细胞凋亡的线粒体途径jsy1

细胞凋亡的线粒体途径蒋舜媛董霞程在全2002-12-17细胞死亡损伤性死亡Necrosis程序化死亡、细胞凋亡ProgrammedCellDeathApoptosis细胞凋亡的特征形态学特征:染色质的凝集,嗜碱性染色增强,细胞核崩解此时线粒体保持形态正常.细胞体积缩小,一部分细胞质和核碎片进入由膜包被的程序死亡小体,他们从细胞表面出芽脱落,并被巨噬细胞.上皮细胞吞噬.生化特征:染色质降解,核小体间连接DNA部位被降解,产生寡聚核小体DNA片段,即180-200DP整数倍的不同长度的DNA片断.Fig.1.Schematicsummaryofbiochemicalmechanismsofapoptosis.MitochondriaandCommitmenttoCellDeath线粒体是真核细胞的重要细胞器，是动物细胞生成ATP的主要地点。线粒体基质的三羧酸循环酶系通过底物脱氢氧化生成NADH。NADH通过线粒体内膜呼吸链氧化。与此同时，导致跨膜质子移位形成跨膜质子梯度和/或跨膜电位。线粒体内膜上的ATP合成酶利用跨膜质子梯度能量合成ATP。合成的ATP通过线粒体内膜ADP/ATP载体与细胞质中ADP交换进入细胞质，参与细胞的各种需能过程。MitochondrialPathwaysinphysiologicalcelldeaththereleaseofcaspaseactivators(suchascytochromec),changesinelectrontransport,lossofmitochondrialtransmembranepotential,alteredcellularoxidation-reduction,participationofpro-andantiapoptoticBcl-2familyproteins.MitochondrialPathwaysinphysiologicalcelldeathIfmitochondriaarepivotalincontrollingcelllifeanddeath,thenhowdotheseorganelleskill?Atleastthreegeneralmechanismsareknown,andtheireffectsmaybeinterrelated,including(i)disruptionofelectrontransport,oxidativephosphorylation,andadenosinetriphosphate(ATP)production;(ii)releaseofproteinsthattriggeractivationofcaspasefamilyproteases;and(iii)alterationofcellularreduction-oxidation(redox)potentialDisruptionofelectrontransportandenergymetabolismdisruptionofelectrontransporthasbeenrecognizedasanearlyfeatureofcelldeath.γ-Irradiationinducesapoptosisinthymocytesandadisruptionintheelectrontransportchain,probablyatthecytochromeb-c1/cytochromec(cytoc)step.Ceramide(asecondmessengerimplicatedinapoptosissignaling)disruptselectrontransportatthesamestepincellsaswellasinisolatedmitochondria.LigationofFasalsoleadstoadisruptionincytocfunctioninelectrontransport.DisruptionofelectrontransportandenergymetabolismOneconsequenceofthelossofelectrontransportshouldbeadropinATPproduction.Althoughsuchadrophasbeenobservedduringapoptosis,itoftenoccursrelativelylateintheprocess(14).Indeed,ATPappearstoberequiredfordownstreameventsinapoptosis(15).Thus,althoughlossofmitochondrialATPproductioncankillacell,itisunlikelythatthisisamechanismforinductionofapoptosis.Disruptionofelectrontransportandenergymetabolism线粒体跨膜电位的耗散与细胞凋亡有密切关系近年来陆续有报道说明线粒体跨膜电位的耗散早于核酸酶的激活，也早于磷酯酰丝氨酸暴露于细胞表面。而一旦线粒体跨膜电位耗散，细胞就会进入不可逆的凋亡过程。线粒体解联的呼吸链会产生大量活性氧，氧化线粒体内膜上的心磷脂。实验证明，用解偶联剂mClCCP会导致淋巴细胞凋亡。而如果能稳定线粒体跨膜电位就能防止细胞凋亡。Releaseofcaspase-activatingproteinsTheimportanceofmitochondriainapoptosiswassuggestedbystudieswithacell-freesysteminwhichspontaneous,Bcl-2-inhibitablenuclearcondensationandDNAfragmentationwerefoundtobedependentonthepresenceofmitochondria(16).Subsequently,studiesinanothercell-freesystemshowedthatinductionofcaspaseactivationbyadditionofdeoxyadenosinetriphosphatedependedonthepresenceofcytocreleasedfrommitochondriaduringextractpreparation(17).Duringapoptosis(invitroandinvivo)cytocisreleasedfrommitochondriaandthisisinhibitedbythepresenceofBcl-2ontheseorganelles(18,19).Cytosoliccytocformsanessentialpartofthevertebrateapoptosome,whichiscomposedofcytoc,Apaf-1,andprocaspase-9(20).Theresultisactivationofcaspase-9,whichthenprocessesandactivatesothercaspasestoorchestratethebiochemicalexecutionofcells.Releaseofcaspase-activatingproteinsSignificantly,caspaseinhibitorsdonotpreventcytocreleaseinducedbyseveralapoptogenicagents,includingUVirradiation,staurosporine,andoverexpressionofBax(14,21,22).AnexceptioniscytocreleasefrommitochondriainducedbythetumornecrosisfactorreceptorfamilymemberFas,inwhichcytocreleaseispreventedbyinhibitionofcaspases(primarilycaspase-8)recruitedtothecytosolicdomainofligatedFas(21).Nevertheless,cytocreleasecansometimescontributetoFas-mediatedapoptosisbyamplifyingtheeffectsofcaspase-8onactivationofdownstreamcaspases(23).Theemergentviewisthatoncecytocisreleased,thiscommitsthecelltodiebyeitherarapidapoptoticmechanisminvolvingApaf-1-mediatedcaspaseactivationoraslowernecroticprocessduetocollapseofelectrontransport,whichoccurswhencytocisdepletedfrommitochondria,resultinginavarietyofdeleterioussequelaeincludinggenerationofoxygenfreeradicalsanddecreasedproductionofATPReactiveoxygenspeciesandcellularredox.Mitochondriaarethemajorsourceofsuperoxideanionproductionincells.Duringtransferofelectronstomolecularoxygen,anestimated1to5%ofelectronsintherespiratorychainlosetheirway,mostparticipatinginformationofO2.Anythingthatdecreasesthecouplingefficiencyofelectronchaintransportcanthereforeincreaseproductionofsuperoxides.Reactiveoxygenspeciesandcellularredox.Superoxidesandlipidperoxidationareincreasedduringapoptosisinducedbymyriadstimuli(28).However,generationofROSmaybearelativelylateevent,occurringaftercellshaveembarkedonaprocessofcaspaseactivation.Inthisregard,attemptstostudyapoptosisunderconditionsofanoxiahavedemonstratedthatatleastsomeproapoptoticstimulifunctionintheabsenceornearabsenceofoxygen,whichimpliesthatROSsarenotthesinequanonofapoptosis(29,30).However,ROSscanbegeneratedunderconditionsofvirtualanaerobiosis(31),andthustheirroleinapoptosiscannotbeexcludedsolelyonthisbasis.Figure2.Modelforcaspaseactivationbymitochondria.osmoticdisequilibriumlead