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

A brain-derived insulin signal encodes protein satiety for nutrient-specific feeding inhibition

The suppressive effect of insulin on food intake has been documented for decades. However, whether insulin signals can encode a certain type of nutrients to regulate nutrient-specific feeding behavior remains elusive. Here, we show that in female Drosophila, a pair of dopaminergic neurons, tritocerebrum 1-dopaminergic neurons (T1-DANs), are directly activated by a protein-intake-induced insulin signal from insulin-producing cells (IPCs). Intriguingly, opto-activating IPCs elicits feeding inhibition for both protein and sugar, while silencing T1-DANs blocks this inhibition only for protein food. Elevating insulin signaling in T1-DANs or opto-activating these neurons is sufficient to mimic protein satiety. Furthermore, this signal is conveyed to local neurons of the protocerebral bridge (PB-LNs) and specifically suppresses protein intake. Therefore, our findings reveal that a brain-derived insulin signal encodes protein satiety and suppresses feeding behavior in a nutrient-specific manner, shedding light on the functional specificity of brain insulin signals in regulating behaviors.

Transcriptional control of a metabolic switch regulating cellular methylation reactions is part of a common response to stress in divergent bee species

Recent global declines in bee health have elevated the need for a more complete understanding of the cellular stress mechanisms employed by diverse bee species. We recently uncovered the biomarker lethal (2) essential for life [l(2)efl] genes as part of a shared transcriptional program in response to a number of cell stressors in the western honey bee (Apis mellifera). Here, we describe another shared stress-responsive gene, glycine N-methyltransferase (Gnmt), which is known as a key metabolic switch controlling cellular methylation reactions. We observed Gnmt induction by both abiotic and biotic stressors. We also found increased levels of the GNMT reaction product sarcosine in the midgut after stress, linking metabolic changes with the observed changes in gene regulation. Prior to this study, Gnmt upregulation had not been associated with cellular stress responses in other organisms. To determine whether this novel stress-responsive gene would behave similarly in other bee species, we first characterized the cellular response to endoplasmic reticulum (ER) stress in lab-reared adults of the solitary alfalfa leafcutting bee (Megachile rotundata) and compared this with age-matched honey bees. The novel stress gene Gnmt was induced in addition to a number of canonical gene targets induced in both bee species upon unfolded protein response (UPR) activation, suggesting that stress-induced regulation of cellular methylation reactions is a common feature of bees. Therefore, this study suggests that the honey bee can serve as an important model for bee biology more broadly, although studies on diverse bee species will be required to fully understand global declines in bee populations.

Octopamine integrates the status of internal energy supply into the formation of food-related memories

The brain regulates food intake in response to internal energy demands and food availability. However, can internal energy storage influence the type of memory that is formed? We show that the duration of starvation determines whether Drosophila melanogaster forms appetitive short-term or longer-lasting intermediate memories. The internal glycogen storage in the muscles and adipose tissue influences how intensely sucrose-associated information is stored. Insulin-like signaling in octopaminergic reward neurons integrates internal energy storage into memory formation. Octopamine, in turn, suppresses the formation of long-term memory. Octopamine is not required for short-term memory because octopamine-deficient mutants can form appetitive short-term memory for sucrose and to other nutrients depending on the internal energy status. The reduced positive reinforcing effect of sucrose at high internal glycogen levels, combined with the increased stability of food-related memories due to prolonged periods of starvation, could lead to increased food intake.

Insulin-like peptides and ovary ecdysteroidogenic hormone differentially stimulate physiological processes regulating egg formation in the mosquito Aedes aegypti

Mosquitoes including Aedes aegypti are human disease vectors because females must blood feed to produce and lay eggs. Blood feeding triggers insulin-insulin growth factor signaling (IIS) which regulates several physiological processes required for egg development. A. aegypti encodes 8 insulin-like peptides (ILPs) and one insulin-like receptor (IR) plus ovary ecdysteroidogenic hormone (OEH) that also activates IIS through the OEH receptor (OEHR). In this study, we assessed the expression of A. aegypti ILPs and OEH during a gonadotrophic cycle and produced each that were functionally characterized to further understand their roles in regulating egg formation. All A. aegypti ILPs and OEH were expressed during a gonadotrophic cycle. Five ILPs (1, 3, 4, 7, 8) and OEH were specifically expressed in the head, while antibodies to ILP3 and OEH indicated each was released after blood feeding from ventricular axons that terminate on the anterior midgut. A subset of ILP family members and OEH stimulated nutrient storage in previtellogenic females before blood feeding, whereas most IIS-dependent processes after blood feeding were activated by one or more of the brain-specific ILPs and/or OEH. ILPs and OEH with different biological activities also exhibited differences in IIS as measured by phosphorylation of the IR, phosphoinositide 3-kinase/Akt kinase (AKT) and mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK). Altogether, our results provide the first results that compare the functional activities of all ILP family members and OEH produced by an insect.

Immunometabolic regulation during the presence of microorganisms and parasitoids in insects

Multicellular organisms live in environments containing diverse nutrients and a wide variety of microbial communities. On the one hand, the immune response of organisms can protect from the intrusion of exogenous microorganisms. On the other hand, the dynamic coordination of anabolism and catabolism of organisms is a necessary factor for growth and reproduction. Since the production of an immune response is an energy-intensive process, the activation of immune cells is accompanied by metabolic transformations that enable the rapid production of ATP and new biomolecules. In insects, the coordination of immunity and metabolism is the basis for insects to cope with environmental challenges and ensure normal growth, development and reproduction. During the activation of insect immune tissues by pathogenic microorganisms, not only the utilization of organic resources can be enhanced, but also the activated immune cells can usurp the nutrients of non-immune tissues by generating signals. At the same time, insects also have symbiotic bacteria in their body, which can affect insect physiology through immune-metabolic regulation. This paper reviews the research progress of insect immune-metabolism regulation from the perspective of insect tissues, such as fat body, gut and hemocytes. The effects of microorganisms (pathogenic bacteria/non-pathogenic bacteria) and parasitoids on immune-metabolism were elaborated here, which provide guidance to uncover immunometabolism mechanisms in insects and mammals. This work also provides insights to utilize immune-metabolism for the formulation of pest control strategies.

Changing ROS, NAD and AMP: A path to longevity via mitochondrial therapeutics

Lifespan of many organisms, from unicellular yeast to extremely complex human organism, strongly depends on the genetic background and environmental factors. Being among most influential target energy metabolism is affected by macronutrients, their caloric values, and peculiarities of catabolism. Mitochondria are central organelles that respond for energy metabolism in eukaryotic cells. Mitochondria generate reactive oxygen species (ROS), which are lifespan modifying metabolites and a kind of biological clock. Oxidized nicotinamide adenine dinucleotide (NAD⁺) and adenosine monophosphate (AMP) are important metabolic intermediates and molecules that trigger or inhibit several signaling pathways involved in gene silencing, nutrient allocation, and cell regeneration and programmed death. A part of NAD⁺ and AMP metabolism is tied to mitochondria. Using substances that able to target mitochondria, as well as allotopic expression of specific enzymes, are envisioned to be innovative approaches to prolong lifespan by modulation of ROS, NAD⁺, and AMP levels. Among substances, an anti-diabetic drug metformin is believed to increase NAD⁺ and AMP levels, indirectly influencing histone deacetylases, involved in gene silencing, and AMP-activated protein kinase, an energy sensor of cells. Mitochondrially targeted derivatives of ubiquinone were found to interact with ROS. A mitochondrially targeted non-proton-pumping NADH dehydrogenase may influence both ROS and NAD⁺ levels. Chapter describes putative how mitochondria-targeted drugs and NADH dehydrogenase extend lifespan, perspectives of creating drugs with similar properties and their usage as senotherapeutic pills are discussed in the chapter.

Insulin-like peptide 8 (Ilp8) regulates female fecundity in flies

Introduction: Insulin-like peptides (Ilps) play crucial roles in nearly all life stages of insects. Ilp8 is involved in developmental stability, stress resistance and female fecundity in several insect species, but the underlying mechanisms are not fully understood. Here we report the functional characterization of Ilp8s in three fly species, including Bactrocera dorsalis, Drosophila mercatorum and Drosophila melanogaster. Methods: Phylogenetic analyses were performed to identify and characterize insect Ilp8s. The amino acid sequences of fly Ilp8s were aligned and the three-dimensional structures of fly Ilp8s were constructed and compared. The tissue specific expression pattern of fly Ilp8s were examined by qRT-PCR. In Bactrocera dorsalis and Drosophila mercatorum, dsRNAs were injected into virgin females to inhibit the expression of Ilp8 and the impacts on female fecundity were examined. In Drosophila melanogaster, the female fecundity of Ilp8 loss-of-function mutant was compared with wild type control flies. The mutant fruit fly strain was also used for sexual behavioral analysis and transcriptomic analysis. Results: Orthologs of Ilp8s are found in major groups of insects except for the lepidopterans and coleopterans, and Ilp8s are found to be well separated from other Ilps in three fly species. The key motif and the predicted three-dimensional structure of fly Ilp8s are well conserved. Ilp8 are specifically expressed in the ovary and are essential for female fecundity in three fly species. Behavior analysis demonstrates that Ilp8 mutation impairs female sexual attractiveness in fruit fly, which results in decreased mating success and is likely the cause of fecundity reduction. Further transcriptomic analysis indicates that Ilp8 might influence metabolism, immune activity, oocyte development as well as hormone homeostasis to collectively regulate female fecundity in the fruit fly. Discussion: Our findings support a universal role of insect Ilp8 in female fecundity, and also provide novel clues for understanding the modes of action of Ilp8.

Gonadulin: A newly discovered insulin-like peptide involved in ovulation and oviposition in Rhodnius prolixus, a vector of Chagas disease

Insulin-like peptides (ILPs) are vital hormones involved in a wide range of physiological processes in all organisms. In insects, insulin signaling has a key role in detecting and interpreting nutrient levels for egg production. Based on publicly available transcriptomes, a new ILP named gonadulin has been reported and suggested to be expressed by the gonads (hence its name). Although the identification of gonadulin establishes its existence, its physiological relevance remains poorly understood. Rhodnius prolixus is an obligate hematophagous insect and a primary vector of Trypanosoma cruzi, the etiological agent of Chagas disease. In this study, we report for the first time the participation of gonadulin in reproductive performance of an hemipteran. By quantitative PCR and fluorescence in situ hybridization (FISH), we find that the R. prolixus gonadulin transcript is highly expressed in the reproductive system, particularly in the calyx, a structure through which eggs move into the lumen of the lateral oviducts during ovulation. The putative gonadulin receptor, a member of the leucine-rich repeat-containing G protein-coupled receptor subfamily (LGR3), is most highly expressed in the central nervous system with lower levels in the reproductive tissue and other tissues. Interestingly, when the gonadulin signaling cascade is impaired using RNA interference (RNAi), eggs are retained primarily in the ovarioles and calyx, indicating that ovulation and oviposition are inhibited. Understanding the physiological processes involved in reproduction in R. prolixus will shed light on potential targets for effective production of biopesticides by translational research, thereby controlling insect populations and transmission of the disease.

Ameliorative effect of bayberry leaves proanthocyanidins on high sugar diet induced Drosophila melanogaster

Bayberry leaves proanthocyanidins (BLPs) were distributed in natural plant food, considered to have the potential for metabolic syndrome. In this study, we raised Drosophila melanogaster on high sugar diet (HSD) from the egg stage to induce hyperglycemia, and the ameliorative effect of BLPs was assessed based on this model. Phenotypical, biochemical, and molecular analyses related to diabetes mellitus pathogenesis were measured. Flies exposed to BLPs were found to suppress the HSD-induced high glucose and high triglycerides levels. Moreover, BLPs showed an inhibitory effect on carbohydrate digestive enzymes (α-amylase and α-glucosidase) activity and mRNA expression, exhibiting the potential for carbohydrate digestion retardation. Transcriptional levels of key genes associated with glycolipid metabolism were further evaluated, including dilp, InR, and downstream dAKT-dFOXO-PEPCK, together with E78, SREBP, FAS, and LSD genes, were all downregulated after BLPs-exposure, suggesting the ameliorative effect of BLPs on dysbiosis associated with the insulin signaling pathway. This study provided a new functional compound, which is beneficial to further antidiabetic therapy studies.

Dietary Choice Reshapes Metabolism in Drosophila by Affecting Consumption of Macronutrients

The precise regulation of metabolism and feeding behavior is important for preventing the development of metabolic diseases. Here we examine the effects on Drosophila metabolism of dietary choice. These changes are predicted to be dependent on both the quantity and quality of the chosen diet. Using a geometric framework for both no-choice and two-choice conditions, we found that feeding decisions led to higher glucose and trehalose levels but lower triglycerides pools. The feeding regimens had similar strategies for macronutrient balancing, and both maximized hemolymph glucose and glycogen content under low protein intake. In addition, the flies showed significant differences in the way they regulated trehalose and triglyceride levels in response to carbohydrate and protein consumption between choice and no-choice nutrition. Under choice conditions, trehalose and triglyceride levels were maximized at the lowest protein and carbohydrate consumption. Thus, we suggest that these changes in carbohydrate and lipid metabolism are caused by differences in the macronutrients consumed by flies. Food choice elicits rapid metabolic changes to maintain energy homeostasis. These results contribute to our understanding of how metabolism is regulated by the revealed nutrient variation in response to food decisions.

Endocrine Regulation of Lifespan in Insect Diapause

Diapause is a physiological adaptation to conditions that are unfavorable for growth or reproduction. During diapause, animals become long-lived, stress-resistant, developmentally static, and non-reproductive, in the case of diapausing adults. Diapause has been observed at all developmental stages in both vertebrates and invertebrates. In adults, diapause traits weaken into adaptations such as hibernation, estivation, dormancy, or torpor, which represent evolutionarily diverse versions of the traditional diapause traits. These traits are regulated through modifications of the endocrine program guiding development. In insects, this typically includes changes in molting hormones, as well as metabolic signals that limit growth while skewing the organism's energetic demands toward conservation. While much work has been done to characterize these modifications, the interactions between hormones and their downstream consequences are incompletely understood. The current state of diapause endocrinology is reviewed here to highlight the relevance of diapause beyond its use as a model to study seasonality and development. Specifically, insect diapause is an emerging model to study mechanisms that determine lifespan. The induction of diapause represents a dramatic change in the normal progression of age. Hormones such as juvenile hormone, 20-hydroxyecdysone, and prothoracicotropic hormone are well-known to modulate this plasticity. The induction of diapause-and by extension, the cessation of normal aging-is coordinated by interactions between these pathways. However, research directly connecting diapause endocrinology to the biology of aging is lacking. This review explores connections between diapause and aging through the perspective of endocrine signaling. The current state of research in both fields suggests appreciable overlap that will greatly contribute to our understanding of diapause and lifespan determination.

CRISPR/Cas9-mediated mutation on an insulin-like peptide encoding gene affects the growth of the ridgetail white prawn Exopalaemon carinicauda

Insulin-like peptides (ILPs) play key roles in animal growth, metabolism and reproduction in vertebrates. In crustaceans, one type of ILPs, insulin-like androgenic gland hormone (IAG) had been reported to be related to the sex differentiations. However, the function of other types of ILPs is rarely reported. Here, we identified another type of ILPs in the ridgetail white prawn Exopalaemon carinicauda (EcILP), which is an ortholog of Drosophila melanogaster ILP7. Sequence characterization and expression analyses showed that EcILP is similar to vertebrate insulin/IGFs and insect ILPs in its heterodimeric structure and expression profile. Using CRISPR/Cas9 genome editing technology, we generated EcILP knockout (KO) prawns. EcILP-KO individuals have a significant higher growth-inhibitory trait and mortality than those in the normal group. In addition, knockdown of EcILP by RNA interference (RNAi) resulted in slower growth rate and higher mortality. These results indicated that EcILP was an important growth regulator in E. carinicauda.