Muscarinic acetylcholine receptor subtypes: physiological roles

总结 以下总结的结果是在合作研究中获得的： 越来越多的证据表明，气道直径和体重的调节是交织在一起的。对不同突变小鼠模型的研究表明，瘦素通过减少气道平滑肌细胞表达的M3 mAChR的副交感神经信号而增加气道直径。此外，无论支气管炎症如何，副交感神经张力的降低都会抑制肥胖小鼠的支气管收缩和肺功能正常化。这些发现对于肥胖相关性哮喘的治疗具有潜在的临床意义。 （Arteaga-Solis E等人，作为极端体重相关哮喘的原因的副交感神经信号的瘦素调节的抑制。Cell Metab 17，35-48，2013） 慢性阻塞性肺疾病（COPD）的特征是副交感神经胆碱能张力增加。最近的数据表明，ACh也在介导气道炎症中发挥作用。为了鉴定参与这种活性的mAChR亚型的性质，将M1、M2和M3 mAChR KO小鼠和WT对照小鼠暴露于香烟烟雾数天。有趣的是，小鼠表型研究的结果表明，M3 mAChR在香烟烟雾诱导的嗜烟性和细胞因子释放中具有促炎作用，而M1和M3 mAChR在该动物模型中发挥抗炎作用。这些发现与用于治疗COPD的新型毒蕈碱药物的开发高度相关。 （Kistemaker LE等人，Muscarinic receptor subtype-specific effects on cigarette smoke-induced inflammation in mice. Eur Respir J Feb 8，2013 Epub ahead of print） 背外侧被盖核（LDT）和脚桥被盖核（PPT）中的胆碱能神经元通过向中脑多巴胺区和大脑其他区域的主要投射来调节奖赏、唤醒和感觉门控。众所周知，这些胆碱能神经元的活性受到毒蕈碱激动剂的调节。为了鉴定参与该活性的mAChR亚型的性质，对各种mAChR KO菌株进行电生理学和钙成像研究。这些实验表明，多个mAChR协调胆碱能流出的LDT在一个意想不到的复杂方式。 （Kohlmeier KA等人，Knockouts reveal overlapping functions of M2 and M4 muscarinic 背侧被盖内的受体和局部多巴胺能回路证据 原子核J Neurophysiol 108，2751-66，2012） 我们最近产生了一种基于M3 mAChR的设计者GPCR，其选择性地激活刺激性G蛋白Gs（Guettier等人，PNAS 106，19197-202，2009）。这种设计受体，我们称之为“Rs”，不能结合内源性mAChR配体ACh，但可以被外源性给药的药物（氯氮平-N-氧化物或短CNO）选择性激活。为了探索Gs信号在纹状体中棘神经元（MSNs）中的行为作用，用在这些神经元中选择性表达Rs构建体的转基因小鼠进行研究。在CNO治疗后，Rs突变小鼠表现出自发和新奇诱导的运动活动减少，并且未能表现出对苯丙胺的行为敏感性。这些研究结果表明，Rs受体，M3 mAChR为基础的设计师GPCR，代表了一个很好的新的工具，用于阐明行为的后果，激活Gs信号在striatopallidal MSN。 （Farrell MS等人，A G s DREADD mouse for selective modulation of cAMP production in striatopallidal neurons. Neuropsychopharmacology 38，854-62，2013） 背侧纹状体在基于奖励的决策中发挥作用，但特定纹状体回路在这些过程中的重要性仍不清楚。通过使用神经元特异性病毒载体，Rs受体（见前一段），一种基于M3 mAChR的设计师GPCR，选择性偶联到Gs，在大鼠背内侧纹状体的直接通路（纹状体黑质）神经元中表达。Hoc介导的Rs设计者受体的激活显著改善了在随后的偏好测试期间用于最大化奖励获得的任务策略的保留。这些数据表明，Gs信号在直接通路纹状体神经元在奖励相关的行为发挥了明确的作用。 （Ferguson SM等人，Direct-pathway striatal neurons regulate the retention of decision-making strategies. J Neurosci 133，11668-76，2013）

SUMMARY The results summarized below were obtained in collaborative studies: Accumulating evidence suggests that the regulation of airway diameter and body weight are intertwined. Studies with different mutant mouse models demonstrated that leptin increased airway diameter by decreasing parasympathetic signaling through M3 mAChRs expressed by airway smooth muscle cells. Moreover, reduction of parasympathetic tone inhibited bronchoconstriction and normalized lung function in obese mice regardless of bronchial inflammation. These findings are of potential clinical relevance for the treatment of obesity-associated asthma. (Arteaga-Solis E, et al. Inhibition of leptin regulation of parasympathetic signaling as a cause of extreme body weight-associated asthma. Cell Metab 17, 35-48, 2013) Chronic obstructive pulmonary disease (COPD) is characterized by an increase in parasympathetic cholinergic tone. Recent data suggest that ACh also plays a role in mediating airway inflammation. To identify the nature of the mAChR subtypes involved in this activity, M1, M2, and M3 mAChR KO mice and WT control mice were exposed to cigarette smoke for several days. Interestingly, the outcome of mouse phenotyping studies indicated that the M3 mAChR has a pro-inflammatory role in cigarette smoke-induced neutrophilia and cytokine release, whereas the M1 and M3 mAChRs exert anti-inflammatory effects in this animal model. These findings are highly relevant for the development of novel muscarinic drugs useful for the treatment of COPD. (Kistemaker LE, et al. Muscarinic receptor subtype-specific effects on cigarette smoke-induced inflammation in mice. Eur Respir J Feb 8, 2013 Epub ahead of print) Cholinergic neurons in the laterodorsal tegmental (LDT) and peduncolopontine tegmental (PPT) nuclei regulate reward, arousal, and sensory gating via major projections to midbrain dopamine regions and other areas of the brain. It is well known that the activity of these cholinergic neurons is modulated by muscarinic agonists. To identify the nature of the mAChR subtypes involved in this activty, various mAChR KO strains were subjected to electrophysiological and calcium imaging studies. These experiments demonstrated that multiple mAChRs coordinate cholinergic outflow from the LDT in an unexpectedly complex manner. (Kohlmeier KA, et al. Knockouts reveal overlapping functions of M2 and M4 muscarinic receptors and evidence for a local glutamatergic circuit within the laterodorsal tegmental nucleus. J Neurophysiol 108, 2751-66, 2012) We recently generated an M3 mAChR-based designer GPCR that selectively activates the stimulatory G protein, Gs (Guettier et al., PNAS 106, 19197-202, 2009). This designer receptor, which we refer to as 'Rs', is unable to bind ACh, the endogenous mAChR ligand, but can be selectively activated by an exogenously administered drug that is otherwise pharmacologically inert (clozapine-N-oxide or short CNO). To explore the behavioral roles of Gs signaling in striatopallidal medium spiny neurons (MSNs), studies were carried out with transgenic mice selectively expressing the Rs construct in these neurons. Following CNO treatment, the Rs mutant mice showed reduced spontaneous and novelty-induced locomotor activity and failed to display behavioral sensitization to amphetamine. These findings demonstrate that the Rs receptor, an M3 mAChR-based designer GPCR, represents an excellent novel tool for elucidating the behavioral consequences of activating Gs signaling in striatopallidal MSNs. (Farrell MS, et al. A Gαs DREADD mouse for selective modulation of cAMP production in striatopallidal neurons. Neuropsychopharmacology 38, 854-62, 2013) The dorsal striatum plays a role in reward-based decision making, but the importance of specific striatal circuits in these processes remains unclear. By using neuron-specific viral vectors, the Rs receptor (see previous paragraph), an M3 mAChR-based designer GPCR that is selectively coupled to Gs, was expressed in direct-pathway (striatonigral) neurons of the dorsomedial striatum of the rat. CNO-mediated activation of the Rs designer receptor significantly improved the retention of task strategies used to maximize reward obtainment during subsequent preference testing. These data demonstrate that Gs signaling in direct-pathway striatal neurons plays a well-defined role in reward-related behavior. (Ferguson SM, et al. Direct-pathway striatal neurons regulate the retention of decision-making strategies. J Neurosci 133, 11668-76, 2013)