Involvement of a TNF homologue in balancing the host immune system of Macrobrachium nipponense

Single von Willebrand factor C-domain protein confers host defense against white spot syndrome virus by functioning as a pattern recognition receptor in Macrobrachium nipponense

The single von Willebrand factor C-domain proteins (SVWCs), also known as Vago, are primarily found in arthropods. Their expression was induced by nutritional status, bacterial and viral infections. Despite the prominence of SVWCs in antiviral immunity, the detailed molecular mechanisms remain poorly explained. SVWC has been proposed to elicit antiviral activities through its function as an interferon analog. In contrast, herein, we illustrate that an SVWC homolog from Macrobrachium nipponense (MnSVWC) confers host defense against white spot syndrome virus (WSSV) and covert mortality nodavirus (CMNV) as a pattern recognition receptor (PRR). qRT-PCR analyses demonstrated that the expression of MnSVWC was enhanced upon WSSV infection in all detected tissues, including gills, nerve cords, and hemocytes. Coating WSSV with recombinant MnSVWC (rMnSVWC) promoted the phagocytic activity of hemocytes and subsequent clearance of invasive WSSV from the prawn. On the other hand, the knockdown of MnSVWC with RNAi improved the proliferation ability of WSSV and CMNV in the prawn. Analysis of ELISA and Co-immunoprecipitation (Co-IP) showed that rMnSVWC could bind WSSV by interacting with the vesicle proteins VP26 and VP28. Co-IP analysis verified the interaction between MnSVWC and calmodulin, which implies a vesicle protein-SVWC-calmodulin-clathrin-dependent mechanism underlying the hemocyte-mediated phagocytosis against WSSV. Subsequently, MnSVWC was recognized to activate the expression of transcription factor STAT and an interferon-stimulating gene Viperin, illustrating its involvement in modulating humoral immunity via activation of the JAK/STAT pathway after WSSV infection. These findings indicate that MnSVWC could bind to WSSV as a PRR and participate in the promotion of hemocyte-mediated phagocytosis and the activation of the JAK/STAT pathway in prawns.

Activating transcription factor 2 (ATF2) negatively regulates the expression of antimicrobial peptide genes through tumor necrosis factor (TNF) in Macrobrachium nipponense

Activating transcription factor 2 (ATF2), a member of the bZIP transcription factor family, is involved in multiple physiological and developmental processes, yet its role in the innate immunity remains unclear. In this study, two isoforms (named as MnATF2a and MnATF2b) of ATF2 gene were identified in Macrobrachium nipponense and were produced by exon skipping. The full length of MnATF2a is 2328 bp with an open reading frame of 2079 bp that encode 692 amino acids. MnATF2a has 237 bp nucleotides more than MnATF2b and the extra 237 bp is a complete exon. MnATF2a and MnATF2b proteins contain the same conserved and typical bZIP domain at the C-terminus. MnATF2a has 79 amino acids more than MnATF2b. MnATF2a and MnATF2b are widely distributed in a variety of immune tissues. After Vibrio parahaemolyticus and Staphylococcus aureus infection, the expression levels of MnATF2a and MnATF2b were significant up-regulated in the gills and stomach at 12 h. RNA interference analysis showed that knockdown of the total MnATF2 gene significantly inhibits the transcription of tumor necrosis factor (TNF) and promotes the expression of crustins (including Cru3, Cru4, and Cru7). Further study showed that knockdown of MnTNF evidently increase the expression of Cru3, Cru4, and Cru7. Our research indicates that ATF2 negatively regulate the expression of AMPs by regulating the transcription of TNF in M. nipponense. This study provides valuable information about the function of ATF2 family in the innate immunity in crustacean.

Tumor Necrosis Factor Superfamily: Ancestral Functions and Remodeling in Early Vertebrate Evolution

The evolution of the tumor necrosis factor superfamily (TNFSF) in early vertebrates is inferred by comparing the TNFSF genes found in humans and nine fishes: three agnathans, two chondrichthyans, three actinopterygians, and the sarcopterygian Latimeria chalumnae. By combining phylogenetic and synteny analyses, the TNFSF sequences detected are classified into five clusters of genes and 24 orthology groups. A model for their evolution since the origin of vertebrates is proposed. Fifteen TNFSF genes emerged from just three progenitors due to the whole-genome duplications (WGDs) that occurred before the agnathan/gnathostome split. Later, gnathostomes not only kept most of the genes emerged in the WGDs but soon added several tandem duplicates. More recently, complex, lineage-specific patterns of duplications and losses occurred in different gnathostome lineages. In agnathan species only seven to eight TNFSF genes are detected, because this lineage soon lost six of the genes emerged in the ancestral WGDs and additional losses in both hagfishes and lampreys later occurred. The orthologs of many of these lost genes are, in mammals, ligands of death-domain-containing TNFSF receptors, indicating that the extrinsic apoptotic pathway became simplified in the agnathan lineage. From the patterns of emergence of these genes, it is deduced that both the regulation of apoptosis and the control of the NF-κB pathway that depends in modern mammals on TNFSF members emerged before the ancestral vertebrate WGDs.

Identification of two carcinin isoforms (MnCarc1 and MnCarc2) and their function in the antimicrobial immunity of Macrobrachium nipponense

Carcinin, a member of the crustin family, plays important roles in crustacean innate immunity. In this study, we identified two carcinin isoforms (MnCarc1 and MnCarc2) produced by alternative splicing from Macrobrachium nipponense. The full length of MnCarc1 and MnCarc2 cDNA are 1554 and 1495 bp with 687 and 609 bp open reading frame-encoding proteins that contain 228 and 202 amino acids, respectively. The genome of carcinin has nine exons and eight introns. MnCarc1 transcript contains all nine exons, whereas MnCarc2 only contains eight exons and lacks exon 4. MnCarc1 and MnCarc2 proteins contain a signal peptide, cysteine-rich regions, and a whey acidic protein domain. The phylogenetic tree shows that MnCarc1 and MnCarc2 are not grouped with other crustins and carcinins. MnCarc1 and MnCarc2 form a subgroup. MnCarc1 and MnCarc2 are widely distributed in various tissues. The expression of MnCarc1 and MnCarc2 were evidently upregulated at multiple time points in hemocytes and the intestine of M. nipponense after white spot syndrome virus, Vibrio parahaemolyticus, and Staphylococcus aureus challenges. Further studies showed that knockdown of MnDorsal or MnStat transcription factor could remarkably inhibit the upregulated expression of MnCarc1 and MnCarc2 caused by viral or bacterial challenges. In addition, recombinant MnCarc1 and MnCarc2 proteins could bind to various bacteria and polysaccharides and inhibit the growth of S. aureus and V. parahaemolyticus in vitro. This study indicated that carcinins from M. nipponense were involved in prawns innate immunity.

A fibrinogen-related protein (Mnfico3) acts as a novel pattern recognition receptor in Macrobrachium nipponense

Fibrinogen-related proteins (FREPs) are widely found in both vertebrates as well as invertebrates, and they play a crucial role in host immunity. In this study, we isolated a novel ficolin gene (Mnfico3) from the oriental river prawn Macrobrachium nipponense. The complete cDNA sequence of Mnfico3 was 1133 bp long, containing an open reading frame of 765 bp coding for Mnfico3, a protein consisting of 254 amino acids. The Mnfico3 protein contained a putative N-terminal signal peptide and a fibrinogen-related protein domain present at the C-terminal. Phylogenetic analysis indicated that Mnfico3 had a closer evolutionary relationship with vertebrate ficolins than with its invertebrate homologues. Tissue distribution analysis indicated that Mnfico3 was predominantly expressed in muscle, in which its transcription was increased following bacterial challenge by Aeromonas veronii. Function analysis using recombinant protein revealed that rMnFico3 had broad-spectrum binding capacity to a variety of microorganisms and pathogen-associated molecular pattern (PAMP) ligands. Furthermore, rMnFico3 exhibited Ca2+-dependent agglutinating activity against microbes in vitro, and ability to attach to the hemocyte surface which promoted phagocytosis and subsequent clearance of invasive bacteria in vivo. Silencing rMnFico3 in prawn through RNAi did not alter the expression of antimicrobial peptide genes (ALF and Crustin). These results manifested that MnFico3 functioned as a potential pattern recognition receptor (PPR) to mediate cellular immune response by recognizing PAMPs, agglutinating invasive microbes, and promoting phagocytosis of hemocytes.

Response of Macrobrachium rosenbergii to Vegetable Oils Replacing Dietary Fish Oil: Insights From Antioxidant Defense

The study was conducted to evaluate the effects of fish oil replacement by vegetable oils on growth performance, histology, and antioxidant capacity of Macrobrachium rosenbergii. Three isonitrogenous and isoenergetic diets were formulated with different lipid sources included. DFO diet contained 6% fish oil, whereas DSO and DRO diets included 6% soybean oil and rapeseed oil (RO) as alternatives for fish oil, respectively. Prawns were fed thrice daily for 8 weeks. The results showed that prawns in DFO group showed significantly lower final weight, weight gain ratio, and specific growth rate (SGR), but higher feed intake and feed coefficient ratio than those in DSO and DRO groups. In hepatocellular ultrastructure, malformed and atrophic nucleus and higher apoptosis ratio were observed in DFO group. In addition, levels of haemolymph proinflammatory cytokines, activities of anti-superoxide anion, inducible-type NO-synthase (iNOS) and content of nitric oxide, and hepatopancreas NF-κB signal pathway gene expression in DFO group increased markedly compared to those of DSO and DRO groups. The results suggested that vegetable oils, such as soybean oil and RO might be the better lipid sources in diets for Macrobrachium rosenbergii than fish oil, it may be attributed to modified oxidative status induced by NF-κB-NO signal pathway.

A 28.6-kD small heat shock protein (MnHSP28.6) protects Macrobrachium nipponense against heavy metal toxicity and oxidative stress by virtue of its anti-aggregation activity

Small heat shock proteins (sHSPs) are ATP-independent chaperones and involved into various physiological and stress processes. In the present study, a 28.6-kD sHSP coding gene, MnHSP28.6, was cloned and characterized from the oriental river prawn Macrobrachium nipponense. Tissue distribution analysis via qPCR and western blot revealed that MnHSP28.6 predominantly expressed in muscle. The temporal transcription of MnHSP28.6 in muscle after bacterial challenge, heavy metal exposure and doxorubicin (DOX) injection was investigated by qPCR. The results showed that the expression of MnHSP28.6 were strongly enhanced by both Cd²⁺ and Cu²⁺ exposure, as well as DOX injection, but not by bacterial infection. Aggregation assays showed that recombinant MnHSP28.6 could effectively prevent temperature-induced aggregation of citrate synthase, and reduction-induced aggregation of insulin in vitro. MnHSP28.6 also could protect muscle extracts from heat-induced protein denaturation and superoxide dismutase (SOD) inactivation. Expressing MnHSP28.6 in E. coli conferred host cell impressive protection against H₂O₂ compared to control. These results suggest a protective role of MnHSP28.6 in maintaining protein homeostasis, preventing aggregation, promoting resistance to heavy metal and keeping redox balance.