Fertility/longevity trade-offs under limiting-male conditions in mating populations of Caenorhabditis elegans

Ganoderma lucidum methyl ganoderate E extends lifespan and modulates aging-related indicators in Caenorhabditis elegans

Methyl Ganoderate E (MGE) is a triterpenoid derived from Ganoderma lucidum (Reishi), an edible mushroom, commonly processed into food forms such as soups, drinks, culinary dishes, and supplements. MGE has been shown to inhibit 3T3-L1 murine adipocyte differentiation when combined with other G. lucidum triterpenes. However, the specific effect of MGE on biological processes remains unknown. In this study, we present the first evidence of MGE's anti-aging effect in Caenorhabditis elegans. Through our screening process using the UPRER regulation ability, we evaluated a library of 74 pure compounds isolated from G. lucidum, and MGE exhibited the most promising results. Subsequent experiments demonstrated that MGE extended the lifespan by 26% at 10 μg ml-1 through daf-16, hsf-1, and skn-1-dependent pathways. MGE also enhanced resistance to various molecular stressors, improved healthspan, increased fertility, and reduced the aggregation of alpha-synuclein and amyloid-beta. Transcriptome data revealed that MGE promoted processes associated with proteolysis and neural activity, while not promoting cell death processes. Collectively, our findings suggest that G. lucidum MGE could be considered as a potential anti-aging intervention, adding to the growing list of such interventions.

Microbes are potential key players in the evolution of life histories and aging in Caenorhabditis elegans

Microbes can have profound effects on host fitness and health and the appearance of late-onset diseases. Host-microbe interactions thus represent a major environmental context for healthy aging of the host and might also mediate trade-offs between life-history traits in the evolution of host senescence. Here, we have used the nematode Caenorhabditis elegans to study how host-microbe interactions may modulate the evolution of life histories and aging. We first characterized the effects of two non-pathogenic and one pathogenic Escherichia coli strains, together with the pathogenic Serratia marcescens DB11 strain, on population growth rates and survival of C. elegans from five different genetic backgrounds. We then focused on an outbred C. elegans population, to understand if microbe-specific effects on the reproductive schedule and in traits such as developmental rate and survival were also expressed in the presence of males and standing genetic variation, which could be relevant for the evolution of C. elegans and other nematode species in nature. Our results show that host-microbe interactions have a substantial host-genotype-dependent impact on the reproductive aging and survival of the nematode host. Although both pathogenic bacteria reduced host survival in comparison with benign strains, they differed in how they affected other host traits. Host fertility and population growth rate were affected by S. marcescens DB11 only during early adulthood, whereas this occurred at later ages with the pathogenic E. coli IAI1. In both cases, these effects were largely dependent on the host genotypes. Given such microbe-specific genotypic differences in host life history, we predict that the evolution of reproductive schedules and senescence might be critically contingent on host-microbe interactions in nature.

Self-sperm induce resistance to the detrimental effects of sexual encounters with males in hermaphroditic nematodes

Sexual interactions have a potent influence on health in several species, including mammals. Previous work in C. elegans identified strategies used by males to accelerate the demise of the opposite sex (hermaphrodites). But whether hermaphrodites evolved counter-strategies against males remains unknown. Here we discover that young C. elegans hermaphrodites are remarkably resistant to brief sexual encounters with males, whereas older hermaphrodites succumb prematurely. Surprisingly, it is not their youthfulness that protects young hermaphrodites, but the fact that they have self-sperm. The beneficial effect of self-sperm is mediated by a sperm-sensing pathway acting on the soma rather than by fertilization. Activation of this pathway in females triggers protection from the negative impact of males. Interestingly, the role of self-sperm in protecting against the detrimental effects of males evolved independently in hermaphroditic nematodes. Endogenous strategies to delay the negative effect of mating may represent a key evolutionary innovation to maximize reproductive success.

A nematode worm known as Caenorhabditis elegans is often used in the laboratory to study how animals grow and develop. There are two types of C. elegans worm: hermaphrodite individuals produce both female sex cells (eggs) and male sex cells (sperm), while male individuals only produce sperm.

The hermaphrodite worms are able to reproduce without mating with another worm, allowing populations of C. elegans to grow rapidly when they are living in favorable conditions. However, when the hermaphrodites do mate with males they tend to produce more offspring. These offspring are also usually healthier because they receive a mixture of genetic material from two different parents.

Although mating is beneficial for the survival of a species it can also harm an individual animal. Previous studies have shown that mating with male worms can accelerate aging of hermaphrodite worms and cause premature death. However, it remained unclear whether hermaphrodite worms have evolved any mechanisms to protect themselves after mating with a male.

To address this question, Booth et al. used genetic techniques to study the lifespans of hermaphrodite worms. The experiments found that the hermaphrodites’ own sperm (known as self-sperm) regulated a sperm-sensing signaling pathway that protected them from the negative impact of mating with males. Hermaphrodites with self-sperm that mated with males lived for a similar length of time as hermaphrodites that did not mate. On the other hand, hermaphrodites that did not have self-sperm (because they were older or had a genetic mutation) had shorter lifespans after mating than worms that did not mate. Modulating the sperm-sensing signaling pathway in worms that lacked self-sperm was sufficient to protect them from the negative effects of mating with males.

Further experiments found that the hermaphrodites of another nematode worm called C. briggsae – which evolved self-sperm independently of C. elegans – also protected themselves from the negative effects of mating with males in a similar way. This suggests that other animals may also have evolved similar mechanisms to protect themselves from harm when mating.

A separate study by Shi et al. has found that the beneficial effects of self-sperm are mediated by a pathway linked to longevity that also exists in mammals. The results of both investigations combined suggest possible avenues for future research into the complex relationship between health, longevity, and reproduction.

Caenorhabditis elegans Genes Affecting Interindividual Variation in Life-span Biomarker Gene Expression

Genetically identical organisms grown in homogenous environments differ in quantitative phenotypes. Differences in one such trait, expression of a single biomarker gene, can identify isogenic cells or organisms that later manifest different fates. For example, in isogenic populations of young adult Caenorhabditis elegans, differences in Green Fluorescent Protein (GFP) expressed from the hsp-16.2 promoter predict differences in life span. Thus, it is of interest to determine how interindividual differences in biomarker gene expression arise. Prior reports showed that the thermosensory neurons and insulin signaling systems controlled the magnitude of the heat shock response, including absolute expression of hsp-16.2. Here, we tested whether these regulatory signals might also influence variation in hsp-16.2 reporter expression. Genetic experiments showed that the action of AFD thermosensory neurons increases interindividual variation in biomarker expression. Further genetic experimentation showed the insulin signaling system acts to decrease interindividual variation in life-span biomarker expression; in other words, insulin signaling canalizes expression of the hsp-16.2-driven life-span biomarker. Our results show that specific signaling systems regulate not only expression level, but also the amount of interindividual expression variation for a life-span biomarker gene. They raise the possibility that manipulation of these systems might offer means to reduce heterogeneity in the aging process.

Mating pheromones of Nematoda: olfactory signaling with physiological consequences

Secreted pheromones have long been known to influence mating in the phylum Nematoda. The study of nematode sexual behavior has greatly benefited in the last decade from the genetic and neurobiological tools available for the model nematode Caenorhabditis elegans, as well as from the chemical identification of many pheromones secreted by this species. The discovery that nematodes can influence one another's physiological development and stress responsiveness through the sharing of pheromones, in addition to simply triggering sexual attraction, is particularly striking. Here we review recent research on nematode mating pheromones, which has been conducted predominantly on C. elegans, but there are beginning to be parallel studies in other species.

Endogenous ROS levels in C. elegans under exogenous stress support revision of oxidative stress theory of life-history tradeoffs

BACKGROUND

The oxidative stress theory of life-history tradeoffs states that oxidative stress caused by damaging free radicals directly underpins tradeoffs between reproduction and longevity by altering the allocation of energetic resources between these tasks. We test this theory by characterizing the effects of exogenous oxidative insult and its interaction with thermal stress and diet quality on a suite of life-history traits and correlations in Caenorhabditis elegans nematodes. We also quantify demographic aging rates and endogenous reactive oxygen species (ROS) levels in live animals.

RESULTS

Our findings indicate a tradeoff between investment in reproduction and antioxidant defense (somatic maintenance) consistent with theoretical predictions, but correlations between standard life-history traits yield little evidence that oxidative stress generates strict tradeoffs. Increasing oxidative insult, however, shows a strong tendency to uncouple positive phenotypic correlations and, in particular, to reduce the correlation between reproduction and lifespan. We also found that mild oxidative insult results in lower levels of endogenous ROS accompanied by hormetic changes in lifespan, demographic aging, and reproduction that disappear in combined-stress treatments--consistent with the oxidative stress theory of aging.

CONCLUSIONS

Our findings demonstrate that oxidative stress is a direct contributor to life-history trait variation and that traditional tradeoffs are not necessary to invoke oxidative stress as a mediator of relationships between life-history traits, supporting previous calls for revisions to theory.

Mating induces shrinking and death in Caenorhabditis mothers

Interactions between the germ line and the soma help optimize reproductive success. We discovered a phenomenon linking reproductive status to longevity: In both hermaphroditic and gonochoristic Caenorhabditis, mating leads to female shrinking and death, compressing postreproductive life span. Male sperm induces germline- and DAF-9/DAF-12-dependent shrinking, osmotic stress susceptibility, and subsequent life-span decrease, whereas seminal fluid induces DAF-16-dependent life-span decrease and fat loss. Our study provides insight into the communication between males and the female germ line and soma to regulate reproduction and longevity, revealing a high-reproduction, low-life-span state induced by mating. Postmating somatic collapse may be an example of the sexually antagonistic influence that males in many species exert on female behavior to maximize their own reproductive success.

Dramatic fertility decline in aging C. elegans males is associated with mating execution deficits rather than diminished sperm quality

Although much is known about female reproductive aging, fairly little is known about the causes of male reproductive senescence. We developed a method that facilitates culture maintenance of Caenorhabditis elegans adult males, which enabled us to measure male fertility as populations age, without profound loss of males from the growth plate. We find that the ability of males to sire progeny declines rapidly in the first half of adult lifespan and we examined potential factors that contribute towards reproductive success, including physical vigor, sperm quality, mating apparatus morphology, and mating ability. Of these, we find little evidence of general physical decline in males or changes in sperm number, morphology, or capacity for activation, at time points when reproductive senescence is markedly evident. Rather, it is the loss of efficient mating ability that correlates most strongly with reproductive senescence. Low insulin signaling can extend male ability to sire progeny later in life, although insulin impact on individual facets of mating behavior is complex. Overall, we suggest that combined modest deficits, predominantly affecting the complex mating behavior rather than sperm quality, sum up to block effective C. elegans male reproduction in middle adult life.