Role of C1q in spleen-derived neutrophil infiltration and neuroinflammation after ICH in mice

Abstract Background: Neuroinflammation is a major detrimental role of secondary brain injury after spontaneously intracerebral hemorrhage (ICH). Neutrophil infiltration plays a key role in the pathophysiology of ICH, but the coming resource and mechanism is unknown. This study aims to investigate whether spleen-derived neutrophil infiltration accelerated neuroinflammation and the role of C1q classical pathway.Methods: Male C57 mice were subjected to collagenase-induced ICH. If necessary, splenectomy was performed 2 weeks prior to ICH induction or anti-C1q neutralizing antibody (50mg/kg) was injected intravenously into the tail vein 15 minutes prior. Immunohistochemistry, Propidium Iodide staining, western blotting, ELISA and qRT-PCR were used to study the change of molecular proteins, neuronal cells and inflammatory factors. 7.0T animal MRI was used to assess hydrocephalus.Results: At 0h, 6h, 12h, 24h and 48h post ICH induction, we found a significant increasing tendency of microglia activation and neutrophil infiltration around hematoma and that C1q upregulation was correlated with neuronal decrease, which peaked at 24h after ICH. Here, we demonstrated spleen atrophy and upregulation of neutrophil in spleen 24h after ICH. Splenectomy prior to ICH mice resulted in significant decrease of microglia and neutrophil infiltration compared with that in group of sham-splenectomy. Moreover, both anti-C1q antibody and splenectomy significantly attenuated neutrophil infiltration and neuron death, restored synapse VGAT, alleviated hydrocephalus and inflammatory factors, such as IL-1β, TNF-α and IL-6 after ICH.Conclusion: The study demonstrated that spleen is a major source of brain neutrophil infiltration after ICH. C1q-targeted inhibition of classic complement pathway could prevent spleen-derived neutrophil infiltration and attenuate ICH induced neuroinflammation, which provides a novel therapeutic approach for hemorrhagical stroke.