Mutation of daf-2 extends lifespan via tissue-specific effectors that suppress distinct life-limiting pathologies

WormSpace μ-TAS enabling automated on-chip multi-strain culturing and multi-function imaging of Caenorhabditis elegans at the single-worm level on the China Space Station

As a model organism for space biology experiments, Caenorhabditis elegans (C. elegans) has low demand for life support and strong resistance to unfavorable environments, making experimentation with C. elegans relatively easy and cost-effective. Previously, C. elegans has been flown in several spaceflight investigations, but there is still an urgent need for analytical platforms enabling on-orbit automated monitoring of multiple phenotypes of worms, such as growth and development, movement, changes of biomarkers, etc. To solve this problem, we presented a fully integrated microfluidic system (WormSpace μ-TAS) with an arrayed microfluidic chip (WormChip-4.8.1) and a replaceable microfluidic module (WormChip cartridge), which was compatible with the experimental facility on the China Space Station (CSS). By adopting technologies of programmed fluid control based on liquid medium CeMM as well as multi-function imaging with a camera mounted on a three-dimensional (3D) transportation stage, automated and long-term experimentation can be performed for on-chip multi-strain culturing and bright-field and fluorescence imaging of C. elegans at the single-worm level. The presented WormSpace μ-TAS enabled its successful application on the CSS, achieving flight launch of the sample unit (WormChip cartridge) at low temperature (controlled by a passive thermal case at 12 °C), automated 30-day cultivation of 4 strains of C. elegans, on-orbit monitoring of multiple phenotypes (growth and development, movement, and changes of fluorescent protein expression) at the single worm-level, on-chip fixation of animals at the end of the experiment and returning the fixed samples to earth. In summary, this study presented a verified microfluidic system and experimental protocols for automated on-chip multi-strain culturing and multi-function imaging of C. elegans at the single-worm level on the CSS. The WormSpace μ-TAS will provide a novel experimental platform for the study of biological effects of space radiation and microgravity, and for the development of protective drugs.

Timing of TORC1 inhibition dictates Pol III involvement in Caenorhabditis elegans longevity

Organismal growth and lifespan are inextricably linked. Target of Rapamycin (TOR) signalling regulates protein production for growth and development, but if reduced, extends lifespan across species. Reduction in the enzyme RNA polymerase III, which transcribes tRNAs and 5S rRNA, also extends longevity. Here, we identify a temporal genetic relationship between TOR and Pol III in Caenorhabditis elegans, showing that they collaborate to regulate progeny production and lifespan. Interestingly, the lifespan interaction between Pol III and TOR is only revealed when TOR signaling is reduced, specifically in adulthood, demonstrating the importance of timing to control TOR regulated developmental versus adult programs. In addition, we show that Pol III acts in C. elegans muscle to promote both longevity and healthspan and that reducing Pol III even in late adulthood is sufficient to extend lifespan. This demonstrates the importance of Pol III for lifespan and age-related health in adult C. elegans.

Combinatorial transcriptomic and genetic dissection of insulin/IGF-1 signaling-regulated longevity in Caenorhabditis elegans

Classical genetic analysis is invaluable for understanding the genetic interactions underlying specific phenotypes, but requires laborious and subjective experiments to characterize polygenic and quantitative traits. Contrarily, transcriptomic analysis enables the simultaneous and objective identification of multiple genes whose expression changes are associated with specific phenotypes. Here, we conducted transcriptomic analysis of genes crucial for longevity using datasets with daf-2/insulin/IGF-1 receptor mutant Caenorhabditis elegans. Our analysis unraveled multiple epistatic relationships at the transcriptomic level, in addition to verifying genetically established interactions. Our combinatorial analysis also revealed transcriptomic changes associated with longevity conferred by daf-2 mutations. In particular, we demonstrated that the extent of lifespan changes caused by various mutant alleles of the longevity transcription factor daf-16/FOXO matched their effects on transcriptomic changes in daf-2 mutants. We identified specific aging-regulating signaling pathways and subsets of structural and functional RNA elements altered by different genes in daf-2 mutants. Lastly, we elucidated the functional cooperation between several longevity regulators, based on the combination of transcriptomic and molecular genetic analysis. These data suggest that different biological processes coordinately exert their effects on longevity in biological networks. Together our work demonstrates the utility of transcriptomic dissection analysis for identifying important genetic interactions for physiological processes, including aging and longevity.

Icariin Improves Stress Resistance and Extends Lifespan in Caenorhabditis elegans through hsf-1 and daf-2-Driven Hormesis

Aging presents an increasingly significant challenge globally, driven by the growing proportion of individuals aged 60 and older. Currently, there is substantial research interest in pro-longevity interventions that target pivotal signaling pathways, aiming not only to extend lifespan but also to enhance healthspan. One particularly promising approach involves inducing a hormetic response through the utilization of natural compounds defined as hormetins. Various studies have introduced the flavonoid icariin as beneficial for age-related diseases such as cardiovascular and neurodegenerative conditions. To validate its potential pro-longevity properties, we employed Caenorhabditis elegans as an experimental platform. The accumulated results suggest that icariin extends the lifespan of C. elegans through modulation of the DAF-2, corresponding to the insulin/IGF-1 signaling pathway in humans. Additionally, we identified increased resistance to heat and oxidative stress, modulation of lipid metabolism, improved late-life healthspan, and an extended lifespan upon icariin treatment. Consequently, a model mechanism of action was provided for icariin that involves the modulation of various players within the stress-response network. Collectively, the obtained data reveal that icariin is a potential hormetic agent with geroprotective properties that merits future developments.

High-resolution imaging and analysis of the intestinal bacterial load of Caenorhabditis elegans during early adulthood

We study the presence within the worm Caenorhabditis elegans (C. elegans) of a fluorescent strain of the worm's bacterial food (Escherichia coli (E. coli) OP50) during early adulthood. Use of a microfluidic chip based on a thin glass coverslip substrate allows investigation of the intestinal bacterial load using a Spinning Disk Confocal Microscope (SDCM) equipped with a high-resolution objective (60×). High-resolution z-stack fluorescence images of the gut bacteria in adult worms, which were loaded in the microfluidic chip and subsequently fixed, were analyzed using IMARIS software and 3D reconstructions of the intestinal bacterial load in the worms were obtained. We present an automated bivariate histogram analysis of the volumes and intensities of the bacterial spots for each worm and find that, as the worms age, the bacterial load in their hindguts increases. We show the advantage of single-worm resolution automated analysis for bacterial load studies and anticipate that the methods described in our work can be easily implemented in existing microfluidic solutions to enable thorough studies of bacterial proliferation.

Targeting the "hallmarks of aging" to slow aging and treat age-related disease: fact or fiction?

Aging is a major risk factor for a number of chronic diseases, including neurodegenerative and cerebrovascular disorders. Aging processes have therefore been discussed as potential targets for the development of novel and broadly effective preventatives or therapeutics for age-related diseases, including those affecting the brain. Mechanisms thought to contribute to aging have been summarized under the term the "hallmarks of aging" and include a loss of proteostasis, mitochondrial dysfunction, altered nutrient sensing, telomere attrition, genomic instability, cellular senescence, stem cell exhaustion, epigenetic alterations and altered intercellular communication. We here examine key claims about the "hallmarks of aging". Our analysis reveals important weaknesses that preclude strong and definitive conclusions concerning a possible role of these processes in shaping organismal aging rate. Significant ambiguity arises from the overreliance on lifespan as a proxy marker for aging, the use of models with unclear relevance for organismal aging, and the use of study designs that do not allow to properly estimate intervention effects on aging rate. We also discuss future research directions that should be taken to clarify if and to what extent putative aging regulators do in fact interact with aging. These include multidimensional analytical frameworks as well as designs that facilitate the proper assessment of intervention effects on aging rate.

Intestine-specific removal of DAF-2 nearly doubles lifespan in Caenorhabditis elegans with little fitness cost

Twenty-nine years following the breakthrough discovery that a single-gene mutation of daf-2 doubles Caenorhabditis elegans lifespan, it remains unclear where this insulin/IGF-1 receptor gene is expressed and where it acts to regulate ageing. Using knock-in fluorescent reporters, we determined that daf-2 and its downstream transcription factor daf-16 are expressed ubiquitously. Using tissue-specific targeted protein degradation, we determined that intracellular DAF-2-to-DAF-16 signaling in the intestine plays a major role in lifespan regulation, while that in the hypodermis, neurons, and germline plays a minor role. Notably, intestine-specific loss of DAF-2 activates DAF-16 in and outside the intestine, causes almost no adverse effects on development and reproduction, and extends lifespan by 94% in a way that partly requires non-intestinal DAF-16. Consistent with intestine supplying nutrients to the entire body, evidence from this and other studies suggests that altered metabolism, particularly down-regulation of protein and RNA synthesis, mediates longevity by reduction of insulin/IGF-1 signaling.

Molecular inhibition of RAS signalling to target ageing and age-related health

The RAS/MAPK pathway is a highly conserved signalling pathway with a well-established role in cancer. Mutations that hyperactivate this pathway are associated with unregulated cell proliferation. Evidence from a range of model organisms also links RAS/MAPK signalling to ageing. Genetic approaches that reduce RAS/MAPK signalling activity extend lifespan and also improve healthspan, delaying the onset and/or progression of age-related functional decline. Given its role in cancer, therapeutic interventions that target and inhibit this pathway's key components are under intense investigation. The consequent availability of small molecule inhibitors raises the possibility of repurposing these compounds to ameliorate the deleterious effects of ageing. Here, we review evidence that RAS/MAPK signalling inhibitors already in clinical use, such as trametinib, acarbose, statins, metformin and dihydromyricetin, lead to lifespan extension and to improved healthspan in a range of model systems. These findings suggest that the repurposing of small molecule inhibitors of RAS/MAPK signalling might offer opportunities to improve health during ageing, and to delay or prevent the development of age-related disease. However, challenges to this approach, including poor tolerance to treatment in older adults or development of drug resistance, first need to be resolved before successful clinical implementation.

Summary: This Review critically discusses the links between RAS signalling and ageing, and how RAS inhibitors could extend lifespan and enhance healthspan.

Invited review: Unearthing the mechanisms of age-related neurodegenerative disease using Caenorhabditis elegans

As human life expectancy increases, neurodegenerative diseases present a growing public health threat, for which there are currently few effective treatments. There is an urgent need to understand the molecular and genetic underpinnings of these disorders so new therapeutic targets can be identified. Here we present the argument that the simple nematode worm Caenorhabditis elegans is a powerful tool to rapidly study neurodegenerative disorders due to their short lifespan and vast array of genetic tools, which can be combined with characterization of conserved neuronal processes and behavior orthologous to those disrupted in human disease. We review how pre-existing C. elegans models provide insight into human neurological disease as well as an overview of current tools available to study neurodegenerative diseases in the worm, with an emphasis on genetics and behavior. We also discuss open questions that C. elegans may be particularly well suited for in future studies and how worms will be a valuable preclinical model to better understand these devastating neurological disorders.

The Replica Set Method is a Robust, Accurate, and High-Throughput Approach for Assessing and Comparing Lifespan in C. elegans Experiments

The advent of feeding based RNAi in Caenorhabditis elegans led to an era of gene discovery in aging research. Hundreds of gerogenes were discovered, and many are evolutionarily conserved, raising the exciting possibility that the underlying genetic basis for healthy aging in higher vertebrates could be quickly deciphered. Yet, the majority of putative gerogenes have still only been cursorily characterized, highlighting the need for high-throughput, quantitative assessments of changes in aging. A widely used surrogate measure of aging is lifespan. The traditional way to measure mortality in C. elegans tracks the deaths of individual animals over time within a relatively small population. This traditional method provides straightforward, direct measurements of median and maximum lifespan for the sampled population. However, this method is time consuming, often underpowered, and involves repeated handling of a set of animals over time, which in turn can introduce contamination or possibly damage increasingly fragile, aged animals. We have previously developed an alternative “Replica Set” methodology, which minimizes handling and increases throughput by at least an order of magnitude. The Replica Set method allows changes in lifespan to be measured for over one hundred feeding-based RNAi clones by one investigator in a single experiment- facilitating the generation of large quantitative phenotypic datasets, a prerequisite for development of biological models at a systems level. Here, we demonstrate through analysis of lifespan experiments simulated in silico that the Replica Set method is at least as precise and accurate as the traditional method in evaluating and estimating lifespan, and requires many fewer total animal observations across the course of an experiment. Furthermore, we show that the traditional approach to lifespan experiments is more vulnerable than the Replica Set method to experimental and measurement error. We find no compromise in statistical power for Replica Set experiments, even for moderate effect sizes, or when simulated experimental errors are introduced. We compare and contrast the statistical analysis of data generated by the two approaches, and highlight pitfalls common with the traditional methodology. Collectively, our analysis provides a standard of measure for each method across comparable parameters, which will be invaluable in both experimental design and evaluation of published data for lifespan studies.

Phytochemical composition and anti-aging activity of n-butanol extract of Hedyotis diffusa in Caenorhabditis elegans

Hedyotis diffusa Willd. ( H. diffusa ), a kind of traditional Chinese medicine, has been evaluated to potential display antioxidant and anti-aging effects in vitro experiments. In this work, we investigated the effects on lifespan and stress resistance of the N-butanol extract from H. diffusa (NHD) in vivo using a Caenorhabditis elegans ( C. elegans ) model. The phytochemicals of NHD were identified by UPLC-ESI-qTOF-MS/MS method. NHD-treated wild-type N2 worms showed an increase in survival time under both normal and stress conditions. Meanwhile, NHD promoted the healthspan of nematodes by stimulating growth and development, reducing the deposition of age pigment, increasing the activities of superoxide dismutase (SOD) and glutathione peroxidase dismutase (GSH-Px), and decreasing the level of ROS without impairing fertility. Moreover, the upregulating of the expression of daf-16 , gst-4 , sod-3 , hsp12.6 genes and the downregulating of the expression of daf-2 were involved in the NHD-mediated lifespan extension. Finally, the increasing of the expression of GST-4::GFP in CL2166 transgenic nematodes and the life-span-extending activity of NHD was completely abolished in daf-2 and daf-16 mutants further revealed that the potential roles for these genes in NHD-induced longevity in C. elegans . Collectively, our findings suggest that NHD may have an active effect in healthy aging and age-related diseases.