Long-term consumption of fatty foods is associated with obesity, macrophage activation and inflammation, metabolic imbalance, and a reduced lifespan. We took advantage of Drosophila genetics to ...investigate the role of macrophages and the pathway(s) that govern their response to dietary stress. Flies fed a lipid-rich diet presented with increased fat storage, systemic activation of JAK-STAT signaling, reduced insulin sensitivity, hyperglycemia, and a shorter lifespan. Drosophila macrophages produced the JAK-STAT-activating cytokine upd3, in a scavenger-receptor (crq) and JNK-dependent manner. Genetic depletion of macrophages or macrophage-specific silencing of upd3 decreased JAK-STAT activation and rescued insulin sensitivity and the lifespan of Drosophila, but did not decrease fat storage. NF-κB signaling made no contribution to the phenotype observed. These results identify an evolutionarily conserved “scavenger receptor-JNK-type 1 cytokine” cassette in macrophages, which controls glucose metabolism and reduces lifespan in Drosophila maintained on a lipid-rich diet via activation of the JAK-STAT pathway.
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•Chronic lipid-rich diet results in JAK-STAT activation in Drosophila•Chronic JAK-STAT activation reduces lifespan and insulin sensitivity•Lipid-rich diet induces JNK pathway-dependent production of upd3 by macrophages•Macrophage upd3 controls JAK-STAT activation, survival, and insulin sensitivity
Consumption of fatty foods is associated across species with inflammation, metabolic imbalance, and reduced lifespan. Woodcock et al. use Drosophila fed a lipid-rich diet to demonstrate that an evolutionarily conserved “scavenger receptor-JNK-type 1 cytokine” cassette in macrophages controls glucose metabolism and reduces lifespan via activation of the JAK-STAT pathway.
Host behavioural changes are among the most apparent effects of infection. ‘Sickness behaviour’ can involve a variety of symptoms, including anorexia, depression, and changed activity levels. Here, ...using a real-time tracking and behavioural profiling platform, we show that in
Drosophila melanogaster
, several systemic bacterial infections cause significant increases in physical activity, and that the extent of this activity increase is a predictor of survival time in some lethal infections. Using multiple bacteria and
D
.
melanogaster
immune and activity mutants, we show that increased activity is driven by at least two different mechanisms. Increased activity after infection with
Micrococcus luteus
, a Gram-positive bacterium rapidly cleared by the immune response, strictly requires the
Toll
ligand
spätzle
. In contrast, increased activity after infection with
Francisella novicida
, a Gram-negative bacterium that cannot be cleared by the immune response, is entirely independent of both Toll and the parallel IMD pathway. The existence of multiple signalling mechanisms by which bacterial infections drive increases in physical activity implies that this effect may be an important aspect of the host response.
Drosophila melanogaster, like other invertebrates, relies solely on its innate immune response to fight invading microbes; by definition, innate immunity lacks adaptive characteristics. However, we ...show here that priming Drosophila with a sublethal dose of Streptococcus pneumoniae protects against an otherwise-lethal second challenge of S. pneumoniae. This protective effect exhibits coarse specificity for S. pneumoniae and persists for the life of the fly. Although not all microbial challenges induced this specific primed response, we find that a similar specific protection can be elicited by Beauveria bassiana, a natural fly pathogen. To characterize this primed response, we focused on S. pneumoniae-induced protection. The mechanism underlying this protective effect requires phagocytes and the Toll pathway. However, activation of the Toll pathway is not sufficient for priming-induced protection. This work contradicts the paradigm that insect immune responses cannot adapt and will promote the search for similar responses overlooked in organisms with an adaptive immune response.
Infections disturb metabolic homeostasis in many contexts, but the underlying connections are not completely understood. To address this, we use paired genetic and computational screens in Drosophila ...to identify transcriptional regulators of immunity and pathology and their associated target genes and physiologies. We show that Mef2 is required in the fat body for anabolic function and the immune response. Using genetic and biochemical approaches, we find that MEF2 is phosphorylated at a conserved site in healthy flies and promotes expression of lipogenic and glycogenic enzymes. Upon infection, this phosphorylation is lost, and the activity of MEF2 changes—MEF2 now associates with the TATA binding protein to bind a distinct TATA box sequence and promote antimicrobial peptide expression. The loss of phosphorylated MEF2 contributes to loss of anabolic enzyme expression in Gram-negative bacterial infection. MEF2 is thus a critical transcriptional switch in the adult fat body between metabolism and immunity.
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•Mef2 is required in Drosophila for immune function and storage of fat and glycogen•MEF2 is phosphorylated in vivo at a conserved site (T20) to promote anabolism•Infection reduces phospho-T20, allowing MEF2 to bind TBP and an immune TATA box•MEF2 dephosphorylation leads to metabolic dysfunction in Gram-negative infection
The transcription factor MEF2 acts as a central switch between metabolic and immune functions in Drosophila, shifting upon infection from activation of anabolic enzymes to immune response genes.
Male and female animals exhibit differences in infection outcomes. One possible source of sexually dimorphic immunity is the sex-specific costs of immune activity or pathology, but little is known ...about the independent effects of immune- versus microbe-induced pathology and whether these may differ for the sexes. Here, by measuring metabolic and physiological outputs in
with wild-type and mutant immune responses, we test whether the sexes are differentially impacted by these various sources of pathology and identify a critical regulator of this difference. We find that the sexes exhibit differential immune activity but similar bacteria-derived metabolic pathology. We show that female-specific immune-inducible expression of
, a negative regulator of the immune deficiency (IMD) pathway, enables females to reduce immune activity in response to reductions in bacterial numbers. In the absence of
, females are more resistant to infection, confirming the functional importance of this regulation and suggesting that female-biased immune restriction comes at a cost.
Animal models have played an essential role in understanding the host–pathogen interactions of pathogenic mycobacteria, including the Mycobacterium tuberculosis and emerging nontuberculous ...mycobacteria (NTM) species such as M. avium and M. abscessus. Drosophila melanogaster has become a well‐established model for the study of innate immunity and is increasingly being used as a tool to study host–pathogen interactions, in part due to its genetic tractability. The use of D. melanogaster has led to greater understanding of the role of the innate immune system in response to mycobacterial infection, including in vitro RNAi screens and in vivo studies. These studies have identified processes and host factors involved in mycobacterial infection, such as those required for cellular entry, those required to control or resist non‐pathogenic mycobacteria, or factors that become dysregulated as a result of mycobacterial infection. Developments in genetic tools for manipulating mycobacterial genomes will allow for more detailed studies into how specific host and pathogen factors interact with one another by using D. melanogaster; however, the full potential of this model has not yet been reached. Here we provide an overview of how D. melanogaster has been used to study mycobacterial infection and discuss the current gaps in our understanding.
Summary of progression of Mycobacterium marinum infection in Drosophila melanogaster. M. marinum is widely used to study the host‐pathogen interactions of M. tuberculosis and other nontuberculous mycobacteria using the D. melanogaster model host organism. At the initial stage of infection, M. marinum is phagocytosed by circulating haemocytes. During the infection, M. marinum blocks phagosomal maturation and begins to replicate intracellularly within the haemocytes. Eventually, M. marinum causes lysis of haemocytes, which is followed by rapid death of the D. melanogaster. Produced in BioRender.
TGF-β superfamily signals play complex roles in regulation of tissue repair and inflammation in mammals 1. Drosophila melanogaster is a well-established model for the study of innate immune function ...2, 3 and wound healing 4–7. Here, we explore the role and regulation of two TGF-β superfamily members, dawdle and decapentaplegic (dpp), in response to wounding and infection in adult Drosophila. We find that both TGF-β signals exhibit complex regulation in response to wounding and infection, each is expressed in a subset of phagocytes, and each inhibits a specific arm of the immune response. dpp is rapidly activated by wounds and represses the production of antimicrobial peptides; flies lacking dpp function display persistent, strong antimicrobial peptide expression after even a small wound. dawdle, in contrast, is activated by Gram-positive bacterial infection but repressed by Gram-negative infection or wounding; its role is to limit infection-induced melanization. Flies lacking dawdle function exhibit melanization even when uninfected. Together, these data imply a model in which the bone morphogenetic protein (BMP) dpp is an important inhibitor of inflammation following sterile injury whereas the activin-like dawdle determines the nature of the induced immune response.
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► BMP and activin signals respond differently to wound- or infection-induced cues ► BMP and activin signals repress different branches of the fly immune response ► These signals are expressed by subsets of hemocytes
Macrophages play important immune and homeostatic roles that depend on the ability to receive and interpret specific signals from environmental stimuli. Here we describe the different activation ...states these cells can exhibit in response to signals and how these states affect and can be affected by bacterial pathogens.
Macrophages play important immune and homeostatic roles that depend on the ability to receive and interpret specific signals from environmental stimuli. Here we describe the different activation states these cells can exhibit in response to signals and how these states affect and can be affected by bacterial pathogens.
Invasive bacteria enter the cytosol of host cells through initial uptake into bacteria‐containing vacuoles (BCVs) and subsequent rupture of the BCV membrane, thereby exposing to the cytosol ...intraluminal, otherwise shielded danger signals such as glycans and sphingomyelin. The detection of glycans by galectin‐8 triggers anti‐bacterial autophagy, but how cells sense and respond to cytosolically exposed sphingomyelin remains unknown. Here, we identify TECPR1 (tectonin beta‐propeller repeat containing 1) as a receptor for cytosolically exposed sphingomyelin, which recruits ATG5 into an E3 ligase complex that mediates lipid conjugation of LC3 independently of ATG16L1. TECPR1 binds sphingomyelin through its N‐terminal DysF domain (N'DysF), a feature not shared by other mammalian DysF domains. Solving the crystal structure of N'DysF, we identified key residues required for the interaction, including a solvent‐exposed tryptophan (W154) essential for binding to sphingomyelin‐positive membranes and the conjugation of LC3 to lipids. Specificity of the ATG5/ATG12‐E3 ligase responsible for the conjugation of LC3 is therefore conferred by interchangeable receptor subunits, that is, the canonical ATG16L1 and the sphingomyelin‐specific TECPR1, in an arrangement reminiscent of certain multi‐subunit ubiquitin E3 ligases.
Synopsis
Upon damage to bacteria‐containing vacuoles sphingomyelin transits from the luminal to the cytosolic face of the membrane. Here we show that TECPR1 detects cytosolically exposed sphingomyelin and directs conjugation of the autophagy effector protein LC3 to those membranes.
TECPR1 is a novel danger receptor that detects sphingomyelin exposed on the cytosolic face of damaged membranes.
The N‐terminal DysF domain of TECPR1 binds sphingomyelin and recruits TECPR1 to damaged membranes.
TECPR1 recruits ATG5 to sphingomyelin‐positive membranes.
The TECPR1‐ATG5‐ATG12 complex is a sphingomyelin‐activated E3 ligase catalyzing the lipid conjugation of LC3.
TECPR1 detects cytosolically‐exposed sphingomyelin and recruits ATG5/ATG12‐E3 ligase to damaged membranes to mediate lipid conjugation of LC3 independently of ATG16L.
The activation of the immune system upon infection exerts a huge energetic demand on an individual, likely decreasing available resources for other vital processes, like reproduction. The factors ...that determine the trade-off between defensive and reproductive traits remain poorly understood. Here, we exploit the experimental tractability of the fruit fly
to systematically assess the impact of immune system activation on pre-copulatory reproductive behaviour. Contrary to expectations, we found that male flies undergoing an immune activation continue to display high levels of courtship and mating success. Similarly, immune-challenged female flies remain highly sexually receptive. By combining behavioural paradigms, a diverse panel of pathogens and genetic strategies to induce the fly immune system, we show that pre-copulatory reproductive behaviours are preserved in infected flies, despite the significant metabolic cost of infection.
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