Rictor/TORC2 regulates fat metabolism, feeding, growth, and life span in Caenorhabditis elegans

Heat-killed probiotic Levilactobacillus brevis MKAK9 and its exopolysaccharide promote longevity by modulating aging hallmarks and enhancing immune responses in Caenorhabditis elegans

BACKGROUND

Proteostasis is a critical aging hallmark responsible for removing damaged or misfolded proteins and their aggregates by improving proteasomal degradation through the autophagy-lysosome pathway (ALP) and the ubiquitin-proteasome system (UPS). Research on the impact of heat-killed probiotic bacteria and their structural components on aging hallmarks and innate immune responses is scarce, yet enhancing these effects could potentially delay age-related diseases.

RESULTS

This study introduces a novel heat-killed Levilactobacillus brevis strain MKAK9 (HK MKAK9), along with its exopolysaccharide (EPS), demonstrating their ability to extend longevity by improving proteostasis and immune responses in wild-type Caenorhabditis elegans. We elucidate the underlying mechanisms through a comprehensive approach involving mRNA- and small RNA sequencing, proteomic analysis, lifespan assays on loss-of-function mutants, and quantitative RT-PCR. Mechanistically, HK MKAK9 and its EPS resulted in downregulation of the insulin-like signaling pathway in a DAF-16-dependent manner, enhancing protein ubiquitination and subsequent proteasomal degradation through activation of the ALP pathway, which is partially mediated by microRNA mir-243. Importantly, autophagosomes engulf ubiquitinylated proteins, as evidenced by increased expression of the autophagy receptor sqst-3, and subsequently fuse with lysosomes, facilitated by increased levels of the lysosome-associated membrane protein (LAMP) lmp-1, suggesting the formation of autolysosomes for degradation of the selected cargo. Moreover, HK MKAK9 and its EPS activated the p38 MAPK pathway and its downstream SKN-1 transcription factor, which are known to regulate genes involved in innate immune response (thn-1, ilys-1, cnc-2, spp-9, spp-21, clec-47, and clec-266) and antioxidation (sod-3 and gst-44), thereby reducing the accumulation of reactive oxygen species (ROS) at both cellular and mitochondrial levels. Notably, SOD-3 emerged as a transcriptional target of both DAF-16 and SKN-1 transcription factors.

CONCLUSION

Our research sets a benchmark for future investigations by demonstrating that heat-killed probiotic and its specific cellular component, EPS, can downregulate the insulin-signaling pathway, potentially improving the autophagy-lysosome pathway (ALP) for degrading ubiquitinylated proteins and promoting organismal longevity. Additionally, we discovered that increased expression of microRNA mir-243 regulates insulin-like signaling and its downstream ALP pathway. Our findings also indicate that postbiotic treatment may bolster antioxidative and innate immune responses, offering a promising avenue for interventions in aging-related diseases.

Extracellular flux assay (Seahorse assay): Diverse applications in metabolic research across biological disciplines

Metabolic networks are fundamental to cellular processes, driving energy production, biosynthesis, redox regulation, and cellular signaling. Recent advancements in metabolic research tools have provided unprecedented insights into cellular metabolism. Among these tools, the extracellular flux analyzer stands out for its real-time measurement of key metabolic parameters: glycolysis, mitochondrial respiration, and fatty acid oxidation, leading to its widespread use. This review provides a comprehensive summary of the basic principles and workflow of the extracellular flux assay (the Seahorse assay) and its diverse applications. We highlight the assay's versatility across various biological models, including cancer cells, immunocytes, Caenorhabditis elegans, tissues, isolated mitochondria, and three-dimensional structures such as organoids, and summarize key considerations for using extracellular flux assay in these models. Additionally, we discuss the limitations of the Seahorse assay and propose future directions for its development. This review aims to enhance the understanding of extracellular flux assay and its significance in biological studies.

Non-cell-autonomous regulation of mTORC2 by Hedgehog signaling maintains lipid homeostasis

Organisms must appropriately allocate energetic resources between essential cellular processes to maintain homeostasis and in turn, maximize fitness. The nutritional and homeostatic regulators of energy homeostasis have been studied in detail; however, how developmental signals might impinge on these pathways to govern cellular metabolism is poorly understood. Here, we identify a non-canonical role for Hedgehog (Hh), a classic regulator of development, in maintaining intestinal lipid homeostasis in C. elegans . We find that expression of two Hh ligands, GRD-3 and GRD-4, is controlled by the LIN-29/EGR transcription factor in the hypodermis, where the Hh secretion factor CHE-14/Dispatched also facilitates non-cell autonomous Hh signaling. We demonstrate, using C. elegans and mouse hepatocytes, that Hh metabolic regulation does not occur through the canonical Hh transcription factor, TRA-1/GLI, but rather through non-canonical signaling that engages mTOR Complex 2 (mTORC2) in the intestine. Hh mutants display impaired lipid homeostasis, including reduced lipoprotein synthesis and fat accumulation, decreased growth, and upregulation of autophagy factors, mimicking loss of mTORC2. Additionally, we found that Hh inhibits p38 MAPK signaling in parallel to mTORC2 activation and that both pathways act together to modulate of lipid homeostasis. Our findings show a non-canonical role for Hedgehog signaling in lipid metabolism via regulation of core homeostatic pathways and reveal a new mechanism by which developmental timing events govern metabolic decisions.

Exposure to an aversive odor alters Caenorhabditis elegans physiology

Perception of external cues is important for enhancing the fitness and survival of animals. However, the role of odor perception in regulation of longevity and health is incompletely defined. Here, we show that the exposure to an aversive odor 2-nonanone reduces life span, brood size, feeding rate, and increases lipid storage in worms. These effects are restored to normal levels in mutant worms lacking functional olfactory AWB neurons, suggesting a potential role of odor perception in the regulation of animal physiology and longevity.

Knockdown of neuronal DAF-15/Raptor promotes healthy aging in C. elegans

The highly conserved target of rapamycin (TOR) pathway plays an important role in aging across species. Previous studies have established that inhibition of the TOR complex 1 (TORC1) significantly extends lifespan in Caenorhabditiselegans. However, it has not been clear whether TORC1 perturbation affects aging in a spatiotemporal manner. Here, we apply the auxin-inducible degradation tool to knock down endogenous DAF-15, the C. elegans ortholog of regulatory associated protein of TOR (Raptor), to characterize its roles in aging. Global or tissue-specific inhibition of DAF-15 during development results in various growth defects, whereas neuron-specific knockdown of DAF-15 during adulthood significantly extends lifespan and healthspan. The neuronal DAF-15 deficiency-induced longevity requires the intestinal activities of DAF-16/FOXO and PHA-4/FOXA transcription factors, as well as the AAK-2/AMP-activated protein kinase α catalytic subunit. Transcriptome profiling reveals that the neuronal DAF-15 knockdown promotes the expression of genes involved in protection. These findings define the tissue-specific roles of TORC1 in healthy aging and highlight the importance of neuronal modulation of aging.

Intestinal Mg2+ accumulation induced by cnnm mutations decreases the body size by suppressing TORC2 signaling in Caenorhabditis elegans

Mg2+ is a vital ion involved in diverse cellular functions by forming complexes with ATP. Intracellular Mg2+ levels are tightly regulated by the coordinated actions of multiple Mg2+ transporters, such as the Mg2+ efflux transporter, cyclin M (CNNM). Caenorhabditis elegans (C. elegans) worms with mutations in both cnnm-1 and cnnm-3 exhibit excessive Mg2+ accumulation in intestinal cells, leading to various phenotypic abnormalities. In this study, we investigated the mechanism underlying the reduction in body size in cnnm-1; cnnm-3 mutant worms. RNA interference (RNAi) of gtl-1, which encodes a Mg2+-intake channel in intestinal cells, restored the worm body size, confirming that this phenotype is due to excessive Mg2+ accumulation. Moreover, RNAi experiments targeting body size-related genes and analyses of mutant worms revealed that the suppression of the target of rapamycin complex 2 (TORC2) signaling pathway was involved in body size reduction, resulting in downregulated DAF-7 expression in head ASI neurons. As the DAF-7 signaling pathway suppresses dauer formation under stress, cnnm-1; cnnm-3 mutant worms exhibited a greater tendency to form dauer upon induction. Collectively, our results revealed that excessive accumulation of Mg2+ repressed the TORC2 signaling pathway in C. elegans worms and suggest the novel role of the DAF-7 signaling pathway in the regulation of their body size.

LPD-3 as a megaprotein brake for aging and insulin-mTOR signaling in C. elegans

Insulin-mechanistic target of rapamycin (mTOR) signaling drives anabolic growth during organismal development; its late-life dysregulation contributes to aging and limits lifespans. Age-related regulatory mechanisms and functional consequences of insulin-mTOR remain incompletely understood. Here, we identify LPD-3 as a megaprotein that orchestrates the tempo of insulin-mTOR signaling during C. elegans aging. We find that an agonist insulin, INS-7, is drastically overproduced from early life and shortens lifespan in lpd-3 mutants. LPD-3 forms a bridge-like tunnel megaprotein to facilitate non-vesicular cellular lipid trafficking. Lipidomic profiling reveals increased hexaceramide species in lpd-3 mutants, accompanied by up-regulation of hexaceramide biosynthetic enzymes, including HYL-1. Reducing the abundance of HYL-1, insulin receptor/DAF-2 or mTOR/LET-363, normalizes INS-7 levels and rescues the lifespan of lpd-3 mutants. LPD-3 antagonizes SINH-1, a key mTORC2 component, and decreases expression with age. We propose that LPD-3 acts as a megaprotein brake for organismal aging and that its age-dependent decline restricts lifespan through the sphingolipid-hexaceramide and insulin-mTOR pathways.

Disrupting the SKN-1 homeostat: mechanistic insights and phenotypic outcomes

The mechanisms that govern maintenance of cellular homeostasis are crucial to the lifespan and healthspan of all living systems. As an organism ages, there is a gradual decline in cellular homeostasis that leads to senescence and death. As an organism lives into advanced age, the cells within will attempt to abate age-related decline by enhancing the activity of cellular stress pathways. The regulation of cellular stress responses by transcription factors SKN-1/Nrf2 is a well characterized pathway in which cellular stress, particularly xenobiotic stress, is abated by SKN-1/Nrf2-mediated transcriptional activation of the Phase II detoxification pathway. However, SKN-1/Nrf2 also regulates a multitude of other processes including development, pathogenic stress responses, proteostasis, and lipid metabolism. While this process is typically tightly regulated, constitutive activation of SKN-1/Nrf2 is detrimental to organismal health, this raises interesting questions surrounding the tradeoff between SKN-1/Nrf2 cryoprotection and cellular health and the ability of cells to deactivate stress response pathways post stress. Recent work has determined that transcriptional programs of SKN-1 can be redirected or suppressed to abate negative health outcomes of constitutive activation. Here we will detail the mechanisms by which SKN-1 is controlled, which are important for our understanding of SKN-1/Nrf2 cytoprotection across the lifespan.

High-content phenotypic analysis of a C. elegans recombinant inbred population identifies genetic and molecular regulators of lifespan

Lifespan is influenced by complex interactions between genetic and environmental factors. Studying those factors in model organisms of a single genetic background limits their translational value for humans. Here, we mapped lifespan determinants in 85 genetically diverse C. elegans recombinant intercross advanced inbred lines (RIAILs). We assessed molecular profiles - transcriptome, proteome, and lipidome - and life-history traits, including lifespan, development, growth dynamics, and reproduction. RIAILs exhibited large variations in lifespan, which positively correlated with developmental time. Among the top candidates obtained from multi-omics data integration and QTL mapping, we validated known and novel longevity modulators, including rict-1, gfm-1 and mltn-1. We translated their relevance to humans using UK Biobank data and showed that variants in RICTOR and GFM1 are associated with an elevated risk of age-related heart disease, dementia, diabetes, kidney, and liver diseases. We organized our dataset as a resource (https://lisp-lms.shinyapps.io/RIAILs/) that allows interactive explorations for new longevity targets.

Environmental carcinogen benzo[a]pyrene alters neutral lipid storage via a cyp-35A2 mediated pathway in Caenorhabditis elegans

Polycyclic aromatic hydrocarbons (PAHs), in particular benzo [a]pyrene (BaP), have been identified as carcinogenic components of tobacco smoke. In mammals, the toxicological response to BaP-diol-epoxide is driven by cytochrome P450 (CYP1A1), a pathway which is absent in Caenorhabditis elegans. In contrast, in worms prominently the CYP-35 enzyme family seems to be induced after BaP exposure. In C. elegans, BaP exposure reduces the accumulation of lysosomal neutral lipids in a dose dependent manner and the deletion of cyp-35A2 results in a significant elevation of neutral lipid metabolism. A cyp-35A2:mCherry;unc-47:GFP dual-labelled reporter strain facilitated the identification of three potential upstream regulators that drive BaP metabolism in worms, namely elt-2, nhr-49 and fos-1. This newly described reporter line is a powerful resource for future large-scale RNAi regarding toxicology and lipid metabolism screens.

GRD-1/PTR-11, the C. elegans hedgehog/patched-like morphogen-receptor pair, modulates developmental rate

Both hedgehog (Hh) and target of rapamycin complex 2 (TORC2) are central, evolutionarily conserved signaling pathways that regulate development and metabolism. In C. elegans, loss of the essential TORC2 component RICTOR (rict-1) causes delayed development, shortened lifespan, reduced brood, small size and increased fat. Here, we report that knockdown of both the hedgehog-related morphogen grd-1 and its patched-related receptor ptr-11 rescues delayed development in TORC2 loss-of-function mutants, and grd-1 and ptr-11 overexpression delays wild-type development to a similar level to that in TORC2 loss-of-function animals. These findings potentially indicate an unexpected role for grd-1 and ptr-11 in slowing developmental rate downstream of a nutrient-sensing pathway. Furthermore, we implicate the chronic stress transcription factor pqm-1 as a key transcriptional effector in this slowing of whole-organism growth by grd-1 and ptr-11. We propose that TORC2, grd-1 and ptr-11 may act linearly or converge on pqm-1 to delay organismal development.

The C. elegans Myc-family of transcription factors coordinate a dynamic adaptive response to dietary restriction

Dietary restriction (DR), the process of decreasing overall food consumption over an extended period of time, has been shown to increase longevity across evolutionarily diverse species and delay the onset of age-associated diseases in humans. In Caenorhabditis elegans, the Myc-family transcription factors (TFs) MXL-2 (Mlx) and MML-1 (MondoA/ChREBP), which function as obligate heterodimers, and PHA-4 (orthologous to forkhead box transcription factor A) are both necessary for the full physiological benefits of DR. However, the adaptive transcriptional response to DR and the role of MML-1::MXL-2 and PHA-4 remains elusive. We identified the transcriptional signature of C. elegans DR, using the eat-2 genetic model, and demonstrate broad changes in metabolic gene expression in eat-2 DR animals, which requires both mxl-2 and pha-4. While the requirement for these factors in DR gene expression overlaps, we found many of the DR genes exhibit an opposing change in relative gene expression in eat-2;mxl-2 animals compared to wild-type, which was not observed in eat-2 animals with pha-4 loss. We further show functional deficiencies of the mxl-2 loss in DR outside of lifespan, as eat-2;mxl-2 animals exhibit substantially smaller brood sizes and lay a proportion of dead eggs, indicating that MML-1::MXL-2 has a role in maintaining the balance between resource allocation to the soma and to reproduction under conditions of chronic food scarcity. While eat-2 animals do not show a significantly different metabolic rate compared to wild-type, we also find that loss of mxl-2 in DR does not affect the rate of oxygen consumption in young animals. The gene expression signature of eat-2 mutant animals is consistent with optimization of energy utilization and resource allocation, rather than induction of canonical gene expression changes associated with acute metabolic stress -such as induction of autophagy after TORC1 inhibition. Consistently, eat-2 animals are not substantially resistant to stress, providing further support to the idea that chronic DR may benefit healthspan and lifespan through efficient use of limited resources rather than broad upregulation of stress responses, and also indicates that MML-1::MXL-2 and PHA-4 may have different roles in promotion of benefits in response to different pro-longevity stimuli.

The role of nutrition and oxidative stress as aging factors in Caenorhabditis elegans

The molecular mechanism of aging, which has been a "black box" for many years, has been elucidated in recent years, and the nematode C. elegans, which is a model animal for aging research, has played a major role in its elucidation. From the analysis of C. elegans longevity-related mutant genes, many signal transduction systems, with the insulin/insulin-like growth factor signal transduction system at the core, have emerged. It has become clear that this signal transduction system is greatly affected by external nutrients and is involved in the downstream regulation of oxidative stress, which is considered to be one of the main causes of aging.

pry-1 interacts with bar-1 to regulate vit-2 expression, lipid levels, and lifespan in Caenorhabditis elegans adults

The C. elegans Axin homolog, PRY-1 , is essential for multiple biological processes including vulval development, lipid metabolism, and lifespan maintenance. pry-1 mutants exhibit lower lipid contents and knockdowns of vit genes in pry-1 mutants can restore lipid levels, implicating vitellogenins' involvement in PRY-1 -mediated lipid homeostasis. As a component of the canonical WNT signal transduction pathway, PRY-1 inhibits the function of the β-catenin ortholog BAR-1 during vulval development and other developmental events. We showed earlier that a constitutively active form of BAR-1 causes a reduction in lipid contents, however, whether PRY-1 interacts with BAR-1 to regulate lipid levels and other processes is unknown. To this end, we examined the phenotypes of pry-1 and bar-1 single and double mutants. Our data suggest that the pry-1 - bar-1 genetic pathway regulates vit-2 expression, lipid homeostasis, and the lifespan of animals.

Ether lipid biosynthesis promotes lifespan extension and enables diverse pro-longevity paradigms in Caenorhabditis elegans

Biguanides, including the world's most prescribed drug for type 2 diabetes, metformin, not only lower blood sugar, but also promote longevity in preclinical models. Epidemiologic studies in humans parallel these findings, indicating favorable effects of metformin on longevity and on reducing the incidence and morbidity associated with aging-related diseases. Despite this promise, the full spectrum of molecular effectors responsible for these health benefits remains elusive. Through unbiased screening in Caenorhabditis elegans, we uncovered a role for genes necessary for ether lipid biosynthesis in the favorable effects of biguanides. We demonstrate that biguanides prompt lifespan extension by stimulating ether lipid biogenesis. Loss of the ether lipid biosynthetic machinery also mitigates lifespan extension attributable to dietary restriction, target of rapamycin (TOR) inhibition, and mitochondrial electron transport chain inhibition. A possible mechanistic explanation for this finding is that ether lipids are required for activation of longevity-promoting, metabolic stress defenses downstream of the conserved transcription factor skn-1/Nrf. In alignment with these findings, overexpression of a single, key, ether lipid biosynthetic enzyme, fard-1/FAR1, is sufficient to promote lifespan extension. These findings illuminate the ether lipid biosynthetic machinery as a novel therapeutic target to promote healthy aging.

mTORC2-NDRG1-CDC42 axis couples fasting to mitochondrial fission

Fasting triggers diverse physiological adaptations including increases in circulating fatty acids and mitochondrial respiration to facilitate organismal survival. The mechanisms driving mitochondrial adaptations and respiratory sufficiency during fasting remain incompletely understood. Here we show that fasting or lipid availability stimulates mTORC2 activity. Activation of mTORC2 and phosphorylation of its downstream target NDRG1 at serine 336 sustains mitochondrial fission and respiratory sufficiency. Time-lapse imaging shows that NDRG1, but not the phosphorylation-deficient NDRG1^Ser336Ala mutant, engages with mitochondria to facilitate fission in control cells, as well as in those lacking DRP1. Using proteomics, a small interfering RNA screen, and epistasis experiments, we show that mTORC2-phosphorylated NDRG1 cooperates with small GTPase CDC42 and effectors and regulators of CDC42 to orchestrate fission. Accordingly, Rictor^KO, NDRG1^Ser336Ala mutants and Cdc42-deficient cells each display mitochondrial phenotypes reminiscent of fission failure. During nutrient surplus, mTOR complexes perform anabolic functions; however, paradoxical reactivation of mTORC2 during fasting unexpectedly drives mitochondrial fission and respiration.

Characterization of the biochemical activity and tumor-promoting role of the dual protein methyltransferase METL-13/METTL13 in Caenorhabditis elegans

The methyltransferase-like protein 13 (METTL13) methylates the eukaryotic elongation factor 1 alpha (eEF1A) on two locations: the N-terminal amino group and lysine 55. The absence of this methylation leads to reduced protein synthesis and cell proliferation in human cancer cells. Previous studies showed that METTL13 is dispensable in non-transformed cells, making it potentially interesting for cancer therapy. However, METTL13 has not been examined yet in whole animals. Here, we used the nematode Caenorhabditis elegans as a simple model to assess the functions of METTL13. Using methyltransferase assays and mass spectrometry, we show that the C. elegans METTL13 (METL-13) methylates eEF1A (EEF-1A) in the same way as the human protein. Crucially, the cancer-promoting role of METL-13 is also conserved and depends on the methylation of EEF-1A, like in human cells. At the same time, METL-13 appears dispensable for animal growth, development, and stress responses. This makes C. elegans a convenient whole-animal model for studying METL13-dependent carcinogenesis without the complications of interfering with essential wild-type functions.

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.

Exploring the precision redox map during fasting-refeeding and satiation in C. elegans

Fasting is a popular dietary strategy because it grants numerous advantages, and redox regulation is one mechanism involved. However, the precise redox changes with respect to the redox species, organelles and tissues remain unclear, which hinders the understanding of the metabolic mechanism, and exploring the precision redox map under various dietary statuses is of great significance. Twelve redox-sensitive C. elegans strains stably expressing genetically encoded redox fluorescent probes (Hyperion sensing H2O2 and Grx1-roGFP2 sensing GSH/GSSG) in three organelles (cytoplasm, mitochondria and endoplasmic reticulum (ER)) were constructed in two tissues (body wall muscle and neurons) and were confirmed to respond to redox challenge. The H2O2 and GSSG/GSH redox changes in two tissues and three organelles were obtained by confocal microscopy during fasting, refeeding, and satiation. We found that under fasting condition, H2O2 decreased in most compartments, except for an increase in mitochondria, while GSSG/GSH increased in the cytoplasm of body muscle and the ER of neurons. After refeeding, the redox changes in H2O2 and GSSG/GSH caused by fasting were reversed in most organelles of the body wall muscle and neurons. In the satiated state, H2O2 increased markedly in the cytoplasm, mitochondria and ER of muscle and the ER of neurons, while GSSG/GSH exhibited no change in most organelles of the two tissues except for an increase in the ER of muscle. Our study systematically and precisely presents the redox characteristics under different dietary states in living animals and provides a basis for further investigating the redox mechanism in metabolism and optimizing dietary guidance.

Targeting the biology of aging with mTOR inhibitors

Inhibition of the protein kinase mechanistic target of rapamycin (mTOR) with the Food and Drug Administration (FDA)-approved therapeutic rapamycin promotes health and longevity in diverse model organisms. More recently, specific inhibition of mTORC1 to treat aging-related conditions has become the goal of basic and translational scientists, clinicians and biotechnology companies. Here, we review the effects of rapamycin on the longevity and survival of both wild-type mice and mouse models of human diseases. We discuss recent clinical trials that have explored whether existing mTOR inhibitors can safely prevent, delay or treat multiple diseases of aging. Finally, we discuss how new molecules may provide routes to the safer and more selective inhibition of mTOR complex 1 (mTORC1) in the decade ahead. We conclude by discussing what work remains to be done and the questions that will need to be addressed to make mTOR inhibitors part of the standard of care for diseases of aging.

The Janus-Faced Role of Lipid Droplets in Aging: Insights from the Cellular Perspective

It is widely accepted that nine hallmarks-including mitochondrial dysfunction, epigenetic alterations, and loss of proteostasis-exist that describe the cellular aging process. Adding to this, a well-described cell organelle in the metabolic context, namely, lipid droplets, also accumulates with increasing age, which can be regarded as a further aging-associated process. Independently of their essential role as fat stores, lipid droplets are also able to control cell integrity by mitigating lipotoxic and proteotoxic insults. As we will show in this review, numerous longevity interventions (such as mTOR inhibition) also lead to strong accumulation of lipid droplets in Saccharomyces cerevisiae, Caenorhabditis elegans, Drosophila melanogaster, and mammalian cells, just to name a few examples. In mammals, due to the variety of different cell types and tissues, the role of lipid droplets during the aging process is much more complex. Using selected diseases associated with aging, such as Alzheimer's disease, Parkinson's disease, type II diabetes, and cardiovascular disease, we show that lipid droplets are "Janus"-faced. In an early phase of the disease, lipid droplets mitigate the toxicity of lipid peroxidation and protein aggregates, but in a later phase of the disease, a strong accumulation of lipid droplets can cause problems for cells and tissues.

Lipid droplets and peroxisomes are co-regulated to drive lifespan extension in response to mono-unsaturated fatty acids

Dietary mono-unsaturated fatty acids (MUFAs) are linked to longevity in several species. But the mechanisms by which MUFAs extend lifespan remain unclear. Here we show that an organelle network involving lipid droplets and peroxisomes is critical for MUFA-induced longevity in Caenorhabditis elegans. MUFAs upregulate the number of lipid droplets in fat storage tissues. Increased lipid droplet number is necessary for MUFA-induced longevity and predicts remaining lifespan. Lipidomics datasets reveal that MUFAs also modify the ratio of membrane lipids and ether lipids-a signature associated with decreased lipid oxidation. In agreement with this, MUFAs decrease lipid oxidation in middle-aged individuals. Intriguingly, MUFAs upregulate not only lipid droplet number but also peroxisome number. A targeted screen identifies genes involved in the co-regulation of lipid droplets and peroxisomes, and reveals that induction of both organelles is optimal for longevity. Our study uncovers an organelle network involved in lipid homeostasis and lifespan regulation, opening new avenues for interventions to delay aging.

Ce Lab, 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, Ce Lab, 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. Ce Lab enables high-throughput simultaneous analysis of lifespan, reproductive span, and progeny production, refuting assumptions about the Disposable Soma hypothesis. Because Ce Lab 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. Ce Lab 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. Ce Lab 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.

Application of Caenorhabditis elegans in Lipid Metabolism Research

Over the last decade, the development and prevalence of obesity have posed a serious public health risk, which has prompted studies on the regulation of adiposity. With the ease of genetic manipulation, the diversity of the methods for characterizing body fat levels, and the observability of feeding behavior, Caenorhabditis elegans (C. elegans) is considered an excellent model for exploring energy homeostasis and the regulation of the cellular fat storage. In addition, the homology with mammals in the genes related to the lipid metabolism allows many aspects of lipid modulation by the regulators of the central nervous system to be conserved in this ideal model organism. In recent years, as the complex network of genes that maintain an energy balance has been gradually expanded and refined, the regulatory mechanisms of lipid storage have become clearer. Furthermore, the development of methods and devices to assess the lipid levels has become a powerful tool for studies in lipid droplet biology and the regulation of the nematode lipid metabolism. Herein, based on the rapid progress of C. elegans lipid metabolism-related studies, this review outlined the lipid metabolic processes, the major signaling pathways of fat storage regulation, and the primary experimental methods to assess the lipid content in nematodes. Therefore, this model system holds great promise for facilitating the understanding, management, and therapies of human obesity and other metabolism-related diseases.

Fatty acids derived from the probiotic Lacticaseibacillus rhamnosus HA-114 suppress age-dependent neurodegeneration

The human microbiota is believed to influence health. Microbiome dysbiosis may be linked to neurological conditions like Alzheimer's disease, amyotrophic lateral sclerosis, and Huntington's disease. We report the ability of a probiotic bacterial strain in halting neurodegeneration phenotypes. We show that Lacticaseibacillus rhamnosus HA-114 is neuroprotective in C. elegans models of amyotrophic lateral sclerosis and Huntington's disease. Our results show that neuroprotection from L. rhamnosus HA-114 is unique from other L. rhamnosus strains and resides in its fatty acid content. Neuroprotection by L. rhamnosus HA-114 requires acdh-1/ACADSB, kat-1/ACAT1 and elo-6/ELOVL3/6, which are associated with fatty acid metabolism and mitochondrial β-oxidation. Our data suggest that disrupted lipid metabolism contributes to neurodegeneration and that dietary intervention with L. rhamnosus HA-114 restores lipid homeostasis and energy balance through mitochondrial β-oxidation. Our findings encourage the exploration of L. rhamnosus HA-114 derived interventions to modify the progression of neurodegenerative diseases.

Riboflavin depletion promotes longevity and metabolic hormesis in Caenorhabditis elegans

Riboflavin is an essential cofactor in many enzymatic processes and in the production of flavin adenine dinucleotide (FAD). Here, we report that the partial depletion of riboflavin through knockdown of the C. elegans riboflavin transporter 1 (rft-1) promotes metabolic health by reducing intracellular flavin concentrations. Knockdown of rft-1 significantly increases lifespan in a manner dependent upon AMP-activated protein kinase (AMPK)/aak-2, the mitochondrial unfolded protein response, and FOXO/daf-16. Riboflavin depletion promotes altered energetic and redox states and increases adiposity, independent of lifespan genetic dependencies. Riboflavin-depleted animals also exhibit the activation of caloric restriction reporters without any reduction in caloric intake. Our findings indicate that riboflavin depletion activates an integrated hormetic response that promotes lifespan and healthspan in C. elegans.

Caenorhabditis elegans as an emerging model in food and nutrition research: importance of standardizing base diet

As a model organism that has helped revolutionize life sciences, Caenorhabditis elegans has been increasingly used in nutrition research. Here we explore the tradeoffs between pros and cons of its use as a dietary model based primarily on literature review from the past decade. We first provide an overview of its experimental strengths as an animal model, focusing on lifespan and healthspan, behavioral and physiological phenotypes, and conservation of key nutritional pathways. We then summarize recent advances of its use in nutritional studies, e.g. food preference and feeding behavior, sugar status and metabolic reprogramming, lifetime and transgenerational nutrition tracking, and diet-microbiota-host interactions, highlighting cutting-edge technologies originated from or developed in C. elegans. We further review current challenges of using C. elegans as a nutritional model, followed by in-depth discussions on potential solutions. In particular, growth scales and throughputs, food uptake mode, and axenic culture of C. elegans are appraised in the context of food research. We also provide perspectives for future development of chemically defined nematode food ("NemaFood") for C. elegans, which is now widely accepted as a versatile and affordable in vivo model and has begun to show transformative potential to pioneer nutrition science.

Diverse states and stimuli tune olfactory receptor expression levels to modulate food-seeking behavior

Animals must weigh competing needs and states to generate adaptive behavioral responses to the environment. Sensorimotor circuits are thus tasked with integrating diverse external and internal cues relevant to these needs to generate context-appropriate behaviors. However, the mechanisms that underlie this integration are largely unknown. Here, we show that a wide range of states and stimuli converge upon a single Caenorhabditis elegans olfactory neuron to modulate food-seeking behavior. Using an unbiased ribotagging approach, we find that the expression of olfactory receptor genes in the AWA olfactory neuron is influenced by a wide array of states and stimuli, including feeding state, physiological stress, and recent sensory cues. We identify odorants that activate these state-dependent olfactory receptors and show that altered expression of these receptors influences food-seeking and foraging. Further, we dissect the molecular and neural circuit pathways through which external sensory information and internal nutritional state are integrated by AWA. This reveals a modular organization in which sensory and state-related signals arising from different cell types in the body converge on AWA and independently control chemoreceptor expression. The synthesis of these signals by AWA allows animals to generate sensorimotor responses that reflect the animal's overall state. Our findings suggest a general model in which sensory- and state-dependent transcriptional changes at the sensory periphery modulate animals' sensorimotor responses to meet their ongoing needs and states.

Cabin1 domain-containing gene picd-1 interacts with pry-1/Axin to regulate multiple processes in Caenorhabditis elegans

The Axin family of scaffolding proteins control diverse processes, such as facilitating the interactions between cellular components and providing specificity to signaling pathways. While several Axin family members have been discovered in metazoans and shown to play crucial roles, their mechanism of action are not well understood. The Caenorhabditis elegans Axin homolog, pry-1, is a powerful tool for identifying interacting genes and downstream effectors that function in a conserved manner to regulate Axin-mediated signaling. Our lab and others have established pry-1's essential role in developmental processes that affect the reproductive system, seam cells, and a posterior P lineage cell, P11.p. Additionally, pry-1 is crucial for lipid metabolism, stress responses, and aging. In this study, we expanded on our previous work on pry-1 by reporting a novel interacting gene named picd-1 (pry-1-interacting and Cabin1 domain-containing). PICD-1 protein shares sequence conservation with CABIN1, a component of the HUCA complex. Our findings have revealed that PICD-1 is involved in several pry-1-mediated processes, including stress response and lifespan maintenance. picd-1's expression overlapped with that of pry-1 in multiple tissues throughout the lifespan. Furthermore, PRY-1 and PICD-1 inhibited CREB-regulated transcriptional coactivator homolog CRTC-1, which promotes longevity in a calcineurin-dependent manner. Overall, our study has demonstrated that picd-1 is necessary for mediating pry-1 function and provides the basis to investigate whether Cabin-1 domain-containing protein plays a similar role in Axin signaling in other systems.

Pharmaceutical and nutraceutical activation of FOXO3 for healthy longevity

Life expectancy has increased substantially over the last 150 years. Yet this means that now most people also spend a greater length of time suffering from various age-associated diseases. As such, delaying age-related functional decline and extending healthspan, the period of active older years free from disease and disability, is an overarching objective of current aging research. Geroprotectors, compounds that target pathways that causally influence aging, are increasingly recognized as a means to extend healthspan in the aging population. Meanwhile, FOXO3 has emerged as a geroprotective gene intricately involved in aging and healthspan. FOXO3 genetic variants are linked to human longevity, reduced disease risks, and even self-reported health. Therefore, identification of FOXO3-activating compounds represents one of the most direct candidate approaches to extending healthspan in aging humans. In this work, we review compounds that activate FOXO3, or influence healthspan or lifespan in a FOXO3-dependent manner. These compounds can be classified as pharmaceuticals, including PI3K/AKT inhibitors and AMPK activators, antidepressants and antipsychotics, muscle relaxants, and HDAC inhibitors, or as nutraceuticals, including primary metabolites involved in cell growth and sustenance, and secondary metabolites including extracts, polyphenols, terpenoids, and other purified natural compounds. The compounds documented here provide a basis and resource for further research and development, with the ultimate goal of promoting healthy longevity in humans.

Surveying Low-Cost Methods to Measure Lifespan and Healthspan in Caenorhabditis elegans

The discovery and development of Caenorhabditis elegans as a model organism was influential in biology, particularly in the field of aging. Many historical and contemporary studies have identified thousands of lifespan-altering paradigms, including genetic mutations, transgenic gene expression, and hormesis, a beneficial, low-grade exposure to stress. With its many advantages, including a short lifespan, easy and low-cost maintenance, and fully sequenced genome with homology to almost two-thirds of all human genes, C. elegans has quickly been adopted as an outstanding model for stress and aging biology. Here, several standardized methods are surveyed for measuring lifespan and healthspan that can be easily adapted into almost any research environment, especially those with limited equipment and funds. The incredible utility of C. elegans is featured, highlighting the capacity to perform powerful genetic analyses in aging biology without the necessity of extensive infrastructure. Finally, the limitations of each analysis and alternative approaches are discussed for consideration.

Transcriptome Analysis of the Nematodes Caenorhabditis elegans and Litoditis marina in Different Food Environments

Diets regulate animal development, reproduction, and lifespan. However, the underlying molecular mechanisms remain elusive. We previously showed that a chemically defined CeMM diet attenuates the development and promotes the longevity of C. elegans, but whether it impacts other nematodes is unknown. Here, we studied the effects of the CeMM diet on the development and longevity of the marine nematode Litoditis marina, which belongs to the same family as C. elegans. We further investigated genome-wide transcriptional responses to the CeMM and OP50 diets for both nematodes, respectively. We observed that the CeMM diet attenuated L. marina development but did not extend its lifespan. Through KEEG enrichment analysis, we found that many of the FOXO DAF-16 signaling and lysosome and xenobiotic metabolism related genes were significantly increased in C. elegans on the CeMM diet, which might contribute to the lifespan extension of C. elegans. Notably, we found that the expression of lysosome and xenobiotic metabolism pathway genes was significantly down-regulated in L. marina on CeMM, which might explain why the CeMM diet could not promote the lifespan of L. marina compared to bacterial feeding. Additionally, the down-regulation of several RNA transcription and protein generation and related processes genes in C. elegans on CeMM might not only be involved in extending longevity, but also contribute to attenuating the development of C. elegans on the CeMM diet, while the down-regulation of unsaturated fatty acids synthesis genes in L. marina might contribute to slow down its growth while on CeMM. This study provided important insights into how different diets regulate development and lifespan, and further genetic analysis of the candidate gene(s) of development and longevity will facilitate exploring the molecular mechanisms underlying how diets regulate animal physiology and health in the context of variable nutritional environments.

Cell autonomous and non-autonomous consequences of deviations in translation machinery on organism growth and the connecting signalling pathways

Translation machinery is responsible for the production of cellular proteins; thus, cells devote the majority of their resources to ribosome biogenesis and protein synthesis. Single-copy loss of function in the translation machinery components results in rare ribosomopathy disorders, such as Diamond-Blackfan anaemia in humans and similar developmental defects in various model organisms. Somatic copy number alterations of translation machinery components are also observed in specific tumours. The organism-wide response to haploinsufficient loss-of-function mutations in ribosomal proteins or translation machinery components is complex: variations in translation machinery lead to reduced ribosome biogenesis, protein translation and altered protein homeostasis and cellular signalling pathways. Cells are affected both autonomously and non-autonomously by changes in translation machinery or ribosome biogenesis through cell-cell interactions and secreted hormones. We first briefly introduce the model organisms where mutants or knockdowns of protein synthesis and ribosome biogenesis are characterized. Next, we specifically describe observations in Caenorhabditis elegans and Drosophila melanogaster, where insufficient protein synthesis in a subset of cells triggers cell non-autonomous growth or apoptosis responses that affect nearby cells and tissues. We then cover the characterized signalling pathways that interact with ribosome biogenesis/protein synthesis machinery with an emphasis on their respective functions during organism development.

Neuronal C/EBPβ/AEP pathway shortens life span via selective GABAnergic neuronal degeneration by FOXO repression

The age-related cognitive decline of normal aging is exacerbated in neurodegenerative diseases including Alzheimer's disease (AD). However, it remains unclear whether age-related cognitive regulators in AD pathologies contribute to life span. Here, we show that C/EBPβ, an Aβ and inflammatory cytokine-activated transcription factor that promotes AD pathologies via activating asparagine endopeptidase (AEP), mediates longevity in a gene dose-dependent manner in neuronal C/EBPβ transgenic mice. C/EBPβ selectively triggers inhibitory GABAnergic neuronal degeneration by repressing FOXOs and up-regulating AEP, leading to aberrant neural excitation and cognitive dysfunction. Overexpression of CEBP-2 or LGMN-1 (AEP) in Caenorhabditis elegans neurons but not muscle stimulates neural excitation and shortens life span. CEBP-2 or LGMN-1 reduces daf-2 mutant-elongated life span and diminishes daf-16-induced longevity. C/EBPβ and AEP are lower in humans with extended longevity and inversely correlated with REST/FOXO1. These findings demonstrate a conserved mechanism of aging that couples pathological cognitive decline to life span by the neuronal C/EBPβ/AEP pathway.

Temporal scaling in C. elegans larval development

An enduring mystery of development is how its timing is controlled, particularly for development after birth, where timing is highly flexible and depends on environmental conditions, such as food availability and diet. We followed timing of cell- and organism-level events in individual Caenorhabditis elegans larvae developing from hatching to adulthood, uncovering widespread variations in event timing, both between isogenic individuals in the same environment and when changing conditions and genotypes. However, in almost all cases, we found that events occurred at the same time, when time was rescaled by the duration of development measured in each individual. This observation of “temporal scaling” poses strong constraints on models to explain timing of larval development.

It is essential that correct temporal order of cellular events is maintained during animal development. During postembryonic development, the rate of development depends on external conditions, such as food availability, diet, and temperature. How timing of cellular events is impacted when the rate of development is changed at the organism level is not known. We used a unique time-lapse microscopy approach to simultaneously measure timing of oscillatory gene expression, hypodermal stem cell divisions, and cuticle shedding in individual Caenorhabditis elegans larvae, as they developed from hatching to adulthood. This revealed strong variability in timing between isogenic individuals under the same conditions. However, this variability obeyed “temporal scaling,” meaning that events occurred at the same time when measured relative to the total duration of development in each individual. We also observed pervasive changes in timing when temperature, diet, or genotype were varied, but with larval development divided in “epochs” that differed in how event timing was impacted. Yet, these variations in timing were still explained by temporal scaling when time was rescaled by the duration of the respective epochs in each individual. Surprisingly, timing obeyed temporal scaling even in mutants lacking lin-42/Period, presumed a core regulator of timing of larval development, that exhibited strongly delayed, heterogeneous timing. However, shifting conditions middevelopment perturbed temporal scaling and changed event order in a highly condition-specific manner, indicating that a complex machinery is responsible for temporal scaling under constant conditions.

Polystyrene microbeads influence lipid storage distribution in C. elegans as revealed by coherent anti-Stokes Raman scattering (CARS) microscopy

The exposure of Caenorhabditis elegans to polystyrene (PS) beads of a wide range of sizes impedes feeding, by reducing food consumption, and has been linked to inhibitory effects on the reproductive capacity of this nematode, as determined in standardized toxicity tests. Lipid storage provides energy for longevity, growth, and reproduction and may influence the organismal response to stress, including the food deprivation resulting from microplastics exposure. However, the effects of microplastics on energy storage have not been investigated in detail. In this study, C. elegans was exposed to ingestible sizes of PS beads in a standardized toxicity test (96 h) and in a multigeneration test (∼21 days), after which lipid storage was quantitatively analyzed in individual adults using coherent anti-Stokes Raman scattering (CARS) microscopy. The results showed that lipid storage distribution in C. elegans was altered when worms were exposed to microplastics in form of PS beads. For example, when exposed to 0.1-μm PS beads, the lipid droplet count was 93% higher, the droplets were up to 56% larger, and the area of the nematode body covered by lipids was up to 79% higher than in unexposed nematodes. The measured values tended to increase as PS bead sizes decreased. Cultivating the nematodes for 96 h under restricted food conditions in the absence of beads reproduced the altered lipid storage and suggested that it was triggered by food deprivation, including that induced by the dilutional effects of PS bead exposure. Our study demonstrates the utility of CARS microscopy to comprehensively image the smaller microplastics (<10 μm) ingested by nematodes and possibly other biota in investigations of the effects at the level of the individual organism.

A Potential Probiotic Lactobacillus plantarum JBC5 Improves Longevity and Healthy Aging by Modulating Antioxidative, Innate Immunity and Serotonin-Signaling Pathways in Caenorhabditis elegans

Since the hypothesis of Dr. Elie Metchnikoff on lactobacilli-mediated healthy aging, several microbes have been reported to extend the lifespan with different features of healthy aging. However, a microbe affecting diverse features of healthy aging is of choice for broader acceptance and marketability as a next-generation probiotic. We employed Caenorhabditis elegans as a model to understand the potential of Lactobacillus plantarum JBC5 (LPJBC5), isolated from fermented food sample on longevity and healthy aging as well as their underlying mechanisms. Firstly, LPJBC5 enhanced the mean lifespan of C. elegans by 27.81% compared with control (untreated). LPBC5-induced longevity was accompanied with better aging-associated biomarkers, such as physical functions, fat, and lipofuscin accumulation. Lifespan assay on mutant worms and gene expression studies indicated that LPJBC5-mediated longevity was due to upregulation of the skinhead-1 (skn-1) gene activated through p38 MAPK signaling cascade. Secondly, the activated transcription factor SKN-1 upregulated the expression of antioxidative, thermo-tolerant, and anti-pathogenic genes. In support, LPJBC5 conferred resistance against abiotic and biotic stresses such as oxidative, heat, and pathogen. LPJBC5 upregulated the expression of intestinal tight junction protein ZOO-1 and improved gut integrity. Thirdly, LPJBC5 improved the learning and memory of worms trained on LPJBC5 compared with naive worms. The results showed upregulation of genes involved in serotonin signaling (ser-1, mod-1, and tph-1) in LPJBC5-fed worms compared with control, suggesting that serotonin-signaling was essential for LPJBC5-mediated improved cognitive function. Fourthly, LPJBC5 decreased the fat accumulation in worms by reducing the expression of genes encoding key substrates and enzymes of fat metabolism (i.e., fat-5 and fat-7). Lastly, LPJBC5 reduced the production of reactive oxygen species and improved mitochondrial function, thereby reducing apoptosis in worms. The capability of a single bacterium on pro-longevity and the features of healthy aging, including enhancement of gut integrity and cognitive functions, makes it an ideal candidate for promotion as a next-generation probiotic.

Molecular mechanisms of dietary restriction promoting health and longevity

Dietary restriction with adequate nutrition is the gold standard for delaying ageing and extending healthspan and lifespan in diverse species, including rodents and non-human primates. In this Review, we discuss the effects of dietary restriction in these mammalian model organisms and discuss accumulating data that suggest that dietary restriction results in many of the same physiological, metabolic and molecular changes responsible for the prevention of multiple ageing-associated diseases in humans. We further discuss how different forms of fasting, protein restriction and specific reductions in the levels of essential amino acids such as methionine and the branched-chain amino acids selectively impact the activity of AKT, FOXO, mTOR, nicotinamide adenine dinucleotide (NAD+), AMP-activated protein kinase (AMPK) and fibroblast growth factor 21 (FGF21), which are key components of some of the most important nutrient-sensing geroprotective signalling pathways that promote healthy longevity.

Translational control in cell ageing: an update

Cellular ageing is one of the main drivers of organismal ageing and holds keys towards improving the longevity and quality of the extended life. Elucidating mechanisms underlying the emergence of the aged cells as well as their altered responses to the environment will help understanding the evolutionarily defined longevity preferences across species with different strategies of survival. Much is understood about the role of alterations in the DNA, including many epigenetic modifications such as methylation, in relation to the aged cell phenotype. While transcriptomes of the aged cells are beginning to be better-characterised, their translational responses remain under active investigation. Many of the translationally controlled homeostatic pathways are centred around mitigation of DNA damage, cell stress response and regulation of the proliferative potential of the cells, and thus are critical for the aged cell function. Translation profiling-type studies have boosted the opportunities in discovering the function of protein biosynthesis control and are starting to be applied to the aged cells. Here, we provide a summary of the current knowledge about translational mechanisms considered to be commonly altered in the aged cells, including the integrated stress response-, mechanistic target of Rapamycin- and elongation factor 2 kinase-mediated pathways. We enlist and discuss findings of the recent works that use broad profiling-type approaches to investigate the age-related translational pathways. We outline the limitations of the methods and the remaining unknowns in the established ageing-associated translation mechanisms, and flag translational mechanisms with high prospective importance in ageing, for future studies.

Workflow for Segmentation of Caenorhabditis elegans from Fluorescence Images for the Quantitation of Lipids

The small and transparent nematode Caenorhabditis elegans is increasingly employed for phenotypic in vivo chemical screens. The influence of compounds on worm body fat stores can be assayed with Nile red staining and imaging. Segmentation of C. elegans from fluorescence images is hereby a primary task. In this paper, we present an image-processing workflow that includes machine-learning-based segmentation of C. elegans directly from fluorescence images and quantifies their Nile red lipid-derived fluorescence. The segmentation is based on a J48 classifier using pixel entropies and is refined by size-thresholding. The accuracy of segmentation was >90% in our external validation. Binarization with a global threshold set to the brightness of the vehicle control group worms of each experiment allows a robust and reproducible quantification of worm fluorescence. The workflow is available as a script written in the macro language of imageJ, allowing the user additional manual control of classification results and custom specification settings for binarization. Our approach can be easily adapted to the requirements of other fluorescence image-based experiments with C. elegans.

Identification of enzymes that have helminth-specific active sites and are required for Rhodoquinone-dependent metabolism as targets for new anthelmintics

Soil transmitted helminths (STHs) are major human pathogens that infect over a billion people. Resistance to current anthelmintics is rising and new drugs are needed. Here we combine multiple approaches to find druggable targets in the anaerobic metabolic pathways STHs need to survive in their mammalian host. These require rhodoquinone (RQ), an electron carrier used by STHs and not their hosts. We identified 25 genes predicted to act in RQ-dependent metabolism including sensing hypoxia and RQ synthesis and found 9 are required. Since all 9 have mammalian orthologues, we used comparative genomics and structural modeling to identify those with active sites that differ between host and parasite. Together, we found 4 genes that are required for RQ-dependent metabolism and have different active sites. Finding these high confidence targets can open up in silico screens to identify species selective inhibitors of these enzymes as new anthelmintics.

Probiotics Interactions and the Modulation of Major Signalling Pathways in Host Model Organism Caenorhabditis elegans

Microorganisms live in the human digestive system and the gut microbiome constitutes part of our prime determining component for healthy aging and wellness. Gut microbiota has broad influences on its host, beginning from the digestion of food and nutrients absorption to protective roles against invading pathogens and host immune system regulation. Dysbiosis of the gut microbial composition has been linked to numerous diseases and there is a need to have a better grasp on what makes a 'good' gut microbiome. Caenorhabditis elegans (C. elegans) model organism is considered as a well-suited in-vivo model system and, is at the frontline of probiotic research because of its well-defined characteristics and prolific nature. Most importantly, C. elegans feeds on bacteria, which speeds up manipulations and investigations in probiotics research tremendously. With its unique salient features of short lifespan, and ease of propagation, different unknown probiotics biological roles can be measured at an organism level with precision in the form of worm's stress responses, survivability, and lifespan. In this review, new insights on the different mechanisms underlying the establishment of probiotics regulations of conserved signalling pathways such as p38 MAPK/SKN-1, DAF-2/DAF-16, and JNK-1/DAF-16 is highlighted based on information obtained from C. elegans studies. Along with the current state of knowledge and the uniqueness of C. elegans as a model organism, explorations of its future contribution and scope in synthetic biology and probiotics engineering strains are also addressed. This is expected to strengthen our understanding of probiotics roles and to facilitate novel discovery and applications, for specific therapeutics against age-related disorders and various pathophysiological conditions.

Fisetin-induced PTEN expression reverses cellular senescence by inhibiting the mTORC2-Akt Ser473 phosphorylation pathway in vascular smooth muscle cells

Cellular senescence is caused by a wide range of intracellular and extracellular stimuli and influences physiological functions, leading to the progression of age-related diseases. Many studies have shown that cellular senescence is related to phosphatase and tension homolog deleted on chromosome ten (PTEN) loss and mammalian target of rapamycin (mTOR) activation. Although it has been reported that mTOR complex 1 (mTORC1) is major anti-aging target in several cell types, the functions and mechanisms of mTOR complex 2 (mTORC2) during aging have not been elucidated in vascular smooth muscle cells (VSMCs). Therefore, the aim of this study was to reveal the relationship between PTEN and mTORC2 during VSMC senescence. We found adriamycin-induced VSMC senescence was accompanied by reduced PTEN protein expression and upregulation of the mTORC2-Akt (Ser 473) pathway and that fisetin treatment reduced VSMC senescence by increasing PTEN and decreasing mTORC2 protein levels. Furthermore, PTEN played a primary role in the anti-aging effect of fisetin, and fisetin-activated PTEN directly regulated the mTORC2-Akt (Ser 473) signaling pathway, and attenuated senescence phenotypes such as senescence-associated β-galactosidase (SA-β-gal) and the p53-p21 signaling pathway in VSMCs. In mouse aortas, fisetin delayed aging by regulating the PTEN-mTORC2-Akt (Ser473) signaling pathway. These results suggest PTEN and mTORC2 are associated with cellular senescence in VSMCs and that the mTORC2-Akt (Ser 473) signaling pathway be considered a new target for preventing senescence-related diseases.

Context-specific regulation of lysosomal lipolysis through network-level diverting of transcription factor interactions

Plasticity in multicellular organisms involves signaling pathways converting contexts-either natural environmental challenges or laboratory perturbations-into context-specific changes in gene expression. Congruently, the interactions between the signaling molecules and transcription factors (TF) regulating these responses are also context specific. However, when a target gene responds across contexts, the upstream TF identified in one context is often inferred to regulate it across contexts. Reconciling these stable TF-target gene pair inferences with the context-specific nature of homeostatic responses is therefore needed. The induction of the Caenorhabditis elegans genes lipl-3 and lipl-4 is observed in many genetic contexts and is essential to survival during fasting. We find DAF-16/FOXO mediating lipl-4 induction in all contexts tested; hence, lipl-4 regulation seems context independent and compatible with across-context inferences. In contrast, DAF-16-mediated regulation of lipl-3 is context specific. DAF-16 reduces the induction of lipl-3 during fasting, yet it promotes it during oxidative stress. Through discrete dynamic modeling and genetic epistasis, we define that DAF-16 represses HLH-30/TFEB-the main TF activating lipl-3 during fasting. Contrastingly, DAF-16 activates the stress-responsive TF HSF-1 during oxidative stress, which promotes C. elegans survival through induction of lipl-3 Furthermore, the TF MXL-3 contributes to the dominance of HSF-1 at the expense of HLH-30 during oxidative stress but not during fasting. This study shows how context-specific diverting of functional interactions within a molecular network allows cells to specifically respond to a large number of contexts with a limited number of molecular players, a mode of transcriptional regulation we name "contextualized transcription."

Knock-down of odr-3 and ife-2 additively extends lifespan and healthspan in C. elegans

Genetic manipulations can ameliorate the aging process and extend the lifespan of model organisms. The aim of this research was to identify novel genetic interventions that promote both lifespan and healthspan, by combining the effects of multiple longevity-associated gene inactivations in C. elegans. For this, the individual and combined effects of the odr-3 mutation and of ife-2 and cku-70 knock-downs were studied, both in the wild type and daf-16 mutant backgrounds. We found that besides increasing the lifespan of wild type animals, the knock-down of ife-2 (starting at L4) also extends the lifespan and healthspan of long-lived odr-3 mutants. In the daf-16 background, ife-2 and odr-3 impairment exert opposing effects individually, while the daf-16; odr-3; ife-2 deficient animals show a similar lifespan and healthspan as daf-16, suggesting that the odr-3 and ife-2 effector outcomes converge downstream of DAF-16. By contrast, cku-70 knock-down did not extend the lifespan of single or double odr-3; ife-2 inactivated animals, and was slightly deleterious to healthspan. In conclusion, we report that impairment of odr-3 and ife-2 increases lifespan and healthspan in an additive and synergistic manner, respectively, and that this result is not improved by further knocking-down cku-70.

Genes in human obesity loci are causal obesity genes in C. elegans

Obesity and its associated metabolic syndrome are a leading cause of morbidity and mortality. Given the disease's heavy burden on patients and the healthcare system, there has been increased interest in identifying pharmacological targets for the treatment and prevention of obesity. Towards this end, genome-wide association studies (GWAS) have identified hundreds of human genetic variants associated with obesity. The next challenge is to experimentally define which of these variants are causally linked to obesity, and could therefore become targets for the treatment or prevention of obesity. Here we employ high-throughput in vivo RNAi screening to test for causality 293 C. elegans orthologs of human obesity-candidate genes reported in GWAS. We RNAi screened these 293 genes in C. elegans subject to two different feeding regimens: (1) regular diet, and (2) high-fructose diet, which we developed and present here as an invertebrate model of diet-induced obesity (DIO). We report 14 genes that promote obesity and 3 genes that prevent DIO when silenced in C. elegans. Further, we show that knock-down of the 3 DIO genes not only prevents excessive fat accumulation in primary and ectopic fat depots but also improves the health and extends the lifespan of C. elegans overconsuming fructose. Importantly, the direction of the association between expression variants in these loci and obesity in mice and humans matches the phenotypic outcome of the loss-of-function of the C. elegans ortholog genes, supporting the notion that some of these genes would be causally linked to obesity across phylogeny. Therefore, in addition to defining causality for several genes so far merely correlated with obesity, this study demonstrates the value of model systems compatible with in vivo high-throughput genetic screening to causally link GWAS gene candidates to human diseases.

Insulin/IGF-1 signaling and heat stress differentially regulate HSF1 activities in germline development

Germline development is sensitive to nutrient availability and environmental perturbation. Heat shock transcription factor 1 (HSF1), a key transcription factor driving the cellular heat shock response (HSR), is also involved in gametogenesis. The precise function of HSF1 (HSF-1 in C. elegans) and its regulation in germline development are poorly understood. Using the auxin-inducible degron system in C. elegans, we uncovered a role of HSF-1 in progenitor cell proliferation and early meiosis and identified a compact but important transcriptional program of HSF-1 in germline development. Interestingly, heat stress only induces the canonical HSR in a subset of germ cells but impairs HSF-1 binding at its developmental targets. Conversely, insulin/insulin growth factor 1 (IGF-1) signaling dictates the requirement for HSF-1 in germline development and functions through repressing FOXO/DAF-16 in the soma to activate HSF-1 in germ cells. We propose that this non-cell-autonomous mechanism couples nutrient-sensing insulin/IGF-1 signaling to HSF-1 activation to support homeostasis in rapid germline growth.

Saturated very long chain fatty acid configures glycosphingolipid for lysosome homeostasis in long-lived C. elegans

The contents of numerous membrane lipids change upon ageing. However, it is unknown whether and how any of these changes are causally linked to lifespan regulation. Acyl chains contribute to the functional specificity of membrane lipids. In this study, working with C. elegans, we identified an acyl chain-specific sphingolipid, C22 glucosylceramide, as a longevity metabolite. Germline deficiency, a conserved lifespan-extending paradigm, induces somatic expression of the fatty acid elongase ELO-3, and behenic acid (22:0) generated by ELO-3 is incorporated into glucosylceramide for lifespan regulation. Mechanistically, C22 glucosylceramide is required for the membrane localization of clathrin, a protein that regulates membrane budding. The reduction in C22 glucosylceramide impairs the clathrin-dependent autophagic lysosome reformation, which subsequently leads to TOR activation and longevity suppression. These findings reveal a mechanistic link between membrane lipids and ageing and suggest a model of lifespan regulation by fatty acid-mediated membrane configuration.

The membrane lipids change with ageing and function as regulatory molecules, but the underlying mechanisms are incompletely understood. Here, the authors identify C22 glucosylceramide as a regulator of the longevity transcription factor SKN-1, and show that C22 glucosylceramide regulates lifespan by controlling lysosome homeostasis and subsequent TOR activation.

Nesfatin-1 in lipid metabolism and lipid-related diseases

Nesfatin-1, an anorexic neuropeptide discovered in 2006, is widely distributed in the central nervous system and peripheral tissues. It has been shown to be involved in the regulation of food intake and lipid metabolism, inhibiting fat accumulation, accelerating lipid decomposition, and in general, inhibiting the development of lipid-related diseases, such as obesity and metabolic syndrome. Potential mechanisms of Nesfatin-1 action in lipid metabolism and lipid-related diseases will be discussed as well as its role as a biomarker in cardiovascular disease. This review expected to provide a new strategy for the diagnosis and prevention of clinically related diseases.