Justin R. DiAngelo

The immune response attenuates growth and nutrient storage in Drosophila by reducing insulin signaling

Innate immunity is the primary and most ancient defense against infection. Although critical to survival, coordinating protection against a foreign organism is energetically costly, creating the need to reallocate substrates from nonessential functions, such as growth and nutrient storage. However, the mechanism by which infection or inflammation leads to a reduction in energy utilization by these dispensable processes is not well understood. Here, we demonstrate that activation of the Toll signaling pathway selectively in the fat body, the major immune and lipid storage organ of the fruit fly, Drosophila melanogaster, leads to both induction of immunity and reallocation of resources. Toll signaling in the fat body suppresses insulin signaling both within these cells and non-autonomously throughout the organism, leading to a decrease in both nutrient stores and growth. These data suggest that communication between these two regulatory systems evolved as a means to divert energy in times of need from organismal growth to the acute requirement of combating infection.

Regulation of Fat Cell Mass by Insulin in Drosophila melanogaster

ABSTRACT A phylogenetically conserved response to nutritional abundance is an increase in insulin signaling, which initiates a set of biological responses dependent on the species. Consequences of augmented insulin signaling include developmental progression, cell and organ growth, and the storage of carbohydrates and lipids. Here, we address the evolutionary origins of insulins positive effects on anabolic lipid metabolism by selectively modulating insulin signaling in the fat body of the fruit fly, Drosophila melanogaster. Analogous to the actions of insulin in higher vertebrates, those in Drosophila include expansion of the insect fat cell mass both by increasing the adipocyte number and by promoting lipid accumulation. The ability of insulin to accomplish the former depends on its capacity to bring about phosphorylation and inhibition of the transcription factor Drosophila FOXO (dFOXO) and the serine/threonine protein kinase shaggy, the fly ortholog of glycogen synthase kinase 3 (GSK3). Increasing the amount of triglyceride per cell also depends on the phosphorylation of shaggy but is independent of dFOXO. Thus, the findings of this study provide evidence that the control of fat mass by insulin is a conserved process and place dFOXO and shaggy/GSK3 downstream of the insulin receptor in controlling adipocyte cell number and triglyceride storage, respectively.

A Course-Based Research Experience: How Benefits Change with Increased Investment in Instructional Time

While course-based research in genomics can generate both knowledge gains and a greater appreciation for how science is done, a significant investment of course time is required to enable students to show gains commensurate to a summer research experience. Nonetheless, this is a very cost-effective way to reach larger numbers of students.

Interaction between sleep and metabolism in Drosophila with altered octopamine signaling.

Background: Octopamine acts through the insulin-producing cells in the Drosophila brain to promote wake. Results: Insulin-like peptides do not mediate effects of octopamine on wake, but contribute to an effect of octopamine on triglyceride levels. Conclusion: Although sleep and metabolic circuitry overlap, octopamine regulates sleep and metabolism independently. Significance: These findings provide insight into the connection between sleep and metabolism. Sleep length and metabolic dysfunction are correlated, but the causal relationship between these processes is unclear. Octopamine promotes wakefulness in the fly by acting through the insulin-producing cells (IPCs) in the fly brain. To determine if insulin signaling mediates the effects of octopamine on sleep:wake behavior, we assayed flies in which insulin signaling activity was genetically altered. We found that increasing insulin signaling does not promote wake, nor does insulin appear to mediate the wake-promoting effects of octopamine. Octopamine also affects metabolism in invertebrate species, including, as we show here, Drosophila melanogaster. Triglycerides are decreased in mutants with compromised octopamine signaling and elevated in flies with increased activity of octopaminergic neurons. Interestingly, this effect is mediated at least partially by insulin, suggesting that effects of octopamine on metabolism are independent of its effects on sleep. We further investigated the relative contribution of metabolic and sleep phenotypes to the starvation response of flies with altered octopamine signaling. Hyperactivity (indicative of foraging) induced by starvation was elevated in octopamine receptor mutants, despite their high propensity for sleep, indicating that their metabolic state dictates their behavioral response under these conditions. Moreover, flies with increased octopamine signaling do not suppress sleep in response to starvation, even though they are normally hyper-aroused, most likely because of their high triglyceride levels. Together, these data suggest that observed correlations between sleep and metabolic phenotypes can result from shared molecular pathways rather than causality, and environmental conditions can lead to the dominance of one phenotype over the other.

Mio/dChREBP coordinately increases fat mass by regulating lipid synthesis and feeding behavior in Drosophila

During nutrient excess, triglycerides are synthesized and stored to provide energy during times of famine. The presence of high glucose leads to the activation of carbohydrate response element binding protein (ChREBP), a transcription factor that induces the expression of a number of glycolytic and lipogenic enzymes. ChREBP is expressed in major metabolic tissues and while we have a basic understanding of ChREBP function in liver, in vivo genetic systems to study the function of ChREBP in other tissues are lacking. In this study, we characterized the role of the Drosophila homolog of ChREBP, Mlx interactor (Mio), in controlling fat accumulation in larvae and adult flies. In Mio mutants, high sugar-induced lipogenic enzyme mRNA expression is blunted and lowering Mio levels specifically in the fat body using RNA interference leads to a lean phenotype. A lean phenotype is also observed when the gene bigmax, the fly homolog of ChREBPs binding partner Mlx, is decreased in the larval fat body. Interestingly, depleting Mio in the fat body results in decreased feeding providing a potential cause of the lowered triglycerides observed in these animals. However, Mio does not seem to function as a general regulator of hunger-induced behaviors as decreasing fat body Mio levels has no effect on sleep under fed or starved conditions. Together, these data implicate a role for Mio in controlling fat accumulation in Drosophila and suggests that it may act as a nutrient sensor in the fat body to coordinate feeding behavior with nutrient availability.

translin Is Required for Metabolic Regulation of Sleep

Dysregulation of sleep or feeding has enormous health consequences. In humans, acute sleep loss is associated with increased appetite and insulin insensitivity, while chronically sleep-deprived individuals are more likely to develop obesity, metabolic syndrome, type II diabetes, and cardiovascular disease. Conversely, metabolic state potently modulates sleep and circadian behavior; yet, the molecular basis for sleep-metabolism interactions remains poorly understood. Here, we describe the identification of translin (trsn), a highly conserved RNA/DNA binding protein, as essential for starvation-induced sleep suppression. Strikingly, trsn does not appear to regulate energy stores, free glucose levels, or feeding behavior suggesting the sleep phenotype of trsn mutant flies is not a consequence of general metabolic dysfunction or blunted response to starvation. While broadly expressed in all neurons, trsn is transcriptionally upregulated in the heads of flies in response to starvation. Spatially restricted rescue or targeted knockdown localizes trsn function to neurons that produce the tachykinin family neuropeptide Leucokinin. Manipulation of neural activity in Leucokinin neurons revealed these neurons to be required for starvation-induced sleep suppression. Taken together, these findings establish trsn as an essential integrator of sleep and metabolic state, with implications for understanding the neural mechanism underlying sleep disruption in response to environmental perturbation.

A Central Support System Can Facilitate Implementation and Sustainability of a Classroom-Based Undergraduate Research Experience (CURE) in Genomics

There have been numerous calls to engage students in science as science is done. A survey of 90-plus faculty members explores barriers and incentives when developing a research-based genomics course. The results indicate that a central core supporting a national experiment can help overcome local obstacles.

The central clock neurons regulate lipid storage in Drosophila.

A proper balance of lipid breakdown and synthesis is essential for achieving energy homeostasis as alterations in either of these processes can lead to pathological states such as obesity. The regulation of lipid metabolism is quite complex with multiple signals integrated to control overall triglyceride levels in metabolic tissues. Based upon studies demonstrating effects of the circadian clock on metabolism, we sought to determine if the central clock cells in the Drosophila brain contribute to lipid levels in the fat body, the main nutrient storage organ of the fly. Here, we show that altering the function of the Drosophila central clock neurons leads to an increase in fat body triglycerides. We also show that although triglyceride levels are not affected by age, they are increased by expression of the amyloid-beta protein in central clock neurons. The effect on lipid storage seems to be independent of circadian clock output as changes in triglycerides are not always observed in genetic manipulations that result in altered locomotor rhythms. These data demonstrate that the activity of the central clock neurons is necessary for proper lipid storage.

Genetic dissection of sleep-metabolism interactions in the fruit fly.

Dysregulation of sleep and metabolism has enormous health consequences. Sleep loss is linked to increased appetite and insulin insensitivity, and epidemiological studies link chronic sleep deprivation to obesity-related disorders including type II diabetes and cardiovascular disease. Interactions between sleep and metabolism involve the integration of signaling from brain regions regulating sleep, feeding, and metabolic function. Investigating the relationship between these processes provides a model to address more general questions of how the brain prioritizes homeostatically regulated behaviors. The availability of powerful genetic tools in the fruit fly, Drosophila melanogaster, allows for precise manipulation of neural function in freely behaving animals. There is a strong conservation of genes and neural circuit principles regulating sleep and metabolic function, and genetic screens in fruit flies have been effective in identifying novel regulators of these processes. Here, we review recent findings in the fruit fly that further our understanding of how the brain modulates sleep in accordance with metabolic state.

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

Animals recognize the availability of nutrients and regulate the intake and storage of these nutrients accordingly. However, the molecular mechanisms underlying nutrient sensing and subsequent changes in behavior and metabolism are not fully understood. Mlx interactor (Mio), the Drosophila homolog of carbohydrate response element binding protein (ChREBP), functions as a transcription factor in the fat body of the fly to control triglyceride storage as well as feeding, suggesting that Mio may act in a nutrient-sensing pathway to coordinate food consumption and metabolism. Here, we show that Mio functions in neurons in Drosophila to regulate feeding and nutrient storage. Pan-neuronal disruption of Mio function leads to increased triglyceride and glycogen storage, and this phenotype is not due to increased food consumption. Interestingly, targeted disruption of Mio specifically in the insulin-producing cells (IPCs) has little effect on nutrient storage, but increases food consumption suggesting that Mio acts in these neurons to control feeding behavior. Since Mio is a transcription factor, one possible way Mio may act in the IPCs to control feeding is through regulating the expression of Drosophila insulin-like peptides (dilps) or drosulfakinin (dsk), neuropeptides produced in the IPCs. Consistent with this hypothesis, IPC-specific knockdown of Mio leads to an increase in dilp3 expression, while not affecting dilp2, 5 or dsk levels. Together, this study indicates a new function for Mio in the Drosophila brain and specifically in the IPCs, controlling neuropeptide gene expression, feeding and metabolism in accordance with nutrient availability.