Ageing in Drosophila: the role of the insulin/Igf and TOR signalling network

Transiently restricting individual amino acids protects Drosophila melanogaster against multiple stressors

Nutrition and resilience are linked, though it is not yet clear how diet confers stress resistance or the breadth of stressors that it can protect against. We have previously shown that transiently restricting an essential amino acid can protect Drosophila melanogaster against nicotine poisoning. Here, we sought to characterize the nature of this dietary-mediated protection and determine whether it was sex, amino acid and/or nicotine specific. When we compared between sexes, we found that isoleucine deprivation increases female, but not male, nicotine resistance. Surprisingly, we found that this protection afforded to females was not replicated by dietary protein restriction and was instead specific to individual amino acid restriction. To understand whether these beneficial effects of diet were specific to nicotine or were generalizable across stressors, we pre-treated flies with amino acid restriction diets and exposed them to other types of stress. We found that some of the diets that protected against nicotine also protected against oxidative and starvation stress, and improved survival following cold shock. Interestingly, we found that a diet lacking isoleucine was the only diet to protect against all these stressors. These data point to isoleucine as a critical determinant of robustness in the face of environmental challenges.

Altering heparan sulfate suppresses cell abnormalities and neuron loss in Drosophila presenilin model of Alzheimer Disease

We examined the function of heparan-sulfate-modified proteoglycans (HSPGs) in pathways affecting Alzheimer disease (AD)-related cell pathology in human cell lines and mouse astrocytes. Mechanisms of HSPG influences on presenilin-dependent cell loss were evaluated in Drosophila using knockdown of the presenilin homolog, Psn, together with partial loss-of-function of sulfateless (sfl), a gene specifically affecting HS sulfation. HSPG modulation of autophagy, mitochondrial function, and lipid metabolism were shown to be conserved in human cell lines, Drosophila, and mouse astrocytes. RNA interference (RNAi) of Ndst1 reduced intracellular lipid levels in wild-type mouse astrocytes or those expressing humanized variants of APOE, APOE3, and APOE4. Neuron-directed knockdown of Psn in Drosophila produced apoptosis and cell loss in the brain, phenotypes suppressed by reductions in sfl expression. Abnormalities in mitochondria, liposomes, and autophagosome-derived structures in animals with Psn knockdown were also rescued by reduction of sfl. These findings support the direct involvement of HSPGs in AD pathogenesis.

IGF-1 and IGFBP-1 as Possible Predictors of Response to Lifestyle Intervention-Results from Randomized Controlled Trials

Lifestyle interventions can prevent type 2 diabetes (T2DM). However, some individuals do not experience anticipated improvements despite weight loss. Biomarkers to identify such individuals at early stages are lacking. Insulin-like growth factor 1 (IGF- 1) and Insulin-like growth factor binding protein 1(IGFBP-1) were shown to predict T2DM onset in prediabetes. We assessed whether these markers also predict the success of lifestyle interventions, thereby possibly guiding personalized strategies. We analyzed the fasting serum levels of IGF-1, IGFBP-1, and Insulin-like growth factor binding protein 2 (IGFBP-2) in relation to changes in metabolic and anthropometric parameters, including intrahepatic lipids (IHLs) and visceral adipose tissue (VAT) volume, measured by magnetic resonance imaging (MRI), in 345 participants with a high risk for prediabetes (54% female; aged 36-80 years). Participants were enrolled in three randomized dietary intervention trials and assessed both at baseline and one year post-intervention. Statistical analyses were performed using IBM SPSS Statistics (version 28), and significance was set at p < 0.05. Within the 1-year intervention, overall significant improvements were observed. Stratifying individuals by baseline IGF-1 and IGFBP-1 percentiles revealed significant differences: higher IGF-1 levels were associated with more favorable changes compared to lower levels, especially in VAT and IHL. Lower baseline IGFBP-1 levels were associated with greater improvements, especially in IHL and 2 h glucose. Higher bioactive IGF-1 levels might predict better metabolic outcomes following lifestyle interventions in prediabetes, potentially serving as biomarkers for personalized interventions.

Anti-aging effect of glycerophosphocholine in Steinernema kraussei 0657L

Glycerophosphocholine (GPC) is a water-soluble small molecule found naturally in humans and foods such as milk and soybeans. It can activate the IIS pathway by regulating the expression of daf-2, ins-18 and daf-16 genes, sek-1 and skn-1 genes of MAPK pathway, sod-3, ctl-1, gst-4 and other antioxidant genes. GPC can relieve symptoms related to aging in organisms. The aim of this study was to probe the effects of GPC on the longevity and stress resistance of the entomopathogenic nematode (EPN) Steinernema kraussei 0657L strain. The results showed that the lifespan of S. kraussei 0657L was significantly prolonged by 50 mM GPC treatment, which was 54.55% longer than that of the control (0 mM GPC). GPC significantly inhibited reactive oxygen species (ROS) and lipofuscin accumulation, but the body size and fecundity of S. kraussei 0657L had little changed. At the same time, the longevity of S. kraussei 0657L exposed to heat shock and UV-B radiation was significantly prolonged than that with no external stress. GPC supplementation increased the activity of antioxidant enzymes and corresponding gene expression. Under treatment with 50 mM GPC, the activities of superoxide dismutase and catalase were increased by 1.90- and 4.13-fold, respectively, the expression of the sod-3 and ctl-1 genes was increased by 3.60- and 0.60-fold, respectively, and harmful reactive oxygen species were removed. In addition, the expression levels of the ins-18, skn-1, sek-1 and gst-4 genes related to the insulin/IGF-1 signaling pathway were upregulated 1.04-, 1.84-, 2.21- and 1.24-fold, respectively. These results indicate that GPC is mainly involved in the lifespan regulation of S. kraussei 0657L and plays an important role in resistance to external stress by activating the insulin/IGF-1 signaling pathway and downstream PI3K/MAPK kinase, creating a new idea for improving the commercial efficacy of S. kraussei. It also laid a theoretical foundation for its further efficient development and utilization in the field of biological control.

Endocrine Regulation of Aging in the Fruit Fly Drosophila melanogaster

The past few decades have witnessed increasing research clarifying the role of endocrine signaling in the regulation of aging in both vertebrates and invertebrates. Studies using the model organism fruit fly Drosophila melanogaster have largely advanced our understanding of evolutionarily conserved mechanisms in the endocrinology of aging and anti-aging. Mutations in single genes involved in endocrine signaling modify lifespan, as do alterations of endocrine signaling in a tissue- or cell-specific manner, highlighting a central role of endocrine signaling in coordinating the crosstalk between tissues and cells to determine the pace of aging. Here, we review the current landscape of research in D. melanogaster that offers valuable insights into the endocrine-governed mechanisms which influence lifespan and age-related physiology.

A genetic toolkit underlying the queen phenotype in termites with totipotent workers

Social insect castes (e.g., queens, workers) are prime examples of phenotypic plasticity (i.e., different phenotypes arising from the same genotype). Yet, the mechanisms that give rise to highly fertile, long-lived queens versus non-reproducing, short-lived workers are not well understood. Recently, a module of co-expressed genes has been identified that characterizes queens compared to workers of the termite Cryptotermes secundus (Kalotermitidae): the Queen Central Module (QCM). We tested whether the QCM is shared in termite species, in which queens gradually develop via early larval and late larval instars, the latter functioning as totipotent workers (linear development). Similar as in C. secundus, gene expression profiles revealed an enrichment of QCM genes in Zootermopsis angusticollis queens, a species from another termite family (Archotermopsidae). The expression of these QCM genes became gradually enriched during development from early larval instars via workers to queens. Thus, our results support the hypothesis of a conserved genetic toolkit that characterizes termite queens with gradual linear development. Our data also imply a strong caste-specific tissue specificity with the QCM signal being restricted to head-prothorax tissues in termite queens. This tissue-specific expression of key aging-related genes might have facilitated the evolution of a long lifespan in termite queens.

Biochemical characterization of the Drosophila insulin receptor kinase and longevity-associated mutants

Drosophila melanogaster (fruit fly) insulin receptor (D-IR) is highly homologous to the human counterpart. Like the human pathway, D-IR responds to numerous insulin-like peptides to activate cellular signals that regulate growth, development, and lipid metabolism in fruit flies. Allelic mutations in the D-IR kinase domain elevate life expectancy in fruit flies. We developed a robust heterologous expression system to express and purify wild-type and longevity-associated mutant D-IR kinase domains to investigate enzyme kinetics and substrate specificities. D-IR exhibits remarkable similarities to the human insulin receptor kinase domain but diverges in substrate preferences. We show that longevity-associated mutations reduce D-IR catalytic activity. Deletion of the unique kinase insert domain portion or mutations proximal to activating tyrosines do not influence kinase activity, suggesting their potential role in substrate recruitment and downstream signaling. Through biochemical investigations, this study enhances our comprehension of D-IR's role in Drosophila physiology, complementing genetic studies and expanding our knowledge on the catalytic functions of this conserved signaling pathway.

A method for in vivo evaluation of α-glucosidase inhibition using Drosophila

The development of α-glucosidase inhibitors is essential for the prevention of type II diabetes. Previous research has investigated in vitro inhibition using isolated α-glucosidase, which may not accurately reflect physical processes. The method presented in this study aims to establish a rapid and inexpensive in vivo method to study the inhibition of α-glucosidase activity using Drosophila as a model organism. This method can be used to calculate the IC50 value of compounds of interest for inhibition of α-glucosidase activity. The method established in this study can be used for in vivo screening of anti-diabetic compounds. •A rapid and inexpensive in vivo method to study the inhibition of α-glucosidase activity.•This method can be used to calculate the IC50 value of compounds of interest for inhibition of α-glucosidase activity.•This is a useful method for in vivo screening of anti-diabetic compounds.

In Vitro and In Vivo Evaluation for Antioxidant and Anti-Diabetic Properties of Cyperus rotundus L. Kombucha

Cyperus rotundus L. exhibits promising potential for the development of functional foods due to its documented pharmacological and biological activities. This study investigated the antioxidant and anti-diabetic properties of C. rotundus kombucha. The results demonstrated potent antioxidant activity with an IC50 value of 76.7 ± 9.6 µL/mL for the DPPH assay and 314.2 ± 16.9 µL/mL for the ABTS assay. Additionally, the kombucha demonstrated alpha-glucosidase inhibitory with an IC50 value of 142.7 ± 5.2 µL/mL. This in vitro antioxidant potential was further validated in vivo using Drosophila. Drosophila fed a high-sugar diet and supplemented with pure kombucha revealed significant increases in DPPH and ABTS free radical scavenging activity. Drosophila on a high-sugar diet supplemented with varying kombucha concentrations manifested enhanced resistance to oxidative stresses induced by H2O2 and paraquat. Concurrently, there was a notable decline in lipid peroxidation levels. Additionally, significant upregulations in CAT, SOD1, and SOD2 activities were observed when the high-sugar diet was supplemented with kombucha. Furthermore, in vivo assessments using Drosophila demonstrated significant reductions in alpha-glucosidase activity when fed with kombucha (reduced by 34.04%, 13.79%, and 11.60% when treated with 100%, 40%, and 10% kombucha, respectively). A comprehensive GC-MS and HPLC analysis of C. rotundus kombucha detected the presence of antioxidative and anti-glucosidase compounds. In conclusion, C. rotundus kombucha exhibits considerable antioxidant and anti-diabetic properties, demonstrating its potential as a beneficial beverage for health promotion.

Advanced maternal age has negative multigenerational impacts during Drosophila melanogaster embryogenesis

Increasing maternal age is commonly accompanied by decreased fitness in offspring. In Drosophila melanogaster, maternal senescence negatively affects multiple facets of offspring phenotype and fitness. These maternal effects are particularly large on embryonic viability. Identifying which embryonic stages are disrupted can indicate mechanisms of maternal effect senescence. Some maternal effects can also carry-over to subsequent generations. We examined potential multi- and transgenerational effects maternal senescence on embryonic development in two laboratory strains of D. melanogaster. We categorized the developmental stages of embryos from every combination of old and young mother, grandmother and great grandmother. We then modelled embryonic survival across the stages and compared these models among the multigenerational maternal age groups in order to identify which developmental processes were most sensitive to the effects of maternal effect senescence. Maternal effect senescence has negative multigenerational effects on multiple embryonic stages, indicating that maternal provisioning and, possibly epigenetics, but not mutation accumulation, contribute to decreased offspring survival. This study shows the large, early and multi-faceted nature of maternal effects senescence in an insect population.

Effects of Food Source Availability, Host Egg:Parasitoid Ratios, and Host Exposure Times on the Developmental Biology of Megacopta cribraria Egg Parasitoids

Parasitoids forage for hosts in dynamic ecosystems and generally have a short period of time to access hosts. The current study examined the optimal reproductive attributes of two egg parasitoids, Paratelenomus saccharalis Dodd (Hymenoptera: Platygastridae) and Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae), of the kudzu bug, Megacopta cribraria Fabricius (Hemiptera: Plataspidae). The proportion of O. nezarae and P. saccharalis adult offspring that emerged from M. cribraria eggs and the sex ratio of the parasitoid offspring were compared among treatments for the effects of different adult parasitoid food sources, host egg-to-adult parasitoid ratios, and host exposure times. Our results suggest that honey solution as a food source, a 21:7 host-to-parasitoid ratio, and three-to-five days of exposure time optimized the production of female O. nezarae offspring. For P. saccharalis, honey solution as a food source, a 21:7 host-to-parasitoid ratio, and one day were optimal for maximizing female offspring production. These findings provide new information about the biology of these egg parasitoids.

Insights into the genetic influences of the microbiota on the life span of a host

Escherichia coli (E. coli) mutant strains have been reported to extend the life span of Caenorhabditis elegans (C. elegans). However, the specific mechanisms through which the genes and pathways affect aging are not yet clear. In this study, we fed Drosophila melanogaster (fruit fly) various E. coli single-gene knockout strains to screen mutant strains with an extended lifespan. The results showed that D. melanogaster fed with E. coli purE had the longest mean lifespan, which was verified by C. elegans. We conducted RNA-sequencing and analysis of C. elegans fed with E. coli purE (a single-gene knockout mutant) to further explore the underlying molecular mechanism. We used differential gene expression (DGE) analysis, enrichment analysis, and gene set enrichment analysis (GSEA) to screen vital genes and modules with significant changes in overall expression. Our results suggest that E. coli mutant strains may affect the host lifespan by regulating the protein synthesis rate (cfz-2) and ATP level (catp-4). To conclude, our study could provide new insights into the genetic influences of the microbiota on the life span of a host and a basis for developing anti-aging probiotics and drugs.

What do we mean by "aging"? Questions and perspectives revealed by studies in Drosophila

What is the nature of aging, and how best can we study it? Here, using a series of questions that highlight differing perspectives about the nature of aging, we ask how data from Drosophila melanogaster at the organismal, tissue, cellular, and molecular levels shed light on the complex interactions among the phenotypes associated with aging. Should aging be viewed as an individual's increasing probability of mortality over time or as a progression of physiological states? Are all age-correlated changes in physiology detrimental to vigor or are some compensatory changes that maintain vigor? Why do different age-correlated functions seem to change at different rates in a single individual as it ages? Should aging be considered as a single, integrated process across the scales of biological resolution, from organismal to molecular, or must we consider each level of biological scale as a separate, distinct entity? Viewing aging from these differing perspectives yields distinct but complementary interpretations about the properties and mechanisms of aging and may offer a path through the complexities related to understanding the nature of aging.

Bioorthogonal Stimulated Raman Scattering Imaging Uncovers Lipid Metabolic Dynamics in Drosophila Brain During Aging

Studies have shown that brain lipid metabolism is associated with biological aging and influenced by dietary and genetic manipulations; however, the underlying mechanisms are elusive. High-resolution imaging techniques propose a novel and potent approach to understanding lipid metabolic dynamics in situ. Applying deuterium water (D2O) probing with stimulated Raman scattering (DO-SRS) microscopy, we revealed that lipid metabolic activity in Drosophila brain decreased with aging in a sex-dependent manner. Female flies showed an earlier occurrence of lipid turnover decrease than males. Dietary restriction (DR) and downregulation of insulin/IGF-1 signaling (IIS) pathway, two scenarios for lifespan extension, led to significant enhancements of brain lipid turnover in old flies. Combining SRS imaging with deuterated bioorthogonal probes (deuterated glucose and deuterated acetate), we discovered that, under DR treatment and downregulation of IIS pathway, brain metabolism shifted to use acetate as a major carbon source for lipid synthesis. For the first time, our study directly visualizes and quantifies spatiotemporal alterations of lipid turnover in Drosophila brain at the single organelle (lipid droplet) level. Our study not only demonstrates a new approach for studying brain lipid metabolic activity in situ but also illuminates the interconnection of aging, dietary, and genetic manipulations on brain lipid metabolic regulation.

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.

Transcriptomic Analysis of the Effect of Torin-2 on the Central Nervous System of Drosophila melanogaster

Torin-2, a synthetic compound, is a highly selective inhibitor of both TORC1 and TORC2 (target of rapamycin) complexes as an alternative to the well-known immunosuppressor, geroprotector, and potential anti-cancer natural compound rapamycin. Torin-2 is effective at hundreds of times lower concentrations and prevents some negative side effects of rapamycin. Moreover, it inhibits the rapamycin-resistant TORC2 complex. In this work, we evaluated transcriptomic changes in D. melanogaster heads induced with lifetime diets containing Torin-2 and suggested possible neuroprotective mechanisms of Torin-2. The analysis included D. melanogaster of three ages (2, 4, and 6 weeks old), separately for males and females. Torin-2, taken at the lowest concentration being tested (0.5 μM per 1 L of nutrient paste), had a slight positive effect on the lifespan of D. melanogaster males (+4% on the average) and no positive effect on females. At the same time, RNA-Seq analysis revealed interesting and previously undiscussed effects of Torin-2, which differed between sexes as well as in flies of different ages. Among the cellular pathways mostly altered by Torin-2 at the gene expression level, we identified immune response, protein folding (heat shock proteins), histone modification, actin cytoskeleton organization, phototransduction and sexual behavior. Additionally, we revealed that Torin-2 predominantly reduced the expression of Srr gene responsible for the conversion of L-serine to D-serine and thus regulating activity of NMDA receptor. Via western blot analysis, we showed than in old males Torin-2 tends to increase the ratio of the active phosphorylated form of ERK, the lowest node of the MAPK cascade, which may play a significant role in neuroprotection. Thus, the complex effect of Torin-2 may be due to the interplay of the immune system, hormonal background, and metabolism. Our work is of interest for further research in the field of NMDA-mediated neurodegeneration.

The remoulding of dietary effects on the fecundity / longevity trade-off in a social insect

BACKGROUND

In many organisms increased reproductive effort is associated with a shortened life span. This trade-off is reflected in conserved molecular pathways that link nutrient-sensing with fecundity and longevity. Social insect queens apparently defy the fecundity / longevity trade-off as they are both, extremely long-lived and highly fecund. Here, we have examined the effects of a protein-enriched diet on these life-history traits and on tissue-specific gene expression in a termite species of low social complexity.

RESULTS

On a colony level, we did not observe reduced lifespan and increased fecundity, effects typically seen in solitary model organisms, after protein enrichment. Instead, on the individual level mortality was reduced in queens that consumed more of the protein-enriched diet - and partially also in workers - while fecundity seemed unaffected. Our transcriptome analyses supported our life-history results. Consistent with life span extension, the expression of IIS (insulin/insulin-like growth factor 1 signalling) components was reduced in fat bodies after protein enrichment. Interestingly, however, genes involved in reproductive physiology (e.g., vitellogenin) were largely unaffected in fat body and head transcriptomes.

CONCLUSION

These results suggest that IIS is decoupled from downstream fecundity-associated pathways, which can contribute to the remoulding of the fecundity/longevity trade-off in termites as compared to solitary insects.

Molecular signatures of diapause in the Asian longhorned beetle: Gene expression

Most previous studies on gene expression during insect diapause do not address among-tissue variation in physiological processes. We measured transcriptomic changes during larval diapause in the Asian longhorned beetle, Anoplophora glabripennis (Coleoptera: Cerambycidae). We conducted RNA-seq on fat body, the supraesophageal ganglion, midgut, hindgut, and Malpighian tubules during pre-diapause, diapause maintenance, post-diapause quiescence, and post-diapause development. We observed a small, but consistent, proportion of genes within each gene expression profile that were shared among tissues, lending support for a core set of diapause-associated genes whose expression is tissue-independent. We evaluated the overarching hypotheses that diapause would be associated with cell cycle arrest, developmental arrest, and increased stress tolerance and found evidence of repressed TOR and insulin signaling, reduced cell cycle activity and increased capacity of stress response via heat shock protein expression and remodeling of the cytoskeleton. However, these processes varied among tissues, with the brain and fat body appearing to maintain higher levels of cellular activity during diapause than the midgut or Malpighian tubules. We also observed temperature-dependent changes in gene expression during diapause maintenance, particularly in genes related to the heat shock response and MAPK, insulin, and TOR signaling pathways. Additionally, we provide evidence for epigenetic reorganization during the diapause/post-diapause quiescence transition and expression of genes involved in post-translational modification, highlighting the need for investigations of the protein activity of these candidate genes and processes. We conclude that diapause development is coordinated via diverse tissue-specific gene expression profiles and that canonical diapause phenotypes vary among tissues.

Sex-biased gene expression in nutrient-sensing pathways

Differences in lifespan between males and females are found across many taxa and may be determined, at least in part, by differential responses to diet. Here we tested the hypothesis that the higher dietary sensitivity of female lifespan is mediated by higher and more dynamic expression in nutrient-sensing pathways in females. We first reanalysed existing RNA-seq data, focusing on 17 nutrient-sensing genes with reported lifespan effects. This revealed, consistent with the hypothesis, a dominant pattern of female-biased gene expression, and among sex-biased genes there tended to be a loss of female-bias after mating. We then tested directly the expression of these 17 nutrient-sensing genes in wild-type third instar larvae, once-mated 5- and 16-day-old adults. This confirmed sex-biased gene expression and showed that it was generally absent in larvae, but frequent and stable in adults. Overall, the findings suggest a proximate explanation for the sensitivity of female lifespan to dietary manipulations. We suggest that the contrasting selective pressures to which males and females are subject create differing nutritional demands and requirements, resulting in sex differences in lifespan. This underscores the potential importance of the health impacts of sex-specific dietary responses.

Behavioral state-dependent modulation of insulin-producing cells in Drosophila

Insulin signaling plays a pivotal role in metabolic control and aging, and insulin accordingly is a key factor in several human diseases. Despite this importance, the in vivo activity dynamics of insulin-producing cells (IPCs) are poorly understood. Here, we characterized the effects of locomotion on the activity of IPCs in Drosophila. Using in vivo electrophysiology and calcium imaging, we found that IPCs were strongly inhibited during walking and flight and that their activity rebounded and overshot after cessation of locomotion. Moreover, IPC activity changed rapidly during behavioral transitions, revealing that IPCs are modulated on fast timescales in behaving animals. Optogenetic activation of locomotor networks ex vivo, in the absence of actual locomotion or changes in hemolymph sugar levels, was sufficient to inhibit IPCs. This demonstrates that the behavioral state-dependent inhibition of IPCs is actively controlled by neuronal pathways and is independent of changes in glucose concentration. By contrast, the overshoot in IPC activity after locomotion was absent ex vivo and after starvation, indicating that it was not purely driven by feedforward signals but additionally required feedback derived from changes in hemolymph sugar concentration. We hypothesize that IPC inhibition during locomotion supports mobilization of fuel stores during metabolically demanding behaviors, while the rebound in IPC activity after locomotion contributes to replenishing muscle glycogen stores. In addition, the rapid dynamics of IPC modulation support a potential role of insulin in the state-dependent modulation of sensorimotor processing.

Antibody development to identify components of IIS and mTOR signaling pathways in lepidopteran species, a set of non-model insects

Nutritional stress impacts many insect species that have differing reproductive strategies and life histories, yet it is unclear how nutrient-sensing signaling pathways mediate tissue-specific responses to changes in dietary input. In Drosophila melanogaster , insulin/insulin-like growth factor (IIS) and mTOR-mediated signaling within adipocytes regulates oogenesis. To facilitate comparative study of nutrient-sensing pathway activity in the fat body, we developed antibodies to assess IIS (anti-FOXO) and mTOR signaling (anti-TOR) across three nymphalid species (Lepidoptera). By optimizing whole-mount fat body immunostaining, we find FOXO nuclear enrichment in adult adipocytes, like that observed in Drosophila . Additionally, we show a previously uncharacterized TOR localization pattern in the fat body.

The deleterious effects of old social partners on Drosophila lifespan and stress resistance

Social interactions play important roles in the modulation of behavior, physiology, and, potentially, lifespan. Although longevity has been studied extensively in different model organisms, due to the complexity of social environments, the social modulation of aging remains poorly investigated. The present study used the fruit fly, Drosophila melanogaster, as a model to study lifespan and stress resistance under different social conditions. Our experiments first showed that social isolation increased fly lifespan, suggesting a potential deleterious effect of social companions. Furthermore, we exposed flies to different aged social partners and found that living with old animals significantly reduced lifespan and stress resistance in young animals. In contrast, living with young animals increased old animal lifespan, although the effects were less robust. Overall, our results suggest that while social interaction can influence fly health, specific social partners may have more pronounced effects than others. This study provides new evidence that different social environments have significant impacts on animal physiology and longevity.

The sooner, the better: ROS, kinases and nutrients at the onset of the damage response in Drosophila

One of the main topics in regeneration biology is the nature of the early signals that trigger the damage response. Recent advances in Drosophila point to the MAP3 kinase Ask1 as a molecular hub that integrates several signals at the onset of regeneration. It has been discovered that reactive oxygen species (ROS) produced in damaged imaginal discs and gut epithelia will activate the MAP3 kinase Ask1. Severely damaged and apoptotic cells produce an enormous amount of ROS, which ensures their elimination by activating Ask1 and in turn the pro-apoptotic function of JNK. However, this creates an oxidative stress environment with beneficial effects that is sensed by neighboring healthy cells. This environment, in addition to the Pi3K/Akt nutrient sensing pathway, can be integrated into Ask1 to launch regeneration. Ultimately the activity of Ask1 depends on these and other inputs and modulates its signaling to achieve moderate levels of p38 and low JNK signaling and thus promote survival and regeneration. This model based on the dual function of Ask1 for early response to damage is discussed here.

The landscape of aging

Aging is characterized by a progressive deterioration of physiological integrity, leading to impaired functional ability and ultimately increased susceptibility to death. It is a major risk factor for chronic human diseases, including cardiovascular disease, diabetes, neurological degeneration, and cancer. Therefore, the growing emphasis on “healthy aging” raises a series of important questions in life and social sciences. In recent years, there has been unprecedented progress in aging research, particularly the discovery that the rate of aging is at least partly controlled by evolutionarily conserved genetic pathways and biological processes. In an attempt to bring full-fledged understanding to both the aging process and age-associated diseases, we review the descriptive, conceptual, and interventive aspects of the landscape of aging composed of a number of layers at the cellular, tissue, organ, organ system, and organismal levels.

Insulin signaling in the long-lived reproductive caste of ants

In most organisms, reproduction is correlated with shorter life span. However, the reproductive queen in eusocial insects exhibits a much longer life span than that of workers. In Harpegnathos ants, when the queen dies, workers can undergo an adult caste switch to reproductive pseudo-queens (gamergates), exhibiting a five-times prolonged life span. To explore the relation between reproduction and longevity, we compared gene expression during caste switching. Insulin expression is increased in the gamergate brain that correlates with increased lipid synthesis and production of vitellogenin in the fat body, both transported to the egg. This results from activation of the mitogen-activated protein kinase (MAPK) branch of the insulin signaling pathway. By contrast, the production in the gamergate developing ovary of anti-insulin Imp-L2 leads to decreased signaling of the AKT/forkhead box O (FOXO) branch in the fat body, which is consistent with their extended longevity.

LncRNA-IRAR-mediated regulation of insulin receptor transcripts in Drosophila melanogaster during nutritional stress

The insulin signalling pathway plays a crucial role in regulating the metabolism of sugars, fats and proteins in cells, thereby affecting the growth, metabolism, reproduction and ageing of organisms. However, little is known about the functions of long non-coding RNAs (lncRNAs) in the regulation of insulin receptors under stress conditions in insects. In this study, we showed that insulin receptor-associated lncRNA (IRAR) regulates insulin receptor transcripts in response to nutritional stress in Drosophila melanogaster. Genome editing by CRISPR-Cas9 showed reduced sensitivity of IRAR mutants to environmental nutritional changes. In contrast, the sensitivity of mutants overexpressing tubulin-gal4 > IRAR increased under low nutrition. The pupation and eclosion timings in IRAR mutants were significantly delayed with an increase in insulin concentration compared with that in the w1118 group. In addition, the expression pattern of IRAR was almost consistent with that of the four transcripts of the insulin receptor from the embryonic period to the adult period. RNA immunoprecipitation assay showed the direct regulation of insulin receptor transcripts by IRAR to the through FOXO binding under nutritional stress. To our knowledge, this is the first study that describes a model of lncRNA-mediated development regulation through insulin receptor transcripts.

Is Turkish coffee protects Drosophila melanogaster on cadmium acetate toxicity by promoting antioxidant enzymes?

With their increasing use in today's industry, heavy metals cause biochemical and biophysical changes by affecting the control and regulatory systems of living things. Cadmium (Cd), a heavy metal, spreads to the environment through both natural sources and industrial activities. It is taken into the organism through water, food, skin contact or smoke. Systems and organs of living things are directly or indirectly affected by Cd toxicity. Besides their recreational usage, herbal products such as coffee are preferred in alternative medicine because of their antioxidant, anti-inflammatory, anticancer and antidiabetic effects. Turkish coffee (TK) is a drink rich in flavorings, phenolic compounds and antioxidant compounds. The study evaluated the possible antioxidant role of TK against oxidative stress induced by Cadmium acetate (CdA) in the fat tissues of old-young female individuals of Drosophila melanogaster. The female flies were fed with either a standard diet, or CdA (10-30 mg), or TK (2%), or both (CdA + TK) for 3 and 10 days. Following the completion of the feeding period, the amounts of fatbody and oxidative stress markers (oxidative stress index, malondialdehyde), activities of antioxidant enzymes (Glutathione-S-transferase, Catalase, and Superoxide dismutase) and their levels were measured. Fat body lipid droplets were high in the individuals exposed to high concentrations of CdA. It was determined that lipid droplets decreased but did not significantly alter oxidative stress in the individuals treated with TK (p = 0.05). This article may be of help in terms of the use of TK compounds as antioxidants to evaluate their effects in preventing heavy metal accumulation and stress in the aging process.

The tobacco phosphatidylethanolamine-binding protein NtFT4 increases the lifespan of Drosophila melanogaster by interacting with the proteostasis network

Proteostasis reflects the well-balanced synthesis, trafficking and degradation of cellular proteins. This is a fundamental aspect of the dynamic cellular proteome, which integrates multiple signaling pathways, but it becomes increasingly error-prone during aging. Phosphatidylethanolamine-binding proteins (PEBPs) are highly conserved regulators of signaling networks and could therefore affect aging-related processes. To test this hypothesis, we expressed PEPBs in a heterologous context to determine their ectopic activity. We found that heterologous expression of the tobacco (Nicotiana tabacum) PEBP NtFT4 in Drosophila melanogaster significantly increased the lifespan of adult flies and reduced age-related locomotor decline. Similarly, overexpression of the Drosophila ortholog CG7054 increased longevity, whereas its suppression by RNA interference had the opposite effect. In tobacco, NtFT4 acts as a floral regulator by integrating environmental and intrinsic stimuli to promote the transition to reproductive growth. In Drosophila, NtFT4 engaged distinct targets related to proteostasis, such as HSP26. In older flies, it also prolonged Hsp26 gene expression, which promotes longevity by maintaining protein integrity. In NtFT4-transgenic flies, we identified deregulated genes encoding proteases that may contribute to proteome stability at equilibrium. Our results demonstrate that the expression of NtFT4 influences multiple aspects of the proteome maintenance system via both physical interactions and transcriptional regulation, potentially explaining the aging-related phenotypes we observed.

Hydroethanolic Cyperus rotundus L. extract exhibits anti-obesity property and increases lifespan expectancy in Drosophila melanogaster fed a high-fat diet

Introduction: Cyperus rotundus L. is suspected of having anti-obesity properties. The purpose of this study was to determine the anti-obesity property of hydroethanolic C. rotundus extract (HECE) using Drosophila as a model organism. Methods: In vitro inhibition of lipase activity by C. rotundus extract was investigated. The effects of C. rotundus extract on obesity-related characteristics, including body weight, triglyceride content, and lifespan extension were evaluated in Drosophila fed a high-fat diet (HFD). The effect of the extract on the reduction of oxidative stress associated with obesity was assessed in vivo using antioxidant assays in Drosophila. Results: HECE inhibited lipase activity in vitro with an IC50 of 128.24 ± 3.65 μg/mL. In vivo lipase inhibition experiments demonstrated that feeding Drosophila 10 mg/mL HECE or 2 μM orlistat lowered lipase activity by 21.51 (P < 0.05) and 42.86% (P < 0.01) and triglyceride levels by 20.67 (P < 0.05) and 28.39% (P < 0.01), respectively, compared to those of the untreated group. After 10 mg/mL HECE or 2 μM orlistat supplementation, an increase in the mean survival rate (10.54 (P < 0.05) and 13.90% (P < 0.01), respectively) and climbing ability (25.03 (P < 0.01) and 28.44% (P < 0.01), respectively) was observed compared to those of flies fed a HFD. The paraquat and H2O2 challenge tests revealed that flies fed HECE in a mixed HFD showed increased survival on flies fed a HFD. Conclusion: This study demonstrates the beneficial effects of dietary HECE supplementation on suppressing pancreatic lipase activity and lowering triglyceride levels and oxidative stress, leading to increased lifespan in Drosophila fed a HFD.

Combining Metabolomics and Experimental Evolution Reveals Key Mechanisms Underlying Longevity Differences in Laboratory Evolved Drosophila melanogaster Populations

Experimental evolution with Drosophila melanogaster has been used extensively for decades to study aging and longevity. In recent years, the addition of DNA and RNA sequencing to this framework has allowed researchers to leverage the statistical power inherent to experimental evolution to study the genetic basis of longevity itself. Here, we incorporated metabolomic data into to this framework to generate even deeper insights into the physiological and genetic mechanisms underlying longevity differences in three groups of experimentally evolved D. melanogaster populations with different aging and longevity patterns. Our metabolomic analysis found that aging alters mitochondrial metabolism through increased consumption of NAD⁺ and increased usage of the TCA cycle. Combining our genomic and metabolomic data produced a list of biologically relevant candidate genes. Among these candidates, we found significant enrichment for genes and pathways associated with neurological development and function, and carbohydrate metabolism. While we do not explicitly find enrichment for aging canonical genes, neurological dysregulation and carbohydrate metabolism are both known to be associated with accelerated aging and reduced longevity. Taken together, our results provide plausible genetic mechanisms for what might be driving longevity differences in this experimental system. More broadly, our findings demonstrate the value of combining multiple types of omic data with experimental evolution when attempting to dissect mechanisms underlying complex and highly polygenic traits such as aging.

Lifespan prolonging mechanisms and insulin upregulation without fat accumulation in long-lived reproductives of a higher termite

Kings and queens of eusocial termites can live for decades, while queens sustain a nearly maximal fertility. To investigate the molecular mechanisms underlying their long lifespan, we carried out transcriptomics, lipidomics and metabolomics in Macrotermes natalensis on sterile short-lived workers, long-lived kings and five stages spanning twenty years of adult queen maturation. Reproductives share gene expression differences from workers in agreement with a reduction of several aging-related processes, involving upregulation of DNA damage repair and mitochondrial functions. Anti-oxidant gene expression is downregulated, while peroxidability of membranes in queens decreases. Against expectations, we observed an upregulated gene expression in fat bodies of reproductives of several components of the IIS pathway, including an insulin-like peptide, Ilp9. This pattern does not lead to deleterious fat storage in physogastric queens, while simple sugars dominate in their hemolymph and large amounts of resources are allocated towards oogenesis. Our findings support the notion that all processes causing aging need to be addressed simultaneously in order to prevent it.

Levels of insulin-like growth factor in bovine, goat, and sheep milk in different lactation periods: The etiological factor of cancer in humans

Background and Aim: Despite the positive aspects of consuming dairy products, there are also some reservations. Recently, a large number of publications have demonstrated convincing evidence of a relationship between the intake of dairy products and the development of cancer in humans. This study aimed to determine the level of insulin-like growth factor [IGF], which can cause cancer in consumers, in the milk of farm animals (cows, goats, and sheep) obtained at different stages of lactation. Materials and Methods: Enzyme-linked immunosorbent assay and statistical method were used for data processing. The IGF level in milk was determined using an enzyme-linked immunosorbent assay. Milk was collected from cows of Holstein and Ukrainian Black-and-White dairy breed, goats of Alpine and Saanen breed, and sheep of Tsigai and East Friesian breed. Milk samples in cows were collected at the beginning, on the peak, and at the end of lactation. Results: The obtained results showed that the highest IGF level was detected in milk obtained at the beginning of lactation, but its level depended on the animal species. More specifically, the highest level of the hormone was typical for goat's milk and for cow's milk of Holstein breed. Slightly lower values were revealed in the milk of cows of Black-and-White Ukrainian breed and sheep. During lactation, the absolute content of IGF in the milk of all studied animal species decreased. It should be noted that the most pronounced decrease in the IGF level in milk during lactation was noted in sheep (25-40 times), and minor changes were observed in goats (12-14 times). The results also showed that there were individual variations in the IGF level in milk in farm animals. Conclusion: The highest IGF level was noted in goat's milk, and the lowest level was observed in sheep's milk. Cow's milk, in this regard, had an intermediate IGF level. The level of this particular hormone depends on the period of lactation and the individual characteristics of the animal. It is advisable to include IGF as one of the assessment factors of dairy products' safety because this hormone can cause cancer in consumers of milk and dairy products.

The potential roles of excitatory-inhibitory imbalances and the repressor element-1 silencing transcription factor in aging and aging-associated diseases

Disruptions to the central excitatory-inhibitory (E/I) balance are thought to be related to aging and underlie a host of neural pathologies, including Alzheimer's disease. Aging may induce an increase in excitatory signaling, causing an E/I imbalance, which has been linked to shorter lifespans in mice, flies, and worms. In humans, extended longevity correlates to greater repression of genes involved in excitatory neurotransmission. The repressor element-1 silencing transcription factor (REST) is a master regulator in neural cells and is believed to be upregulated with senescent stimuli, whereupon it counters hyperexcitability, insulin/insulin-like signaling pathway activity, oxidative stress, and neurodegeneration. This review examines the putative mechanisms that distort the E/I balance with aging and neurodegeneration, and the putative roles of REST in maintaining neuronal homeostasis.

Drosophila melanogaster as a Model Organism to Study Lithium and Boron Bioactivity

The fruit fly Drosophila melanogaster has become a valuable model organism in nutritional science, which can be applied to elucidate the physiology and the biological function of nutrients, including trace elements. Importantly, the application of chemically defined diets enables the supply of trace elements for nutritional studies under highly standardized dietary conditions. Thus, the bioavailability and bioactivity of trace elements can be systematically monitored in D. melanogaster. Numerous studies have already revealed that central aspects of trace element homeostasis are evolutionary conserved among the fruit fly and mammalian species. While there is sufficient evidence of vital functions of boron (B) in plants, there is also evidence regarding its bioactivity in animals and humans. Lithium (Li) is well known for its role in the therapy of bipolar disorder. Furthermore, recent findings suggest beneficial effects of Li regarding neuroprotection as well as healthy ageing and longevity in D. melanogaster. However, no specific essential function in the animal kingdom has been found for either of the two elements so far. Here, we summarize the current knowledge of Li and B bioactivity in D. melanogaster in the context of health and disease prevention.

Circadian autophagy drives iTRF-mediated longevity

Time-restricted feeding (TRF) has recently gained interest as a potential anti-ageing treatment for organisms from Drosophila to humans1-5. TRF restricts food intake to specific hours of the day. Because TRF controls the timing of feeding, rather than nutrient or caloric content, TRF has been hypothesized to depend on circadian-regulated functions; the underlying molecular mechanisms of its effects remain unclear. Here, to exploit the genetic tools and well-characterized ageing markers of Drosophila, we developed an intermittent TRF (iTRF) dietary regimen that robustly extended fly lifespan and delayed the onset of ageing markers in the muscles and gut. We found that iTRF enhanced circadian-regulated transcription and that iTRF-mediated lifespan extension required both circadian regulation and autophagy, a conserved longevity pathway. Night-specific induction of autophagy was both necessary and sufficient to extend lifespan on an ad libitum diet and also prevented further iTRF-mediated lifespan extension. By contrast, day-specific induction of autophagy did not extend lifespan. Thus, these results identify circadian-regulated autophagy as a critical contributor to iTRF-mediated health benefits in Drosophila. Because both circadian regulation and autophagy are highly conserved processes in human ageing, this work highlights the possibility that behavioural or pharmaceutical interventions that stimulate circadian-regulated autophagy might provide people with similar health benefits, such as delayed ageing and lifespan extension.

Factors that regulate expression patterns of insulin-like peptides and their association with physiological and metabolic traits in Drosophila

Insulin-like peptides (ILPs) and components of the insulin signaling pathway are conserved across different animal phyla. Eight ILPs (called DILPs) and two receptors, dInR and Lgr3, have been described in Drosophila. DILPs regulate varied physiological traits including lifespan, reproduction, development, feeding behavior, stress resistance and metabolism. At the same time, different conditions such as nutrition, dietary supplements and environmental factors affect the expression of DILPs. This review focuses primarily on DILP2, DILP3, and DILP5 which are produced by insulin-producing cells in the brain of Drosophila. Although they are produced by the same cells and can potentially compensate for each other, DILP2, DILP3, and DILP5 expression may be differentially regulated at the mRNA level. Thus, we summarized available data on the conditions affecting the expression profiles of these DILPs in adult Drosophila. The accumulated data indicate that transcript levels of DILPs are determined by (a) nutritional conditions such as the protein-to-carbohydrate ratio, (b) carbohydrate type within the diet, (c) malnutrition or complete starvation; (d) environmental factors such as stress or temperature; (e) mutations of single peptides that induce changes in the expression of the other peptides; and (f) dietary supplements of drugs or natural substances. Furthermore, manipulation of specific genes in a cell- and tissue-specific manner affects mRNA levels for DILPs and, thereby, modulates various physiological traits and metabolism in Drosophila.

Loss of p21-activated kinase Mbt/PAK4 causes Parkinson-like phenotypes in Drosophila

Parkinson's disease (PD) provokes bradykinesia, resting tremor, rigidity and postural instability, and also non-motor symptoms such as depression, anxiety, sleep and cognitive impairments. Similar phenotypes can be induced in Drosophila melanogaster through modification of PD-relevant genes or the administration of PD-inducing toxins. Recent studies correlated deregulation of human p21-activated kinase 4 (PAK4) with PD, leaving open the question of a causative relationship of mutations in this gene for manifestation of PD symptoms. To determine whether flies lacking the PAK4 homolog Mushroom bodies tiny (Mbt) show PD-like phenotypes, we tested for a variety of PD criteria. Here, we demonstrate that mbt mutant flies show PD-like phenotypes including age-dependent movement deficits, reduced life expectancy and fragmented sleep. They also react to a stressful situation with higher immobility, indicating an influence of Mbt on emotional behavior. Loss of Mbt function has a negative effect on the number of dopaminergic protocerebral anterior medial (PAM) neurons, most likely caused by a proliferation defect of neural progenitors. The age-dependent movement deficits are not accompanied by a corresponding further loss of PAM neurons. Previous studies highlighted the importance of a small PAM subgroup for age-dependent PD motor impairments. We show that impaired motor skills are caused by a lack of Mbt in this PAM subgroup. In addition, a broader re-expression of Mbt in PAM neurons improves life expectancy. Conversely, selective Mbt knockout in the same cells shortens lifespan. We conclude that mutations in Mbt/PAK4 can play a causative role in the development of PD phenotypes.

Disentangling the aging gene expression network of termite queens

Background

Most insects are relatively short-lived, with a maximum lifespan of a few weeks, like the aging model organism, the fruit-fly Drosophila melanogaster. By contrast, the queens of many social insects (termites, ants and some bees) can live from a few years to decades. This makes social insects promising models in aging research providing insights into how a long reproductive life can be achieved. Yet, aging studies on social insect reproductives are hampered by a lack of quantitative data on age-dependent survival and time series analyses that cover the whole lifespan of such long-lived individuals. We studied aging in queens of the drywood termite Cryptotermes secundus by determining survival probabilities over a period of 15 years and performed transcriptome analyses for queens of known age that covered their whole lifespan.

Results

The maximum lifespan of C. secundus queens was 13 years, with a median maximum longevity of 11.0 years. Time course and co-expression network analyses of gene expression patterns over time indicated a non-gradual aging pattern. It was characterized by networks of genes that became differentially expressed only late in life, namely after ten years, which associates well with the median maximum lifespan for queens. These old-age gene networks reflect processes of physiological upheaval. We detected strong signs of stress, decline, defense and repair at the transcriptional level of epigenetic control as well as at the post-transcriptional level with changes in transposable element activity and the proteostasis network. The latter depicts an upregulation of protein degradation, together with protein synthesis and protein folding, processes which are often down-regulated in old animals. The simultaneous upregulation of protein synthesis and autophagy is indicative of a stress-response mediated by the transcription factor cnc, a homolog of human nrf genes.

Conclusions

Our results show non-linear senescence with a rather sudden physiological upheaval at old-age. Most importantly, they point to a re-wiring in the proteostasis network and stress as part of the aging process of social insect queens, shortly before queens die.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07649-4.

Gene Coexpression Network Reveals Highly Conserved, Well-Regulated Anti-Ageing Mechanisms in Old Ant Queens

Evolutionary theories of ageing predict a reduction in selection efficiency with age, a so-called “selection shadow,” due to extrinsic mortality decreasing effective population size with age. Classic symptoms of ageing include a deterioration in transcriptional regulation and protein homeostasis. Understanding how ant queens defy the trade-off between fecundity and lifespan remains a major challenge for the evolutionary theory of ageing. It has often been discussed that the low extrinsic mortality of ant queens, that are generally well protected within the nest by workers and soldiers, should reduce the selection shadow acting on old queens. We tested this by comparing strength of selection acting on genes upregulated in young and old queens of the ant, Cardiocondyla obscurior. In support of a reduced selection shadow, we find old-biased genes to be under strong purifying selection. We also analyzed a gene coexpression network (GCN) with the aim to detect signs of ageing in the form of deteriorating regulation and proteostasis. We find no evidence for ageing. In fact, we detect higher connectivity in old queens indicating increased transcriptional regulation with age. Within the GCN, we discover five highly correlated modules that are upregulated with age. These old-biased modules regulate several antiageing mechanisms such as maintenance of proteostasis, transcriptional regulation, and stress response. We observe stronger purifying selection on central hub genes of these old-biased modules compared with young-biased modules. These results indicate a lack of transcriptional ageing in old C. obscurior queens, possibly facilitated by strong selection at old age and well-regulated antiageing mechanisms.

The Impact of Age on Response to Infection in Drosophila

This review outlines the known cellular pathways and mechanisms involved in Drosophila age-dependent immunity to pathogenic microorganisms such as bacteria and fungi. We discuss the implication of host signaling pathways such as the Toll, Immune Deficiency (IMD), Janus kinase signal transducer and activator of transcription (JAK/STAT), and Insulin/Insulin Growth Factor/Target of Rapamycin (IIS/TOR) on immune function with aging. Additionally, we review the effects that factors such as sexual dimorphism, environmental stress, and cellular physiology exert on age-dependent immunity in Drosophila. We discuss potential tradeoffs between heightened immune function and longevity in the absence of infection, and we provide detailed tables outlining the various assays and pathogens used in the cited studies, as well as the age, sex, and strains of Drosophila used. We also discuss the overlapping effects these pathways and mechanisms have on one another. We highlight the great utility of Drosophila as a model organism and the importance of a greater focus on age-dependent antiviral immunity for future studies.

Transcriptomic Signatures of Ageing Vary in Solitary and Social Forms of an Orchid Bee

Eusocial insect queens are remarkable in their ability to maximize both fecundity and longevity, thus escaping the typical trade-off between these two traits. Several mechanisms have been proposed to underlie the remolding of the trade-off, such as reshaping of the juvenile hormone (JH) pathway, or caste-specific susceptibility to oxidative stress. However, it remains a challenge to disentangle the molecular mechanisms underlying the remolding of the trade-off in eusocial insects from caste-specific physiological attributes that have subsequently arisen. The socially polymorphic orchid bee Euglossa viridissima represents an excellent model to address the role of sociality per se in longevity as it allows direct comparisons of solitary and social individuals within a common genetic background. We investigated gene expression and JH levels in young and old bees from both solitary and social nests. We found 902 genes to be differentially expressed with age in solitary females, including genes involved in oxidative stress, versus only 100 genes in social dominant females, and 13 genes in subordinate females. A weighted gene coexpression network analysis further highlights pathways related to ageing in this species, including the target of rapamycin pathway. Eleven genes involved in translation, apoptosis, and DNA repair show concurrent age-related expression changes in solitary but not in social females, representing potential differences based on social status. JH titers did not vary with age or social status. Our results represent an important step in understanding the proximate mechanisms underlying the remodeling of the fecundity/longevity trade-off that accompanies the evolutionary transition from solitary life to eusociality.

Why and how do termite kings and queens live so long?

Lifespan varies greatly across the tree of life. Of the various explanations for this phenomenon, those that involve trade-offs between reproduction and longevity have gained considerable support. There is an important exception: social insect reproductives (queens and in termites, also kings) exhibit both high reproductive outputs and extraordinarily long lives. As both the ultimate and proximate mechanisms underlying the absence of the fecundity/longevity trade-off could shed light on the unexpected dynamics and molecular mechanisms of extended longevity, reproductives of social insects have attracted much attention in the field of ageing research. Here, we highlight current ecological and physiological studies on ageing and discuss the various possible evolutionary and molecular explanations of the extended lifespans of termite reproductives. We integrate these findings into a coherent framework revealing the evolution of longevity in these reproductives. Studies on termites may explain why and how ageing is shaped by natural selection. This article is part of the theme issue 'Ageing and sociality: why, when and how does sociality change ageing patterns?'

The effect of environmental stress on ageing in a termite species with low social complexity

Social insects seem to have overcome the almost universal trade-off between fecundity and longevity as queens can be highly fecund and at the same time reach lifespans of decades. By contrast, their non-reproducing workers are often short-lived. One hypothesis to explain the long lifespan of queens is that they are better protected against stress than their workers. However, evidence is controversial and experimental studies are scarce. We aimed at manipulating environmental stress and ageing by exposing colonies of the less-socially complex termite Cryptotermes secundus to temperature regimes that differed in variance. In contrast with expectation, constant temperatures imposed more stress than variable temperatures. Survival of queens and workers as well as queens' fecundity were partly reduced under constant conditions and both castes showed signs of ageing in the transcriptome signature under constant conditions. There was a clear oxidative stress defence signal under constant conditions that was, surprisingly, stronger for workers than queens. We discuss how our results relate to social complexity. We argue that workers that are totipotent to become reproductives, like in C. secundus, should invest more in 'anti-ageing' mechanisms than sterile workers because the former can still reproduce and have not reached maturity yet. This article is part of the theme issue 'Ageing and sociality: why, when and how does sociality change ageing patterns?'

Comparative transcriptomic analysis of the mechanisms underpinning ageing and fecundity in social insects

The exceptional longevity of social insect queens despite their lifelong high fecundity remains poorly understood in ageing biology. To gain insights into the mechanisms that might underlie ageing in social insects, we compared gene expression patterns between young and old castes (both queens and workers) across different lineages of social insects (two termite, two bee and two ant species). After global analyses, we paid particular attention to genes of the insulin/insulin-like growth factor 1 signalling (IIS)/target of rapamycin (TOR)/juvenile hormone (JH) network, which is well known to regulate lifespan and the trade-off between reproduction and somatic maintenance in solitary insects. Our results reveal a major role of the downstream components and target genes of this network (e.g. JH signalling, vitellogenins, major royal jelly proteins and immune genes) in affecting ageing and the caste-specific physiology of social insects, but an apparently lesser role of the upstream IIS/TOR signalling components. Together with a growing appreciation of the importance of such downstream targets, this leads us to propose the TI-J-LiFe (TOR/IIS-JH-Lifespan and Fecundity) network as a conceptual framework for understanding the mechanisms of ageing and fecundity in social insects and beyond. This article is part of the theme issue 'Ageing and sociality: why, when and how does sociality change ageing patterns?'

Tissue-specific modulation of gene expression in response to lowered insulin signalling in Drosophila

Reduced activity of the insulin/IGF signalling network increases health during ageing in multiple species. Diverse and tissue-specific mechanisms drive the health improvement. Here, we performed tissue-specific transcriptional and proteomic profiling of long-lived Drosophila dilp2-3,5 mutants, and identified tissue-specific regulation of >3600 transcripts and >3700 proteins. Most expression changes were regulated post-transcriptionally in the fat body, and only in mutants infected with the endosymbiotic bacteria, Wolbachia pipientis, which increases their lifespan. Bioinformatic analysis identified reduced co-translational ER targeting of secreted and membrane-associated proteins and increased DNA damage/repair response proteins. Accordingly, age-related DNA damage and genome instability were lower in fat body of the mutant, and overexpression of a minichromosome maintenance protein subunit extended lifespan. Proteins involved in carbohydrate metabolism showed altered expression in the mutant intestine, and gut-specific overexpression of a lysosomal mannosidase increased autophagy, gut homeostasis, and lifespan. These processes are candidates for combatting ageing-related decline in other organisms.

Redox regulation of the insulin signalling pathway

The peptide hormone insulin is a key regulator of energy metabolism, proliferation and survival. Binding of insulin to its receptor activates the PI3K/AKT signalling pathway, which mediates fundamental cellular responses. Oxidants, in particular H₂O₂, have been recognised as insulin-mimetics. Treatment of cells with insulin leads to increased intracellular H₂O₂ levels affecting the activity of downstream signalling components, thereby amplifying insulin-mediated signal transduction. Specific molecular targets of insulin-stimulated H₂O₂ include phosphatases and kinases, whose activity can be altered via redox modifications of critical cysteine residues. Over the past decades, several of these redox-sensitive cysteines have been identified and their impact on insulin signalling evaluated. The aim of this review is to summarise the current knowledge on the redox regulation of the insulin signalling pathway.

Transcriptomic analyses of the termite, Cryptotermes secundus, reveal a gene network underlying a long lifespan and high fecundity

Organisms are typically characterized by a trade-off between fecundity and longevity. Notable exceptions are social insects. In insect colonies, the reproducing caste (queens) outlive their non-reproducing nestmate workers by orders of magnitude and realize fecundities and lifespans unparalleled among insects. How this is achieved is not understood. Here, we identified a single module of co-expressed genes that characterized queens in the termite species Cryptotermes secundus. It encompassed genes from all essential pathways known to be involved in life-history regulation in solitary model organisms. By manipulating its endocrine component, we tested the recent hypothesis that re-wiring along the nutrient-sensing/endocrine/fecundity axis can account for the reversal of the fecundity/longevity trade-off in social insect queens. Our data from termites do not support this hypothesis. However, they revealed striking links to social communication that offer new avenues to understand the re-modelling of the fecundity/longevity trade-off in social insects.

Effects of sugar sources on adult longevity, survival and related gene expression in an endoparasitoid, Pteromalus puparum (Hymenoptera: Pteromalidae)

BACKGROUND

Adult parasitic wasps take sugars to meet their energy needs and display different lifespans and fertility in response to different sugar sources. Pteromalus puparum is an endoparasitoid with a wide range of hosts, including many lepidopteran pests. As a potential natural enemy resource, the availability of sugar sources has profound effects for wasp applications and host populations dynamics.

RESULTS

We assessed the effect of feeding sucrose and honey on the lifespan of P. puparum in the range 0-40% (w/v). The results indicated a statistically significant positive effect of sucrose and honey solutions on the lifespan of P. puparum female adults. Correlation analyses confirmed a strong positive correlation between high concentrations of sugar and extended lifespan. The optimum concentration of sucrose solution for wasps was 20%, while 10% for honey. Then, we examined the expression patterns of 15 lifespan-related genes. The results showed that the relative expression levels of 14 genes were significantly correlated with the mean lifespan of sucrose-fed wasps, and six genes correlated with the mean lifespan of honey-fed wasps. In addition, the models for lifespan prediction were constructed.

CONCLUSION

We elaborated the quantitative effects of two sugar sources (sucrose and honey) on P. puparum lifespan, investigated the expression patterns of lifespan-related genes when fed different sugar sources, and developed round lifespan prediction models accordingly. This study provides a novel tool for studying the longevity regulating mechanisms of parasitic wasps, and may be instructive for mass-production of parasitoids as biological control agents. © 2020 Society of Chemical Industry.