Mitochondrial changes in ageing Caenorhabditis elegans--what do we learn from superoxide dismutase knockouts?

Nutritional approaches targeting mitochondria for the prevention of sarcopenia

A decline in function and loss of mass, a condition known as sarcopenia, is observed in the skeletal muscles with aging. Sarcopenia has a negative effect on the quality of life of elderly. Individuals with sarcopenia are at particular risk for adverse outcomes, such as reduced mobility, fall-related injuries, and type 2 diabetes mellitus. Although the pathogenesis of sarcopenia is multifaceted, mitochondrial dysfunction is regarded as a major contributor for muscle aging. Hence, the development of preventive and therapeutic strategies to improve mitochondrial function during aging is imperative for sarcopenia treatment. However, effective and specific drugs that can be used for the treatment are not yet approved. Instead studies on the relationship between food intake and muscle aging have suggested that nutritional intake or dietary control could be an alternative approach for the amelioration of muscle aging. This narrative review approaches various nutritional components and diets as a treatment for sarcopenia by modulating mitochondrial homeostasis and improving mitochondria. Age-related changes in mitochondrial function and the molecular mechanisms that help improve mitochondrial homeostasis are discussed, and the nutritional components and diet that modulate these molecular mechanisms are addressed.

Lactococcus kimchii extends lifespan and alleviates motility decline in Caenorhabditis elegans through ins-20, an insulin-like peptide gene

Lactococcus kimchii is isolated from commercial kimchi, which is a traditional Korean fermented food. This study was conducted to evaluate the probiotic effects of L. kimchii. Caenorhabditis elegans was fed L. kimchii, and its longevity, motility, and gene expression were examined. When fed a 1:1 mixture of Escherichia coli OP50 and L. kimchii (OP+LK), C. elegans had a significantly longer lifespan and increased locomotion than when it was fed OP alone. There was no significant difference in brood size between the OP+LK and OP groups, suggesting that these effects occurred in a dietary restriction-independent manner. RNA sequencing and Gene Ontology analysis showed that the expression of ins-20, an insulin-like peptide and agonist of the insulin receptor, was significantly upregulated in the OP+LK group. The ins-20 mutation annulled the effects of OP+LK on lifespan extension and motility. In addition, OP+LK failed to extend the lifespan of C. elegans deficient in daf-2, a receptor for the insulin-like signaling pathway. These results suggest that L. kimchii extends the lifespan and alleviates motility decline in C. elegans through the insulin signaling pathway, highlighting the potential of using L. kimchii as a beneficial bacterium for probiotics and postbiotics.

Paeonol promotes longevity and fitness in Caenorhabditis elegans through activating the DAF-16/FOXO and SKN-1/Nrf2 transcription factors

Paeonol, as one of the most abundant plant-derived polyphenols, has multiple bioactivities including anti-inflammatory, anti-tumor, and anti-cardiovascular diseases. Nevertheless, the anti-aging effects and related mechanisms of paeonol are rarely reported. In this study, we found that paeonol significantly prolonged the mean lifespan of Caenorhabditis elegans (C. elegans) by 28.49% at a dose of 200 μM. Moreover, paeonol promoted the health of C. elegans by increasing the body bending and pharyngeal pumping rates and reducing the lipofuscin accumulation level. Meanwhile, paeonol induced the expression of stress-related genes or proteins by activating the transcription factors DAF-16/FOXO, SKN-1/Nrf2, and HSF-1, which in turn enhanced oxidative and thermal stress tolerance. The mechanism behind the anti-aging effect of paeonol occurred by down-regulating the insulin/IGF-1 signaling (IIS) pathway. Our findings shed new light on the application of paeonol for longevity promotion and human health.

Feeding on lactic acid bacteria isolated from food extends the lifespan of Caenorhabditis elegans

Lactic acid bacteria (LAB) contribute to human health, and LAB functionality has been studied using Caenorhabditis elegans as an alternative host. However, many studies have focused on the efficacy of a single strain of LAB, and few reports have compared various LAB strains. In this study, we examined the effects of 15 strains of LAB isolated from vegetables, meat, and fermented foods on nematode longevity and healthy lifespan. To reduce the frequency of laborious survival observations, we performed a lifespan assay on agar plates containing 2'-deoxy-5-fluorouridine (FUdR), which inhibits egg hatching and prevents generation mixing. Four beneficial strains showed significant lifespan extension and increased spontaneous nematode mobility, regardless of treatment with or without FUdR and the frequency of survival observation. These results suggested increased longevity and an extended healthy lifespan, confirming the reliability of our method. The four strains are expected to show anti-ageing effects besides longevity and have effects on age-related degenerative diseases. Our labor-saving method can be used as an alternative to conventional methods and enable simultaneous screening of multiple strains. Future research could explore factors contributing to lifespan regulation by comparing and verifying differential strain effects on lifespan.

Improvement of Locomotion Caused by Lactococcus lactis subsp. lactis in the Model Organism Caenorhabditis elegans

Lactococcus lactis subsp. lactis exhibits probiotic properties in humans. Considering that Caenorhabditis elegans can be used to study the effects of microorganisms on animal behavior, owing to its simple nervous system, we assessed the impacts of two strains of Lactococcus lactis subsp. Lactis-a non-nisin-producing strain, NBRC 100933 (LL100933), and a nisin-producing strain, NBRC 12007 (LL12007)-on the lifespan, locomotion, reproductive capacity of, and lipid accumulation in, C. elegans. The lifespan of adult C. elegans fed a mixture (1:1) of Escherichia coli OP50 and LL100933 or LL12007 did not show a significant increase compared to that of the group fed a standard diet of E. coli OP50. However, the nematodes fed Lactococcus strains showed notable enhancement in their locomotion at all of the tested ages. Further, the beneficial effects of LL100933 and LL12007 were observed in the daf-16 mutants, but not in the skn-1 and pmk-1 mutants. The lipid accumulation in the worms of the Lactococcus-fed group was lower than that in the control group at all experimental ages. Overall, LL100933 and LL12007 enhance the locomotor behavior of C. elegans, likely by modulating the PMK-1/p38 MAPK and SKN-1/Nrf2 transcription factors.

Efficiency of Protein Renewal Is Limited by Feed Intake and Not by Protein Lifetime in Aging Caenorhabditis elegans

Protein turnover maintains the proteome's functional integrity. Here, protein turnover efficiency over time in wild-type Caenorhabditis elegans was assessed using inverse [¹⁵N]-pulse labeling up to 7 days after the egg-laying phase at 20 °C. Isotopic analysis of some abundant proteins was executed favoring data quality over quantity for mathematical modeling. Surprisingly, isotopic enrichment over time reached an upper limit showing an apparent cessation of protein renewal well before death, with protein fractions inaccessible to turnover ranging from 14 to 83%. For life span modulation, worms were raised at different temperatures after egg laying. Mathematical modeling of isotopic enrichment points either to a slowdown of protein turnover or to an increasing protein fraction resistant to turnover with time. Most notably, the estimated time points of protein turnover cessation from our mathematical model were highly correlated with the observed median life span. Thrashing and pumping rates over time were linearly correlated with isotopic enrichment, therefore linking protein/tracer intake to protein turnover rate and protein life span. If confirmed, life span extension is possible by optimizing protein turnover rate through modulating protein intake in C. elegans and possibly other organisms. While proteome maintenance benefits from a high protein turnover rate, protein turnover is fundamentally energy-intensive, where oxidative stress contributes to damage that it is supposed to repair.

Prolonged Lifespan, Improved Perception, and Enhanced Host Defense of Caenorhabditis elegans by Lactococcus cremoris subsp. cremoris

Lactic acid bacteria are beneficial to Caenorhabditis elegans; however, bacteria acting as probiotics in nematodes may not necessarily have probiotic functions in humans. Lactococcus cremoris subsp. cremoris reportedly has probiotic functions in humans. Therefore, we determined whether the strain FC could exert probiotic effects in C. elegans in terms of improving host defenses and extending life span. Live FC successfully extended the life span and enhanced host defense compared to Escherichia coli OP50 (OP50), a standard food source for C. elegans. The FC-fed worms were tolerant to Salmonella enterica subsp. enterica serovar Enteritidis or Staphylococcus aureus infection and had better survival than the OP50-fed control worms. Further, the chemotaxis index, an indicator of perception ability, was more stable and significantly higher in FC-fed worms than in the control worms. The increase in autofluorescence from advanced glycation end products (AGEs) with aging was also ameliorated in FC-fed worms. FC showed beneficial effects in daf-16 and pmk-1 mutants, but not in skn-1 mutants. Since SKN-1 is the C. elegans ortholog of Nrf2, we measured the transcription of heme oxygenase-1 (HO-1), which is regulated by Nrf2, in murine macrophages and found that HO-1 mRNA expression was increased >5 times by inoculation with FC cells. Thus, FC could exert antisenescence effects via the SKN-1/Nrf2 pathway. This study showed for the first time that FC supported perceptive function and suppressed AGEs in nematodes as probiotic bacteria. Therefore, C. elegans can be an alternative model to screen for probiotic bacteria that can be used for antisenescence effects in humans.

IMPORTANCE Aging is one of our greatest challenges. The World Health Organization proposed that “active aging” might encourage people to continue to work according to their capacities and preferences as they grow old and would prevent or delay disabilities and chronic diseases that are costly to both individuals and the society, considering that disease prevention is more economical than treatment. Probiotic bacteria, such as lactobacilli, are live microorganisms that exert beneficial effects on human health when ingested in sufficient amounts and can promote longevity. The significance of this study is that it revealed the antisenescence and various beneficial effects of the representative probiotic bacterium Lactococcus cremoris subsp. cremoris strain FC exerted via the SKN-1/Nrf2 pathway in the nematode Caenorhabditis elegans.

Potential anti-Parkinsonian's effect of S-(+)-linalool from Cinnamomum osmophloeum ct. linalool leaves are associated with mitochondrial regulation via gas-1, nuo-1, and mev-1 in Caenorhabditis elegans

Parkinson's disease (PD) is one of the prevalent neurodegenerative diseases, and developing new treatments from natural products is of particular interest. Essential oils from Cinnamomum osmophloeum ct. linalool leaves contain high levels (~95%) of S-(+)-linalool. The neuroprotective effects of linalool have been previously described, yet the underlying molecular mechanisms remain largely unknown. This study aimed to investigate the potential anti-Parkinsonian's effect of S-(+)-linalool on mitochondrial regulation and decipher the underlying molecular mechanisms in Caenorhabditis elegans PD model. Essential oils at 20 mg/L and 20 mg/L S-(+)-linalool each significantly attenuated the damaging effects of 6-hydroxydopamine (6-OHDA) on dopaminergic (DA) neurons and decreased the mitochondrial unfolded protein response (UPR^mt ) to antimycin. RNAi knockdown of mitochondrial complex I (gas-1, nuo-1), and complex II (mev-1) genes prevented the improvement of mitochondrial activity by S-(+)-linalool. The protective effects of S-(+)-linalool on 6-OHDA-induced behavior changes were absent in a DA-specific strain of C. elegans produced by gas-1, nuo-1, and mev-1 RNAi knockdown. These results suggest the potential anti-Parkinsonian's effect of S-(+)-linalool is associated with mitochondrial activity and regulated by gas-1, nuo-1, and mev-1 in C. elegans. Our findings suggest that S-(+)-linalool might be a promising candidate for therapeutic application to inhibit the progression of PD.

Oxidation and Antioxidation of Natural Products in the Model Organism Caenorhabditiselegans

Natural products are small molecules naturally produced by multiple sources such as plants, animals, fungi, bacteria and archaea. They exert both beneficial and detrimental effects by modulating biological targets and pathways involved in oxidative stress and antioxidant response. Natural products’ oxidative or antioxidative properties are usually investigated in preclinical experimental models, including virtual computing simulations, cell and tissue cultures, rodent and nonhuman primate animal models, and human studies. Due to the renewal of the concept of experimental animals, especially the popularization of alternative 3R methods for reduction, replacement and refinement, many assessment experiments have been carried out in new alternative models. The model organism Caenorhabditis elegans has been used for medical research since Sydney Brenner revealed its genetics in 1974 and has been introduced into pharmacology and toxicology in the past two decades. The data from C. elegans have been satisfactorily correlated with traditional experimental models. In this review, we summarize the advantages of C. elegans in assessing oxidative and antioxidative properties of natural products and introduce methods to construct an oxidative damage model in C. elegans. The biomarkers and signaling pathways involved in the oxidative stress of C. elegans are summarized, as well as the oxidation and antioxidation in target organs of the muscle, nervous, digestive and reproductive systems. This review provides an overview of the oxidative and antioxidative properties of natural products based on the model organism C. elegans.

S-allylcysteine Ameliorates Aging Features Via Regulating Mitochondrial Dynamics in Naturally Aged C57BL/6J Mice

SCOPE

S-allylcysteine (SAC) is the most abundant organosulfur molecule derived from aged garlic. We evaluated the effects of S-allylcysteine (SAC) on improving aging in naturally aged C57BL/6J male mice and mitochondrial dynamics in C. elegans and its underlying mechanisms.

METHODS AND RESULTS

When mice had attained reproductive senescence at 60 weeks of age, SAC was supplemented to 0.05% and 0.2% into their normal diet for 12 weeks The results showed that SAC could significantly improve the level of hepatic OPA1 mRNA, which is a key factor for mitochondrial fusion, and consequently elevated the mitochondrial biogenesis-related proteins SIRT1 and PGC-1α, thus ameliorating oxidative stress, such as MDA in the liver and 8-OHdG in urine. Among the biochemical markers of aging, SAC significantly reduced liver GLB1 and SA-βgal, which were induced by replicative senescence. The mitochondria with GFP-tagged transgenic strain SJ4103 C. elegans was incubated with 5 or 50 μM SAC, and SAC treated groups maintained the linear morphology of mitochondria.

CONCLUSION

SAC regulated mitochondrial dynamics and ameliorated aging to a significant degree. This study also confirmed that mitochondrial dynamics are a promising target for screening materials to combat aging and as a direction for anti-aging product development. This article is protected by copyright. All rights reserved.

Mitochondrial mutations in Caenorhabditis elegans show signatures of oxidative damage and an AT-bias

Rapid mutation rates are typical of mitochondrial genomes (mtDNAs) in animals, but it is not clear why. The difficulty of obtaining measurements of mtDNA mutation that are not biased by natural selection has stymied efforts to distinguish between competing hypotheses about the causes of high mtDNA mutation rates. Several studies which have measured mtDNA mutations in nematodes have yielded small datasets with conflicting conclusions about the relative abundance of different substitution classes (i.e., the mutation spectrum). We therefore leveraged Duplex Sequencing, a high-fidelity DNA sequencing technique, to characterize de novo mtDNA mutations in Caenorhabditis elegans. This approach detected nearly an order of magnitude more mtDNA mutations than documented in any previous nematode mutation study. Despite an existing extreme AT bias in the C. elegans mtDNA (75.6% AT), we found that a significant majority of mutations increase genomic AT content. Compared to some prior studies in nematodes and other animals, the mutation spectrum reported here contains an abundance of CG→AT transversions, supporting the hypothesis that oxidative damage may be a driver of mtDNA mutations in nematodes. Furthermore, we found an excess of G→T and C→T changes on the coding DNA strand relative to the template strand, consistent with increased exposure to oxidative damage. Analysis of the distribution of mutations across the mtDNA revealed significant variation among protein-coding genes and as well as among neighboring nucleotides. This high-resolution view of mitochondrial mutations in C. elegans highlights the value of this system for understanding relationships among oxidative damage, replication error, and mtDNA mutation.

Assessment and Validation of Globodera pallida as a Novel In Vivo Model for Studying Alzheimer's Disease

BACKGROUND

Whole transgenic or non-transgenic organism model systems allow the screening of pharmacological compounds for protective actions in Alzheimer's disease (AD).

AIM

In this study, a plant parasitic nematode, Globodera pallida, which assimilates intact peptides from the external environment, was investigated as a new potential non-transgenic model system of AD. Methods: Fresh second-stage juveniles of G. pallida were used to measure their chemosensory, perform immunocytochemistry on their neurological structures, evaluate their survival rate, measure reactive oxygen species, and determine total oxidized glutathione to reduced glutathione ratio (GSSG/GSH) levels, before and after treatment with 100 µM of various amyloid beta (Aβ) peptides (1-40, 1-42, 17-42, 17-40, 1-28, or 1-16). Wild-type N2 C. elegans (strain N2) was cultured on Nematode Growth Medium and directly used, as control, for chemosensory assays.

RESULTS

We demonstrated that: (i) G. pallida (unlike Caenorhabditis elegans) assimilates amyloid-β (Aβ) peptides which co-localise with its neurological structures; (ii) pre-treatment with various Aβ isoforms (1-40, 1-42, 17-42, 17-40, 1-28, or 1-16) impairs G. pallida's chemotaxis to differing extents; (iii) Aβ peptides reduced survival, increased the production of ROS, and increased GSSG/GSH levels in this model; (iv) this unique model can distinguish differences between different treatment concentrations, durations, and modalities, displaying good sensitivity; (v) clinically approved neuroprotective agents were effective in protecting G. pallida from Aβ (1-42) exposure. Taken together, the data indicate that G. pallida is an interesting in vivo model with strong potential for discovery of novel bioactive compounds with anti-AD activity.

Early-life mitochondrial DNA damage results in lifelong deficits in energy production mediated by redox signaling in Caenorhabditis elegans

The consequences of damage to the mitochondrial genome (mtDNA) are poorly understood, although mtDNA is more susceptible to damage resulting from some genotoxicants than nuclear DNA (nucDNA), and many environmental toxicants target the mitochondria. Reports from the toxicological literature suggest that exposure to early-life mitochondrial damage could lead to deleterious consequences later in life (the “Developmental Origins of Health and Disease” paradigm), but reports from other fields often report beneficial (“mitohormetic”) responses to such damage. Here, we tested the effects of low (causing no change in lifespan) levels of ultraviolet C (UVC)-induced, irreparable mtDNA damage during early development in Caenorhabditis elegans. This exposure led to life-long reductions in mtDNA copy number and steady-state ATP levels, accompanied by increased oxygen consumption and altered metabolite profiles, suggesting inefficient mitochondrial function. Exposed nematodes were also developmentally delayed, reached smaller adult size, and were rendered more susceptible to subsequent exposure to chemical mitotoxicants. Metabolomic and genetic analysis of key signaling and metabolic pathways supported redox and mitochondrial stress-response signaling during early development as a mechanism for establishing these persistent alterations. Our results highlight the importance of early-life exposures to environmental pollutants, especially in the context of exposure to chemicals that target mitochondria.

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Early life mtDNA damage led to lifelong deficits in mitochondrial function.

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C. elegans developed slowly and were sensitive to chemical exposures as adults.

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Redox signaling is a mechanism that establishes these persistent alterations.

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Data are consistent with the Developmental Origins of Health and Disease model.

Effects of electrotactic exercise and antioxidant EUK-134 on oxidative stress relief in Caenorhabditis elegans

Antioxidant uptake and regular exercise are two well-acknowledged measures used for rejuvenation and oxidative stress elimination. Previous studies have revealed that moderate exercise mildly increases intracellular signaling oxidant levels and strengthens the ability of an organism to deal with escalating oxidative stress by upregulating antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase. Antioxidant supplementation directly scavenges intracellular reactive oxygen species (ROS) to reduce oxidative stress. However, research to understand the impacts of these enzymes on mitigating oxidative stress from the perspective of simple animals is limited. Herein, we show that exercise combined with antioxidant supplementation ameliorates the physiological phenotypes and markers of aging in wild-type and SOD/CAT-deficient Caenorhabditis elegans. We discovered that treated wild-type and gene-deficient worms show better survivorship, reproduction, and motility compared with their control counterparts. Assays of biochemical indices revealed that variations in sod-3 expression under different stress levels imply an inducible enzyme response resulting from exercise training and antioxidant supplementation. In addition, induced ROS resistance obtained from any type of treatment could persist for several days even after treatment cessation, thus suggesting a potential long-term antioxidative stress effect. Our findings confirm that exercise, antioxidant supplementation, and their combination could significantly improve the ability of C. elegans to withstand adverse stress. Our observations provide promising insights into future therapies of anti-oxidative stress in higher animals.

Inhibition of mTOR decreases insoluble proteins burden by reducing translation in C. elegans

Aging animals accumulate insoluble proteins as a consequence of a decline of proteostatic maintenance with age. In Caenorhabditis elegans, for instance, levels of detergent-insoluble proteins increase with age. In longer-lived strains of C. elegans, this accumulation occurs more slowly, implying a link to lifespan determination. We further explored this link and found that detergent-insoluble proteins accumulate more rapidly at higher temperatures, a condition where lifespan is short. We employed a C. elegans strain carrying a GFP transcriptional reporter under the control of a heat shock (hsp-16.2) promoter to investigate the dynamics of proteostatic failure in individual nematodes. We found that early, sporadic activation of hsp-16.2 was predictive of shorter remaining lifespan in individual nematodes. Exposure to rapamycin, resulting in reduced mTOR signaling, delayed spurious expression, extended lifespan, and delayed accumulation of insoluble proteins, suggesting that targets downstream of the mTOR pathway regulate the accumulation of insoluble proteins. We specifically explored ribosomal S6 kinase (rsks-1) as one such candidate and found that RNAi against rsks-1 also resulted in less age-dependent accumulation of insoluble proteins and extended lifespan. Our results demonstrate that inhibition of protein translation via reduced mTOR signaling resulted in slower accumulation of insoluble proteins, delayed proteostatic crisis, and extended lifespan in C. elegans.

Caernohabditis elegans as a Model Organism to Evaluate the Antioxidant Effects of Phytochemicals

The nematode Caenorhabditis elegans was introduced as a model organism in biological research by Sydney Brenner in the 1970s. Since then, it has been increasingly used for investigating processes such as ageing, oxidative stress, neurodegeneration, or inflammation, for which there is a high degree of homology between C. elegans and human pathways, so that the worm offers promising possibilities to study mechanisms of action and effects of phytochemicals of foods and plants. In this paper, the genes and pathways regulating oxidative stress in C. elegans are discussed, as well as the methodological approaches used for their evaluation in the worm. In particular, the following aspects are reviewed: the use of stress assays, determination of chemical and biochemical markers (e.g., ROS, carbonylated proteins, lipid peroxides or altered DNA), influence on gene expression and the employment of mutant worm strains, either carrying loss-of-function mutations or fluorescent reporters, such as the GFP.

Lifespan and healthspan benefits of exogenous H2S in C. elegans are independent from effects downstream of eat-2 mutation

Caloric restriction (CR) is one of the most effective interventions to prolong lifespan and promote health. Recently, it has been suggested that hydrogen sulfide (H₂S) may play a pivotal role in mediating some of these CR-associated benefits. While toxic at high concentrations, H₂S at lower concentrations can be biologically advantageous. H₂S levels can be artificially elevated via H₂S-releasing donor drugs. In this study, we explored the function of a novel, slow-releasing H₂S donor drug (FW1256) and used it as a tool to investigate H₂S in the context of CR and as a potential CR mimetic. We show that exposure to FW1256 extends lifespan and promotes health in Caenorhabditis elegans (C. elegans) more robustly than some previous H₂S-releasing compounds, including GYY4137. We looked at the extent to which FW1256 reproduces CR-associated physiological effects in normal-feeding C. elegans. We found that FW1256 promoted healthy longevity to a similar degree as CR but with fewer fitness costs. In contrast to CR, FW1256 actually enhanced overall reproductive capacity and did not reduce adult body length. FW1256 further extended the lifespan of already long-lived eat-2 mutants without further detriments in developmental timing or fertility, but these lifespan and healthspan benefits required H₂S exposure to begin early in development. Taken together, these observations suggest that FW1256 delivers exogenous H₂S efficiently and supports a role for H₂S in mediating longevity benefits of CR. Delivery of H₂S via FW1256, however, does not mimic CR perfectly, suggesting that the role of H₂S in CR-associated longevity is likely more complex than previously described.

A cellular surveillance and defense system that delays aging phenotypes in C. elegans

Physiological stresses, such as pathogen infection, are detected by “cellular Surveillance Activated Detoxification and Defenses” (cSADD) systems that trigger host defense responses. Aging is associated with physiological stress, including impaired mitochondrial function. Here, we investigated whether an endogenous cSADD pathway is activated during aging in C. elegans. We provide evidence that the transcription factor ZIP-2, a well-known immune response effector in C. elegans, is activated in response to age-associated mitochondrial dysfunction. ZIP-2 mitigates multiple aging phenotypes, including mitochondrial disintegration and reduced motility of the pharynx and intestine. Importantly, our data suggest that ZIP-2 is activated during aging independently of bacterial infection and of the transcription factors ATFS-1 and CEBP-2. Thus, ZIP-2 is a key component of an endogenous pathway that delays aging phenotypes in C. elegans. Our data suggest that aging coopted a compensatory strategy for regulation of aging process as a guarded process rather than a simple passive deterioration process.

Measurement of Respiration Rate in Live Caenorhabditis elegans

Mitochondrial function and dysfunction are at the core of aging and involved in many age-dependent diseases. Rate of oxygen consumption is a measure of mitochondrial function and energy production rate. The nematode Caenorhabditis elegans (C. elegans) offers an opportunity to study "living" mitochondria without the need for mitochondrial extraction, purification and associated artifacts. Oxygen consumption rate (OCR) is traditionally measured using single-chamber Clark electrodes with or without the addition of metabolic modulators. More recently, multi-well oxygen electrodes with automated injection system have been developed to enable rapid measurement of OCR under different conditions. Here, we describe a detailed protocol that we have adapted from existing protocols to measure coupled and uncoupled mitochondrial respiration (with and without metabolic modulators) in live respiring nematodes using a Seahorse XFe96 extracellular flux analyzer. We present details on our protocol, including preparation of nematode culture, use of metabolic modulators, execution of Seahorse XF assay as well as post-experimental data analysis. As a reference, we provide results of a series of experiments in which the metabolic activity of N2 wild-type nematodes was compared to N2 nematode treated with paraquat, a compound that generates reactive oxygen species (ROS), thus causing oxidative damage and mitochondrial dysfunction. These data illustrate the kind of insights that can be obtained even using a low number of nematodes (10 animals only per well).

Mitochondrial DNA Damage Does Not Determine C. elegans Lifespan

The mitochondrial free radical theory of aging (mFRTA) proposes that accumulation of oxidative damage to macromolecules in mitochondria is a causative mechanism for aging. Accumulation of mitochondrial DNA (mtDNA) damage may be of particular interest in this context. While there is evidence for age-dependent accumulation of mtDNA damage, there have been only a limited number of investigations into mtDNA damage as a determinant of longevity. This lack of quantitative data regarding mtDNA damage is predominantly due to a lack of reliable assays to measure mtDNA damage. Here, we report adaptation of a quantitative real-time polymerase chain reaction (qRT-PCR) assay for the detection of sequence-specific mtDNA damage in C. elegans and apply this method to investigate the role of mtDNA damage in the aging of nematodes. We compare damage levels in old and young animals and also between wild-type animals and long-lived mutant strains or strains with modifications in ROS detoxification or production rates. We confirm an age-dependent increase in mtDNA damage levels in C. elegans but found that there is no simple relationship between mtDNA damage and lifespan. MtDNA damage levels were high in some mutants with long lifespan (and vice versa). We next investigated mtDNA damage, lifespan and healthspan effects in nematode subjected to exogenously elevated damage (UV- or γ-radiation induced). We, again, observed a complex relationship between damage and lifespan in such animals. Despite causing a significant elevation in mtDNA damage, γ-radiation did not shorten the lifespan of nematodes at any of the doses tested. When mtDNA damage levels were elevated significantly using UV-radiation, nematodes did suffer from shorter lifespan at the higher end of exposure tested. However, surprisingly, we also found hormetic lifespan and healthspan benefits in nematodes treated with intermediate doses of UV-radiation, despite the fact that mtDNA damage in these animals was also significantly elevated. Our results suggest that within a wide physiological range, the level of mtDNA damage does not control lifespan in C. elegans.

Age-dependent changes and biomarkers of aging in Caenorhabditis elegans

Caenorhabditis elegans is an exceptionally valuable model for aging research because of many advantages, including its genetic tractability, short lifespan, and clear age‐dependent physiological changes. Aged C. elegans display a decline in their anatomical and functional features, including tissue integrity, motility, learning and memory, and immunity. Caenorhabditis elegans also exhibit many age‐associated changes in the expression of microRNAs and stress‐responsive genes and in RNA and protein quality control systems. Many of these age‐associated changes provide information on the health of the animals and serve as valuable biomarkers for aging research. Here, we review the age‐dependent changes in C. elegans and their utility as aging biomarkers indicative of the physiological status of aging.

Organoruthenium(II) complexes attenuate stress in Caenorhabditis elegans through regulating antioxidant machinery

The 1:1 stoichiometric reactions of 3-methoxy salicylaldehyde-4(N)-substituted thiosemicarbazones (H₂L^1-4) with [RuCpCl(PPh₃)₂] was carried out in methanol. The obtained complexes (1-4) were characterized by analytical, IR, absorption and ¹H NMR spectroscopic studies. The structures of ligand [H₂-3MSal-etsc] (H₂L³) and complex [RuCp(Msal-etsc) (PPh₃)] (3), were characterized by single crystal X-ray diffraction studies. The interaction of the ruthenium(II) complexes (1-4) with calfthymus DNA (CT-DNA) has been explored by absorption and emission titration methods. Based on the observations, an intercalative binding mode of DNA has been proposed. The protein binding abilities of the new complexes were monitored by quenching the tryptophan and tyrosine residues of BSA, as model protein. From the studies, it was found that the new ruthenium metallacycles exhibited better affinity than their precursors. The free radical scavenging assay suggests that all complexes effectively scavenged the DPPH radicals as compared to that of standard control ascorbic acid and scavenging activities of complexes are in the order of 4 > 2 > 3 > 1. In addition, ruthenium(II) complexes (2-4) also exhibited an excellent in vivo antioxidant activity as it was able to increase the survival of worms exposed to lethal oxidative and thermal stresses possibly through reducing the intracellular ROS levels. It was interesting to note that complexes 2-4 failed to increase the lifespan of mev-1 mutant worms having shortened lifespan due to the over production of free radicals. This data confirmed that complexes 2-4 conferred stress resistance in C. elegans, but they also require an endogenous detoxification mechanism for doing so. The genetic and reporter gene expression analysis revealed that complexes 2-4 maintained the intracellular redox status and offered stress protection through transactivation of antioxidant defence machinery genes gst-4 and sod-3 which are directly regulated by SKN-1 and DAF-16 transcription factors, respectively. Altogether, our results suggested that complexes 2-4 might play a crucial role in stress modulation and they perhaps exert almost similar effects in higher models, which is an important issue to be validated in future.

Clostridium butyricum MIYAIRI 588 Increases the Lifespan and Multiple-Stress Resistance of Caenorhabditis elegans

Clostridium butyricum MIYAIRI 588 (CBM 588), one of the probiotic bacterial strains used for humans and domestic animals, has been reported to exert a variety of beneficial health effects. The effect of this probiotic on lifespan, however, is unknown. In the present study, we investigated the effect of CBM 588 on lifespan and multiple-stress resistance using Caenorhabditis elegans as a model animal. When adult C. elegans were fed a standard diet of Escherichia coli OP50 or CBM 588, the lifespan of the animals fed CBM 588 was significantly longer than that of animals fed OP50. In addition, the animals fed CBM588 exhibited higher locomotion at every age tested. Moreover, the worms fed CBM 588 were more resistant to certain stressors, including infections with pathogenic bacteria, UV irradiation, and the metal stressor Cu²⁺. CBM 588 failed to extend the lifespan of the daf-2/insulin-like receptor, daf-16/FOXO and skn-1/Nrf2 mutants. In conclusion, CBM 588 extends the lifespan of C. elegans probably through regulation of the insulin/IGF-1 signaling (IIS) pathway and the Nrf2 transcription factor, and CBM 588 improves resistance to several stressors in C. elegans.

Clonal expansion of mitochondrial DNA deletions is a private mechanism of aging in long-lived animals

Disruption of mitochondrial metabolism and loss of mitochondrial DNA (mtDNA) integrity are widely considered as evolutionarily conserved (public) mechanisms of aging (López-Otín et al., Cell, 153, 2013 and 1194). Human aging is associated with loss in skeletal muscle mass and function (Sarcopenia), contributing significantly to morbidity and mortality. Muscle aging is associated with loss of mtDNA integrity. In humans, clonally expanded mtDNA deletions colocalize with sites of fiber breakage and atrophy in skeletal muscle. mtDNA deletions may therefore play an important, possibly causal role in sarcopenia. The nematode Caenorhabditis elegans also exhibits age-dependent decline in mitochondrial function and a form of sarcopenia. However, it is unclear if mtDNA deletions play a role in C. elegans aging. Here, we report identification of 266 novel mtDNA deletions in aging nematodes. Analysis of the mtDNA mutation spectrum and quantification of mutation burden indicates that (a) mtDNA deletions in nematode are extremely rare, (b) there is no significant age-dependent increase in mtDNA deletions, and (c) there is little evidence for clonal expansion driving mtDNA deletion dynamics. Thus, mtDNA deletions are unlikely to drive the age-dependent functional decline commonly observed in C. elegans. Computational modeling of mtDNA dynamics in C. elegans indicates that the lifespan of short-lived animals such as C. elegans is likely too short to allow for significant clonal expansion of mtDNA deletions. Together, these findings suggest that clonal expansion of mtDNA deletions is likely a private mechanism of aging predominantly relevant in long-lived animals such as humans and rhesus monkey and possibly in rodents.

The Energy Maintenance Theory of Aging: Maintaining Energy Metabolism to Allow Longevity

Fused, elongated mitochondria are more efficient in generating ATP than fragmented mitochondria. In diverse C. elegans longevity pathways, increased levels of fused mitochondria are associated with lifespan extension. Blocking mitochondrial fusion in these animals abolishes their extended longevity. The long-lived C. elegans vhl-1 mutant is an exception that does not have increased fused mitochondria, and is not dependent on fusion for longevity. Loss of mammalian VHL upregulates alternate energy generating pathways. This suggests that mitochondrial fusion facilitates longevity in C. elegans by increasing energy metabolism. In diverse animals, ATP levels broadly decreases with age. Substantial evidence supports the theory that increasing or maintaining energy metabolism promotes the survival of older animals. Increased ATP levels in older animals allow energy-intensive repair and homeostatic mechanisms such as proteostasis that act to prevent cellular aging. These observations support the emerging paradigm that maintaining energy metabolism promotes the survival of older animals.

A novel vibration-induced exercise paradigm improves fitness and lipid metabolism of Caenorhabditis elegans

Exercise has been known to reduce the risk of obesity and metabolic syndrome, but the mechanisms underlying many exercise benefits remain unclear. This is, in part, due to a lack of exercise paradigms in invertebrate model organisms that would allow rapid mechanistic studies to be conducted. Here we report a novel exercise paradigm in Caenorhabditis elegans (C. elegans) that can be implemented under standard laboratory conditions. Mechanical stimulus in the form of vibration was transduced to C. elegans grown on solid agar media using an acoustic actuator. One day post-exercise, the exercised animals showed greater physical fitness compared to the un-exercised controls. Despite having higher mitochondrial reactive oxygen species levels, no mitohormetic adaptations and lifespan extension were observed in the exercised animals. Nonetheless, exercised animals showed lower triacylglycerides (TAG) accumulation than the controls. Among the individual TAG species, the most significant changes were found in mono- and polyunsaturated fatty acid residues. Such alteration resulted in an overall lower double bond index and peroxidation index which measure susceptibility towards lipid peroxidation. These observations are consistent with findings from mammalian exercise literature, suggesting that exercise benefits are largely conserved across different animal models.

UPRmt regulation and output: a stress response mediated by mitochondrial-nuclear communication

The mitochondrial network is not only required for the production of energy, essential cofactors and amino acids, but also serves as a signaling hub for innate immune and apoptotic pathways. Multiple mechanisms have evolved to identify and combat mitochondrial dysfunction to maintain the health of the organism. One such pathway is the mitochondrial unfolded protein response (UPR^mt), which is regulated by the mitochondrial import efficiency of the transcription factor ATFS-1 in C. elegans and potentially orthologous transcription factors in mammals (ATF4, ATF5, CHOP). Upon mitochondrial dysfunction, import of ATFS-1 into mitochondria is reduced, allowing it to be trafficked to the nucleus where it promotes the expression of genes that promote survival and recovery of the mitochondrial network. Here, we discuss recent findings underlying UPR^mt signal transduction and how this adaptive transcriptional response may interact with other mitochondrial stress response pathways.

Role/s of 'Antioxidant' Enzymes in Ageing

Reactive oxygen species (ROS), generated externally and during aerobic metabolism, are a potent cause of cell damage. Oxidative damage is a feature of many diseases and ageing, including age-associated diseases, such as diabetes, cancer, cardiovascular and neurodegenerative diseases. Indeed, this association helped lead to the widely expounded 'Free Radical Theory of Aging', proposing that the accumulation of ROS-induced damage is the underlying cause of ageing. In the last decade, it has become apparent that ROS play more complex roles in ageing than simply causing damage. This includes the induction of signalling pathways that protect against/repair cell damage. Cells encode a variety of enzymes that metabolise ROS, some of which reduce them to less reactive species. In this chapter, we review the evidence that manipulating the levels of these enzymes has any effect/s on ageing. We will also highlight a few examples illustrating why it is an over-simplification to describe the activities of some of these enzymes as 'antioxidants'. We discuss how these studies have helped refine our view of how ROS and ROS-metabolising enzymes contribute to the ageing process.

A multimethod computational simulation approach for investigating mitochondrial dynamics and dysfunction in degenerative aging

Research in biogerontology has largely focused on the complex relationship between mitochondrial dysfunction and biological aging. In particular, the mitochondrial free radical theory of aging (MFRTA) has been well accepted. However, this theory has been challenged by recent studies showing minimal increases in reactive oxygen species (ROS) as not entirely deleterious in nature, and even beneficial under the appropriate cellular circumstances. To assess these significant and nonintuitive observations in the context of a functional system, we have taken an in silico approach to expand the focus of the MFRTA by including other key mitochondrial stress response pathways, as they have been observed in the nematode Caenorhabditis elegans. These include the mitochondrial unfolded protein response (UPR^mt), mitochondrial biogenesis and autophagy dynamics, the relevant DAF‐16 and SKN‐1 axes, and NAD⁺‐dependent deacetylase activities. To integrate these pathways, we have developed a multilevel hybrid‐modeling paradigm, containing agent‐based elements among stochastic system‐dynamics environments of logically derived ordinary differential equations, to simulate aging mitochondrial phenotypes within a population of energetically demanding cells. The simulation experiments resulted in accurate predictions of physiological parameters over time that accompany normal aging, such as the declines in both NAD⁺ and ATP and an increase in ROS. Additionally, the in silico system was virtually perturbed using a variety of pharmacological (e.g., rapamycin, pterostilbene, paraquat) and genetic (e.g., skn‐1, daf‐16, sod‐2) schemes to quantitate the temporal alterations of specific mechanistic targets, supporting insights into molecular determinants of aging as well as cytoprotective agents that may improve neurological or muscular healthspan.

Changes of mitochondrial ultrastructure and function during ageing in mice and Drosophila

Ageing is a progressive decline of intrinsic physiological functions. We examined the impact of ageing on the ultrastructure and function of mitochondria in mouse and fruit flies (Drosophila melanogaster) by electron cryo-tomography and respirometry. We discovered distinct age-related changes in both model organisms. Mitochondrial function and ultrastructure are maintained in mouse heart, whereas subpopulations of mitochondria from mouse liver show age-related changes in membrane morphology. Subpopulations of mitochondria from young and old mouse kidney resemble those described for apoptosis. In aged flies, respiratory activity is compromised and the production of peroxide radicals is increased. In about 50% of mitochondria from old flies, the inner membrane organization breaks down. This establishes a clear link between inner membrane architecture and functional decline. Mitochondria were affected by ageing to very different extents, depending on the organism and possibly on the degree to which tissues within the same organism are protected against mitochondrial damage.

Is there a future for andrographolide to be an anti-inflammatory drug? Deciphering its major mechanisms of action

Andrographis paniculata has long been part of the traditional herbal medicine system in Asia and in Scandinavia. Andrographolide was isolated as a major bioactive constituent of A. paniculata in 1951, and since 1984, andrographolide and its analogs have been scrutinized with modern drug discovery approach for anti-inflammatory properties. With this accumulated wealth of pre-clinical data, it is imperative to review and consolidate different sources of information, to decipher the major anti-inflammatory mechanisms of action in inflammatory diseases, and to provide direction for future studies. Andrographolide and its analogs have been shown to provide anti-inflammatory benefits in a variety of inflammatory disease models. Among the diverse signaling pathways investigated, inhibition of NF-κB activity is the prevailing anti-inflammatory mechanism elicited by andrographolide. There is also increasing evidence supporting endogenous antioxidant defense enhancement by andrographolide through Nrf2 activation. However, the exact pathway leading to NF-κB and Nrf2 activation by andrographolide has yet to be elucidated. Validation and consensus on the major mechanistic actions of andrographolide in different inflammatory conditions are required before translating current findings into clinical settings. There are a few clinical trials conducted using andrographolide in fixed combination formulation which have shown anti-inflammatory benefits and good safety profile. A concerted effort is definitely needed to identify potent andrographolide lead compounds with improved pharmacokinetics and toxicological properties. Taken together, andrographolide and its analogs have great potential to be the next new class of anti-inflammatory agents, and more andrographolide molecules are likely moving towards clinical study stage in the near future.

A bioenergetics assay for studying the effects of environmental stressors on mitochondrial function in vivo in zebrafish larvae

Mitochondria, an integral component of cellular energy metabolism and other key functions, are extremely vulnerable to damage by environmental stressors. Although methods to measure mitochondrial function in vitro exist, sensitive, medium- to high-throughput assays that assess respiration within physiologically-relevant whole organisms are needed to identify drugs and/or chemicals that disrupt mitochondrial function, particularly at sensitive early developmental stages. Consequently, we have developed and optimized an assay to measure mitochondrial bioenergetics in zebrafish larvae using the XF^e24 Extracellular Flux Analyzer. To prevent larval movement from confounding oxygen consumption measurements, we relied on MS-222-based anesthetization. We obtained stable measurement values in the absence of effects on average oxygen consumption rate and subsequently optimized the use of pharmacological agents for metabolic partitioning. To confirm assay reproducibility we demonstrated that triclosan, a positive control, significantly decreased spare respiratory capacity. We then exposed zebrafish from 5 hours post-fertilization (hpf) to 6days post-fertilization (dpf) to three polycyclic aromatic hydrocarbons (PAHs) - benzo(a)pyrene (BaP), phenanthrene (Phe), and fluoranthene (FL) - and measured various fundamental parameters of mitochondrial respiratory chain function, including maximal respiration, spare respiratory capacity, mitochondrial and non-mitochondrial respiration. Exposure to all three PAHs decreased spare respiratory capacity and maximal respiration. Additionally, Phe exposure increased non-mitochondrial respiration and FL exposure decreased mitochondrial respiration and increased non-mitochondrial respiration. Overall, this whole organism-based assay provides a platform for examining mitochondrial dysfunction in vivo at critical developmental stages. It has important implications in biomedical sciences, toxicology and ecophysiology, particularly to examine the effects of environmental chemicals and/or drugs on mitochondrial bioenergetics.

Identification of a previously undetected metabolic defect in the Complex II Caenorhabditis elegans mev-1 mutant strain using respiratory control analysis

Hypometabolism may play an important role in the pathogenesis of ageing and ageing-related diseases. The nematode Caenorhabditis elegans offers the opportunity to study "living mitochondria" in a small (~1 mm) animal replete with a highly stereotypical, yet complex, anatomy and physiology. Basal oxygen consumption rate is often employed as a proxy for energy metabolism in this context. This parameter is traditionally measured using single-chamber Clark electrodes without the addition of metabolic modulators. Recently, multi-well oxygen electrodes, facilitating addition of metabolic modulators and hence study of respiratory control during different mitochondrial respiration states, have been developed. However, only limited official protocols exist for C. elegans, and key limitations of these techniques are therefore unclear. Following modification and testing of some of the existing protocols, we used these methods to explore mitochondrial bioenergetics in live nematodes of an electron transfer chain Complex II mutant strain, mev-1, and identified a previously undetected metabolic defect. We find that mev-1 mutants cannot respond adequately to increased energy demands, suggesting that oxidative phosphorylation is more severely impaired in these animals than has previously been appreciated.

The Role of Mitochondrial Non-Enzymatic Protein Acylation in Ageing

In recent years, various large-scale proteomic studies have demonstrated that mitochondrial proteins are highly acylated, most commonly by addition of acetyl and succinyl groups. These acyl modifications may be enzyme catalysed but can also be driven non-enzymatically. The latter mechanism is promoted in mitochondria due to the nature of the mitochondrial microenvironment, which is alkaline and contains high concentrations of acyl-CoA species. Protein acylation may modify enzyme activity, typically inhibiting it. We posited that organismal ageing might be accompanied by an accumulation of acylated proteins, especially in mitochondria, and that this might compromise mitochondrial function and contribute to ageing. In this study, we used R. norvegicus, C. elegans and D. melanogaster to compare the acylation status of mitochondrial proteins between young and old animals. We observed a specific age-dependent increase in protein succinylation in worms and flies but not in rat. Rats have two substrate-specific mitochondrial deacylases, SIRT3 and SIRT5 while both flies and worms lack these enzymes. We propose that accumulation of mitochondrial protein acylation contributes to age-dependent mitochondrial functional decline and that SIRT3 and SIRT5 enzymes may promote longevity through regulation of mitochondrial protein acylation during ageing.

Long-term monitoring of Ca2+ dynamics in C. elegans pharynx: an in vivo energy balance sensor

Ca2+ is a key signal transducer for muscle contraction. Continuous in vivo monitoring of intracellular Ca2+-dynamics in C. elegans pharynx muscle revealed surprisingly complex Ca2+ patterns. Despite the age-dependent decline of pharynx pumping, we observed unaltered fast Ca2+ oscillations both in young and old worms. In addition, sporadic prolonged Ca2+ increases lasting many seconds or minutes were often observed in between periods of fast Ca2+ oscillations. We attribute them to the inhibition of ATP-dependent Ca2+-pumps upon energy depletion. Accordingly, food deprivation largely augmented the frequency of prolonged [Ca2+] increases. However, paradoxically, prolonged [Ca2+] increases were more frequently observed in young worms than in older ones, and less frequently observed in energy-deficient mitochondrial respiratory chain nuo-6 mutants than in wild-type controls. We hypothesize that young animals are more susceptible to energy depletion due to their faster energy consumption rate, while nuo-6 mutants may keep better the energy balance by slowing energy consumption. Our data therefore suggest that the metabolic state of the pharynx during feeding stimulation depends mainly on the delicate balance between the instant rates of energy production and consumption. Thus, in vivo monitoring of muscle Ca2+ dynamics can be used as a novel tool to study cellular energy availability.

Superoxide dismutase 2 knockdown leads to defects in locomotor activity, sensitivity to paraquat, and increased cuticle pigmentation in Tribolium castaneum

Insects can rapidly adapt to environmental changes through physiological responses. The red flour beetle Tribolium castaneum is widely used as a model insect species. However, the stress-response system of this species remains unclear. Superoxide dismutase 2 (SOD2) is a crucial antioxidative enzyme that is found in mitochondria. T. castaneum SOD2 (TcSOD2) is composed of 215 amino acids, and has an iron/manganese superoxide dismutase domain. qRT-PCR experiments revealed that TcSOD2 was present through all developmental stages. To evaluate TcSOD2 function in T. castaneum, we performed RNAi and also assessed the phenotype and antioxidative tolerance of the knockdown of TcSOD2 by exposing larvae to paraquat. The administration of paraquat resulted in significantly higher 24-h mortality in TcSOD2 knockdown larval groups than in the control groups. The TcSOD2 knockdown adults moved significantly more slowly, had lower ATP content, and exhibited a different body color from the control groups. We found that TcSOD2 dsRNA treatment in larvae resulted in increased expression of tyrosinase and laccase2 mRNA after 10 days. This is the first report showing that TcSOD2 has an antioxidative function and demonstrates that T. castaneum may use an alternative antioxidative system when the SOD2-based system fails.

C. elegans miro-1 Mutation Reduces the Amount of Mitochondria and Extends Life Span

Mitochondria play a critical role in aging, however, the underlying mechanism is not well understood. We found that a mutation disrupting the C. elegans homolog of Miro GTPase (miro-1) extends life span. This phenotype requires simultaneous loss of miro-1 from multiple tissues including muscles and neurons, and is dependent on daf-16/FOXO. Notably, the amount of mitochondria in the miro-1 mutant is reduced to approximately 50% of the wild-type. Despite this reduction, oxygen consumption is only weakly reduced, suggesting that mitochondria of miro-1 mutants are more active than wild-type mitochondria. The ROS damage is slightly reduced and the mitochondrial unfolded protein response pathway is weakly activated in miro-1 mutants. Unlike previously described long-lived mitochondrial electron transport chain mutants, miro-1 mutants have normal growth rate. These results suggest that the reduction in the amount of mitochondria can affect the life span of an organism through activation of stress pathways.

Which Is the Most Significant Cause of Aging?

It becomes clearer and clearer that aging is a result of a significant number of causes and it would seem that counteracting one or several of them should not make a significant difference. Taken at face value, this suggests, for example, that free radicals and reactive oxygen species do not play a significant role in aging and that the lifespan of organisms cannot be significantly extended. In this review, I point to the fact that the causes of aging synergize with each other and discuss the implications involved. One implication is that when two or more synergizing causes increase over time, the result of their action increases dramatically; I discuss a simple model demonstrating this. It is reasonable to conclude that this might explain the acceleration of aging and mortality with age. In this regard, the analysis of results and mortality patterns described in studies involving yeasts and Drosophila provides support for this view. Since the causes of aging are synergizing, it is also concluded that none of them is the major one but many including free radicals, etc. play significant roles. It follows that health/lifespan might be significantly extended if we eliminate or even attenuate the increase of a few or even just one of the causes of aging. While the synergism between the causes of aging is the main topic of this review, several related matters are briefly discussed as well.

Verminoside mediates life span extension and alleviates stress in Caenorhabditis elegans

The discovery of bioactive molecules modulating aging in living organism promotes development of natural therapeutics for curing age-related afflictions. The progression in age-related disorders can be attributed to increment in intracellular reactive oxygen species (ROS) and oxidative stress level. To this end, we isolated an iridoid verminoside (VMS) from Stereospermum suaveolens (Roxb.) DC. and evaluated its effect on Caenorhabditis elegans. The present study delineates VMS-mediated alteration of intracellular ROS, oxidative stress, and life span in C. elegans. The different tested doses of VMS (5 μM, 25 μM, and 50 μM) were able to enhance ROS scavenging and extend mean life span in C. elegans. The maximal life span extension was observed in 25 μM VMS, that is, 20.79% (P < 0.0001) followed by 9.84% (P < 0.0001) in 5 μM VMS and 8.54% (P < 0.0001) in 50 μM VMS. VMS was able to alleviate juglone-induced oxidative stress and enhanced thermotolerance in worms. The stress-modulating and ROS-scavenging potential of VMS was validated by increment in mean survival by 29.54% (P < 0.0001) in VMS-treated oxidative stress hypersensitive mev-1 mutant strain. Furthermore, VMS modulates expression of DAF-16 (a FoxO transcription factor) promoting stress resistance and longevity. Altogether, our results suggest that VMS attenuates intracellular ROS and stress (oxidative and thermal) level promoting longevity. The longevity and stress modulation can be attributed to VMS-mediated alterations in daf-16 expression which regulates insulin signaling pathway. This study opens doors for development of phytomolecule-based therapeutics for prolonging life span and managing age-related severe disorders.

Caenorhabditis elegans: What We Can and Cannot Learn from Aging Worms

SIGNIFICANCE

The nematode Caenorhabditis elegans is a widely used model organism for research into aging. However, nematodes diverged from other animals between 600 and 1300 million years ago. Beyond the intuitive impression that some aspects of aging appear to be universal, is there evidence that insights into the aging process of nematodes may be applicable to humans?

RECENT ADVANCES

There have been a number of results in nematodes that appear to contradict long-held beliefs about mechanisms and causes of aging. For example, ablation of several key antioxidant systems has often failed to result in lifespan shortening in C. elegans.

CRITICAL ISSUES

While it is clear that some central signaling pathways controlling lifespan are broadly conserved across large evolutionary distances, it is less clear to what extent downstream molecular mechanisms of aging are conserved. In this review we discuss the biology of C. elegans and mammals in the context of aging and age-dependent diseases. We consider evidence from studies that attempt to investigate basic, possibly conserved mechanisms of aging especially in the context of the free radical theory of aging. Practical points, such as the need for blinding of lifespan studies and for appropriate biomarkers, are also considered.

FUTURE DIRECTIONS

As data on the aging process(es) in different organisms increase, it is becoming increasingly clear that there are both conserved (public) and private aspects to aging. It is important to explore the dividing lines between these two aspects and to be aware of the large gray areas in-between.

Ozone ameliorates age-related oxidative stress changes in rat liver and kidney: effects of pre- and post-ageing administration

The ageing process is known to be accompanied by increased oxidative stress and compromised antioxidant defenses. Controlled ozone administration has been shown to be effective in various pathophysiological conditions with an underlying oxidative burden. However, its effect on the biochemical alterations associated with the ageing process has been rarely studied. Therefore, the present work was carried out to study the role of ozone in counteracting the state of oxidative stress associated with ageing in rat liver and kidneys using two experimental models. In the pre-ageing model, ozone was administered prior to the onset of ageing at adulthood and continued after the start of the ageing process (3-month-old rats until the age of 15 months). While in the post-ageing model, ozone was administered after ageing has begun and lasted for one month (14-month-old rats until the age of 15 months). The pre-ageing ozone administration effectively reduced lipid and protein oxidation markers, namely, malondialdehyde and protein carbonyl levels and decreased lipofuscin pigment deposition in rat liver and kidneys. Moreover, it significantly restored hepatic and renal reduced glutathione (GSH) contents and normalized cytosolic hepatic glutathione peroxidase activity. Similar but less pronounced effects were observed in the post-ageing ozone-treated group. Nevertheless, in the latter model ozone administration failed to significantly affect liver and kidney lipofuscin levels, as well as kidney GSH contents. These data provide evidences for potentially positive effects of pre-ageing ozone therapy in neutralizing chronic oxidative stress associated with ageing in rat liver and kidneys.

Dormancy and quiescence of skeletal muscle stem cells

The skeletal muscle of vertebrates has a huge regenerative capacity. When destroyed after different types of injury, this organ can regenerate very quickly (less than 20 days following myotoxin injection in the mouse) ad integrum and repeatedly. The cell responsible for this regeneration is the so-called satellite cell, the muscle stem cell that lies on top of the muscle fibre, a giant, multinucleated cell that contains the contractile material. When injected in the muscle, satellite cells can efficiently differentiate into contractile muscle fibres. The satellite cell shows great therapeutic potential; and its regenerative capacity has triggered particular interest in the field of muscular degeneration. In this review we will focus on one particular property of the satellite cell: its quiescence and dormancy. Indeed adult satellite cells are quiescent; they lie between the basal lamina and the basement membrane of the muscle fibre, ready to proliferate, and fuse in order to regenerate myofibers upon injury. It has recently been shown that a subpopulation of satellite cells is able to enter dormancy in human and mice cadavers. Dormancy is defined by a low metabolic state, low mobility, and a long lag before division when plated in vitro, compared to quiescent cells. This definition is also based on current knowledge about long-term hematopoietic stem cells, a subpopulation of stem cells that are described as dormant based on the same criteria (rare division and low metabolism when compared to progeny which are dividing more often). In the first part of this review, we will provide a description of satellite cells which addresses their quiescent state. We will then focus on the uneven distribution of satellite cells in the muscle and describe evidence that suggests that their dormancy differs from one muscle to the next and that one should be cautious when making generalisations regarding this cellular state. In a second part, we will discuss the transition between active dividing cells in developing animals to quiescence. This mechanism could be used or amplified in the switch from quiescence to dormancy. In a third part, we will review the signals and dynamics that actively maintain the satellite cell quiescent. The in-depth understanding of these mechanisms is key to describing how dormancy relies on quiescent state of the cells. In a fourth part, we will deal with dormancy per se: how dormant satellite cells can be obtained, their characteristics, their metabolic profile, and their molecular signature as compared to quiescent cells. Here, we will highlight one of the most important recent findings: that quiescence is a prerequisite for the entry of the satellite cell into dormancy. Since dormancy is a newly discovered phenomenon, we will review the mechanisms responsible for quiescence and activation, as these two cellular states are better known and key to understanding satellite cell dormancy. This will allow us to describe dormancy and its prerequisites.

The BLI-3/TSP-15/DOXA-1 dual oxidase complex is required for iodide toxicity in Caenorhabditis elegans

Iodine is an essential trace element for life. Iodide deficiency can lead to defective biosynthesis of thyroid hormones and is a major cause of hypothyroidism and mental retardation. Excess iodide intake, however, has been linked to different thyroidal diseases. How excess iodide causes harmful effects is not well understood. Here, we found that the nematode Caenorhabditis elegans exhibits developmental arrest and other pleiotropic defects when exposed to excess iodide. To identify the responsible genes, we performed a forward genetic screen and isolated 12 mutants that can survive in excess iodide. These mutants define at least four genes, two of which we identified as bli-3 and tsp-15. bli-3 encodes the C. elegans ortholog of the mammalian dual oxidase DUOX1 and tsp-15 encodes the tetraspanin protein TSP-15, which was previously shown to interact with BLI-3. The C. elegans dual oxidase maturation factor DOXA-1 is also required for the arresting effect of excess iodide. Finally, we detected a dramatically increased biogenesis of reactive oxygen species in animals treated with excess iodide, and this effect can be partially suppressed by bli-3 and tsp-15 mutations. We propose that the BLI-3/TSP-15/DOXA-1 dual oxidase complex is required for the toxic pleiotropic effects of excess iodide.

Black tea increased survival of Caenorhabditis elegans under stress

The present study examined the effects of black tea (Camellia sinensis) extracts (BTE) in Caenorhabditis elegans under various abiotic stressors. Results showed BTE increased nematode resistance to osmosis, heat, and UV irradiation treatments. However, BTE could not increase nematodes' lifespan under normal culture conditions and MnCl2-induced toxicity at concentrations we used. Further studies showed that BTE decreased reactive oxygen species and up-regulated some antioxidant enzymes, including GSH-PX, and genes, such as gsh-px and sod-3. However, only a slight extension in mev-1 mutants mean lifespan was observed without significance. These results indicated that the antioxidant activity of BTE might be necessary but not sufficient to protect against aging to C. elegans. Moreover, BTE increased the mRNA level of stress-response genes such as sir-2.1 and sek-1. Our finding demonstrated BTE might increase heat and UV stress resistance in a sir.2.1-dependent manner. Taken together, BTE enhanced stress resistance with multiple mechanisms in C. elegans.

Molecular control of arsenite-induced apoptosis in Caenorhabditis elegans: roles of insulin-like growth factor-1 signaling pathway

Apoptosis is one of the main cellular processes in responses to arsenic, the well known environmental carcinogen. By using the nematode Caenorhabditis elegans as an in vivo model, we found that insulin-like growth factor-1 networks and their target protein DAF-16/FOXO, known as key regulators of energy metabolism and growth, played important roles in arsenite-induced apoptosis. Inactivation of DAF-2, AGE-1 and AKT-1 caused worms more susceptible to arsenite-induced apoptosis, which could be attenuated by DAF-16 knockout. Worms with inactivated AKT-2 and SGK-1 or with constitutively activated PDK-1 and AKT-1 showed low levels of apoptosis, which could be elevated by DAF-16 mutation. Our results demonstrated that DAF-2/IGF-1R, AGE-1/PI3K, PDK-1/PDK1 and AKT-1/PKB negatively regulated the arsenite-induced apoptosis, whereas AKT-2 and SGK-1 acted proapoptotically. DAF-16/FOXO antagonized IGF-1 signals in signaling the arsenite-induced apoptosis, and apoptosis promoted by DAF-16 inactivation was attributed to its higher sensitivity to oxidative stress.

Hydrogen sulfide is an endogenous regulator of aging in Caenorhabditis elegans

AIMS

To investigate the role of endogenous hydrogen sulfide (H2S) in the control of aging and healthspan of Caenorhabditis elegans.

RESULTS

We show that the model organism, C. elegans, synthesizes H2S. Three H2S-synthesizing enzymes are present in C. elegans, namely cystathionine γ lyase (CSE), cystathionine β synthetase, and 3-mercaptopyruvate transferase (MPST or 3-MST). Genetic deficiency of mpst-1 (3-MST orthologue 1), but not cth-2 (CSE orthologue), reduced the lifespan of C. elegans. This effect was reversed by a pharmacological H2S donor (GYY4137). GYY4137 also reduced detrimental age-dependent changes in a range of physiological indices, including pharyngeal contraction and defecation. Treatment of C. elegans with GYY4137 increased the expression of several age-related, stress response, and antioxidant genes, whereas MitoSOX Red fluorescence, indicative of reactive oxygen species generation, was increased in mpst-1 knockouts and decreased by GYY4137 treatment. GYY4137 additionally increased the lifespan in short-lived mev-1 mutants with elevated oxidative stress and protected wild-type C. elegans against paraquat poisoning. The lifespan-prolonging and health-promoting effects of H2S in C. elegans are likely due to the antioxidant action of this highly cell-permeable gas.

INNOVATION

The possibility that novel pharmacological agents based on the principle of H2S donation may be able to retard the onset of age-related disease by slowing the aging process warrants further study.

CONCLUSION

Our results show that H2S is an endogenous regulator of oxidative damage, metabolism, and aging in C. elegans and provide new insight into the mechanisms, which control aging in this model organism.

Mitochondrial free radical theory of aging: who moved my premise?

First proposed by D Harman in the 1950s, the Mitochondrial Free Radical Theory of Aging (MFRTA) has become one of the most tested and well-known theories in aging research. Its core statement is that aging results from the accumulation of oxidative damage, which is closely linked with the release of reactive oxygen species (ROS) from mitochondria. Although MFRTA has been well acknowledged for more than half a century, conflicting evidence is piling up in recent years querying the causal effect of ROS in aging. A critical idea thus emerges that contrary to their conventional image only as toxic agents, ROS at a non-toxic level function as signaling molecules that induce protective defense in responses to age-dependent damage. Furthermore, the peroxisome, another organelle in eukaryotic cells, might have a say in longevity modulation. Peroxisomes and mitochondria are two organelles closely related to each other, and their interaction has major implications for the regulation of aging. The present review particularizes the questionable sequiturs of the MFRTA, and recommends peroxisome, similarly as mitochondrion, as a possible candidate for the regulation of aging.