Anti-lipopolysaccharide factor D from kuruma shrimp exhibits antiviral activity

Spätzle maintains homeostasis of hemolymph microbiota in Scylla paramamosain through Toll2

The Toll pathway is crucial for innate immune responses in organisms (including Drosophila and mammals). The Spätzle protein outside of cells acts as a ligand for Toll receptors, enabling the transfer of signals from outside the cell to the inside. However, the function of Spätzle in the immune system of mud crab (Scylla paramamosain) remains unclear. This research discovered a novel Spätzle gene (Sp-Spz) in mud crab, which showed extensive expression in all the tissues that were examined. The RNA interference exhibited the correlation between Sp-Spz and the anti-lipopolysaccharide factors (ALFs). Knockdown of Sp-Spz decreased the expression of Sp-Toll2 but not Sp-Toll1. In Drosophila Schneider 2 cells, Sp-Spz was found interacted with Sp-Toll2. Moreover, the depletion of Sp-Spz caused the separation of hepatic lobules from the basement membrane, resulting in the disruption of the structural coherence of hepatopancreatic cells. Additionally, the knockdown of Sp-Spz resulted in changes to the composition of the hemolymph microbiota, specifically affecting the proportions of different phylum and family levels. The findings indicated that Sp-Spz may promote the synthesis of ALFs via Sp-Toll2, thereby influencing the homeostasis of microbiota in the hemolymph. In this study, novel insights into mud crab immunity are provided.

Correlative analysis of transcriptome and proteome in Penaeus vannamei reveals key signaling pathways are involved in IFN-like antiviral regulation mediated by interferon regulatory factor (PvIRF)

Interferon regulatory factors (IRFs) are crucial transcription factors that regulate interferon (IFN) induction in response to pathogen invasion. The regulatory mechanism of IRF has been well studied in vertebrates, but little has been known in arthropods. Therefore, in order to obtain new insights into the potential molecular mechanism of Peneaus vannamei IRF (PvIRF) in response to viral infection, comprehensive comparative analysis of the transcriptome and proteome profiles in shrimp infected with WSSV after knocking down PvIRF was conducted by using RNA sequencing (RNA-seq) and isobaric tags for relative and absolute quantification (iTRAQ). The sequence characterization, molecular functional evolution and 3D spatial structure of PvIRF were analyzed by using bioinformatics methods. PvIRF share the higher homology with different species in N-terminal end (containing DNA binding domain (DBD) including DNA sequence recognition sites and metal binding site) than that in C-terminal end. Within 4 IRF subfamilies of vertebrates, PvIRF had closer relationship with IRF1 subfamily. The DBD of PvIRF and C. gigas IRF1a were composed of α-helices and β-folds which was similar with the DBD structure of M. musculus IRF2. Interestingly, different from the five Tryptophan repeats highly homologous in the DBD of vertebrate IRF, the first and fifth tryptophans of PvIRF mutate to Phenylalanine and Leucine respectively, while the mutations were conserved among shrimp IRFs. RNAi knockdown of PvIRF gene by double-strand RNA could obviously promote the in vivo propagation of WSSV in shrimp and increase the mortality of WSSV-infected shrimp. It suggested that PvIRF was involved in inhibiting the replication of WSSV in shrimp. A total of 8787 transcripts and 2846 proteins were identified with significantly differential abundances in WSSV-infected shrimp after PvIRF knockdown, among which several immune-related members were identified and categorized into 10 groups according to their possible functions. Furthermore, the variation of expression profile from members of key signaling pathways involving JAK/STAT and Toll signaling pathway implied that they might participate IRF-mediated IFN-like regulation in shrimp. Correlative analyses indicated that 722 differentially expressed proteins (DEPs) shared the same expression profiles with their corresponding transcripts, including recognition-related proteins (CTLs and ITGs), chitin-binding proteins (peritrophin), and effectors (ALFs and SWD), while 401 DEPs with the opposite expression profiles across the two levels emphasized the critical role of post-transcriptional and post-translational modification. The results provide candidate signaling pathway including pivotal genes and proteins involved in the regulatory mechanism of interferon mediated by IRF on shrimp antiviral response. This is the first report in crustacean to explore the IFN-like antiviral regulation pathway mediated by IRF on the basis of transcriptome and proteomics correlative analysis, and will provide new ideas for further research on innate immune and defense mechanisms of crustacean.

Scavenger receptor B2, a type III membrane pattern recognition receptor, senses LPS and activates the IMD pathway in crustaceans

The immune deficiency (IMD) pathway is critical for elevating host immunity in both insects and crustaceans. The IMD pathway activation in insects is mediated by peptidoglycan recognition proteins, which do not exist in crustaceans, suggesting a previously unidentified mechanism involved in crustacean IMD pathway activation. In this study, we identified a Marsupenaeus japonicus B class type III scavenger receptor, SRB2, as a receptor for activation of the IMD pathway. SRB2 is up-regulated upon bacterial challenge, while its depletion exacerbates bacterial proliferation and shrimp mortality via abolishing the expression of antimicrobial peptides. The extracellular domain of SRB2 recognizes bacterial lipopolysaccharide (LPS), while its C-terminal intracellular region containing a cryptic RHIM-like motif interacts with IMD, and activates the pathway by promoting nuclear translocation of RELISH. Overexpressing shrimp SRB2 in Drosophila melanogaster S2 cells potentiates LPS-induced IMD pathway activation and diptericin expression. These results unveil a previously unrecognized SRB2-IMD axis responsible for antimicrobial peptide induction and restriction of bacterial infection in crustaceans and provide evidence of biological diversity of IMD signaling in animals. A better understanding of the innate immunity of crustaceans will permit the optimization of prevention and treatment strategies against the arising shrimp diseases.

Immune responses and histopathological analyses of giant river prawn (Macrobrachium rosenbergii, De Man 1879) challenged with a sub-lethal dose of decapod iridescent virus 1 (DIV1) and chemical control investigation

Decapod iridescent virus 1 (DIV1) is a lethal virus that has a significant influence on the shrimp and prawn culture industries. The mechanism through which infected prawns respond to the DIV1 virus is currently unknown. Here, we examined in detail the clinical signs, histopathology, and humoral, cellular, and immune-related gene responses after a sub-lethal dose of DIV1 during the acute infection period of 0-120 hours post infection (hpi). Interestingly, at the end of the experiment, DIV1-infected prawns had black lesions on several external regions. The DIV1-infected prawns also exhibited few karyopyknotic nuclei in the gills and intestine tissues and exhibited increasing immunological responses, as revealed by significant increases in all examined parameters, including total hemocytes, phagocytosis, lysozyme, and overall bactericidal activity, from 6 to 48 hpi. In addition, between 72 and 120 hpi, all immune response activities of DIV1-infected prawn were impaired compared with those of normal prawns, indicating negative impacts on immunological parameters. A viral load analysis of various tissues by qPCR indicated that hemocytes were the dominant initial viral target tissues, followed by the gills and hepatopancreas. An expression analysis of crucial immune-related genes by qRT‒PCR revealed various expression patterns in response to DIV1 infection; in particular, fold changes in the relative expression of anti-lipopolysaccharide factors (ALFs), prophenoloxidase (proPO), lipopolysaccharide and β-1,3-glucan binding protein (LGBP) were observed. Additionally, five common chemicals, calcium hypochlorite [Ca(OCl)₂] at 16.25-130 ppm, hydrogen peroxide (H₂O₂) at 8.75-70 ppm, povidone iodine (PVP-I) at 3-24 ppm, benzalkonium chloride (BKC) at 20-160 ppm, and formalin at 25-200 ppm, had a significant effect on the killing of DIV1 particles in vitro within 24 h after exposure. These data will be helpful for determining the health status and immune defense mechanisms of giant river prawns during DIV1 infection periods. The study performed the first application of very common disinfectants, and the obtained information will be useful for implementing effective strategies to prevent and control DIV1 infection in both hatchery and grow-out ponds.

A novel anti-lipopolysaccharide factor from blue swimmer crab Portunus pelagicus and its cytotoxic effect on the prokaryotic expression host, E. coli on heterologous expression

BACKGROUND

Invertebrates like crabs employ their own immune systems to fight against a number of invasive infections. Anti-lipopolysaccharide factors (ALFs) are an important class of antimicrobial peptides (AMPs) exhibiting binding and neutralizing activities against lipopolysaccharides.

RESULTS

This study identified and characterized a novel homolog of ALF (Pp-ALF) from the blue swimmer crab Portunus pelagicus. Pp-ALF has a 369bp open-reading frame encoding a protein with 123 amino acids. The deduced protein featured an LPS-binding domain and a signal peptide. The predicted tertiary structure of Pp-ALF contains three α helices packed against four β sheets. The deduced amino acid sequence of Pp-ALF had a net positive charge of +10.75 and an isoelectric point of 9.8. Phylogenetic analysis revealed that Pp-ALF has a strong ancestral relationship with crab ALFs.

CONCLUSION

Antibacterial, antiviral, antifungal, anticancer, and antibiofilm activities of Pp-ALF could be revealed by in silico prediction tools. Recombinant expression of Pp-ALF was unsuccessful in the Escherichia coli Rosetta-gami expression system due to the cytotoxic effect of the peptide to the host. The toxic effect of Pp-ALF to the host was displayed by membrane permeabilization and death of the host cells by fluorescent staining with Syto9-Propidium Iodide and CTC-DAPI- FITC.

The sORF-Encoded Peptides, ATP Synthase Subunits, Facilitate WSSV Duplication in Shrimp

Short open reading frames (sORFs) are a newly identified family of genes, and the functions of most sORF genes and their encoded peptides (SEPs) are still unknown. In this study, two ATP synthase subunits were identified in kuruma shrimp (Marsupenaeus japonicus) as SEPs, namely MjATP5I and MjATP5L. They were widely distributed in all of the tested tissues of shrimp and upregulated in hemocytes and intestines in response to WSSV challenge. The injection of recombinant proteins (rMjATP5I and rMjATP5L) increased the expression of Ie1 and Vp28, while the knockdown of MjATP5I and MjATP5L decreased the expression of Ie1 and Vp28. All of the results suggest that MjATP5I and MjATP5L were beneficial for WSSV replication. Further exploration found that MjATP5I and MjATP5L RNAi significantly improved the shrimp survival rates, reduced ATP production, and upregulated the expression of antimicrobial peptide genes post viral challenge, and the two ATPase subunits and Relish negatively regulated each other. These results reveal that MjATP5I and MjATP5L facilitated WSSV duplication by regulating the production of ATP contents and the expression of antimicrobial peptide genes in shrimp.

Lysyl Oxidase-like Protein Recognizes Viral Envelope Proteins and Bacterial Polysaccharides against Pathogen Infection via Induction of Expression of Antimicrobial Peptides

Lysyl oxidases (LOXs) are copper-dependent monoamine oxidases, and they play critical roles in extracellular matrix (ECM) remodeling. The LOX and LOX-like (LOXL) proteins also have a variety of biological functions, such as development and growth regulation, tumor suppression, and cellular senescence. However, the functions of LOXLs containing repeated scavenger receptor cysteine-rich (SRCR) domains in immunity are rarely reported. In this study, we characterized the antiviral and antibacterial functions of a lysyl oxidase-like (LOXL) protein containing tandem SRCR domains in Marsupenaeus japonicus. The mRNA level of LoxL was significantly upregulated in the hemocytes and intestines of shrimp challenged using white spot syndrome virus (WSSV) or bacteria. After the knockdown of LoxL via RNA interference, WSSV replication and bacterial loads were apparently increased, and the survival rate of the shrimp decreased significantly, suggesting that LOXL functions against pathogen infection in shrimp. Mechanistically, LOXL interacted with the envelope proteins of WSSV or with lipopolysaccharide and peptidoglycan from bacteria in shrimp challenged using WSSV or bacteria, and it promoted the expression of a battery of antimicrobial peptides (AMPs) via the induction of Dorsal nuclear translocation against viral and bacterial infection. Moreover, LOXL expression was also positively regulated by Dorsal in the shrimp challenged by pathogens. These results indicate that, by acting as a pattern recognition receptor, LOXL plays vital roles in antiviral and antibacterial innate immunity by enhancing the expression of AMPs in shrimp.