Abstract
To explore the mechanism of TLR4/NF-κB regulation of microglia-mediated inflammation after NSC-Exos transplantation. In this study, a right middle cerebral artery occlusion model (MCAO) was constructed in SD rats, NSC-Exos was injected into the lateral ventricle through brain stereo localization. TAK-242 was given 1 day before MCAO in rats. Histopathological changes, microglia-mediated inflammatory factor, colocalized number of CD86/Iba1 and CD206/Iba1 cells, and TLR4/NF-κB were detected in rats. After brain injury, the number of CD86/Iba1 cells increased, and the expression of pro-inflammatory factors, TLR4 and NF-κB were increased. When treatment with NSC-Exos, the number of CD206/Iba1 cells were increased, and the expression of anti-inflammatory factors, TLR4 and NF-κB were decreased, promoting anti-inflammatory phenotype polarization. More importantly, TAK-242 reversed the effect of NSC-Exos transplantation in animal model. These results suggest that NSC-Exos can improve the microglia-mediated inflammatory response in rats with ischemic brain injury, which may be related to the regulation of TLR4/NF-κB pathway.
Introduction
Cerebral stroke, a fatal cerebrovascular disease, is the second most common cause of death and disability in the world (Chidambaram et al., 2022) . At present, one of the most commonly used treatments for ischemic stroke is intravenous thrombolytic therapy with recombinant tissue plasminogen activator, but thrombolytic therapy can cause brain reperfusion injury (Herpich et al., 2020; Jolugbo et al., 2021). Although the pathophysiological mechanisms of cerebral ischemia-reperfusion injury have been well understood in recent decades, there is still no effective treatment (Giuriati et al., 2021; Ran et al., 2021). More and more evidence shows that neuroinflammation is related to pathogenesis of cerebral ischemia-reperfusion injury, and it is worth mentioning that microglia-mediated inflammatory response plays a key role (Zhu et al., 2021).
Exosomes are extracellular vesicles that can cross the blood-brain barrier as a natural carrier system with low immunogenicity (Yuan et al., 2017), no tumorigenicity and no risk of immune rejection, so they have been widely used as a therapeutic strategy for a variety of central nervous system diseases (Arabpour et al., 2021; Huang et al., 2022). It has been reported that neural stem cell-derived exosomes (NSC-Exos) significantly improve the inflammatory response of animal stroke, alleviating inflammation-induced neurodegeneration (Zhang et al., 2023; Zhu et al., 2023). Other experiments have reported that activation of Toll-like receptor 4 (TLR4) can cause activation of downstream ligand nuclear factor NF-κB (Scalise et al., 2021), promote the activation of microglia and further increase the release of inflammatory factors (Scalise et al., 2021), aggravating brain injury in the early damage of ischemia (Tian et al., 2021). So far, few studies have focused on whether TLR4/NF-κB pathway regulates the polarization of NSC-Exos on microglia during cerebral ischemia, and the specific mechanism of action is unknown (Cui et al., 2022). Therefore, we speculate that TLR4/NF-κB regulation of microglia-mediated NSC-Exos to reduce neuroinflammation may be an effective method for the treatment of ischemic brain injury. Therefore, this study established a rat MCAO model to observe whether NSC-Exos therapy regulates microglial polarization through TLR4/NF-κB, revealing the molecular mechanism of TLR4/NF-κB regulation of microglial involvement in inflammatory response, and providing a new target for exosomes to prevent and treat cerebral ischemia diseases.