肿瘤坏死因子-α在外周神经损伤引起海马记忆功能障碍中的作用及其机制

Abundance clinical evidence has demonstrated that around 2/3 patients with chronic pain suffer from working memory deficits, which reduces patient's life quality and working ability seriously. However, mechanisms underlying this form of memory impairment are unclear. Recently, we reported for first time that perpheral nerve injury, a most common cause of chronic pain, inhibits hippocampal LTP and impairs working memory by up-regulation of TNF-α in hippocampus and in cerebrospinal fluid. The polit experiments of this project showed that peripheral nerve injury reduced the numbers of dentrites and spines of hippocampal pyramidal cells in CA1 region and the effect was prevented by genetic deletion of TNF receptor 1. In cultured hippocampal slices, recombinant rat TNF (rrTNF) miniced the effect of peripheral nerve injury on dentrites and spines. In addition, nerve injury caused the infiltration of macrophages into the hippocampus. Accordingly, we assume that the immunoinflammation might be a main cause for the damage of the structure and funtion of hippocampus. In the present project, we try to answer the following questions. How could peripheral nerve injury lead to the infiltration of immunocells into hippocampus and to the up-regulation of proinflammmatory cytokines? How could TNF-α effect hippocampal structure, function and neurogenesis? Could anti-inflammatory cytokine IL-10 reverse the effect of TNF-α? Unlike Alzheimer's disease, which is mainly implicated in aged population, memory deficits produced by peripheral nerve injury may occur at any ages, especially young adults. Thus, understanding the mechanisms of this form of memory deficits is of important theoretical and clinical significance.

大量临床研究表明，约2/3慢性疼痛病人伴有工作记忆减退，严重影响病人的生活质量和工作能力，但机制不清。我们率先报道，外周神经损伤（慢性疼痛最常见的原因）通过上调海马TNF-α，抑制海马LTP，损害工作记忆。本项目预实验结果显示：外周神经损伤导致海马椎体细胞的树突和树突棘明显减少，敲除TNF受体1可防止该作用；外源性rrTNF在培养海马脑片上可模拟神经损伤此作用；神经损伤还引起海马巨噬细胞浸润。我们推测，免疫炎症可能是海马结构和功能受损的主要原因。本项目拟采用行为学、电生理和分子生物学方法进一步揭示：外周神经损伤如何导致海马免疫细胞浸润和TNF-α上调；TNF-α上调如何影响海马结构功能及神经元再生导致记忆障碍；抗炎细胞因子IL-10能否反转TNF-α的作用。与老年性痴呆不同，外周神经损伤引起的记忆障碍可发生在各类人群，尤其是青壮年。因此，揭示此种类型记忆障碍的机制具有重要的理论和临床意义。

大量临床研究表明，约2/3慢性疼痛病人伴有工作记忆减退，严重影响病人的生活质量和工作能力，但机制不清。我们率先报道，外周神经损伤（慢性疼痛最常见的原因）通过上调海马TNF-α，抑制海马LTP，损害工作记忆(Ren et al., Neuropsychopharmacology.. 2011)。本项目采用了膜片钳、细胞流式、行为学、分子生物学等方法结合工具药和转基因动物从三个方面揭示外周神经损伤引起海马突触可塑性下降和记忆障碍的分子机制： 1）运用静脉注射白介素-1β（IL-1β）、IL-1β中和抗体以及IL-1β受体1（IL1R1）基因敲除动物证实外周神经损伤后局部的IL-1β升高通过血液循环影响中枢神经系统的多个脑区（海马，杏仁）小胶质细胞的激活，从而引起脑区局部IL-1β的表达增加是导致外周神经损伤引起病理性疼痛，记忆障碍和抑郁的关键原因(Gui et al., Mol Pain 2016)；2）外周神经损伤导致海马椎体细胞的树突和树突棘明显减少，敲除TNF受体1可防止该作用，而外源性rrTNF在培养海马脑片上可模拟神经损伤此作用(Liu et al., J Neurosi. 2017)； 3）血液中上调的IL-1β通过激活内皮细胞上调趋化因子CXCL12诱导血液中CXCR4+单核细胞粘附海马腔隙区内皮细胞增多，进而引起血管周内皮细胞和星形胶质细胞的激活和海马的神经炎症导致记忆障碍(Mai et al., 2018, submitted)。与老年性痴呆不同，外周神经损伤引起的记忆障碍可发生在各类人群，尤其是青壮年。因此，揭示此种类型记忆障碍的机制具有重要的理论和临床意义。