© 2014.PublishedbyTheCompanyofBiologistsLtd|JournalExperimentalBiology(2014)217,109-118 doi:10.1242/jeb.089920 ‡ contributed*These equally tothiswork authors CA 94945-1400,USA. Buck Institutefor Research onAging, 8001Redwood Boulevard, Novato, the sametime,anumberof conservedgeneticmechanisms mechanisms areinvolvedintheage-relatedlossofhomeostasis. At integrity, andlossofcoordinationsystemicphysiologicalcontrol metabolism, deregulationofprocessesensuringcellularandtissue damage tobiologicalmacromolecules,sideeffects ofenergy and Kapahi,2010).Itisclearthatacombinationofstress-induced Guarente, 2002;Kenyon,2005;GreerandBrunet,2008;Katewa age-related decline(GuarenteandKenyon,2000;Tissenbaum and and environmentalconditionsthatinfluence,causeprevent this organisms havegeneratedsignificant insightintothegeneticfactors and thusensurehomeostasisintheyoung.Studiesusingmodel decline ofprocessesthatmaintainbiologicalorderandcomplexity, Chang, 2012).Theproximalcauseofthislossistheprogressive 2010; KatewaandKapahi,LiuRando,2011; Randoand 2009; Hayes,2010;Richardson,Schumacher, 2009;Kapahi, et al.,2008;BroughtonandPartridge,2009;CampisiSedivy, (Greer andBrunet,2008;MurphyPartridge,Schumacher of biologicalorganization: molecular, cellular, tissue andorganismic Aging isassociatedwithawidespreadlossoffunctionatalllevels KEY WORDS:Aging,Drosophila,Homeostasis well asinspecificcelltypes,suchstemcellsoftheflyintestine. tissues, includingadiposetissueandinsulin-producingas flies. Thisincludesmodulationofsignalingpathwayactivityinspecific homeostasis andextendlifespanhavebeenestablishedbyworkin protocols totunesuchinteractionsgeneticallyimprove organism isamajorcauseforincreasedmortality. Importantly, consequences foranimalphysiology, anditsderegulationintheaging growth. Theinteractionbetweenthesepathwayshasimportant stress, andsignalingpathwaysthatregulatecellularmetabolism between signalingpathwaysthatgoverntheresponsetooxidative primary regulatoryaxisaddressedinthesestudiesistheinteraction proliferative homeostasisinthefruitfly on thecharacterizationofprocessesthatmaintainmetabolicand tissue functionandlongevity. Here,wereviewsuchstudies,focusing regulatory processesandtheconsequencesoftheirderegulationfor have madesignificantprogressinelucidatingthefunctionofsuch tissue function.Studiesingeneticallyaccessiblemodelorganisms responses tochangingenvironmentalconditions,maintainingcelland related deregulationofregulatoryprocessesthatcoordinatecellular biological systems.Animportantpartofthisdeclineiscausedbyage- Aging ischaracterizedbyawidespreadlossofhomeostasisin Lifen Wang*, JasonKarpac*andHeinrichJasper homeostasis Promoting longevitybymaintainingmetabolicandproliferative REVIEW Loss of homeostasisduringaging Loss of ABSTRACT Author ([email protected]) for correspondence Drosophila melanogaster ‡ . The discussed: signaling mechanismsregulatingmetabolic responsesto of homeostasisintheagingorganism. Two specificareaswillbe that arethebasisforemerging conceptsexplainingthebreakdown is beinggenerated. into possibletherapeuticinterventions againstage-relateddiseases, consequences ofagingisemerging fromthiswork,andnew insight Biteau etal.,2011a). A comprehensive overviewofcausesand processes andregenerativedecline(LeopoldPerrimon,2007; between tissuedamage,metabolicregulation,innateimmune in recentyearswithworkaddressingthecomplexinteractions et al.,2004;Tower, 2011). Thesestudieshavebeencomplemented 1998; Clancyetal.,2001;Tatar etal.,2001;Wang etal.,2003;Sun and activationofstressresponsesignalingpathways(Parkes et al., increased expressionofantioxidantproteinsandproteinchaperones, promote longevity, includingareductionininsulinsignalingactivity, Classic studieshaveestablishedgeneticinterventionsthat can Biteau etal.,2011a; Biteauetal.,2011b; JonesandRando,2011). Partridge, 2009;KarpacandJasper, 2009; Kapahietal.,2010; and Hoffmann, 2007;LeopoldandPerrimon,Broughton in avarietyofenvironmentalconditions(Tatar etal.,2003;Lemaitre inflammation; regulatetissueregeneration;andpromotelongevity activity; coordinatetissueresponsestodamage,infectionand mechanisms thatcontrolcellulardamageresponsesandmetabolic melanogaster, whichhasbeenusedtocharacterizesignaling elucidation oftheseregulatoryinteractionsis are onlybeginningtobeunderstood. proliferative diseases,anditscausesimmediateconsequences regulation isanimportantcauseformanyage-relatedmetabolicand Biteau etal.,2011b). This‘antagonisticpleiotropy’ ofbiological and Jasper, 2009;Toivonen andPartridge,2009;Kapahi,2010; dysfunction intheagingorganism (KahnandOlsen,2010;Karpac cellular, tissueororganismal integrityintheyoungcancause during aging:signalinginteractionsrequiredforthemaintenanceof insight isthecomplexrolethatvariousregulatoryprocessesplay and Dillin,2011; ConboyandRando,2012).Animportantemerging Panowski andDillin,2009;Toivonen andPartridge,2009;Taylor 2008; MairandDillin,BroughtonPartridge,2009; Tissenbaum andGuarente,2002;Kenyon,2005; GreerandBrunet, contributions tolifespanregulation(GuarenteandKenyon,2000; control oflongevity, aswellassessmentoftissue-specific of theinteractionbetweenenvironmentalfactorsandgeneticsin genetically accessiblemodelsystemsandincludesdetailedanalysis analysis oftheagingprocess.Thisworkhasalsobeenfacilitatedby mutations thatinfluencelifespantowardmorecomplexintegrative study ofaginghasprogressedfromtheidentificationsingle-gene the agingprocess,remainsachallenge.Inrecentyears,however, the gaining comprehensiveinsightintothecausesandmechanismsof Understanding theintegrationofthesediverseprocesses,andthus preventing orcounteractingthisdeclinehaveevolved. Here, wereviewrecentfindings inthe A particularlysuccessfulmodel inthecharacterizationand D. melanogaster Drosophila model 109

The Journal of Experimental Biology 110 sugar/high fat) diets orage-relateddysfunction hasbeenproposed deregulation ofadaptiveresponses becauseofmodern(high homeostasis (RobertsandRosenberg, 2006;Lucaetal.,2010), and dietary conditionsisrequired tomaintainmetabolicandenergy organisms, andislikelytiedtoitsroleinlongevity. Adaptationto Metabolic regulationbyFoxo hasbeendescribedinseveral repair functions. regulation, butalsotoFoxo-mediatedcellularstressresponse and observed byreducedIISactivityisthuslinkedtometabolic Demontis andPerrimon,2010). 2002; Brunetetal.,2004;Wang etal.,2005;Luo2007; repair, andcanregulateapoptosis(Brunet etal.,1999;Kops activity ofFoxopromotescellularstressresistanceanddamage et al.,2003;GreerandBrunet,2008;Biteau2011b). This proteins inadditiontometabolicenzymesandregulators(Murphy inducing theexpressionofanumberstressdefenseandrepair and activatestranscriptionwheninsulinsignalingactivityislow, al., 2005;GreerandBrunet,2008).Foxotranslocatestothenucleus et al.,1993;Giannakou2004;HwangboWang et insulin loss-of-functionconditionsinbothwormsandflies(Kenyon signaling, andisessentialforthelifespanextensionobservedin O), whichisnegativelyregulateddownstreamofAktbyinsulin by activationofthetranscriptionfactorFoxo(Forkheadboxprotein Taguchi etal.,2007). increase lifespan(Blüheretal.,2003;Holzenberger etal.,2003; adipose tissueorknockdownofIRS2inthebrainissufficient to increases lifespan,whileknockdownoftheinsulinreceptorin heterozygosity fortheinsulin-likegrowthfactor(IGF)1receptor substrate Chico(Clancyetal.,2001;Tatar etal.,2001).Inmice, strains mutantintheinsulinreceptorand al., 2004).Similargeneticstudiesinfliesidentifiedlong-lived long-lived (Kenyonetal.,1993;Kimura1997;Hertweck in theinsulinreceptordaf-2andAktSGKkinasesas 1988). Furthergeneticstudiesidentifiedloss-of-functionmutations that extendlifespanbymorethan100%(FriedmanandJohnson, in whichmutationsthePI3KhomologueAGE-1wereidentified regulating lifespanwasfirstobtainedfromgeneticscreensinworms, promote longevity. Insightintotheroleofinsulinsignalingin of insulinsignalingactivityinspecifictissuesmicecanalso lifespan inCaenorhabditis elegans loss-of-function mutationsininsulinsignalingcomponentsextend Partridge, 2009;Kenyon,2010;Barzilaietal.,2012).Single-gene 2003; Kenyon,2005;GreerandBrunet,2008;Broughton both invertebratesandvertebrates(Wolkow etal.,2000;Tatar etal., The insulinsignalingpathwayisacentralregulatoroflongevityin towards developmentofintegrativetherapiesagainstsuchdiseases. related metabolicandproliferativediseases,mayleadtheway paradigms provideimportantinsightintothedevelopmentofage- interactions discussedhereareevolutionarilyconserved,these of theseinteractionsintheoldorganism. Becausethesignaling the maintenanceofhomeostasisinyoung,andderegulation growth signalingthroughtheinsulinandTor signalingpathwaysin between stresssignalingpathways,innateimmuneand these areasofresearchistheimportancesignalinginteractions aging intestinalepithelium.Theunifyingconceptemerging from tissue damage,andthecontrolofproliferativehomeostasisin REVIEW IIS/Foxo adaptation functionandmetabolic longevity of regulator Insulin signaling:acentral Through Foxo-inducedgeneexpression,thelifespanextension These longevityeffects ofreducinginsulinsignalingarecaused and D. melanogaster,andloss al., 2006;Badinet2011). other metabolicsyndromes(Shimomuraetal.,2000;Schoenborn et been linkedtothedyslipidemiaassociatedwithtype2diabetesand lipase) andlipogenictranscriptionfactors(suchasSREBP-1c)have changes inIIS/Foxoregulatedlipases(suchasadiposetriglyceride lipid catabolism(Dengetal.,2012;Xu2012).Accordingly, expression ofenzymesandothertranscriptionfactorsinvolvedin Chakrabarti andKandror, 2009;Wang etal.,2011), aswellthe for thelipolysisofstoredlipids(Vihervaara andPuig,2008; Foxo regulatesthetranscriptionoflipasesinadiposetissuerequired are onlypartiallyunderstood.Inboth tissue-specific mechanismsbywhichIISregulateslipidmetabolism metabolism (Kitamuraetal.,2003;Teleman, 2010),yetthecell-and time, alteredIISactivityisalsoassociatedwithabnormallipid Shulman, 2012;EijkelenboomandBurgering, 2013).Atthesame (Saltiel andKahn,2001;AcciliArden,2004;Samuel glycogen synthesisinthemuscleandliveriswellunderstood The functionofinsulinsignalinginregulatingglucoseuptakeand signaling arecausedbychangesinglucoseandlipidmetabolism. (Samuel andShulman,2012;EijkelenboomBurgering, 2013). breakdown oflipidandglucosehomeostasis,promotingdiabetes 2012). Intheseconditions,Foxoactivationcontributestothe that areassociatedwithchronicinsulinresistance(Barzilaietal., reminiscent ofmanyage-relatedmetabolicpathologiesinhumans Suzuki etal.,2010;Mihaylova2011). Thesephenotypesare degenerative diseases(Kidoetal.,2000;Michael tissues (suchasliver, brainandmuscle)resultinmetabolic (Blüher etal.,2003),IISinhibitionandFoxoactivationinother in adiposetissueofmicecanhavepositiveeffects onlifespan are complexandtissue-specific.Whilelossoftheinsulinreceptor health consequencesofreducinginsulinsignalingactivity, however, levels andservinganabolicpurposes(SaltielKahn,2001).The control lipidandcarbohydratemetabolism,stabilizingbloodglucose homeostasis systemicallybymediatingtissueinteractionsthat regulation ofmetabolicadaptationandlongevity. IISgovernsenergy be requiredtofullygraspthecausalrelationshipbetween signaling (IIS)inthecontrolofmetabolichomeostasisislikelyto complex networkoftissue-specificfunctionsinsulin/IGF regulation byinsulinandlifespanremain.Understandingthe understood, butmanyquestionsaboutthelinkbetweenmetabolic diseases intheelderly(RobertsandRosenberg, 2006). This notionissupportedbytheincreasedincidenceofmetabolic as acauseformetabolicdiseases(OdegaardandChawla,2013). well-understood interactionbetweenIISand stresssignalingis can alsobestimulatedbystress-response signalingpathways.A responses, itsactivityisnotonly controlledbyinsulinsignaling,but Brunet, 2008). et al.,2004;Hwangbo Wang etal.,2005; Greerand deprivation orstress)andlongevity (Kenyonetal.,1993;Giannakou worms enterdevelopmentalandmetabolicarrestundernutrient Foxo homologueDaf16inbothdauerformation(wheredeveloping anabolism andrepairisreflectedintheimportanceof preservation andrepair. Thiscentralroleasaswitchbetween shift energy resourcesfrom anabolicfunctionstocellular activation ofFoxoinconditionslowinsulinsignalingcan thus regulates genesencodingstress-responseandrepairproteins. The In additiontogenesthatpromotemetabolichomeostasis,Foxo also Linking stress signaling and metabolic homeostasis signalingandmetabolic Linking stress Many ofthemetabolicconsequencesalteredIISandFoxo The roleofinsulinsignalinginmetabolicprocessesiswell Highlighting theimportanceof Foxoinregulatingcellularstress The JournalofExperimentalBiology(2014)doi:10.1242/jeb.089920 Drosophila and mammals, C. elegans

The Journal of Experimental Biology REVIEW molecule), byphosphorylating 14-3-3proteins anddisruptingtheir substrate (thuspreventing signal transductionthroughthis activity andactivateFoxobyphosphorylating theinsulinreceptor 2007; Emanuellietal.,2008). JNK cansuppressinsulinsignaling al., 2000;Hirosumiet2002; Solinasetal.,2007;Yang etal., as amajorcauseforinsulinresistance inobesepatients(Waeber et mediated repressionofinsulin signaling activityhasbeenproposed pathological disruptionsofmetabolichomeostasis.Infact, JNK- and hasbeenimplicatednotonlyinlifespanextension,butalso in through multiplecell-autonomousandnon-autonomousmechanisms 2007). JNK signalingisconserved(Essersetal.,2004;JaeschkeandDavis, mammalian cells,suggestingthattheinteractionbetweenIIS and Activation ofFoxoproteinsbyJNKhasfurtherbeendescribed in 2005; Wang etal.,2005; Luoetal.,2007;Wolf etal.,2008). to excessiveDNA damage(MatsumotoandAccili,2005;Ohetal., lifespan infliesandworms,butalsotomediateapoptoticresponses cell growth,andFoxoactsdownstreamofJNKsignalingtoextend Accordingly, activationofJNKdominantlysuppressesIIS-induced of genesthatinduceapoptosis(Wang etal.,2005;Luo2007). expression ofgenesthatinhibitgrowthandpromoterepair, butalso Wang etal.,2005).InresponsetoJNKsignaling,Foxopromotesthe JNK signalingaremediatedbyDAF-16/Foxo(Ohetal.,2005; Genetic interactionstudiesrevealthatalltheseprotectiveeffects of et al.,2005). increases lifespanundernormalconditions(Mizunoetal.,2004;Oh protected againstheavymetaltoxicity, andoverexpressionofJNK phosphatase VHP-1(VH1dual-specificityphosphatase)are Worms withincreasedJNKactivityduetoinhibitionofthe consequences ofJNKactivationhavebeendescribedin normal conditions(Wang etal.,2003;Libert2008).Similar heterozygotes orHep-overexpressinganimalsarelong-livedunder Supporting theprotectiveroleforJNKsignalinginflies, the inductionofatranscriptionalstressresponse(Wang etal.,2003). mutant fliesexhibitincreasedstresssensitivityandaredeficientin compound Paraquat(Wang etal.,2003).Similarly, JNKK/Hep neuronal tissue,areresistanttotheoxidativestress-inducing the JNKkinaseHemipterous(JNKK/Hep)isoverexpressedin heterozygous fortheJNKphosphatasePuckered(puc),orinwhich stress toleranceandextendedlifespaninfliesworms.Flies mutants, moderateactivationofJNKsignalingresultsinincreased 2005). Mirroringthelifespanextensionobservedininsulinsignaling and Davis,2002;Manning2003;KarinGallagher, morphogenetic changestoincreasedsurvival(Davis,2000;Weston consequences forthecell,rangingfromapoptosisover expression. Itsactivationhashighlycontext-dependent factors, suchasFoxoandAP-1,leadingtochangesingene (JNK kinasekinases).JNKcommonlyregulatestranscription that isinitiatedbyanumberofstress-specificupstreamkinases heat andinflammatorycytokines)throughaMAP kinasecascade insults (e.g.UV irradiation,reactiveoxygenspecies,DNA damage, Jasper, 2009;Biteauetal.,2011b; SamuelandShulman,2012). the metabolicstatusofcell(Hirosumietal.,2002;Karpacand induce Foxo-mediatedgeneexpressionprogramsindependentlyof Foxo independentlyofinsulinsignaling,providinganavenueto environmental stressors.JNKcanpromotenucleartranslocationof regulates geneexpressioninresponsetoawiderangeof mediated bytheJun-N-terminalkinase(JNK)pathway, which Cell-autonomous JNK/IISinteractions Interestingly, activationofFoxobyJNKsignalingisachieved JNK activityisinducedbyarangeofintrinsicandenvironmental C. elegans. puc ancient andcriticalforsurvival. antagonism betweenJNKandIISthusappearstobeevolutionarily 2005; Nielsenetal.,2008;KarpacandJasper, 2009).The 2004; Tsuruta etal.,2004;Sunayama2005;Yoshida etal., 14-3-3 areconservedinbothfliesand Foxo activation in thistissueisaccompaniedby feedbackrepression peripheral fatbodyalsoleads to lifespanextension.Interestingly, Broughton etal.,2005),and overexpressionofFoxointhe sufficient toextendlifespaninflies(Wessells etal.,2004; Jasper, 2009; RajanandPerrimon,2012).Thus,ablationofIPCsis (Leopold andPerrimon,2007;Russell andKahn,2007;Karpac tissues thatregulatelifespanand metabolichomeostasis(Fig. producing tissues,fat-storingtissuesandperipheralinsulintarget a complexsystemofendocrineinteractionsbetweeninsulin- (Wang etal.,2005;Karpac etal.,2009).Thismechanismispartof tissues toenvironmentalchanges,andextendingthelifespanof flies activity, allowingcoordinatedmetabolicadaptationofinsulintarget IPCs. Asinworms,JNKsignalingthussystemicallyrepresses IIS peptide 2(Dilp2)transcription,andinvolvesFoxoactivation in 2009). Thisisachievedbyrepressionof adaptation understressconditions(Wang etal.,2005;Karpac insulin-producing cells(IPCs)iscrucialformetabolicandgrowth 1).JNKactivationin stress signalinghasbeendescribed(Fig. (Libina etal.,2003;Zhang2013). but Foxoactivityinotherperipheralcellscanalsoextendlifespan tissue intheworm,hasanimportantrolethislifespanextension, lifespan (Libinaetal.,2003).Theintestine,themajorfat-storing peripheral activationofDAF-16,inturn,issufficient toincrease periphery (Bargmann andHorvitz,1991;Lietal.,2003).This starvation anddauerpheromone,activatingDAF-16inthe insulin-like peptideDAF-28,whichisrepressedinresponseto neurons) iscrucialfordauerformation.Theseneuronsexpressthe expression inspecificchemosensoryneuronsthehead(ASI peptides. Accordingly, theregulationofinsulin-likepeptide Foxo, aswellbystress-inducedrepressionofinsulin-like formation andcanbeachievedbystress-inducedactivationof Repression ofinsulinsignalingactivityiscentraltodauer metabolic activityarecurtailedunderunfavorableconditions. elegans, anextremeformofadaptationinwhichdevelopmentand under stressconditions(KarpacandJasper, 2009). activity isanadaptiveprocessthatdecreasesmetabolic diseases, theacuteJNK-mediatedrepressionofinsulinsignaling chronic engagementofthissignalingsystemcancausemetabolic metabolic adaptationstochangingenvironmentalconditions.While JNK thusmediatesimportantcell-autonomousandsystemic liver) (Sabioetal.,2008;SabioandDavis,2010;Han2013). adipose tissueandmacrophagespreventsinsulinsignalinginthe (such asIL-6,whichissecretedinresponsetoJNKactivityfromthe adipokines thatsuppressinsulinsignaltransductionatadistance described above,JNKcanpromotetheexpressionofcytokinesand In additiontothecell-autonomousmechanismsofIISinhibition in the phosphorylation sitesinmammalianIRSorFoxo4arenotconserved (Oh etal.,2005),sequencealignmentshowsthattheJNK 2005). WhileC.elegans 2004; Tsuruta etal.,2004;Sunayama2005;Yoshida etal., directly (Aguirreetal.,2000;Mamay2003;Essers inhibition ofFoxo,aswellbyphosphorylatingFoxoproteins Systemic regulation of IISbyJNK of Systemic regulation In This adaptiveprocessisexemplifiedbydauerformationin Drosophila, similarendocrineregulationofIISactivityby Drosophila The JournalofExperimentalBiology(2014)doi:10.1242/jeb.089920 proteins, whilethephosphorylationsiteson JNK wasshowntophosphorylateDAF-16 C. elegans Drosophila (Essers etal., insulin-like 111

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The Journal of Experimental Biology 112 response. Thisrecovery restoresinsulintranscription inIPCsandis which inturnisrequiredtoinitiate arecoveryphaseoftheadaptive tissue leadstotheactivationof NFkB/Relish signalinginthesecells, transcription inIPCs.Subsequent activationofFoxoinadipose and hemocytes.Thisactivation isrequiredtorepressinsulin IL-6) thatactivatetheJAK/Stat signalingpathwayinadiposetissue inflammatory cytokines(including Upd3,afunctionalanalogueof systemic repressionofinsulinsignalingactivitybyinducing (induced, forexample,byUV irradiation)initiatesatransient regulatory processinflies(Karpacetal.,2011): localtissuedamage stress, innateimmuneandinflammatorysignalsthatgovern this more detail,andhaveestablishedthespatiotemporalcoordination of regulatory network.Recentstudieshaveexploredthisregulation in Stress signalingthroughJNKappearstobeanintegralpartof this insulin-target tissuesinfluence metabolichomeostasisandlifespan. conserved endocrineinteractionsbetweeninsulin-producing and Garelli etal.,2012). overgrowth andtumorformation (Fig. 2011), andsystemicallyregulatinggrowthinresponsetotissue 2010; Sousa-Nunesetal.,2011) andintheintestine(O’Brienetal., insulin-like peptidesactinglocallyinthebrain(ChellandBrand, systemically actinginsulin-likepeptides.Otherexamplesinclude signaling activityinperipheraltissuesbyadiversityoflocallyand from thistissuehighlightthecomplexityofregulationinsulin and thelifespanextensionobservedwhenDilp6isoverexpressed conditions intheadult,repressionofbraininsulin-likepeptides, 2009; Slaidinaetal.,2009).TheinductionofDilp6understarvation growth undersuchconditionsduringdevelopment(Okamotoetal., fasting statesfromthefatbody, andsustainsinsulin-dependent al., 2012).Dilp6isapeptidethatsecretedinnon-feedingand feedback signal(Okamotoetal.,2009;SlaidinaBai body-derived insulin-likepeptide,Dilp6,asacandidateforthis 2004; Hwangboetal.,2004).A recent studyhasidentifiedafat- of insulin-likepeptidegeneexpressioninIPCs(Giannakouetal., REVIEW Feeding Upd2 state Fat body These findingssupportthenotionthatcomplex,evolutionarily Oenocytes Dilp6 Foxo Lipids TAG Glycogen Upd2 Dilp6 Amino acids TOR Slif signaling TOR acids Fatty Intestine Foxo Akt InR uptake Amino acid acids Amino homeostasis 1) (Colombanietal.,2012; Metabolic Systemic Systemic growth aging IPCs Dilps Brain Foxo InR Akt regeneration Tissue Hemocytes Muscle Myc Foxo regulate IIS. which tostudythesignalingmechanisms andtissueinteractionsthat available fortheflymake Drosophila evolutionarily conservedsignaling pathwaysencodedinthe below). Thesimilarityofflyorgans tovertebrateorgan systems,the regulation oftissuehomeostasis andinnateimmunity(reviewed systemic growth,agingandenergy homeostasis,aswellthe mechanistic insightintotheregulationofIISandcontrol of Studies ofphysiologicalcross-talkbetweenflytissuesarerevealing as modelforthestudyoforgan–organ communication(Fig. levels infliesthroughtheregulationofUpd2. signaling maycouplenutrientsensinginthefatbodytoinsulin metabolic adaptation.Itisinterestingtospeculatethat TOR to linkdietaryaminoacidlevelswithcirculatingDilpsduring sensing andIIS-responsiveTOR signalingpathwayinthefatbody amino acidtransporter)isrequiredupstreamoftheamino-acid- insulin releasefromthebrain(Géminardetal.,2009).Slimfast (an acids, sensedbythefatbody, canrelayhumoralsignalstocontrol metazoans. Furthermore,ithasalsobeenshowninfliesthatamino mechanisms thatmaintainmetabolicandgrowthhomeostasisin this system,highlightingtheevolutionaryconservationof activity. Strikingly, humanleptincanfunctionallyreplaceUpd2in secretion inIPCs,andthusregulatessystemicgrowthanabolic IPCs (RajanandPerrimon,2012).ThisinteractioncontrolsDilp GABAergic neuronsinthebrainthathavedirectconnectionsto the fedstateandactivatesJAK/Statsignalinginapopulationof similarity toUpd3,asafactorthatissecretedfromadiposetissuein A recentstudyhasidentifiedUpd2, acytokinewithsignificant signals inthemaintenanceofmetabolichomeostasisvertebrates. responses isreminiscentoftheimportanceadipocyte-derived been repaired(Karpacetal.,2011). crucial toresumegrowthandanabolicfunctionsafterdamagehas 4E-BP Taken together, thesefindingsshowthat The centralroleofthefatbodyincoordinatingthesestress behavior Feeding homeostasis Tissue The JournalofExperimentalBiology(2014)doi:10.1242/jeb.089920 genome, andthehighlydeveloped genetictoolkit receptor; Slif,slimfast. protein; Foxo,ForkheadboxproteinO;InR,insulin BP, eukaryotictranslationinitiationfactor4Ebinding derived hormonessuchasUnpaired2(Upd2). (Jun-N-terminal kinase,JNK)andbyfat-body- derived Dilpsisalsoregulatedbystresssignals secretion ofbrain-derivedDilps.Secretionbrain- (IPCs) inthebraintoregulateexpressionand locally, andmayinteractwithinsulin-producing cells intestine) controlmetabolicandproliferativeactivity tissues (Dilp6inthefatbodyandDilp3 intestinal epithelium.Dilpssecretedfromperipheral survival inhemocytes,andregenerationthe regulation ofmetabolicactivityinthefatbody, nutritional andstressconditions.Thisincludes multiple metabolicandregenerativeresponsesto proliferative homeostasisinfliesbycoordinating central roleintheregulationofmetabolicand Drosophila homeostasis intheadultanimalaresummarized. to dietarychangesandstressmaintain endocrine signalsthatmediatespecificresponses homeostasis inDrosophila.Tissue systemsand regulating metabolicandproliferative Fig.

1. Summaryofendocrineinteractions Drosophila insulin-like peptides(Dilps)playa a crucialmodelorganism in Drosophila is emerging 4E-

1).

The Journal of Experimental Biology REVIEW processes thatmaintain proliferativehomeostasis inhigh-turnover Jang etal.,2011; JonesandRando,2011). Of particularinterestare consequences forregenerative capacity(JasperandJones,2010; deregulation ofinsulin/IGFsignaling, hasimportantdeleterious maintenance ofmanytissuesin vertebrates,andaging,aswell regenerating tissues.Regeneration iscrucialforrenewaland but alsohasamajorimpact onproliferativehomeostasisin not onlyinfluenceslifespanbypromotingmetabolichomeostasis, The interactionbetweenstressandinsulinsignalingdescribedabove restore metabolicandgrowthhomeostasisintheseconditions. target thesesignalinginteractions areexpectedtoberequired and Davis,2010).Newtherapeuticapproachesthatspecifically the liverbyactivatingJAK/Statsignaling(Sabioetal.,2008; Sabio cytokines suchasIL-6,whichinturnpromotesinsulinresistance in activation inadiposetissuehasbeenshowntoinduceinflammatory Hotamisligil, 2006;BouzakriandZierath,2007).Furthermore, JNK 2000; Hirosumietal.,2002;Ozcan2004;Hotamisligil,2005; et al.,1996;Yin etal.,1998;Hotamisligil, 1999;Aguirreetal., and resultsinphosphorylationinhibitionofIRS-1(Hotamisligil concurrent activationofToll-like receptors(Tsukumo etal.,2007), inflammatory signalssuchasfreefattyacidsandTNF- reticulum stressinadipocytes,aswellbyadipose-derived et al.,2013).Inobesemodels,JNKisactivatedbyendoplasmic Solinas etal.,2007;Yang etal.,2007;Emanuelli2008;Han and macrophages(Waeber etal.,2000;Hirosumi2002; interactions betweenJNKactivityintheliver, muscle,adipocytes 2007; Emanuellietal.,2008).Thiseffect involvescomplex al., 2000;Hirosumiet2002;Solinas2007;Yang etal., dietary-induced modelsofobesityandinsulinresistance(Waeber et identified asacentralmediatorofinsulinresistanceingeneticand associated withobesityandaging.Infact,JNKsignalinghasbeen 2).Suchconditionsincludeinflammationthatis activated (Fig. continuously, orwhenstresssignalingisotherwisechronically can causesignificantdamagewhentheorganism isstressed suppression ofIISactivitybyJNKislikelybeneficial,thesystem crucial fortheultimateoutcomeofthissignalingevent.Whileacute seems likelythatthedurationofJNK-mediatedIISrepressionis mechanism thencontributetoage-relatedmetabolicdiseases?It experiences stressfulanddamagingconditions.Whydoesthis promote cellsurvivalandtissuerepairwhentheorganism signaling isthusanevolutionarilyconservedadaptivemechanismto The antagonisticinteractionbetweenstresssignalingandinsulin to DNA damageandinjury. promoting metabolicadaptationandtissuedysfunctioninresponse to providenewinsightintotheacuteaswellchronicmechanisms hormone/IGF signalingremainstobeexploredindetailandislikely complexity oftissue-specificresponsestotheattenuationgrowth associated withprogeroid(oracceleratedaging)phenotypes.The afflicted byincreasedDNA damage,butparadoxically, isalso hormone/IGF axisisbelievedtopromotetissuerepairinorgans 2008; Schumacheretal.,2008).Therepressionofthegrowth (Niedernhofer etal.,2006;vanderPluijm2007;Garinis repression ofIGFsignaling,resultingingrowthattenuation observed inmice.MutationsgenesinvolvedDNA repaircause signaling activityinresponsetoDNA damage,whichhasalsobeen processes infliesandvertebratesistherepressionofinsulin/IGF Drosophila proliferative homeostasisintheaging Maintenance of agoodthing? diseases–toomuch of inflammatory Chronic An interestingexampleofthesimilaritybetweendescribed intestine α andthe lifespan declinesagain. impaired (strongloss-of-functionmutationsininsulinsignalingcomponents), conditions ofstressorinflammation),wheninsulinsignalingisstrongly increasing lifespan.WhenJNKischronicallyorexcessivelyactivated(in signaling capacity),tissueandmetabolichomeostasisaremaximized, in geneticconditionsleadingtomoderateincreasesofJNKorreducedinsulin moderately reducedorJNKsignalingisactivated(undercalorierestriction insulin signaling),longevity(blackline)islow. Wheninsulinsignalingis of abundantnutrientintakeinwild-typesorgeneticconditionsoptimizing insulin signalingishighandJNKlow(forexample,inconditions lifespan (Biteauetal.,2010;Karpac2011). Inconditionsinwhich metabolic andproliferativetissuehomeostasisinflies,significantlyimpacting locally. Thisantagonismbetweenstressandinsulinsignalinginfluencesboth though NFkBcaninhibitinsulinsignalingactivitybothsystemicallyand signaling throughJun-N-terminalkinase(JNK)andinnateimmune immune signalinginthecontrolofhomeostasisandlifespan. Fig. midgut thatcontinuously regeneratethistissue inaprocessthat characterized apopulationofpluripotent tissuestemcellsinthefly tracing techniques,Ohlstein,Micchelli andcolleaguesidentified and Perrimon,2006;Ohlstein Spradling,2006).Usinglineage the intestinalepitheliumregenerates intheadultanimal(Micchelli post-mitotic animals,twoelegant studiesin2006demonstratedthat to studyproliferativehomeostasis. Whileflieswerelongconsidered Drosophila diseases. therapeutic approachesforage-relatedproliferativeanddegenerative understanding ofhumandiseasesandtheestablishment of following, wewilldiscusstheimplicationsofthisresearchfor our regeneration andthelossofproliferativehomeostasis.In the autonomous andsystemicregulationofstemcellfunction,tissue productive andaccessiblemodelsysteminwhichtoexplorethe cell- epithelium of progression ofage-relatedtissuedysfunctionintheintestinal is highlightedbyrecentinsightsintothedevelopmentand interaction betweenstressandmetabolicsignalingontissuehealth or degenerativediseases.Infact,theuniversalimpactof tissues, asderegulationofsuchprocessesislikelytopromotecancer dysplasia The The

.Relationshipbetweeninsulinsignaling activityandstress/innate 2. Relative lifespan Max. Drosophila Min. The JournalofExperimentalBiology(2014)doi:10.1242/jeb.089920 has onlyrecentlybeenrecognizedasamodelinwhich Low stress Anabolism tolerance Drosophila. Thistissuehasemerged asavery growth intestine asamodelsystemfor intestinal JNK/innate immunesignalingactivity Insulin signalingactivity homeostasis homeostasis Metabolic Tissue Impaired tissue regeneration dysfunction Metabolic Stress 113

The Journal of Experimental Biology 114 Fig. Ohlstein andSpradling,2007)(Fig. (ECs) (MicchelliandPerrimon,2006;OhlsteinSpradling, intestinal celltypes:enteroendocrinecells(EEs)andenterocytes intestinal epithelium,andcangiverisetoatleasttwodifferentiated breakdown oflipidhomeostasis(Biteauetal.,2010). tissue homeostasisalsorescuestheage-dependentsystemic influences lifespanin shown thattheregenerativecapacityofstemcellsstrongly Sieber andThummel,2012;Reraetal.,2013).We haverecently 2009a; Biteauetal.,2010;2011a; Reraetal.,2012; inflammation (Biteauetal.,2008;ChoiBuchon regeneration, metabolicregulation,innateimmunityand allowing detailedanalysisofcomplexinteractionsbetweentissue immune functions,andservesasacrucialbarrierepithelium, regenerative capacityofhigh-turnovertissues. intestinal stemcellfunctionaswellage-relatedchangesin as anidealmodelsysteminwhichtocharacterizetheregulationof 3).Thisworkthusintroducedtheflyintestine Spradling, 2007)(Fig. Ohlstein andSpradling,2006;Radtkeetal., intestinal epitheliumofmammals(MicchelliandPerrimon,2006; mechanistically andmorphologicallyresemblescellturnoverinthe REVIEW commensal bacterial populationinthelumen(darkovals). intestinal epithelium. Thisphenotypecorrelateswithan expansionofthe misdifferentiated EB-likecellsthatdisruptstructureandfunction ofthe ISCs. Inagingflies,ISCsoverproliferate, resultingintheaccumulationof consists ofamonolayerECswith interspersedEEsandbasallylocated in homeostasisoftheintestinalepithelium. Inyounganimals,theepithelium signaling, EBsdifferentiate intoeitherEEsorECs.(B)Age-related changes from theISC,drivesEBdifferentiation. Dependingonthelevels ofN enteroendocrine cell(EE).Notch(N)signaling,initiatedbyaDelta(Dl)signal enteroblast (EB),whichdifferentiates intoeitheranenterocyte(EC)or stem cells(ISCs)divideasymmetricallytogiveriseanewISCandan intestinal stemcelllineagein A Intestinal stemcells(ISCs)aretheonlydividingin Interestingly, thistissuealso performsmetabolicandinnate

3. ControloftissueregenerationintheDrosophila EEC EE ISC

Quiescent N Recovery

Active Dl low Stress N high EB Drosophila, andthatimprovingintestinal Drosophila B EC . Inresponsetostress,intestinal

3). WhenISCdivisionis EE 75um 75um ISC EB intestine. (A)The Muscle Young Old (Amcheslavsky etal.,2011; Kapuriaetal.,2012). dietary effects, promotinglong-termmaintenanceofISCs differentiation intoECs.Interestingly, TSC2buffers ISCsfrom mediated suppressionofTSC2expressioninEBsisrequiredfor required inISCstopreventtheirdifferentiation, whileNotch- GTPase activatingproteinandinhibitoroftheTor pathway, is expression oftuberoussclerosiscomplex2(TSC2),theRheb signaling, whichisdifferentially activatedinISCsandEBs.High promoting EEfates.Differentiation ofECsrequiresactivationTor high NotchsignalingpromotingECfates,andlowactivity accordingly bythelevelofNotchsignalingactivityinEB,with EB isdeterminedbythelevelofDlexpressioninISC,and differentiation. ThelineagedecisionbetweenEEandECfatesofthe which inturnactivatesNotchsignalingtheEB,drivingtheir and Tor signalingpathways.ISCsexpresstheNotchligandDelta, and Jasper, 2011). of theISCpopulation(Linetal.,2008;Biteau2011a; Biteau proliferative competence,andhasthusbeendescribedasthe‘niche’ supplying growthfactorsthatpromoteISCmaintenanceand role notonlyinmaintainingasymmetrythiscellpair, butalsoin visceral muscle(Goulasetal.,2012).Theplaysanimportant adhesion ofISCstothebasementmembraneandunderlying ISC/EB pairislikelytobedeterminedbyintegrin-mediated or EEs(OhlsteinandSpradling,2007).Theasymmetryofthe enteroblast (EB),emerges apicallyanddifferentiates intoeitherECs cell thatremainsbasally, while anewlyformedprogenitorcell,the triggered, thesecellsdivideasymmetrically, generatinganewstem stress andinfection. Thesesignalinginteractions arecomplex,yet compensatory proliferationofISCs inresponsetocellulardamage, into acomplexnetworkofregulatory processesthatdetermine homeostasis oftheintestinalepithelium. Thisregulationisintegrated significantly influenceage-related changesinproliferative thus influenceISCactivity and maintenance,canalso the overallnumbersofavailablestemcells. response caninduceISCstodividesymmetrically, thusmanaging the intestinalepithelium(O’Brienetal.,2011). Strikingly, this in responsetofasting/refeedingcycles,regulatingtheoverallsize of contrast, influencesISCproliferationintheyoungmaturinggut and Kapuria etal.,2012).Dilp3secretedfromthevisceralmuscle, in insulin-like signals(Amcheslavskyetal.,2009;Biteau 2010; significantly reduced,highlightingtheimportanceofsystemic producing cellsinthebrainareablated,ISCproliferation is determined bybothlocalandsystemicDilps.Wheninsulin- to ISCs,inturn,inhibitsISCproliferation(Choietal.,2011). signaling inthesecells.Unresolvedadhesionofundifferentiated EBs impairs EBdifferentiation, mostlikelybecauseofreducedTor Kapuria etal.,2012).LossoftheinsulinreceptorinEBs,however, 2009; Biteauetal.,2010;McLeodChoi2011; induce proliferationinwidelyquiescentISCs(Amcheslavskyetal., receptor donotdivide,whileincreasedinsulinsignalingactivitycan roles intheregulationofISCfunction.ISCsmutantforinsulin insulin receptorhasbothcell-autonomousandnon-autonomous pathway, thusinfluencingoveralltissuegrowth.Interestingly, the determine proliferativeactivityofISCsthroughtheinsulinsignaling differentiation ofISCsthroughtheTor signalingpathway, butalso Dietary conditionsandmetabolicsignalsnotonlyinfluence regeneration of signalinginthecontrol Growth andmetabolic ISC self-renewalanddifferentiation iscontrolledbytheNotch Dietary conditions,andtheassociated nutrient-responsivesignals, The activityoftheinsulinsignalingpathwayinISCs is The JournalofExperimentalBiology(2014)doi:10.1242/jeb.089920

The Journal of Experimental Biology REVIEW dysplasia described above.Accordingly, midguts from30-day-old activation ofJNKandJAK/Stat signaling,inducingtheintestinal flies, however, thecommensalpopulationseemstocauseexcessive of epithelialrenewalinyoungflies (Buchonetal.,2009a).Inolder in ISCsbycommensalbacteria issufficient tomaintainlow levels absence ofinfection,basalactivation ofJNKandJak/Statactivities al., 2009b;ChatterjeeandIp, 2009;Jiangetal.,2009).Inthe bacteria (Apidianakisetal.,2009;Buchon2009a; et flora andareactivatedinthegutafterexposuretopathogenic Jak/Stat signalingpathways,whichareinfluencedbythecommensal (Biteau etal.,2008).Thisincludesp38MAPK,JNKand the widespread activationofstress-responsivesignalingpathways of commensalbacteria(Buchonetal.,2009a)andresultsin the oxidative stressintheintestinethatisassociatedwithpresence This phenotypeiscausedbyanage-relatedincreaseinglobal 2009a; Buchonetal.,2009b;Rera2011; Reraetal.,2012). its barrierfunctions,resultinginincreasedmortality(Buchon et al., 2008; Choietal.,2008).Thegutthenlosesbothitsresorptive and of mis-differentiated cellsat thebasementmembrane(Biteauetal., loss ofapico-basalorganization oftheepitheliumandaccumulation (Fig. a large numberofcellsthatundergo incompletedifferentiation become deregulatedinagingflies,overproliferatingandproducing infection tolerance,aswelllifespanofflies.Interestingly, ISCs Jiang etal.,2009),theactivityofISCsstronglyinfluencesstressand damage orinfection(Buchonetal.,2009a;Buchon2009b; homeostatic tissueturnoveraswellforepithelialrecoveryafter As regenerationthroughtheISClineageiscrucialfornormal Jasper, 2011). network thatgovernsISCactivity(Buchonetal.,2010;Biteauand the muscleandECs),thusservesasacrucialnodeinsignaling signaling (whichisactivatedinISCsbyligandsderivedfromboth The FostranscriptionfactorintegratesJNKsignalingwithEGFR however, iscrucialtomaintainingtheproliferativepotentialofISCs. tyrosine kinasepathways(includingInRandEGFRsignaling), ratio ofquiescenttoactivestemcells.Signalingthroughreceptor pathways determinetheactivityofISCpoolbychanging these cellsinresponsetooxidativestress.Allstress-induced activation ofJNKsignalinginISCscanpromoteproliferation triggering proliferation.Atthesametime,cell-autonomous of theHippopathway. Upds activate theJak/StatpathwayinISCs, which occursinresponsetoalossoftissueintegrityandrepression Upd1–3. TheseligandsarealsoinducedbyactivationofYorkie, ECs, whichinturninducesproductionoftheJak/Statligands Stress, infection,injuryortissuedamageleadstoJNKactivationin and paracrineinteractionsinvolvingbothECsthemuscle. These pathwaysregulateISCproliferationthroughanumberoflocal Buchon etal.,2010;BiteauandJasper, 2011; Jiangetal.,2011). Chatterjee andIp,2009;Jiangetal.,Biteau2010; Apidianakis etal.,2009;Buchon2009a;2009b; insulin signaling(Biteauetal.,2008;Amcheslavsky2009; the Jak/Statsignalingpathwayandbyp38MAPK,EGFR ISC proliferationratesareregulatedbyJNKsignaling,butalso (Biteau etal.,2011a). related inflammatoryandproliferativediseasesinvertebrates further insightintotheseprocessesiscrucialtounderstandingage- their impactontissuehomeostasis,healthandlifespansuggestthat a chronic inflammatory condition? a chronic inflammatory proliferative animals: homeostasis inaging Loss of Regenerative totissuedamage response 3). Thistriggersintestinaldysplasia,whichischaracterizedby Rera etal.,2011). dysplasia, andincreaselifespaninthismodel(Biteauetal.,2010; strategies thatwilllimitISCproliferation,delayorprevent overexpressing generalantioxidantgenesandchaperonesareall transcription factor, promotingmitochondrialfunction,aswell Tor activity, limitingJNKactivation,promotingactivityoftheNrf2 reduce dysplasiaandimprovehealthofthetissue.ReducingIIS way toidentifystrategiesthatwillpromotestemcellquiescence, to bebeneficialforhealthandlifespan.Flystudiesareleadingthe cell proliferationinmammalianbarrierepitheliaisthereforelikely (Biteau etal.,2010;Rera2011). Similarmanagementofstem in theagingintestineissufficient toextendlifespanoftheorganism Drosophila related tissuedysplasias.Intestinaldysplasiasignificantlylimits significantly impactourunderstandingofthedevelopmentage- development ofmodelsdiseaseprogressionandarelikelyto regenerative processesintheintestinalepitheliumarethuskeyto the microflora,(2)innateimmuneresponsesand(3) colon tumorformation(Uronisetal.,2009). intestinal inflammationandarerefractorytocarcinogen-induced Qin etal.,2010).Germ-freemice,accordingly, exhibitreduced al., 2009;UronisetKaser2010;Niwa factor forchronicinflammationandcancerdevelopment(Gondaet in microfloracompositionandloadmightbeaprominentetiological to determinethegeneticbasisofcoloncancerindicatethatchanges developing coloncancer(Gondaetal.,2009).Interestingly, studies ulcerative colitisorCrohn’s disease)haveanincreasedriskof Accordingly, patientswithinflammatory boweldiseases(including microorganisms (XavierandPodolsky, 2007;Garrettetal.,2010). which mountfrequentandrequiredimmuneresponsestopathogenic significant inbarrierepitheliasuchastheintestinalepithelium, microenvironments (Mantovani,2005;Grivennikovetal.,2010). while tissueinflammationispresentinmosttumor chronic inflammationdisplayahigherincidenceofvariouscancers, Mantovani, 2009),andindividualsgeneticallypredisposedto an inflammatorystate(Mantovani,2005;Colottaetal.,2009; Loss oftissuehomeostasisandcancerprogressionisassociatedwith deregulation oftissuehomeostasisinbarrierepitheliavertebrates. stem cellactivityandinflammatoryprocessescauseage-related compared withcontrolanimals(Buchonetal.,2009a). well asreducedlevelsofJNKandJak/Statsignalingpathways axenically raisedfliesexhibitamarkeddecreaseinmitoticISCs,as balance degrade withage?Itcanbeexpectedthat furthersystematic responses, tissuerepairandmetabolic adaptation,andwhydoesthis determinants thatmaintainthe balancebetweenacutestress environmental (nutritionalandstress) conditions;whatarethemajor remain: howarethesesignaling pathwaysintegratedunderspecific throughout theorganism (Figs functions, cellgrowthandproliferation, andstressresponses in governinghomeostasisandlongevitybycoordinatingmetabolic (including IIS/FOXO,TOR and JNKsignaling)playacentralrole It isclearthatstress-andnutrient-responsivesignalingpathways understanding ofagingandthedevelopmentage-relateddiseases. longevity infliespromisestosignificantlyadvance our focusing onsystemiccontrolofmetabolichomeostasis,fitness and regulation ofmetabolicandproliferativehomeostasiswithstudies The integrationofstudiescharacterizingthetissue-specific Conclusions directions andfuture Better mechanisticunderstandingof(1)theinteractionsbetween This associationbetweeninflammationandcancerisparticularly It islikelythatsimilarinteractionsbetweensignalsregulate The JournalofExperimentalBiology(2014)doi:10.1242/jeb.089920 lifespan, andreducingtherateofstemcellproliferation

1, 2).However, manyquestions 115

The Journal of Experimental Biology agan .I n ovt,H.R. Horvitz, and C.I. Bargmann, azli . ufa,D . uudr .H n ate A. Bartke, and R.H. Muzumdar, D.M., Huffman, N., Barzilai, M. Tatar, and P. Kang, H., Bai, L. Rahme, and N. Perrimon, C., Pitsouli, Y., Apidianakis, ieu . apc . uoo . eenr,M,Lhan .adJse,H. Jasper, and R. Lehmann, M., Degennaro, S., Supoyo, J., Karpac, B., Biteau, H. Jasper, and C.E. Hochmuth, B., Biteau, H. Jasper, and B. Biteau, ai,P . oce . arl . ibsh . cmt,G,Rsa,A.C., Rustan, G., Schmitz, G., Liebisch, A., Mairal, K., Louche, P. M., Badin, 116 fellowships toJ.K.andL.W. DepositedinPMCforreleaseafter12months. Ellison MedicalFoundation(AG-SS-2224-08),andbyAFAR/Ellison postdoctoral the NationalInstituteonGeneralMedicalSciences(NIHRO1GM100196), This workwassupportedbytheNationalInstituteonAging(NIHRO1AG028127), editing. All threeauthorscontributedtotheconceptofthisreview, aswelltowritingand The authorsdeclarenocompetingfinancialinterests. against age-associatedpathologies. provide newinsightandelucidatepotentialtherapeuticavenues regenerative andmetabolicresponsesintheflywillcontinueto analysis oftherolesignalinginteractionsincontrolstress, REVIEW gir,V,Uhd,T,Yns,L,Dvs .adWie M.F. White, and R. Davis, L., Yenush, T., Uchida, V., Aguirre, K.C. Arden, and D. Accili, ruho,S n atig,L. Partridge, and S. Broughton, ieu . apc . wnb,D n apr H. Jasper, and D. Hwangbo, J., Karpac, B., Biteau, H. Jasper, and C.E. Hochmuth, B., Biteau, mhsasy . t,N,Jag .adI,Y. T. Ip, and J. Jiang, N., Ito, A., Amcheslavsky, mhsasy . in,J n p Y. T. Ip, and J. Jiang, A., Amcheslavsky, References Funding Author contributions Competing interests ruho,S . ie,M . ky,T,Bs,T . aosn . ree Y., Driege, J., Jacobson, T. M., Bass, T., Ikeya, M.D., Piper, S.J., Broughton, lhr . an .B n an C.R. Kahn, and B. 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