Dietary deprivation extends lifespan in Caenorhabditis elegans

Dietary restriction (DR) is well known as a nongenetic intervention that robustly extends lifespan in a variety of species; however, its underlying mechanisms remain unclear. We have found in Caenorhabditis elegans that dietary deprivation (DD) during adulthood, defined as removal of their food source Escherichia coli after the completion of larval development, increased lifespan and enhanced thermotolerance and resistance to oxidative stress. DD-induced longevity was independent of one C. elegans SIRTUIN, sir-2.1, which is required for the effects of DR, and was independent of the daf-2/insulin-like signaling pathway that independently regulates longevity and larval diapause in C. elegans. DD did not significantly alter lifespan of fem-1(hc17); eat-2(ad465) worms, a genetic model of DR. These findings suggest that DD and DR share some downstream effectors. In addition, DD was detrimental for longevity when imposed on reproductively active young adults, suggesting that DD may only be beneficial in the absence of competing metabolic demands, such as fertility. Adult-onset DD offers a new paradigm for investigating dietary regulation of longevity in C. elegans. This study presents the first evidence that long-term DD, instead of being detrimental, can extend lifespan of a multicellular adult organism.     

Pyruvate imbalance mediates metabolic reprogramming and mimics lifespan extension by dietary restriction in Caenorhabditis elegans

Dietary restriction (DR) is the most universal intervention known to extend animal lifespan. DR also prevents tumor development in mammals, and this effect requires the tumor suppressor PTEN. However, the metabolic and cellular processes that underly the beneficial effects of DR are poorly understood. We identified slcf‐1 in an RNAi screen for genes that extend Caenorhabditis elegans lifespan in a PTEN/daf‐18‐dependent manner. We showed that slcf‐1 mutation, which increases average lifespan by 40%, mimics DR in worms fed ad libitum. An NMR‐based metabolomic characterization of slcf‐1 mutants revealed lower lipid levels compared to wild‐type animals, as expected for dietary‐restricted animals, but also higher pyruvate content. Epistasis experiments and metabolic measurements support a model in which the long lifespan of slcf‐1 mutants relies on increased mitochondrial pyruvate metabolism coupled to an adaptive response to oxidative stress. This response requires DAF‐18/PTEN and the previously identified DR effectors PHA‐4/FOXA, HSF‐1/HSF1, SIR‐2.1/SIRT‐1, and AMPK/AAK‐2. Overall, our data show that pyruvate homeostasis plays a central role in lifespan control in C. elegans and that the beneficial effects of DR results from a hormetic mechanism involving the mitochondria. Analysis of the SLCF‐1 protein sequence predicts that slcf‐1 encodes a plasma membrane transporter belonging to the conserved monocarboxylate transporter family. These findings suggest that inhibition of this transporter homolog in mammals might also promote a DR response.     

drr‐2 encodes an eIF4H that acts downstream of TOR in diet‐restriction‐induced longevity of C. elegans

Dietary restriction (DR) results in a robust increase in lifespan while maintaining the physiology of much younger animals in a wide range of species. Here, we examine the role of drr‐2, a DR‐responsive gene recently identified, in determining the longevity of Caenorhabditis elegans. Inhibition of drr‐2 has been shown to increase longevity. However, the molecular mechanisms by which drr‐2 influences longevity remain unknown. We report here that drr‐2 encodes an ortholog of human eukaryotic translation initiation factor 4H (eIF4H), whose function is to mediate the initiation step of mRNA translation. The molecular function of DRR‐2 is validated by the association of DRR‐2 with polysomes and by the decreased rate of protein synthesis observed in drr‐2 knockdown animals. Previous studies have also suggested that DR might trigger a regulated reduction in drr‐2 expression to initiate its longevity response. By examining the effect of increasing drr‐2 expression on DR animals, we find that drr‐2 is essential for a large portion of the longevity response to DR. The nutrient‐sensing target of rapamycin (TOR) pathway has been shown to mediate the longevity effects of DR in C. elegans. Results from our genetic analyses suggest that eIF4H/DRR‐2 functions downstream of TOR, but in parallel to the S6K/PHA‐4 pathway to mediate the lifespan effects of DR. Together, our findings reveal an important role for eIF4H/drr‐2 in the TOR‐mediated longevity responses to DR.     

Recent Progress in Regulation of Aging by Insulin/IGF-1 Signaling in Caenorhabditis elegans

Caenorhabditis elegans has been used as a major model organism to identify genetic factors that regulate organismal aging and longevity. Insulin/insulin-like growth factor 1 (IGF-1) signaling (IIS) regulates aging in many species, ranging from nematodes to humans. C. elegans is a nonpathogenic genetic nematode model, which has been extensively utilized to identify molecular and cellular components that function in organismal aging and longevity. Here, we review the recent progress in the role of IIS in aging and longevity, which involves direct regulation of protein and RNA homeostasis, stress resistance, metabolism and the activities of the endocrine system. We also discuss recently identified genetic factors that interact with canonical IIS components to regulate aging and health span in C. elegans. We expect this review to provide valuable insights into understanding animal aging, which could eventually help develop anti-aging drugs for humans.     

Trehalose extends longevity in the nematode Caenorhabditis elegans

Trehalose is a disaccharide of glucose found in diverse organisms and is suggested to act as a stress protectant against heat, cold, desiccation, anoxia, and oxidation. Here, we demonstrate that treatment of Caenorhabditis elegans with trehalose starting from the young‐adult stage extended the mean life span by over 30% without any side effects. Surprisingly, trehalose treatment starting even from the old‐adult stage shortly thereafter retarded the age‐associated decline in survivorship and extended the remaining life span by 60%. Demographic analyses of age‐specific mortality rates revealed that trehalose extended the life span by lowering age‐independent vulnerability. Moreover, trehalose increased the reproductive span and retarded the age‐associated decrease in pharyngeal‐pumping rate and the accumulation of lipofuscin autofluorescence. Trehalose also enhanced thermotolerance and reduced polyglutamine aggregation. These results suggest that trehalose suppressed aging by counteracting internal or external stresses that disrupt protein homeostasis. On the other hand, the life span‐extending effect of trehalose was abolished in long‐lived insulin/IGF‐1‐like receptor (daf‐2) mutants. RNA interference‐mediated inactivation of the trehalose‐biosynthesis genes trehalose‐6‐phosphate synthase‐1 (tps‐1) and tps‐2, which are known to be up‐regulated in daf‐2 mutants, decreased the daf‐2 life span. These findings indicate that a reduction in insulin/IGF‐1‐like signaling extends life span, at least in part, through the aging‐suppressor function of trehalose. Trehalose may be a lead compound for potential nutraceutical intervention of the aging process.     

饮食限制延长寿命的遗传机制

饮食限制(Dietary restriction,DR)有效延长了哺乳动物的寿命,也使许多年龄依赖性疾病的发病率降低且延缓其进展。理解饮食限制引起长寿的遗传机制,会对将来处理衰老相关的医疗问题产生深远影响。然而直到最近人们对后生动物的这些机制几乎仍一无所知。通过理解能量感知和寿命控制遗传基础的最新进展,在酵母、无脊椎动物和哺乳动物中,已开始解决这个难题。越来越多的证据表明,后生动物大脑在感应饮食限制和促进寿命延长中起关键作用,因此文章综述了近来后生动物DR长寿的调解因子与DR长寿的基因和神经调节机制及有关理论的进展。     

The dynamin-related protein DRP-1 and the insulin signaling pathway cooperate to modulate Caenorhabditis elegans longevity

Here, we report that inactivation of the Caenorhabditis elegans dynamin-related protein DRP-1, a key component responsible for mitochondrial fission and conserved from yeast to humans, dramatically enhanced the effect of reduced insulin signaling (IIS) to extend lifespan. This represents the first report of a beneficial impact of manipulating mitochondrial dynamics on animal lifespan and suggests that mitochondrial morphology and IIS cooperate to modulate aging.     

Temporal requirements of insulin/IGF‐1 signaling for proteotoxicity protection

Toxic protein aggregation (proteotoxicity) is a unifying feature in the development of late‐onset human neurodegenerative disorders. Reduction of insulin/IGF‐1 signaling (IIS), a prominent lifespan, developmental and reproductive regulatory pathway, protects worms from proteotoxicity associated with the aggregation of the Alzheimer’s disease‐linked Aβ peptide. We utilized transgenic nematodes that express human Aβ and found that late life IIS reduction efficiently protects from Aβ toxicity without affecting development, reproduction or lifespan. To alleviate proteotoxic stress in the animal, the IIS requires heat shock factor (HSF)‐1 to modulate a protein disaggregase, while DAF‐16 regulates a presumptive active aggregase, raising the question of how these opposing activities could be co‐regulated. One possibility is that HSF‐1 and DAF‐16 have distinct temporal requirements for protection from proteotoxicity. Using a conditional RNAi approach, we found an early requirement for HSF‐1 that is distinct from the adult functions of DAF‐16 for protection from proteotoxicity. Our data also indicate that late life IIS reduction can protect from proteotoxicity when it can no longer promote longevity, strengthening the prospect that IIS reduction might be a promising strategy for the treatment of neurodegenerative disorders caused by proteotoxicity.     

Reduced expression of alpha-1,2-mannosidase I extends lifespan in Drosophila melanogaster and Caenorhabditis elegans

Exposure to sub-lethal levels of stress, or hormesis, was a means to induce longevity. By screening for mutations that enhance resistance to multiple stresses, we identified multiple alleles of alpha-1,2-mannosidase I ( mas1 ) which, in addition to promoting stress resistance, also extended longevity. Longevity enhancement is also observed when mas1 expression is reduced via RNA interference in both Drosophila melanogaster and Caenorhabditis elegans. The screen also identified Edem1 ( Edm1 ) , a gene downstream of mas1, as a modulator of lifespan. As double mutants for both mas1 and Edm1 showed no additional longevity enhancement, it appeared that both mutations function within a common pathway to extend lifespan. Molecular analysis of these mutants revealed that the expression of BiP , a putative biomarker of dietary restriction (DR), is down-regulated in response to reductions in mas1 expression. These findings suggested that mutations in mas1 may extend longevity by modulating DR.     

AMPK‐mediated formation of stress granules is required for dietary restriction‐induced longevity in Caenorhabditis elegans

Stress granules (SGs) are nonmembranous organelles that are dynamically assembled and disassembled in response to various stressors. Under stressed conditions, polyadenylated mRNAs and translation factors are sequestrated in SGs to promote global repression of protein synthesis. It has been previously demonstrated that SG formation enhances cell survival and stress resistance. However, the physiological role of SGs in organismal aging and longevity regulation remains unclear. In this study, we used TIAR‐1::GFP and GTBP‐1::GFP as markers to monitor the formation of SGs in Caenorhabditis elegans. We found that, in addition to acute heat stress, SG formation could also be triggered by dietary changes, such as starvation and dietary restriction (DR). We found that HSF‐1 is required for the SG formation in response to acute heat shock and starvation but not DR, whereas the AMPK‐eEF2K signaling is required for starvation and DR‐induced SG formation but not heat shock. Moreover, our data suggest that this AMPK‐eEF2K pathway‐mediated SG formation is required for lifespan extension by DR, but dispensable for the longevity by reduced insulin/IGF‐1 signaling. Collectively, our findings unveil a novel role of SG formation in DR‐induced longevity.     

Proteomics analysis in Caenorhabditis elegans to elucidate the response induced by tyrosol,an olive phenol that stimulates longevity and stress resistance

Tyrosol (TYR, 2‐(4‐hydroxyphenyl)ethanol), one of the main phenols in olive oil and olive fruit, significantly strengthens resistance to thermal and oxidative stress in the nematode Caenorhabditis elegans and extends its lifespan. To elucidate the cellular functions regulated by TYR, we have used a proteomic procedure based on 2DE coupled with MS with the aim to identify the proteins differentially expressed in nematodes grown in a medium containing 250 μM TYR. After the comparison of the protein profiles from 250 μM TYR and from control, 28 protein spots were found to be altered in abundance (≥twofold). Analysis by MALDI‐TOF/TOF and PMF allowed the unambiguous identification of 17 spots, corresponding to 13 different proteins. These proteins were as follows: vitellogenin‐5, vitellogenin‐2, bifunctional glyoxylate cycle protein, acyl CoA dehydrogenase‐3, alcohol dehydrogenase 1, adenosylhomocysteinase, elongation factor 2, GTP‐binding nuclear protein ran‐1, HSP‐4, protein ENPL‐1 isoform b, vacuolar H ATPase 12, vacuolar H ATPase 13, GST 4. Western‐blot analysis of yolk protein 170, ras‐related nuclear protein, elongation factor 2, and vacuolar H ATPase H subunit supported the proteome evidence.     

Identification of core 1 O-glycan T-synthase from Caenorhabditis elegans

The common O-glycan core structure in animal glycoproteins is the core 1 disaccharide Galbeta1-3GalNAcalpha1-Ser/Thr, which is generated by the addition of Gal to GalNAcalpha1-Ser/Thr by core 1 UDP-alpha-galactose (UDP-Gal):GalNAcalpha1-Ser/Thr beta1,3-galactosyltransferase (core 1 beta3-Gal-T or T-synthase, EC2.4.1.122). Although O-glycans play important roles in vertebrates, much remains to be learned from model organisms such as the free-living nematode Caenorhabditis elegans, which offer many advantages in exploring O-glycan structure/function. Here, we report the cloning and enzymatic characterization of T-synthase from C. elegans (Ce-T-synthase). A putative C. elegans gene for T-synthase, C38H2.2, was identified in GenBank by a BlastP search using the human T-synthase protein sequence. The full-length cDNA for Ce-T-synthase, which was generated by polymerase chain reaction using a C. elegans cDNA library as the template, contains 1170 bp including the stop TAA. The cDNA encodes a protein of 389 amino acids with typical type II membrane topology and a remarkable 42.7% identity to the human T-synthase. Ce-T-synthase has seven Cys residues in the lumenal domain including six conserved Cys residues in all orthologs. The Ce-T-synthase has four potential N-glycosylation sequons, whereas the mammalian orthologs lack N-glycosylation sequons. Only one gene for Ce-T-synthase was identified in the genome-wide search, and it contains eight exons. Promoter analysis of the Ce-T-synthase using green fluorescent protein (GFP) constructs shows that the gene is expressed at all developmental stages and appears to be in all cells. Unexpectedly, only minimal activity was recovered in the recombinant, soluble Ce-T-synthase secreted from a wide variety of mammalian cell lines, whereas robust enzyme activity was recovered in the soluble Ce-T-synthase expressed in Hi-5 insect cells. Vertebrate T-synthase requires the molecular chaperone Cosmc, but our results show that Ce-T-synthase does not require Cosmc and might require invertebrate-specific factors for the formation of the optimally active enzyme. These results show that the Ce-T-synthase is a functional ortholog to the human T-synthase in generating core 1 O-glycans and open new avenues to explore O-glycan function in this model organism.     

The influence of metabolic rate on longevity in the nematode Caenorhabditis elegans

Much of the recent interest in aging research is due to the discovery of genes in a variety of model organisms that appear to modulate aging. A large amount of research has focused on the use of such long-lived mutants to examine the fundamental causes of aging. While model organisms do offer many advantages for studying aging, it also critical to consider the limitations of these systems. In particular, ectothermic (poikilothermic) organisms can tolerate a much larger metabolic depression than humans. Thus, considering only chronological longevity when assaying for long-lived mutants provides a limited perspective on the mechanisms by which longevity is increased. In order to provide true insight into the aging process additional physiological processes, such as metabolic rate, must also be assayed. This is especially true in the nematode Caenorhabditis elegans, which can naturally enter into a metabolically reduced state in which it survives many times longer than its usual lifetime. Currently it is seen as controversial if long-lived C. elegans mutants retain normal metabolic function. Resolving this issue requires accurately measuring the metabolic rate of C. elegans under conditions that minimize environmental stress. Additionally, the relatively small size of C. elegans requires the use of sensitive methodologies when determining metabolic rates. Several studies indicating that long-lived C. elegans mutants have normal metabolic rates may be flawed due to the use of inappropriate measurement conditions and techniques. Comparisons of metabolic rate between long-lived and wild-type C. elegans under more optimized conditions indicate that the extended longevity of at least some long-lived C. elegans mutants may be due to a reduction in metabolic rate, rather than an alteration of a metabolically independent genetic mechanism specific to aging.     

Altered bacterial metabolism, not coenzyme Q content, is responsible for the lifespan extension in Caenorhabditis elegans fed an Escherichia coli diet lacking coenzyme Q

Coenzyme Q(n) is a fully substituted benzoquinone containing a polyisoprene tail of distinct numbers (n) of isoprene groups. Caenorhabditis elegans fed Escherichia coli devoid of Q(8) have a significant lifespan extension when compared to C. elegans fed a standard 'Q-replete'E. coli diet. Here we examine possible mechanisms for the lifespan extension caused by the Q-less E. coli diet. A bioassay for Q uptake shows that a water-soluble formulation of Q(10) is effectively taken up by both clk-1 mutant and wild-type nematodes, but does not reverse lifespan extension mediated by the Q-less E. coli diet, indicating that lifespan extension is not due to the absence of dietary Q per se. The enhanced longevity mediated by the Q-less E. coli diet cannot be attributed to dietary restriction, different Qn isoforms, reduced pathogenesis or slowed growth of the Q-less E. coli, and in fact requires E. coli viability. Q-less E. coli have defects in respiratory metabolism. C. elegans fed Q-replete E. coli mutants with similarly impaired respiratory metabolism due to defects in complex V also show a pronounced lifespan extension, although not as dramatic as those fed the respiratory deficient Q-less E. coli diet. The data suggest that feeding respiratory incompetent E. coli, whether Q-less or Q-replete, produces a robust life extension in wild-type C. elegans. We believe that the fermentation-based metabolism of the E. coli diet is an important parameter of C. elegans longevity.