Department of Physiology & Pharmacology, 3048 HSN, West Virginia University Health Sciences Center, 64 Medical Center Drive, Morgantown, WV, 26508, USA.
Department of Neuroscience, West Virginia University, Morgantown, WV, 26506-9229, USA.
Neuropsychopharmacology. 2019 Sep;44(10):1728-1741. doi: 10.1038/s41386-019-0423-7. Epub 2019 May 29.
Kappa opioid receptor (KOR) agonists show promise in ameliorating disorders, such as addiction and chronic pain, but are limited by dysphoric and aversive side effects. Clinically beneficial effects of KOR agonists (e.g., analgesia) are predominantly mediated by heterotrimeric G protein signaling, whereas β-arrestin signaling is considered central to their detrimental side effects (e.g., dysphoria/aversion). Here we show that Regulator of G protein Signaling-12 (RGS12), via independent signaling mechanisms, simultaneously attenuates G protein signaling and augments β-arrestin signaling downstream of KOR, exhibiting considerable selectivity in its actions for KOR over other opioid receptors. We previously reported that RGS12-null mice exhibit increased dopamine transporter-mediated dopamine (DA) uptake in the ventral (vSTR), but not dorsal striatum (dSTR), as well as reduced psychostimulant-induced hyperlocomotion; in the current study, we found that these phenotypes are reversed following KOR antagonism. Fast-scan cyclic voltammetry studies of dopamine (DA) release and reuptake suggest that striatal disruptions to KOR-dependent DAergic neurotransmission in RGS12-null mice are restricted to the nucleus accumbens. In both ventral striatal tissue and transfected cells, RGS12 and KOR are seen to interact within a protein complex. Ventral striatal-specific increases in KOR levels and KOR-induced G protein activation are seen in RGS12-null mice, as well as enhanced sensitivity to KOR agonist-induced hypolocomotion and analgesia-G protein signaling-dependent behaviors; a ventral striatal-specific increase in KOR levels was also observed in β-arrestin-2-deficient mice, highlighting the importance of β-arrestin signaling to establishing steady-state KOR levels in this particular brain region. Conversely, RGS12-null mice exhibited attenuated KOR-induced conditioned place aversion (considered a β-arrestin signaling-dependent behavior), consistent with the augmented KOR-mediated β-arrestin signaling seen upon RGS12 over-expression. Collectively, our findings highlight a role for RGS12 as a novel, differential regulator of both G protein-dependent and -independent signaling downstream of KOR activation.
κ 阿片受体 (KOR) 激动剂在改善成瘾和慢性疼痛等疾病方面显示出希望，但受到不愉快和厌恶副作用的限制。KOR 激动剂的临床有益作用（例如，镇痛）主要通过异三聚体 G 蛋白信号传导介导，而β-arrestin 信号传导被认为是其有害副作用（例如，不愉快/厌恶）的核心。在这里，我们表明，Regulator of G protein Signaling-12 (RGS12) 通过独立的信号机制，同时减弱 KOR 下游的 G 蛋白信号传导并增强β-arrestin 信号传导，对 KOR 表现出相当大的选择性，而对其他阿片受体则没有选择性。我们之前报道过，RGS12 敲除小鼠在腹侧 (vSTR) 而不是背侧纹状体 (dSTR) 中表现出多巴胺转运体介导的多巴胺 (DA) 摄取增加，以及减少精神兴奋剂引起的过度运动；在本研究中，我们发现这些表型在 KOR 拮抗后逆转。多巴胺 (DA) 释放和再摄取的快速扫描循环伏安法研究表明，RGS12 敲除小鼠纹状体中 KOR 依赖性多巴胺能神经传递的破坏仅限于伏隔核。在腹侧纹状体组织和转染细胞中，观察到 RGS12 和 KOR 相互作用于一个蛋白质复合物中。在 RGS12 敲除小鼠中观察到腹侧纹状体中 KOR 水平增加和 KOR 诱导的 G 蛋白激活增加，以及对 KOR 激动剂诱导的运动减少和镇痛-G 蛋白信号依赖性行为的敏感性增加；在β-arrestin-2 缺陷小鼠中也观察到腹侧纹状体特异性 KOR 水平增加，突出了β-arrestin 信号传导对该特定脑区中稳态 KOR 水平的重要性。相反，RGS12 敲除小鼠表现出减弱的 KOR 诱导的条件性位置厌恶（被认为是β-arrestin 信号依赖性行为），与 RGS12 过表达时观察到的增强的 KOR 介导的β-arrestin 信号传导一致。总的来说，我们的研究结果强调了 RGS12 作为 KOR 激活下游新型、差异调节 G 蛋白依赖性和非依赖性信号传导的作用。
