Litopenaeus vannamei peritrophin interacts with WSSV and AHPND-causing V. parahaemolyticus to regulate disease pathogenesis

A Peritrophin-44 gene in Litopenaeus vannamei is involved in disease resistance

Peritrophic membrane (PM) is a pellicle structure present in the midgut of some invertebrates, such as insects and crustaceans. It could isolate harmful components and pathogens in food from intestinal epithelial cells; and it also plays a role in improving digestion and absorption efficiency. So PM is important for survival of its owner. In current study, 44 PM proteins were identified in Litopenaeus vannamei by PM proteome analysis. Among these PM proteins, the Peritrophin-44 homologous protein (LvPT44) was further studied. Chitin-binding assay indicated that LvPT44 could bind to colloidal chitin, and immunoeletron microscopy analysis shown that it was located to PM of L. vannamei. Furthermore, LvPT44 promoter was found to be activated by L. vannamei STAT and c-Jun. Besides, LvPT44 was induced by ER-stress as well as white spot syndrome virus infection. Knocked-down expression of LvPT44 by RNA inference increased the cumulative mortality of shrimp that caused by ER-stress or white spot syndrome virus. These results suggested that LvPT44 has an important role in disease resistance.

Bile acid and short chain fatty acid metabolism of gut microbiota mediate high-fat diet induced intestinal barrier damage in Macrobrachium rosenbergii

The limited tolerance of crustacean tissue physiology to a high-fat diet has captured the attention of researchers. Yet, investigations into the physiological response mechanisms of the crustacean intestinal barrier system to a high-fat diet are progressing slowly. Elucidating potential physiological mechanisms and determining the precise regulatory targets would be of great physiological and nutritional significance. This study established a high-fat diet-induced intestinal barrier damage model in Macrobrachium rosenbergii, and systematically investigated the functions of gut microbiota and its functional metabolites. The study achieved this by monitoring phenotypic indicators, conducting 16S rDNA sequencing, targeted metabolomics, and in vitro anaerobic fermentation of intestinal contents. Feeding prawns with control and high-fat diets for 8 weeks, the lipid level of 7 % in the CON diet and 12 % in the HF diet. Results showed that high-fat intake impaired the intestinal epithelial cells, intestinal barrier structure, and permeability of M. rosenbergii, activated the tight junction signaling pathway inhibiting factor NF-κB transcription factor Relish/myosin light chain kinase (MLCK), and suppressed the expression of downstream tight junction proteins zona occludens protein 1 (ZO-1) and Claudin. High-fat intake resulted in a significant increase in abundance of Aeromonas, Enterobacter, and Clostridium sensu stricto 3 genera, while Lactobacillus, Lactococcus, Bacteroides, and Ruminococcaceae UCG-010 genera were significantly decreased. Targeted metabolomics results of bile acids and short-chain fatty acids in intestinal contents and in vitro anaerobic fermentation products showed a marked rise in the abundance of DCA, 12-KetoLCA, 7,12-diketoLCA, and Isovaleric acid, and a significant reduction in the abundance of HDCA, CDCA, and Acetate in the HF group. Pearson correlation analysis revealed a substantial correlation between various genera (Clostridium sensu stricto 3, Lactobacillus, Bacteroides) and secondary metabolites (DCA, HDCA, 12-KetoLCA, Acetate), and the latter was significantly correlated with intestinal barrier function related genes (Relish, ZO-1, MLCK, vitamin D receptor, and ecdysone receptor). These findings indicate that gut microorganisms and their specific bile acids and short-chain fatty acid secondary metabolites play a crucial role in the process of high-fat-induced intestinal barrier damage of M. rosenbergii. Moreover, identifying and targeting these factors could facilitate precise regulation of high-fat nutrition for crustaceans.

Shrimp SIRT4 promotes white spot syndrome virus replication

In WSSV pathogenesis, the molecular mechanisms and the key host factors that regulate the viral replication and morphogenesis remain unclear. However, like most viruses, WSSV is known to induce metabolic reprogramming in several metabolic pathways including the host glutamine metabolism, and several recent reports have suggested that the sirtuins SIRT3, SIRT4, and SIRT5, which belong to a family of NAD+-dependent deacetylases, play an important role in this regulation. Here we focus on characterizing LvSIRT4 from Litopenaeus vannamei and investigate its role in regulating glutamine dehydrogenase (GDH), an important enzyme that promotes glutaminolysis and viral replication. We found that LvSIRT4 silencing led to significant decreases in both WSSV gene expression and the number of viral genome copies. Conversely, overexpression of LvSIRT4 led to significant increases in the expression of WSSV genes and the WSSV genome copy number. Immunostaining in Sf9 insect cells confirmed the presence of LvSIRT4 in the mitochondria and the co-localization of LvSIRT4 and LvGDH in the same cellular locations. In vivo gene silencing of LvSIRT4 significantly reduced the gene expression of LvGDH whereas LvSIRT4 overexpression had no effect. However, neither silencing nor overexpression had any effect on the protein expression levels of LvGDH. Lastly, although GDH activity in uninfected shrimp was unchanged, the GDH enzyme activity in WSSV-infected shrimp was significantly increased after both LvSIRT4 silencing and overexpression. This suggests that although there may be no direct regulation, LvSIRT4 might still be able to indirectly regulate LvGDH via the mediation of one or more WSSV proteins that have yet to be identified.

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.

Resilience and probiotic interventions to prevent and recover from shrimp gut dysbiosis

To counter the recurrent outbreaks of bacterial (acute hepatopancreatic necrosis disease; AHPND) and viral (white spot disease; WSD) shrimp diseases, which still remain a threat to the global industry, shrimp gut microbiota research has been gaining more attention in recent years, and the use of probiotics in aquaculture has had promising results in improving shrimp gut health and immunity. In this review based on our studies on AHPND and WSD, we summarize our current understanding of the shrimp gastrointestinal tract and the role of the microbiota in disease, as well as effects of probiotics. We focus particularly on the concept of microbiota resilience, and consider strategies that can be used to restore shrimp gut health by probiotic intervention at a crucial time during gut microbiota dysbiosis. Based on the available scientific evidence, we argue that the use of probiotics potentially has an important role in controlling disease in shrimp aquaculture.