Wolbachia Modulates Lipid Metabolism in Aedes albopictus Mosquito Cells

Dengue virus dominates lipid metabolism modulations in Wolbachia-coinfected Aedes aegypti

Competition between viruses and Wolbachia for host lipids is a proposed mechanism of Wolbachia-mediated virus blocking in insects. Yet, the metabolomic interaction between virus and symbiont within the mosquito has not been clearly defined. We compare the lipid profiles of Aedes aegypti mosquitoes bearing mono- or dual-infections of the Wolbachia wMel strain and dengue virus serotype 3 (DENV3). We found metabolic signatures of infection-induced intracellular events but little evidence to support direct competition between Wolbachia and virus for host lipids. Lipid profiles of dual-infected mosquitoes resemble those of DENV3 mono-infected mosquitoes, suggesting virus-driven modulation dominates over that of Wolbachia. Interestingly, knockdown of key metabolic enzymes suggests cardiolipins are host factors for DENV3 and Wolbachia replication. These findings define the Wolbachia-DENV3 metabolic interaction as indirectly antagonistic, rather than directly competitive, and reveal new research avenues with respect to mosquito × virus interactions at the molecular level.

Koh, Islam, Ye et al. describe lipid profiles of Aedes aegypti mosquitoes bearing mono- or dual-infections of Wolbachia (wMel) and dengue virus serotype 3 (DENV3), finding that virus modulation dominates the dual-infection lipid profile and that cardiolipins support DENV3 and Wolbachia replication. This study suggests that direct competition for lipids do not underlie Wolbachia-mediated virus blocking.

Artificial Selection Finds New Hypotheses for the Mechanism of Wolbachia-Mediated Dengue Blocking in Mosquitoes

Wolbachia is an intracellular bacterium that blocks virus replication in insects and has been introduced into the mosquito, Aedes aegypti for the biocontrol of arboviruses including dengue, Zika, and chikungunya. Despite ongoing research, the mechanism of Wolbachia-mediated virus blocking remains unclear. We recently used experimental evolution to reveal that Wolbachia-mediated dengue blocking could be selected upon in the A. aegypti host and showed evidence that strong levels of blocking could be maintained by natural selection. In this study, we investigate the genetic variation associated with blocking and use these analyses to generate testable hypotheses surrounding the mechanism of Wolbachia-mediated dengue blocking. From our results, we hypothesize that Wolbachia may block virus replication by increasing the regeneration rate of mosquito cells via the Notch signaling pathway. We also propose that Wolbachia modulates the host’s transcriptional pausing pathway either to prime the host’s anti-viral response or to directly inhibit viral replication.

Roles of Symbiotic Microorganisms in Arboviral Infection of Arthropod Vectors

Arthropod vectors serve as native reservoirs and transmitters of hundreds of arboviruses. In arthropod vectors, symbiotic microorganisms residing in the gut lumen and/or hemocoelic tissues maintain complicated relationships with their host and influence multiple aspects of vector physiology. Recently, accumulating evidence has established an important role for symbiotic microorganisms in vector-virus interactions which could potentially be used to control viral transmission. Herein, we review recent progress on symbiotic microbe-arbovirus interactions and summarize the molecular mechanisms by which commensal microbes act on hosts and arboviruses. Understanding the sophisticated interactions among arthropod vectors, microbiota, and arboviruses may offer new strategies for the prevention of arboviral diseases in the future.

A Role for the Insulin Receptor in the Suppression of Dengue Virus and Zika Virus in Wolbachia-Infected Mosquito Cells

Wolbachia-infected mosquitoes are refractory to super-infection with arthropod-borne pathogens, but the role of host cell signaling proteins in pathogen-blocking mechanisms remains to be elucidated. Here, we use an antibody microarray approach to provide a comprehensive picture of the signaling response of Aedes aegypti-derived cells to Wolbachia. This approach identifies the host cell insulin receptor as being downregulated by the bacterium. Furthermore, siRNA-mediated knockdown and treatment with a small-molecule inhibitor of the insulin receptor kinase concur to assign a crucial role for this enzyme in the replication of dengue and Zika viruses in cultured mosquito cells. Finally, we show that the production of Zika virus in Wolbachia-free live mosquitoes is impaired by treatment with the selective inhibitor mimicking Wolbachia infection. This study identifies Wolbachia-mediated downregulation of insulin receptor kinase activity as a mechanism contributing to the blocking of super-infection by arboviruses.

Tissue-specific analysis of lipid species in Drosophila during overnutrition by UHPLC-MS/MS and MALDI-MSI

Diets high in calories can be used to model metabolic diseases, including obesity and its associated comorbidities, in animals. Drosophila melanogaster fed high-sugar diets (HSDs) exhibit complications of human obesity including hyperglycemia, hyperlipidemia, insulin resistance, cardiomyopathy, increased susceptibility to infection, and reduced longevity. We hypothesize that lipid storage in the high-sugar-fed fly's fat body (FB) reaches a maximum capacity, resulting in the accumulation of toxic lipids in other tissues or lipotoxicity. We took two approaches to characterize tissue-specific lipotoxicity. Ultra-HPLC-MS/MS and MALDI-MS imaging enabled spatial and temporal localization of lipid species in the FB, heart, and hemolymph. Substituent chain length was diet dependent, with fewer odd chain esterified FAs on HSDs in all sample types. By contrast, dietary effects on double bond content differed among organs, consistent with a model where some substituent pools are shared and others are spatially restricted. Both di- and triglycerides increased on HSDs in all sample types, similar to observations in obese humans. Interestingly, there were dramatic effects of sugar feeding on lipid ethers, which have not been previously associated with lipotoxicity. Taken together, we have identified candidate endocrine mechanisms and molecular targets that may be involved in metabolic disease and lipotoxicity.

Technology innovation: advancing capacities for the early detection of and rapid response to invasive species

The 2016–2018National Invasive Species Council (NISC) Management Plan and Executive Order 13751 call for US federal agencies to foster technology development and application to address invasive species and their impacts. This paper complements and draws on an Innovation Summit, review of advanced biotechnologies applicable to invasive species management, and a survey of federal agencies that respond to these high-level directives. We provide an assessment of federal government capacities for the early detection of and rapid response to invasive species (EDRR) through advances in technology application; examples of emerging technologies for the detection, identification, reporting, and response to invasive species; and guidance for fostering further advancements in applicable technologies. Throughout the paper, we provide examples of how federal agencies are applying technologies to improve programmatic effectiveness and cost-efficiencies. We also highlight the outstanding technology-related needs identified by federal agencies to overcome barriers to enacting EDRR. Examples include improvements in research facility infrastructure, data mobilization across a wide range of invasive species parameters (from genetic to landscape scales), promotion of and support for filling key gaps in technological capacity (e.g., portable, field-ready devices with automated capacities), and greater investments in technology prizes and challenge competitions.

Microbial Control of Intestinal Homeostasis via Enteroendocrine Cell Innate Immune Signaling

A community of commensal microbes, known as the intestinal microbiota, resides within the gastrointestinal tract of animals and plays a role in maintenance of host metabolic homeostasis and resistance to pathogen invasion. Enteroendocrine cells, which are relatively rare in the intestinal epithelium, have evolved to sense and respond to these commensal microbes. Specifically, they express G-protein-coupled receptors and functional innate immune signaling pathways that recognize products of microbial metabolism and microbe-associated molecular patterns, respectively. Here we review recent evidence from Drosophila melanogaster that microbial cues recruit antimicrobial, mechanical, and metabolic branches of the enteroendocrine innate immune system and argue that this response may play a role not only in maintaining host metabolic homeostasis but also in intestinal resistance to invasion by bacterial, viral, and parasitic pathogens.

Proteomic analysis of Laodelphax striatellus gonads reveals proteins that may manipulate host reproduction by Wolbachia

Wolbachia are intracellular bacteria that manipulate host reproduction by several mechanisms including cytoplasmic incompatibility (CI). However, the underlying mechanisms of Wolbachia-induced CI are not entirely clear. Here, we monitored the Wolbachia distribution in the male gonads of the small brown planthopper (Laodelphax striatellus, SBPH) at different development stages, and investigated the influence of Wolbachia on male gonads by a quantitative proteomic analysis. A total of 276 differentially expressed proteins were identified, with the majority of them participating in metabolism, modification, and reproduction. Knocking down the expression of outer dense fiber protein (ODFP) and venom allergen 5-like (VA5L) showed decreased egg reproduction, and these two genes might be responsible for Wolbachia improved fecundity in infected L. striatellus; whereas knocking down the expression of cytosol amino-peptidase-like (CAL) significantly decreased the egg hatch rate in Wolbachia-uninfected L. striatellus, but not in the Wolbachia-infected one. Considering that the mRNA/protein level of CAL was downregulated by Wolbachia infection and dsCAL treatment closely mimicked Wolbachia-induced CI, we presumed that CAL might be one of the factors determining the CI phenotype.

Curious entanglements: interactions between mosquitoes, their microbiota, and arboviruses

Mosquitoes naturally harbor a diverse community of microorganisms that play a crucial role in their biology. Mosquito-microbiota interactions are abundant and complex. They can dramatically alter the mosquito immune response, and impede or enhance a mosquito's ability to transmit medically important arboviral pathogens. Yet critically, given the massive public health impact of arboviral disease, few such interactions have been well characterized. In this review, we describe the current state of knowledge of the role of microorganisms in mosquito biology, how microbial-induced changes to mosquito immunity moderate infection with arboviruses, cases of mosquito-microbial-virus interactions with a defined mechanism, and the molecular interactions that underlie the endosymbiotic bacterium Wolbachia's ability to block virus infection in mosquitoes.

How do Wolbachia modify the Drosophila ovary? New evidences support the "titration-restitution" model for the mechanisms of Wolbachia-induced CI

Background

Cytoplasmic incompatibility (CI) is the most common phenotype induced by endosymbiont Wolbachia and results in embryonic lethality when Wolbachia-modified sperm fertilize eggs without Wolbachia. However, eggs carrying the same strain of Wolbachia can rescue this embryonic death, thus producing viable Wolbachia-infected offspring. Hence Wolbachia can be transmitted mainly by hosts’ eggs. One of the models explaining CI is “titration-restitution”, which hypothesized that Wolbachia titrated-out some factors from the sperm and the Wolbachia in the egg would restitute the factors after fertilization. However, how infected eggs rescue CI and how hosts’ eggs ensure the proliferation and transmission of Wolbachia are not well understood.

Results

By RNA-seq analyses, we first compared the transcription profiles of Drosophila melanogaster adult ovaries with and without the wMel Wolbachia and identified 149 differentially expressed genes (DEGs), of which 116 genes were upregulated and 33 were downregulated by Wolbachia infection. To confirm the results obtained from RNA-seq and to screen genes potentially associated with reproduction, 15 DEGs were selected for quantitative RT-PCR (qRT-PCR). Thirteen genes showed the same changing trend as RNA-seq analyses. To test whether these genes are associated with CI, we also detected their expression levels in testes. Nine of them exhibited different changing trends in testes from those in ovaries. To investigate how these DEGs were regulated, sRNA sequencing was performed and identified seven microRNAs (miRNAs) that were all upregulated in fly ovaries by Wolbachia infection. Matching of miRNA and mRNA data showed that these seven miRNAs regulated 15 DEGs. Wolbachia-responsive genes in fly ovaries were involved in biological processes including metabolism, transportation, oxidation-reduction, immunity, and development.

Conclusions

Comparisons of mRNA and miRNA data from fly ovaries revealed 149 mRNAs and seven miRNAs that exhibit significant changes in expression due to Wolbachia infection. Notably, most of the DEGs showed variation in opposite directions in ovaries versus testes in the presence of Wolbachia, which generally supports the “titration-restitution” model for CI. Furthermore, genes related to metabolism were upregulated, which may benefit maximum proliferation and transmission of Wolbachia. This provides new insights into the molecular mechanisms of Wolbachia-induced CI and Wolbachia dependence on host ovaries.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5977-6) contains supplementary material, which is available to authorized users.

Infection of Aedes albopictus Mosquito C6/36 Cells with the wMelpop Strain of Wolbachia Modulates Dengue Virus-Induced Host Cellular Transcripts and Induces Critical Sequence Alterations in the Dengue Viral Genome

Dengue virus (DENV) causes frequent epidemics infecting ∼390 million people annually in over 100 countries. There are no approved vaccines or antiviral drugs for treatment of infected patients. However, there is a novel approach to control DENV transmission by the mosquito vectors, Aedes aegypti and Aedes albopictus, using the Wolbachia symbiont. The wMelPop strain of Wolbachia suppresses DENV transmission and shortens the mosquito life span. However, the underlying mechanism is poorly understood. To clarify this mechanism, either naive A. albopictus (C6/36) or wMelPop-C6/36 cells were infected with DENV serotype 2 (DENV2). Analysis of host transcript profiles by transcriptome sequencing (RNAseq) revealed that the presence of wMelPop dramatically altered the mosquito host cell transcription in response to DENV2 infection. The viral RNA evolved from wMelPop-C6/36 cells contained low-frequency mutations (∼25%) within the coding region of transmembrane domain 1 (TMD1) of E protein. Mutations with >97% frequencies were distributed within other regions of E, the NS5 RNA-dependent RNA polymerase (NS5POL) domain, and the TMDs of NS2A, NS2B, and NS4B. Moreover, while DENV2-infected naive C6/36 cells showed syncytium formation, DENV2-infected wMelPop-C6/36 cells did not. The Wolbachia-induced mutant DENV2 can readily infect and replicate in naive C6/36 cells, whereas in mutant DENV2-infected BHK-21 or Vero cells, virus replication was delayed. In LLC-MK2 cells, the mutant failed to produce plaques. Additionally, in BHK-21 cells, many mutations in the viral genome reverted to the wild type (WT) and compensatory mutations in NS3 gene appeared. Our results indicate that wMelPop impacts significantly the interactions of DENV2 with mosquito and mammalian host cells.IMPORTANCE Mosquito-borne diseases are of global significance causing considerable morbidity and mortality throughout the world. Dengue virus (DENV; serotypes 1 to 4), a member of the Flavivirus genus of the Flaviviridae family, causes millions of infections annually. Development of a safe vaccine is hampered due to absence of cross-protection and increased risk in secondary infections due to antibody-mediated immune enhancement. Infection of vector mosquitoes with Wolbachia bacteria offers a novel countermeasure to suppress DENV transmission, but the mechanisms are poorly understood. In this study, the host transcription profiles and viral RNA sequences were analyzed in naive A. albopictus (C6/36) and wMelPop-C6/36 cells by RNAseq. Our results showed that the wMelPop symbiont caused profound changes in host transcription profiles and morphology of DENV2-infected C6/36 cells. Accumulation of several mutations throughout DENV2 RNA resulted in loss of infectivity of progeny virions. Our findings offer new insights into the mechanism of Wolbachia-mediated suppression of DENV transmission.

Two-By-One model of cytoplasmic incompatibility: Synthetic recapitulation by transgenic expression of cifA and cifB in Drosophila

Wolbachia are maternally inherited bacteria that infect arthropod species worldwide and are deployed in vector control to curb arboviral spread using cytoplasmic incompatibility (CI). CI kills embryos when an infected male mates with an uninfected female, but the lethality is rescued if the female and her embryos are likewise infected. Two phage WO genes, cifA_wMel and cifB_wMel from the wMel Wolbachia deployed in vector control, transgenically recapitulate variably penetrant CI, and one of the same genes, cifA_wMel, rescues wild type CI. The proposed Two-by-One genetic model predicts that CI and rescue can be recapitulated by transgenic expression alone and that dual cifA_wMeland cifB_wMel expression can recapitulate strong CI. Here, we use hatch rate and gene expression analyses in transgenic Drosophila melanogaster to demonstrate that CI and rescue can be synthetically recapitulated in full, and strong, transgenic CI comparable to wild type CI is achievable. These data explicitly validate the Two-by-One model in wMel-infected D. melanogaster, establish a robust system for transgenic studies of CI in a model system, and represent the first case of completely engineering male and female animal reproduction to depend upon bacteriophage gene products.

Releases of Wolbachia-infected mosquitos are underway worldwide because Wolbachia block replication of Zika and Dengue viruses and spread themselves maternally through arthropod populations via cytoplasmic incompatibility (CI). The CI drive system depends on a Wolbachia-induced sperm modification that results in embryonic lethality when an infected male mates with an uninfected female, but this lethality is rescued when the female and her embryos are likewise infected. We recently reported that the phage WO genes, cifA and cifB, cause the sperm modification and cifA rescues the embryonic lethality caused by the wMel Wolbachia strain deployed in vector control. These reports motivated proposal of the Two-by-One model of CI whereby two genes cause lethality and one gene rescues it. Here we provide unequivocal support for the model in the Wolbachia strain used in vector control via synthetic methods that recapitulate CI and rescue in the absence of a Wolbachia infections. Our results reveal the set of phage WO genes responsible for this powerful genetic drive system, act as a proof-of-concept that these genes alone can induce gene drive like crossing patterns, and establish methodologies and hypotheses for future studies of CI in Drosophila. We discuss the implications of the Two-by-One model towards functional mechanisms of CI, the emergence of incompatibility between Wolbachia strains, vector control applications, and CI gene nomenclature.

The Mosquito Immune System and the Life of Dengue Virus: What We Know and Do Not Know

Flaviviruses are largely transmitted to humans by their arthropod vectors such as mosquitoes or ticks. The dengue virus (DENV) is one of the members of the family Flaviviridae and is the causative agent of dengue fever. In the mosquito vector, DENV enters through viremic blood meal and replicates in the mid-gut. Newly formed virion particles circulate to various mosquito organs and get transmitted to the next host in subsequent bites. Aedes aegypti and Aedes albopictus have intricate immune control to allow DENV production at a sub-pathogenic level. In the mosquito, antimicrobial peptides (AMP) and RNA inference (RNAi) are the two main antiviral strategies used against DENV. Apart from innate immunity, mosquito resident microbes play a significant role in modulating DENV replication. In this review, we discuss different immune mechanisms and preventive strategies that act against DENV in two of its vectors: Aedes aegypti and Aedes albopictus.

Discovery of short-course antiwolbachial quinazolines for elimination of filarial worm infections

Parasitic filarial nematodes cause debilitating infections in people in resource-limited countries. A clinically validated approach to eliminating worms uses a 4- to 6-week course of doxycycline that targetsWolbachia, a bacterial endosymbiont required for worm viability and reproduction. However, the prolonged length of therapy and contraindication in children and pregnant women have slowed adoption of this treatment. Here, we describe discovery and optimization of quinazolines CBR417 and CBR490 that, with a single dose, achieve >99% elimination ofWolbachiain the in vivoLitomosoides sigmodontisfilarial infection model. The efficacious quinazoline series was identified by pairing a primary cell-based high-content imaging screen with an orthogonal ex vivo validation assay to rapidly quantifyWolbachiaelimination inBrugia pahangifilarial ovaries. We screened 300,368 small molecules in the primary assay and identified 288 potent and selective hits. Of 134 primary hits tested, only 23.9% were active in the worm-based validation assay, 8 of which contained a quinazoline heterocycle core. Medicinal chemistry optimization generated quinazolines with excellent pharmacokinetic profiles in mice. Potent antiwolbachial activity was confirmed inL. sigmodontis,Brugia malayi, andOnchocerca ochengiin vivo preclinical models of filarial disease and in vitro selectivity againstLoa loa(a safety concern in endemic areas). The favorable efficacy and in vitro safety profiles of CBR490 and CBR417 further support these as clinical candidates for treatment of filarial infections.

Wolbachia endosymbionts subvert the endoplasmic reticulum to acquire host membranes without triggering ER stress

The reproductive parasites Wolbachia are the most common endosymbionts on earth, present in a plethora of arthropod species. They have been introduced into mosquitos to successfully prevent the spread of vector-borne diseases, yet the strategies of host cell subversion underlying their obligate intracellular lifestyle remain to be explored in depth in order to gain insights into the mechanisms of pathogen-blocking. Like some other intracellular bacteria, Wolbachia reside in a host-derived vacuole in order to replicate and escape the immune surveillance. Using here the pathogen-blocking Wolbachia strain from Drosophila melanogaster, introduced into two different Drosophila cell lines, we show that Wolbachia subvert the endoplasmic reticulum to acquire their vacuolar membrane and colonize the host cell at high density. Wolbachia redistribute the endoplasmic reticulum, and time lapse experiments reveal tight coupled dynamics suggesting important signalling events or nutrient uptake. Wolbachia infection however does not affect the tubular or cisternal morphologies. A fraction of endoplasmic reticulum becomes clustered, allowing the endosymbionts to reside in between the endoplasmic reticulum and the Golgi apparatus, possibly modulating the traffic between these two organelles. Gene expression analyses and immunostaining studies suggest that Wolbachia achieve persistent infections at very high titers without triggering endoplasmic reticulum stress or enhanced ERAD-driven proteolysis, suggesting that amino acid salvage is achieved through modulation of other signalling pathways.

Wolbachia are a genus of intracellular bacteria living in symbiosis with millions of arthropod species. They have the ability to block the transmission of arboviruses when introduced into mosquito vectors, by interfering with the cellular resources exploited by these viruses. Despite the biomedical interest of this symbiosis, little is known about the mechanisms by which Wolbachia survive and replicate in the host cell. We show here that the membrane composing the Wolbachia vacuole is acquired from the endoplasmic reticulum, a central organelle required for protein and lipid synthesis, and from which originates a vesicular trafficking toward the Golgi apparatus and the secretory pathway. Wolbachia modify the distribution of this organelle which is a potential source of membrane and likely of nutrients as well. In contrast to some intracellular pathogenic bacteria, the effect of Wolbachia on the cell homeostasis does not induce a stress on the endoplasmic reticulum. One of the consequences of such a stress would be an increased proteolysis used to relieve the cell from an excess of misfolded proteins. Incidentally, this suggests that Wolbachia do not acquire amino acids from the host cell through this strategy.

Cross-Generational Effects of Heat Stress on Fitness and Wolbachia Density in Aedes aegypti Mosquitoes

Aedes aegypti mosquitoes infected with Wolbachia symbionts are now being released into the field to control the spread of pathogenic human arboviruses. Wolbachia can spread throughout vector populations by inducing cytoplasmic incompatibility and can reduce disease transmission by interfering with virus replication. The success of this strategy depends on the effects of Wolbachia on mosquito fitness and the stability of Wolbachia infections across generations. Wolbachia infections are vulnerable to heat stress, and sustained periods of hot weather in the field may influence their utility as disease control agents, particularly if temperature effects persist across generations. To investigate the cross-generational effects of heat stress on Wolbachia density and mosquito fitness, we subjected Ae. aegypti with two different Wolbachia infection types (wMel, wAlbB) and uninfected controls to cyclical heat stress during larval development over two generations. We then tested adult starvation tolerance and wing length as measures of fitness and measured the density of wMel in adults. Both heat stress and Wolbachia infection reduced adult starvation tolerance. wMel Wolbachia density in female offspring was lower when mothers experienced heat stress, but male Wolbachia density did not depend on the rearing temperature of the previous generation. We also found cross-generational effects of heat stress on female starvation tolerance, but there was no cross-generational effect on wing length. Fitness costs of Wolbachia infections and cross-generational effects of heat stress on Wolbachia density may reduce the ability of Wolbachia to invade populations and control arbovirus transmission under specific environmental conditions.

Mapping Arbovirus-Vector Interactions Using Systems Biology Techniques

Studying how arthropod-borne viruses interact with their arthropod vectors is critical to understanding how these viruses replicate and are transmitted. Until recently, these types of studies were limited in scale because of the lack of classical tools available to study virus-host interaction for non-model viruses and non-model organisms. Advances in systems biology "-omics"-based techniques such as next-generation sequencing (NGS) and mass spectrometry can rapidly provide an unbiased view of arbovirus-vector interaction landscapes. In this mini-review, we discuss how arbovirus-vector interaction studies have been advanced by systems biology. We review studies of arbovirus-vector interactions that occur at multiple time and length scales, including intracellular interactions, interactions at the level of the organism, viral and vector populations, and how new techniques can integrate systems-level data across these different scales.

Whole genome screen reveals a novel relationship between Wolbachia levels and Drosophila host translation

Wolbachia is an intracellular bacterium that infects a remarkable range of insect hosts. Insects such as mosquitos act as vectors for many devastating human viruses such as Dengue, West Nile, and Zika. Remarkably, Wolbachia infection provides insect hosts with resistance to many arboviruses thereby rendering the insects ineffective as vectors. To utilize Wolbachia effectively as a tool against vector-borne viruses a better understanding of the host-Wolbachia relationship is needed. To investigate Wolbachia-insect interactions we used the Wolbachia/Drosophila model that provides a genetically tractable system for studying host-pathogen interactions. We coupled genome-wide RNAi screening with a novel high-throughput fluorescence in situ hybridization (FISH) assay to detect changes in Wolbachia levels in a Wolbachia-infected Drosophila cell line JW18. 1117 genes altered Wolbachia levels when knocked down by RNAi of which 329 genes increased and 788 genes decreased the level of Wolbachia. Validation of hits included in depth secondary screening using in vitro RNAi, Drosophila mutants, and Wolbachia-detection by DNA qPCR. A diverse set of host gene networks was identified to regulate Wolbachia levels and unexpectedly revealed that perturbations of host translation components such as the ribosome and translation initiation factors results in increased Wolbachia levels both in vitro using RNAi and in vivo using mutants and a chemical-based translation inhibition assay. This work provides evidence for Wolbachia-host translation interaction and strengthens our general understanding of the Wolbachia-host intracellular relationship.

Zika Virus and the Metabolism of Neuronal Cells

Zika virus (ZIKV) infection is associated with abnormal functions of neuronal cells causing neurological disorders such as microcephaly in the newborns and Guillain-Barré syndrome in the adults. Typically, healthy brain growth is associated with normal neural stem cell proliferation, differentiation, and maturation. This process requires a controlled cellular metabolism that is essential for normal migration, axonal elongation, and dendrite morphogenesis of newly generated neurons. Thus, the remarkable changes in the cellular metabolism during early stages of neuronal stem cell differentiation are crucial for brain development. Recent studies show that ZIKV directly infects neuronal stem cells in the fetus and impairs brain growth. In this review, we highlighted the fact that the activation of P53 and inhibition of the mTOR pathway by ZIKV infection to neuronal stem cells induces early shifting from glycolysis to oxidative phosphorylation (OXPHOS) may induce immature differentiation, apoptosis, and stem cell exhaustion. We hypothesize that ZIKV infection to mature myelin-producing cells and resulting metabolic shift may lead to the development of neurological diseases, such as Guillain-Barré syndrome. Thus, the effects of ZIKV on the cellular metabolism of neuronal cells may lead to the incidence of neurological disorders as observed recently during ZIKV infection.

Diverse Host and Restriction Factors Regulate Mosquito-Pathogen Interactions

Mosquitoes transmit diseases that seriously impact global human health. Despite extensive knowledge of the life cycles of mosquito-borne parasites and viruses within their hosts, control strategies have proven insufficient to halt their spread. An understanding of the relationships established between such pathogens and the host tissues they inhabit is therefore paramount for the development of new strategies that specifically target these interactions, to prevent the pathogens' maturation and transmission. Here we present an updated account of the antagonists and host factors that affect the development of Plasmodium, the parasite causing malaria, and mosquito-borne viruses, such as dengue virus and Zika virus, within their mosquito vectors, and we discuss the similarities and differences between Plasmodium and viral systems, looking toward the elucidation of new targets for disease control.

Conflict in the Intracellular Lives of Endosymbionts and Viruses: A Mechanistic Look at Wolbachia-Mediated Pathogen-blocking

At the forefront of vector control efforts are strategies that leverage host-microbe associations to reduce vectorial capacity. The most promising of these efforts employs Wolbachia, a maternally transmitted endosymbiotic bacterium naturally found in 40% of insects. Wolbachia can spread through a population of insects while simultaneously inhibiting the replication of viruses within its host. Despite successes in using Wolbachia-transfected mosquitoes to limit dengue, Zika, and chikungunya transmission, the mechanisms behind pathogen-blocking have not been fully characterized. Firstly, we discuss how Wolbachia and viruses both require specific host-derived structures, compounds, and processes to initiate and maintain infection. There is significant overlap in these requirements, and infection with either microbe often manifests as cellular stress, which may be a key component of Wolbachia’s anti-viral effect. Secondly, we discuss the current understanding of pathogen-blocking through this lens of cellular stress and develop a comprehensive view of how the lives of Wolbachia and viruses are fundamentally in conflict with each other. A thorough understanding of the genetic and cellular determinants of pathogen-blocking will significantly enhance the ability of vector control programs to deploy and maintain effective Wolbachia-mediated control measures.

Examining heat treatment for stabilization of the lipidome

AIM

To confidently determine lipid-based biomarkers, it is important to minimize variation introduced during preanalytical steps. We evaluated reducing variation associated with lipid measurements in invertebrate sentinel species using a state-of-the-art heat treatment technique.

MATERIALS AND METHODS

Earthworms (Eisenia fetida), house crickets (Acheta domestica) and ghost shrimp (Palaemonetes paludosus) were euthanized either by flash freezing or heat treatment. For both experiments, samples were either immediately extracted after removal from -80°C storage or incubated on ice for one hour prior to sample weighing and extraction. Lipidomics was performed on resulting extracts using liquid chromatography high resolution tandem mass spectrometry. LipidMatch and LipidSearch were used for lipid identification.

RESULTS

Lipid enzymatic products (e.g., phosphatidylmethanols, diglycerides, lysoglycerophospholipids and ether-linked/oxidized lysoglycerophospholipids), were in higher concentrations in flash-frozen samples, when compared with heat-treated samples. Results suggest that heat treatment reduces phospholipase A and phospholipase D activity.

CONCLUSION

Heat treatment reduced enzymatic products and increased precursors of these enzymatic products. We believe heat treatment warrants a closer interrogation for improving the robustness of lipid biomarker research, especially in tissue samples, where enzyme stabilizers are difficult to apply, and for use in field studies, where the stabilization of the collected sample is critical.

Dynamic remodeling of lipids coincides with dengue virus replication in the midgut of Aedes aegypti mosquitoes

We describe the first comprehensive analysis of the midgut metabolome of Aedes aegypti, the primary mosquito vector for arboviruses such as dengue, Zika, chikungunya and yellow fever viruses. Transmission of these viruses depends on their ability to infect, replicate and disseminate from several tissues in the mosquito vector. The metabolic environments within these tissues play crucial roles in these processes. Since these viruses are enveloped, viral replication, assembly and release occur on cellular membranes primed through the manipulation of host metabolism. Interference with this virus infection-induced metabolic environment is detrimental to viral replication in human and mosquito cell culture models. Here we present the first insight into the metabolic environment induced during arbovirus replication in Aedes aegypti. Using high-resolution mass spectrometry, we have analyzed the temporal metabolic perturbations that occur following dengue virus infection of the midgut tissue. This is the primary site of infection and replication, preceding systemic viral dissemination and transmission. We identified metabolites that exhibited a dynamic-profile across early-, mid- and late-infection time points. We observed a marked increase in the lipid content. An increase in glycerophospholipids, sphingolipids and fatty acyls was coincident with the kinetics of viral replication. Elevation of glycerolipid levels suggested a diversion of resources during infection from energy storage to synthetic pathways. Elevated levels of acyl-carnitines were observed, signaling disruptions in mitochondrial function and possible diversion of energy production. A central hub in the sphingolipid pathway that influenced dihydroceramide to ceramide ratios was identified as critical for the virus life cycle. This study also resulted in the first reconstruction of the sphingolipid pathway in Aedes aegypti. Given conservation in the replication mechanisms of several flaviviruses transmitted by this vector, our results highlight biochemical choke points that could be targeted to disrupt transmission of multiple pathogens by these mosquitoes.

Current concerns and perspectives on Zika virus co-infection with arboviruses and HIV

Dissemination of vector-borne viruses, such as Zika virus (ZIKV), in tropical and sub-tropical regions has a complicated impact on the immunopathogenesis of other endemic viruses such as dengue virus (DENV), chikungunya virus (CHIKV) and human immunodeficiency virus (HIV). The consequences of the possible co-infections with these viruses have specifically shown significant impact on the treatment and vaccination strategies. ZIKV is a mosquito-borne flavivirus from African and Asian lineages that causes neurological complications in infected humans. Many of DENV and CHIKV endemic regions have been experiencing outbreaks of ZIKV infection. Intriguingly, the mosquitoes, Aedes Aegypti and Aedes Albopictus, can simultaneously transmit all the combinations of ZIKV, DENV, and CHIKV to the humans. The co-circulation of these viruses leads to a complicated immune response due to the pre-existence or co-existence of ZIKV infection with DENV and CHIKV infections. The non-vector transmission of ZIKV, especially, via sexual intercourse and placenta represents an additional burden that may hander the treatment strategies of other sexually transmitted diseases such as HIV. Collectively, ZIKV co-circulation and co-infection with other viruses have inevitable impact on the host immune response, diagnosis techniques, and vaccine development strategies for the control of these co-infections.

Group B Wolbachia Strain-Dependent Inhibition of Arboviruses

Mosquito-borne viruses, including Zika virus (ZIKV) and dengue virus (DENV), are global threats that continue to infect millions annually. Historically, efforts to combat the spread of these diseases have sought to eradicate the mosquito population. This has had limited success. Recent efforts to combat the spread of these diseases have targeted the mosquito population and the mosquito's ability to transmit viruses by altering the mosquito's microbiome. The introduction of particular strains of Wolbachia bacteria into mosquitos suppresses viral growth and blocks disease transmission. This novel strategy is being tested worldwide to reduce DENV and has early indications of success. The Wolbachia genus comprised divergent strains that are divided in major phylogenetic clades termed supergroups. All Wolbachia field trials currently utilize supergroup A Wolbachia in Aedes aegypti mosquitos to limit virus transmission. Here we discuss our studies of Wolbachia strains not yet used in virus control strategies but that show strong potential to reduce ZIKV replication. These strains are important opportunities in the search for novel tools to reduce the levels of mosquito-borne viruses and provide additional models for mechanistic studies.

Upregulation of Aedes aegypti Vago1 by Wolbachia and its effect on dengue virus replication

Dengue infection along with its related disease conditions poses a significant threat to human health. The pathogen responsible for this infection is dengue virus (DENV) which is primarily transmitted to humans through the bites of Aedes aegypti mosquitoes. Unavailability of a potent vaccine has recently sparked renewed research endeavours aimed at vector control. To date, Wolbachia as an endosymbiotic bacterium has shown promise as a novel biocontrol agent to restrict DENV replication in the vector, although the underlying antiviral mechanism remains elusive. Recent studies have demonstrated the potential role of Vago as a novel secretory protein involved in cross-talk between the innate immune pathways in Culex quinquefasciatus mosquitoes to restrict West Nile virus replication. In this study, we have identified two homologs of the Vago protein in Ae. aegypti and looked into their modulation in the case of Wolbachia wMelPop strain infection. Furthermore, we have investigated the role of AeVago1, that is highly induced by Wolbachia, in the context of Wolbachia-mosquito-DENV interactions. Knockdown studies of the AeVago1 gene in Wolbachia-infected cells led to significant increases in DENV replication, with no effect on Wolbachia density. Our results suggest that the Wolbachia-induced AeVago1 in Ae. aegypti may function as a host factor to suppress DENV replication in the mosquito.

Family level variation in Wolbachia-mediated dengue virus blocking in Aedes aegypti

BACKGROUND

The mosquito vector Aedes aegypti is responsible for transmitting a range of arboviruses including dengue (DENV) and Zika (ZIKV). The global reach of these viruses is increasing due to an expansion of the mosquito's geographic range and increasing urbanization and human travel. Vector control remains the primary means for limiting these diseases. Wolbachia pipientis is an endosymbiotic bacterium of insects that has the ability to block the replication of pathogens, including flaviviruses such as DENV or ZIKV, inside the body of the vector. A strain of Wolbachia called wMel is currently being released into wild mosquito populations to test its potential to limit virus transmission to humans. The mechanism that underpins the virus blocking effect, however, remains elusive.

METHODS

We used a modified full-sib breeding design in conjunction with vector competence assays in wildtype and wMel-infected Aedes aegypti collected from the field. All individuals were injected with DENV-2 intrathoracically at 5-6 days of age. Tissues were dissected 7 days post-infection to allow quantification of DENV and Wolbachia loads.

RESULTS

We show the first evidence of family level variation in Wolbachia-mediated blocking in mosquitoes. This variation may stem from either genetic contributions from the mosquito and Wolbachia genomes or environmental influences on Wolbachia. In these families, we also tested for correlations between strength of blocking and expression level for several insect immunity genes with possible roles in blocking, identifying two genes of interest (AGO2 and SCP-2).

CONCLUSIONS

In this study we show variation in Wolbachia-mediated DENV blocking in Aedes aegypti that may arise from genetic contributions and environmental influences on the mosquito-Wolbachia association. This suggests that Wolbachia-mediated blocking may have the ability to evolve through time or be expressed differentially across environments. The long-term efficacy of Wolbachia in the field will be dependent on the stability of blocking. Understanding the mechanism of blocking will be necessary for successful development of strategies that counter the emergence of evolved resistance or variation in its expression under diverse field conditions.

Recent Perspectives on Genome, Transmission, Clinical Manifestation, Diagnosis, Therapeutic Strategies, Vaccine Developments, and Challenges of Zika Virus Research

One of the potential threats to public health microbiology in 21st century is the increased mortality rate caused by Zika virus (ZIKV), a mosquito-borne flavivirus. The severity of ZIKV infection urged World Health Organization (WHO) to declare this virus as a global concern. The limited knowledge on the structure, virulent factors, and replication mechanism of the virus posed as hindrance for vaccine development. Several vector and non-vector-borne mode of transmission are observed for spreading the disease. The similarities of the virus with other flaviviruses such as dengue and West Nile virus are worrisome; hence, there is high scope to undertake ZIKV research that probably provide insight for novel therapeutic intervention. Thus, this review focuses on the recent aspect of ZIKV research which includes the outbreak, genome structure, multiplication and propagation of the virus, current animal models, clinical manifestations, available treatment options (probable vaccines and therapeutics), and the recent advancements in computational drug discovery pipelines, challenges and limitation to undertake ZIKV research. The review suggests that the infection due to ZIKV became one of the universal concerns and an interdisciplinary environment of in vitro cellular assays, genomics, proteomics, and computational biology approaches probably contribute insights for screening of novel molecular targets for drug design. The review tried to provide cutting edge knowledge in ZIKV research with future insights required for the development of novel therapeutic remedies to curtail ZIKV infection.

Perturbed cholesterol and vesicular trafficking associated with dengue blocking in Wolbachia-infected Aedes aegypti cells

Wolbachia are intracellular maternally inherited bacteria that can spread through insect populations and block virus transmission by mosquitoes, providing an important approach to dengue control. To better understand the mechanisms of virus inhibition, we here perform proteomic quantification of the effects of Wolbachia in Aedes aegypti mosquito cells and midgut. Perturbations are observed in vesicular trafficking, lipid metabolism and in the endoplasmic reticulum that could impact viral entry and replication. Wolbachia-infected cells display a differential cholesterol profile, including elevated levels of esterified cholesterol, that is consistent with perturbed intracellular cholesterol trafficking. Cyclodextrins have been shown to reverse lipid accumulation defects in cells with disrupted cholesterol homeostasis. Treatment of Wolbachia-infected Ae. aegypti cells with 2-hydroxypropyl-β-cyclodextrin restores dengue replication in Wolbachia-carrying cells, suggesting dengue is inhibited in Wolbachia-infected cells by localised cholesterol accumulation. These results demonstrate parallels between the cellular Wolbachia viral inhibition phenotype and lipid storage genetic disorders.

Wolbachia infection of mosquitoes can block dengue virus infection and is tested in field trials, but the mechanism of action is unclear. Using proteomics, Geoghegan et al. here identify effects of Wolbachia on cholesterol homeostasis and dengue virus replication in Aedes aegypti.

Wolbachia-mediated virus blocking in the mosquito vector Aedes aegypti

Viruses transmitted by mosquitoes such as dengue, Zika and West Nile cause a threat to global health due to increased geographical range and frequency of outbreaks. The bacterium Wolbachia pipientis may be the solution reducing disease transmission. Though commonly missing in vector species, the bacterium was artificially and stably introduced into Aedes aegypti to assess its potential for biocontrol. When infected with Wolbachia, mosquitoes become refractory to infection by a range of pathogens, including the aforementioned viruses. How the bacterium is conferring this phenotype remains unknown. Here we discuss current hypotheses in the field for the mechanistic basis of pathogen blocking and evaluate the evidence from mosquitoes and related insects.

Variable Inhibition of Zika Virus Replication by Different Wolbachia Strains in Mosquito Cell Cultures

Mosquito-borne arboviruses are a major source of human disease. One strategy to reduce arbovirus disease is to reduce the mosquito's ability to transmit virus. Mosquito infection with the bacterial endosymbiont Wolbachia pipientis wMel is a novel strategy to reduce Aedes mosquito competency for flavivirus infection. However, experiments investigating cyclic environmental temperatures have shown a reduction in maternal transmission of wMel, potentially weakening the integration of this strain into a mosquito population relative to that of other Wolbachia strains. Consequently, it is important to investigate additional Wolbachia strains. All Zika virus (ZIKV) suppression studies are limited to the wMel Wolbachia strain. Here we show ZIKV inhibition by two different Wolbachia strains: wAlbB (isolated from Aedes albopictus mosquitoes) and wStri (isolated from the planthopper Laodelphax striatellus) in mosquito cells. Wolbachia strain wStri inhibited ZIKV most effectively. Single-cycle infection experiments showed that ZIKV RNA replication and nonstructural protein 5 translation were reduced below the limits of detection in wStri-containing cells, demonstrating early inhibition of virus replication. ZIKV replication was rescued when Wolbachia was inhibited with a bacteriostatic antibiotic. We observed a partial rescue of ZIKV growth when Wolbachia-infected cells were supplemented with cholesterol-lipid concentrate, suggesting competition for nutrients as one of the possible mechanisms of Wolbachia inhibition of ZIKV. Our data show that wAlbB and wStri infection causes inhibition of ZIKV, making them attractive candidates for further in vitro mechanistic and in vivo studies and future vector-centered approaches to limit ZIKV infection and spread.IMPORTANCE Zika virus (ZIKV) has swiftly spread throughout most of the Western Hemisphere. This is due in large part to its replication in and spread by a mosquito vector host. There is an urgent need for approaches that limit ZIKV replication in mosquitoes. One exciting approach for this is to use a bacterial endosymbiont called Wolbachia that can populate mosquito cells and inhibit ZIKV replication. Here we show that two different strains of Wolbachia, wAlbB and wStri, are effective at repressing ZIKV in mosquito cell lines. Repression of virus growth is through the inhibition of an early stage of infection and requires actively replicating Wolbachia Our findings further the understanding of Wolbachia viral inhibition and provide novel tools that can be used in an effort to limit ZIKV replication in the mosquito vector, thereby interrupting the transmission and spread of the virus.

Screening of Wolbachia Endosymbiont Infection in Aedes aegypti Mosquitoes Using Attenuated Total Reflection Mid-Infrared Spectroscopy

Dengue fever is the most common mosquito transmitted viral infection afflicting humans, estimated to generate around 390 million infections each year in over 100 countries. The introduction of the endosymbiotic bacterium Wolbachia into Aedes aegypti mosquitoes has the potential to greatly reduce the public health burden of the disease. This approach requires extensive polymerase chain reaction (PCR) testing of the Wolbachia-infection status of mosquitoes in areas where Wolbachia-A. aegypti are released. Here, we report the first example of small organism mid-infrared spectroscopy where we have applied attenuated total reflection Fourier transform infrared (ATR-FT-IR) spectroscopy and multivariate modeling methods to determine sex, age, and the presence of Wolbachia (wMel strain) in laboratory mosquitoes and sex and age in field mosquitoes. The prediction errors using partial least squares discriminant analysis (PLS-DA) discrimination models for laboratory studies on independent test sets ranged from 0 to 3% for age and sex grading and 3% to 5% for Wolbachia infection diagnosis using dry mosquito abdomens while field study results using an artificial neural network yielded a 10% error. The application of FT-IR analysis is inexpensive, easy to use, and portable and shows significant potential to replace the reliance on more expensive and laborious PCR assays.

Reliance of Wolbachia on High Rates of Host Proteolysis Revealed by a Genome-Wide RNAi Screen of Drosophila Cells

Wolbachia are gram-negative, obligate, intracellular bacteria carried by a majority of insect species worldwide. Here we use a Wolbachia-infected Drosophila cell line and genome-wide RNA interference (RNAi) screening to identify host factors that influence Wolbachia titer. By screening an RNAi library targeting 15,699 transcribed host genes, we identified 36 candidate genes that dramatically reduced Wolbachia titer and 41 that increased Wolbachia titer. Host gene knockdowns that reduced Wolbachia titer spanned a broad array of biological pathways including genes that influenced mitochondrial function and lipid metabolism. In addition, knockdown of seven genes in the host ubiquitin and proteolysis pathways significantly reduced Wolbachia titer. To test the in vivo relevance of these results, we found that drug and mutant inhibition of proteolysis reduced levels of Wolbachia in the Drosophila oocyte. The presence of Wolbachia in either cell lines or oocytes dramatically alters the distribution and abundance of ubiquitinated proteins. Functional studies revealed that maintenance of Wolbachia titer relies on an intact host Endoplasmic Reticulum (ER)-associated protein degradation pathway (ERAD). Accordingly, electron microscopy studies demonstrated that Wolbachia is intimately associated with the host ER and dramatically alters the morphology of this organelle. Given Wolbachia lack essential amino acid biosynthetic pathways, the reliance of Wolbachia on high rates of host proteolysis via ubiquitination and the ERAD pathways may be a key mechanism for provisioning Wolbachia with amino acids. In addition, the reliance of Wolbachia on the ERAD pathway and disruption of ER morphology suggests a previously unsuspected mechanism for Wolbachia's potent ability to prevent RNA virus replication.

Wolbachia Affects Reproduction and Population Dynamics of the Coffee Berry Borer (Hypothenemus hampei): Implications for Biological Control

Wolbachia are widely distributed endosymbiotic bacteria that influence the reproduction and fitness of their hosts. In recent years the manipulation of Wolbachia infection has been considered as a potential tool for biological control. The coffee berry borer (CBB), Hypothenemus hampei, is the most devastating coffee pest worldwide. Wolbachia infection in the CBB has been reported, but until now the role of Wolbachia in CBB reproduction and fitness has not been tested. To address this issue we reared the CBB in artificial diets with and without tetracycline (0.1% w/v) for ten generations. Tetracycline reduced significantly the relative proportion of Wolbachia in the CBB microbiota from 0.49% to 0.04%. This reduction affected CBB reproduction: females fed with tetracycline had significantly fewer progeny, lower fecundity, and fewer eggs per female. Tetracycline also reduced the population growth rate (λ), net reproductive rate (R₀), and mean generation time (T) in CBB; the reduction in population growth was mostly due to variation in fertility, according to life time response experiments (LTREs) analysis. Our results suggest that Wolbachia contribute to the reproductive success of the CBB and their manipulation represents a possible approach to CBB biocontrol mediated by microbiome management.

The transcriptome of the mosquito Aedes fluviatilis (Diptera: Culicidae), and transcriptional changes associated with its native Wolbachia infection

Background

Wolbachia is a bacterial endosymbiont that naturally infects a wide range of insect species, and causes drastic changes to host biology. Stable infections of Wolbachia in mosquitoes can inhibit infection with medically important pathogens such as dengue virus and malaria-causing Plasmodium parasites. However, some native Wolbachia strains can enhance infection with certain pathogens, as is the case for the mosquito Aedes fluviatilis, where infection with Plasmodium gallinaceum is enhanced by the native wFlu Wolbachia strain. To better understand the biological interactions between mosquitoes and native Wolbachia infections, and to investigate the process of pathogen enhancement, we used RNA-Seq to generate the transcriptome of Ae. fluviatilis with and without Wolbachia infection.

Results

In total, we generated 22,280,160 Illumina paired-end reads from Wolbachia-infected and uninfected mosquitoes, and used these to make a de novo transcriptome assembly, resulting in 58,013 contigs with a median sequence length of 443 bp and an N50 of 2454 bp. Contigs were annotated through local alignments using BlastX, and associated with both gene ontology and KEGG orthology terms. Through baySeq, we identified 159 contigs that were significantly upregulated due to Wolbachia infection, and 98 that were downregulated. Critically, we saw no changes to Toll or IMD immune gene transcription, but did see evidence that wFlu infection altered the expression of several bacterial recognition genes, and immune-related genes that could influence Plasmodium infection. wFlu infection also had a widespread effect on a number of host physiological processes including protein, carbohydrate and lipid metabolism, and oxidative stress. We then compared our data set with transcriptomic data for other Wolbachia infections in Aedes aegypti, and identified a core set of 15 gene groups associated with Wolbachia infection in mosquitoes.

Conclusions

While the scale of transcriptional changes associated with wFlu infection might be small, the scope is rather large, which confirms that native Wolbachia infections maintain intricate molecular relationships with their mosquito hosts even after lengthy periods of co-evolution. We have also identified several potential means through which wFlu infection might influence Plasmodium infection in Ae. fluviatilis, and these genes should form the basis of future investigation into the enhancement of Plasmodium by Wolbachia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-3441-4) contains supplementary material, which is available to authorized users.

Diet-Induced Nutritional Stress and Pathogen Interference in Wolbachia-Infected Aedes aegypti

The pathogen interference phenotype greatly restricts infection with dengue virus (DENV) and other pathogens in Wolbachia-infected Aedes aegypti, and is a vital component of Wolbachia-based mosquito control. Critically, the phenotype's causal mechanism is complex and poorly understood, with recent evidence suggesting that the cause may be species specific. To better understand this important phenotype, we investigated the role of diet-induced nutritional stress on interference against DENV and the avian malarial parasite Plasmodium gallinaceum in Wolbachia-infected Ae. aegypti, and on physiological processes linked to the phenotype. Wolbachia-infected mosquitoes were fed one of four different concentrations of sucrose, and then challenged with either P. gallinaceum or DENV. Interference against P. gallinaceum was significantly weakened by the change in diet however there was no effect on DENV interference. Immune gene expression and H2O2 levels have previously been linked to pathogen interference. These traits were assayed for mosquitoes on each diet using RT-qPCR and the Amplex Red Hydrogen Peroxide/Peroxidase Assay Kit, and it was observed that the change in diet did not significantly affect immune expression, but low carbohydrate levels led to a loss of ROS induction in Wolbachia-infected mosquitoes. Our data suggest that host nutrition may not influence DENV interference for Wolbachia-infected mosquitoes, but Plasmodium interference may be linked to both nutrition and oxidative stress. This pathogen-specific response to nutritional change highlights the complex nature of interactions between Wolbachia and pathogens in mosquitoes.

Lipids and flaviviruses, present and future perspectives for the control of dengue, Zika, and West Nile viruses

Flaviviruses are emerging arthropod-borne pathogens that cause life-threatening diseases such as yellow fever, dengue, West Nile encephalitis, tick-borne encephalitis, Kyasanur Forest disease, tick-borne encephalitis, or Zika disease. This viral genus groups >50 viral species of small enveloped plus strand RNA virus that are phylogenetically closely related to hepatitis C virus. Importantly, the flavivirus life cycle is intimately associated to host cell lipids. Along this line, flaviviruses rearrange intracellular membranes from the endoplasmic-reticulum of the infected cells to develop adequate platforms for viral replication and particle biogenesis. Moreover, flaviviruses dramatically orchestrate a profound reorganization of the host cell lipid metabolism to create a favorable environment for viral multiplication. Consistently, recent work has shown the importance of specific lipid classes in flavivirus infections. For instances, fatty acid synthesis is linked to viral replication, phosphatidylserine and phosphatidylethanolamine are involved on the entry of flaviviruses, sphingolipids (ceramide and sphingomyelin) play a key role on virus assembly and pathogenesis, and cholesterol is essential for innate immunity evasion in flavivirus-infected cells. Here, we revise the current knowledge on the interactions of the flaviviruses with the cellular lipid metabolism to identify potential targets for future antiviral development aimed to combat these relevant health-threatening pathogens.