Normobaric hyperoxia alleviates complement C3-mediated synaptic pruning and brain injury after intracerebral hemorrhage

Abstract

Background: Intracerebral hemorrhage (ICH) is a common cerebrovascular disease, and the complement cascade exacerbates brain injury after ICH. As the most abundant component of the complement system, complement component 3 (C3) plays essential roles in all three complement pathways. However, the effects of C3 on neurological impairment and brain injury in ICH patients and the related mechanism have not been fully elucidated. Normobaric hyperoxia (NBO) is regarded as a treatment for ICH patients, and recent clinical studies also have confirmed the neuroprotective role of NBO against acute ICH-mediated brain damage, but the underlying mechanism still remains elusive.

Aims: In the present study, we investigated the effects of complement C3 on NBO-treated ICH patients and model mice, and the underlying mechanism of NBO therapy in ICH-mediated brain injury.

Results: Hemorrhagic injury resulted in the high plasma C3 levels in ICH patients, and the plasma C3 levels were closely related to hemorrhagic severity and clinical outcomes after ICH. BO treatment alleviated neurologic impairments and rescued the hemorrhagic-induced increase in plasma C3 levels in ICH patients and model mice. Moreover, the results indicated that NBO exerted its protective effects of on brain injury after ICH by downregulating the expression of C3 in microglia and alleviating microglia-mediated synaptic pruning.

Conclusions: Our results revealed that NBO exerts its neuroprotective effects by reducing C3-mediated synaptic pruning, which suggested that NBO therapy could be used for the clinical treatment of ICH.

Keywords: complement component 3; intracerebral hemorrhage; microglia; normobaric hyperoxia; synaptic pruning.