Department of Burn and Plastic Surgery, Shenzhen Longhua District Central Hospital, Shenzhen, 518110, Guangdong, China.
Center for Human Tissues and Organs Degeneration, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, Guangdong, China.
Neuromolecular Med. 2023 Dec;25(4):616-631. doi: 10.1007/s12017-023-08764-z. Epub 2023 Oct 5.
Anxiety manifestations and cognitive dysfunction are common sequelae in patients with sepsis-associated encephalopathy (SAE). Microglia-mediated inflammatory signaling is involved in anxiety, depression, and cognitive dysfunction during acute infection with bacterial lipopolysaccharide (LPS). However, the molecular mechanisms underlying microglia activation and behavioral and cognitive deficits in sepsis have not been in fully elucidated. Based on previous research, we speculated that the CD137 receptor/ligand system modulates microglia function during sepsis to mediate classical neurological SAE symptoms. A murine model of SAE was established by injecting male C57BL/6 mice with LPS, and cultured mouse BV2 microglia were used for in vitro assays. RT-qPCR, immunofluorescence staining, flow cytometry, and ELISA were used to assess microglial activation and the expression of CD137L and inflammation-related cytokines in the mouse hippocampus and in cultured BV2 cells. In addition, behavioral tests were conducted in assess cognitive performance and behavioral distress. Immunofluorescence and RT-qPCR analyses showed that hippocampal expression of CD137L was upregulated in activated microglia following LPS treatment. Pre-treatment with the CD137L neutralizing antibody TKS-1 significantly reduced CD137L levels, attenuated the expression of M1 polarization markers in microglia, and inhibited the production of TNF-α, IL-1β, and IL-6 in both LPS-treated mice and BV2 cells. Conversely, stimulation of CD137L signaling by recombinant CD137-Fc fusion protein activated the synthesis and release of pro-inflammatory cytokines in cultures BV2 microglia. Importantly, open field, elevated plus maze, and Y-maze spontaneous alternation test results indicated that TKS-1 administration alleviated anxiety-like behavior and spatial memory decline in mice with LPS-induced SAE. These findings suggest that CD137L upregulation in activated microglia critically contributes to neuroinflammation, anxiety-like behavior, and cognitive dysfunction in the mouse model of LPS-induced sepsis. Therefore, therapeutic modulation of the CD137L/CD137 signaling pathway may represent an effective way to minimize brain damage and prevent cognitive and emotional deficits associated with SAE.
焦虑表现和认知功能障碍是脓毒症相关性脑病（SAE）患者的常见后遗症。小胶质细胞介导的炎症信号参与了急性细菌脂多糖（LPS）感染时的焦虑、抑郁和认知功能障碍。然而，SAE 中小胶质细胞激活以及行为和认知缺陷的分子机制尚未完全阐明。基于先前的研究，我们推测 CD137 受体/配体系统在脓毒症期间调节小胶质细胞功能，介导经典的神经 SAE 症状。通过给雄性 C57BL/6 小鼠注射 LPS 建立 SAE 小鼠模型，并进行体外 BV2 小胶质细胞培养实验。采用 RT-qPCR、免疫荧光染色、流式细胞术和 ELISA 评估小鼠海马和培养的 BV2 细胞中小胶质细胞的激活以及 CD137L 和炎症相关细胞因子的表达。此外，还进行了行为测试以评估认知表现和行为困扰。免疫荧光和 RT-qPCR 分析表明，LPS 处理后激活的小胶质细胞中 CD137L 在海马中的表达上调。用 CD137L 中和抗体 TKS-1 预处理可显著降低 CD137L 水平，减弱小胶质细胞中 M1 极化标志物的表达，并抑制 LPS 处理的小鼠和 BV2 细胞中 TNF-α、IL-1β 和 IL-6 的产生。相反，重组 CD137-Fc 融合蛋白刺激 CD137L 信号会激活培养的 BV2 小胶质细胞中促炎细胞因子的合成和释放。重要的是，旷场、高架十字迷宫和 Y 迷宫自发交替测试结果表明，TKS-1 给药可减轻 LPS 诱导的 SAE 小鼠的焦虑样行为和空间记忆下降。这些发现表明，激活的小胶质细胞中 CD137L 的上调对 LPS 诱导的脓毒症小鼠模型中的神经炎症、焦虑样行为和认知功能障碍起着关键作用。因此，CD137L/CD137 信号通路的治疗性调节可能是减轻脑损伤和预防与 SAE 相关的认知和情绪缺陷的有效方法。
