The Dual Role Of Peroxiredoxin 1/2 In Secondary Brain Injury After Subarachnoid Hemorrhage

Background:Subarachnoid hemorrhage(SAH)is a catastrophic condition in clinical practice characterized by high mortality and morbidity.The most common cause of SAH is the rupture of an intracranial aneurysm.Among the victims,fifty percent of them suffered from permanent neurological deficits,bringing a heavy burden to the family and society.Although the advances in surgical technique and endovascular treatment improved the survival rates of patients,the disability rates remain unchanged.The increased intracranial pressure,decreased cerebral blood flow and global cerebral ischemia strike the brain after SAH.Then the secondary inflammatory response set the brain on fire after the first strike.The current theory suggests that the prognosis of patients after SAH is related to the intensity of secondary inflammatory reaction in the brain.Hence,it is important to clarify the pathophysiology of inflammatory response after SAH before we can find an effective treatment.Peroxiredoxin 1/2(Prx1/2)——two most abundant peroxidases in human body cells.They function as hydrogen peroxide scavengers.It has been shown that Prx 1/2 plays dual role in many diseases,such as cancer and neurodegeneration diseases.We assumed that the intracellular Prx1/2 could protect the brain against oxidative stress after SAH but the extracellular Prx2 would cause damage to brain as a damage-associated molecular pattern(DAMP).Methods:We investigated the distribution of Prx1/2 in the brains of mice both in vivo and in vitro using immunofluorescence staining.The expression of Prx1/2 after SAH was determined by western blot.Adenanthin was used to inhibit Prx1/2 function and Prxl/2 overexpression was achieved by injecting adeno-associated virus.Oxidative stress and neuronal apoptosis were assessed both in vivo and in vitro.The neurological function,inflammatory response,and related cellular signals were analyzed.Then,we introduced a co-culture system of primary neurons and microglia.Prx2 was added to culture medium with oxyhemoglobin(OxyHb)to mimic SAH in vitro.Neuronal cell viability was assessed by lactate dehydrogenase(LDH)assay and neuronal apoptosis was determined by TUNEL staining.Inflammatory factors in culture medium were measured by ELISA and their mRNA levels in microglia were determined by qPCR.Toll-like receptor 4 knockout(TLR4-KO)mice were used to provide TLR4-KO microglia,ST-2825 was used to inhibit MyD88,and pyrrolidine dithiocarbamate(PDTC)was used to inhibit NF-?B.Related cellular signals were analyzed by western blot.Results:Prxl was mainly expressed in astrocytes,and Prx2 was abundant in neurons.The expression of Prxl/2 was elevated after SAH,and their expression levels peaked before pro-inflammatory cytokines.Inhibiting Prxl/2 promoted neuronal apoptosis by increasing the H2O2 levels via the Apoptosis Signal-regulating Kinase 1(ASK1)/p38 pathway.By contrast,overexpression of Prxl/2 attenuated oxidative stress and neuronal apoptosis after SAH.Thus,early expression of Prx1/2 may protect the brain from oxidative damage after SAH.However,the extracellular Prx2 released from damaged neurons and lytic erythrocytes can interacted with TLR4 on microglia after SAH and then activated microglia through TLR4/MyD88/NF-?B signaling pathway.Pro-inflammatory factors were expressed and released,eventually caused neuronal apoptosis.Conclusion:Early expression of Prx1/2 may protect the brain from oxidative damage after SAH and may provide a novel target for treating SAH.Extracellular Prx2 is a DAMP which resulted in microglial activation via TLR4/MyD88/NF-?B pathway then neuronal apoptosis.