Ludewig AH et al. (2013) WormBook "Ascaroside signaling in C. elegans."

Ludewig AH, Schroeder FC

[WormBook, 2013]

Over the past 10 years, the relevance of small-molecule signaling for many aspects of C. elegans development and behavior has become apparent. One prominent group of small-molecule signals are the ascarosides, which control dauer entry and exit as well as a variety of sex-specific and social behaviors, including male attraction, hermaphrodite repulsion, olfactory plasticity, and aggregation. This wide range of biological functions is facilitated by a great diversity of ascaroside chemical structures. These are based on the sugar ascarylose, which is linked to fatty acid-like side chains of varying lengths and often decorated further with building blocks derived from amino acids, folate, and other primary metabolites. Different ascarosides or combinations of ascarosides mediate different phenotypes, and even small differences in chemical structures are often associated with strongly altered activity profiles. Additional complexity arises from concentration-dependent effects and synergism between different ascarosides. The ascarosides are sensed by several types of chemosensory head neurons, including the ASK, ASI, and ADL neurons as well as the male-specific CEM neurons. Ascaroside perception is mediated by diverse families of G-protein coupled membrane receptors that act upstream of conserved signal transduction pathways, including insulin/IGF-1 signaling and transforming growth factor beta (TGF-) signaling. Biosynthesis of the ascarosides appears to integrate input from several primary metabolic pathways, including peroxisomal -oxidation of long-chain fatty acids and amino acid catabolism. Life stage, sex, as well as food availability and other environmental factors affect ascaroside biosynthesis, suggesting that ascaroside signaling communicates detailed information about life history and metabolic state.

Ludewig AH et al. (2000) European Worm Meeting "Identification of DAF-12 interaction partners"

Ludewig AH, Antebi A

[European Worm Meeting, 2000]

The nuclear receptor daf-12 acts as a control gene at the intersection of heterochronic and dauer pathways. Conceivably, some of the proposed genetic interactions might be physical interactions. In addition, it is known that vertebrate nuclear receptors are part of large complexes that regulate transcription. We would like to identify similar and possibly new components of these complexes in C. elegans. As a first approach we performed a yeast 2-hybrid screen to identify putative DAF-12 interacting proteins. We constructed different DAF-12 bait fusion proteins, which were screened against mixed stage C. eleganscDNA libraries. In the first screen we used a version of DAF-12 bait lacking the DNA binding domain. We identified 3 reasonable, so far unknown candidate proteins for interaction. We are continuing screening with other libraries and other DAF-12 baits.

Ludewig, A.H. et al. (2017) International Worm Meeting "Pheromones control lifespan via sirtuins by generating oxidative stress."

Pulido, D.C., Schroeder, F.C., Thornton, S.N., Ludewig, A.H.

[International Worm Meeting, 2017]

Previous work showed that chemosensation of hermaphrodite produced pheromones ascr#2 and ascr#3 increases C. elegans adult lifespan and stress resistance (Ludewig 2013), whereas male-produced pheromones of then unknown identity shorten hermaphrodite lifespan (Gems 2000, Maures 2014). We show that the male-produced ascaroside ascr#10 underlies male-induced hermaphrodite progeria, and that pheromone-mediated lifespan increase and decrease depend on several different sirtuins (Ludewig, 2013; Ludewig, unpublished). Sirtuins, a family of NAD+ dependent histone deacetylases, have been implied as conserved regulators of lifespan and stress resistance in various species ranging from yeast to vertebrates. However, the mechanisms by which sirtuins influence lifespan are purely understood. We show that sensing of lifespan-increasing ascarosides transiently increases reactive oxygen species (ROS) levels in the mitochondria and requires the transcription factor skn-1/Nrf, a general regulator of stress responses. Antioxidants abolish the effects of ascarosides on lifespan, demonstrating that ROS production is necessary for sirtuin-dependent longevity. Mitochondrial ROS production is sirtuin-dependent and requires an intact nicotinamide catabolic pathway, indicating that ascaroside-mediated effects on lifespan depend on conversion of NAD+ into nicotinamide by sirtuins, similar to previously reported effects of sir-2.1 over expression (Schmeisser 2013). Our research uncovered an endogenous lifespan regulatory system based on antagonism of longevity-promoting and progeria-inducing ascarosides that act by modulating sirtuin-dependent ROS production. Furthermore, our work suggests that the intensely discussed variability of sirtuin dependent lifespan phenotypes in C. elegans may be due to the confounding effects of worm-produced ascarosides accumulating on experimental plates, in conjunction with other environmental stimuli activating skn-1/Nrf.

Ludewig, A.H. et al. (2017) International Worm Meeting "Larval crowding accelerates C. elegans development and reduces lifespan."

Ludewig, A.H., Schroeder, F.C., Panda, O., Thornton, S.N., Pulido, D.C., Artyukhin, A.B.

[International Worm Meeting, 2017]

Environmental conditions experienced during animal development have sustained impact on maturation and adult lifespan. We recently showed that in C. elegans developmental rate and adult lifespan depend on larval population density and that this effect is mediated by excreted small molecules. We established the time point of first egg laying as ultimate and easy accessible marker of developmental pace and for full maturity (= egg laying assay). We found that wildtype hermaphrodites raised under high density conditions developed significantly faster than animals raised in isolation. Furthermore, larval population density but not population density during adulthood, strongly affected C. elegans lifespan. Population-density dependent developmental acceleration (Pdda) was dramatically enhanced in fatty acid beta -oxidation mutants that are defective in the production of dauer-inducing ascarosides. In contrast, Pdda is abolished by synthetic ascarosides or steroid hormones that act on the nuclear hormone receptor DAF-12. However neither ascarosides nor any of the known steroid hormones are required for Pdda, instead it is mediated by another larval population density-dependent signal (Ludewig 2017, in press) that antagonizes the effects of the dauer pheromone. We further show that the effects of high larval population density persist through adulthood, as C. elegans larvae raised at high densities exhibit significantly reduced adult lifespan and respond differently to exogenous chemical signals compared to larvae raised at low densities, independent of density during adulthood. Our results demonstrate how inter-organismal signaling during development regulates reproductive maturation and longevity.

Ludewig AH et al. (2019) Nat Chem Biol "An excreted small molecule promotes C. elegans reproductive development and aging."

Schroeder FC, Artyukhin AB, Aprison EZ, Panda O, Pulido DC, Burkhardt RN, Ruvinsky I, Gudibanda P, Zhang YK, Rodrigues PR, Ludewig AH

[Nat Chem Biol, 2019]

Excreted small-molecule signals can bias developmental trajectories and physiology in diverse animal species. However, the chemical identity of these signals remains largely obscure. Here we report identification of an unusual N-acylated glutamine derivative, nacq#1, that accelerates reproductive development and shortens lifespan in Caenorhabditis elegans. Produced predominantly by C. elegans males, nacq#1 hastens onset of sexual maturity in hermaphrodites by promoting exit from the larval dauer diapause and by accelerating late larval development. Even at picomolar concentrations, nacq#1 shortens hermaphrodite lifespan, suggesting a trade-off between reproductive investment and longevity. Acceleration of development by nacq#1 requires chemosensation and is dependent on three homologs of vertebrate steroid hormone receptors. Unlike ascaroside pheromones, which are restricted to nematodes, fatty acylated amino acid derivatives similar to nacq#1 have been reported from humans and invertebrates, suggesting that related compounds may serve signaling functions throughout metazoa.

Ludewig AH et al. (2017) PLoS Genet "Larval crowding accelerates C. elegans development and reduces lifespan."

Ludewig AH, Thornton S, Doring F, Micikas RJ, Gimond C, Judkins JC, Braendle C, Pulido DC, Schroeder FC, Antebi A

[PLoS Genet, 2017]

Environmental conditions experienced during animal development are thought to have sustained impact on maturation and adult lifespan. Here we show that in the model organism C. elegans developmental rate and adult lifespan depend on larval population density, and that this effect is mediated by excreted small molecules. By using the time point of first egg laying as a marker for full maturity, we found that wildtype hermaphrodites raised under high density conditions developed significantly faster than animals raised in isolation. Population density-dependent acceleration of development (Pdda) was dramatically enhanced in fatty acid -oxidation mutants that are defective in the biosynthesis of ascarosides, small-molecule signals that induce developmental diapause. In contrast, Pdda is abolished by synthetic ascarosides and steroidal ligands of the nuclear hormone receptor DAF-12. We show that neither ascarosides nor any known steroid hormones are required for Pdda and that another chemical signal mediates this phenotype, in part via the nuclear hormone receptor NHR-8. Our results demonstrate that C. elegans development is regulated by a push-pull mechanism, based on two antagonistic chemical signals: chemosensation of ascarosides slows down development, whereas population-density dependent accumulation of a different chemical signal accelerates development. We further show that the effects of high larval population density persist through adulthood, as C. elegans larvae raised at high densities exhibit significantly reduced adult lifespan and respond differently to exogenous chemical signals compared to larvae raised at low densities, independent of density during adulthood. Our results demonstrate how inter-organismal signaling during development regulates reproductive maturation and longevity.

Ludewig, A.H. et al. (2015) International Worm Meeting "Population density in Caenorhabditis elegans controls developmental rate via a small molecule-based push-pull strategy ."

Micikas, R.M., Gimond, C., Braendle, C., Ludewig, A.H., Schroeder, F.C., Doering, F., Judkins, J.J.

[International Worm Meeting, 2015]

Adequate sensing and processing of information about the environment is crucial for organismal survival. The nematode C. elegans is a particularly useful model for investigating responses to changes in environmental parameters such as temperature, food availability, and crowding. Here we show that timing of C. elegans reproductive development is controlled by a push-pull mechanism based on two different types of small molecule signals. By using the time point of first egg laying as a marker for full maturity, we found that animals raised under high density conditions developed up to 10 hours faster than animals raised in isolation. Mutant analyses revealed that population-density dependent onset of egg laying (pdde) is controlled by chemosensation of different two groups of endogenously produced small molecule signals. Fatty acid beta-oxidation mutants that are defective in the production of a family of glycolipids, the ascarosides, which previously have been shown to regulate formation of stress-resistant dauer larvae, showed dramatically enhanced pdde, whereas pdde was abolished or greatly reduced in mutants defective in evolutionarily conserved steroid hormone signaling. Correspondingly, addition of synthetic ascarosides or steroid hormones diminished or abolished pdde by either reducing or accelerating developmental rate. We confirmed pdde in two different C. elegans wild-type strains as well as in a related species, C. briggsae. Taken together, our results how that developmental rate in C. elegans is controlled by the interplay of a known class of interorganismal signals, the ascarosides, and bile acid-like steroids called dafachronic acids that previously had been identified as ligands of the nuclear hormone receptor DAF-12, a homolog of vertebrate vitamin D and pregnane-X receptors. Our work shows that the dafachronic acids also function as interorganismal signals that act via chemosensory mechanisms. Moreover, we suggest that measuring onset of egg laying provides an efficient method to measure the effect of environmental changes on developmental rate.

Ludewig AH et al. (2014) Genes Nutr "Identifying evolutionarily conserved genes in the dietary restriction response using bioinformatics and subsequent testing in Caenorhabditis elegans."

Ludewig AH, Doring F, Klapper M

[Genes Nutr, 2014]

Dietary restriction (DR) increases life span, health span and resistance to stress in a wide range of organisms. Work from a large number of laboratories has revealed evolutionarily conserved mechanisms that mediate the DR response. Here, we analyzed the genome-wide gene expression profiles of Caenorhabditis elegans under DR versus ad libitum conditions. Using the Ortho2ExpressMatrix tool, we searched for C. elegans orthologs of mouse genes that have been shown to be differentially expressed under DR conditions in nearly 600 experiments. Based on our bioinformatic approaches, we obtained 189 DR-responsive genes, and 45 of these are highly conserved from worm to man. Subsequent testing of sixteen genes that are up-regulated under DR identified eight genes that abolish the DR-induced resistance to heat stress in C. elegans. Further analyses revealed that fkb-4, dod-22 and ikb-1 genes also abolish increased life span in response to DR. The identified genes that are necessary for the DR response are sensitive to certain stress signals such as metabolic perturbances (dod-22, fkb-4 and nhr-85), DNA damage (ikb-1), heat shock (hsp-12.6) and cancer-like overgrowth (prk-2 and tsp-15). We propose that most of the DR-responsive genes identified are components of the recently discovered cellular surveillance-activated detoxification and defenses pathway, which is, among others, important for the survival of organisms in times of food deprivation.

Ludewig AH et al. (2004) Genes Dev "A novel nuclear receptor/coregulator complex controls C. elegans lipid metabolism, larval development, and aging."

Kober-Eisermann C, Neubert K, Bethke A, Hutter H, Antebi A, Weitzel C, Ludewig AH, Gerisch B

[Genes Dev, 2004]

Environmental cues transduced by an endocrine network converge on Caenorhabditis elegans nuclear receptor DAF-12 to mediate arrest at dauer diapause or continuous larval development. In adults, DAF-12 selects long-lived or short-lived modes. How these organismal choices are molecularly specified is unknown. Here we show that coregulator DIN-1 and DAF-12 physically and genetically interact to instruct organismal fates. Homologous to human corepressor SHARP, DIN-1 comes in long (L) and short (S) isoforms, which are nuclear localized but have distinct functions. DIN-1L has embryonic and larval developmental roles. DIN-1S, along with DAF-12, regulates lipid metabolism, larval stage-specific programs, diapause, and longevity. Epistasis experiments reveal that din-1S acts in the dauer pathways downstream of lipophilic hormone, insulin/IGF, and TGFbeta signaling, the same point as daf-12. We propose that the DIN-1S/DAF-12 complex serves as a molecular switch that implements slow life history alternatives in response to diminished hormonal signals.

Ludewig AH et al. (2013) Proc Natl Acad Sci U S A "Pheromone sensing regulates Caenorhabditis elegans lifespan and stress resistance via the deacetylase SIR-2.1."

Park D, Bethke A, Zimmermann A, Doering F, Fox BW, Riddle DL, Izrayelit Y, Mahanti P, Ludewig AH, Schroeder FC, Malik RU

[Proc Natl Acad Sci U S A, 2013]

Lifespan in Caenorhabditis elegans, Drosophila, and mice is regulated by conserved signaling networks, including the insulin/insulin-like growth factor 1 (IGF-1) signaling cascade and pathways depending on sirtuins, a family of NAD(+)-dependent deacetylases. Small molecules such as resveratrol are of great interest because they increase lifespan in many species in a sirtuin-dependent manner. However, no endogenous small molecules that regulate lifespan via sirtuins have been identified, and the mechanisms underlying sirtuin-dependent longevity are not well understood. Here, we show that in C. elegans, two endogenously produced small molecules, the dauer-inducing ascarosides ascr#2 and ascr#3, regulate lifespan and stress resistance through chemosensory pathways and the sirtuin SIR-2.1. Ascarosides extend adult lifespan and stress resistance without reducing fecundity or feeding rate, and these effects are reduced or abolished when nutrients are restricted. We found that ascaroside-mediated longevity is fully abolished by loss of SIR-2.1 and that the effect of ascr#2 requires expression of the G protein-coupled receptor DAF-37 in specific chemosensory neurons. In contrast to many other lifespan-modulating factors, ascaroside-mediated lifespan increases do not require insulin signaling via the FOXO homolog DAF-16 or the insulin/IGF-1-receptor homolog DAF-2. Our study demonstrates that C. elegans produces specific small molecules to control adult lifespan in a sirtuin-dependent manner, supporting the hypothesis that endogenous regulation of metazoan lifespan functions, in part, via sirtuins. These findings strengthen the link between chemosensory inputs and conserved mechanisms of lifespan regulation in metazoans and suggest a model for communal lifespan regulation in C. elegans.