Normalization of cholesterol metabolism in spinal microglia alleviates neuropathic pain. Normalization of cholesterol metabolism in spinal microglia alleviates neuropathic pain

Neuroinflammation is a major component in the transition to and perpetuation of neuropathic pain states. Spinal neuroinflammation involves activation of TLR4, localized to enlarged, cholesterol-enriched lipid rafts, designated here as inflammarafts. Conditional deletion of cholesterol transporters ABCA1 and ABCG1 in microglia, leading to inflammaraft formation, induced tactile allodynia in naïve mice. The apoA-I binding protein (AIBP) facilitated cholesterol depletion from inflammarafts and reversed neuropathic pain in a model of chemotherapy-induced peripheral neuropathy (CIPN) in wild-type mice, but AIBP failed to reverse allodynia in mice with ABCA1/ABCG1-deficient microglia, suggesting a cholesterol-dependent mechanism. An AIBP mutant lacking the TLR4-binding domain did not bind microglia nor reversed CIPN allodynia. The long-lasting therapeutic effect of a single AIBP dose in CIPN was associated with anti-inflammatory and cholesterol metabolism reprogramming and reduced accumulation of lipid droplets in microglia. These results suggest a cholesterol-driven mechanism of regulation of neuropathic pain by controlling TLR4 inflammarafts and gene expression program in microglia and blocking the perpetuation of neuroinflammation. Overall design: RNA-seq of lumbar spinal microglia from wild type or inducible Abca1 and Abcg1 microglial conditional Knockout mice. Microglia were sorted from naïve and CIPN (chemotherapy-induced peripheral neuropathy) mice treated with Saline or AIBP.

神经炎症是神经性疼痛状态发生转化与持续维持的核心病理环节。脊髓神经炎症涉及Toll样受体4（TLR4）的激活，该受体定位于体积增大、富含胆固醇的脂质筏，本文将此类脂质筏命名为炎症脂质筏（inflammarafts）。在小胶质细胞（microglia）中条件性敲除胆固醇转运蛋白ABCA1与ABCG1以诱导炎症脂质筏形成后，未受刺激的野生型小鼠可出现触觉异常性疼痛。载脂蛋白A-I结合蛋白（apoA-I binding protein, AIBP）可促进炎症脂质筏的胆固醇耗竭，并能逆转野生型小鼠化疗诱导周围神经病（chemotherapy-induced peripheral neuropathy, CIPN）模型中的神经性疼痛；但AIBP无法逆转ABCA1/ABCG1缺陷型小胶质细胞小鼠的触觉异常性疼痛，提示其作用机制依赖胆固醇代谢通路。缺失TLR4结合结构域的AIBP突变体既无法结合小胶质细胞，也不能逆转CIPN模型小鼠的触觉异常性疼痛。单次给予AIBP即可在CIPN模型中产生持久的治疗效果，该效果与小胶质细胞的抗炎反应、胆固醇代谢重编程以及脂滴积累减少密切相关。上述结果表明，通过调控TLR4炎症脂质筏与小胶质细胞的基因表达程序，并阻断神经炎症的持续进展，胆固醇驱动的机制可参与神经性疼痛的调控。
实验整体设计：对野生型小鼠或诱导型ABCA1/ABCG1小胶质细胞条件性敲除小鼠的腰段脊髓小胶质细胞进行RNA测序（RNA-seq）。实验样本取自经生理盐水或AIBP处理的未造模小鼠及CIPN模型小鼠，随后分选出其中的小胶质细胞。