Experimental Neurophysiology and Neuronal Circuits Group, Hospital Nacional de Parapléjicos, Servicio de Salud de Castilla-La Mancha, SESCAM, Toledo, Spain.
Research Unit, Hospital Santa Cristina, Instituto de Investigación Sanitaria Princesa (IIS-IP), Hospital Universitario de la Princesa, Madrid, Spain.
Br J Pharmacol. 2021 Sep;178(17):3395-3413. doi: 10.1111/bph.15488. Epub 2021 Jun 1.
Activation of astrocytes contributes to synaptic remodelling, tissue repair and neuronal survival following traumatic brain injury (TBI). The mechanisms by which these cells interact to resident/infiltrated inflammatory cells to rewire neuronal networks and repair brain functions remain poorly understood. Here, we explored how TLR4-induced astrocyte activation modified synapses and cerebrovascular integrity following TBI.
To determine how functional astrocyte alterations induced by activation of TLR4 pathway in inflammatory cells regulate synapses and neurovascular integrity after TBI, we used pharmacology, genetic approaches, live calcium imaging, immunofluorescence, flow cytometry, blood-brain barrier (BBB) integrity assessment and molecular and behavioural methods.
Shortly after a TBI, there is a recruitment of excitable and reactive astrocytes mediated by TLR4 pathway activation with detrimental effects on post-synaptic density-95 (PSD-95)/vesicular glutamate transporter 1 (VGLUT1) synaptic puncta, BBB integrity and neurological outcome. Pharmacological blockage of the TLR4 pathway with resatorvid (TAK-242) partially reversed many of the observed effects. Synapses and BBB recovery after resatorvid administration were not observed in IP R2 mice, indicating that effects of TLR4 inhibition depend on the subsequent astrocyte activation. In addition, TBI increased the astrocytic-protein thrombospondin-1 necessary to induce a synaptic recovery in a sub-acute phase.
Our data demonstrate that TLR4-mediated signalling, most probably through microglia and/or infiltrated monocyte-astrocyte communication, plays a crucial role in the TBI pathophysiology and that its inhibition prevents synaptic loss and BBB damage accelerating tissue recovery/repair, which might represent a therapeutic potential in CNS injuries and disorders.
星形胶质细胞的激活有助于创伤性脑损伤（TBI）后突触重塑、组织修复和神经元存活。这些细胞与驻留/浸润的炎性细胞相互作用以重塑神经元网络和修复脑功能的机制仍知之甚少。在这里，我们探讨了 TLR4 诱导的星形胶质细胞激活如何在 TBI 后改变突触和脑血管完整性。
为了确定 TLR4 途径激活引起的功能性星形胶质细胞改变如何调节 TBI 后炎症细胞中的突触和神经血管完整性，我们使用了药理学、遗传方法、活钙成像、免疫荧光、流式细胞术、血脑屏障（BBB）完整性评估以及分子和行为方法。
在 TBI 后不久，通过 TLR4 途径激活招募兴奋性和反应性星形胶质细胞，对突触后密度-95（PSD-95）/囊泡谷氨酸转运体 1（VGLUT1）突触小体、BBB 完整性和神经功能结局产生有害影响。用 resatorvid（TAK-242）阻断 TLR4 途径可部分逆转观察到的许多影响。在 IP R2 小鼠中未观察到 resatorvid 给药后的突触和 BBB 恢复，表明 TLR4 抑制的作用取决于随后的星形胶质细胞激活。此外，TBI 增加了星形胶质细胞蛋白血栓素-1，这对于在亚急性阶段诱导突触恢复是必要的。
我们的数据表明，TLR4 介导的信号转导，很可能通过小胶质细胞和/或浸润的单核细胞-星形胶质细胞通讯，在 TBI 病理生理学中发挥关键作用，其抑制可防止突触丢失和 BBB 损伤，加速组织恢复/修复，这可能代表 CNS 损伤和疾病的治疗潜力。
