The Role And Mechanisms Of Progranulin After Subarachnoid Hemorrhage

Background:Subarachonoid hemorrahge(SAH)is a life-threatening cerebrovascular disease that is mainly caused by ruptured aneurysms and has a morbidity and mortality rate.Recent studies have demonstrated that early brain injury(EBI)is the most important cause of the high morbidity and mortality.EBI is the immediate injury to the brain within 72h after SAH and strongly determines the prognosis of SAH patients.Several physiological derangements occur during EBI,including increasing intracranial pres-sure,decreasing cerebral blood flow,and global cerebral ischemia.These immediate events initiate secondary injuries,such as inflammation,blood brain barrier disruption,apoptosis,and oxidative cascades,among these inflammatory reactions have been highlighted as the major contributor to EBI.Clinical studies have demonstrated that increased pro-inflammatory cytokines in the cerebrospinal fluid contributed to the neurological dysfunction and poor outcome of SAH patients.Neutrophils play an important role in inflammatory reactions.Neutrophils,which are induced by inflammation,migrate into brain issue,exaggerate the inflammatory reaction,reduce cerebral blood flow,and aggravate brain injury.In addition,neutrophils contribute to BBB disruption,brain edema,and neural cell injury by releasing proteases,cytokines,and chemokines.Progranulin(PGRN)is cysteine-rich protein that is typically secreted in a highly glycosylated form and a single PGRN gene is situated on chromosome 17q21.32.PGRN is expressed ubiquitously throughout the body.In the central nervous system,it is detected in neurons and microglia,but in astrocytes and ependymal cells,little or no PGRN is detected.It is reported that PGRN performs various biological functions,such as the regulation of cell growth,embryonic development,tissue repair,and the modulation of inflammation.Recently,the anti-inflammatory effects of PGRN in various states were reported,including acute lung injury,neurodegenerative diseases and ischemic stroke.PGRN ha s been reported to have anti-inflammatory properties that may prevent brain injury by reducing the release of pro-inflammatory cytokines or elevating the release of anti-inflammatory factors.In addition,PGRN-deficient mice displayed exaggerated inflammation compared with wild types.Methods:we firstly intended to investigate the levels of PGRN,myeloperoxidase(MPO),interleukin 1p(IL-1p),and tumor necrosis factor-a(TNF-a)in the cerebrospinal fluid from patients by enzyme-linked immunosorbent assay(ELISA).The cerebrospinal fluid was obtained from 43 SAH patients and 4 joint replacement patients(control group).In addition,The expression and distribution of PGRN were also detected in the cerebral cortex after experimental SAH in rats by western blottingimmunohistochemistry(IHC)and immunofluorescent double staining(IF).Recombinant human PGRN(r-PGRN)or an equal volume of phosphate-buffered saline(PBS)was administrated at 30 min after SAH.All rats were subsequently sacrificed at 24 h after SAH.Neurological score and brain water content were assessed.For mechanistic studies,the changes of MPO,MMP-9,ZO-1,Bcl-2,and cleaved caspase-3 were examined by western blotting and the levels of pro-inflammatory cytokines(IL-1β and TNF-α)were determined by ELISA.In addition,neuronal cell apoptosis and blood brain barrier permeability were examined.Results:The clinical study showed high levels of PGRN were detected in the control group,while decreased levels were observed in the cerebrospinal fluid of SAH patients with a bottoming point at 1～3 d after SAH.In addition,the levels of MPO,IL-1 β and TNF-a increased in the SAH groups and reached a highest point at 1-3 d after SAH.In rats,PGRN levels in the brain also decreased after SAH with the lowest level observed at 24 h.In addition,PGRN could be detected neurons and microglia,but in astrocytes little PGRN was detected.Administration of r-PGRN decreased brain water content and improved neurological scores at 24 h after SAH.These changes were associated with marked reductions in MPO,MMP-9,and proinflammation cytokine levels,as well as increased levels of Bcl-2 and ZO-1.In addition,neuronal apoptosis and BBB permeability were alleviated by r-PGRN.Conclusion:our study demonstrated that the levels of PGRN decreased in the cerebrospinal fluid from SAH patients and in the brain cortex of rat s after SAH.In addition,an administration of r-P GRN alleviated EBI,which was associated with inhibiting the inflammatory reaction by suppressing neutrophil recruitment.Moreover,PGRN inhibited blood brain barrier disruption and reduced neural cell apoptosis.