The Role Of Choroid Plexus-related Inflammation In Rat Models Of Hydrocephalus And The Intervention Strategy

BackgroundHydrocephalus is a common neurological disorder affecting diverse populations,which is an independent predictor of worsened outcomes in acute intracerebral hemorrhage.In addition to hemorrhagic stroke,meningitis,brain trauma,and other neurological diseases can lead to hydrocephalus,from infants to the elderly,affecting a wide range of people.At present,the medical treatment of hydrocephalus is relatively limited,surgical treatment will be accompanied by epilepsy,infection,and other complications.Therefore,it is very important to deeply explore and understand the mechanism of hydrocephalus,which will provide us a feasible plan for the further clinical intervention of hydrocephalus.Choroid plexus is the principal source of cerebrospinal fluid and plays a critical role in hydrocephalus.A small but growing number of studies indicate choroid plexusrelated inflammation is involved in many neurological diseases.Choroid plexus macrophages have dual embryonic and adult hematopoietic origins,while microglia are maintained locally by self-renewal throughout adulthood.Choroid plexus macrophages are important immune portals of the central nervous system and play a major role in the choroid plexus inflammation.This work will explore the role of choroid plexus-related inflammation,especially the role of choroid plexus macrophages in rat models of hydrocephalus and enhance our understanding of choroid plexus functions.Two animal models were used in this study.In the first part of this study,rats received an injection of thrombin in the right lateral ventricle to mimic hydrocephalus.In the second part of this study,spontaneously hypertensive rats(SHRs)were used to develop hydrocephalus spontaneously.The development of hydrocephalus and choroid plexus changes in different models were observed,and the occurrence mechanism and intervention strategy of hydrocephalus in different models were discussed.ObjectiveThrombin is an important factor in brain injury,but the role of thrombin in hydrocephalus is unclear.This study aimed to examine the role of choroid plexusrelated inflammation in thrombin-induced hydrocephalus and the effects of SCH79797 on hydrocephalus.Methods1.The hydrocephalus model was induced by the intraventricular injection of thrombin.Rats received an injection of saline or thrombin into the right lateral ventricle randomly.Magnetic resonance imaging(MRI)was applied to measure the lateral ventricle volumes at 24 hours.Evans blue content and albumin leakage were assessed to test the brain barrier function.Immunofluorescence staining was performed to observe the response of the choroid plexus.Western blot was applied to detect the expression of junction proteins in choroid plexus.2.Our study will also define the role and mechanisms of thrombin receptor(protease?activated receptor 1,PAR1)in hydrocephalus by using immunofluorescence staining,Western blot,and MRI.To indicate the downstream of PAR1,our study observed the roles of PAR1 antagonist(SCH79797),Src inhibitor(PP2),p21?activated kinase?1(PAK1)inhibitor(IPA3)in the thrombin?induced hydrocephalus,and their effects on hydrocephalus.Results1.This current study confirmed that injection of thrombin resulted in obvious ventricles dilation on MRI.Compared with the saline injection group,more Evans blue leakage and albumin deposit were detected around the brain ventricles after thrombin injection.Additionally,inflammatory cell infiltration and a significant increase of CD68 positive choroid plexus macrophages were observed in choroid plexus in the thrombin group.Further study indicated that thrombin downregulated vascular endothelial cadherin(VE?cadherin)in the choroid plexus.2.SCH79797 reduced CD68-positive choroid plexus macrophages infiltration in choroid plexus and attenuated thrombin?induced hydrocephalus.Besides,blocking PAR1,Src,or PAK1 all alleviated ventricles dilation and reversed the decrease of VE?cadherin after thrombin injection.Conclusions1.Intraventricular injection of thrombin caused significant hydrocephalus.Our results demonstrated that thrombin contributed to the inflammation in choroid plexus and activated choroid plexus macrophages.Besides,thrombin disrupted the blood-brain barrier,blood-cerebrospinal fluid barrier,and downregulated VE-cadherin in choroid plexus.2.SCH79797 could alleviate the choroid plexus-related inflammation.Moreover,SCH79797 attenuated thrombin-induced hydrocephalus and reversed the decrease of VE?cadherin by inhibiting the PAR1/Src/PAK1 pathway.ObjectiveThis study aimed to examine the development of hydrocephalus in spontaneously hypertensive rats and explore the role of choroid plexus macrophages in hydrocephalus and the effects of minocycline on hydrocephalus.Methods1.All spontaneously hypertensive rats(SHRs)and age-matched Wistar Kyoto(WKY)rats received MRI scanning to determine the ventricle volumes.Immunohistochemistry staining was applied to examine the choroid plexus-related inflammation and choroid plexus macrophages activation.Besides,cognitive deficits,as well as the width of corpus callosum and the hippocampal neuronal number were examined in SHRs.2.SHRs were treated with either deferoxamine or minocycline randomly and the same endpoints were examined.Results1.Hydrocephalus occurred at week 7 and increased at week 9 in both male and female SHRs compared to WKY rats.However,male SHRs had greater hydrocephalus and choroid plexus macrophages activation compared to females.In male rats,SHRs showed bad performances in a novel object recognition test,corpus callosum thinning and decreased number of hippocampal neurons compared to WKY rats.Interestingly,the further study demonstrated that SHRs showed more CD68 positive choroid plexus macrophages compared with WKY rats at week 4when no hydrocephalus was found in SHRs.2.Our results indicated that minocycline treatment for 14 days in male SHRs reduced CD68 positive choroid plexus macrophages,attenuated hydrocephalus development,weakened corpus callosum thinning,reversed hippocampal neuronal loss and improved performances in the novel object recognition test.However,deferoxamine couldn't weaken the hydrocephalus in SHRs.Conclusions1.Our study found that hydrocephalus was observed in SHRs but not in WKY rats.It occurred at the age of seven weeks and deteriorated at week 9.Choroid plexus macrophages activation was closely associated with the hydrocephalus in SHRs and occurred before hydrocephalus.This suggests the possibility that choroid plexus macrophages activation may be the cause rather than the result of hydrocephalus.Additionally,SHRs showed impaired cognitive function,white matter atrophy and the decreased number of hippocampal neurons at week 9.2.This current study investigated the clinically relevant effects of minocycline treatment initiated after the onset of hydrocephalus and found that delayed minocycline treatment alleviated hydrocephalus,choroid plexus macrophages activation,brain pathology and cognitive impairment in SHRs.However,deferoxamine treatment couldn't weaken the hydrocephalus in SHRs.This result suggests the neuroprotective effects of minocycline should not be mediated by iron chelation.