Intestinal FoxO signaling is required to survive oral infection in Drosophila

Differential expression of sNPF in male and female eyestalk leading to sex dimorphism of AMP expression in Procambarus clarkii intestine

Antimicrobial peptide (AMP) is an important component of crustaceans' innate immune system. In this study, a short neuropeptide F (sNPF) gene (Pc-sNPF) and a Forkhead box O (FOXO) gene (PcFOXO) from Procambarus clarkii were identified. Analysis findings showed that the expression level of AMP genes differed between male and female P. clarkii. Furthermore, Pc-sNPF and PcFOXO were related to the sex dimorphism of AMP. Knockdown of Pc-sNPF in the eyestalk significantly upregulated the expression of PcFOXO and two anti-lipopolysaccharide factors (PcALF4 and PcALFL) in the intestine of P. clarkii. The expression of PcFOXO in the intestine of female P. clarkii was higher than in that of males. Results from RNA interference revealed that PcFOXO positively regulated the expression of PcALF4 and PcALFL in the intestine of male and female P. clarkii. In summary, our study showed that differences in Pc-sNPF expression in eyestalk of male and female P. clarkii leading to sex dimorphism of AMP expression in the intestine are mediated by the sNPF-FOXO-AMP signal pathway called the eyestalk-intestine axis.

Cellular and molecular organization of the Drosophila foregut

The animal foregut is the first tissue to encounter ingested food, bacteria, and viruses. We characterized the adult Drosophila foregut using transcriptomics to better understand how it triages consumed items for digestion or immune response and manages resources. Cell types were assigned and validated using GFP-tagged and Gal4 reporter lines. Foregut-associated neuroendocrine cells play a major integrative role by coordinating gut activity with nutrition, the microbiome, and circadian cycles; some express clock genes. Multiple epithelial cell types comprise the proventriculus, the central foregut organ that secretes the peritrophic matrix (PM) lining the gut. Analyzing cell types synthesizing individual PM layers revealed abundant mucin production close to enterocytes, similar to the mammalian intestinal mucosa. The esophagus and salivary gland express secreted proteins likely to line the esophageal surface, some of which may generate a foregut commensal niche housing specific gut microbiome species. Overall, our results imply that the foregut coordinates dietary sensing, hormonal regulation, and immunity in a manner that has been conserved during animal evolution.

White spot syndrome virus hijacks host PP2A-FOXO axes to promote its propagation

Viruses have developed superior strategies to escape host defenses or exploit host components and enable their infection. The forkhead box transcription factor O family proteins (FOXOs) are reportedly utilized by human cytomegalovirus during their reactivation in mammals, but if FOXOs are exploited by viruses during their infection remains unclear. In the present study, we found that the FOXO of kuruma shrimp (Marsupenaeus japonicus) was hijacked by white spot syndrome virus (WSSV) during infection. Mechanistically, the expression of leucine carboxyl methyl transferase 1 (LCMT1) was up-regulated during the early stages of WSSV infection, which activated the protein phosphatase 2A (PP2A) by methylation, leading to dephosphorylation of FOXO and translocation into the nucleus. The FOXO directly promoted transcription of the immediate early gene, wsv079 of WSSV, which functioned as a transcriptional activator to initiate the expression of viral early and late genes. Thus, WSSV utilized the host LCMT1-PP2A-FOXO axis to promote its replication during the early infection stage. We also found that, during the late stages of WSSV infection, the envelope protein of WSSV (VP26) promoted PP2A activity by directly binding to FOXO and the regulatory subunit of PP2A (B55), which further facilitated FOXO dephosphorylation and WSSV replication via the VP26-PP2A-FOXO axis in shrimp. Overall, this study reveals novel viral strategies by which WSSV hijacks host LCMT1-PP2A-FOXO or VP26-PP2A-FOXO axes to promote its propagation, and provides clinical targets for WSSV control in shrimp aquaculture.

FOXO is involved in antimicrobial peptides expression during WSSV infection in Exopalaemon carinicauda

The forkhead box transcription factor O family protein (FOXO) acts as a transcription factor that regulates biological processes regarding DNA repair, immunity, cell cycle regulation, and other biological processes. In this study, EcFOXO was identified from the ridgetail white prawn, Exopalaemon carinicauda. EcFOXO protein contains multiple low-complexity regions and a forkhead (FH) domain. Phylogenetic tree showed that EcFOXO is clustered with crustacean FOXOs. The amino acid sequences of its FH domain are highly similar to the FH domain of FOXOs from other crustaceans. The expression of EcFOXO is altered after white spot syndrome virus (WSSV) stimulation in hepatopancreas and gills. The relationship between EcFOXO and EcRelish was explored by RNA interference (RNAi). Results showed that EcFOXO and EcRelish could positively regulate each other's expression. The expression levels of various antimicrobial peptides (AMPs) significantly reduced after interfering with EcFOXO or EcRelish. These results suggest a positive regulatory loop between EcFOXO and EcRelish, which participates in the innate immunity of ridgetail white prawn by regulating the expression of AMPs during WSSV infection. This study enriches the knowledge about the regulatory mechanism of FOXO in the innate immunity of crustaceans.

Experimental validation and characterization of putative targets of Escargot and STAT, two master regulators of the intestinal stem cells in Drosophila melanogaster

Many organs contain adult stem cells (ASCs) to replace cells due to damage, disease, or normal tissue turnover. ASCs can divide asymmetrically, giving rise to a new copy of themselves (self-renewal) and a sister that commits to a specific cell type (differentiation). Decades of research have led to the identification of pleiotropic genes whose loss or gain of function affect diverse aspects of normal ASC biology. Genome-wide screens of these so-called genetic "master regulator" (MR) genes, have pointed to hundreds of putative targets that could serve as their downstream effectors. Here, we experimentally validate and characterize the regulation of several putative targets of Escargot (Esg) and the Signal Transducer and Activator of Transcription (Stat92E, a.k.a. STAT), two known MRs in Drosophila intestinal stem cells (ISCs). Our results indicate that regardless of bioinformatic predictions, most experimentally validated targets show a profile of gene expression that is consistent with co-regulation by both Esg and STAT, fitting a rather limited set of co-regulatory modalities. A bioinformatic analysis of proximal regulatory sequences in specific subsets of co-regulated targets identified additional transcription factors that might cooperate with Esg and STAT in modulating their transcription. Lastly, in vivo manipulations of validated targets rarely phenocopied the effects of manipulating Esg and STAT, suggesting the existence of complex genetic interactions among downstream targets of these two MR genes during ISC homeostasis.

The intricate triangular interaction between protective microbe, pathogen and host determines fitness of the metaorganism

The microbiota shapes host biology in numerous ways. One example is protection against pathogens, which is likely critical for host fitness in consideration of the ubiquity of pathogens. The host itself can affect abundance of microbiota or pathogens, which has usually been characterized in separate studies. To date, however, it is unclear how the host influences the interaction with both simultaneously and how this triangular interaction determines fitness of the host-microbe assemblage, the so-called metaorganism. To address this current knowledge gap, we focused on a triangular model interaction, consisting of the nematode Caenorhabditis elegans, its protective symbiont Pseudomonas lurida MYb11 and its pathogen Bacillus thuringiensis Bt679. We combined the two microbes with C. elegans mutants with altered immunity and/or microbial colonization, and found that (i) under pathogen stress, immunocompetence has a larger influence on metaorganism fitness than colonization with the protective microbe; (ii) in almost all cases, MYb11 still improves fitness; and (iii) disruption of p38 MAPK signalling, which contributes centrally to immunity against Bt679, completely reverses the protective effect of MYb11, which further reduces nematode survival and fitness upon infection with Bt679. Our study highlights the complex interplay between host, protective microbe and pathogen in shaping metaorganism biology.

Interactions between innate immunity and insulin signaling affect resistance to infection in insects

An active immune response is energetically demanding and requires reallocation of nutrients to support resistance to and tolerance of infection. Insulin signaling is a critical global regulator of metabolism and whole-body homeostasis in response to nutrient availability and energetic needs, including those required for mobilization of energy in support of the immune system. In this review, we share findings that demonstrate interactions between innate immune activity and insulin signaling primarily in the insect model Drosophila melanogaster as well as other insects like Bombyx mori and Anopheles mosquitos. These studies indicate that insulin signaling and innate immune activation have reciprocal effects on each other, but that those effects vary depending on the type of pathogen, route of infection, and nutritional status of the host. Future research will be required to further understand the detailed mechanisms by which innate immunity and insulin signaling activity impact each other.

Gut barrier defects, intestinal immune hyperactivation and enhanced lipid catabolism drive lethality in NGLY1-deficient Drosophila

Intestinal barrier dysfunction leads to inflammation and associated metabolic changes. However, the relative impact of gut bacteria versus non-bacterial insults on animal health in the context of barrier dysfunction is not well understood. Here, we establish that loss of Drosophila N-glycanase 1 (Pngl) in a specific intestinal cell type leads to gut barrier defects, causing starvation and JNK overactivation. These abnormalities, along with loss of Pngl in enterocytes and fat body, result in Foxo overactivation, leading to hyperactive innate immune response and lipid catabolism and thereby contributing to lethality. Germ-free rearing of Pngl mutants rescued their developmental delay but not lethality. However, raising Pngl mutants on isocaloric, fat-rich diets partially rescued lethality. Our data indicate that Pngl functions in Drosophila larvae to establish the gut barrier, and that the lethality caused by loss of Pngl is primarily mediated through non-bacterial induction of immune and metabolic abnormalities.

Sugar restriction and blood ingestion shape divergent immune defense trajectories in the mosquito Aedes aegypti

Immune defense is comprised of (1) resistance: the ability to reduce pathogen load, and (2) tolerance: the ability to limit the disease severity induced by a given pathogen load. The study of tolerance in the field of animal immunity is fairly nascent in comparison to resistance. Consequently, studies which examine immune defense comprehensively (i.e. considering both resistance and tolerance in conjunction) are uncommon, despite their exigency in achieving a thorough understanding of immune defense. Furthermore, understanding tolerance in arthropod disease vectors is uniquely relevant, as tolerance is essential to the cyclical transmission of pathogens by arthropods. Here, we tested the effect(s) of dietary sucrose concentration and blood ingestion on resistance and tolerance to Escherichia coli infection in the yellow fever mosquito Aedes aegypti. Resistance and tolerance were measured concurrently and at multiple timepoints. We found that mosquitoes from the restricted sugar treatment displayed enhanced resistance at all timepoints post-infection compared to those from the laboratory standard sugar treatment. Blood also improved resistance, but only early post-infection. While sucrose restriction had no effect on tolerance, we show that consuming blood prior to bacterial infection ameliorates a temporal decline in tolerance that mosquitoes experience when provided with only sugar meals. Taken together, our findings indicate that different dietary components can have unique and sometimes temporally dynamic impacts on resistance and tolerance.

The tracheal immune system of insects - A blueprint for understanding epithelial immunity

The unique design of respiratory organs in multicellular organisms makes them prone to infection by pathogens. To cope with this vulnerability, highly effective local immune systems evolved that are also operative in the tracheal system of insects. Many pathogens and parasites (including viruses, bacteria, fungi, and metazoan parasites) colonize the trachea or invade the host via this route. Currently, only two modules of the tracheal immune system have been characterized in depth: 1) Immune deficiency pathway-mediated activation of antimicrobial peptide gene expression and 2) local melanization processes that protect the structure from wounding. There is an urgent need to increase our understanding of the architecture of tracheal immune systems, especially regarding those mechanisms that enable the maintenance of immune homeostasis. This need for new studies is particularly exigent for species other than Drosophila.

Gut barrier defects, increased intestinal innate immune response, and enhanced lipid catabolism drive lethality in N -glycanase 1 deficient Drosophila

Intestinal barrier dysfunction leads to inflammation and associated metabolic changes. However, the relative impact of infectious versus non-infectious mechanisms on animal health in the context of barrier dysfunction is not well understood. Here, we establish that loss of Drosophila N -glycanase 1 (Pngl) leads to gut barrier defects, which cause starvation and increased JNK activity. These defects result in Foxo overactivation, which induces a hyperactive innate immune response and lipid catabolism, thereby contributing to lethality associated with loss of Pngl . Notably, germ-free rearing of Pngl mutants did not rescue lethality. In contrast, raising Pngl mutants on isocaloric, fat-rich diets improved animal survival in a dosage-dependent manner. Our data indicate that Pngl functions in Drosophila larvae to establish the gut barrier, and that the immune and metabolic consequences of loss of Pngl are primarily mediated through non-infectious mechanisms.

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.

Unraveling the Role of Antimicrobial Peptides in Insects

Antimicrobial peptides (AMPs) are short, mainly positively charged, amphipathic molecules. AMPs are important effectors of the immune response in insects with a broad spectrum of antibacterial, antifungal, and antiparasitic activity. In addition to these well-known roles, AMPs exhibit many other, often unobvious, functions in the host. They support insects in the elimination of viral infections. AMPs participate in the regulation of brain-controlled processes, e.g., sleep and non-associative learning. By influencing neuronal health, communication, and activity, they can affect the functioning of the insect nervous system. Expansion of the AMP repertoire and loss of their specificity is connected with the aging process and lifespan of insects. Moreover, AMPs take part in maintaining gut homeostasis, regulating the number of endosymbionts as well as reducing the number of foreign microbiota. In turn, the presence of AMPs in insect venom prevents the spread of infection in social insects, where the prey may be a source of pathogens.

Hemocytes and fat body cells, the only professional immune cell types in Drosophila, show strikingly different responses to systemic infections

The fruit fly Drosophila is an excellent model to study the response of different immunocompetent organs during systemic infection. In the present study, we intended to test the hypothesis that the only professional immune organs of the fly, the fat body and hemocytes, show substantial similarities in their responses to systemic infection. However, comprehensive transcriptome analysis of isolated organs revealed highly divergent transcript signatures, with the few commonly regulated genes encoding mainly classical immune effectors from the antimicrobial peptide family. The fat body and the hemocytes each have specific reactions that are not present in the other organ. Fat body-specific responses comprised those enabling an improved peptide synthesis and export. This reaction is accompanied by transcriptomic shifts enabling the use of the energy resources of the fat body more efficiently. Hemocytes, on the other hand, showed enhanced signatures related to phagocytosis. Comparing immune-induced signatures of both cell types with those of whole-body responses showed only a minimal correspondence, mostly restricted again to antimicrobial peptide genes. In summary, the two major immunocompetent cell types of Drosophila show highly specific responses to infection, which are closely linked to the primary function of the respective organ in the landscape of the systemic immune response.

Small immune effectors coordinate peptidoglycan-derived immunity to regulate intestinal bacteria in shrimp

Small antibacterial effectors, including lysozymes, lectins, and antimicrobial peptides, are key regulators of intestinal immunity. However, whether there is coordination among them during regulation is an interesting, but largely unknown, issue. In the present study, we revealed that small effectors synergistically regulate peptidoglycan-derived intestinal immunity in the kuruma shrimp, Marsupenaeus japonicus. A C-type lysozyme (LysC) was screened as a responsive factor for the intestine-bacteria interaction. LysC functions to restrict intestinal bacteria, mainly by cleaving Photobacterium damselae peptidoglycan to generate muropeptides which are powerful stimulators that induce anti-lipopolysaccharides factor B1 (AlfB1), an effective bactericidal peptide. The muropeptides also induce a C-type lectin (Ctl24), which recognizes peptidoglycan and coats bacteria. By counteracting LysC-mediated muropeptide release and AlfB1's bactericidal activity, Ctl24 prevents the continuous elimination of intestinal bacteria. Therefore, this study demonstrates a mechanism by which small immune effectors coordinate to achieve intestinal homeostasis, and provides new insights into peptidoglycan-derived intestinal immunity in invertebrates.

Airway remodeling: The Drosophila model permits a purely epithelial perspective

Airway remodeling is an umbrella term for structural changes in the conducting airways that occur in chronic inflammatory lung diseases such as asthma or chronic obstructive pulmonary disease (COPD). The pathobiology of remodeling involves multiple mesenchymal and lymphoid cell types and finally leads to a variety of hardly reversible changes such as hyperplasia of goblet cells, thickening of the reticular basement membrane, deposition of collagen, peribronchial fibrosis, angiogenesis and hyperplasia of bronchial smooth muscle cells. In order to develop solutions for prevention or innovative therapies, these complex processes must be understood in detail which requires their deconstruction into individual building blocks. In the present manuscript we therefore focus on the role of the airway epithelium and introduce Drosophila melanogaster as a model. The simple architecture of the flies’ airways as well as the lack of adaptive immunity allows to focus exclusively on the importance of the epithelium for the remodeling processes. We will review and discuss genetic and environmentally induced changes in epithelial structures and molecular responses and propose an integrated framework of research for the future.

The forkhead box O transcription factor regulates lipase and anti-microbial peptide expressions to promote lipid catabolism and improve innate immunity in the Eriocheir sinensis with hepatopancreatic necrosis disease

Eriocheir sinensis is a crustacean with great economic value, but the occurrence of hepatopancreatic necrosis disease (HPND) severely restricts the development of crab aquaculture. Study on the survival mechanism of crabs with HPND is beneficial to provide new strategies for disease prevention and control. The Forkhead box O (FOXO) transcription factor family is involved in various key biological processes of organisms. In this study, a FOXO gene (named as EsFOXO) from E. sinensis was cloned. The full-length cDNA of EsFOXO is 2592 bp containing a 2133 bp open reading frame that encodes 710 amino acids. EsFOXO was widely distributed in multiple immune tissues. Further study found that the expression of EsFOXO in the intestine of crabs with HPND was significantly upregulated compared with that in the normal crabs. However, whether EsFOXO is involved in the immune and metabolic regulation of crabs remains unknown. RNA interference analysis showed that EsFOXO participates in the positive regulation of the expression of two pancreatic lipases, three anti-lipopolysaccharide factors, and three crustins. Results from our research suggest that two strategies are adopted by crabs with HPND for survival under starvation: on the one hand, the synthesis of antimicrobial peptides is increased to improve the innate immunity; on the other hand, the expression of enzymes correlated with lipid catabolism is up-regulated that mobilizes the fat in the crab, going through catabolism. Our study provides more evidence for an in-depth understanding of the survival mechanism of crabs with HPND.

Modulation of the cell membrane lipid milieu by peroxisomal β-oxidation induces Rho1 signaling to trigger inflammatory responses

Phagocytosis, signal transduction, and inflammatory responses require changes in lipid metabolism. Peroxisomes have key roles in fatty acid homeostasis and in regulating immune function. We find that Drosophila macrophages lacking peroxisomes have perturbed lipid profiles, which reduce host survival after infection. Using lipidomic, transcriptomic, and genetic screens, we determine that peroxisomes contribute to the cell membrane glycerophospholipid composition necessary to induce Rho1-dependent signals, which drive cytoskeletal remodeling during macrophage activation. Loss of peroxisome function increases membrane phosphatidic acid (PA) and recruits RhoGAPp190 during infection, inhibiting Rho1-mediated responses. Peroxisome-glycerophospholipid-Rho1 signaling also controls cytoskeleton remodeling in mouse immune cells. While high levels of PA in cells without peroxisomes inhibit inflammatory phenotypes, large numbers of peroxisomes and low amounts of cell membrane PA are features of immune cells from patients with inflammatory Kawasaki disease and juvenile idiopathic arthritis. Our findings reveal potential metabolic markers and therapeutic targets for immune diseases and metabolic disorders.

Unraveling the innate immune responses of Bombyx mori hemolymph, fat body, and midgut to Bombyx mori nucleopolyhedrovirus oral infection by metabolomic analysis

Bombyx mori nucleopolyhedrovirus (BmNPV) infection causes a series of physiological and pathological changes in Bombyx mori (B. mori). Here, a metabolomic study of the innate immunity organs including hemolymph, fat body, and midgut of the silkworm strain Dazao following BmNPV challenge was conducted to reveal the metabolic variations in B. mori. Compared to the control, 4964 and 4942 features with 4077 and 4327 high-quality features were generated under positive and negative modes, respectively, from BmNPV-infected larvae. The principal component analysis and supervised learning method using partial least squares discrimination analysis demonstrated good analytical stability and experimental reproducibility of the metabolic profiles. Based on database annotations, a total of 296, 108, and 215 differential expressed metabolites (DEMs) were identified from BmNPV-infected group of hemolymph, fat body, and midgut, respectively, which were all mainly grouped into carboxylic acids and derivatives, fatty acyls, and glycerophospholipids. Kyoto Encyclopedia of Genes and Genomes Database enrichment analysis of the DEMs showed that amino acid metabolism was increased at 24 h after BmNPV infection. BmNPV induction was adopted to significantly alter a series of immune-related pathways including phospholipase D signaling pathway, FoxO signaling pathway, metabolism of xenobiotics by cytochrome P450, melanogenesis, membrane transport, carbohydrate metabolism, and lipid metabolism. The different levels of expression of several DEMs including l-glutamate, naphthalene, 3-succinoylpyridine 1-acyl-sn-glycerol 3-phosphate, and l-tyrosine which were involved in those pathways exhibited the immune responses of B. mori to BmNPV infection. Our findings are valuable for a better understanding of the antiviral mechanism of B. mori underlying the interaction between the silkworm and BmNPV.

Proto-pyroptosis: An Ancestral Origin for Mammalian Inflammatory Cell Death Mechanism in Drosophila melanogaster

Pyroptosis has been described in mammalian systems to be a form of programmed cell death that is important in immune function through the subsequent release of cytokines and immune effectors upon cell bursting. This form of cell death has been increasingly well-characterized in mammals and can occur using alternative routes however, across phyla, there has been little evidence for the existence of pyroptosis. Here we provide evidence for an ancient origin of pyroptosis in an in vivo immune scenario in Drosophila melanogaster. Crystal cells, a type of insect blood cell, were recruited to wounds and ruptured subsequently releasing their cytosolic content in a caspase-dependent manner. This inflammatory-based programmed cell death mechanism fits the features of pyroptosis, never before described in an in vivo immune scenario in insects and relies on ancient apoptotic machinery to induce proto-pyroptosis. Further, we unveil key players upstream in the activation of cell death in these cells including the apoptosome which may play an alternative role akin to the inflammasome in proto-pyroptosis. Thus, Drosophila may be a suitable model for studying the functional significance of pyroptosis in the innate immune system.

Functional conservation in genes and pathways linking ageing and immunity

At first glance, longevity and immunity appear to be different traits that have not much in common except the fact that the immune system promotes survival upon pathogenic infection. Substantial evidence however points to a molecularly intertwined relationship between the immune system and ageing. Although this link is well-known throughout the animal kingdom, its genetic basis is complex and still poorly understood. To address this question, we here provide a compilation of all genes concomitantly known to be involved in immunity and ageing in humans and three well-studied model organisms, the nematode worm Caenorhabditis elegans, the fruit fly Drosophila melanogaster, and the house mouse Mus musculus. By analysing human orthologs among these species, we identified 7 evolutionarily conserved signalling cascades, the insulin/TOR network, three MAPK (ERK, p38, JNK), JAK/STAT, TGF-β, and Nf-κB pathways that act pleiotropically on ageing and immunity. We review current evidence for these pathways linking immunity and lifespan, and their role in the detrimental dysregulation of the immune system with age, known as immunosenescence. We argue that the phenotypic effects of these pathways are often context-dependent and vary, for example, between tissues, sexes, and types of pathogenic infection. Future research therefore needs to explore a higher temporal, spatial and environmental resolution to fully comprehend the connection between ageing and immunity.

The Impact of Age on Response to Infection in Drosophila

This review outlines the known cellular pathways and mechanisms involved in Drosophila age-dependent immunity to pathogenic microorganisms such as bacteria and fungi. We discuss the implication of host signaling pathways such as the Toll, Immune Deficiency (IMD), Janus kinase signal transducer and activator of transcription (JAK/STAT), and Insulin/Insulin Growth Factor/Target of Rapamycin (IIS/TOR) on immune function with aging. Additionally, we review the effects that factors such as sexual dimorphism, environmental stress, and cellular physiology exert on age-dependent immunity in Drosophila. We discuss potential tradeoffs between heightened immune function and longevity in the absence of infection, and we provide detailed tables outlining the various assays and pathogens used in the cited studies, as well as the age, sex, and strains of Drosophila used. We also discuss the overlapping effects these pathways and mechanisms have on one another. We highlight the great utility of Drosophila as a model organism and the importance of a greater focus on age-dependent antiviral immunity for future studies.

Regulatory mechanisms of microbial homeostasis in insect gut

Insects live in incredibly complex environments. The intestinal epithelium of insects is in constant contact with microorganisms, some of which are beneficial and some harmful to the host. Insect gut health and function are maintained through multidimensional mechanisms that can proficiently remove foreign pathogenic microorganisms while effectively maintaining local symbiotic microbial homeostasis. The basic immune mechanisms of the insect gut, such as the dual oxidase-reactive oxygen species (Duox-ROS) system and the immune deficiency (Imd)-signaling pathway, are involved in the maintenance of microbial homeostasis. This paper reviews the role of physical defenses, the Duox-ROS and Imd signaling pathways, the Janus kinase/signal transducers and activators of transcription signaling pathway, and intestinal symbiotic flora in the homeostatic maintenance of the insect gut microbiome.

FOXO regulates the expression of antimicrobial peptides and promotes phagocytosis of hemocytes in shrimp antibacterial immunity

Invertebrates rely on innate immunity, including humoral and cellular immunity, to resist pathogenic infection. Previous studies showed that forkhead box transcription factor O (FOXO) participates in mucosal immune responses of mammals and the gut humoral immune regulation of invertebrates. However, whether FOXO is involved in systemic and cellular immunity regulation in invertebrates remains unknown. In the present study, we identified a FOXO from shrimp (Marsupenaeus japonicus) and found that it was expressed at relatively basal levels in normal shrimp, but was upregulated significantly in shrimp challenged by Vibrio anguillarum. FOXO played a critical role in maintaining hemolymph and intestinal microbiota homeostasis by promoting the expression of Relish, the transcription factor of the immune deficiency (IMD) pathway for expression of antimicrobial peptides (AMPs) in shrimp. We also found that pathogen infection activated FOXO and induced its nuclear translocation by reducing serine/threonine kinase AKT activity. In the nucleus, activated FOXO directly regulated the expression of its target Amp and Relish genes against bacterial infection. Furthermore, FOXO was identified as being involved in cellular immunity by promoting the phagocytosis of hemocytes through upregulating the expression of the phagocytotic receptor scavenger receptor C (Src), and two small GTPases, Rab5 and Rab7, which are related to phagosome trafficking to the lysosome in the cytoplasm. Taken together, our results indicated that FOXO exerts its effects on homeostasis of hemolymph and the enteric microbiota by activating the IMD pathway in normal shrimp, and directly or indirectly promoting AMP expression and enhancing phagocytosis of hemocytes against pathogens in bacteria-infected shrimp. This study revealed the different functions of FOXO in the mucosal (local) and systemic antibacterial immunity of invertebrates.

A mild heat stress increases resistance to heat of dFOXO Drosophila melanogaster mutants but less in wild-type flies

While severe stresses have deleterious effects, mild stresses can have beneficial effects called hormetic effects. This study observed survival time at 37.5 °C and at 13-16 days of age of wild-type Drosophila melanogaster flies and dFOXO mutants, after they were subjected to 5 or 10 min daily at 37.5 °C for 5 days starting at 5 days of age. This mild stress increased survival time of the mutants, this effect being nearly not observed in wild-type flies. Previous studies showed that another mild stress, the cold, can increase survival time to heat of wild-type flies, but not of dFOXO mutants, while hypergravity increased survival time of mutants but not of wild-type flies. Therefore, three mild stresses, cold, hypergravity, and heat can increase resistance to heat but the pathways mediating this effect are seemingly different, as cold does not increase resistance in dFOXO mutants but increases it in wild-type flies, while hypergravity and heat have opposite effects. It appears that dFOXO may be needed or not to observe hormetic effects.

Cell type-specific modulation of healthspan by Forkhead family transcription factors in the nervous system

Reduced activity of insulin/insulin-like growth factor signaling (IIS) increases healthy lifespan among diverse animal species. Downstream of IIS, multiple evolutionarily conserved transcription factors (TFs) are required; however, distinct TFs are likely responsible for these effects in different tissues. Here we have asked which TFs can extend healthy lifespan within distinct cell types of the adult nervous system in Drosophila Starting from published single-cell transcriptomic data, we report that forkhead (FKH) is endogenously expressed in neurons, whereas forkhead-box-O (FOXO) is expressed in glial cells. Accordingly, we find that neuronal FKH and glial FOXO exert independent prolongevity effects. We have further explored the role of neuronal FKH in a model of Alzheimer's disease-associated neuronal dysfunction, where we find that increased neuronal FKH preserves behavioral function and reduces ubiquitinated protein aggregation. Finally, using transcriptomic profiling, we identify Atg17, a member of the Atg1 autophagy initiation family, as one FKH-dependent target whose neuronal overexpression is sufficient to extend healthy lifespan. Taken together, our results underscore the importance of cell type-specific mapping of TF activity to preserve healthy function with age.

Functions of Forkhead Box O on Glucose Metabolism in Abalone Haliotis discus hannai and Its Responses to High Levels of Dietary Lipid

The forkhead box O (FoxO) subfamily is a member of the forkhead transcription factor family. It has regulation functions in glucose metabolism in mammals and fish. In the present study, a gene of the foxo homolog in abalone Haliotis discus hannai was cloned. A conservative forkhead (FH) domain and a transactivation (FoxO-TAD) domain were identified. Abalone foxo-specific siRNA (small interfering RNA) was injected to investigate the functions of foxo on glucose metabolism. Knockdown of foxo inhibited expression of phosphoenolpyruvate carboxykinase (pepck) and significantly increased expressions of hexokinase (hk) and pyruvate kinase (pk), but it failed to inhibit the relative mRNA level of glucose-6-phosphatase (g6pase). Then, a 100-day feeding trial was conducted to investigate the response of foxo and glucose metabolism in abalone fed with 1.57% (LFD, low-fat diet), 3.82% (MFD, middle-fat diet) and 6.72% (HFD, high-fat diet) of dietary lipid, respectively. The insulin-signaling pathway (AKT) was depressed and FoxO was activated by the HFD, but it did not inhibit glycolysis (hk) or improved gluconeogenesis significantly (pepck and g6pase). At the same time, impaired hepatopancreas glycogen storage raised hemolymph glucose levels. In conclusion, abalone foxo can be regulated by dietary lipid and can regulate gluconeogenesis or glycolysis in response to changes of dietary lipid levels, in which glycogen metabolism plays an important role.

The Route of Infection Influences the Contribution of Key Immunity Genes to Antibacterial Defense in Anopheles gambiae

Insect systemic immune responses to bacterial infections have been mainly studied using microinjections, whereby the microbe is directly injected into the hemocoel. While this methodology has been instrumental in defining immune signaling pathways and enzymatic cascades in the hemolymph, it remains unclear whether and to what extent the contribution of systemic immune defenses to host microbial resistance varies if bacteria invade the hemolymph after crossing the midgut epithelium subsequent to an oral infection. Here, we address this question using the pathogenic Serratia marcescens (Sm) DB11 strain to establish systemic infections of the malaria vector Anopheles gambiae, either by septic Sm injections or by midgut crossing after feeding on Sm. Using functional genetic studies by RNAi, we report that the two humoral immune factors, thioester-containing protein 1 and C-type lectin 4, which play key roles in defense against Gram-negative bacterial infections, are essential for defense against systemic Sm infections established through injection, but they become dispensable when Sm infects the hemolymph following oral infection. Similar results were observed for the mosquito Rel2 pathway. Surprisingly, blocking phagocytosis by cytochalasin D treatment did not affect mosquito susceptibility to Sm infections established through either route. Transcriptomic analysis of mosquito midguts and abdomens by RNA-seq revealed that the transcriptional response in these tissues is more pronounced in response to feeding on Sm. Functional classification of differentially expressed transcripts identified metabolic genes as the most represented class in response to both routes of infection, while immune genes were poorly regulated in both routes. We also report that Sm oral infections are associated with significant downregulation of several immune genes belonging to different families, specifically the clip-domain serine protease family. In sum, our findings reveal that the route of infection not only alters the contribution of key immunity genes to host antimicrobial defense but is also associated with different transcriptional responses in midguts and abdomens, possibly reflecting different adaptive strategies of the host.

Host-Microbe-Pathogen Interactions: A Review of Vibrio cholerae Pathogenesis in Drosophila

Most animals maintain mutually beneficial symbiotic relationships with their intestinal microbiota. Resident microbes in the gastrointestinal tract breakdown indigestible food, provide essential nutrients, and, act as a barrier against invading microbes, such as the enteric pathogen Vibrio cholerae. Over the last decades, our knowledge of V. cholerae pathogenesis, colonization, and transmission has increased tremendously. A number of animal models have been used to study how V. cholerae interacts with host-derived resources to support gastrointestinal colonization. Here, we review studies on host-microbe interactions and how infection with V. cholerae disrupts these interactions, with a focus on contributions from the Drosophila melanogaster model. We will discuss studies that highlight the connections between symbiont, host, and V. cholerae metabolism; crosstalk between V. cholerae and host microbes; and the impact of the host immune system on the lethality of V. cholerae infection. These studies suggest that V. cholerae modulates host immune-metabolic responses in the fly and improves Vibrio fitness through competition with intestinal microbes.

cis-regulatory variation modulates susceptibility to enteric infection in the Drosophila genetic reference panel

BACKGROUND

Resistance to enteric pathogens is a complex trait at the crossroads of multiple biological processes. We have previously shown in the Drosophila Genetic Reference Panel (DGRP) that resistance to infection is highly heritable, but our understanding of how the effects of genetic variants affect different molecular mechanisms to determine gut immunocompetence is still limited.

RESULTS

To address this, we perform a systems genetics analysis of the gut transcriptomes from 38 DGRP lines that were orally infected with Pseudomonas entomophila. We identify a large number of condition-specific, expression quantitative trait loci (local-eQTLs) with infection-specific ones located in regions enriched for FOX transcription factor motifs. By assessing the allelic imbalance in the transcriptomes of 19 F1 hybrid lines from a large round robin design, we independently attribute a robust cis-regulatory effect to only 10% of these detected local-eQTLs. However, additional analyses indicate that many local-eQTLs may act in trans instead. Comparison of the transcriptomes of DGRP lines that were either susceptible or resistant to Pseudomonas entomophila infection reveals nutcracker as the only differentially expressed gene. Interestingly, we find that nutcracker is linked to infection-specific eQTLs that correlate with its expression level and to enteric infection susceptibility. Further regulatory analysis reveals one particular eQTL that significantly decreases the binding affinity for the repressor Broad, driving differential allele-specific nutcracker expression.

CONCLUSIONS

Our collective findings point to a large number of infection-specific cis- and trans-acting eQTLs in the DGRP, including one common non-coding variant that lowers enteric infection susceptibility.

A Drosophila model of cigarette smoke induced COPD identifies Nrf2 signaling as an expedient target for intervention

Chronic obstructive pulmonary disease (COPD) is among the most important causes of death. Signaling systems that are relevant for tissue repair and detoxification of reactive oxygen species or xenobiotics are thought to be impaired in lungs of patients suffering from this disease. Here, we developed a simple cigarette smoke induced Drosophila model of COPD based on chronic cigarette smoke exposure that recapitulates major pathological hallmarks of the disease and thus can be used to investigate new therapeutic strategies. Chronic cigarette smoke exposure led to premature death of the animals and induced a set of phenotypes reminiscent of those seen in COPD patients, including reduced physical activity, reduced body fat, increased metabolic rate and a substantial reduction of the respiratory surface. A detailed transcriptomic analysis revealed that especially the TGF-β, Nrf2 and the JAK/STAT signaling pathways are altered by chronic cigarette smoke exposure. Based on these results, we focused on Nrf2 signaling. A pharmacological intervention study performed with oltipraz, an activator of Nrf2 signaling, increased survival of cigarette smoke exposed animals significantly. Thus, the Drosophila COPD model recapitulates many major hallmarks of COPD and it is highly useful to evaluate the potential of alternative therapeutic strategies.

Ingestion of killed bacteria activates antimicrobial peptide genes in Drosophila melanogaster and protects flies from septic infection

Drosophila melanogaster possesses a sophisticated and effective immune system composed of humoral and cellular immune responses, and production of antimicrobial peptides (AMPs) is an important defense mechanism. Expression of AMPs is regulated by the Toll and IMD (immune deficiency) pathways. Production of AMPs can be systemic in the fat body or a local event in the midgut and epithelium. So far, most studies focus on systemic septic infection in adult flies and little is known about AMP gene activation after ingestion of killed bacteria. In this study, we investigated activation of AMP genes in the wild-type w¹¹¹⁸, MyD88 and Imd mutant flies after ingestion of heat-killed Escherichia coli and Staphylococcus aureus. We showed that ingestion of E. coli activated most AMP genes, including drosomycin and diptericin, in the first to third instar larvae and pupae, while ingestion of S. aureus induced only some AMP genes in some larval stages or in pupae. In adult flies, ingestion of killed bacteria activated AMP genes differently in males and females. Interestingly, ingestion of killed E. coli and S. aureus in females conferred resistance to septic infection by both live pathogenic Enterococcus faecalis and Pseudomonas aeruginosa, and ingestion of E. coli in males conferred resistance to P. aeruginosa infection. Our results indicated that E. coli and S. aureus can activate both the Toll and IMD pathways, and systemic and local immune responses work together to provide Drosophila more effective protection against infection.

Immunometabolism: Insights from the Drosophila model

Multicellular organisms inhabit an environment that includes a mix of essential nutrients and large numbers of potentially harmful microbes. Germline-encoded receptors scan the environment for microbe associated molecular patterns, and, upon engagement, activate powerful defenses to protect the host from infection. At the same time, digestive enzymes and transporter molecules sieve through ingested material for building blocks and energy sources necessary for survival, growth, and reproduction. We tend to view immune responses as a potent array of destructive forces that overwhelm potentially harmful agents. In contrast, we view metabolic processes as essential, constructive elements in the maintenance and propagation of life. However, there is considerable evidence of functional overlap between the two processes, and disruptions to one frequently modify outputs of the other. Studies of immunometabolism, or interactions between immunity and metabolism, have increased in prominence with the discovery of inflammatory components to metabolic diseases such as type two diabetes. In this review, we will focus on contributions of studies with the fruit fly, Drosophila melanogaster, to our understanding of immunometabolism. Drosophila is widely used to study immune signaling, and to understand the regulation of metabolism in vivo, and this insect has considerable potential as a tool to build our understanding of the molecular and cellular bridges that connect immune and metabolic pathways.

Regulation of antimicrobial peptide genes via insulin-like signaling pathway in the silkworm Bombyx mori

Antimicrobial peptides (AMPs) are important effector molecules of insect humoral immunity, and expression of AMPs is mainly regulated by the Toll and immune deficiency (IMD) pathways. FoxO, a key downstream regulator of the insulin-like signaling (ILS) pathway, has been recently reported to be involved in the regulation of AMPs in Drosophila melanogaster. In the present study, we investigated AMP gene expression and the regulation pathway controlled by the starvation in the silkworm Bombyx mori. We discovered that antibacterial activity in the hemolymph of B. mori larvae was increased by starvation, and expression of AMP genes (BmCecB6, BmAtta1, BmLeb3 and BmDefB) as well as the ILS target genes (FoxO, InR and Brummer) were strongly activated in the fat body by starvation. Moreover, phosphorylation of Akt kinase was reduced in the Bm-12 cells after starvation, suggesting that the ILS pathway was inhibited by starvation. We then showed that more FoxO protein was present in the cytoplasm than in the nucleus of Bm-12 cells under normal conditions, but more FoxO was detected in the nucleus after cells were starved for 8 h, indicating that FoxO was activated by starvation. In summary, our results indicated that starvation can activate AMP gene expression in B. mori via the ILS/FoxO signaling pathway.

Grow With the Challenge - Microbial Effects on Epithelial Proliferation, Carcinogenesis, and Cancer Therapy

The eukaryotic host is in close contact to myriads of resident and transient microbes, which influence the crucial physiological pathways. Emerging evidence points to their role of host-microbe interactions for controlling tissue homeostasis, cell fate decisions, and regenerative capacity in epithelial barrier organs including the skin, lung, and gut. In humans and mice, it has been shown that the malignant tumors of these organs harbor an altered microbiota. Mechanistic studies have shown that the altered metabolic properties and secreted factors contribute to epithelial carcinogenesis and tumor progression. Exciting recent work points toward a crucial influence of the associated microbial communities on the response to chemotherapy and immune-check point inhibitors during cancer treatment, which suggests that the modulation of the microbiota might be a powerful tool for personalized oncology. In this article, we provide an overview of how the bacterial signals and signatures may influence epithelial homeostasis across taxa from cnidarians to vertebrates and delineate mechanisms, which might be potential targets for therapy of human diseases by either harnessing barrier integrity (infection and inflammation) or restoring uncontrolled proliferation (cancer).

Dysfunctional peroxisomes compromise gut structure and host defense by increased cell death and Tor-dependent autophagy

The gut has a central role in digestion and nutrient absorption, but it also serves in defending against pathogens, engages in mutually beneficial interactions with commensals, and is a major source of endocrine signals. Gut homeostasis is necessary for organismal health and changes to the gut are associated with conditions like obesity and diabetes and inflammatory illnesses like Crohn's disease. We report that peroxisomes, organelles involved in lipid metabolism and redox balance, are required to maintain gut epithelium homeostasis and renewal in Drosophila and for survival and development of the organism. Dysfunctional peroxisomes in gut epithelial cells activate Tor kinase-dependent autophagy that increases cell death and epithelial instability, which ultimately alter the composition of the intestinal microbiota, compromise immune pathways in the gut in response to infection, and affect organismal survival. Peroxisomes in the gut effectively function as hubs that coordinate responses from stress, metabolic, and immune signaling pathways to maintain enteric health and the functionality of the gut-microbe interface.

Silent Witness: Dual-Species Transcriptomics Reveals Epithelial Immunological Quiescence to Helminth Larval Encounter and Fostered Larval Development

Gastrointestinal nematodes are among the most prevalent parasites infecting humans and livestock worldwide. Infective larvae of the soil-transmitted nematode Ascaris spp. enter the host and start tissue migration by crossing the intestinal epithelial barrier. The initial interaction of the intestinal epithelium with the parasite, however, has received little attention. In a time-resolved interaction model of porcine intestinal epithelial cells (IPEC-J2) and infective Ascaris suum larvae, we addressed the early transcriptional changes occurring simultaneously in both organisms using dual-species RNA-Seq. Functional analysis of the host response revealed an overall induction of metabolic activity, without induction of immune responsive genes or immune signaling pathways and showing suppression of chemotactic genes like CXCL8/IL-8 or CHI3L1. Ascaris larvae, when getting in contact with the epithelium, showed induction of genes that orchestrate motor activity and larval development, such as myosin, troponin, myoglobin, and protein disulfide isomerase 2 (PDI-2). In addition, excretory-secretory products that likely facilitate parasite invasion were increased, among them, aspartic protease 6 or hyaluronidase. Integration of host and pathogen data in an interspecies gene co-expression network indicated links between nematode fatty acid biosynthesis and host ribosome assembly/protein synthesis. In summary, our study provides new molecular insights into the early factors of parasite invasion, while at the same time revealing host immunological unresponsiveness. Reproducible software for dual RNA-Seq analysis of non-model organisms is available at https://gitlab.com/mkuhring/project_asuum and can be applied to similar studies.

Drosophila melanogaster as a Versatile Model Organism in Food and Nutrition Research

Drosophila melanogaster has been widely used in the biological sciences as a model organism. Drosophila has a relatively short life span of 60-80 days, which makes it attractive for life span studies. Moreover, approximately 60% of the fruit fly genes are orthologs to mammals. Thus, metabolic and signal transduction pathways are highly conserved. Maintenance and reproduction of Drosophila do not require sophisticated equipment and are rather cheap. Furthermore, there are fewer ethical issues involved in experimental Drosophila research compared with studies in laboratory rodents, such as rats and mice. Drosophila is increasingly recognized as a model organism in food and nutrition research. Drosophila is often fed complex solid diets based on yeast, corn, and agar. There are also so-called holidic diets available that are defined in terms of their amino acid, fatty acid, carbohydrate, vitamin, mineral, and trace element compositions. Feed intake, body composition, locomotor activity, intestinal barrier function, microbiota, cognition, fertility, aging, and life span can be systematically determined in Drosophila in response to dietary factors. Furthermore, diet-induced pathophysiological mechanisms including inflammation and stress responses may be evaluated in the fly under defined experimental conditions. Here, we critically evaluate Drosophila melanogaster as a versatile model organism in experimental food and nutrition research, review the corresponding data in the literature, and make suggestions for future directions of research.

Stem Cell Transcription Factor FoxO Controls Microbiome Resilience in Hydra

The aging process is considered to be the result of accumulating cellular deterioration in an individual organism over time. It can be affected by the combined influence of genetic, epigenetic, and environmental factors including life-style-associated events. In the non-senescent freshwater polyp Hydra, one of the classical model systems for evolutionary developmental biology and regeneration, transcription factor FoxO modulates both stem cell proliferation and innate immunity. This provides strong support for the role of FoxO as a critical rate-of-aging regulator. However, how environmental factors interact with FoxO remains unknown. Here, we find that deficiency in FoxO signaling in Hydra leads to dysregulation of antimicrobial peptide expression and that FoxO loss-of-function polyps are impaired in selection for bacteria resembling the native microbiome and more susceptible to colonization of foreign bacteria. These findings reveal a key role of FoxO signaling in the communication between host and microbiota and embed the evolutionary conserved longevity factor FoxO into the holobiont concept.

Intestinal Homeostasis and Longevity: Drosophila Gut Feeling

The association between intestinal homeostasis and life span has caught the attention of the research community worldwide. There have been multiple evidences which support the role of gut homeostasis in aging. The Drosophila gastrointestinal tract is very similar to the mammalian gut, and therefore it can directly be used as a model to understand the association between gut microbiota, immune system, and aging in humans. In current review we have discussed the importance of gut microbiota in aging. Also we have highlighted the importance of host immune system and gut aging. Since the increased microbial load in the gut activates the host immune system, the dysregulated microbiota can have direct implications in gut aging. The proliferation and renewal of intestinal stem cells can also affect gut aging. Another important aspect that we have discussed is the communication between the gut and the other organ systems which affect the overall aging process. Altogether we propose that the Drosophila gut can be a good model to improve our understanding of human gut aging.

Microbiota-induced peritrophic matrix regulates midgut homeostasis and prevents systemic infection of malaria vector mosquitoes

Manipulation of the mosquito gut microbiota can lay the foundations for novel methods for disease transmission control. Mosquito blood feeding triggers a significant, transient increase of the gut microbiota, but little is known about the mechanisms by which the mosquito controls this bacterial growth whilst limiting inflammation of the gut epithelium. Here, we investigate the gut epithelial response to the changing microbiota load upon blood feeding in the malaria vector Anopheles coluzzii. We show that the synthesis and integrity of the peritrophic matrix, which physically separates the gut epithelium from its luminal contents, is microbiota dependent. We reveal that the peritrophic matrix limits the growth and persistence of Enterobacteriaceae within the gut, whilst preventing seeding of a systemic infection. Our results demonstrate that the peritrophic matrix is a key regulator of mosquito gut homeostasis and establish functional analogies between this and the mucus layers of the mammalian gastrointestinal tract.

When a female mosquito takes a blood meal from a human, the bacteria residing within its gut grow significantly. Following a blood meal, female mosquitoes produce a barrier within their gut, known as the peritrophic matrix, which physically separates the blood meal from the cells of the epithelium. Here, we show that the presence of bacteria in the gut is required for the synthesis of the peritrophic matrix. By experimentally disrupting this barrier, we find that this structure plays a role in limiting the extent to which bacteria of one particular family are able to grow and persist in the mosquito gut. We also find that the peritrophic matrix ensures that bacteria remain within the gut, preventing them from invading the mosquito body cavity. These results will be useful in designing disease control strategies that depend on the ability of bacteria to colonize and persist in relevant tissues in the mosquito host.

Antimicrobial peptides extend lifespan in Drosophila

Antimicrobial peptides (AMPs) are important defense molecules of the innate immune system. High levels of AMPs are induced in response to infections to fight pathogens, whereas moderate levels induced by metabolic stress are thought to shape commensal microbial communities at barrier tissues. We expressed single AMPs in adult flies either ubiquitously or in the gut by using the inducible GeneSwitch system to tightly regulate AMP expression. We found that activation of single AMPs, including Drosocin, resulted in a significant extension of Drosophila lifespan. These animals showed reduced activity of immune pathways over lifetime, less intestinal regenerative processes, reduced stress response and a delayed loss of gut barrier integrity. Furthermore, intestinal Drosocin induction protected the animals against infections with the natural Drosophila pathogen Pseudomonas entomophila, whereas a germ-reduced environment prevented the lifespan extending effect of Drosocin. Our study provides new insights into the crosstalk of innate immunity, intestinal homeostasis and ageing.

Modulation of gut microbiota and delayed immunosenescence as a result of syringaresinol consumption in middle-aged mice

Age-associated immunological dysfunction (immunosenescence) is closely linked to perturbation of the gut microbiota. Here, we investigated whether syringaresinol (SYR), a polyphenolic lignan, modulates immune aging and the gut microbiota associated with this effect in middle-aged mice. Compared with age-matched control mice, SYR treatment delayed immunosenescence by enhancing the numbers of total CD3⁺ T cells and naïve T cells. SYR treatment induced the expression of Bim as well as activation of FOXO3 in Foxp3⁺ regulatory T cells (Tregs). Furthermore, SYR treatment significantly enhanced the Firmicutes/Bacteroidetes ratio compared with that in age-matched controls by increasing beneficial bacteria, Lactobacillus and Bifidobacterium, while reducing the opportunistic pathogenic genus, Akkermansia. In addition, SYR treatment reduced the serum level of lipopolysaccharide-binding protein, an inflammatory marker, and enhanced humoral immunity against influenza vaccination to the level of young control mice. Taken together, these findings suggest that SYR may rejuvenate the immune system through modulation of gut integrity and microbiota diversity as well as composition in middle-aged mice, which may delay the immunosenescence associated with aging.

Friend, foe or food? Recognition and the role of antimicrobial peptides in gut immunity and Drosophila-microbe interactions

Drosophila melanogaster lives, breeds and feeds on fermenting fruit, an environment that supports a high density, and often a diversity, of microorganisms. This association with such dense microbe-rich environments has been proposed as a reason that D. melanogaster evolved a diverse and potent antimicrobial peptide (AMP) response to microorganisms, especially to combat potential pathogens that might occupy this niche. Yet, like most animals, D. melanogaster also lives in close association with the beneficial microbes that comprise its microbiota, or microbiome, and recent studies have shown that antimicrobial peptides (AMPs) of the epithelial immune response play an important role in dictating these interactions and controlling the host response to gut microbiota. Moreover, D. melanogaster also eats microbes for food, consuming fermentative microbes of decaying plant material and their by-products as both larvae and adults. The processes of nutrient acquisition and host defence are remarkably similar and use shared functions for microbe detection and response, an observation that has led to the proposal that the digestive and immune systems have a common evolutionary origin. In this manner, D. melanogaster provides a powerful model to understand how, and whether, hosts differentiate between the microbes they encounter across this spectrum of associations.This article is part of the themed issue 'Evolutionary ecology of arthropod antimicrobial peptides'.