脂代谢紊乱参与脊髓小胶质细胞活化和中枢敏化疼痛机制

Brain has the highest lipid concentration next to adipose tissue. Deregulated lipid metabolism has been reported to be of particular importance for the central nervous system (CNS) injuries and certain neurological disorders by potentiating immune and inflammatory processes. Microglia are the resident immune cells of CNS and share many immunological characteristics with peripheral macrophage. Microglial activation plays important roles in central sensitization contributing to chronic pain. We hypothesized that deregulated lipid metabolism may also induce spinal microglial activation and contribute to chronic pain. In the present study, firstly we will determine the association of deregulated lipid metabolism with spinal microglial activation and animal pain behaviors by using high-dose lipid diet-induced obese mice, ApoE knockout mice and ob/ob obese mice. Further, we will investigate possible cellular and molecular mechanisms using in vivo/vitro experiments. We supposed that some metabolic intermediates of cholesterol synthesis such as mevalonate (MVA) and isoprenoids such as farnesyl pyrophosphate (FPP) and geranylgeranyl pyrophosphate (GGPP) may activate spinal microglia by Rho/Rho kinase (ROCK) signaling pathway and involve in the initiation and maintenance of hyperalgesia. Our project presents the novel concept that will help to further understand molecular pain mechanisms scientifically and the relation of chronic pain with other systemic diseases such as lipid metabolic disorders clinically. The specific roles of Rho/ROCK signaling pathway and the deregulated lipid metabolism will open new opportunities for drug development and therapies for chronic pain control. Lipid-lowering drugs may also be tried in controlling chronic pain as well in the future.

脑和脊髓是脂肪组织外含脂类物质最丰富的组织，脂代谢紊乱可以影响中枢神经系统炎症免疫性疾病的进展。小胶质细胞是中枢神经系统的免疫细胞。小胶质细胞的活化在中枢痛觉敏化机制中发挥至关重要的作用。我们推测，脂代谢、小胶质细胞活化、和慢性疼痛存在一定的联系。本研究将采用脂代谢紊乱小鼠（高脂饲养、载脂蛋白基因敲除和肥胖小鼠）来探讨脂代谢紊乱是否激活小胶质细胞和影响疼痛行为。再通过多种体内和体外实验来探讨一个具体的分子机制：脂代谢的中间产物，如胆固醇代谢中间产物二羟甲基戊酸（MVA）和焦磷酸法尼酯(FPP)等，激活Rho/ROCK信号通路，形成以小胶质细胞活化为中心的炎症免疫反应，导致中枢痛觉敏化。本项目提出了一个新的观点，对于慢性疼痛的分子机制及其与全身健康的关系具有重要的理论和临床意义，针对Rho/ROCK通路和相应的脂代谢产物有望成为治疗慢性疼痛的新靶点。降脂药物亦有可能用于慢性疼痛的辅助治疗。

本研究采用脂代谢紊乱小鼠（高脂饲养和载脂蛋白基因敲除小鼠）来探讨脂代谢紊乱是否激活小胶质细胞和影响疼痛行为，再通过多种体内和体外实验来探讨具体的分子机制。主要结果：1）高脂饮食可以导致动物疼痛阈值减低、对外周伤害性刺激有更强的疼痛反应；2）高脂肥胖组小鼠脊髓的小胶质细胞和星形胶质细胞均呈相对激活状态，炎症相关的细胞因子的表达，也明显升高；3）外周组织损伤可以激活脊髓RhoA信号通路，以神经损伤最为显著4）鞘内持续给予胆固醇合成抑制剂辛伐他汀能抑制福尔马林模型长时程的机械痛敏，而且可以抑制福尔马林诱发的脊髓小胶质细胞活化和磷酸化p38 MAPK和RhoA信号通路的激活；5）无论是鞘内，还是腹腔给予阿仑膦酸钠均可明显抑制了神经病理性疼痛模型的热敏性疼痛和机械刺激痛，同时显著减轻模型大鼠脊髓中小胶质细胞的活化和磷酸化的p38的表达；6）不同浓度的阿仑膦酸钠处理LPS刺激的小胶质细胞，可以减少小胶质细胞磷酸化的p38蛋白表达，下调炎性介质TNF-α, IL-1β和IL-6的基因表达。胆固醇代谢通路中的FPP和GGPP可以一定程度上呈浓度梯度状逆转阿仑膦酸钠对小胶质细胞活化的抑制作用。本项目的主要结论：高脂饮食不仅导致机体以肥胖为特征的脂代谢紊乱，还可以导致机体疼痛阈值减低、对外周伤害性刺激有更强的疼痛反应。高脂饮食后，脂代谢的中间产物如胆固醇代谢中间产物焦磷酸法尼酯(FPP) 和牛龙牛儿(基)焦膦酸(GGPP)等，激活脊髓组织中RhoA-p38MAPK信号通路，形成以小胶质细胞活化为中心的炎症免疫反应，导致中枢痛觉敏化。本研究的学术观点对于慢性疼痛的分子机制及其高脂饮食与全身健康的关系具有重要的理论和临床意义，针对Rho/MAPK信号通路和相应的脂代谢产物有望成为研究和治疗慢性疼痛的分子靶点，相应的药物亦有可能用于慢性疼痛的辅助治疗。