| Aging is characterized by multi-level changes and deterioration.In the past thirty years,the aging research community has revealed numerous genetic factors and environmental factors that can delay these age-related phenotypes.However,an emerging question is:are these age-related phenotypes reversible?To shed light on this question,I focus on how age-related phenotypes change during starvation and refeeding in C.elegans.When starvation was initiated at the fourth larval stage(L4),worms completed development their post-refeeding lifespan was not shortened.These observations lead to questions that:(1)Do worms acquire age-related phenotypes during starvation?(2)If yes,are these phenotypes reversed after refeeding?(3)If yes,what is the underlying mechanism of reversal?In this study,firstly,the comprehensive characterization revealed that multi-level age-related phenotypes emerged during starvation,including transcriptomic aging clock,expression of aging marker genes,abnormality in nuclear morphology,mitochondrial fragmentation,breakdown of the intestinal barrier and impaired locomotion.Amazingly,after refeeding,these age-related phenotypes were reversed within 1 day and then gradually showed up again.Detailed observation showed that the restoration was initiated within several hours and completed within a dozen hours.Thus,a transient and rapid restoration occurs after refeeding.Basing on these observations,I hypothesized that some repairing mechanism should be transiently and rapidly activated after refeeding.Analysis of transcriptomic dynamics revealed that after refeeding,hundreds of genes were upregulated within 3 hours,and then were gradually downregulated.These genes were enriched in multiple homeostasismaintaining pathways,such as ER unfolded protein response,oxidative stress response,immune response.Inositol-requiring enzyme 1(IRE-1)is a critical sensor that activates unfolded protein response in ER.The classical downstream genes of IRE-1,hsp-3 and hsp-4,were transiently and rapidly up-regulated in an IRE-1 dependent manner,confirming the activation of IRE-1 branch.Inactivating IRE-1 impaired the reversal of multiple age-related phenotypes,including transcriptomic aging clock,abnormality in nuclear morphology,breakdown of the intestinal barrier and impaired locomotion.Through transcriptomic comparation of wild-type and ire-1 loss-of-function mutant,the transiently and rapidly up-regulated genes were further classified into "IRE-1 dependent" and "IRE-1 independent".Several genes that promote protein folding or translocation,such as pdi-2/3/6,trap-1/2/3 and hsp-3/4,were predicted to be key downstream genes of IRE-1.Interestingly,knocking down hsp-4 impaired restoration of nuclear morphology and locomotion,confirming a key role of hsp-4.Basing on these observations,I proposed that maintaining protein homeostasis is the basis of reversing age-related phenotypes.Further,I showed that age-related phenotypes were not completely reversed if starvation was initiated during adult stage.This study echoes the previous finding that L1 starved worms displayed reversible age-related phenotypes.Similarly,(1)age-related phenotypes emerged during starvation and were erased after refeeding;(2)reversal of these phenotypes relied on IRE-1 activity;(3)post-refeeding lifespan was not affected by the duration of starvation.Further,(1)L4 starved worms completed development;(2)I showed that after reversal,age-related phenotypes emerged again;(3)I captured the temporal dynamic of UPRER activation;(4)analysis of downstream genes of IRE-1 indicated the key role of protein homeostasis.Overall,in this study,I proposed that after refeeding,some repairing mechanism should be transiently and rapidly activated.Basing on this idea,I found that the activation of ER unfolded protein response underlies the reversal of key age-related phenotypes in refed C.elegans(Eureka). |
