外周组织损伤破坏脊髓"GABA能持久性抑制"的分子机制

The reduction of GABAA receptors-mediated inhibition (GABAergic disinhibition) in spinal dorsal horn plays an essential role in the initiation and development of pathological pain. In addition to cluster at inhibitory synapses, recent studies have demonstrated that GABAA receptors are widely distributed at extrasynaptic sites, where they persistently generate the tonic inhibition to control the neuronal excitability. However, it is unclear as yet how peripheral tissue injury modulates GABAergic tonic inhibition in spinal dorsal horn during inflammatory pain. Notably, our preliminary experiments, when exploring the mechanisms responsible for GABAergic disinhibition, unveiled for the first time that peripheral tissue injury was able to impair the surface expression of extrasynaptic GABAA receptors and reduce the current amplitudes of GABAergic tonic inhibition, possibly by specifically enhancing the interaction of extrasynaptic GABAA receptors with protein tyrosine phosphatase SHP1 via spinal mGluR1/5 receptor signalings. Based on these novel observations, the applicants put forward the following hypothesis: The disinhibition of the tonic inhibition in spinal dorsal horn contributes to the formation of inflammatory pain. This project aims to systematically investigate the molecular mechanisms for peripheral tissue injury to impair the tonic inhibition and to elucidate the pathological significance of the reduced tonic inhibition in inflammatory pain.

脊髓背角GABAA受体的抑制功能减弱（即:GABA能去抑制），被认为是诱发和维持病理性疼痛的核心因素之一。目前发现：GABAA受体除了定位于突触，还大量分布于突触外膜上，通过连续不断地产生持久性抑制（Tonic inhibition），密切控制着神经细胞的兴奋性。然而，外周组织损伤对持久性抑制的调节作用及其与炎性疼痛的关系，目前为止却一无所知。而申请者的预实验，在探讨"GABA能去抑制"的形成机制时，首次发现：外周组织损伤，会强烈抑制突触外GABAA受体的膜表达、显著降低持久性抑制的电流幅值，而组织损伤的这一作用，可能与激活脊髓mGluR1/5受体、特异性增强一种酪氨酸磷酸酶SHP1与突触外GABAA受体的相互作用有关。基于这一全新的发现，申请者提出：持久性抑制的"去抑制"，可能参与慢性炎性疼痛的形成。本项目的目标，在于全面揭示组织损伤破坏持久性抑制的分子机制及其在诱发炎性疼痛中的重要意义

脊髓背角GABAA 受体的抑制功能减弱，被认为是诱发和维持病理性疼痛的核心因素之一。GABAA 受体除了定位于突触后膜，还大量分布于突触外膜上，通过连续不断地产生持久性抑制，密切控制着神经细胞的兴奋性和反应性。然而，外周损伤对GABA能持久性抑制的影响及其与慢性炎性疼痛的关系，目前为止却知之甚少。本项目以突触外膜包含α5亚基的GABAA 受体（α5-GABAAR）为研究对象，深入探讨了α5-GABAAR的痛觉调控机制，发现选择性抑制α5-GABAAR的活性，会显著增强痛觉信息的突触传入，易化痛觉突触可塑性的形成，诱发正常动物的痛觉敏化，说明了α5-GABAAR对脊髓痛觉传递与整合的固有性抑制作用；外周组织损伤能够激活酪氨酸磷酸酶SHP1信号通路，通过催化α5-GABAAR的去磷酸化，诱发α5-GABAAR的内陷，显著降低α5-GABAAR在细胞膜表面的表达，导致GABA能持久性抑制电流的明显减弱；抑制炎性疼痛动物脊髓背角SHP1的活性，会显著提高持久性抑制的电流幅值，有效缓解炎性疼痛症状，提示SHP1信号通路在解除GABA能持久性抑制中的关键作用。本项目的研究，从突触外膜GABAA 受体的角度，阐释了病理性疼痛过程中GABA能去抑制的发生机制，探讨了以突触外膜GABAA 受体为靶点的新的镇痛治疗策略。