Perioperative neurocognitive disorder (PND) is a long-term postoperative complication in elderly surgical patients. The underlying mechanism of PND is unclear, and no effective therapies are currently available. It is believed that neuroinflammation plays an important role in triggering PND. The secreted glycoprotein myeloid differentiation factor 2 (MD2) functions as an activator of the Toll-like receptor 4 (TLR4) inflammatory pathway, and α5GABAA receptors (α5GABAARs) are known to play a key role in regulating inflammation-induced cognitive deficits. Thus, in this study, we aimed to investigate the role of MD2 in PND and determine whether α5GABAARs are involved in the function of MD2. Eighteen-month-old C57BL/6J mice were subjected to laparotomy under isoflurane anesthesia to induce PND. The Barnes maze was used to assess spatial reference learning and memory, and the expression of hippocampal MD2 was assayed by western blotting. MD2 expression was downregulated by bilateral injection of AAV-shMD2 into the hippocampus or tail vein injection of the synthetic MD2 degrading peptide Tat-CIRP-CMA (TCM) to evaluate the effect of MD2. Primary cultured neurons from brain tissue block containing cortices and hippocampus were treated with Tat-CIRP-CMA to investigate whether downregulating MD2 expression affected the expression of α5GABAARs. Electrophysiology was employed to measure tonic currents. For α5GABAARs intervention experiments, L-655,708 and L-838,417 were used to inhibit or activate α5GABAARs, respectively. Surgery under inhaled isoflurane anesthesia induced cognitive impairments and elevated the expression of MD2 in the hippocampus. Downregulation of MD2 expression by AAV-shMD2 or Tat-CIRP-CMA improved the spatial reference learning and memory in animals subjected to anesthesia and surgery. Furthermore, Tat-CIRP-CMA treatment decreased the expression of membrane α5GABAARs and tonic currents in CA1 pyramidal neurons in the hippocampus. Inhibition of α5GABAARs by L-655,708 alleviated cognitive impairments after anesthesia and surgery. More importantly, activation of α5GABAARs by L-838,417 abrogated the protective effects of Tat-CIRP-CMA against anesthesia and surgery-induced spatial reference learning and memory deficits. MD2 contributes to the occurrence of PND by regulating α5GABAARs in aged mice, and Tat-CIRP-CMA is a promising neuroprotectant against PND.

中文翻译：

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MD2通过调节老年小鼠的α5GABAA受体参与围手术期神经认知障碍的发病机制

围手术期神经认知障碍（PND）是老年外科患者的长期术后并发症。PND的潜在机制尚不清楚，目前尚无有效的治疗方法。认为神经炎症在触发PND中起重要作用。分泌的糖蛋白骨髓分化因子 2 (MD2) 作为 Toll 样受体 4 (TLR4) 炎症通路的激活剂起作用，并且已知 α5GABAA 受体 (α5GABAARs) 在调节炎症诱导的认知缺陷中起关键作用。因此，在本研究中，我们旨在研究 MD2 在 PND 中的作用，并确定 α5GABAARs 是否参与 MD2 的功能。18 个月大的 C57BL/6J 小鼠在异氟醚麻醉下进行剖腹手术以诱导 PND。Barnes迷宫用于评估空间参考学习和记忆，并通过蛋白质印迹测定海马MD2的表达。通过将 AAV-shMD2 双侧注射到海马或尾静脉注射合成的 MD2 降解肽 Tat-CIRP-CMA (TCM) 来下调 MD2 表达，以评估 MD2 的作用。用 Tat-CIRP-CMA 处理来自含有皮质和海马的脑组织块的原代培养神经元，以研究下调 MD2 表达是否影响 α5GABAARs 的表达。电生理学被用来测量强直电流。对于 α5GABAARs 干预实验，L-655,708 和 L-838,417 分别用于抑制或激活 α5GABAARs。吸入异氟醚麻醉下的手术会导致认知障碍并提高海马中 MD2 的表达。AAV-shMD2 或 Tat-CIRP-CMA 下调 MD2 表达改善了接受麻醉和手术的动物的空间参考学习和记忆。此外，Tat-CIRP-CMA 治疗降低了海马 CA1 锥体神经元中膜 α5GABAAR 和强直电流的表达。L-655,708 对 α5GABAARs 的抑制减轻了麻醉和手术后的认知障碍。更重要的是，L-838,417 对 α5GABAARs 的激活消除了 Tat-CIRP-CMA 对麻醉和手术引起的空间参考学习和记忆缺陷的保护作用。MD2通过调节老年小鼠的α5GABAARs促进PND的发生，