Modulation of lipid biosynthesis contributes to stress resistance and longevity of C. elegans mutants

DAF-16/FoxO in Caenorhabditis elegans and Its Role in Metabolic Remodeling

DAF-16, the only forkhead box transcription factors class O (FoxO) homolog in Caenorhabditis elegans, integrates signals from upstream pathways to elicit transcriptional changes in many genes involved in aging, development, stress, metabolism, and immunity. The major regulator of DAF-16 activity is the insulin/insulin-like growth factor 1 (IGF-1) signaling (IIS) pathway, reduction of which leads to lifespan extension in worms, flies, mice, and humans. In C. elegans daf-2 mutants, reduced IIS leads to a heterochronic activation of a dauer survival program during adulthood. This program includes elevated antioxidant defense and a metabolic shift toward accumulation of carbohydrates (i.e., trehalose and glycogen) and triglycerides, and activation of the glyoxylate shunt, which could allow fat-to-carbohydrate conversion. The longevity of daf-2 mutants seems to be partially supported by endogenous trehalose, a nonreducing disaccharide that mammals cannot synthesize, which points toward considerable differences in downstream mechanisms by which IIS regulates aging in distinct groups.

The role of lipid metabolism in aging, lifespan regulation, and age-related disease

An emerging body of data suggests that lipid metabolism has an important role to play in the aging process. Indeed, a plethora of dietary, pharmacological, genetic, and surgical lipid‐related interventions extend lifespan in nematodes, fruit flies, mice, and rats. For example, the impairment of genes involved in ceramide and sphingolipid synthesis extends lifespan in both worms and flies. The overexpression of fatty acid amide hydrolase or lysosomal lipase prolongs life in Caenorhabditis elegans, while the overexpression of diacylglycerol lipase enhances longevity in both C. elegans and Drosophila melanogaster. The surgical removal of adipose tissue extends lifespan in rats, and increased expression of apolipoprotein D enhances survival in both flies and mice. Mouse lifespan can be additionally extended by the genetic deletion of diacylglycerol acyltransferase 1, treatment with the steroid 17‐α‐estradiol, or a ketogenic diet. Moreover, deletion of the phospholipase A2 receptor improves various healthspan parameters in a progeria mouse model. Genome‐wide association studies have found several lipid‐related variants to be associated with human aging. For example, the epsilon 2 and epsilon 4 alleles of apolipoprotein E are associated with extreme longevity and late‐onset neurodegenerative disease, respectively. In humans, blood triglyceride levels tend to increase, while blood lysophosphatidylcholine levels tend to decrease with age. Specific sphingolipid and phospholipid blood profiles have also been shown to change with age and are associated with exceptional human longevity. These data suggest that lipid‐related interventions may improve human healthspan and that blood lipids likely represent a rich source of human aging biomarkers.

Agephagy - Adapting Autophagy for Health During Aging

Autophagy is a major cellular recycling process that delivers cellular material and entire organelles to lysosomes for degradation, in a selective or non-selective manner. This process is essential for the maintenance of cellular energy levels, components, and metabolites, as well as the elimination of cellular molecular damage, thereby playing an important role in numerous cellular activities. An important function of autophagy is to enable survival under starvation conditions and other stresses. The majority of factors implicated in aging are modifiable through the process of autophagy, including the accumulation of oxidative damage and loss of proteostasis, genomic instability and epigenetic alteration. These primary causes of damage could lead to mitochondrial dysfunction, deregulation of nutrient sensing pathways and cellular senescence, finally causing a variety of aging phenotypes. Remarkably, advances in the biology of aging have revealed that aging is a malleable process: a mild decrease in signaling through nutrient-sensing pathways can improve health and extend lifespan in all model organisms tested. Consequently, autophagy is implicated in both aging and age-related disease. Enhancement of the autophagy process is a common characteristic of all principal, evolutionary conserved anti-aging interventions, including dietary restriction, as well as inhibition of target of rapamycin (TOR) and insulin/IGF-1 signaling (IIS). As an emerging and critical process in aging, this review will highlight how autophagy can be modulated for health improvement.

Mechanisms by which PE21, an extract from the white willow Salix alba, delays chronological aging in budding yeast

We have recently found that PE21, an extract from the white willow Salix alba, slows chronological aging and prolongs longevity of the yeast Saccharomyces cerevisiae more efficiently than any of the previously known pharmacological interventions. Here, we investigated mechanisms through which PE21 delays yeast chronological aging and extends yeast longevity. We show that PE21 causes a remodeling of lipid metabolism in chronologically aging yeast, thereby instigating changes in the concentrations of several lipid classes. We demonstrate that such changes in the cellular lipidome initiate three mechanisms of aging delay and longevity extension. The first mechanism through which PE21 slows aging and prolongs longevity consists in its ability to decrease the intracellular concentration of free fatty acids. This postpones an age-related onset of liponecrotic cell death promoted by excessive concentrations of free fatty acids. The second mechanism of aging delay and longevity extension by PE21 consists in its ability to decrease the concentrations of triacylglycerols and to increase the concentrations of glycerophospholipids within the endoplasmic reticulum membrane. This activates the unfolded protein response system in the endoplasmic reticulum, which then decelerates an age-related decline in protein and lipid homeostasis and slows down an aging-associated deterioration of cell resistance to stress. The third mechanisms underlying aging delay and longevity extension by PE21 consists in its ability to change lipid concentrations in the mitochondrial membranes. This alters certain catabolic and anabolic processes in mitochondria, thus amending the pattern of aging-associated changes in several key aspects of mitochondrial functionality.

Cold-induced lipid dynamics and transcriptional programs in white adipose tissue

Background

In mammals, cold exposure induces browning of white adipose tissue (WAT) and alters WAT gene expression and lipid metabolism to boost adaptive thermogenesis and maintain body temperature. Understanding the lipidomic and transcriptomic profiles of WAT upon cold exposure provides insights into the adaptive changes associated with this process.

Results

Here, we applied mass spectrometry and RNA sequencing (RNA-seq) to provide a comprehensive resource for describing the lipidomic or transcriptome profiles in cold-induced inguinal WAT (iWAT). We showed that short-term (3-day) cold exposure induces browning of iWAT, increases energy expenditure, and results in loss of body weight and fat mass. Lipidomic analysis shows that short-term cold exposure leads to dramatic changes of the overall composition of lipid classes WAT. Notably, cold exposure induces significant changes in the acyl-chain composition of triacylglycerols (TAGs), as well as the levels of glycerophospholipids and sphingolipids in iWAT. RNA-seq and qPCR analysis suggests that short-term cold exposure alters the expression of genes and pathways involved in fatty acid elongation, and the synthesis of TAGs, sphingolipids, and glycerophospholipids. Furthermore, the cold-induced lipid dynamics and gene expression pathways in iWAT are contrary to those previously observed in metabolic syndrome, neurodegenerative disorders, and aging, suggesting beneficial effects of cold-induced WAT browning on health and lifespan.

Conclusion

We described the significant alterations in the composition of glyphospholipids, glycerolipids, and sphingolipids and expression of genes involved in thermogenesis, fatty acid elongation, and fatty acid metabolism during the response of iWAT to short-term cold exposure. We also found that some changes in the levels of specific lipid species happening after cold treatment of iWAT are negatively correlated to metabolic diseases, including obesity and T2D.

Electronic supplementary material

The online version of this article (10.1186/s12915-019-0693-x) contains supplementary material, which is available to authorized users.

Metabolic regulation of lifespan from a C. elegans perspective

Decline of cellular functions especially cognitive is a major deficit that arises with age in humans. Harnessing the strengths of small and genetic tractable model systems has revealed key conserved regulatory biochemical and signaling pathways that control aging. Here, we review some of the key signaling and biochemical pathways that coordinate aging processes with special emphasis on Caenorhabditis elegans as a model system and discuss how nutrients and metabolites can regulate lifespan by coordinating signaling and epigenetic programs. We focus on central nutrient-sensing pathways such as mTOR and insulin/insulin-like growth factor signaling and key transcription factors including the conserved basic helix-loop-helix transcription factor HLH-30/TFEB.

Deuterated Polyunsaturated Fatty Acids Reduce Oxidative Stress and Extend the Lifespan of C. elegans

Chemically reinforced essential fatty acids (FAs) promise to fight numerous age-related diseases including Alzheimer’s, Friedreich’s ataxia and other neurological conditions. The reinforcement is achieved by substituting the atoms of hydrogen at the bis-allylic methylene of these essential FAs with the isotope deuterium. This substitution leads to a significantly slower oxidation due to the kinetic isotope effect, inhibiting membrane damage. The approach has the advantage of preventing the harmful accumulation of reactive oxygen species (ROS) by inhibiting the propagation of lipid peroxidation while antioxidants potentially neutralize beneficial oxidative species. Here, we developed a model system to mimic the human dietary requirement of omega-3 in Caenorhabditis elegans to study the role of deuterated polyunsaturated fatty acids (D-PUFAs). Deuterated trilinolenin [D-TG(54:9)] was sufficient to prevent the accumulation of lipid peroxides and to reduce the accumulation or ROS. Moreover, D-TG(54:9) significantly extended the lifespan of worms under normal and oxidative stress conditions. These findings demonstrate that D-PUFAs can be used as a food supplement to decelerate the aging process, resulting in extended lifespan.

A universal transcriptomic signature of age reveals the temporal scaling of Caenorhabditis elegans aging trajectories

We collected 60 age-dependent transcriptomes for C. elegans strains including four exceptionally long-lived mutants (mean adult lifespan extended 2.2- to 9.4-fold) and three examples of lifespan-increasing RNAi treatments. Principal Component Analysis (PCA) reveals aging as a transcriptomic drift along a single direction, consistent across the vastly diverse biological conditions and coinciding with the first principal component, a hallmark of the criticality of the underlying gene regulatory network. We therefore expected that the organism's aging state could be characterized by a single number closely related to vitality deficit or biological age. The "aging trajectory", i.e. the dependence of the biological age on chronological age, is then a universal stochastic function modulated by the network stiffness; a macroscopic parameter reflecting the network topology and associated with the rate of aging. To corroborate this view, we used publicly available datasets to define a transcriptomic biomarker of age and observed that the rescaling of age by lifespan simultaneously brings together aging trajectories of transcription and survival curves. In accordance with the theoretical prediction, the limiting mortality value at the plateau agrees closely with the mortality rate doubling exponent estimated at the cross-over age near the average lifespan. Finally, we used the transcriptomic signature of age to identify possible life-extending drug compounds and successfully tested a handful of the top-ranking molecules in C. elegans survival assays and achieved up to a +30% extension of mean lifespan.

Lipidomic alteration and stress-defense mechanism of soil nematode Caenorhabditis elegans in response to extremely low-frequency electromagnetic field exposure

To assess the impacts of man-made extremely low-frequency electromagnetic field (ELF-EMF) on soil ecosystems, the soil nematode was applied as a biological indicator to characterize ecotoxicity of ELF-EMF. In this paper, a soil-living model organism, Caenorhabditis elegans (C. elegans) was exposed to 50 Hz, 3 mT ELF-EMF. The integrated lipidome, proteome and transcriptome analysis were applied to elucidate physiological acclimations. Lipidomic analysis showed that ELF-EMF exposure induced significant alterations of 64 lipids, including significant elevation of triacylglycerols (TGs). Proteome results implied 157 changed protein expressions under ELF-EMF exposure. By transcriptomic analysis, 456 differently expressed genes were identified. Gene Ontology (GO) function and pathway analyses showed lipidomic alteration, mitochondrial dysfunction and the stress defense responses following ELF-EMF exposure in C. elegans. Conjoint analysis of proteome and transcriptome data showed that a higher expression of genes (sip-1, mtl-1 and rpl-11.1, etc.) were involved in stress defense responses to ELF-EMF exposure. These results indicated that ELF-EMF can induce effects on soil nematodes, mainly through disturbing lipid metabolism such as increasing TGs content, and eliciting stress defense responses. This study provided a new understanding in ELF-EMF exposure effects on soil nematodes and suggested a potential way of interpreting ELF-EMF influences on soil ecosystems.

What is the rate-limiting step towards aging? Chemical reaction kinetics might reconcile contradictory observations in experimental aging research

Modern geroscience is divided as regards the validity of the free radical theory of aging. Thermodynamic arguments and observations from comparative zoology support it, whereas results from experimental manipulations in representative animal species sometimes strongly contradict it. From a comparison of the multi-step aging process with a linear metabolic pathway (glycolysis), we here argue that the identification of the rate-limiting kinetic steps of the aging cascade is essential to understand the overall flux through the cascade, i.e., the rate of aging. Examining free radical reactions as a case in point, these reactions usually occur as chain reactions with three kinetically independent steps: initiation, propagation, and termination, each of which can be rate-limiting. Revisiting the major arguments in favor and against a role of free radicals in aging, we find that the majority of arguments in favor point to radical propagation as relevant and rate-limiting, whereas almost all arguments in disfavor are based on experimental manipulations of radical initiation or radical termination which turned out to be ineffective. We conclude that the overall lack of efficacy of antioxidant supplementation (which fosters termination) and antioxidant enzyme overexpression (which inhibits initiation) in longevity studies is attributable to the fact that initiation and termination are not the rate-limiting steps of the aging cascade. The biological and evolutionary plausibility of this interpretation is discussed. In summary, radical propagation is predicted to be rate-limiting for aging and should be explored in more detail.

Linking Lipid Metabolism to Chromatin Regulation in Aging

The lifespan of an organism is strongly influenced by environmental factors (including diet) and by internal factors (notably reproductive status). Lipid metabolism is critical for adaptation to external conditions or reproduction. Interestingly, specific lipid profiles are associated with longevity, and increased uptake of certain lipids extends longevity in Caenorhabditis elegans and ameliorates disease phenotypes in humans. How lipids impact longevity, and how lipid metabolism is regulated during aging, is just beginning to be unraveled. This review describes recent advances in the regulation and role of lipids in longevity, focusing on the interaction between lipid metabolism and chromatin states in aging and age-related diseases.

Honeybee caste lipidomics in relation to life-history stages and the long life of the queen

Honey bees have evolved a system in which fertilised eggs transit through the same developmental stages but can become either workers or queens. This difference is determined by their diet through development. Whereas workers live for weeks (normally 2-6 weeks), queens can live for years. Unfertilised eggs also develop through the same stages but result in a short living male caste (drones). Workers and drones are fed pollen throughout their late larval and adult life stages, while queens are fed exclusively on royal jelly and do not eat pollen. Pollen has high content of polyunsaturated fatty acids (PUFA) while royal jelly has a negligible amount of PUFA. To investigate the role of dietary PUFA lipids, and their oxidation in the longevity difference of honey bees, membrane fatty acid composition of the three castes was characterised at six different life-history stages (larvae, pupa, emergent, and different adult stages) through mass spectrometry. All castes were found to share a similar membrane phospholipid composition during early larval development. However, at pupation, drones and workers increased their level of PUFA, whilst queens increased their level of monounsaturated fatty acids. After emergence, worker bees further increased their level of PUFA by 5-fold across most phospholipid classes. In contrast, the membrane phospholipids of adult queens remained highly monounsaturated throughout their adult life. We postulate that this diet-induced increase in membrane PUFA results in more oxidative damage and is potentially responsible for the much shorter lifespans of worker bees compared to long-living queens.

Identification of key pathways and metabolic fingerprints of longevity in C. elegans

Impaired insulin/IGF-1 signaling (IIS) and caloric restriction (CR) prolong lifespan in the nematode C. elegans. However, a cross comparison of these longevity pathways using a multi-omics integration approach is lacking. In this study, we aimed to identify key pathways and metabolite fingerprints of longevity that are shared between IIS and CR worm models using multi-omics integration. We generated transcriptomics and metabolomics data from long-lived worm strains, i.e. daf-2 (impaired IIS) and eat-2 (CR model) and compared them with the wild-type strain N2. Transcriptional profiling identified shared longevity signatures, such as an upregulation of lipid storage and defense responses, and downregulation of macromolecule synthesis and developmental processes. Metabolomics profiling identified an increase in the levels of glycerol‑3P, adenine, xanthine, and AMP, and a decrease in the levels of the amino acid pool, as well as the C18:0, C17:1, C19:1, C20:0 and C22:0 fatty acids. After we integrated transcriptomics and metabolomics data based on the annotations in KEGG, our results highlighted increased amino acid metabolism and an upregulation of purine metabolism as a commonality between the two long-lived mutants. Overall, our findings point towards the existence of shared metabolic pathways that are likely important for lifespan extension and provide novel insights into potential regulators and metabolic fingerprints for longevity.

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Multi-omics integration identified common longevity signatures.

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Amino acid metabolism was increased in both daf-2 and eat-2 mutants.

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Purine biosynthesis pathway was enhanced in the long-lived mutants.

Emerging topics in C. elegans aging research: Transcriptional regulation, stress response and epigenetics

Key discoveries in aging research have been made possible with the use of model organisms. Caenorhabditis elegans is a short-lived nematode that has become a well-established system to study aging. The practicality and powerful genetic manipulations associated with this metazoan have revolutionized our ability to understand how organisms age. 25 years after the publication of the discovery of the daf-2 gene as a genetic modifier of lifespan, C. elegans remains as relevant as ever in the quest to understand the process of aging. Nematode aging research has proven useful in identifying transcriptional regulators, small molecule signals, cellular mechanisms, epigenetic modifications associated with stress resistance and longevity, and lifespan-extending compounds. Here, we review recent discoveries and selected topics that have emerged in aging research using this incredible little worm.

[De novo biosynthesis of glycerophospholipids and longevity]

BACKGROUND

The glycerophospholipids, synthesised from diacylglycerol (DAG), are one of the main lipid components of cell membranes. The lipid profile is an optimised feature associated with animal longevity. In this context, the hypothesis is presented that the DAG biosynthesis rate, and thus, the glycerophospholipids content, is related to animal longevity.

MATERIAL AND METHODS

A plasma lipidomic analysis was performed based on the mass spectrometry of 11 mammalian species with a maximum longevity ranging from 3.5 to 120 years. Lipid identification was based on exact mass, retention time, and isotopic distribution. ANOVA test was applied to differentiate the lipids between animal species. The relationship between these lipids and longevity was carried out with a Spearman correlation. Data was analysed using SPSS and MetaboAnalyst.

RESULTS

Among the 1,061 different lipid molecular species found between species, 47 were defined as DAG. Interestingly, 14 of them showed a negative correlation with mammalian maximum longevity. Multivariate statistics revealed that 14 DAGs were enough to define mammalian species and their maximum longevity.

CONCLUSIONS

Data suggest that long-lived mammalian species have a lower rate of glycerophospholipids synthesis through the de novo pathway, possibly associated with a lower rate of membrane lipid exchange, which in turn is related to lower energy expenditure.

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.

PIP3-binding proteins promote age-dependent protein aggregation and limit survival in C. elegans

Class-I phosphatidylinositol 3-kinase (PI3KI) converts phosphatidylinositol 4,5-bisphosphate (PIP2) to phosphatidylinositol 3,4,5-triphosphate (PIP3). PIP3 comprises two fatty-acid chains that embed in lipid-bilayer membranes, joined by glycerol to inositol triphosphate. Proteins with domains that specifically bind that head-group (e.g. pleckstrin-homology [PH] domains) are thus tethered to the inner plasma-membrane surface where they have an enhanced likelihood of interaction with other PIP3-bound proteins, in particular other components of their signaling pathways. Null alleles of the C. elegans age-1 gene, encoding the catalytic subunit of PI3KI, lack any detectable class-I PI3K activity and so cannot form PIP3. These mutant worms survive almost 10-fold longer than the longest-lived normal control, and are highly resistant to a variety of stresses including oxidative and electrophilic challenges. Traits associated with age-1 mutation are widely believed to be mediated through AKT-1, which requires PIP3 for both tethering and activation. Active AKT complex phosphorylates and thereby inactivates the DAF-16/FOXO transcription factor. However, extensive evidence indicates that pleiotropic effects of age-1-null mutations, including extreme longevity, cannot be explained by insulin like-receptor/AKT/FOXO signaling alone, suggesting involvement of other PIP3-binding proteins. We used ligand-affinity capture to identify membrane-bound proteins downstream of PI3KI that preferentially bind PIP3. Computer modeling supports a subset of candidate proteins predicted to directly bind PIP3 in preference to PIP2, and functional testing by RNAi knockdown confirmed candidates that partially mediate the stress-survival, aggregation-reducing and longevity benefits of PI3KI disruption. PIP3-specific candidate sets are highly enriched for proteins previously reported to affect translation, stress responses, lifespan, proteostasis, and lipid transport.

Absolute quantitative lipidomics reveals lipidome-wide alterations in aging brain

INTRODUCTION

The absolute quantitation of lipids at the lipidome-wide scale is a challenge but plays an important role in the comprehensive study of lipid metabolism.

OBJECTIVES

We aim to develop a high-throughput quantitative lipidomics approach to enable the simultaneous identification and absolute quantification of hundreds of lipids in a single experiment. Then, we will systematically characterize lipidome-wide changes in the aging mouse brain and provide a link between aging and disordered lipid homeostasis.

METHODS

We created an in-house lipid spectral library, containing 76,361 lipids and 181,300 MS/MS spectra in total, to support accurate lipid identification. Then, we developed a response factor-based approach for the large-scale absolute quantifications of lipids.

RESULTS

Using the lipidomics approach, we absolutely quantified 1212 and 864 lipids in human cells and mouse brains, respectively. The quantification accuracy was validated using the traditional approach with a median relative error of 12.6%. We further characterized the lipidome-wide changes in aging mouse brains, and dramatic changes were observed in both glycerophospholipids and sphingolipids. Sphingolipids with longer acyl chains tend to accumulate in aging brains. Membrane-esterified fatty acids demonstrated diverse changes with aging, while most polyunsaturated fatty acids consistently decreased.

CONCLUSION

We developed a high-throughput quantitative lipidomics approach and systematically characterized the lipidome-wide changes in aging mouse brains. The results proved a link between aging and disordered lipid homeostasis.

Four Genome-Wide Association Studies Identify New Extreme Longevity Variants

The search for the genetic determinants of extreme human longevity has been challenged by the phenotype's rarity and its nonspecific definition by investigators. To address these issues, we established a consortium of four studies of extreme longevity that contributed 2,070 individuals who survived to the oldest one percentile of survival for the 1900 U.S. birth year cohort. We conducted various analyses to discover longevity-associated variants (LAV) and characterized those LAVs that differentiate survival to extreme age at death (eSAVs) from those LAVs that become more frequent in centenarians because of mortality selection (eg, survival to younger years). The analyses identified new rare variants in chromosomes 4 and 7 associated with extreme survival and with reduced risk for cardiovascular disease and Alzheimer's disease. The results confirm the importance of studying truly rare survival to discover those combinations of common and rare variants associated with extreme longevity and longer health span.

Cellular lifespan and senescence: a complex balance between multiple cellular pathways

The study of cellular senescence and proliferative lifespan is becoming increasingly important because of the promises of autologous cell therapy, the need for model systems for tissue disease and the implication of senescent cell phenotypes in organismal disease states such as sarcopenia, diabetes and various cancers, among others. Here, we explain the concepts of proliferative cellular lifespan and cellular senescence, and we present factors that have been shown to mediate cellular lifespan positively or negatively. We review much recent literature and present potential molecular mechanisms by which lifespan mediation occurs, drawing from the fields of telomere biology, metabolism, NAD(+) and sirtuin biology, growth factor signaling and oxygen and antioxidants. We conclude that cellular lifespan and senescence are complex concepts that are governed by multiple independent and interdependent pathways, and that greater understanding of these pathways, their interactions and their convergence upon specific cellular phenotypes may lead to viable therapies for tissue regeneration and treatment of age-related pathologies, which are caused by or exacerbated by senescent cells in vivo.

Good Ol' Fat: Links between Lipid Signaling and Longevity

Aging is the single greatest risk factor for the development of disease. Understanding the biological molecules and mechanisms that modulate aging is therefore critical for the development of health-maximizing interventions for older people. The effect of fats on longevity has traditionally been disregarded as purely detrimental. However, new studies are starting to uncover the possible beneficial effects of lipids working as signaling molecules on health and longevity. These studies highlight the complex links between aging and lipid signaling. In this review we summarize accumulating evidence that points to changes in lipid metabolism, and in particular lipid signaling, as an underlying mechanism for healthy aging.

Combination of Metabolomic and Proteomic Analysis Revealed Different Features among Lactobacillus delbrueckii Subspecies bulgaricus and lactis Strains While In Vivo Testing in the Model Organism Caenorhabditis elegans Highlighted Probiotic Properties

Lactobacillus delbrueckii represents a technologically relevant member of lactic acid bacteria, since the two subspecies bulgaricus and lactis are widely associated with fermented dairy products. In the present work, we report the characterization of two commercial strains belonging to L. delbrueckii subspecies bulgaricus, lactis and a novel strain previously isolated from a traditional fermented fresh cheese. A phenomic approach was performed by combining metabolomic and proteomic analysis of the three strains, which were subsequently supplemented as food source to the model organism Caenorhabditis elegans, with the final aim to evaluate their possible probiotic effects. Restriction analysis of 16S ribosomal DNA revealed that the novel foodborne strain belonged to L. delbrueckii subspecies lactis. Proteomic and metabolomic approaches showed differences in folate, aminoacid and sugar metabolic pathways among the three strains. Moreover, evaluation of C. elegans lifespan, larval development, brood size, and bacterial colonization capacity demonstrated that L. delbrueckii subsp. bulgaricus diet exerted beneficial effects on nematodes. On the other hand, both L. delbrueckii subsp. lactis strains affected lifespan and larval development. We have characterized three strains belonging to L. delbrueckii subspecies bulgaricus and lactis highlighting their divergent origin. In particular, the two closely related isolates L. delbrueckii subspecies lactis display different galactose metabolic capabilities. Moreover, the L. delbrueckii subspecies bulgaricus strain demonstrated potential probiotic features. Combination of omic platforms coupled with in vivo screening in the simple model organism C. elegans is a powerful tool to characterize industrially relevant bacterial isolates.

Effect of oregano essential oil supplementation to a reduced-protein, amino acid-supplemented diet on meat quality, fatty acid composition, and oxidative stability of Longissimus thoracis muscle in growing-finishing pigs

This study investigated the effects of reduced-protein, amino acid-supplemented diet supplementation with oregano essential oil (OEO) in pigs, from growing period to slaughter, on the meat quality, fatty acid composition, and oxidative stability of Longissimus thoracis (LT) muscle. Thirty-six barrows were randomly divided into three experimental treatments, namely, normal protein diet (NPD), reduced-protein, amino acid-supplemented diet (RPD), and identical RPD supplemented (250mg/kg feed) with OEO (OEO) treatments. Dietary RPD and OEO increased the b*_45min, tenderness, overall acceptance, and intramuscular fat (IMF) content of pork compared with dietary NPD. The percentage of n-3 polyunsaturated fatty acid (n-3 PUFA) and the percentage of monounsaturated fatty acid in OEO muscle were higher and lower than those in RPD muscle, respectively. Dietary OEO improved oxidative stability, total antioxidative capacity, and catalase but decreased drip loss in LT muscle. Results indicated that dietary OEO enhanced the sensory attributes and anti-oxidative status of pork meat by improving IMF and n-3 PUFA proportion and antioxidative capacity.

Mechanisms Underlying the Essential Role of Mitochondrial Membrane Lipids in Yeast Chronological Aging

The functional state of mitochondria is vital to cellular and organismal aging in eukaryotes across phyla. Studies in the yeast Saccharomyces cerevisiae have provided evidence that age-related changes in some aspects of mitochondrial functionality can create certain molecular signals. These signals can then define the rate of cellular aging by altering unidirectional and bidirectional communications between mitochondria and other organelles. Several aspects of mitochondrial functionality are known to impact the replicative and/or chronological modes of yeast aging. They include mitochondrial electron transport, membrane potential, reactive oxygen species, and protein synthesis and proteostasis, as well as mitochondrial synthesis of iron-sulfur clusters, amino acids, and NADPH. Our recent findings have revealed that the composition of mitochondrial membrane lipids is one of the key aspects of mitochondrial functionality affecting yeast chronological aging. We demonstrated that exogenously added lithocholic bile acid can delay chronological aging in yeast because it elicits specific changes in mitochondrial membrane lipids. These changes allow mitochondria to operate as signaling platforms that delay yeast chronological aging by orchestrating an institution and maintenance of a distinct cellular pattern. In this review, we discuss molecular and cellular mechanisms underlying the essential role of mitochondrial membrane lipids in yeast chronological aging.

Mono-unsaturated fatty acids link H3K4me3 modifiers to C. elegans lifespan

Chromatin and metabolic states both influence lifespan, but how they interact in lifespan regulation is largely unknown. The COMPASS chromatin complex, which trimethylates lysine 4 on histone H3 (H3K4me3), regulates lifespan in Caenorhabditis elegans. However, the mechanism by which H3K4me3 modifiers affect longevity, and whether this mechanism involves metabolic changes, remain unclear. Here we show that a deficiency in H3K4me3 methyltransferase, which extends lifespan, promotes fat accumulation in worms with a specific enrichment of mono-unsaturated fatty acids (MUFAs). This fat metabolism switch in H3K4me3 methyltransferase-deficient worms is mediated at least in part by the downregulation of germline targets, including S6 kinase, and by the activation of an intestinal transcriptional network that upregulates delta-9 fatty acid desaturases. Notably, the accumulation of MUFAs is necessary for the lifespan extension of H3K4me3 methyltransferase-deficient worms, and dietary MUFAs are sufficient to extend lifespan. Given the conservation of lipid metabolism, dietary or endogenous MUFAs could extend lifespan and healthspan in other species, including mammals.

Autophagy-mediated longevity is modulated by lipoprotein biogenesis

Autophagy-dependent longevity models in C. elegans display altered lipid storage profiles, but the contribution of lipid distribution to life-span extension is not fully understood. Here we report that lipoprotein production, autophagy and lysosomal lipolysis are linked to modulate life span in a conserved fashion. We find that overexpression of the yolk lipoprotein VIT/vitellogenin reduces the life span of long-lived animals by impairing the induction of autophagy-related and lysosomal genes necessary for longevity. Accordingly, reducing vitellogenesis increases life span via induction of autophagy and lysosomal lipolysis. Life-span extension due to reduced vitellogenesis or enhanced lysosomal lipolysis requires nuclear hormone receptors (NHRs) NHR-49 and NHR-80, highlighting novel roles for these NHRs in lysosomal lipid signaling. In dietary-restricted worms and mice, expression of VIT and hepatic APOB (apolipoprotein B), respectively, are significantly reduced, suggesting a conserved longevity mechanism. Altogether, our study demonstrates that lipoprotein biogenesis is an important mechanism that modulates aging by impairing autophagy and lysosomal lipolysis.

Gain-of-Function Alleles in Caenorhabditis elegans Nuclear Hormone Receptor nhr-49 Are Functionally Distinct

Nuclear hormone receptors (NHRs) are transcription factors that regulate numerous physiological and developmental processes and represent important drug targets. NHR-49, an ortholog of Hepatocyte Nuclear Factor 4 (HNF4), has emerged as a key regulator of lipid metabolism and life span in the nematode worm Caenorhabditis elegans. However, many aspects of NHR-49 function remain poorly understood, including whether and how it regulates individual sets of target genes and whether its activity is modulated by a ligand. A recent study identified three gain-of-function (gof) missense mutations in nhr-49 (nhr-49(et7), nhr-49(et8), and nhr-49(et13), respectively). These substitutions all affect the ligand-binding domain (LBD), which is critical for ligand binding and protein interactions. Thus, these alleles provide an opportunity to test how three specific residues contribute to NHR-49 dependent gene regulation. We used computational and molecular methods to delineate how these mutations alter NHR-49 activity. We find that despite originating from a screen favoring the activation of specific NHR-49 targets, all three gof alleles cause broad upregulation of NHR-49 regulated genes. Interestingly, nhr-49(et7) and nhr-49(et8) exclusively affect nhr-49 dependent activation, whereas the nhr-49(et13) surprisingly affects both nhr-49 mediated activation and repression, implicating the affected residue as dually important. We also observed phenotypic non-equivalence of these alleles, as they unexpectedly caused a long, short, and normal life span, respectively. Mechanistically, the gof substitutions altered neither protein interactions with the repressive partner NHR-66 and the coactivator MDT-15 nor the subcellular localization or expression of NHR-49. However, in silico structural modeling revealed that NHR-49 likely interacts with small molecule ligands and that the missense mutations might alter ligand binding, providing a possible explanation for increased NHR-49 activity. In sum, our findings indicate that the three nhr-49 gof alleles are non-equivalent, and highlight the conserved V411 residue affected by et13 as critical for gene activation and repression alike.

Target of rapamycin activation predicts lifespan in fruit flies

Aging and age-related diseases are one of the most important health issues that the world will confront during the 21^st century. Only by understanding the proximal causes will we be able to find treatments to reduce or delay the onset of degenerative diseases associated with aging. Currently, the prevalent paradigm in the field is the accumulation of damage. However, a new theory that proposes an alternative explanation is gaining momentum. The hyperfunction theory proposes that aging is not a consequence of a wear and tear process, but a result of the continuation of developmental programs during adulthood. Here we use Drosophila melanogaster, where evidence supporting both paradigms has been reported, to identify which parameters that have been previously related with lifespan best predict the rate of aging in wild type flies cultured at different temperatures. We find that mitochondrial function and mitochondrial reactive oxygen species (mtROS) generation correlates with metabolic rate, but not with the rate of aging. Importantly, we find that activation of nutrient sensing pathways (i.e. insulin-PI3K/Target of rapamycin (Tor) pathway) correlates with lifespan, but not with metabolic rate. Our results, dissociate metabolic rate and lifespan in wild type flies and instead link nutrient sensing signaling with longevity as predicted by the hyperfunction theory.

Using Caenorhabditis elegans to Uncover Conserved Functions of Omega-3 and Omega-6 Fatty Acids

The nematode Caenorhabditis elegans is a powerful model organism to study functions of polyunsaturated fatty acids. The ability to alter fatty acid composition with genetic manipulation and dietary supplementation permits the dissection of the roles of omega-3 and omega-6 fatty acids in many biological process including reproduction, aging and neurobiology. Studies in C. elegans to date have mostly identified overlapping functions of 20-carbon omega-6 and omega-3 fatty acids in reproduction and in neurons, however, specific roles for either omega-3 or omega-6 fatty acids are beginning to emerge. Recent findings with importance to human health include the identification of a conserved Cox-independent prostaglandin synthesis pathway, critical functions for cytochrome P450 derivatives of polyunsaturated fatty acids, the requirements for omega-6 and omega-3 fatty acids in sensory neurons, and the importance of fatty acid desaturation for long lifespan. Furthermore, the ability of C. elegans to interconvert omega-6 to omega-3 fatty acids using the FAT-1 omega-3 desaturase has been exploited in mammalian studies and biotechnology approaches to generate mammals capable of exogenous generation of omega-3 fatty acids.

Lipid Profiles and Signals for Long Life

Historically, fat was considered detrimental to health and lifespan. However, lipidomics, the quantification of all lipid molecules in a biological sample, and genetic studies in model organisms are revealing specific fats that may promote longevity. These emerging findings provide insight into the complex relationship between lipids and longevity.

Phospholipid fatty acid composition linking larval-density to lifespan of adult Drosophila melanogaster

Pre-adult density-associated alterations in the composition of storage lipids may affect the cell membrane fatty acid profile (mainly phospholipids), membrane integrity, and cell function. The present study evaluated the impact of pre-adult density conditions, sex, and the selection regime on the composition of phospholipid fatty acids and lifespan of Drosophila melanogaster. The phospholipid profile of adult flies developed under larval crowding contained a higher proportion of polyunsaturated fatty acids, lower proportion of monounsaturated fatty acids, and greater risk of peroxidation. There was also a negative correlation between the peroxidation index (PI) and longevity. The longevity-selected females showed a lower PI compared with control lines under both densities. The present results indicate that pre-adult density may play a significant role in the lifespan of adult flies by altering the composition of phospholipids and shaping cell membrane bilayers with different susceptibilities to peroxidation.

Of mice, pigs and humans: An analysis of mitochondrial phospholipids from mammals with very different maximal lifespans

The maximal lifespan (MLS) of mammals is inversely correlated with the peroxidation index, a measure of the proportion and level of unsaturation of polyunsaturated fatty acids (PUFA) in membranes. This relationship is likely related to the fact that PUFA are highly susceptible to damage by peroxidation. Previous comparative work has examined membrane composition at the level of fatty acids, and relatively little is known regarding the distribution of PUFA across phospholipid classes or phospholipid molecules. In addition, data for humans is extremely rare in this area. Here we present the first shotgun lipidomics analysis of mitochondrial membranes and the peroxidation index of skeletal muscle, liver, and brain in three mammals that span the range of mammalian longevity. The species compared were mice (MLS of 4 years), pigs (MLS of 27 years), and humans (MLS of 122 years). Mouse mitochondria contained highly unsaturated PUFA in all phospholipid classes. Human mitochondria had lower PUFA content and a lower degree of unsaturation of PUFA. Pig mitochondria shared characteristics of both mice and humans. We found that membrane susceptibility to peroxidation was primarily determined by a limited number of phospholipid molecules that differed between both tissues and species.

Perspectives on the membrane fatty acid unsaturation/pacemaker hypotheses of metabolism and aging

The membrane pacemaker hypotheses of metabolism and aging are distinct, but interrelated hypotheses positing that increases in unsaturation of lipids within membranes are correlated with increasing basal metabolic rate and decreasing longevity, respectively. The two hypotheses each have evidence that either supports or contradicts them, but consensus has failed to emerge. In this review, we identify sources of weakness of previous studies supporting and contradicting these hypotheses and suggest different methods and lines of inquiry. The link between fatty acyl composition of membranes and membrane-bound protein activity is a central tenet of the membrane pacemaker hypothesis of metabolism, but the mechanism by which unsaturation would change protein activity is not well defined and, whereas fatty acid desaturases have been put forward by some as the mechanism behind evolutionary differences in fatty acyl composition of phospholipids among organisms, there have been no studies to differentiate whether desaturases have been more affected by natural selection on aging and metabolic rate than have elongases or acyltransferases. Past analyses have been hampered by potentially incorrect estimates of the peroxidizability of lipids and longevity of study animals, and by the confounding effect of phylogeny. According to some authors, body mass may also be a confounding effect that should be taken into account, though this is not universally accepted. Further research on this subject should focus more on mechanisms and take weaknesses of past studies into account.

The double mutation of cytochrome P450's and fatty acid desaturases affect lipid regulation and longevity in C. elegans

An imbalance between energy uptake and energy expenditure can lead to obesity and increase the risk of coronary heart disease, high blood pressure, stroke, type II diabetes and some cancers. Given that key elements of the energy pathway are evolutionary conserved, invertebrate research is an attractive alternative that overcomes the many legislative, financial and experimental hurdles typical of research with higher metazoan animals. Recent studies have suggested that some members of the cytochrome P450 superfamily are involved in lipid metabolism in addition to the traditional xenobiotic activity. To investigate this notion in more detail, the present study aimed to pinpoint phenotypic, genetic and genomic-level responses of Caenorhabditis elegans using selected deletion mutants including fat-5 (a member of the Δ9 desaturases) and cyp-35A2 (a member of the cytochrome P450 family). The creation of a fat-5(tm420);cyp-35A2(gk317) mutant uncovered that the deletion of both genes resulted in a strain which is marked by an extended lifespan. Furthermore, it diminished the overall level of Nile Red positive compartments, which is indicative of a change in lipid metabolism. Comprehensive transcriptomics revealed that several genes involved in aging and lipid transport/homeostasis were modulated following the double deletion of fat-5 and cyp-35A2. Taken together, the results suggest the presence of a putative correlation between longevity and lipid regulation and given that both genes have human homologs, this finding may offer a new lead to investigate in higher organisms.

Analysis of the effect of the mitochondrial prohibitin complex, a context-dependent modulator of longevity, on the C. elegans metabolome

The mitochondrial prohibitin complex, composed of two proteins, PHB-1 and PHB-2, is a context-dependent modulator of longevity. Specifically, prohibitin deficiency shortens the lifespan of otherwise wild type worms, while it dramatically extends the lifespan under compromised metabolic conditions. This extremely intriguingly phenotype has been linked to alterations in mitochondrial function and in fat metabolism. However, the true function of the mitochondrial prohibitin complex remains elusive. Here, we used gas chromatography coupled to a flame ionization detector (GC/FID) and ¹H NMR spectroscopy to gain molecular insights into the effect of prohibitin depletion on the Caenorhabditis elegans metabolome. We analysed the effect of prohibitin deficiency in two different developmental stages and under two different conditions, which result in opposing longevity phenotypes, namely wild type worms and daf-2(e1370) insulin signalling deficient mutants. Prohibitin depletion was shown to alter the fatty acid (GC/FID) and ¹H NMR metabolic profiles of wild type animals both at the fourth larval stage of development (L4) and at the young adult (YA) stage, while being more pronounced at the later stage. Furthermore, wild type and the diapause mutant daf-2(e1370), either expressing or not prohibitin, were clearly distinguishable based on their metabolic profiles, revealing changes in fatty acid composition, as well as in carbohydrate and amino acid metabolism. Moreover, the metabolic data indicate that daf-2(e1370) mutants are more robust than the wild type animals to changes induced by prohibitin depletion. The impact of prohibitin depletion on the C. elegans metabolome will be discussed herein in the scope of its effect on longevity. This article is part of a Special Issue entitled: Mitochondrial Dysfunction in Aging. Guest Editor: Aleksandra Trifunovic

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Impact of the mitochondrial prohibitin (PHB) complex on the C. elegans metabolome

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Depletion of individual PHB subunits results in similar metabolic profiles.

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PHB affects fatty acid composition, amino acid and carbohydrate metabolism.

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daf-2 mutants are more robust than wild type worms to the effect of PHB depletion.

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Modulation of fermentation may contribute to the longevity of PHB-depleted worms.

The transcriptional repressor CTBP-1 functions in the nervous system of Caenorhabditis elegans to regulate lifespan

C-terminal binding proteins (CtBPs) are recruited by a variety of transcription factors to mediate gene repression. Nematode CTBP-1 has previously been shown to play a role in the regulation of lifespan; Caenorhabditis elegans strains carrying a deletion in the ctbp-1 gene showed a 10-20% increase in mean and maximal lifespan compared with wild-type control strains. We set out to identify the tissues in which CTBP-1 functions to regulate lifespan in C. elegans. Our analysis of reporter genes shows that CTBP-1 is predominantly expressed in the nervous system with lower levels detectable in the hypodermis. Tissue-specific rescue experiments demonstrated that CTBP-1 functions in the nervous system to regulate lifespan. Previously, the lifespan extension in a ctbp-1 mutant was attributed, at least in part, to the misregulation of a lipase gene, lips-7. We therefore focussed on lips-7 and found that expressing CTBP-1 solely in the nervous system of a ctbp-1 mutant significantly reduced lips-7 transcription. In addition, we studied another ctbp-1 mutant allele that also displayed a long-lived phenotype. In this case, lips-7 expression was unaffected. This observation argues that, while lips-7 may play a role in lifespan, its de-repression is not essential for the extension of lifespan phenotype. We show that a prominent site of LIPS-7 expression is the hypodermis, one of the sites of fat storage in C. elegans. Interestingly, we did not observe co-localisation of CTBP-1 and lips-7 transcription in the nervous system, indicating that CTBP-1 may be acting indirectly, in a cell non-autonomous manner. In summary, our data confirm that CTBP-1 is involved in the regulation of lips-7 transcription but suggest that it may perform additional roles in the nervous system that contribute to the regulation of longevity.

Spermidine feeding decreases age-related locomotor activity loss and induces changes in lipid composition

Spermidine is a natural polyamine involved in many important cellular functions, whose supplementation in food or water increases life span and stress resistance in several model organisms. In this work, we expand spermidine's range of age-related beneficial effects by demonstrating that it is also able to improve locomotor performance in aged flies. Spermidine's mechanism of action on aging has been primarily related to general protein hypoacetylation that subsequently induces autophagy. Here, we suggest that the molecular targets of spermidine also include lipid metabolism: Spermidine-fed flies contain more triglycerides and show altered fatty acid and phospholipid profiles. We further determine that most of these metabolic changes are regulated through autophagy. Collectively, our data suggests an additional and novel lipid-mediated mechanism of action for spermidine-induced autophagy.

Lifelong treatment with atenolol decreases membrane fatty acid unsaturation and oxidative stress in heart and skeletal muscle mitochondria and improves immunity and behavior, without changing mice longevity

The membrane fatty acid unsaturation hypothesis of aging and longevity is experimentally tested for the first time in mammals. Lifelong treatment of mice with the β1-blocker atenolol increased the amount of the extracellular-signal-regulated kinase signaling protein and successfully decreased one of the two traits appropriately correlating with animal longevity, the membrane fatty acid unsaturation degree of cardiac and skeletal muscle mitochondria, changing their lipid profile toward that present in much more longer-lived mammals. This was mainly due to decreases in 22:6n-3 and increases in 18:1n-9 fatty acids. The atenolol treatment also lowered visceral adiposity (by 24%), decreased mitochondrial protein oxidative, glycoxidative, and lipoxidative damage in both organs, and lowered oxidative damage in heart mitochondrial DNA. Atenolol also improved various immune (chemotaxis and natural killer activities) and behavioral functions (equilibrium, motor coordination, and muscular vigor). It also totally or partially prevented the aging-related detrimental changes observed in mitochondrial membrane unsaturation, protein oxidative modifications, and immune and behavioral functions, without changing longevity. The controls reached 3.93 years of age, a substantially higher maximum longevity than the best previously described for this strain (3.0 years). Side effects of the drug could have masked a likely lowering of the endogenous aging rate induced by the decrease in membrane fatty acid unsaturation. We conclude that it is atenolol that failed to increase longevity, and likely not the decrease in membrane unsaturation induced by the drug.

Making heads or tails of mitochondrial membranes in longevity and aging: a role for comparative studies

Mitochondria play vital roles in metabolic energy transduction, intermediate molecule metabolism, metal ion homeostasis, programmed cell death and regulation of the production of reactive oxygen species. As a result of their broad range of functions, mitochondria have been strongly implicated in aging and longevity. Numerous studies show that aging and decreased lifespan are also associated with high reactive oxygen species production by mitochondria, increased mitochondrial DNA and protein damage, and with changes in the fatty acid composition of mitochondrial membranes. It is possible that the extent of fatty acid unsaturation of the mitochondrial membrane determines susceptibility to lipid oxidative damage and downstream protein and genome toxicity, thereby acting as a determinant of aging and lifespan. Reviewing the vast number of comparative studies on mitochondrial membrane composition, metabolism and lifespan reveals some evidence that lipid unsaturation ratios may correlate with lifespan. However, we caution against simply relating these two traits. They may be correlative but have no functional relation. We discuss an important methodology for body mass and phylogenetic correction in comparative studies.

Rapamycin extends life- and health span because it slows aging

Making headlines, a thought-provocative paper by Neff, Ehninger and coworkers claims that rapamycin extends life span but has limited effects on aging. How is that possibly possible? And what is aging if not an increase of the probability of death with age. I discuss that the JCI paper actually shows that rapamycin slows aging and also extends lifespan regardless of its direct anti-cancer activities. Aging is, in part, MTOR-driven: a purposeless continuation of developmental growth. Rapamycin affects the same processes in young and old animals: young animals' traits and phenotypes, which continuations become hyperfunctional, harmful and lethal later in life.