ASIC Channels and Pain

描述(申请人提供)：伤害性感觉是初级传入躯体感觉神经元识别和响应伤害性刺激的过程。除了启动急性疼痛反应外，伤害性感受器的激活还会产生局部炎症，导致疼痛过敏症。组织酸中毒(即局部pH降低)是这种反应的一个重要标志，并与一系列生理损害有关，如感染、缺血、肿瘤生长和关节炎。事实上，细胞外质子增强初级传入的兴奋性。 伤害性感受器，从而产生剧烈疼痛和/或疼痛过敏。酸敏感离子通道(ASIC)家族的成员被认为是细胞外质子的感受器，在伤害性感受和疼痛中发挥重要作用。例如，ASIC3亚型可能与支配骨骼肌或心肌的神经元中大的、快速失活的质子诱发电流有关的缺血性疼痛。然而，由于各种原因，ASIC通道在伤害性感受中的其他作用仍然是个谜。首先，缺乏药理学工具使得在体内操纵这些通道变得困难。其次，缺乏特定ASIC通道亚型的小鼠在酸引起的疼痛或其他伤害性感受方面未能表现出清晰或强健的表型。第三，全面分析ASIC通道的表达和定位-这对于破译ASIC通道的生理作用至关重要 这些在伤害性感受和疼痛中的通道仍然不完整。最后，一些ASIC亚型(例如ASIC2a)只对极端的细胞外酸化(pH和lt；5)做出反应，这表明在组织损伤和/或慢性炎症的病理生理条件下，这些通道可能存在其他内源性调节剂。这项建议的目的是通过应用遗传学、生理学和生化方法来解决这些和其他问题，以发展对ASIC亚型功能、药理学和在躯体感觉系统中表达的全面看法。其具体目的是(I)利用基因靶向报告小鼠建立ASIC通道表达的全面图谱，以精确灵敏和逼真地显示ASIC阳性神经纤维；(Ii)使用一系列电生理学和活细胞成像方法表征这些基因标记小鼠中表达ASIC的感觉神经元和神经纤维的功能特性；(Iii) 使用一系列生化、功能和行为分析在正常和损伤组织的提取液中筛选新的内源性ASIC调节剂。总之，这些目标将解决有关ASIC功能的重要悬而未决的问题，作为合理开发针对一系列慢性炎症性疼痛综合征的新型治疗剂的关键步骤。

DESCRIPTION (provided by applicant): Nociception is the process whereby primary afferent somatosensory neurons recognize and respond to noxious stimuli. In addition to initiating acute pain responses, nociceptor activation can produce local inflammation leading to pain hypersensitivity. Tissue acidosis (i.e. reduction in local pH) is an important hallmark of this response, and is associated with a range of physiological insults, such as infection, ischemia, tumor growth, and arthritis. Indeed, extracellular protons enhance excitability of primary afferent nociceptors, thereby producing acute pain and/or pain hypersensitivity. Members of the acid sensing ion channel (ASIC) family are believed to play important roles in nociception and pain by functioning as sensors for extracellular protons. For example, the ASIC3 subtype likely accounts for ischemic pain associated with large, rapidly inactivating proton-evoked currents in neurons that innervate skeletal or cardiac muscle. However, additional roles for ASIC channels in nociception have remained enigmatic for a variety of reasons. First, a dearth of pharmacological tools has made it difficult to manipulate these channels in vivo. Second, mice lacking specific ASIC channel subtypes have failed to revealed clear or robust phenotypes in regard to acid-evoked pain or other aspects of nociception. Third, a comprehensive analysis of ASIC channel expression and localization - which is critical to deciphering physiological roles for these channels in nociception and pain - remains incomplete. Finally, some ASIC subtypes (e.g. ASIC2a) respond only to extreme extracellular acidosis (pH < 5), suggesting the existence of other endogenous modulators for these channels that may be produced under pathophysiological conditions of tissue injury and/or chronic inflammation. The goal of this proposal is to address these and other questions by applying genetic, physiologic, and biochemical methods to develop a comprehensive view of ASIC subtype function, pharmacology, and expression in the somatosensory system. The specific aims are to (i) develop a comprehensive map of ASIC channel expression using gene targeted reporter mice to visualize ASIC-positive nerve fibers with exquisite sensitivity and fidelity; (ii) characterize functional properties of ASIC-expressing sensory neurons and nerve fibers from these genetically-labeled mice using a range of electrophysiological and live-cell imaging methods; (iii) screen for novel endogenous ASIC modulators in extracts of normal and injured tissues using a range of biochemical, functional, and behavioral assays. Together, these aims will address important unresolved questions concerning ASIC function as key steps toward the rational development of novel therapeutic agents that target a range of chronic inflammatory pain syndromes.