神经营养因子与神经生长和修复

神经营养因子与神经生长和修复第1页/共35页2Butnowthatthinkinghasbeenturnedupsidedown.Scientistsrecentlyhavediscoveredawholefamilyofproteinscalledneurotrophicfactors.Theseproteinsplayacrucialroleinthedevelopmentandsurvivalofnervecells,orneurons,andinsupportingadultneuronstokeepthemhealthythroughoutlife.第2页/共35页31934:VictorHamburgerdiscoveredthatremovalofalimbbudresultedinreducednumbersofsensoryandmotorneuronsinthespinalcord.Theneurotrophicfactorhypothesis第3页/共35页4EffectofRemovingorAugmentingNeuralTargetsontheSurvivalofRelatedNeuronsPN23092.JPG1939:VictorHamburgershowedthattransplantationofasupernumerarylimbresultedinincreasednumbersofsensoryandmotorneuronsinthespinalcord.第4页/共35页5Based

onhislimb-budexperiments,V.Hamburgerhypothesizedthatthetargetsofinnervatingneuronsprovidesignalsthatrecruitundifferentiatedcellstodevelopintosensoryormotorneurons.(hewaswrong)In1942,Levi-MontalciniandLeviproposedthattarget

derivedsignalsmaintainsurvivalofdifferentiatingneurons.In1949,HamburgerandLevi-Montalcinirepeatedthelimbbudexperimentsandfoundthattheirresultssupportedtheneurotrophichypothesis.Hamburger,V.andLevi-Montalcini,R.(1949)J.Exp.Zool.111:457-502.Theneurotrophicfactorhypothesis第5页/共35页6第6页/共35页71954:neuriteoutgrowthassay–extract+extract1969:NGFpurifiedtohomogeneityStanleyCohenRitaLevi-Montalcini1986:Levi-MontalciniandCohensplittheNobelprizeforPhysiologyorMedicine“fortheirdiscoveryofgrowthfactors”1960:NGFpurified第7页/共35页8NGF: sympatheticneuronsandsomesensory neurons(CNSneuronsdonotrequireNGFforsurvival)BDNF: NGF-relatedfactorpurifiedin1982frompig brain (shares~50%homologwithNGF)NT-3andNT-4/5:wereobtainedbyPCRcloningAllthesefactorsaresynthesizedas~250aaprecursorsthatareprocessedinto120aaproteinsThemainListofNeurotrophicFactors第8页/共35页9NeurotrophinsBDNF(brainderivedneurotrophicfactor)oncorticalneurons第9页/共35页10第10页/共35页11第11页/共35页12第12页/共35页13TrkreceptorsignalingWhenaneurotrophinbindstoatrkreceptor,thekinasedomainisactivatedresultinginautophosphorylation.Autophoshorylationresultsinfurtheractivationofthekinasedomain,leadingtoactivationofthreepotentialsignalingcascades:MAPKPI3KPLC-g第13页/共35页14第14页/共35页15OtherneurotrophicFactors第15页/共35页16第16页/共35页17StructureofneurotrophicFactorreceptors第17页/共35页18AlternativesplicinggeneratesmanyTrkreceptorisoformsRouxandBarker(2002)ProgNeurobiol67:203-233NGFKDforTrkA=10-11M第18页/共35页19p75NTRstructureNGFKD=10-9M(allneurotrophinscanbindp75NTR)RouxandBarker(2002)ProgNeurobiol67:203-233第19页/共35页20ModelsforTrkandp75NTRinteractionChaoandBothwell(2002)Neuron33:9-12第20页/共35页21TheeffectofNT/NTRknockoutsonneuronsintheDRG

Fariñasetal.(2002)BrainResBull57:809-816第21页/共35页22Ouraxonscanbe>1minlength---howdoestheneurotrophin/receptorcomplexsignaltotheneuronalcellbody?MillerandKaplan(2001)Neuron32:767-770第22页/共35页23Campenot,RB(1977)Localcontrolofneuritedevelopmentbynervegrowthfactor.ProcNatlAcadSciUSA.74(10):4516-9.(AmethodthatcanbeusedtostudyhowNTsaddedtodistalaxonssignalretrogradely)MillerandKaplan(2001)Neuron32:767-770NGF+K252a第23页/共35页24第24页/共35页25ActivatedTrkcansignallocallyandretrogradelyusingdifferentsignallingpathwaysMillerandKaplan(2001)Neuron32:767-770Slow(2-20mm/hr)第25页/共35页26DifferentialcontrolofTrkAtraffickingandsignalingmayalsobethebasisforthedifferentfunctionsofNGFandNT-3Kuruvillaetal.(2004)Cell118:243-255第26页/共35页27InvitroassayshaveshownthatNTsenhancebothaxonalanddendriticgrowthInvivo,thesituationismoredifficulttostudyWhy? Instandardknockouts,itisdifficulttoseparatethesurvivaleffectsofNTsfromtheireffectsonthemorphologyofneurons.Thisproblemhasbeguntobeaddressedbyusingconditionalknockouts,orbycrossingNTknockoutswithmousemutantslackingpro-apoptoticgenes.RecentevidencefromthesekindsofexperimentssuggeststhatlongdistanceperipheralsensoryaxongrowthinvivoisNT-dependent.第27页/共35页28NT’srolesinneuronaldevelopmentandfunctionNT’sareexpressedinregionsofthedevelopingembryothataretraversedbysensoryaxonsenroutetotheirtargets.NT’saffecttheproliferationanddifferentiationofCNSneuroepithelialprogenitors,neuralcrestcells,andprogenitorsofentericneuronsinvitro(andinsomecasesalsoconfirmedinvivo).IntheCNS,BDNF/TrkBsignalingisimplicatedinthedevelopmentandmaintenanceofcorticalcircuits.第28页/共35页29NT’sintheCNSThehighestlevelsofNTsarefoundinthehippocampusLindsayetal.(1995)TrendsNeurosci17:182-190.第29页/共35页30CytokinesandGrowthFactorsintheNervousSystemCNTF,LIF(oncostatinM,cardiotrophin-1):neuropoieticcytokines.Thesefactorsmaybeimportantinneuronalresponsetoinjury.GDNF,neurturin,artemin,persephin:exhibitdistanthomologywiththeTGF-bfamily.TheysignalthroughareceptorcomplexcomposedoftheRettyrosinekinaseandaGPI-linkedbindingsubunit(GFRafamily;GFRa1,a2,a3,anda4).Thesefactorsarepotentaxon-promotinggrowthfactorsinvivofordevelopingsympatheticandparasympatheticneurons.第30页/共35页31SummaryNeurotrophicfactorsplayessentialrolesinthedevelopingandmaturenervoussystem.Nowmorethan50yearsold,thisfieldofstudycontinuestocontributebreakthroughdiscoveriesregardingthefundamentalbiologyofcell-cellcommunicationandthedevelopmentandmaintenanceofthemostcomplexandelegantbiologicalmachine-thebrain.Neurotrophicfactorsinfluencecellproliferation,survival,differentiation,migration,axonanddendritegrowth,synapticplasticityandtheinteractionsofneuronalandglialcells.第31页/共35页32Whatisagrowthfactor?

Whatisatrophicfactor?DEFINITIONGrowthfactorsincludesubstancesthatstimulatecellstodivide(hyperplasia)orincreaseinsize(hypertrophy).ManygrowthfactorsarenowknowntoexistTrophicfactorsincludethosesubstancesthathaveeffectsoncelldifferentiation,cellsurvival,expressionofaspecificcellularphenotype(e.g.acellbecomesaninhibitoryoranexcitatoryneuron),cellularmorphologicalplasticity,aswellascellhypertrophyincluding,forexample,theinductionofneuriteextention(alsoconsidereda"trophic"action).Importantly,somegrowthfactors