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

Pesticide immunotoxicity on insects - Are agroecosystems at risk?

Recent years have witnessed heightened scrutiny of the non-target sublethal effects of pesticides on behavioural and physiological traits of insects. Traditionally, attention has focused on investigating pesticides' primary modes of action, often overlooking the potential secondary mechanisms. This review brings forth the nuanced impacts of sublethal pesticide exposure on the immune system of target and non-target insect species. Pesticides, such as for example neonicotinoids, suppress immune response, while others, like certain organophosphates and some insect growth regulators (IGRs), appear to bolster immunocompetence under certain circumstances. Beyond their individual impacts, the synergic effects of pesticide mixtures on insect immunity are garnering increasing interest. This review thus summarizes recent advances in the immunomodulatory effects of pesticides, detailing both mechanisms and consequences of such interactions. The implications of these effects for ecosystem preservation and viability of beneficial organisms, such as pollinators and natural enemies of pests, are discussed. The review also considers further research directions on pesticide secondary modes of action and explores potential implications for integrated pest management (IPM) programs, as several model organisms studied are crop pest species. While current data provide an expansive overview of how insect innate immunity is modulated, concrete endpoints remain elusive requiring further research into pesticide secondary modes of actions.

Insect Antimicrobial Peptides as Guardians of Immunity and Beyond: A Review

Antimicrobial peptides (AMPs), as immune effectors synthesized by a variety of organisms, not only constitute a robust defense mechanism against a broad spectrum of pathogens in the host but also show promising applications as effective antimicrobial agents. Notably, insects are significant reservoirs of natural AMPs. However, the complex array of variations in types, quantities, antimicrobial activities, and production pathways of AMPs, as well as evolution of AMPs across insect species, presents a significant challenge for immunity system understanding and AMP applications. This review covers insect AMP discoveries, classification, common properties, and mechanisms of action. Additionally, the types, quantities, and activities of immune-related AMPs in each model insect are also summarized. We conducted the first comprehensive investigation into the diversity, distribution, and evolution of 20 types of AMPs in model insects, employing phylogenetic analysis to describe their evolutionary relationships and shed light on conserved and distinctive AMP families. Furthermore, we summarize the regulatory pathways of AMP production through classical signaling pathways and additional pathways associated with Nitric Oxide, insulin-like signaling, and hormones. This review advances our understanding of AMPs as guardians in insect immunity systems and unlocks a gateway to insect AMP resources, facilitating the use of AMPs to address food safety concerns.

Maintaining Toll signaling in Drosophila brain is required to sustain autophagy for dopamine neuron survival

Macroautophagy/autophagy is a conserved process in eukaryotic cells to degrade and recycle damaged intracellular components. Higher level of autophagy in the brain has been observed, and autophagy dysfunction has an impact on neuronal health, but the molecular mechanism is unclear. In this study, we showed that overexpression of Toll-1 and Toll-7 receptors, as well as active Spätzle proteins in Drosophila S2 cells enhanced autophagy, and Toll-1/Toll-7 activated autophagy was dependent on Tube-Pelle-PP2A. Interestingly, Toll-1 but not Toll-7 mediated autophagy was dMyd88 dependent. Importantly, we observed that loss of functions in Toll-1 and Toll-7 receptors and PP2A activity in flies decreased autophagy level, resulting in the loss of dopamine (DA) neurons and reduced fly motion. Our results indicated that proper activation of Toll-1 and Toll-7 pathways and PP2A activity in the brain are necessary to sustain autophagy level for DA neuron survival.

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.

Untargeted Lipidomics Analysis Unravels the Different Metabolites in the Fat Body of Mated Bumblebee (Bombus terrestris) Queens

The fat body has important functions in energy, fertility, and immunity. In female insects, mating stimulates physiological, behavioral, and gene expression changes. However, it remains unclear whether the metabolites in the fat body are affected after the bumblebee (Bombus terrestris) queen mates. Here, the ultrastructure and lipid metabolites in fat body of mated queens were compared with those of virgins. The fat body weight of mated bumblebee queens was significantly increased, and the adipocytes were filled with lipid droplets. Using LC-MS/MS-based untargeted lipidomics, 949 and 748 differential metabolites were identified in the fat body of virgin and mated bumblebee queens, respectively, in positive and negative ion modes. Most lipid metabolites were decreased, especially some biomembrane components. In order to explore the relationship between the structures of lipid droplets and metabolite accumulation, transmission electron microscopy and fluorescence microscopy were used to observe the fat body ultrastructure. The size/area of lipid droplets was larger, and the fusion of lipid droplets was increased in the mated queen's fat body. These enlarged lipid droplets may store more energy and nutrients. The observed differences in lipid metabolites in the fat body of queens contribute to understanding the regulatory network of bumblebees post mating.

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.

Disruption of peritrophic matrix chitin metabolism and gut immune by chlorantraniliprole results in pathogenic bacterial infection in Bombyx mori

Chlorantraniliprole (CAP) is widely used in pest control, and its environmental residues affect the disease resistance of non-target insect silkworms. Studies have demonstrated that changes in gut microbial communities of insects are associated with susceptibility to pathogens. In the present study, we examined the effects of CAP exposure on the immune system and gut microbial community structure of silkworms. The results showed that after 96 h of exposure to low-concentration CAP, the peritrophic matrix (PM) of silkworm larvae was disrupted, and pathogenic bacteria invaded hemolymph. The trehalase activity in the midgut was significantly decreased, while the activities of chitinase, β-N-acetylglucosaminidase, and chitin deacetylase were increased considerably, resulting in decreased chitin content in PM. In addition, exposure to CAP reduced the expressions of key genes in the Toll, IMD, and JAK/STAT pathways, ultimately leading to the downregulation of antimicrobial peptides (AMPs) genes and alterations in the structure of the gut microbial community. Therefore, after infection with the conditional pathogen Enterobacter cloacae (E. cloacae), CAP-exposed individuals exhibited significantly lower body weight and higher mortality. These findings showed that exposure to low-concentration CAP impacted the biological defense system of silkworms, changed the gut microbial community structure, and increased silkworms' susceptibility to bacterial diseases. Collectively, these findings provided a new perspective for the safety evaluation of low-concentration CAP exposure in sericulture.

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.

Bombyx mori as a model for Niallia circulans pathogenicity

Increasing incidences of resistance to antibiotics by pathogenic bacteria is a worldwide concern and isolation of antibiotic-resistant strains of Niallia circulans (formerly known as Bacillus circulans), an opportunistic human pathogen, has been reported. Due to their lack of ethical constraints as well as their cost-effective rearing, invertebrates have been commonly used to study infection by bacteria pathogenic to humans. In this study, we demonstrate that a foodborne strain of N. circulans kills larvae of the silkworm, Bombyx mori within 48 h after hemolymph injection. The infected larvae turned black with an increase in the phenoloxidase (PO) activity in the hemolymph. Midgut injection of N. circulans resulted in the killing of larvae within 96 h. A significant increase in bacterial load was observed in the hemolymph 12 h after infection. The viable hemocyte number decreased to 48% within 12 h of injection. RT-qPCR analysis revealed that upon hemolymph infection with N. circulans the expression of the antimicrobial peptide (AMP) genes, Bmdefensin-B and Bmgloverin-3, were upregulated 2.5- and 1.8-fold, respectively, whereas 1.6-fold upregulation was observed for BmToll-2 in the larval fat body. Therapeutic effects of antibiotics like tetracycline, imipenem, ceftriaxone, ampicillin, and clindamycin were observed against N. circulans in the Bombyx larvae with varying efficacies. Results from this study suggest that larvae of B. mori can be used as infection models for screening therapeutics that are effective against N. circulans.

Metabolic reprogramming of Helicoverpa armigera larvae by HearNPV facilitates viral replication and host immune suppression

Baculoviruses are highly evolved parasites that genetically reprogram the developing phenotype of their host insect to produce a vessel for virus replication and dispersal. Here we show that larvae of Helicoverpa armigera infected with HearNPV accumulate glucose in the midgut, which reduces food consumption and alters the dynamics of pathways governing metabolism and immunity. We used transcriptomics to demonstrate the role of the insulin signalling pathway in regulating the HearNPV infection process. Dietary restriction decreased mortality of infected larvae and reduced viral replication prior to death, whereas dietary supplementation with glucose produced the opposite effects. The expression of most tricarboxylic acid cycle (TCA) and energy metabolism-related genes was reduced in infected larvae, whereas the expression of immunity-, glycolysis- and insulin-related genes was enhanced. Treatment of infected larvae with insulin increased their survival, reduced viral replication and inhibited climbing behaviour compared to a control treatment with DMSO, whereas RNAi suppression of the insulin receptor gene produced the opposite effects. Inhibition of glycolysis with dichloroacetate (DCA) promoted viral replication and accelerated larval death, but inhibition of the TCA cycle with 2-deoxyglucose (2-DG) did not, although both diminished climbing behaviour. This work demonstrates that successful baculovirus infections hinge on metabolic reprogramming of the host and concurrent suppression of immune responses in the larval midgut, with the insulin signalling pathway mediating a trade-off between glucose metabolism and virus resistance.

Toxicity of nitenpyram to silkworm (Bombyx mori L.) and its potential mechanisms

Silkworm (Bombyx mori L.), as an economic insect, occupies a certain position in the development of China's economy. The neonicotinoid insecticide nitenpyram is commonly used in farmland to control planthoppers and aphids. In China, mulberry orchards are often planted adjacent to fields or commercial crops, and mist drifts occur during application, which may affect the production safety of Bombyx mori. In this study, a risk assessment of nitenpyram was carried out, and the results showed that there were risks in spraying nitenpyram around the periphery and subperipheries of mulberry fields. However, few studies have reported the mechanism underlying nitenpyram's toxic effect on silkworms. Here, we validated 25 differentially expressed (DE) miRNAs in the nitenpyram treatment group of silkworms, and the significantly enriched mTOR signaling pathway, oxidative phosphorylation and FoxO signaling pathway were verified. Among them, bmo-miR-2766-5P was up-regulated by 2.122-fold, and the expression of its regulated target gene 101,741,287 was up-regulated. After the injection of bmo-miR-2766-5P inhibitor, the Log₂FC value of 101,741,287 was changed from 1.26 to -2.19. Bmo-miR-3326, bmo-miR-3378-5P and bmo-miR-2761-3P were down-regulated by 2.386-fold, 1.158-fold and 2.359-fold, respectively. After injecting miRNA mimics into silkworms, the Log₂FC values of the target genes 100,302,609, 101,740,730 and 101,746,319 were changed from 1.24 to -11.94, -1.12 changed to 2.84 and 1.93 changed to -0.37, respectively. In addition, nitenpyram induced oxidative damage in silkworms, and the degree of DNA damage increased with the increase of concentration and time. Meanwhile Imd was significantly up-regulated in IMD-related pathways (38.7-fold, p < 0.01). The results indicated that nitenpyram could affect the growth and development process of silkworms, and these DE-miRNAs may have an important impact on the stress response of silkworms to nitenpyram.

Nutrition regulates the expression of storage proteins in Bombyx mori via insulin-like/FoxO signaling pathway

Insect serum proteins, also termed storage proteins (SPs), are hexamer proteins that form amino acid reservoirs important for the development of pupae and embryos in most insects. In this study, we investigated the SP genes expression and regulation pathways in silkworms (Bombyx mori). We observed that B. mori SPs (BmSPs) in the fat body of larvae were strongly decreased by starvation, suggesting they respond to nutrition deprivation. Further, we examined the relationship between BmSP expression and the insulin-like signaling pathway (ILS) to study the regulation of BmSPs expression. The results showed that insulin up-regulated the expression of BmSPs, but an inhibitor of the ILS pathway protein PI3K downregulated the expression of BmSPs in B. mori larvae. Similar results were observed in cultured fat body in vitro and BmE cells. We then over-expressed FoxO, an ILS transcriptional factor, in BmE cells and B. mori larvae to further verify the regulatory role of ILS on expression of BmSPs and found BmFoxO negatively regulates the expression of BmSPs in both BmE cells and larvae. Moreover, BmFoxO was dephosphorylated and translocated from the cytoplasm to the nucleus under starvation treatment. Finally, an element on -2627-2644 bp upstream of the transcription start site of BmSP1 was identified as the binding site of BmFoxO by electrophoretic mobility shift assay and verified by chromatin immunoprecipitation. In summary, our results indicate that nutrient uptake triggers the expression of BmSPs via the ILS/FoxO signaling pathway. This study provides a reference for further study on the expression and regulation of insect SP genes.

Parasitism by the Tachinid Parasitoid Exorista japonica Leads to Suppression of Basal Metabolism and Activation of Immune Response in the Host Bombyx mori

The dipteran tachinid parasitoids are important biocontrol agents, and they must survive the harsh environment and rely on the resources of the host insect to complete their larval stage. We have previously demonstrated that the parasitism by the tachinid parasitoid Exoristajaponica, a pest of the silkworm, causes pupation defects in Bombyx mori. However, the underlying mechanism is not fully understood. Here, we performed transcriptome analysis of the fat body of B. mori parasitized by E. japonica. We identified 1361 differentially expressed genes, with 394 genes up-regulated and 967 genes down-regulated. The up-regulated genes were mainly associated with immune response, endocrine system and signal transduction, whereas the genes related to basal metabolism, including energy metabolism, transport and catabolism, lipid metabolism, amino acid metabolism and carbohydrate metabolism were down-regulated, indicating that the host appeared to be in poor nutritional status but active in immune response. Moreover, by time-course gene expression analysis we found that genes related to amino acid synthesis, protein degradation and lipid metabolism in B. mori at later parasitization stages were inhibited. Antimicrobial peptides including Cecropin A, Gloverin and Moricin, and an immulectin, CTL11, were induced. These results indicate that the tachinid parasitoid perturbs the basal metabolism and induces the energetically costly immunity of the host, and thus leading to incomplete larval-pupal ecdysis of the host. This study provided insights into how tachinid parasitoids modify host basal metabolism and immune response for the benefit of developing parasitoid larvae.

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.

Functional analysis of a peptidoglycan recognition protein involved in the immune response in the common cutworm, Spodoptera litura

Peptidoglycan recognition proteins (GRPs) are family of pattern recognition receptors (PRRs), which can recognize the peptidoglycan and trigger the innate immune system against the microorganisms in insects. In this study, we identified a GRP-LB from Spodoptera litura genome database and named SlGRP-LB, which contained a complete open reading frame (ORF) of 639 bp, encoding a protein of 212 amino acids with a signal peptide and GRP domain. Phylogenetic tree analysis suggested that the SlGRP-LB has a close relationship with Helicoverpa armigera GRP-LB (HaGRP-LB). Tissue expression analysis revealed that SlGRP-LB had a high expression level in the fat body. The expression levels of SlGRP-LB were significantly upregulated in the hemolymph, fat body, and midgut from 3 to 12 h after injection of Escherichia coli and Staphylococcus aureus, while the expression levels were not downregulated at 24 h postinfection. Knockdown of SlGRP-LB expression by RNA interference reduced the expression of antibacterial peptide-related genes in the fat body and midgut, while their expression levels were upregulated in the hemolymph. In addition, the recombinant SlGRP-LB was expressed by using E. coli expression system, and it exhibited binding activity to E. coli. Taken together, the data suggest that S. litura GRP-LB might play a crucial role in regulating immune response in S. litura.

A heat shock protein protects against oxidative stress induced by lambda-cyhalothrin in the green peach aphid Myzus persicae

Lambda-cyhalothrin (LCT) is a pyrethroid insecticide widely used to control insect pests. Insect exposure to LCT may cause abnormal accumulation of reactive oxygen species (ROS) and result in oxidative damage. Heat shock proteins (HSPs) may help protect against oxidative stress. However, little is known about the role of HSPs in response to LCT in the green peach aphid, Myzus persicae. This insect is an important agricultural pest causing severe yield losses in crops. In this study, we characterized a cDNA sequence (MpHsp70) encoding a member of the HSP70 family in M. persicae. MpHsp70 encoded a 623 amino acid protein putatively localized in the cytosol. The highest expression level of MpHsp70 occurred in fourth-instar nymphs. Treatment of M. persicae with LCT resulted in oxidative stress and significantly increased H₂O₂ and malondialdehyde levels. This led to an elevated transcription level of MpHsp70. Injection of H₂O₂ into M. persicae also upregulated the MpHsp70 expression level, suggesting that MpHsp70 is responsive to ROS, particularly H₂O₂, induced by LCT. Recombinant MpHSP70 protein was expressed in Escherichia coli. E. coli cells overexpressing MpHSP70 exhibited significant tolerance to H₂O₂ and the ROS generators, cumene hydroperoxide and paraquat. This indicated that MpHSP70 protects against oxidative stress. Furthermore, knockdown of MpHsp70 by RNA interference resulted in increased susceptibility in apterous adults of M. persicae to LCT. These findings indicate that MpHsp70 plays an important role in defense against LCT-induced oxidative stress and insecticide susceptibility in M. persicae.

Increased insulin signaling in the Anopheles stephensi fat body regulates metabolism and enhances the host response to both bacterial challenge and Plasmodium falciparum infection

In vertebrates and invertebrates, the insulin/insulin-like growth factor 1 (IGF1) signaling (IIS) cascade is highly conserved and plays a vital role in many different physiological processes. Among the many tissues that respond to IIS in mosquitoes, the fat body has a central role in metabolism, lifespan, reproduction, and innate immunity. We previously demonstrated that fat body specific expression of active Akt, a key IIS signaling molecule, in adult Anopheles stephensi and Aedes aegypti activated the IIS cascade and extended lifespan. Additionally, we found that transgenic females produced more vitellogenin (Vg) protein than non-transgenic mosquitoes, although this did not translate into increased fecundity. These results prompted us to further examine how IIS impacts immunity, metabolism, growth and development of these transgenic mosquitoes. We observed significant changes in glycogen, trehalose, triglycerides, glucose, and protein in young (3-5 d) transgenic mosquitoes relative to non-transgenic sibling controls, while only triglycerides were significantly changed in older (18 d) transgenic mosquitoes. More importantly, we demonstrated that enhanced fat body IIS decreased both the prevalence and intensity of Plasmodium falciparum infection in transgenic An. stephensi. Additionally, challenging transgenic An. stephensi with Gram-positive and Gram-negative bacteria altered the expression of several antimicrobial peptides (AMPs) and two anti-Plasmodium genes, nitric oxide synthase (NOS) and thioester complement-like protein (TEP1), relative to non-transgenic controls. Increased IIS in the fat body of adult female An. stephensi had little to no impact on body size, growth or development of progeny from transgenic mosquitoes relative to non-transgenic controls. This study both confirms and expands our understanding of the critical roles insulin signaling plays in regulating the diverse functions of the mosquito fat body.

Scavenger receptor C regulates antimicrobial peptide expression by activating toll signaling in silkworm, Bombyx mori

Scavenger receptor is pattern-recognition receptor (PRR) that plays a crucial function in host defense against pathogens. Scavenger receptor C (SR-C) is present only in invertebrates and its function has not been studied in detail. In this study, an SR-C homologous gene from the silkworm, Bombyx mori, was identified and characterized. SR-C was largely expressed in hemocytes and Malpighian tubules, with continuous expression in hemocytes. The peak expression was observed in hemocytes during molting and wandering stages both at mRNA and protein levels. Furthermore, immunofluorescence demonstrated it to be mainly distributed in the cell membranes of hemocytes, including oenocytoids and granulocytes. The recombinant SR-C protein (rSR-C) could bind to different types of bacteria and pathogen-associated molecular patterns (PAMPs), with strong binding to gram-positive bacteria and Lys-type peptidoglycans. The overexpression of SR-C induced the expression of genes related to the Toll pathway and antibacterial peptides. While the knockdown of SR-C reduced the expression of AMPs and inhibited the Toll pathway, it impaired the bacterial clearance ability of silkworm larvae, thus decreasing silkworm larvae's survival rate. Altogether, SR-C is a PRR that protect silkworms against bacterial pathogens by enhancing the expression of AMPs expression via the Toll pathway in hemocytes.

A toxicological perspective of plastic biodegradation by insect larvae

Larvae of some insect species (Coleoptera and Lepidoptera) can consume and biodegrade synthetic polymers, including polyethylene, polystyrene, polyvinyl chloride, and polypropylene. Multiple chemical (polymer mass loss and shift of the molecular weight, alterations in chemical functionality, formation of biodegraded intermediates, CO₂ production), physical (surface hydrophobicity, thermal analysis), and biological approaches (antibiotic treatment, gut dysbiosis, isolation of plastic microbial degraders) have provided evidence for polymer biodegradation in the larva digestive tract. However, the extent and rate of biodegradation largely depend on the physicochemical structure of the polymer as well as the presence of additives. Additionally, toxicology associated with plastic biodegradation has not been investigated. This knowledge gap is critical to understand the gut symbiont-host interaction in the biodegradation process, its viability in the long term, the effects of plastic additives and their metabolites, and the phenotypic traits linked to a plastic-rich diet might be transferred in successive generations. Likewise, plastic-eating larvae represent a unique case study for elucidating the mechanisms of toxic action by micro- and nanoplastics because of the high concentration of plastics these organisms may be intentionally exposed to. This perspective review graphically summarizes the current knowledge on plastic biodegradation by insect larvae and describes the physiological processes (digestive and immune systems) that may be disrupted by micro- and nanoplastics. It also provides an outlook to advance current knowledge on the toxicity assessment of plastic-rich diets and the environmental risks of plastic-containing by-products (e.g., insect manure used as fertilizer).

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.

Proteomic Study Reveals Major Pathways Regulating the Development of Black Soldier Fly

Nowadays, biodegrading organic waste, as a solution to confront environmental challenges, has attracted wide attention. A dipteran insect, black soldier fly (BSF), exhibits outstanding capability to convert organic waste into proteins and lipid resources, and thus, much interest has been shown in it. However, information of fundamental biology of BSF is still limited besides its recycling efficiency. In this work, we present a complete proteomic database of BSF at all instars (before prepupa). We further formulated the pathways corresponding to BSF development and built a relationship with the current genetic database. To achieve this, we investigated the proteomics of BSF during different periods. We identified 5036 proteins, and among them, 3905 proteins were annotated in the protein function database. illustrated three pathways related to major physiological processes including the insulin signaling pathway for feeding and growth, fatty acid biosynthesis pathway for fatty acid using, and toll/immune deficiency pathway for immune behavior. The proteins in these three pathways were matched with a published genetic database, and this reference library could be used for future BSF genetic engineering. In conclusion, this work provided a comprehensive protein library of BSF and expands the basic knowledge of BSF for future research.

The involvement of insulin/ToR signaling pathway in reproductive performance of Rhodnius prolixus

Insulins are peptide hormones widely studied for their important regulatory roles in metabolism, growth and development. In insects, insulin signaling along with the target of rapamycin (ToR) are involved in detecting and interpreting nutrient levels. Recently, by transcriptome analysis we reported an up-regulation of transcripts involved in insulin/ToR signaling in unfed Rhodnius prolixus; however, this signaling pathway is only activated in fed insects. Here, continuing with the blood-gorging triatomine R. prolixus as a model, we report the direct effect of insulin/ToR signaling on reproductive performance. By immunofluorescence we identified cells in the brain with positive signal to the R. prolixus ILP (Rhopr-ILP1) and show that the insulin receptor and protein effectors downstream of insulin/ToR signaling activation, are differentially expressed in ovarian follicles dependent on their developmental stage. Using qPCR we find that the expression of transcripts involved in insulin signaling in the central nervous system (CNS), fat body and ovaries increase as the state of starvation progresses, promoting a more highly sensitized state to respond rapidly to ILP/IGF levels. In addition, using dsRNA injection and in vivo and ex vivo assays to promote signaling activation we demonstrate a direct participation of insulin/ToR signaling in coordinating the synthesis of the main yolk protein precursor, vitellogenin, thereby influencing the numbers of eggs laid per female. We thereby show a mechanism by which nutritional signaling regulates reproductive performance in a vector of Chagas disease. As reproduction is responsible for propagation of insect populations, this work is important for the development of innovative biocontrol methods.

Bombyx mori nucleopolyhedrovirus downregulates transcription factor BmFoxO to elevate virus infection

Forkhead-box O (FoxO) is the primary transcriptional effector of the insulin-like signaling pathway that enhances gluconeogenesis through transcriptional activation of PEPCK and G6Pase in mammals. We have previously demonstrated the involvement of phosphoenolpyruvate carboxykinase (BmPEPCK-2) in antiviral immunity against the multiplication of Bombyx mori nuclearpolyhedrosisvirus (BmNPV) in silkworm. Therefore, we speculated that BmFoxO might suppress BmNPV by regulating the expression of PEPCK in silkworm. In the present study, we found that the expression of BmFoxO decreased after BmNPV infection in Bombyx mori; this finding was consistent with BmPEPCK-2 expression. In addition, the expression of BmFoxO was altered, and it was found that reduced expression of BmFoxO (dsBmFoxO) downregulated the expression of BmPEPCK-2 and increased the viral fluorescence and content in silkworm embryonic cell line BmE cells, and vice versa. BmFoxO could upregulate the expression of BmPEPCK-2 by binding to the BmPEPCK-2 promoter. Moreover, overexpression of BmFoxO significantly increased the expression of autophagy genes ATG6/7/8 after infection with BmNPV, consistent with BmPEPCK-2. These results indicate that BmNPV downregulates transcription factor BmFoxO to elevate virus infection, and BmFoxO overexpression upregulates BmPEPCK-2 expression and enhances silkworm antiviral resistance.

Influence of Hyperproteinemia on Insect Innate Immune Function of the Circulatory System in Bombyx mori

Simple Summary

Hyperproteinemia, a condition of elevated protein levels in the blood, is associated with a diverse range of human and animal diseases. However, there is no reliable hyperproteinemia disease models or modeling methods in mammal or other organisms, and the effect of hyperproteinemia on immunity is still unknown. Our work succeeded in constructing an animal model of hyperproteinemia with no primary disease effects and a controllable plasma protein concentration (PPC) in an invertebrate model organism, Bombyx mori. Our work confirmed that high PPC enhances hemolymph phagocytosis via a rapid increase in granulocytes and inhibited hemolymph melanization due to inhibition of the prophenoloxidase (PPO) signaling pathway, and also upregulated the gene expression of antimicrobial peptides via activating the Toll and Imd pathways in NF-κB signaling, and showed an inconsistent antibacterial activity for Gram-positive and Gram-negative bacteria. Our results show that high PPC had multiple significant effects on the innate immune function of the silkworm circulatory system and is expected to be improved by endocrine hormones. Our work explores the pathogenesis of hyperproteinemia in an invertebrate model, and expands the scope for silkworm biomedical applications, even use for a potential drug development platform.

Abstract

Metabolic disorders of the circulatory system of animals (e.g., hyperglycemia and hyperlipidemia) can significantly affect immune function; however, since there is currently no reliable animal model for hyperproteinemia, its effects on immunity remain unclear. In this study, we established an animal model for hyperproteinemia in an invertebrate silkworm model, with a controllable plasma protein concentration (PPC) and no primary disease effects. We evaluated the influence of hyperproteinemia on innate immunity. The results showed that high PPC enhanced hemolymph phagocytosis via inducing a rapid increase in granulocytes. Moreover, while oenocytoids increased, the plasmacytes quickly dwindled. High PPC inhibited hemolymph melanization due to decreased phenoloxidase (PO) activity in the hemolymph via inhibiting the expression of the prophenoloxidase-encoding genes, PPO1 and PPO2. High PPC upregulated the gene expression of antimicrobial peptides via differential activation of the Toll and Imd signaling pathways associated with NF-κB signaling, followed by an induction of inconsistent antibacterial activity towards Gram-positive and Gram-negative bacteria in an animal model of high PPC. Therefore, high PPC has multiple significant effects on the innate immune function of the silkworm circulatory system.

How insects protect themselves against combined starvation and pathogen challenges, and the implications for reductionism

An explosion of data has provided detailed information about organisms at the molecular level. For some traits, this information can accurately predict phenotype. However, knowledge of the underlying molecular networks often cannot be used to accurately predict higher order phenomena, such as the response to multiple stressors. This failure raises the question of whether methodological reductionism is sufficient to uncover predictable connections between molecules and phenotype. This question is explored in this paper by examining whether our understanding of the molecular responses to food limitation and pathogens in insects can be used to predict their combined effects. The molecular pathways underlying the response to starvation and pathogen attack in insects demonstrates the complexity of real-world physiological networks. Although known intracellular signaling pathways suggest that food restriction should enhance immune function, a reduction in food availability leads to an increase in some immune components, a decrease in others, and a complex effect on disease resistance in insects such as the caterpillar Manduca sexta. However, our inability to predict the effects of food restriction on disease resistance is likely due to our incomplete knowledge of the intra- and extracellular signaling pathways mediating the response to single or multiple stressors. Moving from molecules to organisms will require novel quantitative, integrative and experimental approaches (e.g. single cell RNAseq). Physiological networks are non-linear, dynamic, highly interconnected and replete with alternative pathways. However, that does not make them impossible to predict, given the appropriate experimental and analytical tools. Such tools are still under development. Therefore, given that molecular data sets are incomplete and analytical tools are still under development, it is premature to conclude that methodological reductionism cannot be used to predict phenotype.

Effects of phoxim pesticide on the immune system of silkworm midgut

Silkworm (Bombyx mori) is an important economic insect. Bombyx mori, which is exposed to sublethal doses of pesticides, has a low or no mortality rate, while it is susceptible to infections triggered by foreign pathogens. The immune regulatory mechanism of silkworms caused by trace pesticides still remains unclear. The midgut is the major organ of silkworm for digestion and nutrient absorption, and it plays a critical defensive role against pathogens. In the present study, the silkworm was susceptible to Enterobacter cloacae sp. (E. cloacae) after exposure to sublethal dose of phoxim. The body weight and survival rate of the phoxim-E. cloacae co-treatment group were significantly decreased after 120 h of treatment compared with the phoxim treatment group. The immune responses and expressions of immune-related genes were dysregulated in the midgut of silkworm following exposure to phoxim. Digital gene expression (DGE) analysis revealed that 44 immune response-related and immune defense-related genes were differentially expressed. qRT-PCR results indicated that the transcriptional levels of antimicrobial peptide genes Bmdefensin1, BmcecA, Bmglv1, Bmglv2, Bmmoricin and BmmoricinB3 were down-regulated by 0.77-, 0.37-, 0.05-, 0.19-, 0.34- and 0.54-fold, respectively. The transcriptional levels of Toll signaling pathway genes Bmcactus, Bmspatzle and Bmrel were down-regulated by 0.4-, 0.37- and 0.96-fold, respectively. Peritrophic membrane (PM) protein-related genes BmCBP-02, BmPM-41, BmPM-43 and BmCDA7 were down-regulated by 0.18-, 0.02-, 0.66- and 0.16-fold, respectively. The expressions of Toll signaling pathway genes were down-regulated at 48 h and 72 h. Immune deficiency (IMD) and Janus kinase and signal transducer and activator of transcription (JAK/STAT) signaling pathway genes were dysregulated after phoxim exposure. These results indicated that phoxim might cause damage to the PM and reduce the immune response of the silkworm, leading to susceptibility of silkworm to disease and damage from foreign pathogens.