RoleofglutamateonT-cellmediatedimmunityRodrigoPachecoa,b,,TeresaGallar - PDF document

RoleofglutamateonT-cellmediatedimmunityRodrigoPachecoa,b,,TeresaGallart,CarmenLluis,RafaelFrancoa,bDepartmentofBiochemistryandMolecularBiology,FacultyofBiology,UniversityofBarcelona,Barcelona,SpainInstitutd'InvestigacionsBiomèdiquesAugustPiiSunyer,Barcelona,Spain www.elsevier.com/locate/jneuroim Abbreviations:-aminoadipicacid;AMPA,-amino-3-hydroxy-5-methyl-4-isoxazolepropionicacid;APC,antigenpresentingcells;CA,cysteicacid;CSA,cysteinesulfinicacid;CNS,centralnervoussystem;DC,dendriticcells;EAAC1,excitatoryaminoacidcarrier1;EAAT,excitatoryaminoacidtransporter;ERK1/2,extracellularsignalregulatedprotein GroupIIIcontainsmGlu4R,mGlu6R,mGlu7RandmGlu8R,whichagainnegativelycoupletoadenylatecyclase-2-amino-4-phosphonobutyricacidistheirmostpotentagonist.Ontheotherhand,threemajorgroupsofiGluRsarerecognized(Hinoietal.,2004),basedontheirsequencehomologyandselectiveactivationbytheagonists-aspartate(NMDA),kainate(KA)or-amino-3-hydroxy-5-methyl-4-isoxazolepropionicacid(AMPA).Duetoitspivotalroleasneurotransmitter,extracellularglutamatelevelsaretightlyregulatedintheCNS.Underphysiologicalconditions,clearanceofglutamateisachievedbyuptakeviathehigh-affinityNa-dependentglutamate/aspartate/cystinetransporter(Xsystem)expressedmainlyinastrocytes(Benderetal.,2000;Schwartzetal.,)andviaexcitatoryaminoacidtransporters(EAATsorsystem)expressedonastrocytes,oligodendrocytesandneurons(Matuteetal.,2006;Nedergaardetal.,2002;Schwartzetal.,2003).Incontrast,afteraninsultthesiteofinjuryisdepletedofastrocytes,andinsteadrepopulatedbymicroglia.Dependingonthecontextofactivation,microglialcellsexpressdifferentlevelsofthecystine/glutamateantiporter(Xsystem)andofglutamate/aspartatetranspor-ters(Xsystem)(PianiandFontana,1994;Rimanioletal.,2001;Schwartzetal.,2003).Thus,thisbalanceofglutamatetransportersystemscanleadtoeitheraccumulationorclearanceofextracellularglutamate(Pianietal.,1991,1992;PianiandFontana,1994;Schwartzetal.,2003Glutamate-mediatedsignalinghasnotonlybeende-scribedintheCNS(Ciruelaetal.,2001,2005;Ferreetal.,2002;Nakanishi,1992),butalsoinseveralperipheraltissuesBoldyrevetal.,2005;Hinoietal.,2004;Nedergaardetal.,).Inrecentyears,growingevidencepointstoanimportantroleofiGluRs(Boldyrevetal.,2004;Ganoretal.,2003;Lombardietal.,2001)andmGluRs(Boldyrevetal.,2004;Miglioetal.,2005;Pachecoetal.,2004;Poulopoulouetal.,2005a,b;Rezzanietal.,2003;Stortoetal.,2000)onTcell-mediatedimmunityandT-celldevelopment.Inaddition,ithasrecentlybeendescribedthatdendriticcells(DC),whichhaveakeyroleintheinitiationandregulationofT-cellmediatedimmunity(BanchereauandSteinman,1998;LanzavecchiaandSallusto,2001),releaseglutamatetherebycontributingtomodulatetheT-cellactivation(Pachecoetal.,).Also,asignificantnumberofclinicalstudieshaveconsistentlyshownstrongcorrelationbetweenderegulationofplasmaglutamatelevelsandimmunodeficiency,suchasAIDS(Drogeetal.,1993;Ecketal.,1989;Ferrareseetal.,)ormalignancies(Ecketal.,1990;Ollenschlageretal.,).InadditiontoDC,othercellsthatbelongtotheimmunesystemarealsoabletoreleaseglutamatesuchasneutrophils(Collardetal.,2002)andmacrophages(nioletal.,2001).Despitethisknowledge,morestudiesarenecessarytoelucidatetherelevanceofmacrophage-orneutrophil-derivedglutamateintheregulationofT-cellmediatedimmunity.AlthoughrestingTcellspatrollingintheperipheryareunabletoenterintoCNS,activatedTcellscanenterintoCNSviaanotwellunderstoodmechanism(Hickeyetal.,1991;Ludowyketal.,1992).Inthisregard,afteraninsulttotheintegrityoftheCNS,self-antigen-specificTcellsprotectneuronsagainstglutamateneurotoxicity(Kipnisetal.,2001,2002a;Nevoetal.,2003;Schorietal.,2001a,2002;Schwartzetal.,2003,Shakedetal.,2004,2005).ThisprotectiveautoimmunityoccursbyinducingdifferentmicroglialphenotypesviaamechanismregulatedbyautoreactiveT-cell-derivedIFN-Shakedetal.,2005Althoughtheimplicationofglutamatetransportregulationonthesurfaceofglialcellsduringprotectiveautoimmunityhavebeendescribed(Kornetal.,2005;Shakedetal.,2005theroleofglutamatereceptorsexpressedonthesurfaceofactivatedTcellsintheCNShasnotbeenyetexplored.Inthisarticletheroleofglutamateasakeyimmuno-modulatorintheinitiationanddevelopmentofadaptiveimmuneresponsesispresented,includingdataontheexpressionandfunctionofglutamatereceptorsandgluta-matetransportersinTcellsandothercellsinvolvedintheT-cellmediatedimmunity.Furthermore,thisreviewhighlightsrecentfindingsthatpointtowardaroleofglutamateasalinkbetweentheimmunesystemandthenervoussystem.2.GlutamatereceptorsexpressedonimmunesystemcellsIn1997,Kostanyanetal.(1997)performedpioneerstudieswhichdescribedthespecificbindingofradio-labelledglutamatetohumanbloodlymphocytes,thussuggestingthepresenceofglutamatereceptorsand/orglutamatetransportersinthesecells.Threeyearslater,Stortoetal.(2000)reportedthepresenceoffunctionalgroupIandgroupIImGluRsinmurinethymocytes,theTlymphocyteprecursors.AddressingthegroupImGluRsexpressiononthymocytes,Stortoetal.(2000)showedthatmGlu1RbutnotmGlu5RisexpressedinimmatureCD4thymocytes,whereasmGlu5RispresentinmorematureCD4andCD4cells.Inaddition,groupIImGluRs(mGlu2/3R)areexpressedinimmature/CD8aswellasmatureCD4/CD8andCD4thymocytes(Stortoetal.,2000).ByimmunohistochemicalanalysisRezzanietal.(2003)demonstratedthatimmaturethymocytesfromcorticalratthymus,weaklyexpressmGlu2/3RandmGlu4R,andthatmaturethymocytesfrommedullarratthymus,expressalsomGlu5R.In2004,wedescribedforthefirsttimethepresenceofmGluRsonthesurfaceofhumanTcellsfromperipheralblood(Pachecoetal.,2004).Insuchstudy,itwasshownthatmGlu5RisconstitutivelyexpressedontheT-cellsurfaceanditmediatesadenylatecyclasestimulationand,consequently,inhibitionofanti-CD3antibody-inducedT-cellproliferation.Interestingly,expressionofmGlu1R,whichiscoupledtoMEK-ERK1/2-pathway,isonlyinducedafterT-cellactiva-tion.StimulationofinduciblemGlu1RinTcellsundergoingactivationcounteractedthemGlu5R-mediatedinhibitoryeffectintheT-cellproliferation(Pachecoetal.,2004R.Pachecoetal./JournalofNeuroimmunology185(2007)9 Morerecently,wehavedemonstratedthatthemGlu5R-mediatedinhibitoryeffectonT-cellproliferationoccursviainhibitionofIL-6production(Pachecoetal.,2006),whereasthemGlu1R-triggeredco-stimulatoryeffectismediatedbyenhancedsecretionofIL-2,IL-6,IL-10,TNF-andIFN-Pachecoetal.,2006).ThreemorestudiesshowingexpressionofmGluRsinhumanrestingTcellsweresubsequentlyreported.Thefirststudy,describesthatstimulationofgroupIandgroupIImGluRsfacilitateactivationofpotassiumcurrentsthroughKv1.3channelsatlowglutamateconcentrations(1M),butdecreasethesepotassiumcurrentsathighglutamatelevels(Poulopoulouetal.,2005a).ThesecondstudyshowstheexpressionofmRNAsformGlu1R,mGlu2R,mGlu3RandmGlu8RinrestingTlymphocytesfromhealthydonors;thefunctionalityforthesereceptorswashowevernottestedPoulopoulouetal.,2005b).Thethirdstudy,describestheincreaseofintracellularcalciumandsubsequentinductionofandc-expressionpromotedbygroupImGluRsstimulation(Miglioetal.,2005).Thisfindingcontrastswithourpreviousreport(Pachecoetal.,2004)wherenon-detec-tablechangesonintracellularcalciumlevelswerefoundaftergroupImGluRsstimulationinhumanTcells.Boldyrevetal.havereportedthatincontrasttodataavailableforhumanTcells,rodentlymphocytesexpressgroupIIImGluRs,butneithergroupInorgroupIImGluRsarepresentinthesecells.TheexpressionandfunctionofmGluRsinTcellsandthymocytesaresummarizedinTable1ThefirststudydescribingthepresenceofiGluRsinhumanrestingTlymphocyteswasreportedin2001byLombardietal.(2001).TheauthorsdemonstratedthefunctionalityofNMDA,AMPAaswellasKAreceptorsbymediatingpotentiationofPHA-oranti-CD3antibodyinducedintracel-lularcalciumrise(Lombardietal.,2001).Twoyearslater,Ganoretal.(2003),demonstratedtheexpressionoftheAMPAreceptoriGlu3RinrestinghumanTcells,whichpromotesintegrin-mediatedadhesiontolamininandfibro-nectinandSDF-1-inducedchemotacticmigration.InadditiontostudiesperformedinhumanTcells,Boldyrevetal.(2004)demonstratedthatrodentlymphocytesexpressNMDAreceptors,whichmediateincreasesofintracellularcalciumandreactiveoxygenspecies(ROS).TheexpressionandfunctionofiGluRsinTcellsarealsosummarizedinTable1AlthoughlessextensivelythaninTcells,glutamatereceptorshavealsobeenstudiedinothercellsoftheimmunesystem.ThemGlu7RisexpressedinhumanCD19Bcellsfromhealthydonors,butthisreceptorisdown-regulatedbyhypermethylationofthegenepromoterinCD19cellsfrompatientswithchroniclymphocyticleukemia,Rushetal.,2004).Also,mGluRshavebeenfoundinratthymicDC(Rezzanietal.,2003).WhereascorticalDCexpressmGlu2/3RandmGlu4Rweakly,medullarDCshowmoderatemGlu2/3RandmGlu4RandstrongmGlu5Rexpression(Rezzanietal.,2003).However,wehaverecentlydemonstratedthatneithermGlu1RnormGlu5Rareexpressedonhumanmonocyte-derivedDCsurface(Pachecoetal.,2006).ThisdiscrepancyintheexpressionofmGlu5RinDCmaybeduetoadifferentpatternofexpressionofglutamatereceptorsinDCsfromdifferentspeciesandinDCsfromdifferentlocations.3.GlutamatetransportersexpressedonimmunesystemcellsGlutamatetransportersarekeyregulatorsofextracellularglutamatelevelsactingbyeitherreleasingoruptakingglutamate.Sofar,threemainglutamatetransportsystemshavebeendescribed.First,aNa-dependenthigh-affinityglutamatetransportersfamily,EAATs,expressedinmam-maliantissueswasclonedin1992(KanaiandHediger,1992;Pinesetal.,1992;Storcketal.,1992).Thistransporters Table1ExpressionandfunctionalityofglutamatereceptorsinTcellsandTcellSpecieCellsmGluRs/effectiGluR/effectHumanRestingTcellsmGlu5R,cAMP(a)KA,modulateKv1.3channels?(b)mGlu1/5R,modulateKv1.3channels(b)NMDA,potentiationmGlu2/3R,modulateKv1.3channels(b)AMPA,potentiationmGlu1/5R,KA,potentiationmGlu1R,mGlu2R,mGlu3R,mGlu8R(e)AMPA(iGlu3R),chemotaxis(f)ActivatedTcellsmGlu5R,cAMP(a)ERK1/2(a)MouseCD4IP3(g)cAMP(g)IP3(g)cAMP(g)IP3(g)cAMP(g)RatImmaturemGlu2/3R,mGlu4R(h)mGlu2/3R,mGlu5R(h)mGlu4/6/7/8R,potentiateROS(i)ROS(I)Datafrom:a,Pachecoetal.(2004);b,Poulopoulouetal.(2005a)Lombardietal.(2001);d,Miglioetal.(2005);e,Poulopoulouetal.;f,Ganoretal.(2003);g,Stortoetal.(2000);h,Rezzanietal.;i,Boldyrevetal.(2004).ND,notdetermined.R.Pachecoetal./JournalofNeuroimmunology185(2007)9 istriggeredbyT-cellactivation(Table1),itisinferredthatglutamateisanimportantregulatorofT-cellfunction.Moreover,differentialexpressionofglutamatereceptorshasalsobeendescribedinrodentthymocytesduringdifferentmaturationalstages(Table1),whichsuggestthattheaminoacidcouldplayaroleduringT-celldevelopment.PatrollingrestingTcellsencounterplasmaglutamate,whoseconcentrationfluctuatesintherange10DivinoFilhoetal.,1998;Grahametal.,2000;TsaiandHuang,1999)inphysiologicalconditions.Afterthymicmaturation,restingTcellsexpressgroupImGluRs(mGlu5R),groupIImGluRs(mGlu2/3R),thegroupIIImGluRmembermGlu8RandionotropicreceptorsNMDA,AMPAandKA(Table1).Bystimulatingtheadenylatecyclase-coupledmGlu5R(Pachecoetal.,2004),plasmaglutamatemaykeepelevatedintracellularcAMPlevelswithsubsequentPKAactivation.ItshouldbenotedthatmGlu5Rincellsofthenervoussystemareusuallycoupledtophos-pholipaseCandnottoadenylatecyclase.ThisconstitutesadistinctivefeatureofsignallingviamGlu5RinTlympho-cytes(Pachecoetal.,2004).InTcells,PKAasmuchascAMPevokeinhibitionofERK(Ramstadetal.,2000)andJNKactivation(Haradaetal.,1999),activateC-terminalSrckinase(CSK)(Vangetal.,2001)andblockNFBacti-vation(Hershfield,2005;Jimenezetal.,2001).AlloftheseintracellularbiochemicaleventsinduceamarkedimpairmentonT-cellactivationwithinhibitionofT-cellproliferationandofcytokineproduction(Aandahletal.,2002).Inthisregard,aconsiderablenumberofclinicalstudieshaveshownelevationofplasmaglutamatelevelsunderpathophysiolog-icalconditionssuchasinneurologicdisorders,malignanciesandimmunodeficiencies(Table3).Thus,mGlu5Rstimula-tionbyplasmaglutamatewouldpromoteahighthresholdforT-cellactivation(Fig.1),whichcouldbeexacerbatedinsomepathologies(Table3).RegardingthefunctionoftheAMPAreceptoriGlu3RinTcells,itseemsthatuponstimulationitmediatesimpairmentofIL-10productionPachecoetal.,2006),andallowsthechemotacticmigrationandintegrin-mediatedadhesionofpatrollingrestingTcellsGanoretal.,2003Fig.1).Inaddition,theamplitudeofcalciuminfluxduringtheinitiationofT-cellactivationmayberegulatedbyNMDAandKAreceptorsviatheircationchannelactivity(Lombardietal.,2001),andbygroupIImGluRs,whichmodulatepotassiumcurrentsthroughKv1.3channels(Poulopoulouetal.,2005a).FurtherexperimentalworkisnecessarytoprovideanintegratedviewoftheroleoftheseglutamatereceptorsintheT-cellphysiology.NotonlyplasmaglutamatemayactivateglutamatereceptorsexpressedinpatrollingrestingTcells,butalsohomocysteine(HC)andHCmetabolicderivativessuchashomocysteinesulfinicacid(HCSA),homocysteicacid(HCA),cyteinesulfinicacid(CSA)andcysteicacid(CA)maystimulateeithermGluRsoriGluRs(Lazarewiczetal.,2003;Shietal.,2003).NormalplasmaHClevelsareintherange5M,buttheymayincreaseupto100Min Table3Elevationofplasmaglutamatelevelsinneurologicdisorders,malignanciesandimmunodeficiencyClassificationPathology[Glutamate](Glutamateincrease(In-fold)NeurologicdisordersAmyotrophiclateralsclerosis164±1174.8±3.4Iwasakietal.(1992a)Epilepsy53±252.7±1.3Janjuaetal.(1992)Headache(cerebralinfarction)321±1501.4±0.6Castilloetal.(1995)HIV-associatedementia200±305.9±0.9Ferrareseetal.(2001)Parkinson'sdisease72±92.1±0.3Iwasakietal.(1992b)MalignanciesBreastcancer54832.0Ollenschlageretal.(1989)Colorectalcarcinoma47861.7Ollenschlageretal.(1989)ImmunodeficiencyAIDS54702.0Ollenschlageretal.(1989)Plasmaglutamatelevels.Increaseofplasmaglutamatelevelsareexpressedastheratioofaverageofglutamateconcentrationinplasmafrompatientsversusaverageofglutamateconcentrationinplasmafromhealthydonors.TheRangeofplasmaglutamatelevelsorrangeofelevationofplasmaglutamatelevelsarerespectivelyindicated. Fig.1.FunctionofglutamatereceptorsinrestingTcells.GlutamatereceptorsexpressedonthesurfaceofrestingTcellsaresubjecttoactionofplasmaglutamate(glu,graydots).StimulationofmGlu5RincreasesintracellularcAMPlevels,whichinturninducesactivationofC-terminalSrcKinase(CSK),inhibitionofRas/ERKpathway,inhibitionofJNKsandinactivatesNF-B(a).AllthesemGlu5R-mediatedeffectsleadtoanimpairedstateforT-cellactivation.Ontheotherhand,stimulationofiGlu3RbyplasmaglutamateallowschemotacticmigrationinpatrollingTcells,probablybyinhibitingIL-10production(b).ActivationofNMDAandKAiGluRsaswellasmGlu2/3Rcouldhavearolebyregulatingtheamplitudeof+andK+currents,respectively(c).Arrowheadsrepresentactivation,whileflatheadsrepresentinhibition.R.Pachecoetal./JournalofNeuroimmunology185(2007)9 pathophysiologicalconditionssuchasinneurodegenerativeorcardiovasculardiseases(Gortzetal.,2004AdaptiveimmuneresponsesareinitiatedwhentheantigenispresentedtospecificTcellsbyanAPCand,consequently,Tcellsbecomeactivated.DCsarethemostpotentAPCspecializedintheinitiationofimmuneresponsesbydirectingtheactivationanddifferentiationofnaïveTlymphocytesBanchereauandSteinman,1998;LanzavecchiaandSal-lusto,2001).ImmatureDC(iDC)resideinmosttissuesinordertouptakeantigen;theyareengagedwhenexposedtodangersignalsproducedbymicroorganisms,inflammatorycytokines,nucleotides,andcelldamage(GallucciandMatzinger,2001).Uponexposuretosuchfactors,DClosetheirphagocytoticcapacity,migratetodraininglymphnodes,andundergoamaturationprocess,acquiringhighlevelsofmembranemajorhistocompatibilitycomplex(MHC)andco-stimulatorymoleculessuchasCD80andCD86.Inthelymphnodes,matureDC(mDC)presentthecapturedandprocessedantigentospecificTcells,therebydirectingtheinitiationanddevelopmentofimmuneresponses.Dependingonthecontext,DCcanstimulatethepolarizedoutgrowthofdistinctTcellsubsets,includingThelper1(Th1)andThelper2(Th2)(BanchereauandSteinman,1998;LanzavecchiaandSallusto,2001;Pachecoetal.,2005).Th1orTh2polarizationorchestratestheimmuneeffectormechanismmostappropriatetocombattheinvadingpathogen.Th1cellspromotecellularimmunityprotectingagainstintracellularinfectionandcancer,whereasTh2cellspromotehumoralimmunity,whichishighlyeffectiveagainstextracellularpathogens,andplayaroleintolerancemechanismsandallergicdiseases(DelPrete,1998Recently,wehavedemonstratedthatundergoingmatura-tionandduringantigenpresentation,DCreleaseglutamateviatheXsystem(Pachecoetal.,2006).Inagreementwith Fig.2.PutativeroleofDC-releasedglutamateduringT-cell-DCinteractioninthelymphnodes.Leftpanel:Whenanon-cognateantigenispresentedbyDCtoTcellsinthelymphnodes,glutamatereleasedbyDC(graydots)viathecystine/glutamateantiporter(Xsystem)stimulatestheconstitutivelyexpressedmGlu5RinrestingTcells.ThemGlu5RstimulationevokesanincreaseofintracellularcAMP,thusavoidingtheerroneousT-cellactivation(i.e.byinhibitionofIL-6production).Ontheotherhand,stimulationofconstitutivelyexpressediGlu3RbypromotinganinhibitionofIL-10production,allowschemotacticmigrationofrestingTcells.InadditiontoDC-releasedglutamate,themacrophage-derivedglutamatecontributestoregulateglutamatelevelsinthemicroenvironmentoflymphnodes.Rightpanel:WhencognatepeptideispresentedbyDCtoaTcell,theTCR-triggeredpathwayisstrongenoughtoovercomethemGlu5R-triggeinhibitorypathwayandthereforeT-cellactivationbegins.Duringcellactivation,mGlu1RexpressionisinducedinTcellsandsubsequentlythisreceptorisstimulatedbyextracellularglutamateinducingabypassofmGlu5R-triggeredpathwayandpromotingenhancedproductionofTh1(IL-2andIFN-)andpro-inflammatorycytokines(IL-6andTNF-)aswellasIL-10(a).TheincreaseofIL-2andIFN-levelsfurtherpromotesaTh1response,whereasIL-2andIL-6promoteco-stimulationbyparallelpathways.ThemGlu1R-inducedsecretionofTNF-establishesapositivefeedbackpromotingenhancedglutamatesecretion(boldlinearrows)byDC(b)aswellasbymacrophages(c).Also,themGlu1R-inducedpotentiationofIL-10secretioncounteractstheiGlu3R-mediatedeffectonchemotacticmigration(d),therebymediatingTcellretentionintolymphnodesduringactivation.Dottedlineswitharrowheadsrepresentstimulation/up-regulation,whiletheflatheadsrepresentinhibition/down-regulation.Solidlinearrowsrepresentglutamateflows.R.Pachecoetal./JournalofNeuroimmunology185(2007)9 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