在 TRPM8 中鉴定出两个蛋白激酶 C 磷酸化的共有位点，S1040 和 S1041，并且其定点突变能够防止 MOR 诱导的 TRPM8 脱敏减少。我们的结果表明，吗啡激活 MOR：1）促进表达 TRPM8 的神经元的过度兴奋，2）诱导 PKCβ介导的 TRPM8 脱敏减少。这种 MOR-PKCβ 依赖性的 TRPM8 调节可能是重复给予吗啡引起的冷痛觉过敏的基础。我们的研究结果表明，TRPM8 通道和 PKCβ 是阿片类药物引起冷超敏反应的重要靶点。
