Hemichannels, astrocytic release, and neuropathic pain

描述（由申请人提供）：疼痛状况是美国的一个主要健康问题，导致数百万美国人的医疗发病率和生活质量下降。慢性神经性疼痛尤其难以治疗。一个很大程度上未解决的挑战是从急性疼痛到慢性神经性疼痛的转变是如何发生的，以及如何预防和逆转这种转变在患者中。脊髓突触可塑性和长期增强（LTP）与慢性神经性疼痛的发展密切相关。越来越多的证据也指出神经胶质细胞在神经性疼痛发病机制中的重要作用。星形胶质细胞是中枢神经系统中最丰富的细胞类型，维持中枢神经系统的稳态。星形胶质细胞半通道如连接蛋白-43 （Cx43）是胶质递质释放的重要途径。虽然Cx43通常被认为调节星形胶质细胞之间的间隙连接通信，但在损伤条件下，这种功能可能通过ATP和谷氨酸释放转换为旁分泌信号。我们的中心假设是神经损伤后半通道介导的胶质递质释放通过调节脊髓突触可塑性和LTP参与急性疼痛向慢性神经性疼痛的转变。我们将通过解决以下4个具体目标来验证我们的中心假设：目标1将验证脊髓神经损伤增加脊髓星形胶质细胞中谷氨酸和ATP释放的假设；目的2将验证cx43介导的星形细胞ATP释放在脊髓损伤后小胶质细胞活化和小胶质增生中起主要作用的假设；目的3将确定cx43药物治疗的星形胶质细胞释放在神经损伤后脊髓突触可塑性和LTP中的作用；目的4将明确星形细胞Cx43在神经损伤后神经性疼痛发展和维持中的作用。该提案将涉及在Ji博士和Nedergaard博士之间形成创新的合作伙伴关系，Ji博士是研究神经性疼痛的神经元-胶质相互作用和神经可塑性的疼痛科学家，Nedergaard博士研究脊髓损伤和中风后星形细胞ATP和谷氨酸释放的专业知识。该应用将采用多学科方法，包括使用带有转基因星形胶质细胞的可诱导转基因小鼠，脊髓中ATP释放（生物发光）、小胶质细胞运动和Ca2+变化（2光子）的体内成像，神经损伤后诱发和持续神经性疼痛的行为测试，以及脊髓的体外和体内电生理学。提出的研究将提供神经损伤引发的神经元-神经胶质相互作用的逐步分析，并可能包括预防和治疗慢性疼痛的有效手段。

DESCRIPTION (provided by applicant): Pain conditions are a major health problem in the US and lead to medical morbidity and a reduced quality of life for millions of Americans. Chronic neuropathic pain conditions are especially difficult to treat. A largely unaddressed challenge is how the transition from acute pain to chronic neuropathic pain occurs and how to prevent and reverse this transition in patients. Spinal cord synaptic plasticity and long-term potentiation (LTP) have been strongly implicated in chronic neuropathic pain development. Accumulating evidence also points to an important role of glial cells in the pathogenesis of neuropathic pain. Astrocytes are the most abundant cell type in the CNS and maintain the homeostasis of the CNS. It is well established that astrocytic hemichannels such as connexin-43 (Cx43) constitute an important pathway for gliotransmitter release. Although Cx43 was typically thought to regulate gap junction communication between astrocytes, this function could be switched to paracrine signaling via ATP and glutamate release under injury conditions. Our central hypothesis is hemichannels-mediated gliotransmitter release after nerve injury contributes to transition from acute pain to chronic neuropathic pain by modulating spinal cord synaptic plasticity and LTP. We will test our central hypothesis by addressing the following 4 specific aims: Aim 1 will test the hypothesis that spinal nerve injury increases glutamate and ATP release from spinal cord astrocytes; Aim 2 will test the hypothesis that Cx43-mediated astrocytic ATP release plays a chief role in microglia activation and microgliosis in the spinal cord after spinal nerve injury; Aim 3 will determine the role of Cx43-medicated astrocytic gliotransmitter release in spinal cord synaptic plasticity and LTP after nerve injury; Aim 4 will define the role o astrocytic Cx43 in neuropathic pain development and maintenance after nerve injury. This proposal will involve formation of an innovative partnership between Dr. Ji, a pain scientist with expertise in studying neuronal-glial interactions and neural plasticity in neuropathic pain, and Dr Nedergaard with expertise in studying astrocytic ATP and glutamate release after spinal cord injury and stroke. This application will employ a multidisciplinary approach including the use of inducible transgenic mice with genetically modified astrocytes, in vivo imaging of ATP release (bioluminescence) and microglia motility and Ca2+ changes (2-photon) in the spinal cord, behavioral testing of evoked and ongoing neuropathic pain after nerve injury, and ex vivo and in vivo electrophysiology in the spinal cord. The proposed studies will provide a step-by-step analysis of neuron- glia interactions initiated by nerve injury and may comprise an efficient means to prevent and treat chronic pain. PUBLIC HEALTH RELEVANCE: Dysfunction of spinal cord astrocytes after nerve injury may contribute to the development of neuropathic pain via releasing gliotransmitters such as ATP and glutamate. We will employ multidisciplinary approaches such as transgenic mice with genetically modified astrocytes, two-photon imaging, behavioral analyses of evoked and ongoing pain, and ex vivo and in vivo electrophysiology to define the role of connexin-43 hemichannels expressed by spinal astrocytes in regulating synaptic plasticity and neuropathic pain. Given the incomplete understanding of neuropathic pain mechanisms and insufficient treatment of neuropathic pain, this application will provide new information about transition of acute pain to chronic neuropathic pain and offer new strategy for neuropathic pain management.