Expression, purification and characterization of an atypical 2-Cys peroxiredoxin from the silkworm, Bombyx mori

Peroxiredoxin-4 supplementation modulates the immune response, shapes the intestinal microbiome, and enhances AHPND resistance in Penaeus vannamei

Peroxiredoxin-4 from Penaeus vannamei (LvPrx4) is considered a damage-associated molecular pattern (DAMP) that can activate the expression of immune-related genes through the Toll pathway. We previously demonstrated that the recombinant LvPrx4 (rLvPrx4) can enhance shrimp resistance against Vibrio parahaemolyticus, causing acute hepatopancreatic necrosis disease (VP_AHPND), which causes great production losses in shrimp farming. Herein, we showed that the rLvPrx4 had a thermal tolerance of around 60 °C and that the ionic strength had no noticeable effect on its activity. We discovered that feeding a diet containing rLvPrx4 to shrimp for three weeks increased the expression of the immune-related genes LvPEN4 and LvVago5. Furthermore, pre-treatment with rLvPrx4 feeding could significantly prolong shrimp survival following the VP_AHPND challenge. The shrimp intestinal microbiome was then characterized using PCR amplification of the 16S rRNA gene and Illumina sequencing. Three weeks of rLvPrx4 supplementation altered the bacterial community structure (beta diversity) and revealed the induction of differentially abundant families, including Cryomorphaceae, Flavobacteriaceae, Pirellulaceae, Rhodobacteraceae, and Verrucomicrobiaceae, in the rLvPrx4 group. Metagenomic predictions indicated that some amino acid metabolism pathways, such as arginine and proline metabolism, and genetic information processing were significantly elevated in the rLvPrx4 group compared to the control group. This study is the first to describe the potential use of rLvPrx4 supplementation to enhance shrimp resistance to VP_AHPND and alter the composition of a beneficial bacterial community in shrimp, making rLvPrx4 a promising feed supplement as an alternative to antibiotics for controlling VP_AHPND infection in shrimp aquaculture.

A thioredoxin peroxidase protects Pieris rapae from oxidative stress induced by chlorantraniliprole exposure

Chlorantraniliprole (CAP) is an insecticide widely used to control the small white butterfly (SWB), Pieris rapae. Exposure to CAP can cause oxidative injury in SWB; however, it is unclear if antioxidant enzymes are involved in the defense process. In this study, a thioredoxin peroxidase (PrTPX1) gene was identified from SWB by using a homology search method. The gene encoded a 195 amino-acid PrTPX1 protein. Sequence characteristics and phylogenetic analysis indicated that PrTPX1 was a typical "2-Cys" TPX, and the PrTPX1 gene consisted of four exons and three introns. Reverse transcription-quantitative polymerase chain reaction analysis indicated that the messenger RNA levels of PrTPX1 were highest in third-, fourth- and fifth-instar larval stages and in the larval midgut. Treatment with sublethal doses (LD₂₀ and LD₅₀ ) of CAP for 6, 12, 18, and 24 h resulted in increased H₂ O₂ concentration in SWB larvae, indicating insecticide-induced oxidative stress. The transcriptional levels of PrTPX1 were significantly enhanced in larvae exposed to CAP. Recombinant PrTPX1 protein was expressed in Escherichia coli. Enzymatic assay revealed that the protein displayed antioxidant activity and was able to protect against oxidative challenge. These results indicated that PrTPX1 plays an important role in oxidative stress responses and may contribute to the CAP tolerance in SWB.

Lepidopteran insects: emerging model organisms to study infection by enteropathogens

The in vivo analysis of a pathogen is a critical step in gaining greater knowledge of pathogen biology and host-pathogen interactions. In the last two decades, there has been a notable rise in the number of studies on developing insects as a model for studying pathogens, which provides various benefits, such as ethical acceptability, relatively short life cycle, and cost-effective care and maintenance relative to routinely used rodent infection models. Furthermore, lepidopteran insects provide many advantages, such as easy handling and tissue extraction due to their large size relative to other invertebrate models, like Caenorhabditis elegans. Additionally, insects have an innate immune system that is highly analogous to vertebrates. In the present review, we discuss the components of the insect's larval immune system, which strengthens its usage as an alternative host, and present an updated overview of the research findings involving lepidopteran insects (Galleria mellonella, Manduca sexta, Bombyx mori, and Helicoverpa armigera) as infection models to study the virulence by enteropathogens due to the homology between insect and vertebrate gut.

Synechococcus sp. PCC7002 Uses Peroxiredoxin to Cope with Reactive Sulfur Species Stress

Cyanobacteria are a widely distributed group of microorganisms in the ocean, and they often need to cope with the stress of reactive sulfur species, such as sulfide and sulfane sulfur. Sulfane sulfur refers to the various forms of zero-valent sulfur, including persulfide, polysulfide, and element sulfur (S₈). Although sulfane sulfur participates in signaling transduction and resistance to reactive oxygen species in cyanobacteria, it is toxic at high concentrations and induces sulfur stress, which has similar effects to oxidative stress. In this study, we report that Synechococcus sp. PCC7002 uses peroxiredoxin to cope with the stress of cellular sulfane sulfur. Synechococcus sp. PCC7002 contains six peroxiredoxins, and all were induced by S₈. Peroxiredoxin I (PrxI) reduced S₈ to H₂S by forming a disulfide bond between residues Cys⁵³ and Cys¹⁵³ of the enzyme. A partial deletion strain of Synechococcus sp. PCC7002 with decreased copy numbers of the prxI gene was more sensitive to S₈ than was the wild type. Thus, peroxiredoxin is involved in maintaining the homeostasis of cellular sulfane sulfur in cyanobacteria. Given that peroxiredoxin evolved before the occurrence of O₂ on Earth, its original function could have been to cope with reactive sulfur species stress, and that function has been preserved. IMPORTANCE Cyanobacteria are the earliest microorganisms that perform oxygenic photosynthesis, which has played a key role in the evolution of life on Earth, and they are the most important primary producers in the modern oceans. The cyanobacterium Synechococcus sp. PCC7002 uses peroxiredoxin to reduce high levels of sulfane sulfur. That function is possibly the original role of peroxiredoxin, as the enzyme evolved before the appearance of O₂ on Earth. The preservation of the reduction of sulfane sulfur by peroxiredoxin5-type peroxiredoxins may offer cyanobacteria an advantage in the complex environment of the modern oceans.

Molecular mechanism and potential application of bacterial infection in the silkworm, Bombyx mori

As a representative species of Lepidoptera, Bombyx mori has been widely studied and applied. However, bacterial infection has always been an important pathogen threatening the growth of silkworms. Bombyx mori can resist various pathogenic bacteria through their own physical barrier and innate immune system. However, compared with other insects, such as Drosophila melanogaster, research on the antibacterial mechanism of silkworms is still in its infancy. This review systematically summarized the routes of bacterial infection in silkworms, the antibacterial mechanism of silkworms after ingestion or wounding infection, and the intestinal bacteria and infection of silkworms. Finally, we will discuss silkworms as a model animal for studying bacterial infectious diseases and screening antibacterial drugs.

FoxO-promoted peroxiredoxin1 expression induced by Helicoverpa armigera single nucleopolyhedrovirus infection mediates host development and defensive responses

Helicoverpa armigera single nucleopolyhedrovirus (HearNPV) has a long coevolutionary history with its host, exerting profound effects on larval development, physiology and immune responses, although the mechanisms mediating these effects remain unclear. We demonstrate that HearNPV infection constrains the growth and development of larvae by inducing high levels of reactive oxygen species (ROS), which increase the expression of forkhead box O transcription factor (FoxO). FoxO upregulates the expression of peroxiredoxin 1 (Prx1) which serves to regulate larval development and immune responses following HearNPV infection. Collectively, our results provide novel insights into the role of Prx1 in larval development and immunity subsequent to HearNPV infection. Further investigation of the oxidative stress induced by HearNPV in H. armigera and its interactions with host immunity could yield novel insights useful in agricultural pest control.

The OxrA Protein of Aspergillus fumigatus Is Required for the Oxidative Stress Response and Fungal Pathogenesis

An efficient reactive oxygen species (ROS) detoxification system is vital for the survival of the pathogenic fungus Aspergillus fumigatus within the host high-ROS environment of the host. Therefore, identifying and targeting factors essential for oxidative stress response is one approach to developing novel treatments for fungal infections. The oxidation resistance 1 (Oxr1) protein is essential for protection against oxidative stress in mammals, but its functions in pathogenic fungi remain unknown. The present study aimed to characterize the role of an Oxr1 homolog in A. fumigatus. The results indicated that the OxrA protein plays an important role in oxidative stress resistance by regulating the catalase function in A. fumigatus, and overexpression of catalase can rescue the phenotype associated with OxrA deficiency. Importantly, the deficiency of oxrA decreased the virulence of A. fumigatus and altered the host immune response. Using the Aspergillus-induced lung infection model, we demonstrated that the ΔoxrA mutant strain induced less tissue damage along with decreased levels of lactate dehydrogenase (LDH) and albumin release. Additionally, the ΔoxrA mutant caused inflammation at a lower degree, along with a markedly reduced influx of neutrophils to the lungs and a decreased secretion of cytokine usually associated with recruitment of neutrophils in mice. These results characterize the role of OxrA in A. fumigatus as a core regulator of oxidative stress resistance and fungal pathogenesis. IMPORTANCE Knowledge of ROS detoxification in fungal pathogens is useful in the design of new antifungal drugs and could aid in the study of oxidative stress resistance mechanisms. In this study, we demonstrate that OxrA protein localizes to the mitochondria and functions to protect against oxidative damage. We demonstrate that OxrA contributes to oxidative stress resistance by regulating catalase function, and overexpression of catalase (CatA or CatB) can rescue the phenotype that is associated with OxrA deficiency. Remarkably, a loss of OxrA attenuated the fungal virulence in a mouse model of invasive pulmonary aspergillosis and altered the host immune response. Therefore, our finding indicates that inhibition of OxrA might be an effective approach for alleviating A. fumigatus infection. The present study is, to the best of our knowledge, a pioneer in reporting the vital role of Oxr1 protein in pathogenic fungi.

Reactive oxygen species and antimicrobial peptides are sequentially produced in silkworm midgut in response to bacterial infection

The silkworm, Bombyx mori, is utilized as a research model in many aspects of biological studies, including genetics, development and immunology. Previous biochemical and genomic studies have elucidated the silkworm immunity in response to infections elicited by bacteria, fungi, microsporidia, and viruses. The intestine serves as the front line in the battle between insects and ingested harmful microorganisms. In this study, we performed RNA sequencing (RNA-seq) of the larval silkworm midgut after oral infection with the Gram-positive bacterium Bacillus bombysepticus and the Gram-negative bacterium Yersinia pseudotuberculosis. This enables us to get a comprehensive understanding of the midgut responses to bacterial infection. We found that B. bombysepticus induced much stronger immune responses than Y. pseudotuberculosis did. Bacterial infection resulted in more energy consumption including carbohydrates and fatty acids. The midgut immune system was characterized by the generation of reactive oxygen species and antimicrobial peptides. The former played a critical role in eliminating invading bacteria during early stage, while the latter executed during late stage. Our results provide an integrated insight into the midgut systematic responses to bacterial infection.

Molecular characterization of a typical 2-Cys thioredoxin peroxidase from the Asiatic rice borer Chilo suppressalis and its role in oxidative stress

In insects, thioredoxin peroxidase (TPX) plays an important role in protecting against oxidative damage. However, studies on the molecular characteristics of TPXs in the Asiatic rice borer, Chilo suppressalis, are limited. In this work, a cDNA sequence (CsTpx3) encoding a TPX was identified from C. suppressalis. The deduced CsTPX3 protein shares high sequence identity and two positionally conserved cysteines with orthologs from other insect species, and was classified as a typical 2-Cys TPX. CsTpx3 was expressed most highly during the fifth-instar larval stage, and transcripts were most abundant in the midgut. Recombinant CsTPX3 protein expressed in Escherichia coli displayed the expected peroxidase activity by removing H₂ O₂ . Furthermore, CsTPX3 protected DNA from oxidative damage, and E. coli cells overexpressing CsTPX3 exhibited long-term resistance to oxidative stress. Exposure to various oxidative stressors, such as cold (8°C), heat (35°C), bacteria (E. coli), and two insecticides (chlorpyrifos and lambda-cyhalothrin), significantly upregulated transcription of CsTpx3. However, exposure to abamectin had no such effect. Our results provide valuable information for future studies on the antioxidant mechanism in this insect species.

Immune responses to bacterial and fungal infections in the silkworm, Bombyx mori

The silkworm Bombyx mori, an economically important insect that is usually reared indoors, is susceptible to various pathogens, including bacteria, fungi, viruses, and microsporidia. As with other insects, the silkworm lacks an adaptive immune system and relies solely on innate immunity to defend itself against infection. Compared to other intensively studied insects, such as the fruit fly and tobacco hornworm, the principal immune pathways in the silkworm remain unclear. In this article, we review the literature concerning silkworm immune responses to bacteria and fungi and present our perspectives on future research into silkworm immunity.

Possible Insecticidal Mechanisms Mediated by Immune-Response-Related Cry-Binding Proteins in the Midgut Juice of Plutella xylostella and Spodoptera exigua

Cry toxins are insecticidal toxin proteins produced by a spore-forming Gram-positive bacterium Bacillus thuringiensis. Interactions between the Cry toxins and the receptors from midgut brush border membrane vesicles (BBMVs), such as cadherin, alkaline phosphatase, and aminopeptidase, are key steps for the specificity and insecticidal activity of Cry proteins. However, little is known about the midgut juice proteins that may interfere with Cry binding to the receptors. To validate the hypothesis that there exist Cry-binding proteins that can interfere with the insecticidal process of Cry toxins, we applied Cry1Ab1-coupled Sepharose beads to isolate Cry-binding proteins form midgut juice of Plutella xylostella and Spodoptera exigua. Trypsin-like serine proteases and Dorsal were found to be Cry1Ab1-binding proteins in the midgut juice of P. xylostella. Peroxidase-C (POX-C) was found to be the Cry1Ab1-binding protein in the midgut juice of S. exigua. We proposed possible insecticidal mechanisms of Cry1Ab1 mediated by the two immune-related proteins: Dorsal and POX-C. Our results suggested that there exist, in the midgut juice, Cry-binding proteins, which are different from BBMV-specific receptors.

Oxidation resistance 1 (OXR1) participates in silkworm defense against bacterial infection through the JNK pathway

Bacterial infection causes enhanced reactive oxygen species (ROS) levels in insects. Oxidation resistance 1 (OXR1) plays an antioxidant role in eukaryotic organisms, including insects. In this report, we demonstrated that Pseudomonas aeruginosa and Staphylococcus aureus infection and hydrogen peroxide (H₂ O₂ ) injection induced the expression of specific transcriptional isoforms of OXR1 in larval silkworms. We further showed that a Jun kinase (JNK) pathway inhibitor, SP600125, down-regulated expression of OXR1 during infection, leading to elevated H₂ O₂ levels in the hemolymph, resulting in lower viability of the injected bacteria inside the silkworm larvae. Our study suggests that OXR1 participates in protecting larval silkworms from oxidative stress and bacterial infection through the JNK pathway.

Gut immunity in Lepidopteran insects

Lepidopteran insects constitute one of the largest fractions of animals on earth, but are considered pests in their relationship with man. Key to the success of this order of insects is its ability to digest food and absorb nutrition, which takes place in the midgut. Because environmental microorganisms can easily enter Lepidopteran guts during feeding, the innate immune response guards against pathogenic bacteria, virus and microsporidia that can be devoured with food. Gut immune responses are complicated by both resident gut microbiota and the surrounding peritrophic membrane and are distinct from immune responses in the body cavity, which depend on the function of the fat body and hemocytes. Due to their relevance to agricultural production, studies of Lepidopteran insect midgut and immunity are receiving more attention, and here we summarize gut structures and functions, and discuss how these confer immunity against different microorganisms. It is expected that increased knowledge of Lepidopteran gut immunity may be utilized for pest biological control in the future.

2-Cys peroxiredoxin is required in successful blood-feeding, reproduction, and antioxidant response in the hard tick Haemaphysalis longicornis

BACKGROUND

Ticks are obligate hematophagous arthropods that feed on vertebrate blood that contains iron. Ticks also concentrate host blood with iron; this concentration of the blood leads to high levels of iron in ticks. The host-derived iron reacts with oxygen in the tick body and this may generate high levels of reactive oxygen species, including hydrogen peroxide (H2O2). High levels of H2O2 cause oxidative stress in organisms and therefore, antioxidant responses are necessary to regulate H2O2. Here, we focused on peroxiredoxin (Prx), an H2O2-scavenging enzyme in the hard tick Haemaphysalis longicornis.

METHODS

The mRNA and protein expression profiles of 2-Cys peroxiredoxin (HlPrx2) in H. longicornis were investigated in whole ticks and internal organs, and developmental stages, using real-time PCR and Western blot analysis during blood-feeding. The localization of HlPrx2 proteins in tick tissues was also observed by immunostaining. Moreover, knockdown experiments of HlPrx2 were performed using RNA interference to evaluate its function in ticks.

RESULTS

Real-time PCR showed that HlPrx2 gene expression in whole ticks and internal organs was significantly upregulated by blood-feeding. However, protein expression, except in the midgut, was constant throughout blood-feeding. Knockdown of the HlPrx2 gene caused significant differences in the engorged body weight, egg weight and hatching rate for larvae as compared to the control group. Finally, detection of H2O2 after knockdown of HlPrxs in ticks showed that the concentration of H2O2 significantly increased before and after blood-feeding.

CONCLUSION

Therefore, HlPrx2 can be considered important for successful blood-feeding and reproduction through the regulation of H2O2 concentrations in ticks before and after blood-feeding. This study contributes to the search for a candidate target for tick control and further understanding of the tick's oxidative stress coping mechanism during blood-feeding.

Identification and characterization of an atypical 2-cys peroxiredoxin from the silkworm, Bombyx mori

Peroxiredoxins (Prxs) play an important role in the protection of insects against the toxicity of reactive oxygen species. Here, we identified and characterized a novel, atypical 2-cysteine (Cys) peroxiredoxin (BmPrx3) from an expressed sequence tag database in a lepidopteran insect, Bombyx mori. The BmPrx3 cDNA contained an open reading frame of 684 bp that encodes a 228-amino-acid protein with a calculated molecular mass of 25 kDa. Sequence comparison revealed that BmPrx3 belongs to the atypical 2-Cys Prxs. Quantitative real-time PCR revealed that BmPrx3 can be detected in all tissues and developmental stages. Recombinant BmPrx3 purified from Escherichia coli exhibited antioxidant activity that removed hydrogen peroxide and protected DNA from oxidative damage. Disc diffusion and viability assays revealed that recombinant BmPrx3 increased bacterial survival under H2 O2 -mediated oxidative stress. In addition, quantitative real-time PCR analysis indicated that BmPrx3 transcription levels were significantly increased in response to various oxidative stresses. Furthermore, BmPrx3 transcription levels in the midgut were regulated by bacterial infection. Taken together, these results suggest that BmPrx3 acts as an antioxidant enzyme to protect the silkworm from various oxidative stresses.

Multiple Roles of Peroxiredoxins in Inflammation

Inflammation is a pathophysiological response to infection or tissue damage during which high levels of reactive oxygen and nitrogen species are produced by phagocytes to kill microorganisms. Reactive oxygen and nitrogen species serve also in the complex regulation of inflammatory processes. Recently, it has been proposed that peroxiredoxins may play key roles in innate immunity and inflammation. Indeed, peroxiredoxins are evolutionarily conserved peroxidases able to reduce, with high rate constants, hydrogen peroxide, alkyl hydroperoxides and peroxynitrite which are generated during inflammation. In this minireview, we point out different possible roles of peroxiredoxins during inflammatory processes such as cytoprotective enzymes against oxidative stress, modulators of redox signaling, and extracellular pathogen- or damage-associated molecular patterns. A better understanding of peroxiredoxin functions in inflammation could lead to the discovery of new therapeutic targets.

Peroxiredoxin 1 protects the pea aphid Acyrthosiphon pisum from oxidative stress induced by Micrococcus luteus infection

Reactive oxygen species (ROSs) are generated in organisms in response to infections caused by invading microbes. However, excessive ROSs will inflict oxidative damage on the host. Peroxiredoxins (Prxs) are antioxidative enzymes that may eliminate ROSs efficiently. In this study, ApPrx1 from the pea aphid Acyrthosiphon pisum was cloned, and its function was investigated in vitro and in vivo. In the presence of DTT, recombinant ApPrx1 protein from Escherichia coli showed antioxidative activity by eliminating H2O2 effectively. The H2O2 levels were significantly higher in Micrococcus luteus-infected aphids than in uninfected aphids, and ApPrx1 expression was remarkably up-regulated when the aphids were infected with M. luteus or injected with H2O2. When ApPrx1 expression was reduced by dsRNA injection, the survival of the aphids decreased significantly after M. luteus infection. Knockdown of ApPrx1 decreased M. luteus loads inside the aphids 48h post-infection. While under infection conditions, the H2O2 levels were much higher in ApPrx1 knockdown aphids than in dsGFP-injected aphids, indicating that the decreased survival of the aphids was caused by increased oxidative stress. Taken together, our results reveal that ApPrx1 plays a protective role in oxidative stress caused by bacterial infection.