Inflammatory modulation mediated by microglial M1/M2 polarization is one of the main pathophysiological processes involved in early brain injury (EBI) after subarachnoid haemorrhage (SAH). Previous studies have shown that recombinant human erythropoietin (rhEPO) alleviates EBI following experimental SAH. However, the mechanisms of this beneficial effect are still poorly understood. Recent research has suggested that EPO shows anti-inflammatory properties. Therefore, we tried to analyse whether rhEPO administration influenced microglial M1/M2 polarization in early brain injury after SAH and to identify the underlying molecular mechanism of any such effect. We found that treatment with rhEPO markedly ameliorated SAH-induced EBI, as shown by reductions in brain cell apoptosis, neuronal necrosis, albumin exudation and brain edema. Moreover, the expression levels of p-JAK2 and p-STAT3 were significantly increased in the cortex after SAH induction and were further increased by EPO treatment; in addition, the p-JAK2 inhibitor AZD1480 impaired the protective effect of EPO against SAH-induced EBI in vivo. Furthermore, EPO promoted the polarization of microglia towards the protective M2 phenotype and alleviated inflammation. In cultured microglia under oxyhemoglobin (OxyHb) treatment, EPO up-regulated the expression of the EPO receptor (EPOR), which did not occur in response to OxyHb treatment alone, and EPO magnified OxyHb-induced increases in p-JAK2 and p-STAT3 and modulated OxyHb-challenged microglial polarization towards M2. Interestingly, the effect of EPO on microglia polarization was cancelled by EPOR knockdown or by p-JAK2 or p-STAT3 inhibition, suggesting a core role of the EPOR/JAK2/STAT3 pathway in modulating microglial function and phenotype. In conclusion, the therapeutic effect of rhEPO on the early brain injury after SAH may relate to its modulation of inflammatory response and microglia M1/M2 polarization, which may be mediated in part by the EPOR/JAK2/STAT3 signalling pathway. These results improved the understanding of the anti-inflammatory effect of EPO on microglia polarization, which might optimize the therapeutic modalities of EPO treatment with SAH.
Keywords: Early brain injury; Erythropoietin; Inflammation; Microglial polarization; Subarachnoid haemorrhage.
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