2-Transmembrane C-type lectin from oriental river prawn Macrobrachium nipponense participates in antibacterial immune response

Binding of Infectious Hypodermal and Haematopoietic Necrosis Virus-Like Particles to Mannose Receptor Stimulates Antimicrobial Responses in Immune-Related Tissues of Peneaus vannamei

Mannose receptor (MR) is a transmembrane protein and a type of pattern-recognition receptor (PRR) that plays a critical role in the immunity of mammals and fish. In this study, we examined the role of MR in binding with infectious hypodermal and haematopoietic necrosis virus-like particle (IHHN-VLP) and the downstream immune pathway that it triggers in the shrimp Peneaus vannamei. Upon IHHN-VLP challenge, transcripts of MR in P. vannamei (PvMR) increased significantly in all examined tissues, particularly those related to shrimp immunity, including hemocyte, hepatopancreas and gill tissues. Specifically, IHHN-VLP bound to the 34-kDa PvMR protein in shrimp-tissue extracts. Immunohistochemistry results of hemocytes showed that PvMR was initially localised on the plasma membrane but later internalised and dispersed throughout the cytoplasm after IHHN-VLP administration. Binding between IHHN-VLP and PvMR also induced significant upregulation of genes for the antimicrobial peptides (AMPs) penaeidin 3 and crustin, presumably to protect the shrimp against the viral infection. However, knocking down PvMR resulted in down-regulation of all immune-related genes examined. Overall, as an immune-related PRR, PvMR serves as a receptor for invading viruses, which then trigger the expression of AMPs. Strategic designs using PvMR could be developed to either block the interaction of native virus with the host cells or provoke its up-regulation to enhance shrimp immunity, which could open up opportunities to fight against IHHNV infection in shrimp.

Comparative transcriptome analysis reveals the different responding mechanisms of ovary and hepatopancreas following polyI:C challenge in Macrobrachium nipponense

The ovary in mammals has developed specialized mechanisms for protection against pathogen infections; however, the understanding of the innate immune system in the ovary of crustaceans is still limited. To elucidate the ovary's defense mechanisms in response to viral challenges, we subjected oriental river prawns (Macrobrachium nipponense) to poly I:C, a double-stranded RNA analog that emulates viral dsRNA, and analyzed the ovary's transcriptome profiles. Concurrently, RNA-seq analysis was performed on the hepatopancreas, a well-recognized immune-related tissue, following poly I:C challenge to investigate the distinct response mechanisms of the ovary and hepatopancreas and to gain a comprehensive understanding of the immune responses in both tissues. The results indicate that 1368 genes are differentially expressed in the ovary, with 903 genes upregulated and 465 genes downregulated. Subsequent analysis reveals that these differentially expressed genes (DEGs) include numerous genes associated with innate immunity, such as members of the C-type lectin, fibrinogen-related protein (Frep), Toll-like receptor, and NOD-like receptor (NLR) gene families, as well as acid phosphatase, scavenger receptor, crustin, Down syndrome cell adhesion molecule (Dscam), hemocyanin, and lipopolysaccharide and beta-1,3-glucan binding protein (LGBP). Furthermore, the DEGs include several genes related to ovary development, such as sox8, vitellogenin, progranulin, cyclin-dependent kinase, ecdysone receptor, frizzled, and members of the Fox gene family. In the hepatopancreas, a total of 729 DEGs were identified. Comparison of the DEGs in both tissues indicates that only 91 genes are common to both groups, highlighting significant tissue-specific responses to poly I:C stimulation. This study aims to enhance our understanding of the immune protective mechanisms employed by the ovary in response to pathogen exposure and establishes a foundation for investigating ovarian reproductive immunity in crustaceans.

Immunological lectins in shrimp Penaeus vannamei challenged with infectious myonecrosis virus (IMNV) under low-salinity conditions

Lectins are proteins capable of recognizing and binding to glycan in a specific way. In invertebrates, lectins are a crucial group of Pattern Recognition Proteins (PRRs), activating cellular and humoral responses in the innate immune system. The shrimp Penaeus vannamei is the main crustacean cultivated worldwide, however, the productivity of cultures is strongly affected by diseases, mainly viral ones, such as Infectious Myonecrosis (IMN). Thus, we investigated the participation of five lectins (LvAV, LvCTL4, LvCTL5, LvCTLU, and LvLdlrCTL) in IMNV-challenged shrimp. We verified upregulation gene profiles of lectins after IMNV-challenge, especially in hepatopancreas and gills, in addition to an increase in total hemocytes count (THC) after to 12 h post-infection (hpi). The bioinformatics characterization also revealed several sites of post-translational modification (PTM), such as phosphorylation and glycosylation, which possibly influence the action and stabilization of these lectins. We conclude that LvLdlrCTL and LvCTL5 are the lectins with greater participation in the activation of the immune system against IMNV, showing the greatest potential for PTM, higher upregulation levels, and overlapping with the THC and IMNV viral load.

Impact of Titanium Dioxide-Graphene Oxide (TiO2-GO) Composite Nanoparticle on the Juveniles of the Giant River Prawn, Macrobrachium rosenbergii: Physio-Biochemistry and Transcriptional Response

Nanomaterials are used in many fields, resulting in inevitably releasing into the aquatic environment. The presence of nanomaterials, including TiO₂-GO in the aquatic environment, can be toxic to aquatic organisms. However, few studies have focused on the effects of TiO₂-GO composite nanoparticle on crustaceans. In the present study, the giant river prawn Macrobrachium rosenbergii juveniles were exposed to two concentrations of TiO₂-GO composite nanoparticle (0.1 and 0.5 mg/L). The effects of TiO₂-GO composite exposure on activities of digestive and antioxidant-related enzymes and expressions of growth and immune-related genes at the transcriptome were studied. The results showed that the survival rate and growth performance were not negatively affected by TiO₂-GO composite at the two exposure levels. Nevertheless, exposure to TiO₂-GO composite causes an effect on the activities of digestive and antioxidant enzymes in the juvenile prawns. The enzyme activities of CAT, SOD, GSH-Px, AMS, TPS, and LPS in the 0.1 mg/L TiO₂-GO composite experimental group were markedly reduced than those in the control group. Additionally, the expression level of genes involved in growth and immunity was significantly affected by TiO₂-GO composite. After exposure to the 0.1 mg/L TiO₂-GO composite, the mRNA expression level of MSTN was significantly increased, but the level of EcR, Raptor, and CaBP was significantly decreased. However, the mRNA levels of the CTL, TLR, JAK, and STAT were significantly increased after exposure to the 0.5 mg/L concentration of TiO₂-GO composite. Furthermore, to understand the molecular mechanism of M. rosenbergii under TiO₂-GO composite exposure, RNA-Seq was employed to analyze the changes of the muscle and hepatopancreas transcriptome. Compared with the control group, we identified 5166 and 4784 differentially expressed genes (DEGs) in the muscle and hepatopancreas, respectively (p < 0.05). Based on gene ontology and KEGG analysis, significant differences were observed in the DEGs involved in activity and binding, metabolism, immune response, and environmental information processing. These results showed that exposure to TiO₂-GO composite nanoparticle led to the changes of enzyme activity and gene expression, suggesting that TiO₂-GO composite existing in aquatic environments would disrupt the physiology of M. rosenbergii. This study will serve as a foundation for subsequent research into the evaluation of nanomaterial toxicity on crustacean species.

Molecular cloning, sequence characterization, and expression analysis of C-type lectin (CTL) and ER-Golgi intermediate compartment 53-kDa protein (ERGIC-53) homologs from the freshwater prawn, Macrobrachium rosenbergii

Lectin protein families are diverse and multi-functional in crustaceans. The carbohydrate-binding domains (CRDs) of lectins recognize the molecular patterns associated with pathogens and orchestrate important roles in crustacean defense. In this study, two lectin homologs, a single CRD containing C-type lectin (CTL) and an L-type lectin (LTL) domain containing endoplasmic reticulum Golgi intermediate compartment 53 kDa protein (ERGIC-53) were identified from the freshwater prawn, Macrobrachium rosenbergii. The open reading frames of MrCTL and MrERGIC-53 were 654 and 1,515 bp, encoding polypeptides of 217 and 504 amino acids, respectively. Further, MrCTL showed a 20-amino acid transmembrane helix region and 10 carbohydrate-binding residues within the CRD. MrERGIC-53 showed a signal peptide region, a type-I transmembrane region, and a coiled-coil region at the C-terminus. Phylogenetic analysis revealed a close relationship between MrCTL and MrLectin and M. nipponense CTL (MnCTL), whereas MrERGIC-53 shared high sequence identity with Eriocheir sinensis ERGIC-53 and Penaeus vannamei MBL-1. A homology-based model predicted small carbohydrate-combining sites with a metal-binding site for ligand binding (Ca²⁺ binding site) in MrCTL and beta-sheets connected by short loops and beta-bends forming a dome-shaped beta-barrel structure representing the LTL domain of MrERGIC-53. Quantitative real-time polymerase chain reaction detected MrCTL and MrERGIC-53 transcripts in all examined tissues, with particularly high levels observed in hemocytes, hepatopancreas, and mucosal-associated tissues, such as the stomach and intestine. Further, the expression levels of MrCTL and MrERGIC-53 transcripts were remarkably altered after V. harveyi challenge, suggesting putative function in host innate immunity.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10499-022-00845-3.

Expression and functional characterization of the mannose receptor (MR) from Nile tilapia (Oreochromis niloticus) in response to bacterial infection

Mannose receptor (MR) as a member of the pattern recognition receptors (PRRs) plays an important role in the immune response. In mammals, the role of MR in the regulation of phagocytosis is clarified; however, its contribution to opsonize phagocytosis remains unclear in bony fish. In this study, the expression pattern of Nile tilapia mannose receptor gene (OnMR) was investigated and its regulation of the phagocytosis of monocytes/macrophages to pathogenic bacteria was identified. The full-length of OnMR open reading frame is 4314 bp, encoding a peptide containing 1437 amino acid residues. The deduced amino acid sequence revealed that OnMR contained a cysteine-rich domain, a fibronectin type II domain, multiple C-type lectin-like domains, a transmembrane domain and a short cytoplasmic domain. Tissue distribution analysis showed the OnMR transcripts was widely distribute in the ten detected tissues, and highly expressed in head kidney, hind kidney, intestine and spleen. After S. agalactiae and A. hydrophila infection, the expression of OnMR in head kidney and spleen increased significantly. Moreover, the expression of OnMR in MO/Mø were also upregulated post the infection of bacteria and mannose solutions in vitro. This suggested that MR, as a mannose receptor on macrophage surface, could respond strongly to the stimulation of pathogenic bacteria. In addition, the (r)OnMR protein could effectively bind and agglutinate S. agalactiae and A. hydrophila, and regulate the phagocytic ability of monocytes/macrophages to pathogenic bacteria. These results suggest that OnMR is involved in response against bacterial infection in Nile tilapia, and this study will help us better understand the function of MR in teleost fish.

A proteomics investigation of 'immune priming' in Penaeus vannamei as shown by isobaric tags for relative and absolute quantification

Invertebrates are considered completely dependent on their innate immunity to defend themselves against pathogens as they lack an adaptive immunity. However, a growing body of evidence has indicated a specific acquired immunity called 'immune priming' may exist. The Pacific white shrimp, Penaeus vannamei is one of the most economically important shrimp species in the world. In the previous research, we investigated the hepatopancreas immune response of shrimp immunized with trans -vp28 gene Synechocystis sp. PCC6803 at the protein level. In this study, on the basis of the previous research, the shrimp were then challenged with WSSV, and hepatopancreas analyzed using isobaric tags for relative and absolute quantification (i TRAQ) labeling. In total, 308 differentially expressed proteins (DEPs) were identified including 84 upregulated and 224 downregulated. Upregulated proteins such as calmodulin B and calreticulin, and downregulated proteins such as calnexin, and signaling pathways like Ras, mTOR were differentially expressed in both studies. Data from this study are more significant than previous work and indicate increased sensitivity to WSSV after immunization with trans-vp28 gene Synechocystis sp. PCC6803. In addition, selected DEPs (upregulated: A0A3R7QHH6 and downregulated: A0A3R7PEF6, A0A3R7MGX8, A0A423TPJ4, and A0A3R7QCC2) were randomly analyzed using parallel reaction monitoring (PRM). These data preliminarily confirm immune priming in P. vannamei, and show that the initial stimulation with trans -vp28 gene Synechocystis sp. PCC6803 regulate P. vannamei immune responses and they provide shrimp with enhanced immune protection against secondary stimulation.

iTRAQ-based quantitative proteomic analysis of differentially expressed proteins in the hepatopancreas of Litopenaeus vannamei after WSSV infection

White spot syndrome virus (WSSV) is the most destructive virus among invertebrates. In this study, we analyzed the immune response after WSSV infection in Pacific white shrimp Litopenaeus vannamei using isobaric tags for relative and absolute quantitation (iTRAQ). We identified 325 differentially expressed proteins (DEPs) in the hepatopancreas of L. vannamei. Among them, 212 were up-regulated proteins, and several of them might be related to immunity (e.g. arginine kinase and peroxiredoxin). Of the 113 down-regulated proteins, some were related to immunity (e.g. cathepsin C and cathepsin L) and others to the antioxidant defense process (e.g. glutathione peroxidase and catalase). One down-regulated DEP (C7M84_014268) and 3 up-regulated DEPs (C7M84_003456, C7M84_020702, and C7M84_007135) were randomly selected and analyzed using parallel reaction monitoring. This study is an important step for a comprehensive understanding of the immune relationship between L. vannamei and WSSV and provides valuable information for the prevention of viral diseases in the crustacean aquaculture industry.

A newly identified Hippo homologue from the oriental river prawn Macrobrachium nipponense is involved in the antimicrobial immune response

The Hippo signalling pathway plays a vital role in organ size control, cell proliferation, apoptosis, and immune regulation. In this study, a Hippo homologue with three isoforms (named MnHippo-a, MnHippo-b, and MnHippo-c) was isolated and characterized for the first time from the freshwater prawn Macrobrachium nipponense. The deduced amino acid sequences of MnHippo-a (698 aa), MnHippo-b (688 aa), and MnHippo-c (656 aa) were highly similar, and they all contained an N-terminal S_TKc (serine/threonine protein kinase catalytic) domain and a C-terminal Mst1_SARAH (Sav/Rassf/Hpo) domain. MnHippo-a and MnHippo-c were derived from alternative splicing. Phylogenetic analysis was performed, and the results revealed that MnHippo was a member of the clade containing STPK4 and Hippo of Penaeus vannamei. The expression distribution showed that MnHippo was constitutively expressed in various tissues of uninfected prawns and highly expressed in the hepatopancreas and intestine. In prawns challenged with Vibrio parahaemolyticus and Staphylococcus aureus, the expression of MnHippo in haemocytes was significantly upregulated. Furthermore, in MnHippo-knockdown prawns injected with V. parahaemolyticus or S. aureus, the transcription levels of five antimicrobial peptides were downregulated. MnHippo silencing weakened the clearance of V. parahaemolyticus and S. aureus in prawns. The survival rate of the MnHippo-dsRNA group was obviously decreased from 2 to 6 days post-injection with V. parahaemolyticus or S. aureus. Hence, MnHippo might be involved in the antibacterial immune defence of M. nipponense.

Innate immune responses against viral pathogens in Macrobrachium

Some members of genus Macrobrachium are important economically prawns and valuable objects for studying the innate immune defense mechanism of crustaceans. Studies have focused on immune responses against bacterial and fungal infections and have expanded to include antiviral immunity over the past two decades. Similar to all living organisms, prawns are exposed to viruses, including white spot syndrome virus, Macrobrachium rosenbergii nodavirus, and Decapod iridescent virus 1 and develop effective defense mechanisms. Here, we review current understanding of the antiviral host defense in two species of Macrobrachium. The main antiviral defense of Macrobrachium is the activation of intracellular signaling cascades, leading to the activation of cellular responses (apoptosis) and humoral responses (immune-related signaling pathways, antimicrobial and antiviral peptides, lectins, and prophenoloxidase-activating system).

Aeromonas hydrophila associated with red spot disease in Macrobrachium nipponense and host immune-related gene expression profiles

In September 2018, a serious disease causing high mortality with red spot syndrome occurred in a Macrobrachium nipponense aquaculture farm in Jintan County, Jiangsu Province, China. In this study, a pathogenic isolate 5-S3 was isolated from diseased M. nipponense and was identified as Aeromonas hydrophila by phenotypically and molecularly. The pathogenicity of the isolate 5-S3 to M. nipponense was determined by challenge experiments. Results of artificial challenge showed A. hydrophila was pathogenic to M. nipponense, the LD₅₀ was 9.58 × 10⁴ CFU/mL, and histopathological analysis revealed that the hepatopancreas of infected M. nipponense exhibited obvious inflammatory responses to A. hydrophila infection. The isolate showed significant phenotypical activities such as the lecithinase, esterase, caseinase and hemolysin which are indicative of their virulence potential. Besides, virulence genes such as aerA, act, fla, ahpβ, alt, lip, eprCAI, hlyA, acg and gcaT were detected in the isolate 5-S3. Subsequently, the immune-related genes expression in M. nipponense were evaluated by quantitative real-time PCR (qRT-PCR), and the results showed that the expression levels of dorsal, relish, crustin1, crustin2, anti-lipopolysaccharide factors 1 (ALF1), anti-lipopolysaccharide factors 2 (ALF2), hemocyanin, i-lysozyme and prophenoloxidase were significantly up-regulated in hepatopancreas of M. nipponense after A. hydrophila infection, the stat, p38, crustin3, anti-lipopolysaccharide factors 3 (ALF3) genes had no significant change during the infection. The present results reveal that A. hydrophila was an etiological agent causing red spot syndrome and mass mortality of M. nipponense and the influence of A. hydrophila infection on host immune genes.

In silico characterization and expression analysis of eight C-type lectins in obscure puffer Takifugu obscurus

C-type lectins (CTLs) are a group of carbohydrate-binding proteins that play crucial roles in innate immune defense against invading pathogens. CTLs have been extensively studied in lower vertebrates, such as fish, for their roles in eliminating pathogens; however, their homologs in pufferfish are not well known. In the present study, eight CTLs from obscure puffer Takifugu obscurus (designated as ToCTL3-10 according to the order they were discovered) were obtained. All predicted ToCTL proteins contained a single carbohydrate recognition domain (CRD). ToCTL7 also contained one calcium-binding epidermal growth factor (EGF)-like domain (EGF_CA) and a transmembrane region. ToCTL9 also contained an SCP domain, an EGF domain, and an EGF-like domain. Bioinformatics analysis revealed that ToCTL3-10 mainly clustered with the corresponding CTL homologs of other pufferfish species. Tissue distribution analysis detected ToCTL3-10 in all tissues examined, including kidneys, liver, gills, spleen, intestines, and heart. Moreover, the expressions of ToCTL3-10 were significantly induced in the kidneys of obscure puffer following challenges with three Gram-negative bacterial pathogens, namely, Vibrio harveyi, Aeromonas hydrophila, and Edwardsiella tarda, and a synthetic analog of double-stranded RNA poly(I:C). The expression patterns of ToCTL3-10 in response to different immune stimulants were different. Our results indicated that the eight ToCTLs obtained herein might be involved in host defense against bacterial and poly(I:C) infections in T. obscurus.

A novel SNW/SKIP domain-containing protein, Bx42, is involved in the antibacterial responses of Macrobrachium nipponense

Bx42, the homologue of SNW1 in mammals, is involved in pre-mRNA splicing and transcriptional regulation. However, the presence and function of Bx42 have remained poorly understood in invertebrates until now. In the current study, a novel SNW domain-containing protein (MnBx42) from Macrobrachium nipponense was identified, and its potential role in the immune response was investigated. The full-length MnBx42 was 7467 bp with an open reading frame of 1653 bp, encoding 550 amino acids. Real-time PCR analysis suggested that MnBx42 was predominantly expressed in the intestine, gills and hepatopancreas, and immunofluorescence assays indicated that it was located in the nucleus. Its expression level was significantly decreased in M. nipponense post-challenge with white spot syndrome virus (WSSV) as well as Aeromonas hydrophila and Staphylococcus aureus, implying its participation in the innate immune response. The knockdown of MnBx42 in vivo notably increased the susceptibility of the prawns to bacterial infection, markedly increased the bacterial load in the gills, and significantly attenuated the phagocytic activity of haemocytes. Dual-luciferase reporter assays illustrated that MnBx42 could activate the NF-κB pathway. Consistent with this, when MnBx42 was silenced in vivo, the expression levels of antimicrobial peptides (AMPs), including ALF2, ALF3, ALF4, ALF5, Cru1 and Cru2, and NF-κB signalling genes, including dorsal, relish, TAK1, TAB1, Ikkβ, and Ikkε, were significantly reduced. Taken together, these findings may provide new insights about Bx42 in crustaceans and pave the way for a better understanding of the crustacean innate immune system.

Research progress in innate immunity of freshwater crustaceans

Invertebrates lack adaptive immunity and innate immunity plays important roles in combating foreign invasive pathogens. Freshwater crustaceans, which are invertebrates, depend completely on their innate immune system. In recent years, many immune-related molecules in freshwater crustaceans, as well as their functions, have been identified. Three main immune signaling pathways, namely, Toll, immune deficiency (IMD), and Janus kinase-signal transducer activator of transcription (JAK/STAT) pathways, were found in freshwater crustaceans. A series of pattern recognition receptors (PRRs), including Toll receptors, lectins, lipopolysaccharide and β-1,3-glucan binding protein, scavenger receptors, Down syndrome cell adhesion molecules, and thioester-containing proteins, were reported. Prophenoloxidase activation system and antimicrobial peptide synthesis are two important immune effector systems. These components are involved in the innate immunity of freshwater crustaceans, and they function in the innate immune defense against invading pathogens. This review mainly summarizes innate immune signaling pathways, PRRs, and effector molecules in freshwater crustaceans.