七氟烷麻醉下老龄化记忆减退的新机制：B2M调控的海马DG区神经发生

Sevoflurane induced age-related memory deficits is the hotspot issue in the field of anesthesia and perioperative medicine. However, the pathogenesis of inhaled anesthetics induced memory deficits is poorly understood and an effective prevention and treatment has not been established. It has been identified that adult neurogenesis in the dentate gyrus of the hippocampus regulate neural activity, learning and memory. In our previous study, we observed sevoflurane decreased number of neurospheres within the hippocampus of aged mice. Considering the assosiation between systemic β2-microglobulin (B2M) levels and cognitive decline, and having identified B2M as a potential pro-aging factor associated with decreased neurogenesis, we hypothesized that sevoflurane exposure would lead to changes in B2M level, and that this would progressively predispose these aging mice to memory deficits in response to loss of regenerative faculties. To test this hypothesis, experiments using B2M-/- mice and heterochronic parabiosis, in which the circulatory systems of young and old animals are joined, indicate that sevoflurane increase B2M level in aged mice, and the increased endogenous B2M decreased adult hippocampal neurogenesis. Furthermore, exposure of primary mouse hippocampal neural progenitor cells (NPCs) to soluble B2M and sevoflurane, we investigated the effect of sevoflurane on self-renewal, pro-liferation, neuronal differentiation and cell migration in vitro. It will also provide new ideas and methods for the recovery of momery function after general anesthesia in senile patients.

吸入全麻药七氟烷加重老年患者记忆减退是麻醉与围术期医学关注的热点问题，但具体机制尚不清楚。研究表明，成年海马齿状回区（DG）的神经发生参与学习记忆等高级神经功能活动；B2M是诱发海马依赖性认知功能减退的关键衰老因子，与神经发生密切相关。我们前期研究发现七氟烷减少老龄小鼠海马新生神经元数量，因此我们假设七氟烷可能影响生理性老化过程中B2M水平，诱导神经发生障碍，从而促进老龄化记忆功能减退。本项目将拟通过B2M基因敲除小鼠和“联体共生”动物模型，证实七氟烷麻醉下老龄机体DG区新生神经元形成和迁移异常导致了记忆减退，探讨B2M调控神经发生的治疗作用。在此基础上，进一步在细胞和分子水平，研究七氟烷对B2M干预下海马神经前体细胞增殖以及颗粒细胞迁移的影响，阐明七氟烷麻醉下老龄化记忆减退的机制。为老年患者全麻下记忆减退的早期防治提供新的研究思路。

手术和麻醉导致老年患者术后认知功能障碍（POCD）增加了术后并发症的发生率，延长住院时间，是舒适化医疗和围术期快速康复亟待解决的问题。吸入全麻药七氟烷诱导老年患者记忆减退是麻醉与围术期医学关注的热点问题。本课题组前期研究已证实七氟烷减少老龄小鼠海马新生神经元数量，然而具体机制仍未阐明清楚。文献报道B2M是全身系统的衰老因子，B2M-MHCI复合物抑制成体神经发生，影响学习和记忆。内源性B2M基因表达缺失可降低年龄相关性认知减退并提高老龄小鼠的神经发生。因此，本项目提出假说：七氟烷麻醉下老龄化记忆减退，可能与B2M调控的海马神经发生和迁移作用有关。. 本研究首先观察七氟烷暴露对老龄小鼠增龄性记忆减退和机体衰老因子B2M水平的持续性影响，揭示了七氟烷麻醉导致老龄机体海马糖代谢水平降低，海马DG区神经发生减退，并抑制神经元迁移。行为学检测结果提示七氟烷暴露老龄小鼠明显降低了其空间记忆和工作记忆，与机体内B2M水平相关。其次，原代培养神经元进行人重组体B2M干预，海马定位注射B2M干预野生小鼠，证实了B2M促进神经元的衰老。在胚胎小鼠神经干细胞培养中，人重组体B2M干预建立老化神经元模型，给予3%七氟烷37℃孵育2h，证实了七氟烷诱导了颗粒细胞异常迁移，减少了神经元的轴突数量和最长轴突的长度，显著降低神经轴突导向因子Slit2/Robo1的表达。最后，采用野生型小鼠，B2M-/-小鼠和异时联体模型，证实减轻老龄小鼠机体B2M水平，可缓解七氟烷麻醉对老年认知的影响，是通过恢复海马DG区神经发生和增加新生神经元的迁移实现的。本研究证实B2M是七氟烷诱导的老年POCD的关键因素，为改善全麻药物导致的持续性记忆减退提供了新思路，阻断麻醉因素诱发的衰老记忆减退的发生、发展，对增加老龄患者的术后快速康复具有重要的临床意义。