Mio acts in the Drosophila brain to control nutrient storage and feeding

Drosophila melanogaster as a low-cost and valuable model for studying type 2 diabetes

Drosophila melanogaster has been used as the most successful invertebrate model for studying metabolic diseases such as type 2 diabetes (T2D). We induced T2D by feeding Drosophila larvae on a high-sugar diet (HSD). The glucose and trehalose, glycogen, lipid, triglyceride, and protein levels were determined in HSD-fed larvae. Moreover, larval food intake, water content, size, and weight in addition to the development until pupation were observed. Levels of Drosophila insulin-like peptides (DILPs 2, 3, and 5), as well as adipokinetic hormone (AKH), were also determined in HSD-fed larvae by quantitative real-time polymerase chain reaction. The results demonstrated that HSD could induce elevated levels of glucose, trehalose, glycogen, and proteins in larvae. The larvae consumed less food intake and were smaller, lighter, and less developed on HSD than those on the control diet. Moreover, the water content of larvae fed HSD was similar to that fed the control diet. HSD induced higher expression of DILP3 and AKH, confirming hyperglycemia with insulin resistance. In sum, Drosophila offers an appropriate model for quick and inexpensive in vivo experimentation on human metabolic diseases.

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

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

Causative and Sanative dynamicity of ChREBP in Hepato-Metabolic disorders

ChREBP is the master regulator of carbohydrate dependent glycolytic and lipogenic flux within metabolic tissues. It plays a vital role in hyper-calorific milieu by activating glycolysis, lipogenesis along with pentose phosphate shunt and glycogen synthesis, fostering immediate reduction in the systemic glycemic levels. Liver being the primary organ to sense disproportionate dietary intake and linked physiological stress, stimulates ChREBP to perform the aforementioned processes. Activated ChREBP also inhibits lipolysis and encourages proper disposal of excessive triglycerides into adipocytes from the liver ablating hepatic intracellular lipid trafficking. Chronic overeating or onset of positive energy balance, hyper-activates ChREBP and signals development, intensification of hepato-metabolic disorders, and allied discrepancies in the whole-body metabolic functioning. ChREBP thus gets negatively connotated as the primary regulator of hepatic disorders, owing to its inherent features as the primary glycemic sensor and the only transcription factor that can transduce glucose-dependent glycolytic and lipogenic signals. Through this review, we - try to recapitulate and emphasize on the sanative events coordinated by ChREBP in several pathophysiological states. In totality, we aim to uncouple the disease-causing aspects of ChREBP from its positive attributes evoked during a metabolic crisis, in hepato-metabolic diseases.

Neuronal Mechanisms that Drive Organismal Aging Through the Lens of Perception

Sensory neurons provide organisms with data about the world in which they live, for the purpose of successfully exploiting their environment. The consequences of sensory perception are not simply limited to decision-making behaviors; evidence suggests that sensory perception directly influences physiology and aging, a phenomenon that has been observed in animals across taxa. Therefore, understanding the neural mechanisms by which sensory input influences aging may uncover novel therapeutic targets for aging-related physiologies. In this review, we examine different perceptive experiences that have been most clearly linked to aging or age-related disease: food perception, social perception, time perception, and threat perception. For each, the sensory cues, receptors, and/or pathways that influence aging as well as the individual or groups of neurons involved, if known, are discussed. We conclude with general thoughts about the potential impact of this line of research on human health and aging.

Regulation of Carbohydrate Energy Metabolism in Drosophila melanogaster

Carbohydrate metabolism is essential for cellular energy balance as well as for the biosynthesis of new cellular building blocks. As animal nutrient intake displays temporal fluctuations and each cell type within the animal possesses specific metabolic needs, elaborate regulatory systems are needed to coordinate carbohydrate metabolism in time and space. Carbohydrate metabolism is regulated locally through gene regulatory networks and signaling pathways, which receive inputs from nutrient sensors as well as other pathways, such as developmental signals. Superimposed on cell-intrinsic control, hormonal signaling mediates intertissue information to maintain organismal homeostasis. Misregulation of carbohydrate metabolism is causative for many human diseases, such as diabetes and cancer. Recent work in Drosophila melanogaster has uncovered new regulators of carbohydrate metabolism and introduced novel physiological roles for previously known pathways. Moreover, genetically tractable Drosophila models to study carbohydrate metabolism-related human diseases have provided new insight into the mechanisms of pathogenesis. Due to the high degree of conservation of relevant regulatory pathways, as well as vast possibilities for the analysis of gene-nutrient interactions and tissue-specific gene function, Drosophila is emerging as an important model system for research on carbohydrate metabolism.

Drosophila as a model to study obesity and metabolic disease

Excess adipose fat accumulation, or obesity, is a growing problem worldwide in terms of both the rate of incidence and the severity of obesity-associated metabolic disease. Adipose tissue evolved in animals as a specialized dynamic lipid storage depot: adipose cells synthesize fat (a process called lipogenesis) when energy is plentiful and mobilize stored fat (a process called lipolysis) when energy is needed. When a disruption of lipid homeostasis favors increased fat synthesis and storage with little turnover owing to genetic predisposition, overnutrition or sedentary living, complications such as diabetes and cardiovascular disease are more likely to arise. The vinegar fly Drosophila melanogaster (Diptera: Drosophilidae) is used as a model to better understand the mechanisms governing fat metabolism and distribution. Flies offer a wealth of paradigms with which to study the regulation and physiological effects of fat accumulation. Obese flies accumulate triacylglycerols in the fat body, an organ similar to mammalian adipose tissue, which specializes in lipid storage and catabolism. Discoveries in Drosophila have ranged from endocrine hormones that control obesity to subcellular mechanisms that regulate lipogenesis and lipolysis, many of which are evolutionarily conserved. Furthermore, obese flies exhibit pathophysiological complications, including hyperglycemia, reduced longevity and cardiovascular function - similar to those observed in obese humans. Here, we review some of the salient features of the fly that enable researchers to study the contributions of feeding, absorption, distribution and the metabolism of lipids to systemic physiology.

Modeling dietary influences on offspring metabolic programming in Drosophila melanogaster

The influence of nutrition on offspring metabolism has become a hot topic in recent years owing to the growing prevalence of maternal and childhood obesity. Studies in mammals have identified several factors correlating with parental and early offspring dietary influences on progeny health; however, the molecular mechanisms that underlie these factors remain undiscovered. Mammalian metabolic tissues and pathways are heavily conserved in Drosophila melanogaster, making the fly an invaluable genetic model organism for studying metabolism. In this review, we discuss the metabolic similarities between mammals and Drosophila and present evidence supporting its use as an emerging model of metabolic programming.

The regulation and role of carbohydrate response element-binding protein in metabolic homeostasis and disease

The transcription factor carbohydrate response element-binding protein (ChREBP) is a member of the basic helix-loop-helix leucine zipper transcription factor family. Under high-glucose conditions, it has a role in regulating the expression of key genes involved in various pathways, including glycolysis, gluconeogenesis and lipogenesis. It does this by forming a tetrameric complex made up of two ChREBP/Mlx heterodimers, which enables it to bind to the carbohydrate response element (ChoRE) in the promoter region of its target genes to regulate transcription. Because ChREBP plays a key role in glucose signalling and metabolism, and aberrations in glucose homeostasis are often present in metabolic diseases, this transcription factor presents itself as an enticing target with respect to further understanding metabolic disease mechanisms and potentially uncovering new therapeutic targets.

Sweet Sixteenth for ChREBP: Established Roles and Future Goals

With the identification of ChREBP in 2001, our interest in understanding the molecular control of carbohydrate sensing has surged. While ChREBP was initially studied as a master regulator of lipogenesis in liver and fat tissue, it is now clear that ChREBP functions as a central metabolic coordinator in a variety of cell types in response to environmental and hormonal signals, with wide implications in health and disease. Celebrating its sweet sixteenth birthday, we review here the current knowledge about the function and regulation of ChREBP throughout usual and less explored tissues, to recapitulate ChREBP's role as a whole-body glucose sensor.

MondoA/ChREBP: The usual suspects of transcriptional glucose sensing; Implication in pathophysiology

Identification of the Mondo glucose-responsive transcription factors family, including the MondoA and MondoB/ChREBP paralogs, has shed light on the mechanism whereby glucose affects gene transcription. They have clearly emerged, in recent years, as key mediators of glucose sensing by multiple cell types. MondoA and ChREBP have overlapping yet distinct expression profiles, which underlie their downstream targets and separate roles in regulating genes involved in glucose metabolism. MondoA can restrict glucose uptake and influences energy utilization in skeletal muscle, while ChREBP signals energy storage through de novo lipogenesis in liver and white adipose tissue. Because Mondo proteins mediate metabolic adaptations to changing glucose levels, a better understanding of cellular glucose sensing through Mondo proteins will likely uncover new therapeutic opportunities in the context of the imbalanced glucose homeostasis that accompanies metabolic diseases such as type 2 diabetes and cancer. Here, we provide an overview of structural homologies, transcriptional partners as well as the nutrient and hormonal mechanisms underlying Mondo proteins regulation. We next summarize their relative contribution to energy metabolism changes in physiological states and the evolutionary conservation of these pathways. Finally, we discuss their possible targeting in human pathologies.

Using Drosophila to discover mechanisms underlying type 2 diabetes

Mechanisms of glucose homeostasis are remarkably well conserved between the fruit flyDrosophila melanogasterand mammals. From the initial characterization of insulin signaling in the fly came the identification of downstream metabolic pathways for nutrient storage and utilization. Defects in these pathways lead to phenotypes that are analogous to diabetic states in mammals. These discoveries have stimulated interest in leveraging the fly to better understand the genetics of type 2 diabetes mellitus in humans. Type 2 diabetes results from insulin insufficiency in the context of ongoing insulin resistance. Although genetic susceptibility is thought to govern the propensity of individuals to develop type 2 diabetes mellitus under appropriate environmental conditions, many of the human genes associated with the disease in genome-wide association studies have not been functionally studied. Recent advances in the phenotyping of metabolic defects have positionedDrosophilaas an excellent model for the functional characterization of large numbers of genes associated with type 2 diabetes mellitus. Here, we examine results from studies modeling metabolic disease in the fruit fly and compare findings to proposed mechanisms for diabetic phenotypes in mammals. We provide a systematic framework for assessing the contribution of gene candidates to insulin-secretion or insulin-resistance pathways relevant to diabetes pathogenesis.

Insulin/IGF signaling in Drosophila and other insects: factors that regulate production, release and post-release action of the insulin-like peptides

Insulin, insulin-like growth factors (IGFs) and insulin-like peptides (ILPs) are important regulators of metabolism, growth, reproduction and lifespan, and mechanisms of insulin/IGF signaling (IIS) have been well conserved over evolution. In insects, between one and 38 ILPs have been identified in each species. Relatively few insect species have been investigated in depth with respect to ILP functions, and therefore we focus mainly on the well-studied fruitfly Drosophila melanogaster. In Drosophila eight ILPs (DILP1-8), but only two receptors (dInR and Lgr3) are known. DILP2, 3 and 5 are produced by a set of neurosecretory cells (IPCs) in the brain and their biosynthesis and release are controlled by a number of mechanisms differing between larvae and adults. Adult IPCs display cell-autonomous sensing of circulating glucose, coupled to evolutionarily conserved mechanisms for DILP release. The glucose-mediated DILP secretion is modulated by neurotransmitters and neuropeptides, as well as by factors released from the intestine and adipocytes. Larval IPCs, however, are indirectly regulated by glucose-sensing endocrine cells producing adipokinetic hormone, or by circulating factors from the intestine and fat body. Furthermore, IIS is situated within a complex physiological regulatory network that also encompasses the lipophilic hormones, 20-hydroxyecdysone and juvenile hormone. After release from IPCs, the ILP action can be modulated by circulating proteins that act either as protective carriers (binding proteins), or competitive inhibitors. Some of these proteins appear to have additional functions that are independent of ILPs. Taken together, the signaling with multiple ILPs is under complex control, ensuring tightly regulated IIS in the organism.