apoptosis细胞凋亡.

细胞凋亡Apoptosis(ProgrammedCellDeath)Apoptosis?•Celldeathplaysacruciallyimportantpartinanimalandplantdevelopment,anditusuallycontinuesintoadulthood.•Inahealthyadulthuman,billionsofcellsdieinthebonemarrowandintestineeveryhour.Ourtissuesdonotshrinkbecause,byunknownregulatorymechanisms,celldivisionexactlybalancesthecelldeath.•These“normal”celldeathsaresuicides,inwhichthecellsactivateanintracellulardeathprogramandkillthemselvesinacontrolledway–aprocessknownasprogrammedcelldeath(PCD).CharacterizationofApoptosis•Cellsdiebymurderorsuicidebyanactiveprocessofprogrammedcelldeath,characterizedbycleavageofchromosomalDNA,chromatincondensation,andfragmentationofboththenucleusandthecell.Programmedcelldeathplayakeyrolebothinthemaintenanceofadulttissuesandinembryonicdevelopment.•Incontrasttotheaccidentaldeathofcellsresultingfromanacuteinjury,programmedcelldeathtakesplacebyanactiveprocessandGenesresponsibleforboththeregulationandexecutionofapoptosisareconservedfromnematodestohumans.Twodistinctformsofcelldeath:apoptosisandnecrosis坏死Theseelectronmicrographsshowcellsthathavediedbyapoptosis(AandB)orbyatypeofaccidentalcelldeathcallednecrosis(C).Thecellsin(A)and(C)diedinaculturedish,whereasthecellin(B)diedindevelopingtissueandhasbeenehgulfedbyaphagocyticcell.Notethatthecellsin(A)and(B)havecondensedbutseemrelativelyintact,whereasthecellin(C)seemstohaveexploded.Thelargevacuolesvisibleinthecytoplasmofthecellin(A)areavariablefeatureofapoptosis.ApoptosisduringthemetamorphosisifatadpoleintoafrogAsatadpolechangesintoafrog,thecellsinthetadpoletailareinducedtoundergoapoptosis;asaconsequence,thetailislost.Anincreaseinthyroidhormoneinthebloodstimulatesallthechangesthatoccurduringmetamorphosis,includingapoptosisinthetail.13.1PCDEliminatesUnwantedCellsSculptingthedigitsinthedevelopingmousepawbyapoptosis.(A)Thepawinthismousefetushasbeenstainedwithadyethatspecificallylabelscellsthathaveundergoneapoptosis.Theapoptoticcellsappearasbrightgreendotsbetweenthedevelopingdigits.(B)Theinterdigitalcelldeathhaseliminatedthetissuebetweenthedevelopingdigits,asseenonedaylater,whenthereareveryfewapoptoticcells.(FromW.Woodetal.,Development2000)TheroleofsurvivalfactorsandcelldeathinadjustingthenumberofdevelopingnervecellstotheamountoftargettissueMorenervecellsareproducedthancanbesupportedbythelimitedamountofsurvivalfactorsreleasedbythetargetcells.Therefore,somecellsreceiveaninsufficientamountofsurvivalfactorstoavoidapoptosis.Thisstrategyofoverproductionfollowedbycullingensuresthatalltargetcellsarecontactedbynervecellsandthattheextranervecellsareautomaticallyeliminated.Delormeetal.,PlantPhysi200013.2ApoptoticCellsAreMorphologicalandBiochemicallyRecognizableNormalCellApoptoticCellDNAfragmentationduringtheprocessofapoptosisNormalCellApoptoticCellTheProcedureofApoptosis◆Earlystageofapoptosis凋亡的起始:细胞表面的特化结构如微绒毛消失，细胞间接触的消失，但细胞膜依然完整；线粒体大体完整，但核糖体逐渐从内质网上脱离，内质网囊腔膨胀，并逐渐与质膜融合；染色质固缩，形成新月形帽状结构等形态，沿着核膜分布◆Formingapoptoticbody凋亡小体的形成：核染色质断裂为大小不等的片段，与某些细胞器如线粒体一起聚集，为反折的细胞质膜所包围。细胞表面产生了许多泡状或芽状突起，逐渐形成单个的凋亡小体◆Apoptoticbodyarephagocytosedbysurroundingcells吞噬.13.2ApoptoticCellsAreMorphologicalandBiochemicallyRecognizableMarkersofapoptosis–DNAladderCleavageofnuclearDNAintoacharacteristicladderpatternoffragments.Mousethymuslymphocytesweretreatedwithanantibodyagainstthecell-surfucedeathreceptorFas,inducingthecellstoundergoapoptosis.Aftervarioustimes,DNAwasextracted,andthefragmentswereseparatedbysizebyelectrophoresisinanagarosegelandstainedethidiumbromide.TUNELtechniqueTUNELwasusedtolabelthecutendsofDNAfragmentsinthenucleiofapoptoticcellsinatissuesectionofadevelopingchicklegbud;thiscrosssectionthroughtheskinandunderlyingdrawing.TheprocedureiscalledtheTUNEL(TDT-mediateddUTPnickendlabeling)techniquebecausetheenzymeterminaldeoxynucleotidyltransferase(TdT)addschainsoflabeleddeoxynucleotide(dUTP)tothe3’-OHendsofDNAfragments.(Zuzarte-LuisandHurle,Int.J.Dev.Biol.2002)13.3ApoptosisDependsonanIntracellularProteolyticCascadeThatIsMediatedbyCaspases•TheIntracellularmachineryresponsibleforapoptosisissimilarinallanimalcells.Itdependsonafamilyofproteasesthathaveacysteineattheiractivesiteandcleavetheirtargetproteinsatspecificasparticacids.•Caspases:cforcysterineandaspforasparticacid.•Caspasesaresynthesizedinthecellasinactiveprecursors,orprocaspases,whichistypicallyactivatedbyproteolyticcleavage.ProcaspaseactivationduringapoptosisEachcaspaseisinitiallymadeasaninactiveproenzyme(procaspase).Someprocaspasesareactivatedbyproteolyticcleavagebyanactivatedcaspase:twocleavedfragmentsfromeachoftwoprocaspasemoleculesassociatetoformanactivecaspase,whichistetrameroftwosmallandtwolargesubunits;theprodomainsareusuallydiscarded.Thefirstprocaspasesactivatedarecalledinitiatorprocaspases,whichthencleaveandactivatemanyexecutionerprocaspasesmolecules,producinganamplifyingchainreaction(aproteolyticcaspasecascade).Theexecutionercaspasesthencleaveavarietyofkeyproteinsinthecell,includingspecificcytosolicproteinsandnuclearlamins,leadingtothecontrolleddeathofthecell.Theinitiatorprocaspasesareactivatedbyadaptorproteinsthatbringtheproca