A DNA synthesis inhibitor is protective against proteotoxic stressors via modulation of fertility pathways in Caenorhabditis elegans

Mechanical force of uterine occupation enables large vesicle extrusion from proteostressed maternal neurons

Large vesicle extrusion from neurons may contribute to spreading pathogenic protein aggregates and promoting inflammatory responses, two mechanisms leading to neurodegenerative disease. Factors that regulate extrusion of large vesicles, such as exophers produced by proteostressed C. elegans touch neurons, are poorly understood. Here we document that mechanical force can significantly potentiate exopher extrusion from proteostressed neurons. Exopher production from the C. elegans ALMR neuron peaks at adult day 2 or 3, coinciding with the C. elegans reproductive peak. Genetic disruption of C. elegans germline, sperm, oocytes, or egg/early embryo production can strongly suppress exopher extrusion from the ALMR neurons during the peak period. Conversely, restoring egg production at the late reproductive phase through mating with males or inducing egg retention via genetic interventions that block egg-laying can strongly increase ALMR exopher production. Overall, genetic interventions that promote ALMR exopher production are associated with expanded uterus lengths and genetic interventions that suppress ALMR exopher production are associated with shorter uterus lengths. In addition to the impact of fertilized eggs, ALMR exopher production can be enhanced by filling the uterus with oocytes, dead eggs, or even fluid, supporting that distention consequences, rather than the presence of fertilized eggs, constitute the exopher-inducing stimulus. We conclude that the mechanical force of uterine occupation potentiates exopher extrusion from proximal proteostressed maternal neurons. Our observations draw attention to the potential importance of mechanical signaling in extracellular vesicle production and in aggregate spreading mechanisms, making a case for enhanced attention to mechanobiology in neurodegenerative disease.

A novel endoplasmic reticulum adaptation is critical for the long-lived Caenorhabditis elegans rpn-10 proteasomal mutant

The loss of proteostasis due to reduced efficiency of protein degradation pathways plays a key role in multiple age-related diseases and is a hallmark of the aging process. Paradoxically, we have previously reported that the Caenorhabditis elegans rpn-10(ok1865) mutant, which lacks the RPN-10/RPN10/PSMD4 subunit of the 19S regulatory particle of the 26S proteasome, exhibits enhanced cytosolic proteostasis, elevated stress resistance and extended lifespan, despite possessing reduced proteasome function. However, the response of this mutant against threats to endoplasmic reticulum (ER) homeostasis and proteostasis was unknown. Here, we find that the rpn-10 mutant is highly ER stress resistant compared to the wildtype. Under unstressed conditions, the ER unfolded protein response (UPR) is activated in the rpn-10 mutant as signified by increased xbp-1 splicing. This primed response appears to alter ER homeostasis through the upregulated expression of genes involved in ER protein quality control (ERQC), including those in the ER-associated protein degradation (ERAD) pathway. Pertinently, we find that ERQC is critical for the rpn-10 mutant longevity. These changes also alter ER proteostasis, as studied using the C. elegans alpha-1 antitrypsin (AAT) deficiency model, which comprises an intestinal ER-localised transgenic reporter of an aggregation-prone form of AAT called ATZ. The rpn-10 mutant shows a significant reduction in the accumulation of the ATZ reporter, thus indicating that its ER proteostasis is augmented. Via a genetic screen for suppressors of decreased ATZ aggregation in the rpn-10 mutant, we then identified ecps-2/H04D03.3, a novel ortholog of the proteasome-associated adaptor and scaffold protein ECM29/ECPAS. We further show that ecps-2 is required for improved ER proteostasis as well as lifespan extension of the rpn-10 mutant. Thus, we propose that ECPS-2-proteasome functional interactions, alongside additional putative molecular processes, contribute to a novel ERQC adaptation which underlies the superior proteostasis and longevity of the rpn-10 mutant.

CeLab, a microfluidic platform for the study of life history traits, reveals metformin and SGK-1 regulation of longevity and reproductive span

The potential to carry out high-throughput assays in a whole organism in a small space is one of the benefits of C. elegans, but worm assays often require a large sample size with frequent physical manipulations, rendering them highly labor-intensive. Microfluidic assays have been designed with specific questions in mind, such as analysis of behavior, embryonic development, lifespan, and motility. While these devices have many advantages, current technologies to automate worm experiments have several limitations that prevent widespread adoption, and most do not allow analyses of reproduction-linked traits. We developed a miniature C. elegans lab-on-a-chip device, CeLab, a reusable, multi-layer device with 200 separate incubation arenas that allows progeny removal, to automate a variety of worm assays on both individual and population levels. CeLab enables high-throughput simultaneous analysis of lifespan, reproductive span, and progeny production, refuting assumptions about the disposable soma hypothesis. Because CeLab chambers require small volumes, the chip is ideal for drug screens; we found that drugs previously shown to increase lifespan also increase reproductive span, and we discovered that low-dose metformin increases both. CeLab reduces the limitations of escaping and matricide that typically limit plate assays, revealing that feeding with heat-killed bacteria greatly extends lifespan and reproductive span of mated animals. CeLab allows tracking of life history traits of individuals, which revealed that the nutrient-sensing mTOR pathway mutant, sgk-1, reproduces nearly until its death. These findings would not have been possible to make in standard plate assays, in low-throughput assays, or in normal population assays.

Large-scale sampling of C. elegans on E. coli HT115 RNAi-compatible bacteria

As opposed to standard culturing, growing large numbers of C. elegans worms on Nematode Growth Medium-based RNA interference (RNAi) plates requires multiple transferring steps to prevent starvation, which increase handling time and reduce practical efficiency. We here provide an optimized method to grow four times more worms in RNAi conditions, thus saving on required resources and handling steps.

The mitochondrial permeability transition pore activates the mitochondrial unfolded protein response and promotes aging

Mitochondrial activity determines aging rate and the onset of chronic diseases. The mitochondrial permeability transition pore (mPTP) is a pathological pore in the inner mitochondrial membrane thought to be composed of the F-ATP synthase (complex V). OSCP, a subunit of F-ATP synthase, helps protect against mPTP formation. How the destabilization of OSCP may contribute to aging, however, is unclear. We have found that loss OSCP in the nematode Caenorhabditis elegans initiates the mPTP and shortens lifespan specifically during adulthood, in part via initiation of the mitochondrial unfolded protein response (UPR^mt). Pharmacological or genetic inhibition of the mPTP inhibits the UPR^mt and restores normal lifespan. Loss of the putative pore-forming component of F-ATP synthase extends adult lifespan, suggesting that the mPTP normally promotes aging. Our findings reveal how an mPTP/UPR^mt nexus may contribute to aging and age-related diseases and how inhibition of the UPR^mt may be protective under certain conditions.

Effects of FUdR on gene expression in the C. elegans bacterial diet OP50

Objective

Many C. elegans aging studies use the compound 5-fluro-2ʹ-deoxyuridine (FUdR) to produce a synchronous population of worms. However, the effects of FUdR on the bacterial gene expression of OP50 E. coli, the primary laboratory C. elegans food source, is not fully understood. This is particularly relevant as studies suggest that intestinal microbes can affect C. elegans physiology. Therefore, it is imperative that we understand how exposure to FUdR can affect gene expression changes in OP50 E. coli.

Results

An RNAseq dataset comprised of expression patterns of 2900 E. coli genes in the strain OP50, which were seeded on either nematode growth media (NGM) plates or on FUdR (50 µM) supplemented NGM plates, was analyzed. Analysis showed differential gene expression in genes involved in general transport, amino acid biosynthesis, transcription, iron transport, and antibiotic resistance. We specifically highlight metabolic enzymes in the l-histidine biosynthesis pathway as differentially expressed between NGM and FUdR exposed OP50. We conclude that OP50 exposed to FUdR results in differential expression of many genes, including those in amino acid biosynthetic pathways.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13104-021-05624-6.

Health and longevity studies in C. elegans: the "healthy worm database" reveals strengths, weaknesses and gaps of test compound-based studies

Several biogerontology databases exist that focus on genetic or gene expression data linked to health as well as survival, subsequent to compound treatments or genetic manipulations in animal models. However, none of these has yet collected experimental results of compound-related health changes. Since quality of life is often regarded as more valuable than length of life, we aim to fill this gap with the “Healthy Worm Database” (http://healthy-worm-database.eu). Literature describing health-related compound studies in the aging model Caenorhabditis elegans was screened, and data for 440 compounds collected. The database considers 189 publications describing 89 different phenotypes measured in 2995 different conditions. Besides enabling a targeted search for promising compounds for further investigations, this database also offers insights into the research field of studies on healthy aging based on a frequently used model organism. Some weaknesses of C. elegans-based aging studies, like underrepresented phenotypes, especially concerning cognitive functions, as well as the convenience-based use of young worms as the starting point for compound treatment or phenotype measurement are discussed. In conclusion, the database provides an anchor for the search for compounds affecting health, with a link to public databases, and it further highlights some potential shortcomings in current aging research.

Inhibition of PAR-1 delays aging via activating AMPK in C. elegans

The antagonistic pleiotropy theory of aging suggests that genes essential for growth and development are likely to modulate aging later in life. Previous studies in C. elegans demonstrate that inhibition of certain developmentally essential genes during adulthood leads to significant lifespan extension. PAR-1, a highly conserved serine/threonine kinase, functions as a key cellular polarity regulator during the embryonic development. However, the role of PAR-1 during adulthood remains unknown. Here we show that inhibition of par-1 either by a temperature-sensitive mutant or by RNAi knockdown only during adulthood is sufficient to extend lifespan in C. elegans. Inhibition of par-1 also improves healthspan, as indicated by increased stress resistance, enhanced proteotoxicity resistance, as well as reduced muscular function decline over time. Additionally, tissue-enriched RNAi knockdown analysis reveals that PAR-1 mainly functions in the epidermis to regulate lifespan. Further genetic epistatic and molecular studies demonstrate that the effect of par-1 on lifespan requires the AMP-activated protein kinase (AMPK), and RNAi knockdown of par-1 results in age-dependent AMPK activation and reduced lipid accumulation in the metabolic tissue. Taken together, our findings reveal a previously undescribed function of PAR-1 in adulthood, which will help to understand the molecular links between development and aging.

NemaLife chip: a micropillar-based microfluidic culture device optimized for aging studies in crawling C. elegans

In this study, we report a microfluidic device for the whole-life culture of the nematode Caenorhabditis elegans that allows the scoring of animal survival and health measures. This device referred to as the NemaLife chip features: (1) an optimized micropillar arena in which animals can crawl, (2) sieve channels that separate progeny and prevent the loss of adults from the arena during culture maintenance, and (3) ports that allow rapid accessibility for feeding the adult-only population and introducing reagents as needed. The pillar arena geometry was optimized to accommodate the growing body size during culture and emulate the body gait and locomotion of animals reared on agar. Likewise, feeding protocols were optimized to recapitulate longevity outcomes typical of standard plate growth. Key benefits of the NemaLife Chip include eliminating the need to perform repeated manual transfers of adults during survival assays, negating the need for progeny-blocking chemical interventions, and avoiding the swim-induced stress across lifespan in animals reared in liquid. We also show that the culture of animals in pillar-less microfluidic chambers reduces lifespan and introduces physiological stress by increasing the occurrence of age-related vulval integrity disorder. We validated our pillar-based device with longevity analyses of classical aging mutants (daf-2, age-1, eat-2, and daf-16) and animals subjected to RNAi knockdown of age-related genes (age-1 and daf-16). We also showed that healthspan measures such as pharyngeal pumping and tap-induced stimulated reversals can be scored across the lifespan in the NemaLife chip. Overall, the capacity to generate reliable lifespan and physiological data underscores the potential of the NemaLife chip to accelerate healthspan and lifespan investigations in C. elegans.

Quantification of Insoluble Protein Aggregation in Caenorhabditis elegans during Aging with a Novel Data-Independent Acquisition Workflow

We and others have shown that the aging process results in a proteome-wide accumulation of insoluble proteins. Knocking down genes encoding the insoluble proteins over 40% of the time results in an extension of the lifespan in C. elegans, suggesting that many of these proteins are key determinants of the aging process. Isolation and quantitative identification of these insoluble proteins are crucial to understand key biological processes that occur during aging. Here, we present a modified and improved protocol that details how to extract and isolate the SDS-insoluble proteins (insolublome) from C. elegans more efficiently to streamline mass spectrometric workflows via a novel label-free quantitative proteomics analysis. This improved protocol utilizes a highly efficient sonicator for worm lysis that greatly increases efficiency for protein extraction and allows us to use significantly less starting material (approximately 3,000 worms) than in previous protocols (typically using at least 40,000 worms). Subsequent quantitative proteomic analysis of the insolublome was performed using data-dependent acquisition (DDA) for protein discovery and identification and data-independent acquisition (DIA) for comprehensive and more accurate protein quantification. Bioinformatic analysis of quantified proteins provides potential candidates that can be easily followed up with other molecular methods in C. elegans. With this workflow, we routinely identify more than 1000 proteins and quantify more than 500 proteins. This new protocol enables efficient compound screening with C. elegans. Here, we validated and applied this improved protocol to wild-type C. elegans N2-Bristol strain and confirmed that aged day-10 N2 worms showed greater accumulation of the insolublome than day-2 young worms.

Phenotypic Screening in C. elegans as a Tool for the Discovery of New Geroprotective Drugs

Population aging is one of the largest challenges of the 21st century. As more people live to advanced ages, the prevalence of age-related diseases and disabilities will increase placing an ever larger burden on our healthcare system. A potential solution to this conundrum is to develop treatments that prevent, delay or reduce the severity of age-related diseases by decreasing the rate of the aging process. This ambition has been accomplished in model organisms through dietary, genetic and pharmacological interventions. The pharmacological approaches hold the greatest opportunity for successful translation to the clinic. The discovery of such pharmacological interventions in aging requires high-throughput screening strategies. However, the majority of screens performed for geroprotective drugs in C. elegans so far are rather low throughput. Therefore, the development of high-throughput screening strategies is of utmost importance.

Microfluidic Technologies for High Throughput Screening Through Sorting and On-Chip Culture of C. elegans

The nematode Caenorhabditis elegans is a powerful model organism that has been widely used to study molecular biology, cell development, neurobiology, and aging. Despite their use for the past several decades, the conventional techniques for growth, imaging, and behavioral analysis of C. elegans can be cumbersome, and acquiring large data sets in a high-throughput manner can be challenging. Developments in microfluidic “lab-on-a-chip” technologies have improved studies of C. elegans by increasing experimental control and throughput. Microfluidic features such as on-chip control layers, immobilization channels, and chamber arrays have been incorporated to develop increasingly complex platforms that make experimental techniques more powerful. Genetic and chemical screens are performed on C. elegans to determine gene function and phenotypic outcomes of perturbations, to test the effect that chemicals have on health and behavior, and to find drug candidates. In this review, we will discuss microfluidic technologies that have been used to increase the throughput of genetic and chemical screens in C. elegans. We will discuss screens for neurobiology, aging, development, behavior, and many other biological processes. We will also discuss robotic technologies that assist in microfluidic screens, as well as alternate platforms that perform functions similar to microfluidics.

Reactivation of RNA metabolism underlies somatic restoration after adult reproductive diapause in C. elegans

The mechanisms underlying biological aging are becoming recognized as therapeutic targets to delay the onset of multiple age-related morbidities. Even greater health benefits can potentially be achieved by halting or reversing age-associated changes. C. elegans restore their tissues and normal longevity upon exit from prolonged adult reproductive diapause, but the mechanisms underlying this phenomenon remain unknown. Here, we focused on the mechanisms controlling recovery from adult diapause. Here, we show that functional improvement of post-mitotic somatic tissues does not require germline signaling, germline stem cells, or replication of nuclear or mitochondrial DNA. Instead a large expansion of the somatic RNA pool is necessary for restoration of youthful function and longevity. Treating animals with the drug 5-fluoro-2'-deoxyuridine prevents this restoration by blocking reactivation of RNA metabolism. These observations define a critical early step during exit from adult reproductive diapause that is required for somatic rejuvenation of an adult metazoan animal.

Sex-specific regulation of aging in Caenorhabditis elegans

A fascinating aspect of sexual dimorphism in various animal species is that the two sexes differ substantially in lifespan. In humans, for example, women's life expectancy exceeds that of men by 3-7 years. Whether this trait can be attributed to dissimilar lifestyles or genetic (regulatory) factors remains to be elucidated. Herein, we demonstrate that in the nematode Caenorhabditis elegans, the significantly longer lifespan of hermaphrodites-which are essentially females capable of sperm production-over males is established by TRA-1, the terminal effector of the sex-determination pathway. This transcription factor directly controls the expression of daf-16/FOXO, which functions as a major target of insulin/IGF-1 signaling (IIS) and key modulator of aging across diverse animal phyla. TRA-1 extends hermaphrodite lifespan through promoting daf-16 activity. Furthermore, TRA-1 also influences reproductive growth in a DAF-16-dependent manner. Thus, the sex-determination machinery is an important regulator of IIS in this organism. These findings provide a mechanistic insight into how longevity and development are specified unequally in the two genders. As TRA-1 is orthologous to mammalian GLI (glioma-associated) proteins, a similar sex-specific mechanism may also operate in humans to determine lifespan.

A Simple Method for High Throughput Chemical Screening in Caenorhabditis Elegans

Caenorhabditis elegans is a useful organism for testing chemical effects on physiology. Whole organism small molecule screens offer significant advantages for identifying biologically active chemical structures that can modify complex phenotypes such as lifespan. Described here is a simple protocol for producing hundreds of 96-well culture plates with fairly consistent numbers of C. elegans in each well. Next, we specified how to use these cultures to screen thousands of chemicals for effects on the lifespan of the nematode C. elegans. This protocol makes use of temperature sensitive sterile strains, agar plate conditions, and simple animal handling to facilitate the rapid and high throughput production of synchronized animal cultures for screening.

Methods to Study Changes in Inherent Protein Aggregation with Age in Caenorhabditis elegans

In the last decades, the prevalence of neurodegenerative disorders, such as Alzheimer's disease (AD) and Parkinson's disease (PD), has grown. These age-associated disorders are characterized by the appearance of protein aggregates with fibrillary structure in the brains of these patients. Exactly why normally soluble proteins undergo an aggregation process remains poorly understood. The discovery that protein aggregation is not limited to disease processes and instead part of the normal aging process enables the study of the molecular and cellular mechanisms that regulate protein aggregation, without using ectopically expressed human disease-associated proteins. Here we describe methodologies to examine inherent protein aggregation in Caenorhabditis elegans through complementary approaches. First, we examine how to grow large numbers of age-synchronized C. elegans to obtain aged animals and we present the biochemical procedures to isolate highly-insoluble-large aggregates. In combination with a targeted genetic knockdown, it is possible to dissect the role of a gene of interest in promoting or preventing age-dependent protein aggregation by using either a comprehensive analysis with quantitative mass spectrometry or a candidate-based analysis with antibodies. These findings are then confirmed by in vivo analysis with transgenic animals expressing fluorescent-tagged aggregation-prone proteins. These methods should help clarify why certain proteins are prone to aggregate with age and ultimately how to keep these proteins fully functional.

Quantification of Information Encoded by Gene Expression Levels During Lifespan Modulation Under Broad-range Dietary Restriction in C. elegans

Sensory systems allow animals to detect, process, and respond to their environment. Food abundance is an environmental cue that has profound effects on animal physiology and behavior. Recently, we showed that modulation of longevity in the nematode Caenorhabditis elegans by food abundance is more complex than previously recognized. The responsiveness of the lifespan to changes in food level is determined by specific genes that act by controlling information processing within a neural circuit. Our framework combines genetic analysis, high-throughput quantitative imaging and information theory. Here, we describe how these techniques can be used to characterize any gene that has a physiological relevance to broad-range dietary restriction. Specifically, this workflow is designed to reveal how a gene of interest regulates lifespan under broad-range dietary restriction; then to establish how the expression of the gene varies with food level; and finally, to provide an unbiased quantification of the amount of information conveyed by gene expression about food abundance in the environment. When several genes are examined simultaneously under the context of a neural circuit, this workflow can uncover the coding strategy employed by the circuit.

Bacillus subtilis biofilm extends Caenorhabditis elegans longevity through downregulation of the insulin-like signalling pathway

Beneficial bacteria have been shown to affect host longevity, but the molecular mechanisms mediating such effects remain largely unclear. Here we show that formation of Bacillus subtilis biofilms increases Caenorhabditis elegans lifespan. Biofilm-proficient B. subtilis colonizes the C. elegans gut and extends worm lifespan more than biofilm-deficient isogenic strains. Two molecules produced by B. subtilis — the quorum-sensing pentapeptide CSF and nitric oxide (NO) — are sufficient to extend C. elegans longevity. When B. subtilis is cultured under biofilm-supporting conditions, the synthesis of NO and CSF is increased in comparison with their production under planktonic growth conditions. We further show that the prolongevity effect of B. subtilis biofilms depends on the DAF-2/DAF-16/HSF-1 signalling axis and the downregulation of the insulin-like signalling (ILS) pathway.

Probiotic bacteria can improve host health, but the mechanisms underlying such beneficial effects are often unclear. Here, the authors show that biofilm formation of the probiotic bacterium B. subtilis extends the lifespan of its host, the nematode C. elegans, by reducing insulin-like signalling.

FUdR extends the lifespan of the short-lived AP endonuclease mutant in Caenorhabditis elegans in a fertility-dependent manner

The anticancer drug 5-fluorouracil (5-FU) and its metabolite 5-fluoro-2'-deoxyuridine (FUdR) inhibit thymidylate synthase and induce uracil bases in DNA. FUdR is commonly used for inhibiting fertility when measuring the lifespan of the nematode Caenorhabditis elegans. However, it is not known whether DNA damage induced by FUdR affects lifespan. EXO-3 is an apurinic/apyrimidinic endonuclease in C. elegans, and we reported previously that deletion of the exo-3 gene causes reproductive abnormalities and decreased lifespan. In this study, we found that FUdR extended the lifespan of exo-3 mutants. We measured the lifespan of multiple germline mutants to examine whether this lifespan extension effect was dependent on fertility. In the presence of a fem-1 mutation, which causes a deficiency in sperm production, FUdR did not extend the lifespan of the exo-3 mutant. In glp-1 mutants, which do not develop gonads, the exo-3 mutant was not short-lived, and FUdR did not extend its lifespan. These results suggest that the lifespan extension effect of FUdR depends on fertility and the presence of gonads. fem-3 mutants, which do not produce oocytes, had increased lifespan in the presence of FUdR, independent of the exo-3 mutation. It is possible that the fem-3 mutant was susceptible to the lifespan extension effect of FUdR. From these results, we suggest that FUdR affects the lifespan of C. elegans in two ways: by interfering with fertility, which extends lifespan, and by inducing DNA base damage, which reduces lifespan.

Cranberry Product Decreases Fat Accumulation in Caenorhabditis elegans

Cranberry phenolic compounds have been linked to many health benefits. A recent report suggested that cranberry bioactives inhibit adipogenesis in 3T3-L1 adipocytes. Thus, we investigated the effects and mechanisms of the cranberry product (CP) on lipid metabolism using the Caenorhabditis elegans (C. elegans) model. CP (0.016% and 0.08%) dose-dependently reduced overall fat accumulation in C. elegans (N2, wild type) by 43% and 74%, respectively, without affecting its pumping rates or locomotive activities. CP decreased fat accumulation in aak-2 (an ortholog of AMP-activated kinase α) and tub-1 (an ortholog of TUBBY) mutants significantly, but only minimal effects were observed in sbp-1 (an ortholog of sterol response element-binding protein-1) and nhr-49 (an ortholog of peroxisome proliferator-activated receptor-α) mutant strains. We further confirmed that CP downregulated sbp-1, cebp, and hosl-1 (an ortholog of hormone-sensitive lipase homolog) expression, while increasing the expression of nhr-49 in wild-type C. elegans. These results suggest that CP could effectively reduce fat accumulation in C. elegans dependent on sbp-1, cebp, and nhr-49, but not aak-2 and tub-1.

C. elegans lifespan extension by osmotic stress requires FUdR, base excision repair, FOXO, and sirtuins

Moderate stress can increase lifespan by hormesis, a beneficial low-level induction of stress response pathways. 5'-fluorodeoxyuridine (FUdR) is commonly used to sterilize Caenorhabditis elegans in aging experiments. However, FUdR alters lifespan in some genotypes and induces resistance to thermal and proteotoxic stress. We report that hypertonic stress in combination with FUdR treatment or inhibition of the FUdR target thymidylate synthase, TYMS-1, extends C. elegans lifespan by up to 30%. By contrast, in the absence of FUdR, hypertonic stress decreases lifespan. Adaptation to hypertonic stress requires diminished Notch signaling and loss of Notch co-ligands leads to lifespan extension only in combination with FUdR. Either FUdR treatment or TYMS-1 loss induced resistance to acute hypertonic stress, anoxia, and thermal stress. FUdR treatment increased expression of DAF-16 FOXO and the osmolyte biosynthesis enzyme GPDH-1. FUdR-induced hypertonic stress resistance was partially dependent on sirtuins and base excision repair (BER) pathways, while FUdR-induced lifespan extension under hypertonic stress conditions requires DAF-16, BER, and sirtuin function. Combined, these results demonstrate that FUdR, through inhibition of TYMS-1, activates stress response pathways in somatic tissues to confer hormetic resistance to acute and chronic stress. C. elegans lifespan studies using FUdR may need re-interpretation in light of this work.

It's all in your mind: determining germ cell fate by neuronal IRE-1 in C. elegans

The C. elegans germline is pluripotent and mitotic, similar to self-renewing mammalian tissues. Apoptosis is triggered as part of the normal oogenesis program, and is increased in response to various stresses. Here, we examined the effect of endoplasmic reticulum (ER) stress on apoptosis in the C. elegans germline. We demonstrate that pharmacological or genetic induction of ER stress enhances germline apoptosis. This process is mediated by the ER stress response sensor IRE-1, but is independent of its canonical downstream target XBP-1. We further demonstrate that ire-1-dependent apoptosis in the germline requires both CEP-1/p53 and the same canonical apoptotic genes as DNA damage-induced germline apoptosis. Strikingly, we find that activation of ire-1, specifically in the ASI neurons, but not in germ cells, is sufficient to induce apoptosis in the germline. This implies that ER stress related germline apoptosis can be determined at the organism level, and is a result of active IRE-1 signaling in neurons. Altogether, our findings uncover ire-1 as a novel cell non-autonomous regulator of germ cell apoptosis, linking ER homeostasis in sensory neurons and germ cell fate.

Fluorodeoxyuridine enhances the heat shock response and decreases polyglutamine aggregation in an HSF-1-dependent manner in Caenorhabditis elegans

The heat shock response (HSR) protects cells from protein-denaturing stress through the induction of chaperones. The HSR is conserved in all organisms and is mediated by the transcription factor HSF-1. We show here that a compound commonly used to prevent larval development in Caenorhabditis elegans, 5-fluoro-2'-deoxyuridine (FUdR), can enhance heat shock induction of hsp mRNA in an HSF-1-dependent manner. Treatment with FUdR can also decrease age-dependent polyglutamine aggregation in a Huntington's disease model, and this effect depends on HSF-1 as well. Therefore, FUdR treatment can modulate the HSR and proteostasis, and should be used with caution when used to inhibit reproduction.

Effects of 5'-fluoro-2-deoxyuridine on mitochondrial biology in Caenorhabditis elegans

5-Fluoro-2'-deoxyuridine (FUdR) is a DNA synthesis inhibitor commonly used to sterilize Caenorhabditis elegans in order to maintain a synchronized aging population of nematodes, without contamination by their progeny, in lifespan experiments. All somatic cells in the adult nematode are post-mitotic and therefore do not require nuclear DNA synthesis. However, mitochondrial DNA (mtDNA) replicates independently of the cell cycle and thus represents a potential target for FUdR toxicity. Inhibition of mtDNA synthesis can lead to mtDNA depletion, which is linked to a number of diseases in humans. Furthermore, alterations in mitochondrial biology can affect lifespan in C. elegans. We characterized the effects of FUdR exposure on mtDNA and nuclear DNA (nucDNA) copy numbers, DNA damage, steady state ATP levels, nematode size, mitochondrial morphology, and lifespan in the germ line deficient JK1107 glp-1(q244) and PE255 glp-4(bn2) strains. Lifespan was increased very slightly by 25 μM FUdR, but was reduced by 400 μM. Both concentrations reduced mtDNA and nucDNA copy numbers, but did not change their ratio. There was no detectable effect of FUdR on mitochondrial morphology. Although both concentrations of FUdR resulted in smaller sized animals, changes to steady-state ATP levels were either not detected or restricted to the higher dose and/or later timepoints, depending on the method employed and strain tested. Finally, we determined the half-life of mtDNA in somatic cells of adult C. elegans to be between 8 and 13 days; this long half-life very likely explains the small or undetectable impact of FUdR on mitochondrial endpoints in our experiments. We discuss the relative pitfalls associated with using FUdR and germline deficient mutant strains as tools for the experimental elimination of progeny.