Mitochondrial S-adenosylmethionine deficiency induces mitochondrial unfolded protein response and extends lifespan in Caenorhabditis elegans.

S-adenosylmethionine (SAM), generated from methionine and ATP by S-adenosyl methionine synthetase (SAMS), is the universal methyl group donor required for numerous cellular methylation reactions. In Caenorhabditis elegans, silencing sams-1, the major isoform of SAMS, genetically or via dietary restriction induces a robust mitochondrial unfolded protein response (UPRmt) and lifespan extension. In this study, we found that depleting SAMS-1 markedly decreases mitochondrial SAM levels. Moreover, RNAi knockdown of SLC-25A26, a carrier protein responsible for transporting SAM from the cytoplasm into the mitochondria, significantly lowers the mitochondrial SAM levels and activates UPRmt, suggesting that the UPRmt induced by sams-1 mutations might result from disrupted mitochondrial SAM homeostasis. Through a genetic screen, we then identified a putative mitochondrial tRNA methyltransferase TRMT-10C.2 as a major downstream effector of SAMS-1 to regulate UPRmt and longevity. As disruption of mitochondrial tRNA methylation likely leads to impaired mitochondrial tRNA maturation and consequently reduced mitochondrial translation, our findings suggest that depleting mitochondrial SAM level might trigger UPRmt via attenuating protein translation in the mitochondria. Together, this study has revealed a potential mechanism by which SAMS-1 regulates UPRmt and longevity.

Reduced Ribose-5-Phosphate Isomerase A-1 Expression in Specific Neurons and Time Points Promotes Longevity in Caenorhabditis elegans.

Deregulation of redox homeostasis is often associated with an accelerated aging process. Ribose-5-phosphate isomerase A (RPIA) mediates redox homeostasis in the pentose phosphate pathway (PPP). Our previous study demonstrated that Rpi knockdown boosts the healthspan in Drosophila. However, whether the knockdown of rpia-1, the Rpi ortholog in Caenorhabditis elegans, can improve the healthspan in C. elegans remains unknown. Here, we report that spatially and temporally limited knockdown of rpia-1 prolongs lifespan and improves the healthspan in C. elegans, reflecting the evolutionarily conserved phenotypes observed in Drosophila. Ubiquitous and pan-neuronal knockdown of rpia-1 both enhance tolerance to oxidative stress, reduce polyglutamine aggregation, and improve the deteriorated body bending rate caused by polyglutamine aggregation. Additionally, rpia-1 knockdown temporally in the post-developmental stage and spatially in the neuron display enhanced lifespan. Specifically, rpia-1 knockdown in glutamatergic or cholinergic neurons is sufficient to increase lifespan. Importantly, the lifespan extension by rpia-1 knockdown requires the activation of autophagy and AMPK pathways and reduced TOR signaling. Moreover, the RNA-seq data support our experimental findings and reveal potential novel downstream targets. Together, our data disclose the specific spatial and temporal conditions and the molecular mechanisms for rpia-1 knockdown-mediated longevity in C. elegans. These findings may help the understanding and improvement of longevity in humans.

SAMS-1 coordinates HLH-30/TFEB and PHA-4/FOXA activities through histone methylation to mediate dietary restriction-induced autophagy and longevity.

Dietary restriction (DR) is known to promote autophagy to exert its longevity effect. While SAMS-1 (S-adenosyl methionine synthetase-1) has been shown to be a key mediator of the DR response, little is known about the roles of S-adenosyl methionine (SAM) and SAM-dependent methyltransferase in autophagy and DR-induced longevity. In this study, we show that DR and SAMS-1 repress the activity of SET-2, a histone H3K4 methyltransferase, by limiting the availability of SAM. Consequently, the reduced H3K4me3 levels promote the expression and activity of two transcription factors, HLH-30/TFEB and PHA-4/FOXA, which both regulate the transcription of autophagy-related genes. We then find that HLH-30/TFEB and PHA-4/FOXA act collaboratively on their common target genes to mediate the transcriptional response of autophagy-related genes and consequently the lifespan of the animals. Our study thus shows that the SAMS-1-SET-2 axis serves as a nutrient-sensing module to epigenetically coordinate the activation of HLH-30/TFEB and PHA-4/FOXA transcription factors to control macroautophagy/autophagy and longevity in response to DR.Abbreviations: ChIP: chromatin immunoprecipitation; ChIP-seq: chromatin immuno precipitation-sequencing; COMPASS: complex of proteins associated with Set1; DR: dietary restriction; GO: gene ontology; SAM: S-adenosyl methionine; SAMS-1: S-adenosyl methionine synthetase-1; TSS: transcription start site; WT: wild-type.

Isocitrate Dehydrogenase Alpha-1 Modulates Lifespan and Oxidative Stress Tolerance in Caenorhabditis elegans.

Altered metabolism is a hallmark of aging. The tricarboxylic acid cycle (TCA cycle) is an essential metabolic pathway and plays an important role in lifespan regulation. Supplementation of α-ketoglutarate, a metabolite converted by isocitrate dehydrogenase alpha-1 (idha-1) in the TCA cycle, increases lifespan in C. elegans. However, whether idha-1 can regulate lifespan in C. elegans remains unknown. Here, we reported that the expression of idha-1 modulates lifespan and oxidative stress tolerance in C. elegans. Transgenic overexpression of idha-1 extends lifespan, increases the levels of NADPH/NADP+ ratio, and elevates the tolerance to oxidative stress. Conversely, RNAi knockdown of idha-1 exhibits the opposite effects. In addition, the longevity of eat-2 (ad1116) mutant via dietary restriction (DR) was reduced by idha-1 knockdown, indicating that idha-1 may play a role in DR-mediated longevity. Furthermore, idha-1 mediated lifespan may depend on the target of rapamycin (TOR) signaling. Moreover, the phosphorylation levels of S6 kinase (p-S6K) inversely correlate with idha-1 expression, supporting that the idha-1-mediated lifespan regulation may involve the TOR signaling pathway. Together, our data provide new insights into the understanding of idha-1 new function in lifespan regulation probably via DR and TOR signaling and in oxidative stress tolerance in C. elegans.

Graptopetalum paraguayense Extract Ameliorates Proteotoxicity in Aging and Age-Related Diseases in Model Systems.

Declines in physiological functions are the predominant risk factors for age-related diseases, such as cancers and neurodegenerative diseases. Therefore, delaying the aging process is believed to be beneficial in preventing the onset of age-related diseases. Previous studies have demonstrated that Graptopetalum paraguayense (GP) extract inhibits liver cancer cell growth and reduces the pathological phenotypes of Alzheimer's disease (AD) in patient IPS-derived neurons. Here, we show that GP extract suppresses ß-amyloid pathology in SH-SYS5Y-APP695 cells and APP/PS1 mice. Moreover, AMP-activated protein kinase (AMPK) activity is enhanced by GP extract in U87 cells and APP/PS1 mice. Intriguingly, GP extract enhances autophagy in SH-SYS5Y-APP695 cells, U87 cells, and the nematode Caenorhabditis elegans, suggesting a conserved molecular mechanism by which GP extract might regulate autophagy. In agreement with its role as an autophagy activator, GP extract markedly diminishes mobility decline in polyglutamine Q35 mutants and aged wild-type N2 animals in C. elegans. Furthermore, GP extract significantly extends lifespan in C. elegans.

Oil Red O Staining for Lipid Content in Caenorhabditis elegans.

The nematode Caenorhabditis elegans has emerged as a popular model system for studying the regulation of lipid metabolism. Therefore, it is critical to develop a method for determining fat storage in individual worms. Oil Red O (ORO) staining has been validated as an accurate assessment for major fat storage in C. elegans. Here, we describe an optimized protocol for ORO staining of C. elegans and provide detailed instructions for quantifying the intensity of ORO signal in images acquired by light microscopy.

S-adenosyl methionine synthetase SAMS-5 mediates dietary restriction-induced longevity in Caenorhabditis elegans.

S-adenosyl methionine synthetase (SAMS) catalyzes the biosynthesis of S-adenosyl methionine (SAM), which serves as a universal methyl group donor for numerous biochemical reactions. Previous studies have clearly demonstrated that SAMS-1, a C. elegans homolog of mammalian SAMS, is critical for dietary restriction (DR)-induced longevity in Caenorhabditis elegans. In addition to SAMS-1, three other SAMS paralogs have been identified in C. elegans. However, their roles in longevity regulation have never been explored. Here, we show that depletion of sams-5, but not sams-3 or sams-4, can extend lifespan in worms. However, the phenotypes and expression pattern of sams-5 are distinct from sams-1, suggesting that these two SAMSs might regulate DR-induced longevity via different mechanisms. Through the genetic epistasis analysis, we have identified that sams-5 is required for DR-induced longevity in a pha-4/FOXA dependent manner.

High-throughput small molecule screening reveals Nrf2-dependent and -independent pathways of cellular stress resistance.

Aging is the dominant risk factor for most chronic diseases. Development of antiaging interventions offers the promise of preventing many such illnesses simultaneously. Cellular stress resistance is an evolutionarily conserved feature of longevity. Here, we identify compounds that induced resistance to the superoxide generator paraquat (PQ), the heavy metal cadmium (Cd), and the DNA alkylator methyl methanesulfonate (MMS). Some rescue compounds conferred resistance to a single stressor, while others provoked multiplex resistance. Induction of stress resistance in fibroblasts was predictive of longevity extension in a published large-scale longevity screen in Caenorhabditis elegans, although not in testing performed in worms and flies with a more restricted set of compounds. Transcriptomic analysis and genetic studies implicated Nrf2/SKN-1 signaling in stress resistance provided by two protective compounds, cardamonin and AEG 3482. Small molecules identified in this work may represent attractive tools to elucidate mechanisms of stress resistance in mammalian cells.

HSB-1/HSF-1 pathway modulates histone H4 in mitochondria to control mtDNA transcription and longevity.

Heat shock factor-1 (HSF-1) is a master regulator of stress responses across taxa. Overexpression of HSF-1 or genetic ablation of its conserved negative regulator, heat shock factor binding protein 1 (HSB-1), results in robust life-span extension in Caenorhabditis elegans Here, we found that increased HSF-1 activity elevates histone H4 levels in somatic tissues during development, while knockdown of H4 completely suppresses HSF-1-mediated longevity. Moreover, overexpression of H4 is sufficient to extend life span. Ablation of HSB-1 induces an H4-dependent increase in micrococcal nuclease protection of both nuclear chromatin and mitochondrial DNA (mtDNA), which consequently results in reduced transcription of mtDNA-encoded complex IV genes, decreased respiratory capacity, and a mitochondrial unfolded protein response-dependent life-span extension. Collectively, our findings reveal a previously unknown role of HSB-1/HSF-1 signaling in modulation of mitochondrial function via mediating histone H4-dependent regulation of mtDNA gene expression and concomitantly acting as a determinant of organismal longevity.

Short-term enhancement of motor neuron synaptic exocytosis during early aging extends lifespan in Caenorhabditis elegans.

IMPACT STATEMENT: The functional decline of motor activity is a common feature in almost all aging animals that leads to frailty, loss of independence, injury, and even death in the elderly population. Thus, understanding the molecular mechanism that drives the initial stage of this functional decline and developing strategies to increase human healthspan and even lifespan by targeting this process would be of great interests to the field. In this study, we found that by precisely targeting the motor neurons to potentiate its synaptic releases either genetically or pharmacologically, we can not only delay the functional aging at NMJs but also slow the rate of aging at the organismal level. Most importantly, we have demonstrated that a critical window of time, that is the early stage of NMJs functional decline, is required for the beneficial effects. A short-term treatment within this time period is sufficient to extend the animals' lifespan.

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

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

Reciprocal Changes in Phosphoenolpyruvate Carboxykinase and Pyruvate Kinase with Age Are a Determinant of Aging in Caenorhabditis elegans.

Aging involves progressive loss of cellular function and integrity, presumably caused by accumulated stochastic damage to cells. Alterations in energy metabolism contribute to aging, but how energy metabolism changes with age, how these changes affect aging, and whether they can be modified to modulate aging remain unclear. In locomotory muscle of post-fertile Caenorhabditis elegans, we identified a progressive decrease in cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C), a longevity-associated metabolic enzyme, and a reciprocal increase in glycolytic pyruvate kinase (PK) that were necessary and sufficient to limit lifespan. Decline in PEPCK-C with age also led to loss of cellular function and integrity including muscle activity, and cellular senescence. Genetic and pharmacologic interventions of PEPCK-C, muscle activity, and AMPK signaling demonstrate that declines in PEPCK-C and muscle function with age interacted to limit reproductive life and lifespan via disrupted energy homeostasis. Quantifications of metabolic flux show that reciprocal changes in PEPCK-C and PK with age shunted energy metabolism toward glycolysis, reducing mitochondrial bioenergetics. Last, calorie restriction countered changes in PEPCK-C and PK with age to elicit anti-aging effects via TOR inhibition. Thus, a programmed metabolic event involving PEPCK-C and PK is a determinant of aging that can be modified to modulate aging.

Integrin-linked kinase modulates longevity and thermotolerance in C. elegans through neuronal control of HSF-1.

Integrin-signaling complexes play important roles in cytoskeletal organization and cell adhesion in many species. Components of the integrin-signaling complex have been linked to aging in both Caenorhabditis elegans and Drosophila melanogaster, but the mechanism underlying this function is unknown. Here, we investigated the role of integrin-linked kinase (ILK), a key component of the integrin-signaling complex, in lifespan determination. We report that genetic reduction of ILK in both C. elegans and Drosophila increased resistance to heat stress, and led to lifespan extension in C. elegans without majorly affecting cytoskeletal integrity. In C. elegans, longevity and thermotolerance induced by ILK depletion was mediated by heat-shock factor-1 (HSF-1), a major transcriptional regulator of the heat-shock response (HSR). Reduction in ILK levels increased hsf-1 transcription and activation, and led to enhanced expression of a subset of genes with roles in the HSR. Moreover, induction of HSR-related genes, longevity and thermotolerance caused by ILK reduction required the thermosensory neurons AFD and interneurons AIY, which are known to play a critical role in the canonical HSR. Notably, ILK was expressed in neighboring neurons, but not in AFD or AIY, implying that ILK reduction initiates cell nonautonomous signaling through thermosensory neurons to elicit a noncanonical HSR. Our results thus identify HSF-1 as a novel effector of the organismal response to reduced ILK levels and show that ILK inhibition regulates HSF-1 in a cell nonautonomous fashion to enhance stress resistance and lifespan in C. elegans.

Enhanced energy metabolism contributes to the extended life span of calorie-restricted Caenorhabditis elegans.

Caloric restriction (CR) markedly extends life span and improves the health of a broad number of species. Energy metabolism fundamentally contributes to the beneficial effects of CR, but the underlying mechanisms that are responsible for this effect remain enigmatic. A multidisciplinary approach that involves quantitative proteomics, immunochemistry, metabolic quantification, and life span analysis was used to determine how CR, which occurs in the Caenorhabditis elegans eat-2 mutants, modifies energy metabolism of the worm, and whether the observed modifications contribute to the CR-mediated physiological responses. A switch to fatty acid metabolism as an energy source and an enhanced rate of energy metabolism by eat-2 mutant nematodes were detected. Life span analyses validated the important role of these previously unknown alterations of energy metabolism in the CR-mediated longevity of nematodes. As observed in mice, the overexpression of the gene for the nematode analog of the cytosolic form of phosphoenolpyruvate carboxykinase caused a marked extension of the life span in C. elegans, presumably by enhancing energy metabolism via an altered rate of cataplerosis of tricarboxylic acid cycle anions. We conclude that an increase, not a decrease in fuel consumption, via an accelerated oxidation of fuels in the TCA cycle is involved in life span regulation; this mechanism may be conserved across phylogeny.

HSF-1 regulators DDL-1/2 link insulin-like signaling to heat-shock responses and modulation of longevity.

Extended longevity is often correlated with increased resistance against various stressors. Insulin/IGF-1-like signaling (IIS) is known to have a conserved role in aging and cellular mechanisms against stress. In C. elegans, genetic studies suggest that heat-shock transcription factor HSF-1 is required for IIS to modulate longevity. Here, we report that the activity of HSF-1 is regulated by IIS. This regulation occurs at an early step of HSF-1 activation via two HSF-1 regulators, DDL-1 and DDL-2. Inhibition of DDL-1/2 increases longevity and thermotolerance in an hsf-1-dependent manner. Furthermore, biochemical analyses suggest that DDL-1/2 negatively regulate HSF-1 activity by forming a protein complex with HSF-1. The formation of this complex (DHIC) is affected by the phosphorylation status of DDL-1. Both the formation of DHIC and the phosphorylation of DDL-1 are controlled by IIS. Our findings point to DDL-1/2 as a link between IIS and the HSF-1 pathway.

Solid plate-based dietary restriction in Caenorhabditis elegans.

Reduction of food intake without malnutrition or starvation is known to increase lifespan and delay the onset of various age-related diseases in a wide range of species, including mammals. It also causes a decrease in body weight and fertility, as well as lower levels of plasma glucose, insulin, and IGF-1 in these animals. This treatment is often referred to as dietary restriction (DR) or caloric restriction (CR). The nematode Caenorhabditis elegans has emerged as an important model organism for studying the biology of aging. Both environmental and genetic manipulations have been used to model DR and have shown to extend lifespan in C. elegans. However, many of the reported DR studies in C. elegans were done by propagating animals in liquid media, while most of the genetic studies in the aging field were done on the standard solid agar in petri plates. Here we present a DR protocol using standard solid NGM agar-based plate with killed bacteria.

Celecoxib extends C. elegans lifespan via inhibition of insulin-like signaling but not cyclooxygenase-2 activity.

One goal of aging research is to develop interventions that combat age-related illnesses and slow aging. Although numerous mutations have been shown to achieve this in various model organisms, only a handful of chemicals have been identified to slow aging. Here, we report that celecoxib, a nonsteroidal anti-inflammatory drug widely used to treat pain and inflammation, extends Caenorhabditis elegans lifespan and delays the age-associated physiological changes, such as motor activity decline. Celecoxib also delays the progression of age-related proteotoxicity as well as tumor growth in C. elegans. Celecoxib was originally developed as a potent cyclooxygenase-2 (COX-2) inhibitor. However, the result from a structural-activity analysis demonstrated that the antiaging effect of celecoxib might be independent of its COX-2 inhibitory activity, as analogs of celecoxib that lack COX-2 inhibitory activity produce a similar effect on lifespan. Furthermore, we found that celecoxib acts directly on 3'-phosphoinositide-dependent kinase-1, a component of the insulin/IGF-1 signaling cascade to increase lifespan.

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

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

Genome-wide hypomethylation in human glioblastomas associated with specific copy number alteration, methylenetetrahydrofolate reductase allele status, and increased proliferation.

Genome-wide reduction in 5-methylcytosine is an epigenetic hallmark of human tumorigenesis. Experimentally induced hypomethylation in mice promotes genomic instability and is sufficient to initiate tumorigenesis. Here, we report that global hypomethylation is common in primary human glioblastomas [glioblastoma multiforme (GBM)] and can affect up to an estimated 10 million CpG dinucleotides per haploid tumor genome. Demethylation involves satellite 2 (Sat2) pericentromeric DNA at chromosomes 1 and 16, the subtelomeric repeat sequence D4Z4 at chromosomes 4q and 10q, and interspersed Alu elements. Severe hypomethylation of Sat2 sequences is associated with copy number alterations of the adjacent euchromatin, suggesting that hypomethylation may be one factor predisposing to specific genetic alterations commonly occurring in GBMs. An additional apparent consequence of global hypomethylation is reactivation of the cancer-testis antigen MAGEA1 via promoter demethylation, but only in GBMs and GBM cell lines exhibiting a 5-methylcytosine content below a threshold of approximately 50%. Primary GBMs with significant hypomethylation tended to be heterozygous or homozygous for the low-functioning Val allele of the rate-limiting methyl group metabolism gene methylenetetrahydrofolate reductase (MTHFR), or had a deletion encompassing this gene at 1p36. Tumors with severe genomic hypomethylation also had an elevated proliferation index and deletion of the MTHFR gene. These data suggest a model whereby either excessive cell proliferation in the context of inadequate methyl donor production from MTHFR deficiency promotes genomic hypomethylation and further genomic instability, or that MTHFR deficiency-associated demethylation leads to increased proliferative activity in GBM.

Epigenome analyses using BAC microarrays identify evolutionary conservation of tissue-specific methylation of SHANK3.

CpG islands are present in one-half of all human and mouse genes and typically overlap with promoters or exons. We developed a method for high-resolution analysis of the methylation status of CpG islands genome-wide, using arrays of BAC clones and the methylation-sensitive restriction enzyme NotI. Here we demonstrate the accuracy and specificity of the method. By computationally mapping all NotI sites, methylation events can be defined with single-nucleotide precision throughout the genome. We also demonstrate the unique expandability of the array method using a different methylation-sensitive restriction enzyme, BssHII. We identified and validated new CpG island loci that are methylated in a tissue-specific manner in normal human tissues. The methylation status of the CpG islands is associated with gene expression for several genes, including SHANK3, which encodes a structural protein in neuronal postsynaptic densities. Defects in SHANK3 seem to underlie human 22q13 deletion syndrome. Furthermore, these patterns for SHANK3 are conserved in mice and rats.