Metabolic and transcriptional response to a high-fat diet in Drosophila melanogaster

Influence of α-lipoic acid on longevity and stress resistance in Drosophila melanogaster fed with a high-fat diet

Consumption of a high-fat diet is accompanied by the risks of obesity and early onset of age-associated complications for which dietary interventions are imperative to combat. α-lipoic acid has been shown to hinder diet-induced obesity and induce lifespan-extending efficacy in model organisms. In this study, α-lipoic acid was investigated for its efficacy in improving lifespan and stress resistance in the Canton-S strain of Drosophila melanogaster fed with a high-fat diet. Furthermore, as mating status significantly impacts survival in fruit flies, flies were reared in two experimental groups-group one, in which males and females were bred together, and group two, in which males and females were bred separately. In group one, α-lipoic acid improved the mean lifespan, reduced the fecundity of females, and reduced the mean body weight of flies at a dose range of 2-2.5 mM, respectively. In group two, α-lipoic acid improved the mean lifespan, reduced the fecundity of females, and reduced the mean body weight of flies at a dose range of 1-2.5 mM, respectively. Improved climbing efficiency was observed with α-lipoic acid at the dose range of 1.5-2.5 mM in flies of group one and 1-2.5 mM in flies of group two, respectively. Administration of α-lipoic acid improved resistance to oxidative stress in only female flies of group one at 2.5 mM, whereas in group two, both male and female flies exhibited enhanced resistance to oxidative stress with α-lipoic acid at a dose range of 2-2.5 mM, respectively. Male and female flies of only group one showed improved resistance to heat shock stress with α-lipoic acid at a dose range of 2-2.5 mM. Only female flies of group two exhibited a slight improvement in recovery time following cold shock with α-lipoic acid only at 2.5 mM. No significant change in resistance to starvation stress was observed with any dose of α-lipoic acid in either group of flies. To summarize, data from this study suggested a probable dose and gender-dependent efficacy of α-lipoic acid in flies fed with a high-fat diet, which was significantly influenced by the mating status of flies due to varied rearing conditions.

Investigating SARS-CoV-2 virus-host interactions and mRNA expression: Insights using three models of D. melanogaster

Responsible for COVID-19, SARS-CoV-2 is a coronavirus in which contagious variants continue to appear. Therefore, some population groups have demonstrated greater susceptibility to contagion and disease progression. For these reasons, several researchers have been studying the SARS-CoV-2/human interactome to understand the pathophysiology of COVID-19 and develop new pharmacological strategies. D. melanogaster is a versatile animal model with approximately 90 % human protein orthology related to SARS-CoV-2/human interactome and is widely used in metabolic studies. In this context, our work assessed the potential interaction between human proteins (ZNF10, NUP88, BCL2L1, UBC9, and RBX1) and their orthologous proteins in D. melanogaster (gl, Nup88, Buffy, ubc9, and Rbx1a) with proteins from SARS-CoV-2 (nsp3, nsp9, E, ORF7a, N, and ORF10) using computational approaches. Our results demonstrated that all the proteins have the potential to interact, and we compared the binding sites between humans and fruit flies. The stability and consistency in the structure of the gl_nsp3 complex, specifically, could be crucial for its specific biological functions. Lastly, to enhance the understanding of the influence of host factors on coronavirus infection, we also analyse the mRNA expression of the five genes (mbo, gl, lwr, Buffy, and Roc1a) responsible for encoding the fruit fly proteins. Briefly, we demonstrated that those genes were differentially regulated according to diets, sex, and age. Two groups showed higher positive gene regulation than others: females in the HSD group and males in the aging group, which could imply a higher virus-host susceptibility. Overall, while preliminary, our work contributes to the understanding of host defense mechanisms and potentially identifies candidate proteins and genes for in vivo viral studies against SARS-CoV-2.

High-fat diets induce inflammatory IMD/NFκB signaling via gut microbiota remodeling in Drosophila

High-fat diets (HFDs), a prevailing daily dietary style worldwide, induce chronic low-grade inflammation in the central nervous system and peripheral tissues, promoting a variety of diseases including pathologies associated with neuroinflammation. However, the mechanisms linking HFDs to inflammation are not entirely clear. Here, using a Drosophila HFD model, we explored the mechanism of HFD-induced inflammation in remote tissues. We found that HFDs activated the IMD/NFκB immune pathway in the head through remodeling of the commensal gut bacteria. Removal of gut microbiota abolished such HFD-induced remote inflammatory response. Further experiments revealed that HFDs significantly increased the abundance of Acetobacter malorum in the gut, and the re-association of this bacterium was sufficient to elicit inflammatory response in remote tissues. Mechanistically, Acetobacter malorum produced a greater amount of peptidoglycan (PGN), a well-defined microbial molecular pattern that enters the circulation and remotely activates an inflammatory response. Our results thus show that HFDs trigger inflammation mediated by a bacterial molecular pattern that elicits host immune response.

Fasting as a precursor to high-fat diet enhances mitochondrial resilience in Drosophila melanogaster

Changes in diet type and nutrient availability can impose significant environmental stress on organisms, potentially compromising physiological functions and reproductive success. In nature, dramatic fluctuations in dietary resources are often observed and adjustments to restore cellular homeostasis are crucial to survive this type of stress. In this study, we exposed male Drosophila melanogaster to two modulated dietary treatments: one without a fasting period before exposure to a high-fat diet and the other with a 24-h fasting period. We then investigated mitochondrial metabolism and molecular responses to these treatments. Exposure to a high-fat diet without a preceding fasting period resulted in disrupted mitochondrial respiration, notably at the level of complex I. On the other hand, a short fasting period before the high-fat diet maintained mitochondrial respiration. Generally, transcript abundance of genes associated with mitophagy, heat-shock proteins, mitochondrial biogenesis, and nutrient sensing pathways increased either slightly or significantly following a fasting period and remained stable when flies were subsequently put on a high-fat diet, whereas a drastic decrease of almost all transcript abundances was observed for all these pathways when flies were exposed directly to a high-fat diet. Moreover, mitochondrial enzymatic activities showed less variation after the fasting period than the treatment without a fasting period. Overall, our study sheds light on the mechanistic protective effects of fasting prior to a high-fat diet and highlights the metabolic flexibility of Drosophila mitochondria in response to abrupt dietary changes and have implication for adaptation of species to their changing environment.

Regular Exercise Modulates the dfoxo/dsrebp Pathway to Alleviate High-Fat-Diet-Induced Obesity and Cardiac Dysfunction in Drosophila

Obesity is a prevalent metabolic disorder associated with various diseases, including cardiovascular conditions. While exercise is recognized as an effective approach for preventing and treating obesity, its underlying molecular mechanisms remain unclear. This study aimed to explore the impact of regular exercise on high-fat-diet-induced obesity and cardiac dysfunction in Drosophila, shedding light on its molecular mechanisms by identifying its regulation of the dfoxo and dsrebp signaling pathways. Our findings demonstrated that a high-fat diet leads to weight gain, fat accumulation, reduced climbing performance, and elevated triglyceride levels in Drosophila. Additionally, cardiac microfilaments in these flies exhibited irregularities, breakages, and shortening. M-mode analysis revealed that high-fat-diet-fed Drosophila displayed increased heart rates, shortened cardiac cycles, decreased systolic intervals, heightened arrhythmia indices, reduced diastolic diameters, and diminished fractional shortening. Remarkably, regular exercise effectively ameliorated these adverse outcomes. Further analysis showed that regular exercise reduced fat synthesis, promoted lipolysis, and mitigated high-fat-diet-induced cardiac dysfunction in Drosophila. These results suggest that regular exercise may mitigate high-fat-diet-induced obesity and cardiac dysfunction in Drosophila by regulating the dfoxo and dsrebp signaling pathways, offering valuable insights into the mechanisms underlying the beneficial effects of exercise on obesity and cardiac dysfunction induced by a high-fat diet.

Drosophila melanogaster as a Translational Model System to Explore the Impact of Phytochemicals on Human Health

Fruits, vegetables, and spices are natural sources of bioactive phytochemicals, such as polyphenols, carotenoids, flavonoids, curcuminoids, terpenoids, and capsaicinoids, possessing multiple health benefits and relatively low toxicity. These compounds found in the diet play a central role in organism development and fitness. Given the complexity of the whole-body response to dietary changes, invertebrate model organisms can be valuable tools to examine the interplay between genes, signaling pathways, and metabolism. Drosophila melanogaster, an invertebrate model with its extensively studied genome, has more than 70% gene homology to humans and has been used as a model system in biological studies for a long time. The notable advantages of Drosophila as a model system, such as their low maintenance cost, high reproductive rate, short generation time and lifespan, and the high similarity of metabolic pathways between Drosophila and mammals, have encouraged the use of Drosophila in the context of screening and evaluating the impact of phytochemicals present in the diet. Here, we review the benefits of Drosophila as a model system for use in the study of phytochemical ingestion and describe the previously reported effects of phytochemical consumption in Drosophila.

The interplay between macronutrients and sleep: focus on circadian and homeostatic processes

Sleep disturbances are an emerging risk factor for metabolic diseases, for which the burden is particularly worrying worldwide. The importance of sleep for metabolic health is being increasingly recognized, and not only the amount of sleep plays an important role, but also its quality. In this review, we studied the evidence in the literature on macronutrients and their influence on sleep, focusing on the mechanisms that may lay behind this interaction. In particular, we focused on the effects of macronutrients on circadian and homeostatic processes of sleep in preclinical models, and reviewed the evidence of clinical studies in humans. Given the importance of sleep for health, and the role of circadian biology in healthy sleep, it is important to understand how macronutrients regulate circadian clocks and sleep homeostasis.

A protein restricted diet induces a stable increased fat storage phenotype in flies

Background

Scientific evidence has revealed possible confounders in diet induced obesity models of Drosophila melanogaster. High Sugar Diet (HSD) induction of obesity in flies has been associated with fly hyperosmolarity and glucotoxicity, while High Fat Diet (HFD) induction has been associated with lipotoxicity. The objective of this study was to assess for a healthy obesity phenotype by comparison of fly survival, physio-chemical and biochemical changes associated with HSD, HFD and Protein Restricted Diet (PRD) obesity induction models of male Drosophila melanogaster. Here, we provide information on a PRD as the plausible option in obesity research not involving cancer, diabetes, glucotoxicity and lipotoxicity studies.

Methods

Obesity was induced by exposing Drosophila melanogaster white mutant w¹¹¹⁸ to four experimental diets for four weeks. Group 1 was fed regular food (control), group 2 was fed a 0.5% less yeast than in regular feed (PRD), group 3 was fed a 30% w/v sucrose to regular cornmeal food (HSD) and group 4 was fed a 10% w/v food-grade coconut oil to regular cornmeal food (HFD). Peristaltic waves were measured on 3rd instar larvae of all experimental groups. Negative geotaxis, fly survival, body mass, catalase activity, triglycerides (TG/TP), sterol, and total protein were measured in adult Drosophila melanogaster after four weeks.

Results

Triglycerides (TG/TP) and total protein levels were significantly higher in HSD phenotype. Sterols were higher in HFD phenotype. Though catalase enzyme activity was highest in PRD phenotype, this activity was not statistically significant when compared to that of HSD and HFD phenotypes. However, PRD phenotype had the lowest mass, highest survival rate and the highest negative geotaxis, thus demonstrating a balanced, stable and more viable metabolic status in the experimental model.

Conclusion

A protein restricted diet induces a stable increased fat storage phenotype in Drosophila melanogaster.

"Effect of time-restricted feeding on high-fat diet-induced metabolic dysfunction in Drosophila melanogaster"

BACKGROUND

Metabolic alterations associated with obesity have been related to chronodisruption i.e., the desynchronization of molecular clocks that regulate circadian rhythms. The search for tools that improve the dietary treatment of obesity has recently focused on behaviors related to chronodisruption, and intermittent fasting is increasingly gaining interest. Studies in animal models have identified the benefits of time-restricted feeding (TRF) on metabolic alterations associated with changes in circadian rhythms induced by a high-fat diet. We aimed to evaluate the effect of TRF in flies with metabolic damage and chronodisruption.

METHODS

Using high-fat diet fed Drosophila melanogaster as a model of metabolic damage and chronodisruption, we determined the impact of 12-h TRF on metabolic and molecular markers. Flies with metabolic dysfunction were switched to a control diet and randomly assigned to Ad libitum or a TRF regimen for seven days. We evaluated total triglyceride content, glycemia, weight, and 24 h mRNA expression rhythms of Nlaz (insulin resistance marker), clock genes (circadian rhythm molecular markers), and the neuropeptide Cch-amide2.

RESULTS

Flies with metabolic damage that received TRF showed lower total triglyceride content, Nlaz expression, circulating glucose, and weight compared to Ad libitum. We observed the recovery of some of the high-fat diet-induced alterations in the amplitude of the circadian rhythm, particularly in the peripheral clock.

CONCLUSIONS

TRF produced a partial reversal of metabolic dysfunction and chronodisruption of circadian cycles.

GENERAL SIGNIFICANCE

TRF could be a useful tool to help to ameliorate metabolic and chronobiologic damage induced by a high-fat diet.

Wds-Mediated H3K4me3 Modification Regulates Lipid Synthesis and Transport in Drosophila

Lipid homeostasis is essential for insect growth and development. The complex of proteins associated with Set 1 (COMPASS)-catalyzed Histone 3 lysine 4 trimethylation (H3K4me3) epigenetically activates gene transcription and is involved in various biological processes, but the role and molecular mechanism of H3K4me3 modification in lipid homeostasis remains largely unknown. In the present study, we showed in Drosophila that fat body-specific knockdown of will die slowly (Wds) as one of the COMPASS complex components caused a decrease in lipid droplet (LD) size and triglyceride (TG) levels. Mechanistically, Wds-mediated H3K4me3 modification in the fat body targeted several lipogenic genes involved in lipid synthesis and the Lpp gene associated with lipid transport to promote their expressions; the transcription factor heat shock factor (Hsf) could interact with Wds to modulate H3K4me3 modification within the promoters of these targets; and fat body-specific knockdown of Hsf phenocopied the effects of Wds knockdown on lipid homeostasis in the fat body. Moreover, fat body-specific knockdown of Wds or Hsf reduced high-fat diet (HFD)-induced oversized LDs and high TG levels. Altogether, our study reveals that Wds-mediated H3K4me3 modification is required for lipid homeostasis during Drosophila development and provides novel insights into the epigenetic regulation of insect lipid metabolism.

Nutrigenomic Effects of White Rice and Brown Rice on the Pathogenesis of Metabolic Disorders in a Fruit Fly Model

Consumption of white rice (WR) has been shown to predispose individuals to metabolic disorders. However, brown rice (BR), which is relatively richer in bioactive compounds, possesses anti-glycaemic and antioxidant effects. In this study, fifteen cultivars of paddy rice that are predominantly consumed in North West Nigeria were analysed for their nutritional composition, bioactive contents and effects on metabolic outcomes in a fruit fly model. Gene expression analyses were conducted on the whole fly, targeting dPEPCK, dIRS, and dACC. The protein, carbohydrate, and fibre contents and bioactives of all BR cultivars were significantly different (p < 0.05) from the WR cultivars. Moreover, it was demonstrated that the glucose and trehalose levels were significantly higher (p < 0.05), while glycogen was significantly lower (p < 0.05) in the WR groups compared to the BR groups. Similarly, the expression of dACC and dPEPCK was upregulated, while that of dIRS was downregulated in the WR groups compared to the BR groups. Sex differences (p < 0.05) were observed in the WR groups in relation to the nutrigenomic effects. Our findings confirm metabolic perturbations in fruit flies following consumption of WR via distortion of insulin signalling and activation of glycogenolysis and gluconeogenesis. BR prevented these metabolic changes possibly due to its richer nutritional composition.

Time-dependent metabolome and fatty acid profile changes following a high-fat diet exposure in Drosophila melanogaster

High-fat diets (HFDs) are often used to study metabolic disorders using different animal models. However, the underlying cellular mechanisms pertaining to the concurrent loss of metabolic homeostasis characteristics of these disorders are still unclear mainly because the effects of such diets are also dependent on the time frame of the experiments. Here, we used the fruit fly, Drosophila melanogaster, to investigate the metabolic dynamic effects following 0, 2, 4, 7 and 9 days of an exposure to a HFD (standard diet supplemented with 20% w/v coconut oil, rich in 12:0 and 14:0) by combining NMR metabolomics and GC-FID fatty acid profiling. Our results show that after 2 days, the ingested 12:0 and 14:0 fatty acids are used for both lipogenesis and fatty acid oxidation. After 4 days, metabolites from several different pathways are highly modulated in response to the HFD, and an accumulation of 12:0 is also observed, suggesting that the balance of lipid, amino acid and carbohydrate metabolism is profoundly perturbed at this specific time point. Following a longer exposure to the HFD (and notably after 9 days), an accumulation of many metabolites is observed indicating a clear dysfunction of the metabolic system. Overall, our study highlights the relevance of the Drosophila model to study metabolic disorders and the importance of the duration of the exposure to a HFD to study the dynamics of the fundamental mechanisms that control metabolism following exposure to dietary fats. This knowledge is crucial to understand the development and progression of metabolic diseases.

Fat Quality Impacts the Effect of a High-Fat Diet on the Fatty Acid Profile, Life History Traits and Gene Expression in Drosophila melanogaster

Feeding a high-fat diet (HFD) has been shown to alter phenotypic and metabolic parameters in Drosophila melanogaster. However, the impact of fat quantity and quality remains uncertain. We first used butterfat (BF) as an example to investigate the effects of increasing dietary fat content (3-12%) on male and female fruit flies. Although body weight and body composition were not altered by any BF concentration, health parameters, such as lifespan, fecundity and larval development, were negatively affected in a dose-dependent manner. When fruit flies were fed various 12% HFDs (BF, sunflower oil, olive oil, linseed oil, fish oil), their fatty acid profiles shifted according to the dietary fat qualities. Moreover, fat quality was found to determine the effect size of the response to an HFD for traits, such as lifespan, climbing activity, or fertility. Consistently, we also found a highly fat quality-specific transcriptional response to three exemplary HFD qualities with a small overlap of only 30 differentially expressed genes associated with the immune/stress response and fatty acid metabolism. In conclusion, our data indicate that not only the fat content but also the fat quality is a crucial factor in terms of life-history traits when applying an HFD in D. melanogaster.

The Drosophila melanogaster ACE2 ortholog genes are differently expressed in obesity/diabetes and aging models: Implications for COVID-19 pathology

The Spike glycoprotein of SARS-CoV-2, the virus responsible for coronavirus disease 2019, binds to its ACE2 receptor for internalization in the host cells. Elderly individuals or those with subjacent disorders, such as obesity and diabetes, are more susceptible to COVID-19 severity. Additionally, several SARS-CoV-2 variants appear to enhance the Spike-ACE2 interaction, which increases transmissibility and death. Considering that the fruit fly is a robust animal model in metabolic research and has two ACE2 orthologs, Ance and Acer, in this work, we studied the effects of two hypercaloric diets (HFD and HSD) and aging on ACE2 orthologs mRNA expression levels in Drosophila melanogaster. To complement our work, we analyzed the predicted binding affinity between the Spike protein with Ance and Acer. We show for the first time that Ance and Acer genes are differentially regulated and dependent on diet and age in adult flies. At the molecular level, Ance and Acer proteins exhibit the potential to bind to the Spike protein in different regions, as shown by a molecular docking approach. Acer, in particular, interacts with the Spike protein in the same region as in humans. Overall, we suggest that the D. melanogaster is a promising animal model for translational studies on COVID-19 associated risk factors and ACE2.

Peppers in Diet: Genome-Wide Transcriptome and Metabolome Changes in Drosophila melanogaster

The habanero pepper (Capsicum chinense) is an increasingly important spice and vegetable crop worldwide because of its high capsaicin content and pungent flavor. Diets supplemented with the phytochemicals found in habanero peppers might cause shifts in an organism’s metabolism and gene expression. Thus, understanding how these interactions occur can reveal the potential health effects associated with such changes. We performed transcriptomic and metabolomic analyses of Drosophila melanogaster adult flies reared on a habanero pepper diet. We found 539 genes/59 metabolites that were differentially expressed/accumulated in flies fed a pepper versus control diet. Transcriptome results indicated that olfactory sensitivity and behavioral responses to the pepper diet were mediated by olfactory and nutrient-related genes including gustatory receptors (Gr63a, Gr66a, and Gr89a), odorant receptors (Or23a, Or59a, Or82a, and Orco), and odorant-binding proteins (Obp28a, Obp83a, Obp83b, Obp93a, and Obp99a). Metabolome analysis revealed that campesterol, sitosterol, and sucrose were highly upregulated and azelaic acid, ethyl phosphoric acid, and citric acid were the major metabolites downregulated in response to the habanero pepper diet. Further investigation by integration analysis between transcriptome and metabolome data at gene pathway levels revealed six unique enriched pathways, including phenylalanine metabolism; insect hormone biosynthesis; pyrimidine metabolism; glyoxylate, and dicarboxylate metabolism; glycine, serine, threonine metabolism; and glycerolipid metabolism. In view of the transcriptome and metabolome findings, our comprehensive analysis of the response to a pepper diet in Drosophila have implications for exploring the molecular mechanism of pepper consumption.

Metabolic Syndrome: Lessons from Rodent and Drosophila Models

Overweight and obesity are health conditions tightly related to a number of metabolic complications collectively called “metabolic syndrome” (MetS). Clinical diagnosis of MetS includes the presence of the increased waist circumference or so-called abdominal obesity, reduced high density lipoprotein level, elevated blood pressure, and increased blood glucose and triacylglyceride levels. Different approaches, including diet-induced and genetically induced animal models, have been developed to study MetS pathogenesis and underlying mechanisms. Studies of metabolic disturbances in the fruit fly Drosophila and mammalian models along with humans have demonstrated that fruit flies and small mammalian models like rats and mice have many similarities with humans in basic metabolic functions and share many molecular mechanisms which regulate these metabolic processes. In this paper, we describe diet-induced, chemically and genetically induced animal models of the MetS. The advantages and limitations of rodent and Drosophila models of MetS and obesity are also analyzed.

The first study on the effect of crocodile oil from Crocodylus siamensis on hepatic mitochondrial function for energy homeostasis in rats

Background and Aim:

Consumption of fatty acids (FA) can alter hepatic energy metabolism and mitochondrial function in the liver. Crocodile oil (CO) is rich in mono-and polyunsaturated FAs, which have natural anti-inflammatory and healing properties. In rat livers, we investigated the effect of CO on mitochondrial function for energy homeostasis.

Materials and Methods:

Twenty-one male Sprague-Dawley rats were divided into three groups at random. Group 1 rats were given sterile water (RO), Group 2 rats were given CO (3% v/w), and Group 3 rats were given palm oil (PO) (3% v/w). For 7 weeks, rats were given sterile water, CO, and PO orally. The researchers looked at body weight, food intake, liver weight, energy intake, blood lipid profiles, and mitochondria-targeted metabolites in the liver. The liver’s histopathology, mitochondrial architecture, and hydrolase domain containing 3 (HDHD3) protein expression in liver mitochondria were studied.

Results:

Body weight, liver weight, liver index, dietary energy intake, and serum lipid profiles were all unaffected by CO treatment. The CO group consumed significantly less food than the RO group. The CO group also had significantly higher levels of oxaloacetate and malate than the PO group. CO treatment significantly ameliorated hepatic steatosis, as evidenced by a greater decrease in the total surface area of lipid particles than PO treatment. CO administration preserved mitochondrial morphology in the liver by upregulating the energetic maintenance protein HDHD3. Furthermore, chemical-protein interactions revealed that HDHD3 was linked to the energy homeostatic pathway.

Conclusion:

CO may benefit liver function by preserving hepatic mitochondrial architecture and increasing energy metabolic activity.

Genetic variation of macronutrient tolerance in Drosophila melanogaster

Carbohydrates, proteins and lipids are essential nutrients to all animals; however, closely related species, populations, and individuals can display dramatic variation in diet. Here we explore the variation in macronutrient tolerance in Drosophila melanogaster using the Drosophila genetic reference panel, a collection of ~200 strains derived from a single natural population. Our study demonstrates that D. melanogaster, often considered a "dietary generalist", displays marked genetic variation in survival on different diets, notably on high-sugar diet. Our genetic analysis and functional validation identify several regulators of macronutrient tolerance, including CG10960/GLUT8, Pkn and Eip75B. We also demonstrate a role for the JNK pathway in sugar tolerance and de novo lipogenesis. Finally, we report a role for tailless, a conserved orphan nuclear hormone receptor, in regulating sugar metabolism via insulin-like peptide secretion and sugar-responsive CCHamide-2 expression. Our study provides support for the use of nutrigenomics in the development of personalized nutrition.

Comparative metabolomic analysis of polyphenic horn development in the dung beetle Onthophagus taurus

Organisms alter their phenotypes in response to changing environmental conditions. The developmental basis of this phenomenon, phenotypic plasticity, is a topic of broad interest in many fields of biology. While insects provide a suitable model for studying the genetic basis of phenotypic plasticity, the physiological aspects of plasticity are not fully understood. Here, we report the physiological basis of polyphenism, an extreme form of phenotypic plasticity by utilizing a dung beetle species, Onthophagus taurus. We highlighted the metabolome between sexes as well as two distinct male morphs—large and small horns. Unlike results from previous transcriptomic studies, the comparative metabolomic study revealed that differences in metabolite level were more prominent between animals with different body sizes than different sexes. Our results also indicate that specific metabolites and biochemical pathways may be active during horn size determination.

Phenotyping of Drosophila melanogaster—A Nutritional Perspective

The model organism Drosophila melanogaster was increasingly applied in nutrition research in recent years. A range of methods are available for the phenotyping of D. melanogaster, which are outlined in the first part of this review. The methods include determinations of body weight, body composition, food intake, lifespan, locomotor activity, reproductive capacity and stress tolerance. In the second part, the practical application of the phenotyping of flies is demonstrated via a discussion of obese phenotypes in response to high-sugar diet (HSD) and high-fat diet (HFD) feeding. HSD feeding and HFD feeding are dietary interventions that lead to an increase in fat storage and affect carbohydrate-insulin homeostasis, lifespan, locomotor activity, reproductive capacity and stress tolerance. Furthermore, studies regarding the impacts of HSD and HFD on the transcriptome and metabolome of D. melanogaster are important for relating phenotypic changes to underlying molecular mechanisms. Overall, D. melanogaster was demonstrated to be a valuable model organism with which to examine the pathogeneses and underlying molecular mechanisms of common chronic metabolic diseases in a nutritional context.

Sexual Dimorphism in Metabolic Responses to Western Diet in Drosophila melanogaster

Obesity is a chronic disease affecting millions of people worldwide. The fruit fly (Drosophila melanogaster) is an interesting research model to study metabolic and transcriptomic responses to obesogenic diets. However, the sex-specific differences in these responses are still understudied and perhaps underestimated. In this study, we exposed adult male and female Dahomey fruit flies to a standard diet supplemented with sugar, fat, or a combination of both. The exposure to a diet supplemented with 10% sugar and 10% fat efficiently induced an increase in the lipid content in flies, a hallmark for obesity. This increase in lipid content was more prominent in males, while females displayed significant changes in glycogen content. A strong effect of the diets on the ovarian size and number of ma-ture oocytes was also present in females exposed to diets supplemented with fat and a combina-tion of fat and sugar. In both males and females, fat body morphology changed and was associ-ated with an increase in lipid content of fat cells in response to the diets. The expression of me-tabolism-related genes also displayed a strong sexually dimorphic response under normal condi-tions and in response to sugar and/or fat-supplemented diets. Here, we show that the exposure of adult fruit flies to an obesogenic diet containing both sugar and fat allowed studying sexual dimorphism in metabolism and the expression of genes regulating metabolism.

Palm Oil-Rich Diet Affects Murine Liver Proteome and S-Palmitoylome

Palmitic acid (C16:0) is the most abundant saturated fatty acid in animals serving as a substrate in synthesis and β-oxidation of other lipids, and in the modification of proteins called palmitoylation. The influence of dietary palmitic acid on protein S-palmitoylation remains largely unknown. In this study we performed high-throughput proteomic analyses of a membrane-enriched fraction of murine liver to examine the influence of a palm oil-rich diet (HPD) on S-palmitoylation of proteins. HPD feeding for 4 weeks led to an accumulation of C16:0 and C18:1 fatty acids in livers which disappeared after 12-week feeding, in contrast to an accumulation of C16:0 in peritoneal macrophages. Parallel proteomic studies revealed that HPD feeding induced a sequence of changes of the level and/or S-palmitoylation of diverse liver proteins involved in fatty acid, cholesterol and amino acid metabolism, hemostasis, and neutrophil degranulation. The HPD diet did not lead to liver damage, however, it caused progressing obesity, hypercholesterolemia and hyperglycemia. We conclude that the relatively mild negative impact of such diet on liver functioning can be attributed to a lower bioavailability of palm oil-derived C16:0 vs. that of C18:1 and the efficiency of mechanisms preventing liver injury, possibly including dynamic protein S-palmitoylation.

What You Eat Matters: Nutrient Inputs Alter the Metabolism and Neuropeptide Expression in Egyptian Cotton Leaf Worm, Spodoptera littoralis (Lepidoptera: Noctuidae)

Lipids and carbohydrates are the two primary energy sources for both animals and insects. Energy homeostasis is under strict control by the neuroendocrine system, and disruption of energy homeostasis leads to the development of various disorders, such as obesity, diabetes, fatty liver syndrome, and cardiac dysfunction. One critical factor in this respect is feeding habits and diet composition. Insects are good models to study the physiological and biochemical background of the effect of diet on energy homeostasis and related disorders; however, most studies are based on a single model species, Drosophila melanogaster. In the current study, we examined the effects of four different diets, high fat (HFD), high sugar (HSD), calcium-rich (CRD), and a plant-based (PBD) on energy homeostasis in younger (third instar) and older (fifth instar) larvae of the Egyptian cotton leafworm, Spodoptera littoralis (Lepidoptera: Noctuidae) in comparison to a regular artificial bean diet. Both HSD and HFD led to weight gain, while CRD had the opposite effect and PBD had no effect in fifth instar larvae and pupae. The pattern was the same for HSD and CRD in third instar larvae while a reduction in weight was detected with HFD and PBD. Larval development was shortest with the HSD, while HFD, CRD, and PBD led to retardation compared to the control. Triglyceride (TG) levels were higher with HFD, HSD, and PBD, with larger lipid droplet sizes, while CRD led to a reduction of TG levels and lipid droplet size. Trehalose levels were highest with HSD, while CRD led to a reduction at third instar larvae, and HFD and PBD had no effect. Fifth instar larvae had similar levels of trehalose with all diets. There was no difference in the expression of the genes encoding neuropeptides SpoliAKH and SpoliILP1-2 with different diets in third instar larvae, while all three genes were expressed primarily with HSD, and SpolisNPF was primarily expressed with HFD in fifth instar larvae. In summary, different diet treatments alter the development of insects, and energy and metabolic pathways through the regulation of peptide hormones.

Crème de la Créature: Dietary Influences on Behavior in Animal Models

In humans, alterations in cognitive, motivated, and affective behaviors have been described with consumption of processed diets high in refined sugars and saturated fats and with high body mass index, but the causes, mechanisms, and consequences of these changes remain poorly understood. Animal models have provided an opportunity to answer these questions and illuminate the ways in which diet composition, especially high-levels of added sugar and saturated fats, contribute to brain physiology, plasticity, and behavior. Here we review findings from invertebrate (flies) and vertebrate models (rodents, zebrafish) that implicate these diets with changes in multiple behaviors, including eating, learning and memory, and motivation, and discuss limitations, open questions, and future opportunities.

Exercise-Training Regulates Apolipoprotein B in Drosophila to Improve HFD-Mediated Cardiac Function Damage and Low Exercise Capacity

Apolipoprotein B plays an essential role in systemic lipid metabolism, and it is closely related to cardiovascular diseases. Exercise-training can regulate systemic lipid metabolism, improve heart function, and improve exercise capacity, but the molecular mechanisms involved are poorly understood. We used a Drosophila model to demonstrate that exercise-training regulates the expression of apoLpp (a homolog of apolipoprotein B) in cardiomyocytes, thereby resisting heart insufficiency and low exercise capacity caused by obesity. The apoLpp is an essential lipid carrier produced in the heart and fat body of Drosophila. In a Drosophila genetic screen, low expression of apoLpp reduced obesity and cardiac dysfunction induced by a high-fat diet (HFD). Cardiac-specific inhibition indicated that reducing apoLpp in the heart during HFD reduced the triglyceride content of the whole-body and reduced heart function damage caused by HFD. In exercise-trained flies, the result was similar to the knockdown effect of apoLpp. Therefore, the inhibition of apoLpp plays an important role in HFD-induced cardiac function impairment and low exercise capacity. Although the apoLpp knockdown of cardiomyocytes alleviated damage to heart function, it did not reduce the arrhythmia and low exercise capacity caused by HFD. Exercise-training can improve this condition more effectively, and the possible reason for this difference is that exercise-training regulates climbing ability in ways to promote metabolism. Exercise-training during HFD feeding can down-regulate the expression of apoLpp, reduce the whole-body TG levels, improve cardiac recovery, and improve exercise capacity. Exercise-training can downregulate the expression of apoLpp in cardiomyocytes to resist cardiac function damage and low exercise capacity caused by HFD. The results revealed the relationship between exercise-training and apoLpp and their essential roles in regulating heart function and climbing ability.

High fat diet induced abnormalities in metabolism, growth, behavior, and circadian clock in Drosophila melanogaster

AIMS

The current lifestyle trend has made people vulnerable to diabetes and related diseases. Years of scientific research have not been able to yield a cure to the disease completely. The current study aims to investigate a link between high-fat diet mediated diabesity and circadian rhythm in the Drosophila model and inferences that might help in establishing a cure to the dreaded disease.

MAIN METHODS

Several experimental methods including phenotypical, histological, biochemical, molecular, and behavioral assays were used in the study to detect obesity, diabetes, and changes in the circadian clock in the fly model.

KEY FINDINGS

The larva and adults of Drosophila melanogaster exposed to high-fat diet (HFD) displayed excess deposition of fat as lipid droplets and micronuclei formation in the gut, fat body, and crop. Larva and adults of HFD showed behavioral defects. The higher amount of triglyceride, glucose, trehalose in the whole body of larva and adult fly confirmed obesity-induced hyperglycemia. The overexpression of insulin gene (Dilp2) and tribble (trbl) gene expression confirmed insulin resistance in HFD adults. We also observed elevated ROS level, developmental delay, altered metal level, growth defects, locomotory rhythms, sleep fragmentation, and expression of circadian genes (per, tim, and clock) in HFD larva and adults. Thus, HFD impairs the metabolism to produce obesity, insulin resistance, disruption of clock, and circadian clock related co-mordities in D. melanogaster.

SIGNIFICANCE

The circadian gene expression provides an innovative perspective to understand and find a new treatment for type-II diabetes and circadian anomalies.

Sestrin regulates acute chill coma recovery in Drosophila melanogaster

When chill-susceptible insects are exposed to low temperatures they enter a temporary state of paralysis referred to as a chill coma. The most well-studied physiological mechanism of chill coma onset and recovery involves regulation of ion homeostasis. Previous studies show that changes in metabolism may also underlie the ability to recovery quickly, but the roles of genes that regulate metabolic homeostasis in chill coma recovery time (CCRT) are not well understood. Here, we investigate the roles of Sestrin and Spargel (Drosophila homolog of PGC-1α), which are involved in metabolic homeostasis and substrate oxidation, on CCRT in Drosophila melanogaster. We find that sestrin and spargel mutants have impaired CCRT. sestrin is required in the muscle and nervous system tissue for normal CCRT and spargel is required in muscle and adipose. On the basis that exercise induces sestrin and spargel, we also test the interaction of cold and exercise. We find that pre-treatment with one of these stressors does not consistently confer acute protection against the other. We conclude that Sestrin and Spargel are important in the chill coma response, independent of their role in exercise.

Systemic and mitochondrial effects of metabolic inflexibility induced by high fat diet in Drosophila melanogaster

Metabolic inflexibility is a condition that occurs following a nutritional stress which causes blunted fuel switching at the mitochondrial level in response to hormonal and cellular signalling. Linked to obesity and obesity related disorders, chronic exposure to a high-fat diet (HFD) in animal models has been extensively used to induce metabolic inflexibility and investigate the development of various metabolic diseases. However, many questions concerning the systemic and mitochondrial responses to metabolic inflexibility remain. In this study, we investigated the global and mitochondrial variations following a 10-day exposure to a HFD in adult Drosophila melanogaster. Our results show that following 10-day exposure to the HFD, mitochondrial respiration rates measured in isolated mitochondria at the level of complex I were decreased. This was associated with increased contributions of non-classical providers of electrons to the electron transport system (ETS) such as the proline dehydrogenase (ProDH) and the mitochondrial glycerol-3-phosphate dehydrogenase (mtG3PDH) alleviating complex I dysfunctions, as well as with increased ROS production per molecule of oxygen consumed. Our results also show an accumulation of metabolites from multiple different metabolic pathways in whole adult Drosophila and a drastic shift in the lipid profile which translated into decreased proportion of saturated and monounsaturated fatty acids combined with an increased proportion of polyunsaturated fatty acids. Thus, our results demonstrate the various responses to the HFD treatment in adult Drosophila melanogaster that are hallmarks of the development of metabolic inflexibility and reinforce this organism as a suitable model for the study of metabolic disorders.

The Drosophila melanogaster Neprilysin Nepl15 is involved in lipid and carbohydrate storage

The prototypical M13 peptidase, human Neprilysin, functions as a transmembrane "ectoenzyme" that cleaves neuropeptides that regulate e.g. glucose metabolism, and has been linked to type 2 diabetes. The M13 family has undergone a remarkable, and conserved, expansion in the Drosophila genus. Here, we describe the function of Drosophila melanogaster Neprilysin-like 15 (Nepl15). Nepl15 is likely to be a secreted protein, rather than a transmembrane protein. Nepl15 has changes in critical catalytic residues that are conserved across the Drosophila genus and likely renders the Nepl15 protein catalytically inactive. Nevertheless, a knockout of the Nepl15 gene reveals a reduction in triglyceride and glycogen storage, with the effects likely occurring during the larval feeding period. Conversely, flies overexpressing Nepl15 store more triglycerides and glycogen. Protein modeling suggests that Nepl15 is able to bind and sequester peptide targets of catalytically active Drosophila M13 family members, peptides that are conserved in humans and Drosophila, potentially providing a novel mechanism for regulating the activity of neuropeptides in the context of lipid and carbohydrate homeostasis.

Preference and detrimental effects of high fat, sugar, and salt diet in wild-caught Drosophila simulans are reversed by flight exercise

High saturated fat, sugar, and salt contents are a staple of a Western diet (WD), contributing to obesity, metabolic syndrome, and a plethora of other health risks. However, the combinatorial effects of these ingredients have not been fully evaluated. Here, using the wild-caught Drosophila simulans, we show that a diet enriched with saturated fat, sugar, and salt is more detrimental than each ingredient separately, resulting in a significantly decreased lifespan, locomotor activity, sleep, reproductive function, and mitochondrial function. These detrimental effects were more pronounced in female than in male flies. Adding regular flight exercise to flies on the WD markedly negated the adverse effects of a WD. At the molecular level, the WD significantly increased levels of triglycerides and caused mitochondrial dysfunction, while exercise counterbalanced these effects. Interestingly, fruit flies developed a preference for the WD after pre-exposure, which was averted by flight exercise. The results demonstrate that regular aerobic exercise can mitigate adverse dietary effects on fly mitochondrial function, physiology, and feeding behavior. Our data establish Drosophila simulans as a novel model of diet-exercise interaction that bears a strong similarity to the pathophysiology of obesity and eating disorders in humans.

Insects' potential: Understanding the functional role of their gut microbiome

The study of insect-associated microbial communities is a field of great importance in agriculture, principally because of the role insects play as pests. In addition, there is a recent focus on the potential of the insect gut microbiome in areas such as biotechnology, given some microorganisms produce molecules with biotechnological and industrial applications, and also in biomedicine, since some bacteria and fungi are a reservoir of antibiotic resistance genes (ARGs). To date, most studies aiming to characterize the role of the gut microbiome of insects have been based on high-throughput sequencing of the 16S rRNA gene and/or metagenomics. However, recently functional approaches such as metatranscriptomics, metaproteomics and metabolomics have also been employed. Besides providing knowledge about the taxonomic distribution of microbial populations, these techniques also reveal their functional and metabolic capabilities. This information is essential to gain a better understanding of the role played by microbes comprising the microbial communities in their hosts, as well as to indicate their possible exploitation. This review provides an overview of how far we have come in characterizing insect gut functionality through omics, as well as the challenges and future perspectives in this field.

A robust, integrated platform for comprehensive analyses of acyl-coenzyme As and acyl-carnitines revealed chain length-dependent disparity in fatty acyl metabolic fates across Drosophila development

Acyl-coenzyme A thioesters (acyl-CoAs) denote a key class of intermediary metabolites that lies at the hub of major metabolic pathways. The great diversity in polarity between short- and long-chain acyl-CoAs makes it technically challenging to cover an inclusive range of acyl-CoAs within a single method. Levels of acyl-carnitines, which function to convey fatty acyls into mitochondria matrix for β-oxidation, indicate the efficiency of mitochondrial import and utilization of corresponding acyl-CoAs. Herein, we report a robust, integrated platform to allow simultaneous quantitation of endogenous acyl-CoAs and acyl-carnitines. Using this method, we monitored changes in intermediary lipid profiles across Drosophila development under control (ND) and high-fat diet (HFD). We observed specific accumulations of medium-chain (C8-C12) and long-chain (≥C16) acyl-carnitines distinct to L3 larval and pupal stages, respectively. These observations suggested development-specific, chain length-dependent disparity in metabolic fates of acyl-CoAs across Drosophila development, which was validated by deploying the same platform to monitor isotope incorporation introduced from labelled 12:0 and 16:0 fatty acids into extra- and intra-mitochondrial acyl-CoA pools. We found that pupal mitochondria preferentially import and oxidise C12:0-CoAs (accumulated as C12:0-carnitines in L3 stage) over C16:0-CoAs. Preferential oxidation of medium-chain acyl-CoAs limits mitochondrial utilization of long-chain acyl-CoAs (C16-C18), leading to pupal-specific accumulation of long-chain acyl-carnitines mediated by enhanced CPT1-6A activity. HFD skewed C16:0-CoAs towards catabolism over anabolism in pupa, thereby adversely affecting overall development. Our developed platform emphasizes the importance of integrating biological knowledge in the design of pathway-oriented platforms to derive maximal physiological insights from analysis of complex biological systems.

Functional Characterization of Gomisin N in High-Fat-Induced Drosophila Obesity Models

Gomisin N (GN) is lignin derived from Schisandra chinensis that has been reported to exhibit hepato-protective, anti-cancer, and anti-inflammatory effects. However, its role in whole-body energetic homeostasis remains unclear. In this study, we employed Drosophila melanogaster as a diet-induced obese model to elucidate the effects of GN on lipid and glucose metabolism by measuring climbing activity, triglyceride levels, and lifespan under a rearing condition of a high-fat diet (HFD) containing 20% coconut oil, with or without GN. Constant exposure of flies to an HFD resulted in increased body weight and decreased climbing activity, along with a shortened life span. Importantly, the administration of GN to HFD groups lowered their body weight and induced a specific upregulation of lipid storage droplet (Lsd)-2 and hormone-sensitive lipase (Hsl), in addition to improved lifespan. Importantly, GN in HFD groups appeared to downregulate heat shock protein Hsp90 family member (dGRP94), a key regulator of the endoplasmic reticulum stress response, which may also contribute to improved life span in the presence of GN. Taken together, these in vivo findings suggest that GN could serve as a useful agent for the prevention and treatment of obesity.

Virgin Coconut Oil Associated with High-Fat Diet Induces Metabolic Dysfunctions, Adipose Inflammation, and Hepatic Lipid Accumulation

Obesity reaches an epidemic level worldwide, and this condition is associated with chronic low-grade inflammation and secondary comorbidities, largely driven by global changes in lifestyle and diet. Various dietary approaches are proposed for the obesity treatment and its associated metabolic disorders. Good taste, antioxidant functions, and vitamins have been attributed to virgin coconut oil (VCO). However, VCO contains a large amount of saturated fatty acids, and the consumption of this fat is associated with a number of secondary diseases. We evaluate the effects of VCO supplementation on biochemical, inflammatory, and oxidative stress parameters in rats fed with high-fat diet (HFD). After feeding with HFD for 12 weeks, the animals were supplemented with VCO for 30 days. HFD+VCO group increased in diet intake, weight gain, low-density lipoprotein cholesterol level, and aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels. These findings were accompanied by increased in hepatic lipid profile and fat deposition in the liver. Adipocyte hypertrophy was observed in the HFD+VCO group, which was associated with elevated expression of tumor necrosis factor alpha (TNF-α) in adipose tissue. These results revealed that VCO associated with HFD induced important metabolic alterations, adipose inflammation, and hepatic lipid accumulation in rats.

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.

Diverse biological processes coordinate the transcriptional response to nutritional changes in a Drosophila melanogaster multiparent population

Background

Environmental variation in the amount of resources available to populations challenge individuals to optimize the allocation of those resources to key fitness functions. This coordination of resource allocation relative to resource availability is commonly attributed to key nutrient sensing gene pathways in laboratory model organisms, chiefly the insulin/TOR signaling pathway. However, the genetic basis of diet-induced variation in gene expression is less clear.

Results

To describe the natural genetic variation underlying nutrient-dependent differences, we used an outbred panel derived from a multiparental population, the Drosophila Synthetic Population Resource. We analyzed RNA sequence data from multiple female tissue samples dissected from flies reared in three nutritional conditions: high sugar (HS), dietary restriction (DR), and control (C) diets. A large proportion of genes in the experiment (19.6% or 2471 genes) were significantly differentially expressed for the effect of diet, and 7.8% (978 genes) for the effect of the interaction between diet and tissue type (LRT, P_adj. < 0.05). Interestingly, we observed similar patterns of gene expression relative to the C diet, in the DR and HS treated flies, a response likely reflecting diet component ratios. Hierarchical clustering identified 21 robust gene modules showing intra-modularly similar patterns of expression across diets, all of which were highly significant for diet or diet-tissue interaction effects (FDR P_adj. < 0.05). Gene set enrichment analysis for different diet-tissue combinations revealed a diverse set of pathways and gene ontology (GO) terms (two-sample t-test, FDR < 0.05). GO analysis on individual co-expressed modules likewise showed a large number of terms encompassing many cellular and nuclear processes (Fisher exact test, P_adj. < 0.01). Although a handful of genes in the IIS/TOR pathway including Ilp5, Rheb, and Sirt2 showed significant elevation in expression, many key genes such as InR, chico, most insulin peptide genes, and the nutrient-sensing pathways were not observed.

Conclusions

Our results suggest that a more diverse network of pathways and gene networks mediate the diet response in our population. These results have important implications for future studies focusing on diet responses in natural populations.

Dietary fatty acids promote sleep through a taste-independent mechanism

Consumption of foods that are high in fat contribute to obesity and metabolism-related disorders. Dietary lipids are comprised of triglycerides and fatty acids, and the highly palatable taste of dietary fatty acids promotes food consumption, activates reward centers in mammals and underlies hedonic feeding. Despite the central role of dietary fats in the regulation of food intake and the etiology of metabolic diseases, little is known about how fat consumption regulates sleep. The fruit fly, Drosophila melanogaster, provides a powerful model system for the study of sleep and metabolic traits, and flies potently regulate sleep in accordance with food availability. To investigate the effects of dietary fats on sleep regulation, we have supplemented fatty acids into the diet of Drosophila and measured their effects on sleep and activity. We found that flies fed a diet of hexanoic acid, a medium-chain fatty acid that is a by-product of yeast fermentation, slept more than flies starved on an agar diet. To assess whether dietary fatty acids regulate sleep through the taste system, we assessed sleep in flies with a mutation in the hexanoic acid receptor Ionotropic receptor 56D, which is required for fatty acid taste perception. We found that these flies also sleep more than agar-fed flies when fed a hexanoic acid diet, suggesting the sleep promoting effect of hexanoic acid is not dependent on sensory perception. Taken together, these findings provide a platform to investigate the molecular and neural basis for fatty acid-dependent modulation of sleep.

Therapeutic effects of noni fruit water extract and polysaccharide on oxidative stress and inflammation in mice under high-fat diet

This study aims to compare the therapeutic effects of noni fruit water extract (NFW) and noni fruit polysaccharide (NFP) on oxidative stress and inflammation in mice under high-fat diet.

Arterio-venous metabolomics exploration reveals major changes across liver and intestine in the obese Yucatan minipig

Blood circulation mainly aims at distributing the nutrients required for tissue metabolism and collecting safely the by-products of all tissues to be further metabolized or eliminated. The simultaneous study of arterial (A) and venous (V) specific metabolites therefore has appeared to be a more relevant approach to understand and study the metabolism of a given organ. We propose to implement this approach by applying a metabolomics (NMR) strategy on paired AV blood across the intestine and liver on high fat/high sugar (HFHS)-fed minipigs. Our objective was to unravel kinetically and sequentially the metabolic adaptations to early obesity/insulin resistance onset specifically on these two tissues. After two months of HFHS feeding our study of AV ratios of the metabolome highlighted three major features. First, the hepatic metabolism switched from carbohydrate to lipid utilization. Second, the energy demand of the intestine increased, resulting in an enhanced uptake of glutamine, glutamate, and the recruitment of novel energy substrates (choline and creatine). Third, the uptake of methionine and threonine was considered to be driven by an increased intestine turnover to cope with the new high-density diet. Finally, the unique combination of experimental data and modelling predictions suggested that HFHS feeding was associated with changes in tryptophan metabolism and fatty acid β-oxidation, which may play an important role in lipid hepatic accumulation and insulin sensitivity.

Ginger prevents obesity through regulation of energy metabolism and activation of browning in high-fat diet-induced obese mice

Numerous natural herbs have been proven as safe anti-obesity resources. Ginger, one of the most widely consumed spices, has shown beneficial effects against obesity and related metabolic disorders. The present study aimed to examine whether the antiobesity effect of ginger is associated with energy metabolism. Mice were maintained on either a normal control diet or a high-fat diet (HFD) with or without 500 mg/kg (w/w) ginger supplementation. After 16 weeks, ginger supplementation alleviated the HFD-induced increases in body weight, fat accumulation, and levels of serum glucose, triglyceride and cholesterol. Indirect calorimetry showed that ginger administration significantly increased the respiratory exchange ratio (RER) and heat production in both diet models. Furthermore, ginger administration corrected the HFD-induced changes in concentrations of intermediates in glycolysis and the TCA cycle. Moreover, ginger enhanced brown adipose tissue function and activated white adipose tissue browning by altering the gene expression and protein levels of some brown and beige adipocyte-selective markers. Additionally, stimulation of the browning program by ginger may be partly regulated by the sirtuin-1 (SIRT1)/AMP-activated protein kinase (AMPK)/peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) pathway. Taken together, these results indicate that dietary ginger prevents body weight gain by remodeling whole-body energy metabolism and inducing browning of white adipose tissue (WAT). Thus, ginger is an edible plant that plays a role in the therapeutic treatment of obesity and related disorders.

As time flies by: Investigating cardiac aging in the short-lived Drosophila model

Aging is associated with a decline in heart function across the tissue, cellular, and molecular levels. The risk of cardiovascular disease grows significantly over time, and as developed countries continue to see an increase in lifespan, the cost of cardiovascular healthcare for the elderly will undoubtedly rise. The molecular basis for cardiac function deterioration with age is multifaceted and not entirely clear, and there is a limit to what investigations can be performed on human subjects or mammalian models. Drosophila melanogaster has emerged as a useful model organism for studying aging in a short timeframe, benefitting from a suite of molecular and genetic tools and displaying highly conserved traits of cardiac senescence. Here, we discuss recent advances in our understanding of cardiac aging and how the fruit fly has aided in these developments.

Drosophila melanogaster as an alternative model organism in nutrigenomics

Nutrigenomics explains the interaction between the genome, the proteome, the epigenome, the metabolome, and the microbiome with the nutritional environment of an organism. It is therefore situated at the interface between an organism's health, its diet, and the genome. The diet and/or specific dietary compounds are able to affect not only the gene expression patterns, but also the epigenetic mechanisms as well as the production of metabolites and the bacterial composition of the microbiota. Drosophila melanogaster provides a well-suited model organism to unravel these interactions in the context of nutrigenomics as it combines several advantages including an affordable maintenance, a short generation time, a high fecundity, a relatively short life expectancy, a well-characterized genome, and the availability of several mutant fly lines. Furthermore, it hosts a mammalian-like intestinal system with a clear microbiota and a fat body resembling the adipose tissue with liver-equivalent oenocytes, supporting the fly as an excellent model organism not only in nutrigenomics but also in nutritional research. Experimental approaches that are essentially needed in nutrigenomic research, including several sequencing technologies, have already been established in the fruit fly. However, studies investigating the interaction of a specific diet and/or dietary compounds in the fly are currently very limited. The present review provides an overview of the fly's morphology including the intestinal microbiome and antimicrobial peptides as modulators of the immune system. Additionally, it summarizes nutrigenomic approaches in the fruit fly helping to elucidate host-genome interactions with the nutritional environment in the model organism Drosophila melanogaster.

Epigallocatechin gallate (EGCG) alters body fat and lean mass through sex-dependent metabolic mechanisms in Drosophila melanogaster

There is increasing interest in the potential role of epigallocatechin gallate (EGCG) in changing body composition to lower body fat with increased lean mass. In this study, we examined the sex-dependent effect of EGCG on body composition, locomotion, feeding behaviour, sugar levels, and transcription levels of key regulators in lipid, carbohydrate, and energy metabolisms in Drosophila melanogaster. EGCG had no effects on body weights in both females and males, but decreased fat accumulation in females compared to the control, accompanied by a reduction in food intake. EGCG treatments increased lean mass and locomotor activity, and downregulated transcription levels of brummer (bmm), adipokinetic hormone (akh), and Drosophila insulin-like peptide 2 (dilp2), and upregulated spargel (srl) in males. In addition, EGCG decreased sugar levels in both females and males. In conclusion, EGCG promotes lean phenotype in D. melanogaster via sex-specific metabolic regulations.

A high-fat diet impacts memory and gene expression of the head in mated female Drosophila melanogaster

Obesity predisposes humans to a range of life-threatening comorbidities, including type 2 diabetes and cardiovascular disease. Obesity also aggravates neural pathologies, such as Alzheimer's disease, but this class of comorbidity is less understood. When Drosophila melanogaster (flies) are exposed to high-fat diet (HFD) by supplementing a standard medium with coconut oil, they adopt an obese phenotype of decreased lifespan, increased triglyceride storage, and hindered climbing ability. The latter development has been previously regarded as a potential indicator of neurological decline in fly models of neurodegenerative disease. Our objective was to establish the obesity phenotype in Drosophila and identify a potential correlation, if any, between obesity and neurological decline through behavioral assays and gene expression microarray. We found that mated female w1118 flies exposed to HFD maintained an obese phenotype throughout adult life starting at 7 days, evidenced by increased triglyceride stores, diminished life span, and impeded climbing ability. While climbing ability worsened cumulatively between 7 and 14 days of exposure to HFD, there was no corresponding alteration in triglyceride content. Microarray analysis of the mated female w1118 fly head revealed HFD-induced changes in expression of genes with functions in memory, metabolism, olfaction, mitosis, cell signaling, and motor function. Meanwhile, an Aversive Phototaxis Suppression assay in mated female flies indicated reduced ability to recall an entrained memory 6 h after training. Overall, our results support the suitability of mated female flies for examining connections between diet-induced obesity and nervous or neurobehavioral pathology, and provide many directions for further investigation.

Dynamic mitochondrial responses to a high-fat diet in Drosophila melanogaster

Mitochondria can utilize different fuels according to physiological and nutritional conditions to promote cellular homeostasis. However, during nutrient overload metabolic inflexibility can occur, resulting in mitochondrial dysfunctions. High-fat diets (HFDs) are usually used to mimic this metabolic inflexibility in different animal models. However, how mitochondria respond to the duration of a HFD exposure is still under debate. In this study, we investigated the dynamic of the mitochondrial and physiological functions in Drosophila melanogaster at several time points following an exposure to a HFD. Our results showed that after two days on the HFD, mitochondrial respiration as well as ATP content of thorax muscles are increased, likely due to the utilization of carbohydrates. However, after four days on the HFD, impairment of mitochondrial respiration at the level of complex I, as well as decreased ATP content were observed. This was associated with an increased contribution of complex II and, most notably of the mitochondrial glycerol-3-phosphate dehydrogenase (mG3PDH) to mitochondrial respiration. We suggest that this increased mG3PDH capacity reflects the occurrence of metabolic inflexibility, leading to a loss of homeostasis and alteration of the cellular redox status, which results in senescence characterized by decreased climbing ability and premature death.

High fat diet induces sex-specific differential gene expression in Drosophila melanogaster

Currently about 2 billion adults globally are estimated to be overweight and ~13% of them are obese. High fat diet (HFD) is one of the major contributing factor to obesity, heart disease, diabetes and cancer. Recent findings on the role of HFD in inducing abnormalities in neurocognition and susceptibility to Alzheimer’s disease are highly intriguing. Since fundamental molecular pathways are often conserved across species, studies involving Drosophila melanogaster as a model organism can provide insight into the molecular mechanisms involving human disease. In order to study some of such mechanisms in the central nervous system as well in the rest of the body, we investigated the effect of HFD on the transcriptome in the heads and bodies of male and female flies kept on either HFD or regular diet (RD). Using comprehensive genomic analyses which include high-throughput transcriptome sequencing, pathway enrichment and gene network analyses, we found that HFD induces a number of responses that are sexually dimorphic in nature. There was a robust transcriptional response consisting of a downregulation of stress-related genes in the heads and glycoside hydrolase activity genes in the bodies of males. In the females, the HFD led to an increased transcriptional change in lipid metabolism. A strong correlation also existed between the takeout gene and hyperphagic behavior in both males and females. We conclude that a) HFD induces a differential transcriptional response between males and females, in heads and bodies and b) the non-dimorphic transcriptional response that we identified was associated with hyperphagia. Therefore, our data on the transcriptional responses in flies to HFD provides potentially relevant information to human conditions including obesity.

Transgenerational inheritance of cold temperature response in Drosophila

Intergenerational inheritance of transcriptional responses induced by low temperature rearing has recently been shown in Drosophila. Besides germline inheritance, fecal transfer experiments indirectly suggested that the acquired microbiome may also have contributed to the transcriptional responses in offspring. Here, we analyze expression data on inheritance of the cold-induced effects in conjunction with previously reported transcriptomic differences between flies with a microbiota or axenic flies and provide support for a contribution of the acquired microbiome to the offspring phenotype. Also, based on a similar analysis in conjunction with diet- and metabolism-related fly transcriptome data, we predicted and, then, experimentally confirmed that cold regulates triglyceride levels both inter- as well as trans-generationally.