Balance between macronutrients affects life span and functional senescence in fruit fly Drosophila melanogaster

Alpha-ketoglutarate supplementation in long-lived Drosophila melanogaster: Impact on lifespan and metabolic responses

Studies on antiaging remedies in insect models sometimes show discrepancies in results. These discrepancies could be explained by different responses of short- and long-lived strains on the antiaging remedies. The purpose of the study was to test whether life-prolonging effects of alpha-ketoglutarate (AKG), observed in nematodes and fruit flies, would be reproduced in long-lived Drosophila melanogaster flies. Lifespan was assayed in flies kept in demographic cages. Fecundity, proportion of flies capable of negative geotaxis, starvation resistance, time of heat coma onset, levels of triacyglycerols, body glucose, glycogen, activities of glutamate dehydrogenase, catalase, glutathione-S-transferase, hexokinase, phosphofructokinase, pyruvate kinase, lactate, and glutamate dehydrogenases were assessed. Dietary AKG did not affect fly lifespan on the diet with 5% yeast and 5% sucrose (5Y:5S) and on the diet with 9% yeast and 1% sucrose (9Y:1S), but increased lifespan on the low-protein diet (1Y:9S). Twenty-five-day-old female flies fed a 5Y:5S diet with 10 mM AKG for 3 weeks, did not differ from the control group (without AKG) in climbing activity, resistance to heat stress, and starvation. The levels of glucose and glycogen were unaffected but the levels of triacylglycerols were lower in AKG-fed female flies. No differences in activities of glycolytic enzymes, NADPH-producing enzymes, glutamate dehydrogenase, oxygen consumption, and levels of oxidative stress markers were observed between the control and AKG-fed flies. However, AKG-fed flies had lower activities of catalase and glutathione-S-transferase. These results suggest that potential antiaging remedies, such as AKG, may not extend lifespan in long-living organisms despite influencing several metabolic parameters.

Strong Sex-Dependent Effects of Malnutrition on Life- and Healthspan in Drosophila melanogaster

Insufficient intake of essential nutrients, malnutrition is a major issue for millions of people and has a strong impact on the distribution and abundance of species in nature. In this study, we investigated the effect of malnutrition on several fitness components in the vinegar fly Drosophila melanogaster. Four diets with different nutritional values, including three diluted diets of an optimal nutritional balanced diet, were used as feed sources. The effect of malnutrition on fitness components linked to healthspan, the period of life spent in good health conditions, was evaluated by quantifying the flies' lifespan, locomotor activity, heat stress tolerance, lipid content, and dry weight. The results showed that malnutrition had severe negative impact, such as reduced lifespan, locomotor activity, heat stress tolerance, fat content, and dry weight. The negative phenotypic effects were highly sex-dependent, with males being more negatively impacted by malnutrition compared to females. These findings highlight important detrimental and sex-specific effects of malnutrition not only on lifespan but also on traits related to healthspan.

Specific and combined effects of dietary ethanol and arginine on Drosophila melanogaster

In this study, we have investigated specific and combined effects of essential amino acid, l-arginine, and ethanol (EtOH), a natural component of Drosophila melanogaster food, on a range of physiological and biochemical parameters of the flies. Rearing of D. melanogaster during two weeks on the food supplemented with 50 mM l-arginine decreased activities of catalase, glucose-6-phosphate dehydrogenase, and glutathione-S-transferase in males by about 28%, 60%, and 60%, respectively. At the same time, arginine-fed males had 40% higher levels of lipid peroxides and arginine-fed females had 36% low-molecular mass thiol levels as compared to the control. Arginine decreased resistance of fruit flies to heat stress in both sexes, resistance to starvation in females, and resistance to sodium nitroprusside (SNP) in males. Nevertheless, arginine increased resistance to SNP in females. Consumption of food supplemented with 10% EtOH increased resistance of fruit flies to starvation but made them more sensitive to SNP. On the contrary, arginine abrogated the ability of EtOH to increase starvation resistance in males and to decrease SNP resistance in both sexes.

Gender-specific effects of pro-longevity interventions in Drosophila

Sex differences in lifespan are well recognized in the majority of animal species. For example, in male versus female Drosophila melanogaster there are significant differences in behavior and physiology. However, little is known about the underlying mechanisms of gender differences in responses to pro-longevity interventions in this model organism. Here we summarize the existing data on the effects of nutritional and pharmacological anti-aging interventions such as nutrition regimens, diet and dietary supplementation on the lifespan of male and female Drosophila. We demonstrate that males and females have different sensitivities to interventions and that the effects are highly dependent on genetic background, mating, dose and exposure duration. Our work highlights the importance of understanding the mechanisms that underlie the gender-specific effect of anti-aging manipulations. This will provide insight into how these benefits may be valuable for elucidating the primary physiological and molecular targets involved in aging and lifespan determination.

Insect Models in Nutrition Research

Insects are the most diverse organisms on earth, accounting for ~80% of all animals. They are valuable as model organisms, particularly in the context of genetics, development, behavior, neurobiology and evolutionary biology. Compared to other laboratory animals, insects are advantageous because they are inexpensive to house and breed in large numbers, making them suitable for high-throughput testing. They also have a short life cycle, facilitating the analysis of generational effects, and they fulfil the 3R principle (replacement, reduction and refinement). Many insect genomes have now been sequenced, highlighting their genetic and physiological similarities with humans. These factors also make insects favorable as whole-animal high-throughput models in nutritional research. In this review, we discuss the impact of insect models in nutritional science, focusing on studies investigating the role of nutrition in metabolic diseases and aging/longevity. We also consider food toxicology and the use of insects to study the gut microbiome. The benefits of insects as models to study the relationship between nutrition and biological markers of fitness and longevity can be exploited to improve human health.

Parental dietary protein effects on offspring viability in insects and other oviparous invertebrates: a meta-analysis

Dietary protein is a key regulator of reproductive effort in animals, but protein consumption also tends to accelerate senescence and reduce longevity. Given this protein-mediated trade-off between reproduction and survival, how does protein consumption by parents affect the viability of their offspring? In insects, protein consumption by females enhances fecundity, but trade-offs between offspring quantity and quality could result in negative effects of protein consumption on offspring viability. Likewise, protein consumption by males tends to enhance the expression of sexual traits but could have negative effects on offspring viability, mediated by epigenetic factors transmitted via the ejaculate. It remains unclear whether dietary protein has consistent effects on offspring viability across species, and whether these effects are sex-specific. To address this, we conducted a meta-analysis of experimental studies that examined the effects of protein content in the maternal and/or paternal diet in insects and other oviparous invertebrates. We did not find consistent effects of paternal or maternal protein consumption on offspring viability. Rather, effects of dietary protein on offspring vary in both magnitude and sign across taxonomic groups. Further studies are needed to determine how the effects of dietary protein on offspring relate to variation in reproductive biology across species. Our findings also highlight important gaps in the literature and limitations in experiment design.

Chili pepper extends lifespan in a concentration-dependent manner and confers cold resistance on Drosophila melanogaster cohorts by influencing specific metabolic pathways

Chili powder is a widely used spice with pungent taste, often consumed on a daily basis in several countries. Recent prospective cohort studies showed that the regular use of chili pepper improves healthspan in humans. Indeed, chili pepper fruits contain phenolic substances which are structurally similar to those that show anti-aging properties. The objective of our study was to test whether consumption of chili-supplemented food by the fruit fly, Drosophila melanogaster, would prolong lifespan and in which way this chili-supplemented food affects animal metabolism. Chili powder added to food in concentrations of 0.04%-0.12% significantly extended median lifespan in fruit fly cohorts of both genders by 9% to 13%. However, food supplemented with 3% chili powder shortened lifespan of male cohorts by 9%. Lifespan extension was accompanied by a decrease in age-independent mortality (i.e., death in early ages). The metabolic changes caused by consumption of chili-supplemented food had a pronounced dependence on gender. A characteristic of both fruit fly sexes that ate chili-supplemented food was an increased resistance to cold shock. Flies of both sexes had lower levels of hemolymph glucose when they ate food supplemented with low concentrations of chili powder, as compared with controls. However, males fed on food with 3% chili had lower levels of storage lipids and pyruvate reducing activity of lactate dehydrogenase compared with controls. Females fed on this food showed lower activities of hexokinase and pyruvate kinase, as well as lower ADP/O ratios, compared with control flies.

Anise Hyssop Agastache foeniculum Increases Lifespan, Stress Resistance, and Metabolism by Affecting Free Radical Processes in Drosophila

Anise hyssop, Agastache foeniculum, is a widely used medicinal herb with known antioxidant properties. We studied how dietary supplementation with dried A. foeniculum leaf powder affected physiological and metabolic traits as well as activities of antioxidant enzymes and markers of oxidative stress in Drosophila melanogaster. Dietary hyssop extended the lifespan in a sex and genotype independent manner over a broad range of concentrations up to 30 mg/ml. Dietary supplementation with the herb significantly increased fecundity, resistance to oxidative stress and starvation. Higher transcript levels of Drosophila insulin-like peptide (dilp2) and decreased dilp3 and dilp6 transcripts together with increased levels of glycogen and triacylglycerols support an alteration of insulin signaling by the plant extract. Increased enzymatic activities of superoxide dismutase and aconitase as well as elevated protein and low molecular mass thiols also supported an alteration of free radical process in flies treated with dietary A. foeniculum leaf powder. Thus, physiological and metabolic traits as well as free radical processed may be affected by active compounds detected in extracts of anise hyssop leaves and contribute to the increased lifespan and reproductive (egg-laying) activity observed.

Development of fly tolerance to consuming a high-protein diet requires physiological, metabolic and transcriptional changes

Mortality in insects consuming high-protein-and-low-carbohydrate diets resembles a type III lifespan curve with increased mortality at an early age and few survivors that live a relatively long lifespan. We selected for a Drosophila line able to live for a long time on an imbalanced high-protein-low-carbohydrate diet by carrying out five rounds of breeding to select for the most long-lived survivors. Adaptation to this diet in the selected line was studied at the biochemical, physiological and transcriptomic levels. The selected line of flies consumed less of the imbalanced food but also accumulated more storage metabolites: glycogen, triacylglycerides, and trehalose. Selected flies also had a higher activity of alanine transaminase and a higher urea content. Adaptation of the selected line on the transcriptomic level was characterized by down-regulation of genes encoding serine endopeptidases (Jon25i, Jon25ii, betaTry, and others) but up-regulation of genes encoding proteins related to the immune system, such as antimicrobial peptides, Turandot-family humoral factors, hexamerin isoforms, and vitellogenin. These sets of down- and up-regulated genes were similar to those observed in fruit flies with suppressed juvenile hormone signaling. Our data show that the physiological adaptation of fruit flies to a high-protein-low-carbohydrate diet occurs via intuitive pathways, namely a decrease in food consumption, conversion of amino acids into ketoacids to compensate for the lack of carbohydrate, and accumulation of storage metabolites to eliminate the negative effects of excess amino acids. Nevertheless, transcriptomic adaptation occurs in a counter-intuitive way likely via an influence of gut microbiota on food digestion.

Dietary macronutrient content, age-specific mortality and lifespan

Protein and calorie restrictions extend median lifespan in many organisms. However, studies suggest that among-individual variation in the age at death is also affected. Ultimately, both of these outcomes must be caused by effects of nutrition on underlying patterns of age-specific mortality (ASM). Using model life tables, we tested for effects of dietary macronutrients on ASM in mice ( Mus musculus). High concentrations of protein and fat relative to carbohydrates were associated with low life expectancy and high variation in the age at death, a result caused predominantly by high mortality prior to middle age. A lifelong diet comprising the ratio of macronutrients self-selected by mouse (in early adulthood) was associated with low mortality up until middle age, but higher late-life mortality. This pattern results in reasonably high life expectancy, but very low variation in the age at death. Our analyses also indicate that it may be possible to minimize ASM across life by altering the ratio of dietary protein to carbohydrate in the approach to old age. Mortality in early and middle life was minimized at around one-part protein to two-parts carbohydrate, whereas in later life slightly greater than equal parts protein to carbohydrate reduced mortality.

Mating status affects Drosophila lifespan, metabolism and antioxidant system

In Drosophila melanogaster, lifespan and fitness traits were investigated as a function of mating status. Four mating protocols were used: virgin males and females, males and females allowed to copulate only once; males and females that had multiple copulations with one partner over the 5-day mating period; and polygamous males and females that had multiple copulations with different partners over the 5-day mating period. Virgin females had the longest lifespan, and polygamous females had the shortest lifespan, potentially due to injuries, infections or exposure to toxic accessory gland products obtained from different males. Reduced lifespan was also observed in males mated to multiple females. Unexpectedly, mating decreased the amount of food eaten by flies. Mating to different partners decreased the amount of fat in both sexes. The number of eggs laid and their quality was increased in females mated to multiple males. Mating status influenced superoxide dismutase (SOD) and peroxidase (PX) activities, as well as the content of advanced glycation end products (AGEs). The mRNA levels of the insulin receptor (InR) gene were significantly increased in the polygamously mated female group compared to the virgin group. Levels of dTOR mRNA were lower in polygamous females. These results indicate that insulin/IGF-1 signaling (IIS) and Drosophila target of rapamycin (dTOR) pathways can mediate the link between mating status and longevity in Drosophila.

Gene-Diet Interactions: Dietary Rescue of Metabolic Effects in spen-Depleted Drosophila melanogaster

Obesity and its comorbidities are a growing health epidemic. Interactions between genetic background, the environment, and behavior (i.e., diet) greatly influence organismal energy balance. Previously, we described obesogenic mutations in the gene Split ends (Spen) in Drosophila melanogaster, and roles for Spen in fat storage and metabolic state. Lipid catabolism is impaired in Spen-deficient fat storage cells, accompanied by a compensatory increase in glycolytic flux and protein catabolism. Here, we investigate gene-diet interactions to determine if diets supplemented with specific macronutrients can rescue metabolic dysfunction in Spen-depleted animals. We show that a high-yeast diet partially rescues adiposity and developmental defects. High sugar partially improves developmental timing as well as longevity of mated females. Gene-diet interactions were heavily influenced by developmental-stage-specific organismal needs: extra yeast provides benefits early in development (larval stages) but becomes detrimental in adulthood. High sugar confers benefits to Spen-depleted animals at both larval and adult stages, with the caveat of increased adiposity. A high-fat diet is detrimental according to all tested criteria, regardless of genotype. Whereas Spen depletion influenced phenotypic responses to supplemented diets, diet was the dominant factor in directing the whole-organism steady-state metabolome. Obesity is a complex disease of genetic, environmental, and behavioral inputs. Our results show that diet customization can ameliorate metabolic dysfunction underpinned by a genetic factor.

Insulin Signaling in Intestinal Stem and Progenitor Cells as an Important Determinant of Physiological and Metabolic Traits in Drosophila

The insulin–IGF-1 signaling (IIS) pathway is conserved throughout multicellular organisms and regulates many traits, including aging, reproduction, feeding, metabolism, stress resistance, and growth. Here, we present evidence of a survival-sustaining role for IIS in a subset of gut cells in Drosophila melanogaster, namely the intestinal stem cells (ISCs) and progenitor cells. Using RNAi to knockdown the insulin receptor, we found that inhibition of IIS in ISCs statistically shortened the lifespan of experimental flies compared with non-knockdown controls, and also shortened their survival under starvation or malnutrition conditions. These flies also showed decreased reproduction and feeding, and had lower amounts of glycogen and glucose in the body. In addition, increased expression was observed for the Drosophila transcripts for the insulin-like peptides dilp2, dilp5, and dilp6. This may reflect increased insulin signaling in peripheral tissues supported by up-regulation of the target of the brain insulin gene (tobi). In contrast, activation of IIS (via knockdown of the insulin pathway inhibitor PTEN) in intestinal stem and progenitor cells decreased fly resistance to malnutrition, potentially by affecting adipokinetic hormone signaling. Finally, Pten knockdown to enhance IIS also activated JAK–STAT signaling in gut tissue by up-regulation of upd2, upd3, and soc36 genes, as well as genes encoding the EGF receptor ligands spitz and vein. These results clearly demonstrate that manipulating insulin levels may be used to modulate various fly traits, which are important determinants of organismal survival.

The prandial process in flies

Feeding is fundamental to any heterotroph organism; in its role to quell hunger it overrides most other motivational states. But feeding also literally opens the door to harmful risks, especially for a saprophagous animal like Drosophila; ingestion of poisonous substrate can lead to irreversible damage. Thus feeding incorporates a series of steps with several checkpoints to guarantee that the ingestion remains beneficial and provides a balanced diet, or the feeding process is interrupted. Subsequently, we will summarize and describe the feeding process in Drosophila in a comprehensive manner. We propose eleven distinct steps for feeding, grouped into four categories, to address our current knowledge of prandial regulatory mechanisms in Drosophila.

Alternative NADH dehydrogenase extends lifespan and increases resistance to xenobiotics in Drosophila

Mitochondrial alternative NADH dehydrogenase (aNDH) was found to extend lifespan when expressed in the fruit fly. We have found that fruit flies expressing aNDH from Ciona intestinalis (NDX) had 17–71% lifespan prolongation on media with different protein-tocarbohydrate ratios except NDX-expressing males that had 19% shorter lifespan than controls on a high protein diet. NDX-expressing flies were more resistant to organic xenobiotics, 2,4-dichlorophenoxyacetic acid and alloxan, and inorganic toxicant potassium iodate, and partially to sodium molybdate treatments. On the other hand, NDX-expressing flies were more sensitive to catechol and sodium chromate. Enzymatic analysis showed that NDX-expressing males had higher glucose 6-phosphate dehydrogenase activity, whilst both sexes showed increased glutathione S-transferase activity.

The effects of crizotinib in a transgenic Drosophila model expressing the human TPM4-ALK fusion gene or TPM4

Anaplastic lymphoma kinase (ALK) fusion events lead to constitutive activation of the ALK kinase domain, thereby functioning as oncogenic drivers. These fusion proteins have been identified in numerous cancers. Crizotinib, a small molecule inhibitor of c-Met and ALK, is a Food and Drug Administration-approved drug with reported efficacy in the treatment of cancer. Tropomyosins (TPMs) are a family of actin filament-binding proteins. Altered TPM expression has been found in a variety of human tumors. Inhibitors of cancer-associated TPMs and actin-targeting compounds have been developed, but anti-actin agents have cardiac and respiratory muscle toxicities. In this study, we investigated the sensitivities of human TPM4 (hTPM4), human ALK (hALK), and their fusion gene (hTPM4-hALK) to crizotinib by measuring the lifespan of transgenic Drosophila. Flies overexpressing hTPM4-hALK, hTPM4 and hALK showed decreased lifespans compared with controls. Although crizotinib is an inhibitor of ALK, treatment with crizotinib significantly extended the lifespans of Drosophila expressing hTPM4 and hTPM4-hALK but had no effect on hALK-expressing flies. Autophosphorylation of Tyr¹²⁷⁸ is necessary for full activation of the ALK domain. We confirmed that hTPM4-hALK was phosphorylated at Tyr¹²⁷⁸ in a ligand-independent manner, and hTPM4-hALK-expressing flies treated with crizotinib showed a decreased level of Tyr¹²⁷⁸ phosphorylation compared with untreated hTPM4-hALK-expressing flies, with a greater decrease induced by 1 µM compared with 200 nM crizotinib. Taken together, the results suggest that crizotinib is effective for treating ALK-driven cancer and might be a new therapeutic drug, without cardiac or respiratory muscle toxic effects, for TPM4-expressing cancers.

Summary: In this study, we find that crizotinib extends the lifespan of Drosophila overexpressing hTPM4-ALK and hTPM4, which are linked with a variety of human tumors.

Protective effects of alpha-ketoglutarate against aluminum toxicity in Drosophila melanogaster

In recent years, Drosophila melanogaster has emerged as a model for studies on aluminum toxicity. The current study aimed to disclose the mechanisms of aluminum toxicity in D. melanogaster at larval and adult stages and examined the potential protective effects of dietary alpha-ketoglutarate (AKG). Flies were reared on food containing 10 mM AlCl₃, 10 mM AKG or both additives. Rearing on an AlCl₃-containing diet induced behavioral defects, and decreased fecundity and long-term survival of female flies. The addition of dietary AKG did not ameliorate locomotor and taste behavior defects or the higher sensitivity to oxidative stress, but improved heat stress resistance, egg-laying capability and survival of females treated with AlCl₃. Metabolic effects of AlCl₃ exposure on flies included an imbalance of metal content, decreased glucose levels, increased free iron and storage triacylglyceride (TAG) levels, mitochondria dysfunction, and the development of oxidative stress. Dietary AKG did not prevent AlCl₃ effects on glucose and TAG, but improved metal homeostasis, inhibited the increase in free Fe and restored the functional activity of iron-containing enzymes such as aconitase. In addition, AKG decreased the intensity of oxidative stress seen in AlCl₃-reared adult flies, probably due to inhibition of iron mobilization. The results show that AKG is not a full antidote against Al toxicity but is able to relieve multiple metabolic effects of high aluminum. Furthermore, the modulating ability of AKG can clearly be helpful in exploring the molecular mechanisms of Al toxicity.

Neuromuscular degeneration and locomotor deficit in a Drosophila model of mucopolysaccharidosis VII is attenuated by treatment with resveratrol

Mucopolysaccharidosis VII (MPS VII) is a recessively inherited lysosomal storage disorder caused by β-glucuronidase enzyme deficiency. The disease is characterized by widespread accumulation of non-degraded or partially degraded glycosaminoglycans, leading to cellular and multiple tissue dysfunctions. The patients exhibit diverse clinical symptoms, and eventually succumb to premature death. The only possible remedy is the recently approved enzyme replacement therapy, which is an expensive, invasive and lifelong treatment procedure. Small-molecule therapeutics for MPS VII have so far remained elusive primarily due to lack of molecular insights into the disease pathogenesis and unavailability of a suitable animal model that can be used for rapid drug screening. To address these issues, we developed a Drosophila model of MPS VII by knocking out the CG2135 gene, the fly β-glucuronidase orthologue. The CG2135-/- fly recapitulated cardinal features of MPS VII, such as reduced lifespan, progressive motor impairment and neuropathological abnormalities. Loss of dopaminergic neurons and muscle degeneration due to extensive apoptosis was implicated as the basis of locomotor deficit in this fly. Such hitherto unknown mechanistic links have considerably advanced our understanding of the MPS VII pathophysiology and warrant leveraging this genetically tractable model for deeper enquiry about the disease progression. We were also prompted to test whether phenotypic abnormalities in the CG2135-/- fly can be attenuated by resveratrol, a natural polyphenol with potential health benefits. Indeed, resveratrol treatment significantly ameliorated neuromuscular pathology and restored normal motor function in the CG2135-/- fly. This intriguing finding merits further preclinical studies for developing an alternative therapy for MPS VII.This article has an associated First Person interview with the first author of the paper.

How various concentrations of nutrients affect basal redox homeostasis of fruit flies according to gender and aging

We evaluated the effects of type of nutrients on redox status according to age and gender in Drosophila melanogaster. Flies were raised on different dose of sucrose and fixed concentration of protein containing media and separated according to their gender and age. Redox status biomarkers such as protein carbonyl groups, dityrosine, kynurenine, lipid hydroperoxides, advanced glycation end products, and Cu,Zn superoxide dismutase were assessed. We found that all of the males had higher levels of basal oxidative stress biomarkers except protein carbonyl. On the other hand, Cu,Zn-superoxide dismutase activity was elevated. We found that high concentration of sucrose leads to impaired redox status. We also observed that high protein content in sucrose-based media fecundity rate was increased and also transition to adult flies and survival ratio were decreased. Further studies are needed to focus on evaluation of the relation between median life span, nutritional mechanisms, and redox status biomarkers. PRACTICAL APPLICATIONS: Aging is characterized by functional decline in whole body system. Unfortunately, many of the life span extension strategies may lead to age-related disorders. It is widely accepted that impaired redox homeostasis is one of the signs of age-related pathophysiological changes. Due to difficulties in the establishment and validation of mimetic aging models in rodents, D. melanogaster is becoming/getting widely used model organism in gerontological studies. Currently, high protein and low carbohydrate-based nutrition regimes have become one of the most popular nutritional choice in aging population. Favorable nutrition type is considered one of the important factors for preventing age-related pathologies and promote healthy aging. In this study, we aimed to evaluate redox modulatory effects of different nutrition types as combination of various sucrose and constant protein concentration on basal redox status in D. melanogaster. Due to evolutionally conservation, we hypothesize that similar findings may be observed in aging population. Favorable nutrition type may ameliorate or postpone age-related degenerative processes and promote healthy aging.

Insulin-Like Peptides Regulate Feeding Preference and Metabolism in Drosophila

Fruit flies have eight identified Drosophila insulin-like peptides (DILPs) that are involved in the regulation of carbohydrate concentrations in hemolymph as well as in accumulation of storage metabolites. In the present study, we investigated diet-dependent roles of DILPs encoded by the genes dilp1–5, and dilp7 in the regulation of insect appetite, food choice, accumulation of triglycerides, glycogen, glucose, and trehalose in fruit fly bodies and carbohydrates in hemolymph. We have found that the wild type and the mutant lines demonstrate compensatory feeding for carbohydrates. However, mutants on dilp2,3, dilp3, dilp5, and dilp7 showed higher consumption of proteins on high yeast diets. To evaluate metabolic differences between studied lines on different diets we applied response surface methodology. High nutrient diets led to a moderate increase in concentration of glucose in hemolymph of the wild type flies. Mutations on dilp genes changed this pattern. We have revealed that the dilp2 mutation led to a drop in glycogen levels independently on diet, lack of dilp3 led to dramatic increase in circulating trehalose and glycogen levels, especially at low protein consumption. Lack of dilp5 led to decreased levels of glycogen and triglycerides on all diets, whereas knockout on dilp7 caused increase in glycogen levels and simultaneous decrease in triglyceride levels at low protein consumption. Fruit fly appetite was influenced by dilp3 and dilp7 genes. Our data contribute to the understanding of Drosophila as a model for further studies of metabolic diseases and may serve as a guide for uncovering the evolution of metabolic regulatory pathways.

Drosophila melanogaster as a Versatile Model Organism in Food and Nutrition Research

Drosophila melanogaster has been widely used in the biological sciences as a model organism. Drosophila has a relatively short life span of 60-80 days, which makes it attractive for life span studies. Moreover, approximately 60% of the fruit fly genes are orthologs to mammals. Thus, metabolic and signal transduction pathways are highly conserved. Maintenance and reproduction of Drosophila do not require sophisticated equipment and are rather cheap. Furthermore, there are fewer ethical issues involved in experimental Drosophila research compared with studies in laboratory rodents, such as rats and mice. Drosophila is increasingly recognized as a model organism in food and nutrition research. Drosophila is often fed complex solid diets based on yeast, corn, and agar. There are also so-called holidic diets available that are defined in terms of their amino acid, fatty acid, carbohydrate, vitamin, mineral, and trace element compositions. Feed intake, body composition, locomotor activity, intestinal barrier function, microbiota, cognition, fertility, aging, and life span can be systematically determined in Drosophila in response to dietary factors. Furthermore, diet-induced pathophysiological mechanisms including inflammation and stress responses may be evaluated in the fly under defined experimental conditions. Here, we critically evaluate Drosophila melanogaster as a versatile model organism in experimental food and nutrition research, review the corresponding data in the literature, and make suggestions for future directions of research.

The sex-specific effects of diet quality versus quantity on morphology in Drosophila melanogaster

Variation in the quality and quantity of nutrition is a major contributor to phenotypic variation in animal populations. Although we know much of how dietary restriction impacts phenotype, and of the molecular-genetic and physiological mechanisms that underlie this response, we know much less of the effects of dietary imbalance. Specifically, although dietary imbalance and restriction both reduce overall body size, it is unclear whether both have the same effect on the size of individual traits. Here, we use the fruit fly Drosophila melanogaster to explore the effect of dietary food versus protein-to-carbohydrate ratio on body proportion and trait size. Our results indicate that body proportion and trait size respond differently to changes in diet quantity (food concentration) versus diet quality (protein-to-carbohydrate ratio), and that these effects are sex specific. While these differences suggest that Drosophila use at least partially distinct developmental mechanisms to respond to diet quality versus quantity, further analysis indicates that the responses can be largely explained by the independent and contrasting effects of protein and carbohydrate concentration on trait size. Our data highlight the importance of considering macronutrient composition when elucidating the effect of nutrition on trait size, at the levels of both morphology and developmental physiology.

Dietary L-arginine accelerates pupation and promotes high protein levels but induces oxidative stress and reduces fecundity and life span in Drosophila melanogaster

L-Arginine, a precursor of many amino acids and of nitric oxide, plays multiple important roles in nutrient metabolism and regulation of physiological functions. In this study, the effects of L-arginine-enriched diets on selected physiological responses and metabolic processes were assessed in Drosophila melanogaster. Dietary L-arginine at concentrations 5-20 mM accelerated larval development and increased body mass, and total protein concentrations in third instar larvae, but did not affect these parameters when diets contained 100 mM arginine. Young (2 days old) adult flies of both sexes reared on food supplemented with 20 and 100 mM L-arginine possessed higher total protein concentrations and lower glucose and triacylglycerol concentrations than controls. Additionally, flies fed 20 mM L-arginine had higher proline and uric acid concentrations. L-Arginine concentration in the diet also affected oxidative stress intensity in adult flies. Food with 20 mM L-arginine promoted lower protein thiol concentrations and higher catalase activity in flies of both sexes and higher concentrations of low molecular mass thiols in males. When flies were fed on a diet with 100 mM L-arginine, lower catalase activities and concentrations of protein thiols were found in both sexes as well as lower low molecular mass thiols in females. L-Arginine-fed males demonstrated higher climbing activity, whereas females showed higher cold tolerance and lower fecundity, compared with controls. Food containing 20 mM L-arginine shortened life span in both males and females. The results suggest that dietary L-arginine shows certain beneficial effects at the larval stage and in young adults. However, the long-term consumption of L-arginine-enriched food had unfavorable effects on D. melanogaster due to decreasing fecundity and life span.

The impact of low-protein high-carbohydrate diets on aging and lifespan

Most research on nutritional effects on aging has focussed on the impact of manipulating single dietary factors such as total calorie intake or each of the macronutrients individually. More recent studies using a nutritional geometric approach called the Geometric Framework have facilitated an understanding of how aging is influenced across a landscape of diets that vary orthogonally in macronutrient and total energy content. Such studies have been performed using ad libitum feeding regimes, thus taking into account compensatory feeding responses that are inevitable in a non-constrained environment. Geometric Framework studies on insects and mice have revealed that diets low in protein and high in carbohydrates generate longest lifespans in ad libitum-fed animals while low total energy intake (caloric restriction by dietary dilution) has minimal effect. These conclusions are supported indirectly by observational studies in humans and a heterogeneous group of other types of interventional studies in insects and rodents. Due to compensatory feeding for protein dilution, low-protein, high-carbohydrate diets are often associated with increased food intake and body fat, a phenomenon called protein leverage. This could potentially be mitigated by supplementing these diets with interventions that influence body weight through physical activity and ambient temperature.

OXIDIZED LIPIDS DID NOT REDUCE LIFESPAN IN THE FRUIT FLY, Drosophila melanogaster

Aging is often associated with accumulation of oxidative damage in proteins and lipids. However, some studies do not support this view, raising the question of whether high levels of oxidative damage are associated with lifespan. In the current investigation, Drosophila melanogaster flies were kept on diets with 2 or 10% of either glucose or fructose. The lifespan, fecundity, and feeding as well as amounts of protein carbonyls (PC) and lipid peroxides (LOOH), activities of superoxide dismutase (SOD), catalase, glutathione-S-transferase (GST), and glutathione reductase activity of thioredoxin reductase (TrxR) were measured in "young" (10-day old) and "aged" (50-day old) flies. Flies maintained on diets with 10% carbohydrate lived longer than those on the 2% diets. However, neither lifespan nor fecundity was affected by the type of carbohydrate. The amount of PC was unaffected by diet and age, whereas flies fed on diets with 10% carbohydrate had about fivefold higher amounts of LOOH compared to flies maintained on the 2% carbohydrate diets. Catalase activity was significantly lower in flies fed on diets with 10% carbohydrates compared to flies on 2% carbohydrate diets. The activities of SOD, GST, and TrxR were not affected by the diet or age of the flies. The higher levels of LOOH in flies maintained on 10% carbohydrate did not reduce their lifespan, from which we infer that oxidative damage to only one class of biomolecules, particularly lipids, is not sufficient to influence lifespan.

Food odors trigger an endocrine response that affects food ingestion and metabolism

Food odors stimulate appetite and innate food-seeking behavior in hungry animals. The smell of food also induces salivation and release of gastric acid and insulin. Conversely, sustained odor exposure may induce satiation. We demonstrate novel effects of food odors on food ingestion, metabolism and endocrine signaling in Drosophila melanogaster. Acute exposure to attractive vinegar odor triggers a rapid and transient increase in circulating glucose, and a rapid upregulation of genes encoding the glucagon-like hormone adipokinetic hormone (AKH), four insulin-like peptides (DILPs) and some target genes in peripheral tissues. Sustained exposure to food odors, however, decreases food intake. Hunger-induced strengthening of synaptic signaling from olfactory sensory neurons (OSNs) to brain neurons increases food-seeking behavior, and conversely fed flies display reduced food odor sensitivity and feeding. We show that increasing the strength of OSN signaling chronically by genetic manipulation of local peptide neuromodulation reduces feeding, elevates carbohydrates and diminishes lipids. Furthermore, constitutively strengthened odor sensitivity altered gene transcripts for AKH, DILPs and some of their targets. Thus, we show that food odor can induce a transient anticipatory endocrine response, and that boosted sensitivity to this odor affects food intake, as well as metabolism and hormonal signaling.

High sucrose consumption promotes obesity whereas its low consumption induces oxidative stress in Drosophila melanogaster

The effects of sucrose in varied concentrations (0.25-20%) with constant amount of yeasts in larval diet on development and metabolic parameters of adult fruit fly Drosophila melanogaster were studied. Larvae consumed more food at low sucrose diet, overeating with yeast. On high sucrose diet, larvae ingested more carbohydrates, despite consuming less food and obtaining less protein derived from yeast. High sucrose diet slowed down pupation and increased pupa mortality, enhanced levels of lipids and glycogen, increased dry body mass, decreased water content, i.e. resulted in obese phenotype. Furthermore, it suppressed reactive oxygen species-induced oxidation of lipids and proteins as well as the activity of superoxide dismutase. The activity of catalase was gender-related. In males, at all sucrose concentrations used catalase activity was higher than at its concentration of 0.25%, whereas in females sucrose concentration virtually did not influence the activity. High sucrose diet increased content of protein thiols and the activity of glucose-6-phosphate dehydrogenase. The increase in sucrose concentration also enhanced uric acid level in females, but caused opposite effects in males. Development on high sucrose diets was accompanied by elevated steady-state insulin-like peptide 3 mRNA level. Finally, carbohydrate starvation at yeast overfeeding on low sucrose diets resulted in oxidative stress reflected by higher levels of oxidized lipids and proteins accompanied by increased superoxide dismutase activity. Potential mechanisms involved in regulation of redox processes by carbohydrates are discussed.

Feeding on frozen live yeast has some deleterious effects in Drosophila melanogaster

Many experiments have shown that dietary restriction, for instance by removing live yeast or modifying the protein/carbohydrate ratio, can modulate lifespan, fecundity, resistance to severe stresses and behaviour in Drosophila melanogaster flies. The present study tested whether feeding flies with frozen yeast rather than with fresh yeast could have some effect on these traits, the other components of the food being similar in the two groups. Freezing altered live yeast quality and flies feeding on frozen yeast lived slightly less (males), were less fecund at older ages, and poorly resisted to some severe stresses (cold and starvation), no negative effect being observed on resistance to heat. It seems that, like in humans, feeding on a low quality food can negatively impact healthspan and that an appropriate food is not only a food with optimal number of calories and appropriate ratios of proteins, carbohydrates, and fat.

The Role of Storage Lipids in the Relation between Fecundity, Locomotor Activity, and Lifespan of Drosophila melanogaster Longevity-Selected and Control Lines

The contribution of insect fat body to multiple processes, such as development, metamorphosis, activity, and reproduction results in trade-offs between life history traits. In the present study, age-induced modulation of storage lipid composition in Drosophila melanogaster longevity-selected (L) and non-selected control (C) lines was studied and the correlation between total body fat mass and lifespan assessed. The trade-offs between fecundity, locomotor activity, and lifespan were re-evaluated from a lipid-related metabolic perspective. Fewer storage lipids in the L lines compared to the C lines supports the impact of body fat mass on extended lifespan. The higher rate of fecundity and locomotor activity in the L lines may increase the lipid metabolism and enhance the lipolysis of storage lipids, reducing fat reserves. The correlation between neutral lipid fatty acids and fecundity, as well as locomotor activity, varied across age groups and between the L and C lines. The fatty acids that correlated with egg production were different from the fatty acids that correlated with locomotor activity. The present study suggests that fecundity and locomotor activity may positively affect the lifespan of D. melanogaster through the inhibition of fat accumulation.

High consumption of fructose rather than glucose promotes a diet-induced obese phenotype in Drosophila melanogaster

During the last 20 years, there has been a considerable scientific debate about the possible mechanisms of induction of metabolic disorders by reducing monosaccharides such as glucose or fructose. In this study, we report the metabolic rearrangement in response to consumption of these monosaccharides at concentrations ranging from 0.25% to 20% in a Drosophila model. Flies raised on high-glucose diet displayed delay in pupation and increased developmental mortality compared with fructose consumers. Both monosaccharides at high concentrations promoted an obese-like phenotype indicated by increased fly body mass, levels of uric acid, and circulating and stored carbohydrates and lipids; and decreased percentage of water in the body. However, flies raised on fructose showed lower levels of circulating glucose and higher concentrations of stored carbohydrates, lipids, and uric acid. The preferential induction of obesity caused by fructose in Drosophila was associated with increased food consumption and reduced mRNA levels of DILP2 and DILP5 in the brain of adult flies. Our data show that glucose and fructose differently affect carbohydrate and lipid metabolism in Drosophila in part by modulation of insulin/insulin-like growth factor signaling. Some reported similarities with effects observed in mammals make Drosophila as a useful model to study carbohydrate influence on metabolism and development of metabolic disorders.

Overexpression of dilp2 causes nutrient-dependent semi-lethality in Drosophila

Insulin/insulin-like growth factor (IGF) plays an important role as a systemic regulator of metabolism in multicellular organisms. Hyperinsulinemia, a high level of blood insulin, is often associated with impaired physiological conditions such as hypoglycemia, insulin resistance, and diabetes. However, due to the complex pathophysiology of hyperinsulinemia, the causative role of excess insulin/IGF signaling has remained elusive. To investigate the biological effects of a high level of insulin in metabolic homeostasis and physiology, we generated flies overexpressing Drosophila insulin-like peptide 2 (Dilp2), which has the highest potential of promoting tissue growth among the Ilp genes in Drosophila. In this model, a UAS-Dilp2 transgene was overexpressed under control of sd-Gal4 that drives expression predominantly in developing imaginal wing discs. Overexpression of Dilp2 caused semi-lethality, which was partially suppressed by mutations in the insulin receptor (InR) or Akt1, suggesting that dilp2-induced semi-lethality is mediated by the PI3K/Akt1 signaling. We found that dilp2-overexpressing flies exhibited intensive autophagy in fat body cells. Interestingly, the dilp2-induced autophagy as well as the semi-lethality was partially rescued by increasing the protein content relative to glucose in the media. Our results suggest that excess insulin/IGF signaling impairs the physiology of animals, which can be ameliorated by controlling the nutritional balance between proteins and carbohydrates, at least in flies.

Lifespan extension and delay of age-related functional decline caused by Rhodiola rosea depends on dietary macronutrient balance

Background

This study was conducted to evaluate the effects of rhizome powder from the herb Rhodiola rosea, a traditional Western Ukraine medicinal adaptogen, on lifespan and age-related physiological functions of the fruit fly Drosophila melanogaster.

Results

Flies fed food supplemented with 5.0 mg/ml and 10.0 mg/ml of R. rosea rhizome powder had a 14% to 17% higher median lifespan, whereas at 30.0 mg/ml lifespan was decreased by 9% to 12%. The preparation did not decrease fly fecundity.

The effect of R. rosea supplement on lifespan was dependent on diet composition. Lifespan extension by 15% to 21% was observed only for diets with protein-to-carbohydrate ratios less than 1. Lifespan extension was also dependent on total concentration of macronutrients. Thus, for the diet with 15% yeast and 15% sucrose there was no lifespan extension, while for the diet with protein-to-carbohydrate ratio 20:1 R. rosea decreased lifespan by about 10%.

Flies fed Rhodiola preparation were physically more active, less sensitive to the redox-cycling compound menadione and had a longer time of heat coma onset compared with controls. Positive effects of Rhodiola rhizome on stress resistance and locomotor activity were highest at the ‘middle age’.

Conclusions

The present data show that long-term food supplementation with R. rosea rhizome not only increases D. melanogaster lifespan, but also delays age-related decline of physical activity and increases stress resistance, what depends on protein-to-carbohydrate ratio of the diet.

High carbohydrate-low protein consumption maximizes Drosophila lifespan

Dietary restriction extends lifespan in a variety of organisms, but the key nutritional components driving this process and how they interact remain uncertain. In Drosophila, while a substantial body of research suggests that protein is the major dietary component affecting longevity, recent studies claim that carbohydrates also play a central role. To clarify how nutritional factors influence longevity, nutrient consumption and lifespan were measured on a series of diets with varying yeast and sugar content. We show that optimal lifespan requires both high carbohydrate and low protein consumption, but neither nutrient by itself entirely predicts lifespan. Increased dietary carbohydrate or protein concentration does not always result in reduced feeding-the regulation of food consumption is best described by a constant daily caloric intake target. Moreover, due to differences in food intake, increased concentration of a nutrient within the diet does not necessarily result in increased consumption of that particular nutrient. Our results shed light on the issue of dietary effects on lifespan and highlight the need for accurate measures of nutrient intake in dietary manipulation studies.

Aging-induced dysregulation of dicer1-dependent microRNA expression impairs angiogenic capacity of rat cerebromicrovascular endothelial cells

Age-related impairment of angiogenesis is likely to play a central role in cerebromicrovascular rarefaction and development of vascular cognitive impairment, but the underlying mechanisms remain elusive. To test the hypothesis that dysregulation of Dicer1 (ribonuclease III, a key enzyme of the microRNA [miRNA] machinery) impairs endothelial angiogenic capacity in aging, primary cerebromicrovascular endothelial cells (CMVECs) were isolated from young (3 months old) and aged (24 months old) Fischer 344 × Brown Norway rats. We found an age-related downregulation of Dicer1 expression both in CMVECs and in small cerebral vessels isolated from aged rats. In aged CMVECs, Dicer1 expression was increased by treatment with polyethylene glycol-catalase. Compared with young cells, aged CMVECs exhibited altered miRNA expression profile, which was associated with impaired proliferation, adhesion to vitronectin, collagen and fibronectin, cellular migration (measured by a wound-healing assay using electric cell-substrate impedance sensing technology), and impaired ability to form capillary-like structures. Overexpression of Dicer1 in aged CMVECs partially restored miRNA expression profile and significantly improved angiogenic processes. In young CMVECs, downregulation of Dicer1 (siRNA) resulted in altered miRNA expression profile associated with impaired proliferation, adhesion, migration, and tube formation, mimicking the aging phenotype. Collectively, we found that Dicer1 is essential for normal endothelial angiogenic processes, suggesting that age-related dysregulation of Dicer1-dependent miRNA expression may be a potential mechanism underlying impaired angiogenesis and cerebromicrovascular rarefaction in aging.

Dietary composition regulates Drosophila mobility and cardiac physiology

The impact of dietary composition on exercise capacity is a subject of intense study in both humans and model organisms. Interactions between diet and genetics are a crucial component of optimized dietary design. However, the genetic factors governing exercise response are still not well understood. The recent development of invertebrate models for endurance exercise is likely to facilitate study designs examining the conserved interactions between diet, exercise and genetics. As a first step, we used the Drosophila model to describe the effects of varying dietary composition on several physiological indices, including fatigue tolerance and climbing speed, cardiac performance, lipid storage and autophagy. We found that flies of two divergent genetic backgrounds optimize endurance and cardiac performance on relatively balanced low calorie diets. When flies are provided with unbalanced diets, diets higher in sugar than in yeast facilitate greater endurance at the expense of cardiac performance. Importantly, we found that dietary composition has a profound effect on various physiological indices, whereas total caloric intake per se has very little predictive value for performance. We also found that the effects of diet on endurance are completely reversible within 48 h if flies are switched to a different diet.