Aging during C. elegans L1 quiescence

When C. elegans emb yos ha ch in he absence o ood, de elopmen a es s a he i s la al s age (L1). This p ocess in ol es quiescence o he cells ha no mally di ide a he beginning o pos emb yonic de elopmen . When a es ed L1s encoun e ood, cell di isions esume and pos emb yonic de elopmen p oceeds. Fo his eason, his s age o a es is ou inely used in many C. elegans labs o synch onize la a. L1 a es was desc ibed as a non-aging s a e, since he ime spen on i did no accoun owa ds he o al li espan once he animals esumed de elopmen [1]. Howe e , Roux e al. showed ha L1 la ae unde go a p ocess simila o adul aging. Rema kably, he signals o aging accumula ed du ing a es we e e ased upon eeding o he a es ed la ae [2], explaining why he ime spen in a es does no educe he li espan o he adul . Clea ance o aging signs seemed necessa y o esume de elopmen . Al hough i was somehow implici ha he ex en o aging sings would ma k he ime necessa y o eco e , he lack o quan i a i e me hods o assess he iming o eco e y p e en ed es ing his idea. Now, we ha e bene i ed om a quan i a i e me hod ha we de eloped o measu e la al de elopmen al iming [3] o quan i y he ime o eco e a e p olonged L1 a es . In a ecen publica ion [4], we ha e shown ha ma ke s o aging ha accumula e du ing L1 a es con ibu e o inc ease he ime needed o eco e a e p olonged a es . Fu he mo e, inc eased ac i i y o he ansc ip ion ac o DAF-16, as ha ound in he insulin ecep o mu an da -2, led o as e eco e y. Con e sely, da -16 mu an s showed s ong delays in eco e y, e en a e sho pe iods o a es . This ole o Insulin signaling was su p ising, as ac i a ion o DAF- 16 is commonly ela ed o ep ession o p oli e a ion. da -16 mu an s a e de ec i e in L1 a es and a ac ion o he la ae in he popula ion ini ia e pos emb yonic cell di isions, wha was a ibu ed o a lowe ac i a ion o he cyclin dependen kinase inhibi o cki-1 [5]. Howe e , his only happens when he e is e hanol p esen in he media o a es ed L1, no mally used o dilu e he choles e ol supplemen a ion o C. elegans. Ins ead, we used media wi hou e hanol and obse ed he same le els o cki-1 exp ession in he wild- ype s ain and da -16 mu an s. Analysis o he ini ial di isions o pos emb yonic de elopmen e ealed ha he da -16 mu an no only did no show p ema u e di isions, bu hey su e ed an impo an delay compa ed Edi o ial o he wild ype. Then, how do we explain he ep ession o cell di isions in he da -16 mu an ? Ou hypo hesis was ha insulin signaling modula es he a e o aging du ing L1 a es , as i does o adul aging [6]. Indeed, we could con i m ha ac i a ion o DAF-16 educes he a e o L1 aging. The e o e, he delay in he ini ia ion o pos emb yonic de elopmen in he da -16 mu an i is no ela ed o a di ec ole o his ansc ip ion ac o in he con ol o cell di isions du ing eco e y bu o he lack o ac i a ion o he s ess esponse du ing L1 a es , leading o a as e a e o L1 aging. The as e accumula ion o L1 aging ma ke s en ails longe eco e y imes o clea hem, delaying he ini ia ion o pos emb yonic di isions [4]. The lack o homogenei y o L1 a es esembles he p ocess o quiescence deepening unde gone by mam- malian cells. Capaci y o quiescen cells o eco e p oli e a ion po en ial depends on he dep h o quiescence. This p ocess has been s udied in de ail in Ra Emb yonic Fib oblas s. Cells in shallow quiescence espond as e o g ow h s imuli han hose in deep quiescence, which need s onge s imuli and longe imes o ini ia e p oli e a ion. Deep quiescen cells sha e gene-exp ession signa u es wi h senescen and aged cells, wha sugges s quiescence deepening as a ansi ional s a e owa d senescence and aging. Cells cul u ed o long pe iods unde quiescence condi ions mo e om shallow o deep quiescence and, ul ima ely, hey i e e sibly a es as senescen cells [7]. Simila o wha we ha e desc ibed in C. elegans o a es ed L1s [4], accumula ion o signs o aging du ing p olonged pe iods o quiescence delays he eac i a ion o cell p oli e a ion. Lysosomal unc ion con ols quiescence deepening by educing he accumula ion o Reac i e oxygen species (ROS) [7]. Cells subjec ed o long- e m se um s a a ion unde wen lysosomal unc ion impai men leading o a highe ROS accumula ion, esul ing in a loss o capaci y o een e cell cycle [7]. In his way, when quiescen cells we e pha macologically ea ed o inhibi lysosomal unc ion o o induce oxida i e s ess, hey we e pushed in o a deepe quiescen s a e and hey needed s onge s imula ion o eco e [7]. As ROS, accumula ion o p o ein agg e- ga es also leads o quiescence deepening. Lysosomal ac i a ion is also impo an o clea p o ein agg ega es in quiescen cells o keep hem in a shallowe quiescen s a e [8]. This is in conco dance wi h ou indings, Aging du ing C. elegans L1 quiescence Alejand o Ma a-Cabana, F ancisco Ja ie Rome o-Expósi o, Ma ía Olmedo www.aging-us.com AGING 2020, Vol. 12, No. 18 www.aging-us.com 17756 AGING whe e a es ed la ae wi h highe le els o ROS and p o ein agg ega ion needed longe imes o eco e and o ini ia e pos -emb yonic de elopmen . This leads us o aise he idea o he quiescence dep h in he con ex o C. elegans and o p opose a es ed L1 la ae as a model o he s udy o his p ocess. The con ol o he quiescence dep h is undamen al o main ain he issue egene a i e po en ial, bu also, he dys egula ion o he cellula quiescence can esul in hype p oli e a ion ha leads o cance . The e o e, he unde s anding o he molecula mechanisms unde lying his phenomenon is o special in e es and he C. elegans model is a use ul ool o gain knowledge abou hese p ocesses (Figu e 1). REFERENCES 1. Johnson TE, e al. Mech Ageing De . 1984; 28:23–40. h ps://doi.o g/10.1016/0047-6374(84)90150-7 PMID:6542614 2. Roux AE, e al. Cell Me ab. 2016; 23:1113–26. h ps://doi.o g/10.1016/j.cme .2016.05.024 PMID:27304510 3. Olmedo M, e al. Gene ics. 2015; 201:443–48. h ps://doi.o g/10.1534/gene ics.115.179242 PMID:26294666 4. Olmedo M, e al. Aging Cell. 2020; 19:e13085. h ps://doi.o g/10.1111/acel.13085 PMID:31852031 5. Baugh LR, S e nbe g PW. Cu Biol. 2006; 16:780–85. h ps://doi.o g/10.1016/j.cub.2006.03.021 PMID:16631585 6. Kenyon CJ. Na u e. 2010; 464:504–12. h ps://doi.o g/10.1038/na u e08980 PMID:20336132 7. Fujimaki K, e al. P oc Na l Acad Sci USA. 2019; 116:22624–34. h ps://doi.o g/10.1073/pnas.1915905116 PMID:31636214 8. Leeman DS, e al. Lysosome ac i a ion clea s agg ega es and enhances quiescen neu al s em cell ac i a ion du ing aging. Science. 2018; 359:1277–83. h ps://doi.o g/10.1126/science.aag3048 PMID:29590078 Figu e 1. Pa allelisms be ween quiescence deepening and L1 ageing. (A) Upon emo al o g ow h ac o s, REF (Ra Emb yonic Fib oblas ) en e cell quiescence, a e e sible, non-p oli e a i e s a e. Cells p og essi ely unde go quiescence deepening as hey accumula e ROS and p o ein agg ega es. A e p olonged quiescence, cells equi e s onge s imula ion and ake longe o exi quiescence and e u n o p oli e a ion. E en ually cells each senescence, an i e e sible s a e o cell a es . (B) L1 a es ed C. elegans la ae show a simila p ocess o quiescence deepening. P olonged a es en ails a p ocess named L1 aging, ha also in ol es accumula ion o ROS and p o ein agg ega es. We ha e shown ha p olonged quiescence leads o a delay in he ini ia ion o pos emb yonic cell di isions. Be o e dying as a es ed L1, la ae lose he capaci y o eco e om L1 a es , a p ocess ha could be compa ed o cell senescence. (C) Insulin signalling modula ed he p ocess o L1 aging. Ac i a ion o he ansc ip ion ac o DAF-16, as ha sound in da -2 mu an s, leads o a slowe a e o L1 aging. As a consequence, a e he same ime in L1 a es , da -2 mu an s accumula e less ma ke s o aging. This allows a as e eco e y once la ae encoun e ood. da -16 mu an s, show as e L1 ageing and he ini ia ion o pos emb yonic di isions upon eeding is delayed compa ed o he wild ype. www.aging-us.com 17757 AGING Ma ía Olmedo: Depa amen o de Gené ica, Facul ad de Biología, Uni e sidad de Se illa, Se illa 41012, Spain Co espondence: Ma ía Olmedo Email: ma iaolme[email p o ec ed] Keywo ds: L1 aging, quiescence, C. elegans, insulin signalling Copy igh : © 2020 Ma a-Cabana e al. This is an open access a icle dis ibu ed unde he e ms o he C ea i e Commons A ibu ion License (CC BY 3.0), which pe mi s un es ic ed use, dis ibu ion, and ep oduc ion in any medium, p o ided he o iginal au ho and sou ce a e c edi ed Recei ed: Augus 18, 2020 Published: Sep embe 27, 2020 www.aging-us.com 17758 AGING