TLR4受体在小鼠三叉神经损伤诱导的脊髓内中枢敏化的扩散中的作用及机制研究

Chronic widespread pain is devastating for patients from both physical and psychological point view due to its unbearable intensity, long-lasting course, widespread referred area as well as accompanying severe pain syndrome. However, its pathogenesis has not been elucidated yet. Our previous pilot study reveals that partial infraorbital nerve (one of the branches of the trigeminal nerve) injury (pIONX) induced pain hypersensitivity in the hindpaw in some strains of inbred mice. Moreover, neuronal hyperexcitability and microglial activation was observed in the lumbar spinal dorsal horn. These results indicate the spreading of trigeminal pain and central sensitization in the spinal cord. In addition, a negative correlation was detected in the early phase after pIONX between the pain intensity in the face and the hindpaw, but was no longer present in the late phase, implying the development of a "new pain focus". Our latest experiments showed that pIONX induced an upregulation of TLR4 in the lumbar cord, and LPS-RS, a TLR4 antagonist and deficiency of TLR4 gene inhibited the spreading of pain hypersensitivity from the face to the hindpaw, indicating that TLR4 signaling pathway may be involved in the spreading process. Taking advantage of TLR4 knockout and inducible conditional TLR4- as well Myd88- knockout mice as well as techniques including behavioral tests, electrophysiological recording, microPET imaging and gene manipulation, the present study aims to extensively study the roles of TLR4 receptors （especially in microglia） in widespread trigeminal pain. The results will reveal the spinal mechanisms of widespread pain and provide reliable experimental evidence for drug development targeting microglial TLR4 for the treatment of chronic widespread pain.

慢性扩散性疼痛因疼痛剧烈，持续时间长，分布区域广，并伴随严重的疼痛综合征，严重影响患者的身心健康，但其发病机制尚未阐明。课题组预实验发现，部分损伤三叉神经分支眶下神经（pIONX）可诱导小鼠出现后爪疼痛增敏，伴腰髓背角神经元兴奋性增高和小胶质细胞激活，提示三叉神经痛和中枢敏化的扩散。而且早期扩散性疼痛与原发疼痛的程度呈负相关，后期相关性消失，提示在远隔部位形成了独立的新"痛点"。最新预实验还发现pIONX后腰髓TLR4受体表达增加，抑制其功能可减轻扩散性疼痛，提示TLR4受体可能参与中枢敏化扩散及新"痛点"形成。本研究拟利用TLR4基因敲除和条件性敲除小胶质细胞TLR4和Myd88的小鼠，结合行为学、电生理学、影像学、基因干预等技术，深入研究TLR4受体在扩散性三叉神经痛中的作用和机制，阐明扩散性疼痛的脊髓内机制，为小胶质细胞TLR4受体靶向的药物用于治疗扩散性疼痛提供可靠的实验依据

慢性扩散性疼痛因疼痛剧烈，持续时间长，分布区域广，并伴随严重的疼痛综合征，严重影响患者的身心健康，但其发病机制尚未阐明。本研究发现，部分损伤三叉神经分支眶下神经可诱导MRL/MPJ小鼠出现口面部和躯体部位如后爪的疼痛增敏和早发性焦虑。早期扩散性疼痛与原发疼痛的程度呈负相关，后期相关性消失，提示在远隔部位形成了独立的新“痛点”。手术后腰髓背角神经元兴奋性增高，小胶质细胞被激活，早期抑制小胶质细胞激活可减轻扩散性痛敏，提示脊髓内中枢敏化的扩散参与痛敏的扩散。腰髓TLR4-MyD88信号通路被激活，炎症因子TNF表达增加。TLR4点突变或基因缺失或用药物抑制其功能均可减轻扩散性机械痛觉超敏，但不影响扩散性热痛过敏。抑制TLR4功能不影响原发三叉神经痛的形成和维持，提示TLR4信号通路特异性参与扩散性机械痛超敏的病理过程。此外，TLR4的内源性配体HMGB1在痛敏扩散中发挥作用。本研究明确了慢性扩散性疼痛伴随脊髓内中枢敏化的扩散，TLR4信号通路在中枢敏化的扩散中发挥作用，为TLR4受体靶向的药物用于治疗扩散性疼痛提供了可靠的实验依据。