GSK3β Plays a Negative Role During White Spot Syndrome Virus (WSSV) Infection by Regulating NF-κB Activity in Shrimp Litopenaeus vannamei

Immunometabolic crosstalk in Aedes fluviatilis and Wolbachia pipientis symbiosis

Wolbachia pipientis is a maternally transmitted symbiotic bacterium that mainly colonizes arthropods, potentially affecting different aspects of the host's physiology, e.g., reproduction, immunity, and metabolism. It has been shown that Wolbachia modulates glycogen metabolism in mosquito Aedes fluviatilis (Ae. fluviatilis). Glycogen synthesis is controlled by the enzyme GSK3, which is also involved in immune responses in both vertebrate and invertebrate organisms. Here we investigated the mechanisms behind immune changes mediated by glycogen synthase kinase β (GSK3β) in the symbiosis between Ae. fluviatilis and W. pipientis using a GSK3β inhibitor or RNAi-mediated gene silencing. GSK3β inhibition or knockdown increased glycogen content and Wolbachia population, together with a reduction in Relish2 and gambicin transcripts. Furthermore, knockdown of Relish2 or Caspar revealed that the immunodeficiency pathway acts to control Wolbachia numbers in the host. In conclusion, we describe for the first time the involvement of GSK3β in Ae. fluviatilis immune response, acting to control the Wolbachia endosymbiotic population.

The Dynamics of Gene Expression Unraveling the Immune Response of Macrobrachium rosenbergii Infected by Aeromonas veronii

To further investigate the immune response of Macrobrachium rosenbergii against Aeromonas veronii, comparative transcriptomic analyses of the M. rosenbergii hepatopancreas were conducted on challenge and control groups at 6, 12, and 24 h post-infection (hpi), independently. A total of 51,707 high-quality unigenes were collected from the RNA-seq data, and 8060 differentially expressed genes (DEGs) were discovered through paired comparisons. Among the three comparison groups, a KEGG pathway enrichment analysis showed that 173 immune-related DEGs were considerably clustered into 28 immune-related pathways, including the lysosome, the phagosome, etc. Moreover, the expression levels of the four key immune-related genes (TOLL, PAK1, GSK3β, and IKKα) were evaluated at various stages following post-infection in the hepatopancreas, hemolymph, and gills. Both PAK1 and GSK3β genes were highly up-regulated in all three tissues at 6 hpi with A. veronii; TOLL was up-regulated in the hepatopancreas and hemolymph but down-regulated in the gill at 6 hpi, and IKKα was up-regulated in hemolymph and gill, but down-regulated in the hepatopancreas at 6 hpi. These findings lay the groundwork for understanding the immune mechanism of M. rosenbergii after contracting A. veronii.

Transcriptome Analysis Reveals the Immunoregulation of Replacing Fishmeal with Cottonseed Protein Concentrates on Litopenaeus vannamei

Cottonseed protein concentrate (CPC) is a new non-food protein source with high crude protein, low price, and abundant resources, making it an ideal substitute for fishmeal. In this study, we investigated the effects of CPC re placing fishmeal on the immune response of Litopenaeus vannamei using transcriptome sequencing. L. vannamei (initial body weight: 0.42 ± 0.01 g) were fed four isonitrogenous and isolipid feeds for eight weeks, with CPC replacing fishmeal at 0% (control, FM), 15% (CPC15), 30% (CPC30), and 45% (CPC45), respectively. At the end of the feeding trial, the changes of the activities and expression of immune-related enzymes were consistent in L. vannamei in the CPC-containing group when compared with the FM group. Among them, the activities of ACP, PO, and LZM in the group whose diet was CPC30 were significantly higher than those in the FM group. Moreover, the activities of AKP, SOD, and CAT were significantly higher in the group containing CPC than in the FM group. Furthermore, all CPC groups had considerably lower MDA levels than the FM group. This suggests that the substitution of fishmeal with CPC leads to a significant immune response in L. vannamei. Compared with the FM group, transcriptome analysis identified 805 differentially expressed genes (DEGs) (484 down and 321 up), 694 (266 down and 383 up), and 902 (434 down and 468 up) in CPC15, CPC30, and CPC45, respectively. Among all DEGs, 121 DEGs were shared among different CPC-containing groups compared with the FM group. Most of these differential genes are involved in immune-related signaling pathways. The top 20 signaling pathways enriched for differential genes contained toxoplasmosis, pathogenic Escherichia coli infection, insulin resistance, and Toll and immune deficiency (IMD) pathways, in which NF-kappa-B inhibitor Cactus were involved. In addition, trend analysis comparison of the DEGs shared by the group with CPC in the diet and the FM group showed that Cactus genes were significantly down-regulated in the group with CPC in the diet and were lowest in the CPC30 group. Consistently, the expression of antimicrobial peptide genes was significantly higher in both diet-containing CPC groups than in the FM group. In conclusion, the moderate amount of CPC substituted for fishmeal may improve the immunity of L. vannamei by suppressing the expression of Cactus genes, thereby increasing the expression of antimicrobial peptide (AMP) genes.

Characterization and functional analysis of GSK3β from Epinephelus coioides in Singapore grouper iridovirus infection

Glycogen synthase kinase 3β (GSK3β), a serine/threonine protein kinase, is a crucial regulator of several signaling pathways and plays a vital role in cell proliferation, growth, apoptosis, and immune responses. However, the role of GSK3β during viral infection in teleosts remains largely unknown. In the present study, a GSK3β homologue from Epinephelus coioides (EcGSK3β) was cloned and characterized. The open reading frame of EcGSK3β consists of 1323 bp, encoding a 440 amino acid protein, with a predicted molecular mass of 48.23 kDa. Similar to its mammalian counterpart, EcGSK3β contains an S_TKc domain. EcGSK3β shares 99.77% homology with the giant grouper (Epinephelus lanceolatus). Quantitative real-time PCR analysis indicated that EcGSK3β mRNA was broadly expressed in all tested tissues, with abundant expression in the skin, blood, and intestines. Additionally, the expression of EcGSK3β increased after Singapore grouper iridovirus (SGIV) infection in grouper spleen (GS) cells. Intracellular localization analysis demonstrated that EcGSK3β is mainly distributed in the cytoplasm. EcGSK3β overexpression promoted SGIV replication during viral infection in vitro. In contrast, silencing of EcGSK3β inhibited SGIV replication. EcGSK3β significantly downregulated the activities of interferon-β, interferon-sensitive response element, and NF-κB. Taken together, these findings are important for a better understanding of the function of GSK3β in fish and reveal its involvement in the host response to viral immune challenge.

Combined dynamic transcriptomics and metabolomics analyses revealed the effects of trans-vp28 gene Synechocystis sp. PCC6803 on the hepatopancreas of Litopenaeus vannamei

Litopenaeus vannamei is the most important shrimp species throughout the world. However, diseases are increasing with the development of the industry, so enhancing the immunity of shrimp is of great significance. In this study, 1800 shrimp were divided into two groups randomly: the control group (N, feed with brine shrimp flake) and the experimental group (M, feed with mutant of Synechocystis sp. cells) (300 shrimp/group/replication) and each trial was conducted in triplicates. After immunization, sixty shrimp (with three replicates of twenty) were collected at 0 h in group N and 24, 72, and 144 h in group M, respectively, and the hepatopancreas were isolated for transcriptomic and metabolomic analysis. Transcriptome data revealed that compared with group N, genes related to antimicrobial peptides, cytoskeleton remodeling, detoxification, apoptosis, blood coagulation, immune defense, and antioxidant systems were differentially expressed in group M. In addition, combined transcriptomic and metabolomic analysis revealed that some immune-related differential genes or differential metabolites were consistently expressed in both omics. All the above results indicated that trans-vp28 gene Synechocystis sp. PCC6803 could improve the immunity of L. vannamei. This is the first report of the integration of dynamic transcriptomics combined with metabolomics to study the effect of trans-vp28 gene Synechocystis sp. PCC6803 in the hepatopancreas of L. vannamei and provided important information about the defense and immune mechanisms used by invertebrates against pathogens.

Catalytic and regulatory subunits of casein kinase 2 in Penaeus vannamei: Cloning, identification, expression profiles and functional analysis

As a highly conserved serine/threonine kinase with catalytic and regulatory subunits distributed ubiquitously in eukaryotic organisms, casein kinase 2 (CK2) is involved in multiple cellular functions, including immune regulation. In this study, two variants of the catalytic subunit (designated PvCK2α-1 and PvCK2α-2) and the regulatory subunit homologs (designated PvCK2β-1 and PvCK2β-2) in Penaeus vannamei were cloned and characterised. PvCK2α-1 and PvCK2α-2 shared the same genomic sequence consisting of six exons and five introns and encoded the same protein of 350 amino acids with an S_TKc domain, although there was a sequence deletion in 3'-UTR in PvCK2α-2 when compared with PvCK2α-1. Because of the sequence deletion in the ORF, PvCK2β-1 and PvCK2β-2 encoded different proteins with a CK_II_beta domain. The gene structures of PvCK2β-1 and PvCK2β-2 were identical and consisted of four exons and three introns. Semi-quantitative RT-PCR analyses revealed that PvCK2α and PvCK2β were constitutively expressed in all P. vannamei tissues tested, with higher levels detected in the immune-related tissues including hemocytes, hepatopancreas, gills and intestine. In these four tissue types, all variants of PvCK2α and PvCK2β were induced upon challenge with white spot syndrome virus (WSSV), Vibrio parahaemolyticus and Staphyloccocus aureus. The inhibition of PvCK2α, PvCK2β-1 and PvCK2βComb (the amount of PvCK2β-1 and PvCK2β-2) significantly reduced the survival rates of P. vannamei after WSSV infection and significantly increased the WSSV viral loads. Knockdown of PvCK2 by RNAi could distinctly decrease the expression of NF-κB related genes. All of these results suggest that PvCK2 plays an important role in the innate immune response to pathogen challenges in P. vannamei, with a positive role in anti-WSSV response which may be mediated through regulating the expression of NF-κB drived antimicrobial peptide genes.

Phenylalanine hydroxylase (PAH) plays a positive role during WSSV and Vibrio parahaemolyticus infection in Litopenaeus vannamei

Phenylalanine hydroxylase (PAH) is involved in immune defence reactions by providing the starting material, tyrosine, to synthesise catecholamines and melanin. PAH is an important metabolic enzyme of aromatic amino acids and the rate-limiting enzyme in the hydroxylation of amino acid phenylalanine to tyrosine. In the present study, a PAH gene, LvPAH, was cloned and identified from Litopenaeus vannamei. The open reading frame (ORF) of LvPAH was 1383 bp, encoding a protein of 460 amino acids comprised of an ACT domain and a Biopterin_H domain. LvPAH was constitutively expressed in healthy L. vannamei, with the highest expression levels in the eyestalk and the lowest in the hepatopancreas. Both white spot syndrome virus (WSSV) and Vibrio parahaemolyticus infection upregulated LvPAH expression in hemocytes, hepatopancreas and gills of L. vannamei. Inhibition of LvPAH resulted in a significantly lower survival rate of L. vannamei after WSSV infection than the control group, consistent with the observation that WSSV viral load was significantly higher in LvPAH-silenced L. vannamei. After a V. parahaemolyticus challenge, there was no significant difference between the survival rate of LvPAH-silenced and the control L. vannamei. However, the load of V. parahaemolyticus in LvPAH-silenced L. vannamei was significantly higher than the control population for L. vannamei. The effect of LvPAH on L. vannamei from a neuroendocrinological perspective was assessed by measuring l-DOPA, dopamine (DA) and noradrenaline (NE) levels in the hemocytes after the knockdown of LvPAH. The results showed that phenoloxidase (PO), l-DOPA and DA levels in the hemolymph of LvPAH-silenced L. vannamei were significantly decreased starting from 24hpi. In contrast, the NE levels in the hemolymph of shrimp decreased significantly at first and then increased. The results suggest that LvPAH may play an important role in antiviral and bacterial immunity in L. vannamei.