The role of ubiquinone in Caenorhabditis elegans longevity

Aging is an irreversible physiological process that affects all living organisms. Different mutations in the insulin signaling pathway and caloric restriction have been shown to retard aging in Caenorhabditis elegans. In addition, mutations or RNAi silencing of components of the respiratory chain results in the modification of adult life span. Another class of genes that affect life span in C. elegans is the clock (clk) genes. Particularly interesting is clk-1, which encodes an enzyme required for ubiquinone (coenzyme Q, CoQ) biosynthesis. Down-regulation by RNAi silencing of the genes required for ubiquinone biosynthesis also extends life span in C. elegans, and CoQ supplied in the diet also affects nematode longevity in both clk-1 and wild-type strains. Although there are many aspects that can be considered in aging, we focus this review on the role of CoQ in the longevity of C. elegans. We will review the current information about the biosynthesis of CoQ and its dietary supplementation related to the extension of life span. We will also analyze the function of CoQ in the electron transport chain and reactive oxygen species production in the context of aging. We hypothesize that the role of CoQ on longevity of C. elegans supports the oxidative damage theory of aging.     

Increased longevity of some C. elegans mitochondrial mutants explained by activation of an alternative energy-producing pathway

The Caenorhabditis elegans misc-1 gene encodes a mitochondrial carrier with a role in oxidative stress response. The knock-out mutant has no lifespan phenotype and fails to upregulate the gei-7-mediated glyoxylate shunt, an extra-mitochondrial pathway of energy production. We show that gei-7 is required for the longevity of the mitochondrial mutant clk-1. Our data suggest that only mitochondrial mutants that upregulate gei-7 can achieve longevity.     

Curcumin-mediated lifespan extension in Caenorhabditis elegans

Curcumin is the active ingredient in the herbal medicine and dietary spice, turmeric (Curcuma longa). It has a wide range of biological activities, including anti-inflammatory, antioxidant, chemopreventive, and chemotherapeutic activities. We examined the effects of curcumin on the lifespan and aging in Caenorhabditis elegans, and found that it responded to curcumin with an increased lifespan and reduced intracellular reactive oxygen species and lipofuscin during aging. We analyzed factors that might influence lifespan extension by curcumin. We showed that lifespan extension by curcumin in C. elegans is attributed to its antioxidative properties but not its antimicrobial properties. Moreover, we showed that lifespan extension had effects on body size and the pharyngeal pumping rate but not on reproduction. Finally, lifespan tests with selected stress- and lifespan-relevant mutant strains revealed that the lifespan-extending phenotype was absent from the osr-1, sek-1, mek-1, skn-1, unc-43, sir-2.1, and age-1 mutants, whereas curcumin treatment prolonged the lifespan of mev-1 and daf-16 mutants. Our study has unraveled a diversity of modes of action and signaling pathways to longevity and aging with curcumin exposure in vivo.     

Effects of resveratrol on lifespan in Drosophila melanogaster and Caenorhabditis elegans

It was recently reported that the plant polyphenol resveratrol, found, e.g., in grape berry skins, extended lifespan in the fruit fly Drosophila melanogaster and the nematode worm Caenorhabditis elegans. This lifespan extension was dependent on an NAD(+)-dependent histone deacetylase, Sir2 in Drosophila and SIR-2.1 in C. elegans. The extension of lifespan appeared to occur through a mechanism related to dietary restriction (DR), the reduction of available nutrients without causing malnutrition, an intervention that extends lifespan in diverse organisms from yeast to mammals. In Drosophila, lifespan extension by DR is associated with a reduction in fecundity. However, a slight increase in fecundity was reported upon treatment with resveratrol, suggesting a mode of action at least partially distinct from that of DR. To probe this mechanism further, we initiated a new study of the effects of resveratrol on Drosophila. We saw no significant effects on lifespan in seven independent trials. We analysed our resveratrol and found that its structure was normal, with no oxidative modifications. We therefore re-tested the effects of resveratrol in C. elegans, in both wild-type and sir-2.1 mutant worms. The results were variable, with resveratrol treatment resulting in slight increases in lifespan in some trials but not others, in both wild type and sir-2.1 mutant animals. We postulate that the effect of resveratrol upon lifespan in C. elegans could reflect induction of phase 2 drug detoxification or activation of AMP kinase.     

Effects of a potent antioxidant, platinum nanoparticle, on the lifespan of Caenorhabditis elegans

We have shown that platinum nanoparticles (nano-Pt) are a superoxide dismutase (SOD)/catalase mimetic. Various data have shown extension of the Caenorhabditis elegans lifespan by antioxidant treatment. The present study was designed to elucidate the survival benefit conferred by nano-Pt, as compared to the well-known SOD/catalase mimetic EUK-8. At 0.5mM, nano-Pt significantly extended the lifespan of wild-type N2 nematodes and at 0.25 and 0.5mM, nano-Pt recovered the shortened lifespan of the mev-1(kn1) mutant, which is due to excessive oxidative stress. In both instances, EUK-8 at 0.05, 0.5, and 5mM did not extend nematode lifespan. Even when 0.4M paraquat was loaded exogenously, nano-Pt (0.1 and 0.5mM) and EUK-8 (0.5 and 5mM) were effective in rescuing worms. Moreover, 0.5mM nano-Pt significantly reduced the accumulation of lipofuscin and ROS induced by paraquat. We measured the in vitro dose-dependent quenching of O(2)(-) and H(2)O(2), indicating that nano-Pt is a more potent SOD/catalase mimetic than EUK-8. Nano-Pt prolonged the worm lifespan, regardless of thermotolerance or dietary restriction. Taken together, nano-Pt has interesting anti-ageing properties.     

Fluorodeoxyuridine affects the identification of metabolic responses to daf-2 status in Caenorhabditis elegans

Fluorodeoxyuridine (FUdR) is often used to help maintain synchronous populations of Caenorhabditis elegans adults, for instance as would typically be the case in studying age-related effects. However, given that FUdR inhibits DNA synthesis and therefore reproduction, it will clearly have significant wide-ranging biological effects. It is often assumed that these can be compensated for using appropriate controls. We show here that this is not the case for a metabolomic analysis of a long-lived daf-2 mutant strain: not only were the effects of FUdR much greater than the effects of the mutation, there were clear interactions between FUdR and genotype, such that identification of daf-2-dependent metabolites would have been compromised on FUdR plates. This indicates that FUdR should only be used with caution for C. elegans ageing experiments, and should not be assumed to be independent of other factors being studied.     

Repeated temperature fluctuation extends the life span of Caenorhabditis elegans in a daf-16-dependent fashion

Thermocyclers were utilized to regularly shift nematodes between 12 degrees C and 25 degrees C throughout their life spans. When wild-type worms (N2) were "thermocycled" between 12 degrees C and 25 degrees C at 10-min intervals they lived almost as long as those that were incubated constantly at 12 degrees C. Shifting at 1-min or 1-h intervals lessened this effect. Similar results were observed for the long-lived mutants daf-2, eat-2 and clk-1, each of which prolongs life span through different mechanisms. In contrast, the life span of a daf-16 mutant was not prolonged by thermocycling worms, indicating that the effect is mediated by an insulin-like signaling pathway. To elucidate the molecular basis for the life span extension, two transgenic strains were employed in which heat shock proteins (HSPs) drove expression of the green fluorescent protein (GFP) gene. As expected, both HSPs were expressed at significantly higher levels in animals grown at 25 degrees C. Moreover, HSP expression in the thermocycled worms approximated that of animals grown at 25 degrees C more so than animals grown at 12 degrees C. This suggests that incubation at the higher temperatures for short time intervals induced stress-responsive gene expression that led to significant life span extension.     

Ethanol interferes with gustatory plasticity in Caenorhabditis elegans

Ethanol affects the formation of learning and memory in many species. However, the molecular mechanisms underlying the behavioral effects of ethanol are still poorly understood. In Caenorhabditis elegans, gustatory plasticity is a simple learning paradigm, in which animals after prolonged pre-exposure to a chemo-attractive salt in the absence of food show chemo-aversion to this salt during subsequent chemotaxis test stage. We characterized the effect of ethanol on this simple learning model. Our results showed that ethanol administration interfered with gustatory plasticity during pre-exposure or test stage in well-fed worms. Genetic analysis revealed that one mutant previously implicated involved in acute ethanol responses, slo-1, as well as two mutants with defects in serotonin synthesis, tph-1 and bas-1, failed to exhibit ethanol interference with gustatory plasticity. Furthermore, two metabotropic serotonin receptors, SER-4 and SER-7, were found to be involved in ethanol-mediated gustatory plasticity. In addition, the tph-1 and ser-4 loci were also involved in ethanol's effect on locomotion behavior. These data suggested an essential role of serotonin signaling in modulating acute effects of ethanol.     

Coenzyme Q10 can prolong C. elegans lifespan by lowering oxidative stress

The mev-1 gene encodes cytochrome b, a large subunit of the Complex II enzyme succinate-CoQ oxidoreductase. The mev-1(kn1) mutants are hypersensitive to oxidative stress and age precociously, probably because of elevated superoxide anion production in mitochondria. Coenzyme Q (CoQ) is essential for the mitochondrial respiratory chain. Here, we show that CoQ(10) and Vitamin E extended the life span of wild-type Caenorhabditis elegans. Conversely, only CoQ(10) recovered the life shortening effects seen in mev-1. We also show that CoQ(10) but not Vitamin E reduced superoxide anion levels in wild type and mev-1. Another previously described phenotype of mev-1 animals is the presence of supernumerary apoptotic cells. We now demonstrate that CoQ(10) (but not Vitamin E) suppressed these supernumerary apoptoses. Collectively these data suggest that exogenously supplied CoQ(10) can play a significant anti-aging function. It may do so either by acting as an antioxidant to dismutate the free radical superoxide anion or by reducing the uncoupling of reactions during election transport that could otherwise result in superoxide anion production. The latter activity has not been ascribed to CoQ(10); however, it is known that conditions that uncouple electron transport reactions can lead to elevated superoxide anion production.     

Life span and stress resistance of Caenorhabditis elegans are differentially affected by glutathione transferases metabolizing 4-hydroxynon-2-enal

The lipid peroxidation product 4-hydroxynon-2-enal (4-HNE) forms as a consequence of oxidative stress, and acts as a signaling molecule or, at superphysiological levels, as a toxicant. The steady-state concentration of the compound reflects the balance between its generation and its metabolism, primarily through glutathione conjugation. Using an RNAi-based screen, we identified in Caenorhabditis elegans five glutathione transferases (GSTs) capable of catalyzing 4-HNE conjugation. RNAi knock-down of these GSTs (products of the gst-5, gst-6, gst-8, gst-10, and gst-24 genes) sensitized the nematode to electrophilic stress elicited by exposure to 4-HNE. However, interference with the expression of only two of these genes (gst-5 and gst-10) significantly shortened the life span of the organism. RNAi knock-down of the other GSTs resulted in at least as much 4-HNE adducts, suggesting tissue specificity of effects on longevity. Our results are consistent with the oxidative stress theory of organismal aging, broadened by considering electrophilic stress as a contributing factor. According to this extended hypothesis, peroxidation of lipids leads to the formation of 4-HNE in a chain reaction which amplifies the original damage. 4-HNE then acts as an "aging effector" via the formation of 4-HNE-protein adducts, and a resulting change in protein function.     

Intensity discrimination deficits cause habituation changes in middle-aged Caenorhabditis elegans

The ability to learn and remember is critical for all animals to survive in the ever-changing environment. As we age, many of our biological faculties decay and of these, decline in learning and memory can be the most distressing. To carefully define age-dependent changes in learning during reproductive age in the nematode Caenorhabditis elegans, we performed a parametric behavioral study of habituation to nonlocalized mechanical stimuli (petri plate taps) over a range of intensities in middle-aged worms. We found that as worms age (from the onset of reproduction to the end of egg laying), response probability habituation increases (at both 10- and 60-second interstimulus intervals) and that these age-related changes were associated with a decrease in the discrimination between stimuli of different intensities. We also used optogenetics to investigate where these age-dependent changes occur. Our data suggest that the changes occur upstream of mechanosensory neuron depolarization. These data support the idea that declines in stimulus intensity discrimination abilities during aging may be one variable underlying age-related cognitive deficits.     

The protein L-isoaspartyl-O-methyltransferase functions in the Caenorhabditis elegans stress response

The efficient use of nutrients is important in development and aging. In this study, we asked if the protein repair methyltransferase has a related or additional role in energy metabolism and stress response in the nematode Caenorhabditis elegans. Worms lacking the pcm-1 gene encoding this enzyme exhibit reduced longevity as SDS-isolated dauer larvae and as arrested L1 larvae under starvation stress, while overexpression leads to increased adult longevity. These findings led us to question whether pcm-1 deficient C. elegans may have inappropriate metabolic responses to stress. We assayed dauer and dauer-like larvae for starvation survival and observed a two-fold reduction of median survival time for pcm-1 mutants compared to N2 wild-type worms. Under these conditions, pcm-1 deficient dauer larvae had reduced fat stores, suggesting that PCM-1 may have a role in the initiation of the correct metabolic responses to stress starvation. We show expression of the pcm-1 gene in neurons, body wall and reproductive tissues. Upon heat shock and dauer formation-inducing conditions, we observe additional pcm-1 expression in body wall muscle nuclei and actomyosin filaments and in hypodermal cells. These results suggest that this enzyme may be important in stress response pathways, including proper decision making for energy storage.     

Semaphorin controls epidermal morphogenesis by stimulating mRNA translation via eIF2alpha in Caenorhabditis elegans

Conserved semaphorin-plexin signaling systems govern various aspects of animal development, including axonal guidance in vertebrates and epidermal morphogenesis in Caenorhabditis elegans. Here we provide in vivo evidence that stimulation of mRNA translation via eukaryotic initiation factor 2alpha (eIF2alpha) is an essential downstream event of semaphorin signaling in C. elegans. In semaphorin/plexin mutants, a marked elevation in the phosphorylation of eIF2alpha is observed, which causes translation repression and is causally related to the morphological epidermal phenotype in the mutants. Conversely, removal of constraints on translation by genetically reducing the eIF2alpha phosphorylation largely bypasses requirement for the semaphorin signal in epidermal morphogenesis. We also identify an actin-depolymerizing factor/cofilin, whose expression in the mutants is predominantly repressed, as a major translational target of semaphorin signaling. Thus, our results reveal a physiological significance for translation of mRNAs for cytoskeletal regulators, linking environmental cues to cytoskeletal rearrangement during cellular morphogenesis in vivo.     

Automated assays to study longevity in C. elegans

The nematode Caenorhabditis elegans is excellently suited as a model for studying the genetic and molecular genetic basis of aging, and to test chemical compounds that interfere with the aging process. Mutants of factors in both the insulin and target of rapamycin (TOR) signalling pathways have been shown to extend life span of the worm. Phenotypic similarities among those mutants suggested that, exploiting the corresponding phenotypes in a semiautomated way, may increase the speed of investigating life span and aging in C. elegans. Here, we discuss several methodological approaches to automate longevity assays in the nematode.