Department of Anesthesiology, Peking University First Hospital, Beijing, China.
Liangzhu Laboratory, MOE Frontier Science Center for Brain Science and Brain-Machine Integration, State Key Laboratory of Brain-Machine Intelligence, Zhejiang University, Hangzhou, 311121, China.
J Neuroinflammation. 2023 May 8;20(1):110. doi: 10.1186/s12974-023-02786-x.
Depression and dysosmia have been regarded as primary neurological symptoms in COVID-19 patients, the mechanism of which remains unclear. Current studies have demonstrated that the SARS-CoV-2 envelope (E) protein is a pro-inflammatory factor sensed by Toll-like receptor 2 (TLR2), suggesting the pathological feature of E protein is independent of viral infection. In this study, we aim to ascertain the role of E protein in depression, dysosmia and associated neuroinflammation in the central nervous system (CNS).
Depression-like behaviors and olfactory function were observed in both female and male mice receiving intracisternal injection of E protein. Immunohistochemistry was applied in conjunction with RT-PCR to evaluate glial activation, blood-brain barrier status and mediators synthesis in the cortex, hippocampus and olfactory bulb. TLR2 was pharmacologically blocked to determine its role in E protein-related depression-like behaviors and dysosmia in mice.
Intracisternal injection of E protein evoked depression-like behaviors and dysosmia in both female and male mice. Immunohistochemistry suggested that the E protein upregulated IBA1 and GFAP in the cortex, hippocampus and olfactory bulb, while ZO-1 was downregulated. Moreover, IL-1β, TNF-α, IL-6, CCL2, MMP2 and CSF1 were upregulated in both cortex and hippocampus, whereas IL-1β, IL-6 and CCL2 were upregulated in the olfactory bulb. Furtherly, inhibiting microglia, rather than astrocytes, alleviated depression-like behaviors and dysosmia induced by E protein. Finally, RT-PCR and immunohistochemistry suggested that TLR2 was upregulated in the cortex, hippocampus and olfactory bulb, the blocking of which mitigated depression-like behaviors and dysosmia induced by E protein.
Our study demonstrates that envelope protein could directly induce depression-like behaviors, dysosmia, and obvious neuroinflammation in CNS. TLR2 mediated depression-like behaviors and dysosmia induced by envelope protein, which could serve as a promising therapeutic target for neurological manifestation in COVID-19 patients.
抑郁和嗅觉障碍已被认为是 COVID-19 患者的主要神经症状，但其机制尚不清楚。目前的研究表明，SARS-CoV-2 包膜（E）蛋白是 Toll 样受体 2（TLR2）感知的促炎因子，表明 E 蛋白的病理特征独立于病毒感染。在这项研究中，我们旨在确定 E 蛋白在中枢神经系统（CNS）中抑郁、嗅觉障碍和相关神经炎症中的作用。
通过侧脑室注射 E 蛋白观察雌性和雄性小鼠的抑郁样行为和嗅觉功能。免疫组织化学结合 RT-PCR 用于评估皮质、海马和嗅球中的神经胶质细胞激活、血脑屏障状态和介质合成。用药物阻断 TLR2 以确定其在 E 蛋白相关的抑郁样行为和嗅觉障碍中的作用。
E 蛋白侧脑室注射可引起雌性和雄性小鼠的抑郁样行为和嗅觉障碍。免疫组织化学表明 E 蛋白上调了皮质、海马和嗅球中的 IBA1 和 GFAP，而下调了 ZO-1。此外，IL-1β、TNF-α、IL-6、CCL2、MMP2 和 CSF1 在皮质和海马中上调，而 IL-1β、IL-6 和 CCL2 在嗅球中上调。进一步，抑制小胶质细胞而非星形胶质细胞可减轻 E 蛋白引起的抑郁样行为和嗅觉障碍。最后，RT-PCR 和免疫组织化学表明，TLR2 在皮质、海马和嗅球中上调，阻断 TLR2 可减轻 E 蛋白引起的抑郁样行为和嗅觉障碍。
我们的研究表明，包膜蛋白可直接诱导中枢神经系统中的抑郁样行为、嗅觉障碍和明显的神经炎症。TLR2 介导了 E 蛋白引起的抑郁样行为和嗅觉障碍，这可能成为 COVID-19 患者神经表现的有希望的治疗靶点。
