A role for triglyceride lipase brummer in the regulation of sex differences in Drosophila fat storage and breakdown

Cholesterol Metabolism in Neurodegenerative Diseases

SIGNIFICANCE

Cholesterol plays a crucial role in brain, where it is highly concentrated and tightly regulated to support normal brain functions. It serves as a vital component of cell membranes, ensuring their integrity, and acts as a key regulator of various brain processes. Dysregulation of cholesterol metabolism in the brain has been linked to impaired brain function and the onset of neurodegenerative diseases such as Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD).

RECENT ADVANCES

A significant advancement has been the identification of astrocyte-derived ApoE as a key regulator of de novo cholesterol biosynthesis in neurons, providing insights into how extracellular signals influence neuronal cholesterol levels. Additionally, the development of antibody-based therapies, particularly for AD, presents promising opportunities for therapeutic interventions.

CRITICAL ISSUES

Despite significant research, the association between cholesterol and neurodegenerative diseases remains inconclusive. It is crucial to distinguish between plasma cholesterol and brain cholesterol, as these pools are relatively independent. This differentiation should be considered when evaluating statin-based treatment approaches. Assessing not only the total cholesterol content in the brain but also its distribution among different types of brain cells is essential.

FUTURE DIRECTION

Establishing a causal link between changes in brain/plasma cholesterol levels and the onset of brain dysfunction/neurodegenerative diseases remains a key objective. Additionally, conducting cell-specific analyses of cholesterol homeostasis in various types of brain cells under pathological conditions will enhance our understanding of cholesterol metabolism in neurodegenerative diseases. Manipulating cholesterol levels to restore homeostasis may represent a novel approach for alleviating neurological symptom.

An important role for triglyceride in regulating spermatogenesis

Drosophila is a powerful model to study how lipids affect spermatogenesis. Yet, the contribution of neutral lipids, a major lipid group which resides in organelles called lipid droplets (LD), to sperm development is largely unknown. Emerging evidence suggests LD are present in the testis and that loss of neutral lipid- and LD-associated genes causes subfertility; however, key regulators of testis neutral lipids and LD remain unclear. Here, we show LD are present in early-stage somatic and germline cells within the Drosophila testis. We identified a role for triglyceride lipase brummer (bmm) in regulating testis LD, and found that whole-body loss of bmm leads to defects in sperm development. Importantly, these represent cell-autonomous roles for bmm in regulating testis LD and spermatogenesis. Because lipidomic analysis of bmm mutants revealed excess triglyceride accumulation, and spermatogenic defects in bmm mutants were rescued by genetically blocking triglyceride synthesis, our data suggest that bmm-mediated regulation of triglyceride influences sperm development. This identifies triglyceride as an important neutral lipid that contributes to Drosophila sperm development, and reveals a key role for bmm in regulating testis triglyceride levels during spermatogenesis.

Transcriptional Control of Lipid Metabolism

Transcriptional control of lipid metabolism uses a framework that parallels the control of lipid metabolism at the protein or enzyme level, via feedback and feed-forward mechanisms. Increasing the substrates for an enzyme often increases enzyme gene expression, for example. A paucity of product can likewise potentiate transcription or stability of the mRNA encoding the enzyme or enzymes needed to produce it. In addition, changes in second messengers or cellular energy charge can act as on/off switches for transcriptional regulators to control transcript (and protein) abundance. Insects use a wide range of DNA-binding transcription factors (TFs) that sense changes in the cell and its environment to produce the appropriate change in transcription at gene promoters. These TFs work together with histones, spliceosomes, and additional RNA processing factors to ultimately regulate lipid metabolism. In this chapter, we will first focus on the important TFs that control lipid metabolism in insects. Next, we will describe non-TF regulators of insect lipid metabolism such as enzymes that modify acetylation and methylation status, transcriptional coactivators, splicing factors, and microRNAs. To conclude, we consider future goals for studying the mechanisms underlying the control of lipid metabolism in insects.

Reference genes to study the sex-biased expression of genes regulating Drosophila metabolism

Sex is an important variable in biology. Notable differences have been observed between male and female Drosophila in regulation of metabolism, in response to nutritional challenges, and in phenotypes relevant for obesity and metabolic disorders. The differences between males and females can be expected to result from differences in gene expression. We observed that expression levels of reference genes commonly used for normalization of qRT-PCR results such as GAPDH, β-actin, and 18SrRNA, show prominent sexual dimorphism. Since this will impact relative expression and conclusions related to that, we performed a systematic analysis of candidate reference genes with the objective of identifying reference genes with stable expression in male and female Drosophila. These reference genes (LamCa, βTub60D and βTub97EF) were then used to assess sex-specific differences in expression of metabolism associated genes. Additionally, we evaluated the utility of these reference genes following a nutritional challenge and showed that LamCa and βtub97EF are stably expressed between sexes and under different nutritional conditions and are thus suitable as reference genes. Our results highlight the importance of evaluating the stability of reference genes when sex-specific differences in gene expression are studied, and identify structural genes as a category worth exploring as reference genes in other species. Finally, we also uncovered hitherto unknown sexually dimorphic expression of a number of metabolism-associated genes, information of interest to others working in the field of metabolic disorders.

A neuron-glia lipid metabolic cycle couples daily sleep to mitochondrial homeostasis

Sleep is thought to be restorative to brain energy homeostasis, but it is not clear how this is achieved. We show here that Drosophila glia exhibit a daily cycle of glial mitochondrial oxidation and lipid accumulation that is dependent on prior wake and requires the Drosophila APOE orthologs NLaz and GLaz, which mediate neuron-glia lipid transfer. In turn, a full night of sleep is required for glial lipid clearance, mitochondrial oxidative recovery and maximal neuronal mitophagy. Knockdown of neuronal NLaz causes oxidative stress to accumulate in neurons, and the neuronal mitochondrial integrity protein, Drp1, is required for daily glial lipid accumulation. These data suggest that neurons avoid accumulation of oxidative mitochondrial damage during wake by using mitophagy and passing damage to glia in the form of lipids. We propose that a mitochondrial lipid metabolic cycle between neurons and glia reflects a fundamental function of sleep relevant for brain energy homeostasis.

Pharmaceuticals and endocrine disrupting compounds modulate adverse effects of climate change on resource quality in freshwater food webs

Freshwater biodiversity, ecosystem functions and services are changing at an unprecedented rate due to the impacts of vast number of stressors overlapping in time and space. Our study aimed at characterizing individual and combined impacts of pollution with pharmaceuticals (PhACs) and endocrine disrupting compounds (EDCs) and increased water temperature (as a proxy for climate change) on primary producers and first level consumers in freshwaters. We conducted a microcosm experiment with a simplified freshwater food web containing moss (Bryophyta) and shredding caddisfly larvae of Micropterna nycterobia (Trichoptera). The experiment was conducted with four treatments; control (C), increased water temperature + 4 °C (T2), emerging contaminants' mix (EC = 15 PhACs & 5 EDCs), and multiple stressor treatment (MS = EC + T2). Moss exhibited an overall mild response to selected stressors and their combination. Higher water temperature negatively affected development of M. nycterobia through causing earlier emergence of adults and changes in their lipidome profiles. Pollution with PhACs and EDCs had higher impact on metabolism of all life stages of M. nycterobia than warming. Multiple stressor effect was recorded in M. nycterobia adults in metabolic response, lipidome profiles and as a decrease in total lipid content. Sex specific response to stressor effects was observed in adults, with impacts on metabolome generally more pronounced in females, and on lipidome in males. Thus, our study highlights the variability of both single and multiple stressor impacts on different traits, different life stages and sexes of a single insect species. Furthermore, our research suggests that the combined impacts of warming, linked to climate change, and contamination with PhACs and EDCs could have adverse consequences on the population dynamics of aquatic insects. Additionally, these findings point to a potential decrease in the quality of resources available for both aquatic and potentially terrestrial food webs.

Nazo, the Drosophila homolog of the NBIA-mutated protein-c19orf12, is required for triglyceride homeostasis

Lipid dyshomeostasis has been implicated in a variety of diseases ranging from obesity to neurodegenerative disorders such as Neurodegeneration with Brain Iron Accumulation (NBIA). Here, we uncover the physiological role of Nazo, the Drosophila melanogaster homolog of the NBIA-mutated protein-c19orf12, whose function has been elusive. Ablation of Drosophila c19orf12 homologs leads to dysregulation of multiple lipid metabolism genes. nazo mutants exhibit markedly reduced gut lipid droplet and whole-body triglyceride contents. Consequently, they are sensitive to starvation and oxidative stress. Nazo is required for maintaining normal levels of Perilipin-2, an inhibitor of the lipase-Brummer. Concurrent knockdown of Brummer or overexpression of Perilipin-2 rescues the nazo phenotype, suggesting that this defect, at least in part, may arise from diminished Perilipin-2 on lipid droplets leading to aberrant Brummer-mediated lipolysis. Our findings potentially provide novel insights into the role of c19orf12 as a possible link between lipid dyshomeostasis and neurodegeneration, particularly in the context of NBIA.

Auxin exposure disrupts feeding behavior and fatty acid metabolism in adult Drosophila

The ease of genetic manipulation in Drosophila melanogaster using the Gal4/UAS system has been beneficial in addressing key biological questions. Current modifications of this methodology to temporally induce transgene expression require temperature changes or exposure to exogenous compounds, both of which have been shown to have detrimental effects on physiological processes. The recently described auxin-inducible gene expression system (AGES) utilizes the plant hormone auxin to induce transgene expression and is proposed to be the least toxic compound for genetic manipulation, with no obvious effects on Drosophila development and survival in one wild-type strain. Here, we show that auxin delays larval development in another widely used fly strain, and that short- and long-term auxin exposure in adult Drosophila induces observable changes in physiology and feeding behavior. We further reveal a dosage response to adult survival upon auxin exposure, and that the recommended auxin concentration for AGES alters feeding activity. Furthermore, auxin-fed male and female flies exhibit a significant decrease in triglyceride levels and display altered transcription of fatty acid metabolism genes. Although fatty acid metabolism is disrupted, auxin does not significantly impact adult female fecundity or progeny survival, suggesting AGES may be an ideal methodology for studying limited biological processes. These results emphasize that experiments using temporal binary systems must be carefully designed and controlled to avoid confounding effects and misinterpretation of results.

Dhr96[1] mutation and maternal tudor[1] mutation increase life span and reduce the beneficial effects of mifepristone in mated female Drosophila

Mating and receipt of male Sex Peptide hormone cause increased egg laying, increased midgut size and decreased life span in female Drosophila. Feeding mated females with the synthetic steroid mifepristone decreases egg production, reduces midgut size, and increases life span. Here, several gene mutations were assayed to investigate possible mechanisms for mifepristone action. Drosophila Dhr96 is a hormone receptor, and a key positive regulator of midgut lipid uptake and metabolism. Dhr96[1] null mutation increased female life span, and reduced the effects of mifepristone on life span, suggesting that Dhr96[1] mutation and mifepristone may act in part through the same mechanism. Consistent with this idea, lipidomics analysis revealed that mating increases whole-body levels of triglycerides and fatty-acids in triglycerides, and these changes are reversed by mifepristone. Maternal tudor[1] mutation results in females that lack the germ-line and produce no eggs. Maternal tudor[1] mutation increased mated female life span, and reduced but did not eliminate the effects of mating and mifepristone on life span. This indicates that decreased egg production may be related to the life span benefits of mifepristone, but is not essential. Mifepristone increases life span in w[1118] mutant mated females, but did not increase life span in w[1118] mutant virgin females. Mifepristone decreased egg production in w[1118] mutant virgin females, indicating that decreased egg production is not sufficient for mifepristone to increase life span. Mifepristone increases life span in virgin females of some, but not all, white[+] and mini-white[+] strains. Backcrossing of mini-white[+] transgenes into the w[1118] background was not sufficient to confer a life span response to mifepristone in virgin females. Taken together, the data support the hypothesis that mechanisms for mifepristone life span increase involve reduced lipid uptake and/or metabolism, and suggest that mifepristone may increase life span in mated females and virgin females through partly different mechanisms.

Auxin Exposure Disrupts Feeding Behavior and Fatty Acid Metabolism in Adult Drosophila

The ease of genetic manipulation in Drosophila melanogaster using the Gal4/UAS system has been beneficial in addressing key biological questions. Current modifications of this methodology to temporally induce transgene expression require temperature changes or exposure to exogenous compounds, both of which have been shown to have detrimental effects on physiological processes. The recently described auxin-inducible gene expression system (AGES) utilizes the plant hormone auxin to induce transgene expression and is proposed to be the least toxic compound for genetic manipulation, with no obvious effects on Drosophila development and survival in one wild-type strain. Here we show that auxin delays larval development in another widely-used fly strain, and that short- and long-term auxin exposure in adult Drosophila induces observable changes in physiology and feeding behavior. We further reveal a dosage response to adult survival upon auxin exposure, and that the recommended auxin concentration for AGES alters feeding activity. Furthermore, auxin fed male and female flies exhibit a significant decrease in triglyceride levels and display altered transcription of fatty acid metabolism genes. Although fatty acid metabolism is disrupted, auxin does not significantly impact adult female fecundity or progeny survival, suggesting AGES may be an ideal methodology for studying limited biological processes. These results emphasize that experiments using temporal binary systems must be carefully designed and controlled to avoid confounding effects and misinterpretation of results.

Cooperation of acylglycerol hydrolases in neuronal lipolysis

Genetic and biochemical evidence has established DDHD-domain containing 2 (DDHD2) as the principal triacylglycerol (TAG) hydrolase in neuronal lipolysis of cytosolic lipid droplets. In this issue of Journal of Lipid Research, Hofer et al. report that DDHD2 cooperates with adipose triglyceride lipase, the principal TAG hydrolase in adipose lipolysis, contributing to cytosolic hydrolysis of both TAG and diacylglycerols in murine neuroblastoma cells and primary cortical neurons via different configurations of the lipases. This finding highlights the complexity of cytosolic acylglycerol hydrolysis and raises many new questions in the field of lipid metabolism.

Spenito-dependent metabolic sexual dimorphism intrinsic to fat storage cells

Metabolism in males and females is distinct. Differences are usually linked to sexual reproduction, with circulating signals (e.g. hormones) playing major roles. In contrast, sex differences prior to sexual maturity and intrinsic to individual metabolic tissues are less understood. We analyzed Drosophila melanogaster larvae and find that males store more fat than females, the opposite of the sexual dimorphism in adults. We show that metabolic differences are intrinsic to the major fat storage tissue, including many differences in the expression of metabolic genes. Our previous work identified fat storage roles for Spenito (Nito), a conserved RNA-binding protein and regulator of sex determination. Nito knockdown specifically in the fat storage tissue abolished fat differences between males and females. We further show that Nito is required for sex-specific expression of the master regulator of sex determination, Sex-lethal (Sxl). "Feminization" of fat storage cells via tissue-specific overexpression of a Sxl target gene made larvae lean, reduced the fat differences between males and females, and induced female-like metabolic gene expression. Altogether, this study supports a model in which Nito autonomously controls sexual dimorphisms and differential expression of metabolic genes in fat cells in part through its regulation of the sex determination pathway.

Cooperative lipolytic control of neuronal triacylglycerol by spastic paraplegia-associated enzyme DDHD2 and ATGL

Intracellular lipolysis-the enzymatic breakdown of lipid droplet-associated triacylglycerol (TAG)-depends on the cooperative action of several hydrolytic enzymes and regulatory proteins, together designated as lipolysome. Adipose triglyceride lipase (ATGL) acts as a major cellular TAG hydrolase and core effector of the lipolysome in many peripheral tissues. Neurons initiate lipolysis independently of ATGL via DDHD domain-containing 2 (DDHD2), a multifunctional lipid hydrolase whose dysfunction causes neuronal TAG deposition and hereditary spastic paraplegia. Whether and how DDHD2 cooperates with other lipolytic enzymes is currently unknown. In this study, we further investigated the enzymatic properties and functions of DDHD2 in neuroblastoma cells and primary neurons. We found that DDHD2 hydrolyzes multiple acylglycerols in vitro and substantially contributes to neutral lipid hydrolase activities of neuroblastoma cells and brain tissue. Substrate promiscuity of DDHD2 allowed its engagement at different steps of the lipolytic cascade: In neuroblastoma cells, DDHD2 functioned exclusively downstream of ATGL in the hydrolysis of sn-1,3-diacylglycerol (DAG) isomers but was dispensable for TAG hydrolysis and lipid droplet homeostasis. In primary cortical neurons, DDHD2 exhibited lipolytic control over both, DAG and TAG, and complemented ATGL-dependent TAG hydrolysis. We conclude that neuronal cells use noncanonical configurations of the lipolysome and engage DDHD2 as dual TAG/DAG hydrolase in cooperation with ATGL.

A high-sugar diet, but not obesity, reduces female fertility in Drosophila melanogaster

Obesity is linked to reduced fertility in various species, from Drosophila to humans. Considering that obesity is often induced by changes in diet or eating behavior, it remains unclear whether obesity, diet, or both reduce fertility. Here, we show that Drosophila females on a high-sugar diet become rapidly obese and less fertile as a result of increased death of early germline cysts and vitellogenic egg chambers (or follicles). They also have high glycogen, glucose and trehalose levels and develop insulin resistance in their fat bodies (but not ovaries). By contrast, females with adipocyte-specific knockdown of the anti-obesity genes brummer or adipose are obese but have normal fertility. Remarkably, females on a high-sugar diet supplemented with a separate source of water have mostly normal fertility and glucose levels, despite persistent obesity, high glycogen and trehalose levels, and fat body insulin resistance. These findings demonstrate that a high-sugar diet affects specific processes in oogenesis independently of insulin resistance, that high glucose levels correlate with reduced fertility on a high-sugar diet, and that obesity alone does not impair fertility.

Adipose triglyceride lipase promotes prostaglandin-dependent actin remodeling by regulating substrate release from lipid droplets

Lipid droplets (LDs), crucial regulators of lipid metabolism, accumulate during oocyte development. However, their roles in fertility remain largely unknown. During Drosophila oogenesis, LD accumulation coincides with the actin remodeling necessary for follicle development. Loss of the LD-associated Adipose Triglyceride Lipase (ATGL) disrupts both actin bundle formation and cortical actin integrity, an unusual phenotype also seen when the prostaglandin (PG) synthase Pxt is missing. Dominant genetic interactions and PG treatment of follicles indicate that ATGL acts upstream of Pxt to regulate actin remodeling. Our data suggest that ATGL releases arachidonic acid (AA) from LDs to serve as the substrate for PG synthesis. Lipidomic analysis detects AA-containing triglycerides in ovaries, and these are increased when ATGL is lost. High levels of exogenous AA block follicle development; this is enhanced by impairing LD formation and suppressed by reducing ATGL. Together, these data support the model that AA stored in LD triglycerides is released by ATGL to drive the production of PGs, which promote the actin remodeling necessary for follicle development. We speculate that this pathway is conserved across organisms to regulate oocyte development and promote fertility.

Y chromosome toxicity does not contribute to sex-specific differences in longevity

While sex chromosomes carry sex-determining genes, they also often differ from autosomes in size and composition, consisting mainly of silenced heterochromatic repetitive DNA. Even though Y chromosomes show structural heteromorphism, the functional significance of such differences remains elusive. Correlative studies suggest that the amount of Y chromosome heterochromatin might be responsible for several male-specific traits, including sex-specific differences in longevity observed across a wide spectrum of species, including humans. However, experimental models to test this hypothesis have been lacking. Here we use the Drosophila melanogaster Y chromosome to investigate the relevance of sex chromosome heterochromatin in somatic organs in vivo. Using CRISPR-Cas9, we generated a library of Y chromosomes with variable levels of heterochromatin. We show that these different Y chromosomes can disrupt gene silencing in trans, on other chromosomes, by sequestering core components of the heterochromatin machinery. This effect is positively correlated to the level of Y heterochromatin. However, we also find that the ability of the Y chromosome to affect genome-wide heterochromatin does not generate physiological sex differences, including sexual dimorphism in longevity. Instead, we discovered that it is the phenotypic sex, female or male, that controls sex-specific differences in lifespan, rather than the presence of a Y chromosome. Altogether, our findings dismiss the 'toxic Y' hypothesis that postulates that the Y chromosome leads to reduced lifespan in XY individuals.

Amplification is the primary mode of gene-by-sex interaction in complex human traits

Sex differences in complex traits are suspected to be in part due to widespread gene-by-sex interactions (GxSex), but empirical evidence has been elusive. Here, we infer the mixture of ways in which polygenic effects on physiological traits covary between males and females. We find that GxSex is pervasive but acts primarily through systematic sex differences in the magnitude of many genetic effects ("amplification") rather than in the identity of causal variants. Amplification patterns account for sex differences in trait variance. In some cases, testosterone may mediate amplification. Finally, we develop a population-genetic test linking GxSex to contemporary natural selection and find evidence of sexually antagonistic selection on variants affecting testosterone levels. Our results suggest that amplification of polygenic effects is a common mode of GxSex that may contribute to sex differences and fuel their evolution.

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

BACKGROUND

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

RESULTS

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

CONCLUSION

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

Regulating metabolism to shape immune function: Lessons from Drosophila

Infection with pathogenic microbes is a severe threat that hosts manage by activating the innate immune response. In Drosophila melanogaster, the Toll and Imd signaling pathways are activated by pathogen-associated molecular patterns to initiate cellular and humoral immune processes that neutralize and kill invaders. The Toll and Imd signaling pathways operate in organs such as fat body and gut that control host nutrient metabolism, and infections or genetic activation of Toll and Imd signaling also induce wide-ranging changes in host lipid, carbohydrate and protein metabolism. Metabolic regulation by immune signaling can confer resistance to or tolerance of infection, but it can also lead to pathology and susceptibility to infection. These immunometabolic phenotypes are described in this review, as are changes in endocrine signaling and gene regulation that mediate survival during infection. Future work in the field is anticipated to determine key variables such as sex, dietary nutrients, life stage, and pathogen characteristics that modify immunometabolic phenotypes and, importantly, to uncover the mechanisms used by the immune system to regulate metabolism.

A Perspective on the Link between Mitochondria-Associated Membranes (MAMs) and Lipid Droplets Metabolism in Neurodegenerative Diseases

Mitochondria interact with the endoplasmic reticulum (ER) through contacts called mitochondria-associated membranes (MAMs), which control several processes, such as the ER stress response, mitochondrial and ER dynamics, inflammation, apoptosis, and autophagy. MAMs represent an important platform for transport of non-vesicular phospholipids and cholesterol. Therefore, this region is highly enriched in proteins involved in lipid metabolism, including the enzymes that catalyze esterification of cholesterol into cholesteryl esters (CE) and synthesis of triacylglycerols (TAG) from fatty acids (FAs), which are then stored in lipid droplets (LDs). LDs, through contact with other organelles, prevent the toxic consequences of accumulation of unesterified (free) lipids, including lipotoxicity and oxidative stress, and serve as lipid reservoirs that can be used under multiple metabolic and physiological conditions. The LDs break down by autophagy releases of stored lipids for energy production and synthesis of membrane components and other macromolecules. Pathological lipid deposition and autophagy disruption have both been reported to occur in several neurodegenerative diseases, supporting that lipid metabolism alterations are major players in neurodegeneration. In this review, we discuss the current understanding of MAMs structure and function, focusing on their roles in lipid metabolism and the importance of autophagy in LDs metabolism, as well as the changes that occur in neurogenerative diseases.

Aging and memory are altered by genetically manipulating lactate dehydrogenase in the neurons or glia of flies

The astrocyte-neuron lactate shuttle hypothesis posits that glial-generated lactate is transported to neurons to fuel metabolic processes required for long-term memory. Although studies in vertebrates have revealed that lactate shuttling is important for cognitive function, it is uncertain if this form of metabolic coupling is conserved in invertebrates or is influenced by age. Lactate dehydrogenase (Ldh) is a rate limiting enzyme that interconverts lactate and pyruvate. Here we genetically manipulated expression of Drosophila melanogaster lactate dehydrogenase (dLdh) in neurons or glia to assess the impact of altered lactate metabolism on invertebrate aging and long-term courtship memory at different ages. We also assessed survival, negative geotaxis, brain neutral lipids (the core component of lipid droplets) and brain metabolites. Both upregulation and downregulation of dLdh in neurons resulted in decreased survival and memory impairment with age. Glial downregulation of dLdh expression caused age-related memory impairment without altering survival, while upregulated glial dLdh expression lowered survival without disrupting memory. Both neuronal and glial dLdh upregulation increased neutral lipid accumulation. We provide evidence that altered lactate metabolism with age affects the tricarboxylic acid (TCA) cycle, 2-hydroxyglutarate (2HG), and neutral lipid accumulation. Collectively, our findings indicate that the direct alteration of lactate metabolism in either glia or neurons affects memory and survival but only in an age-dependent manner.

Spenito-dependent metabolic sexual dimorphism intrinsic to fat storage cells

Metabolism in males and females is distinct. Differences are usually linked to sexual reproduction, with circulating signals (e.g. hormones) playing major roles. By contrast, sex differences prior to sexual maturity and intrinsic to individual metabolic tissues are less understood. We analyzed Drosophila melanogaster larvae and find that males store more fat than females, the opposite of the sexual dimorphism in adults. We show that metabolic differences are intrinsic to the major fat storage tissue, including many differences in the expression of metabolic genes. Our previous work identified fat storage roles for Spenito (Nito), a conserved RNA-binding protein and regulator of sex determination. Nito knockdown specifically in the fat storage tissue abolished fat differences between males and females. We further show that Nito is required for sex-specific expression of the master regulator of sex determination, Sex-lethal (Sxl). "Feminization" of fat storage cells via tissue-specific overexpression of a Sxl target gene made larvae lean, reduced the fat differences between males and females, and induced female-like metabolic gene expression. Altogether, this study supports a model in which Nito autonomously controls sexual dimorphisms and differential expression of metabolic genes in fat cells in part through its regulation of the sex determination pathway.

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.

Functional insight and cell-specific expression of the adipokinetic hormone/corazonin-related peptide in the human disease vector mosquito, Aedes aegypti

The adipokinetic hormone/corazonin-related peptide (ACP) is an insect neuropeptide structurally intermediate between corazonin (CRZ) and adipokinetic hormone (AKH). Unlike the AKH and CRZ signaling systems that are widely known for their roles in the mobilization of energy substrates and stress responses, respectively, the main role of ACP and its receptor (ACPR) remains unclear in most arthropods. The current study aimed to localize the distribution of ACP in the nervous system and provide insight into its physiological roles in the disease vector mosquito, Aedes aegypti. Immunohistochemical analysis and fluorescence in situ hybridization localized the ACP peptide and transcript within a number of cells in the central nervous system, including two pairs of laterally positioned neurons in the protocerebrum of the brain and a few ventrally localized neurons within the pro- and mesothoracic regions of the fused thoracic ganglia. Further, extensive ACP-immunoreactive axonal projections with prominent blebs and varicosities were observed traversing the abdominal ganglia. Given the prominent enrichment of ACPR expression within the abdominal ganglia of adult A. aegypti mosquitoes as determined previously, the current results indicate that ACP may function as a neurotransmitter and/or neuromodulator facilitating communication between the brain and posterior regions of the nervous system. In an effort to elucidate a functional role for ACP signaling, biochemical measurement of energy substrates in female mosquitoes revealed a reduction in abdominal fat body in response to ACP that matched the actions of AKH, but interestingly, a corresponding hypertrehalosaemic effect was only found in response to AKH since ACP did not influence circulating carbohydrate levels. Comparatively, both ACP and AKH led to a significant increase in haemolymph carbohydrate levels in male mosquitoes while both peptides had no influence on their glycogen stores. Neither ACP nor AKH influenced circulating or stored lipid levels in both male and female mosquitoes. Collectively, these results reveal ACP signaling in mosquitoes may have complex sex-specific actions, and future research should aim to expand knowledge on the role of this understudied neuropeptide.

The genomic basis of copper tolerance in Drosophila is shaped by a complex interplay of regulatory and environmental factors

BACKGROUND

Escalation in industrialization and anthropogenic activity have resulted in an increase of pollutants released into the environment. Of these pollutants, heavy metals such as copper are particularly concerning due to their bio-accumulative nature. Due to its highly heterogeneous distribution and its dual nature as an essential micronutrient and toxic element, the genetic basis of copper tolerance is likely shaped by a complex interplay of genetic and environmental factors.

RESULTS

In this study, we utilized the natural variation present in multiple populations of Drosophila melanogaster collected across Europe to screen for variation in copper tolerance. We found that latitude and the degree of urbanization at the collection sites, rather than any other combination of environmental factors, were linked to copper tolerance. While previously identified copper-related genes were not differentially expressed in tolerant vs. sensitive strains, genes involved in metabolism, reproduction, and protease induction contributed to the differential stress response. Additionally, the greatest transcriptomic and physiological responses to copper toxicity were seen in the midgut, where we found that preservation of gut acidity is strongly linked to greater tolerance. Finally, we identified transposable element insertions likely to play a role in copper stress response.

CONCLUSIONS

Overall, by combining genome-wide approaches with environmental association analysis, and functional analysis of candidate genes, our study provides a unique perspective on the genetic and environmental factors that shape copper tolerance in natural D. melanogaster populations and identifies new genes, transposable elements, and physiological traits involved in this complex phenotype.

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.

Systemic lipolysis promotes physiological fitness in Drosophila melanogaster

Since interventions such as caloric restriction or fasting robustly promote lipid catabolism and improve aging-related phenotypical markers, we investigated the direct effect of increased lipid catabolism via overexpression of bmm (brummer, FBgn0036449), the major triglyceride hydrolase in Drosophila, on lifespan and physiological fitness. Comprehensive characterization was carried out using RNA-seq, lipidomics and metabolomics analysis. Global overexpression of bmm strongly promoted numerous markers of physiological fitness, including increased female fecundity, fertility maintenance, preserved locomotion activity, increased mitochondrial biogenesis and oxidative metabolism. Increased bmm robustly upregulated the heat shock protein 70 (Hsp70) family of proteins, which equipped the flies with higher resistance to heat, cold, and ER stress via improved proteostasis. Despite improved physiological fitness, bmm overexpression did not extend lifespan. Taken together, these data show that bmm overexpression has broad beneficial effects on physiological fitness, but these effects did not impact lifespan.

An aqueous extract of the brown alga Eisenia bicyclis extends lifespan in a sex-specific manner by interfering with the Tor-FoxO axis

Food has a decisive influence on our health, to the extent where even lifespan can be directly affected by it. In the present work, we have examined the effects of an aqueous extract of the marine brown alga Eisenia bicyclis in terms of its potential to extend lifespan. For this purpose, we used the fruit fly Drosophila melanogaster as a model. The experiments showed that small amounts of Eisenia extract can extend lifespan by up to 40%. This effect is not only related to the median but also to the maximum lifespan. Interestingly, this life-extending effect is sex-specific, i.e. it occurs exclusively in females. Even under stressful nutritional conditions such as a high sugar diet, this effect is detectable. Mechanistic studies showed that this life-prolonging effect depends on a functional Tor and a functional FoxO signaling pathway. It can be concluded that components of the Eisenia extract prolong lifespan by interacting with the Tor-FoxO axis. This study may serve to stimulate further investigations, which on the one hand show such a life-prolonging effect also in other organisms and on the other hand identify the substances responsible for this effect. Finally, it may also encourage the increased use of arame as a health-promoting food supplement.

Measuring metabolic rate in single flies during sleep and waking states via indirect calorimetry

BACKGROUND

Drosophila melanogaster is a leading genetic model for studying the neural regulation of sleep. Sleep is associated with changes in behavior and physiological state that are largely conserved across species. The investigation of sleep in flies has predominantly focused on behavioral readouts of sleep because physiological measurements, including changes in brain activity and metabolic rate, are less accessible. We have previously used stop-flow indirect calorimetry to measure whole body metabolic rate in single flies and have shown that in flies, like mammals, metabolic rate is reduced during sleep.

NEW METHOD

Here, we describe a modified version of this system that allows for efficient and highly sensitive acquisition of CO2 output from single flies.

RESULTS

In this modified system, we show that sleep-dependent changes in metabolic rate are diminished in aging flies, supporting the notion that sleep quality is reduced as flies age. We also describe a modification that allows for simultaneous acquisition of CO2 and O2 levels, providing a respiratory quotient that quantifies how metabolic stores are utilized. We find that the respiratory quotient identified in flies on an all-sugar diet is suggestive of lipogenesis, where the dietary sugar provided to the flies is being converted to fat.

COMPARISON WITH EXISTING METHODS AND CONCLUSIONS

Taken together, the measurement of metabolic rate via indirect calorimetry not only provides a physiological readout of sleep depth, but also provides insight the metabolic regulation of nutrient utilization, with broad applications to genetic studies in flies.

Effects of Drosophila melanogaster regular exercise and apolipoprotein B knockdown on abnormal heart rhythm induced by a high-fat diet

Abnormal heart rhythm is a common cardiac dysfunction in obese patients, and its pathogenesis is related to systemic lipid accumulation. The cardiomyocyte-derived apoLpp (homologous gene in Drosophila of the human apolipoprotein B) plays an important role in whole-body lipid metabolism of Drosophila under a high-fat diet (HFD). Knockdown of apoLpp derived from cardiomyocytes can reduce HFD-induced weight gain and abdominal lipid accumulation. In addition, exercise can reduce the total amount of apoLpp in circulation. However, the relationship between regular exercise, cardiomyocyte-derived apoLpp and abnormal heart rhythm is unclear. We found that an HFD increased the level of triglyceride (TG) in the whole-body, lipid accumulation and obesity in Drosophila. Moreover, the expression of apoLpp in the heart increased sharply, the heart rate and arrhythmia index increased and fibrillation occurred. Conversely, regular exercise or cardiomyocyte-derived apoLpp knockdown reduced the TG level in the whole-body of Drosophila. This significantly reduced the arrhythmia induced by obesity, including the reduction of heart rate, arrhythmia index, and fibrillation. Under HFD conditions, flies with apoLpp knockdown in the heart could resist the abnormal cardiac rhythm caused by obesity after receiving regular exercise. HFD-induced obesity and abnormal cardiac rhythm may be related to the acute increase of cardiomyocyte-derived apoLpp. Regular exercise and inhibition of cardiomyocyte-derived apoLpp can reduce the HFD-induced abnormal cardiac rhythm.

Sex-specific regulation of development, growth and metabolism

Adult females and males of most species differ in many aspects of their morphology, physiology and behavior, in response to sex-specific selective pressures that maximize fitness. While we have an increasingly good understanding of the genetic mechanisms that initiate these differences, the sex-specific developmental trajectories that generate them are much less well understood. Here we review recent advances in the sex-specific regulation of development focusing on two models where this development is increasingly well understood: Sexual dimorphism of body size in the fruit fly Drosophila melanogaster and sexual dimorphism of horns in the horned beetle Onthophagus taurus. Because growth and development are also supported by metabolism, the regulation of sex-specific metabolism during and after development is an important aspect of the generation of female and male phenotypes. Hitherto, the study of sex-specific development has largely been independent of the study of sex-specific metabolism. Nevertheless, as we discuss in this review, recent research has begun to reveal considerable overlap in the cellular and physiological mechanisms that regulate sex-specific development and metabolism.

Functions of Stress-Induced Lipid Droplets in the Nervous System

Lipid droplets are highly dynamic intracellular organelles that store neutral lipids such as cholesteryl esters and triacylglycerols. They have recently emerged as key stress response components in many different cell types. Lipid droplets in the nervous system are mostly observed in vivo in glia, ependymal cells and microglia. They tend to become more numerous in these cell types and can also form in neurons as a consequence of ageing or stresses involving redox imbalance and lipotoxicity. Abundant lipid droplets are also a characteristic feature of several neurodegenerative diseases. In this minireview, we take a cell-type perspective on recent advances in our understanding of lipid droplet metabolism in glia, neurons and neural stem cells during health and disease. We highlight that a given lipid droplet subfunction, such as triacylglycerol lipolysis, can be physiologically beneficial or harmful to the functions of the nervous system depending upon cellular context. The mechanistic understanding of context-dependent lipid droplet functions in the nervous system is progressing apace, aided by new technologies for probing the lipid droplet proteome and lipidome with single-cell type precision.

Endocrine control of glycogen and triacylglycerol breakdown in the fly model

Over the last decade, the combination of genetics, transcriptomic and proteomic approaches yielded substantial insights into the mechanisms behind the synthesis and breakdown of energy stores in the model organisms. The fruit fly Drosophila melanogaster has been particularly useful to unravel genetic regulations of energy metabolism. Despite the considerable evolutionary distance between humans and flies, the energy storage organs, main metabolic pathways, and even their genetic regulations remained relatively conserved. Glycogen and fat are universal energy reserves used in all animal phyla and several of their endocrine regulators, such as the insulin pathway, are highly evolutionarily conserved. Nevertheless, some of the factors inducing catabolism of energy stores have diverged significantly during evolution. Moreover, even within a single insect species, D. melanogaster, there are substantial developmental and context-dependent variances in the regulation of energy stores. These differences include, among others, the endocrine pathways that govern the catabolic events or the predominant fuel which is utilized for the given process. For example, many catabolic regulators that control energy reserves in adulthood seem to be largely dispensable for energy mobilization during development. In this review, we focus on a selection of the most important catabolic regulators from the group of peptide hormones (Adipokinetic hormone, Corazonin), catecholamines (octopamine), steroid hormones (20-hydroxyecdysone), and other factors (extracellular adenosine, regulators of lipase Brummer). We discuss their roles in the mobilization of energy reserves for processes such as development through non-feeding stages, flight or starvation survival. Finally, we conclude with future perspectives on the energy balance research in the fly model.

A low-sugar diet enhances Drosophila body size in males and females via sex-specific mechanisms

In Drosophila, changes to dietary protein elicit different body size responses between the sexes. Whether these differential body size effects extend to other macronutrients remains unclear. Here, we show that lowering dietary sugar (0S diet) enhanced body size in male and female larvae. Despite an equivalent phenotypic effect between the sexes, we detected sex-specific changes to signalling pathways, transcription and whole-body glycogen and protein. In males, the low-sugar diet augmented insulin/insulin-like growth factor signalling pathway (IIS) activity by increasing insulin sensitivity, where increased IIS was required for male metabolic and body size responses in 0S. In females reared on low sugar, IIS activity and insulin sensitivity were unaffected, and IIS function did not fully account for metabolic and body size responses. Instead, we identified a female-biased requirement for the Target of rapamycin pathway in regulating metabolic and body size responses. Together, our data suggest the mechanisms underlying the low-sugar-induced increase in body size are not fully shared between the sexes, highlighting the importance of including males and females in larval studies even when similar phenotypic outcomes are observed.

The gut hormone Allatostatin C/Somatostatin regulates food intake and metabolic homeostasis under nutrient stress

The intestine is a central regulator of metabolic homeostasis. Dietary inputs are absorbed through the gut, which senses their nutritional value and relays hormonal information to other organs to coordinate systemic energy balance. However, the gut-derived hormones affecting metabolic and behavioral responses are poorly defined. Here we show that the endocrine cells of the Drosophila gut sense nutrient stress through a mechanism that involves the TOR pathway and in response secrete the peptide hormone allatostatin C, a Drosophila somatostatin homolog. Gut-derived allatostatin C induces secretion of glucagon-like adipokinetic hormone to coordinate food intake and energy mobilization. Loss of gut Allatostatin C or its receptor in the adipokinetic-hormone-producing cells impairs lipid and sugar mobilization during fasting, leading to hypoglycemia. Our findings illustrate a nutrient-responsive endocrine mechanism that maintains energy homeostasis under nutrient-stress conditions, a function that is essential to health and whose failure can lead to metabolic disorders.

Glia fuel neurons with locally synthesized ketone bodies to sustain memory under starvation

During starvation, mammalian brains can adapt their metabolism, switching from glucose to alternative peripheral fuel sources. In the Drosophila starved brain, memory formation is subject to adaptative plasticity, but whether this adaptive plasticity relies on metabolic adaptation remains unclear. Here we show that during starvation, neurons of the fly olfactory memory centre import and use ketone bodies (KBs) as an energy substrate to sustain aversive memory formation. We identify local providers within the brain, the cortex glia, that use their own lipid store to synthesize KBs before exporting them to neurons via monocarboxylate transporters. Finally, we show that the master energy sensor AMP-activated protein kinase regulates both lipid mobilization and KB export in cortex glia. Our data provide a general schema of the metabolic interactions within the brain to support memory when glucose is scarce.

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.

Abnormal accumulation of lipid droplets in neurons induces the conversion of alpha-Synuclein to proteolytic resistant forms in a Drosophila model of Parkinson's disease

Parkinson’s disease (PD) is a neurodegenerative disorder characterized by alpha-synuclein (αSyn) aggregation and associated with abnormalities in lipid metabolism. The accumulation of lipids in cytoplasmic organelles called lipid droplets (LDs) was observed in cellular models of PD. To investigate the pathophysiological consequences of interactions between αSyn and proteins that regulate the homeostasis of LDs, we used a transgenic Drosophila model of PD, in which human αSyn is specifically expressed in photoreceptor neurons. We first found that overexpression of the LD-coating proteins Perilipin 1 or 2 (dPlin1/2), which limit the access of lipases to LDs, markedly increased triacylglyclerol (TG) loaded LDs in neurons. However, dPlin-induced-LDs in neurons are independent of lipid anabolic (diacylglycerol acyltransferase 1/midway, fatty acid transport protein/dFatp) and catabolic (brummer TG lipase) enzymes, indicating that alternative mechanisms regulate neuronal LD homeostasis. Interestingly, the accumulation of LDs induced by various LD proteins (dPlin1, dPlin2, CG7900 or Klarsicht^LD-BD) was synergistically amplified by the co-expression of αSyn, which localized to LDs in both Drosophila photoreceptor neurons and in human neuroblastoma cells. Finally, the accumulation of LDs increased the resistance of αSyn to proteolytic digestion, a characteristic of αSyn aggregation in human neurons. We propose that αSyn cooperates with LD proteins to inhibit lipolysis and that binding of αSyn to LDs contributes to the pathogenic misfolding and aggregation of αSyn in neurons.

Parkinson’s disease (PD) is a neurodegenerative disease characterized by the neurotoxic aggregation of the alpha-synuclein (αSyn) protein. Cellular models of the disease are also associated with an abnormal fat storage in the form of lipid droplets (LDs). However, in which cells, neuron or glial cells, LDs accumulate in the organism remains unknown. To understand the relationship between αSyn and the accumulation of LDs, we used a Drosophila (fruit fly) model of PD. We found that, in the presence of a protein that coats LDs, perilipin, LDs accumulate in photoreceptor neurons of the fly. Interestingly, the accumulation of LDs induced by perilipin or other LD-coating proteins was enhanced in the presence of αSyn. Using human neuronal cell lines and the fly, we could show that LD-coating and αSyn proteins localize at the surface of LDs. Finally, we observed that the process of αSyn aggregation was enhanced in the presence of LDs by using a biochemical approach. We thus propose that the association of αSyn with LDs could contribute to αSyn aggregation and progression of the pathology.

Sex determination gene transformer regulates the male-female difference in Drosophila fat storage via the adipokinetic hormone pathway

Sex differences in whole-body fat storage exist in many species. For example, Drosophila females store more fat than males. Yet, the mechanisms underlying this sex difference in fat storage remain incompletely understood. Here, we identify a key role for sex determination gene transformer (tra) in regulating the male-female difference in fat storage. Normally, a functional Tra protein is present only in females, where it promotes female sexual development. We show that loss of Tra in females reduced whole-body fat storage, whereas gain of Tra in males augmented fat storage. Tra's role in promoting fat storage was largely due to its function in neurons, specifically the Adipokinetic hormone (Akh)-producing cells (APCs). Our analysis of Akh pathway regulation revealed a male bias in APC activity and Akh pathway function, where this sex-biased regulation influenced the sex difference in fat storage by limiting triglyceride accumulation in males. Importantly, Tra loss in females increased Akh pathway activity, and genetically manipulating the Akh pathway rescued Tra-dependent effects on fat storage. This identifies sex-specific regulation of Akh as one mechanism underlying the male-female difference in whole-body triglyceride levels, and provides important insight into the conserved mechanisms underlying sexual dimorphism in whole-body fat storage.

Developmental mechanisms of sex differences: from cells to organisms

Male-female differences in many developmental mechanisms lead to the formation of two morphologically and physiologically distinct sexes. Although this is expected for traits with prominent differences between the sexes, such as the gonads, sex-specific processes also contribute to traits without obvious male-female differences, such as the intestine. Here, we review sex differences in developmental mechanisms that operate at several levels of biological complexity - molecular, cellular, organ and organismal - and discuss how these differences influence organ formation, function and whole-body physiology. Together, the examples we highlight show that one simple way to gain a more accurate and comprehensive understanding of animal development is to include both sexes.

Physiological and metabolomic consequences of reduced expression of the Drosophila brummer triglyceride Lipase

Disruption of lipolysis has widespread effects on intermediary metabolism and organismal phenotypes. Defects in lipolysis can be modeled in Drosophila melanogaster through genetic manipulations of brummer (bmm), which encodes a triglyceride lipase orthologous to mammalian Adipose Triglyceride Lipase. RNAi-mediated knock-down of bmm in all tissues or metabolic specific tissues results in reduced locomotor activity, altered sleep patterns and reduced lifespan. Metabolomic analysis on flies in which bmm is downregulated reveals a marked reduction in medium chain fatty acids, long chain saturated fatty acids and long chain monounsaturated and polyunsaturated fatty acids, and an increase in diacylglycerol levels. Elevated carbohydrate metabolites and tricarboxylic acid intermediates indicate that impairment of fatty acid mobilization as an energy source may result in upregulation of compensatory carbohydrate catabolism. bmm downregulation also results in elevated levels of serotonin and dopamine neurotransmitters, possibly accounting for the impairment of locomotor activity and sleep patterns. Physiological phenotypes and metabolomic changes upon reduction of bmm expression show extensive sexual dimorphism. Altered metabolic states in the Drosophila model are relevant for understanding human metabolic disorders, since pathways of intermediary metabolism are conserved across phyla.

Loss of Stearoyl-CoA desaturase 1 leads to cardiac dysfunction and lipotoxicity

Diets high in carbohydrates are associated with type 2 diabetes and its co-morbidities, including hyperglycemia, hyperlipidemia, obesity, hepatic steatosis and cardiovascular disease. We used a high-sugar diet to study the pathophysiology of diet-induced metabolic disease in Drosophila melanogaster. High-sugar diets produce hyperglycemia, obesity, insulin resistance and cardiomyopathy in flies, along with ectopic accumulation of toxic lipids, or lipotoxicity. Stearoyl-CoA desaturase 1 is an enzyme that contributes to long-chain fatty acid metabolism by introducing a double bond into the acyl chain. Knockdown of stearoyl-CoA desaturase 1 in the fat body reduced lipogenesis and exacerbated pathophysiology in flies reared on high-sucrose diets. These flies exhibited dyslipidemia and growth deficiency in addition to defects in cardiac and gut function. We assessed the lipidome of these flies using tandem mass spectrometry to provide insight into the relationship between potentially lipotoxic species and type 2 diabetes-like pathophysiology. Oleic acid supplementation is able to rescue a variety of phenotypes produced by stearoyl-CoA desaturase 1 RNAi, including fly mass, triglyceride storage, gut development and cardiac failure. Taken together, these data suggest a protective role for monounsaturated fatty acids in diet-induced metabolic disease phenotypes.

Sequestration to lipid droplets promotes histone availability by preventing turnover of excess histones

Because both dearth and overabundance of histones result in cellular defects, histone synthesis and demand are typically tightly coupled. In Drosophila embryos, histones H2B, H2A and H2Av accumulate on lipid droplets (LDs), which are cytoplasmic fat storage organelles. Without LD binding, maternally provided H2B, H2A and H2Av are absent; however, how LDs ensure histone storage is unclear. Using quantitative imaging, we uncover when during oogenesis these histones accumulate, and which step of accumulation is LD dependent. LDs originate in nurse cells (NCs) and are transported to the oocyte. Although H2Av accumulates on LDs in NCs, the majority of the final H2Av pool is synthesized in oocytes. LDs promote intercellular transport of the histone anchor Jabba and thus its presence in the ooplasm. Ooplasmic Jabba then prevents H2Av degradation, safeguarding the H2Av stockpile. Our findings provide insight into the mechanism for establishing histone stores during Drosophila oogenesis and shed light on the function of LDs as protein-sequestration sites.

Arc1 and the microbiota together modulate growth and metabolic traits in Drosophila

Perturbations to animal-associated microbial communities (the microbiota) have deleterious effects on various aspects of host fitness, but the molecular processes underlying these impacts are poorly understood. Here, we identify a connection between the microbiota and the neuronal factor Arc1 that affects growth and metabolism in Drosophila. We find that Arc1 exhibits tissue-specific microbiota-dependent expression changes, and that germ-free flies bearing a null mutation of Arc1 exhibit delayed and stunted larval growth, along with a variety of molecular, cellular and organismal traits indicative of metabolic dysregulation. Remarkably, we show that the majority of these phenotypes can be fully suppressed by mono-association with a single Acetobacter sp. isolate, through mechanisms involving both bacterial diet modification and live bacteria. Additionally, we provide evidence that Arc1 function in key neuroendocrine cells of the larval brain modulates growth and metabolic homeostasis under germ-free conditions. Our results reveal a role for Arc1 in modulating physiological responses to the microbial environment, and highlight how host-microbe interactions can profoundly impact the phenotypic consequences of genetic mutations in an animal host.

Drosophila Antimicrobial Peptides and Lysozymes Regulate Gut Microbiota Composition and Abundance

The gut microbiota affects the physiology and metabolism of animals and its alteration can lead to diseases such as gut dysplasia or metabolic disorders. Several reports have shown that the immune system plays an important role in shaping both bacterial community composition and abundance in Drosophila, and that immune deficit, especially during aging, negatively affects microbiota richness and diversity. However, there has been little study at the effector level to demonstrate how immune pathways regulate the microbiota. A key set of Drosophila immune effectors are the antimicrobial peptides (AMPs), which confer defense upon systemic infection. AMPs and lysozymes, a group of digestive enzymes with antimicrobial properties, are expressed in the gut and are good candidates for microbiota regulation. Here, we take advantage of the model organism Drosophila melanogaster to investigate the role of AMPs and lysozymes in regulation of gut microbiota structure and diversity. Using flies lacking AMPs and newly generated lysozyme mutants, we colonized gnotobiotic flies with a defined set of commensal bacteria and analyzed changes in microbiota composition and abundance in vertical transmission and aging contexts through 16S rRNA gene amplicon sequencing. Our study shows that AMPs and, to a lesser extent, lysozymes are necessary to regulate the total and relative abundance of bacteria in the gut microbiota. We also decouple the direct function of AMPs from the immune deficiency (IMD) signaling pathway that regulates AMPs but also many other processes, more narrowly defining the role of these effectors in the microbial dysbiosis observed in IMD-deficient flies upon aging.

Discovering signaling mechanisms governing metabolism and metabolic diseases with Drosophila

There has been rapid growth in the use of Drosophila and other invertebrate systems to dissect mechanisms governing metabolism. New assays and approaches to physiology have aligned with superlative genetic tools in fruit flies to provide a powerful platform for posing new questions, or dissecting classical problems in metabolism and disease genetics. In multiple examples, these discoveries exploit experimental advantages as-yet unavailable in mammalian systems. Here, we illustrate how fly studies have addressed long-standing questions in three broad areas-inter-organ signaling through hormonal or neural mechanisms governing metabolism, intestinal interoception and feeding, and the cellular and signaling basis of sexually dimorphic metabolism and physiology-and how these findings relate to human (patho)physiology. The imaginative application of integrative physiology and related approaches in flies to questions in metabolism is expanding, and will be an engine of discovery, revealing paradigmatic features of metabolism underlying human diseases and physiological equipoise in health.

Lipid droplets in the nervous system

Lipid droplets are dynamic intracellular lipid storage organelles that respond to the physiological state of cells. In addition to controlling cell metabolism, they play a protective role for many cellular stressors, including oxidative stress. Despite prior descriptions of lipid droplets appearing in the brain as early as a century ago, only recently has the role of lipid droplets in cells found in the brain begun to be understood. Lipid droplet functions have now been described for cells of the nervous system in the context of development, aging, and an increasing number of neuropathologies. Here, we review the basic mechanisms of lipid droplet formation, turnover, and function and discuss how these mechanisms enable lipid droplets to function in different cell types of the nervous system under healthy and pathological conditions.