Microglia aggravate white matter injury via C3/C3aR pathway after experimental subrachnoid hemorrhage

Activation of microglia induces neuroinflammation in acute and chronic phase is closely related to the white matter injury (WMI) pathophysiologyafter subrachnoid hemorrhage (SAH). The complement C3a receptor (C3aR) has a dual role in regulating inflammation and plays a role in neurodevelopment, neuroplasticity and neurodegeneration, but it’s effect on WMI during SAH re'mairemains unknown. In this study, 175 male C57BL/6J mice received SAH by endovascular perforation. oxy-Hb was used to simulate SAH in vitro. Multiple technical approaches, including immunohistochemistry, transcriptome sequencing, neurological function assessment, and various molecular biotechnologies, were used to assess the activation of the C3-C3aR pathway after SAH and its effects on microglial polarizations and WMI after SAH. The results showed that abnormal microglial activation after SAH was accompanied by upregulation of complement C3 and C3aR. C3aR inhibition reduced abnormal microglial activation, attenuated neuroinflammation, ameliorated WMI and cognitive deficits after SAH. RNA-Seq revealed that C3aR inhibition downregulated several immune and inflammatory pathways and ameliorated cellular injury by downregulating Pidd1 expression. The adverse effects of C3-C3aR in SAH may be related to Endoplasmic reticulum (ER) stress-dependent cellular injury and formation of inflammasome. PERK agonists exacerbate cellular injury and neuroinflammation attenuated by C3aR inhibition. Intranasal C3a treatment during the subacute phase of SAH helps to reduce astrocyte reactivity and ameliorate cognitive deficits after SAH. In conclusion, these findings suggest that C3aR plays a critical role in the regulation of neuroinflammation and WMI after SAH, providing new therapeutic targets to ameliorate WMI and cognitive deficits after SAH.