RGD-binding integrins mediated phagocytosis involved in the entry of Edwardsiella tarda into mudskipper MO/MФ

Construction of an attenuated glutamyl endopeptidase deletion strain of Nocardia seriolae

The glutamyl endopeptidase homolog of Nocardia seriolae (GluNS) has been proved to be a potential virulence factor in our previous study. Present investigation was carried out to construct an attenuated N. seriolae strain by deletion with GluNS gene and evaluate its protective immunity in head snakehead. A deletion strain (NS-ΔGluNS) was established by knockout of gene GluNS from wild strain N. seriolae ZJ0503 via homologous recombination. The LD50 of NS-ΔGluNS in 3.41 × 10⁶ cfu/mL was significantly increased than that of wild strain in 4.75 × 10⁵ cfu/mL, indicating that the virulence of N. seriolae has been attenuated with the knockout of GluNS. Meanwhile, applying NS-ΔGluNS as an attenuated live vaccine to immune hybrid snakehead, the non-specific immunity parameters (serum LYZ, POD, ACP, and AKP activities), specific antibody (IgM) titers production and immune-related genes (MHCIα, CD4, and IL-8) expression were up-regulated in different tissues, which indicated that they were able to trigger humoral and cell-mediated immune responses. Furthermore, the protective efficacy in hybrid snakehead after vaccination with NS-ΔGluNS shown 73.53% relative percentage survival (RPS). Taken together, the attenuated NS-ΔGluNS was obtained successfully and it could elicit strong immune response and supply protective efficacy to hybrid snakehead against N. seriolae wild strain.

Toxicological damages on copper exposure to IgM+ B cells of Nile tilapia (Oreochromis niloticus) and mitigation of its adverse effects by β-glucan administration

Present investigation was carried out to study toxicological damages of copper exposure and mitigation of its adverse effects with β-glucan administration in IgM⁺ B cells which processes multiple roles similar to macrophages in Nile tilapia (Oreochromis niloticus). IgM⁺ B cells were pretreated with β-glucan (25 μg/mL) for 24 h before exposed to cupric oxide nanoparticles (CuO NPs) or cupric chloride (Cu ions) at the doses of 0, 5, 10, and 20 μg/mL for 24 h, respectively. Our results demonstrated that β-glucan increased reduced glutathione (GSH) to against oxidative damage from CuO NPs and Cu ions exposure in IgM⁺ B cells. The apoptosis process through mitochondrial signaling pathway was depressed in IgM⁺ B cells since the mitochondrial membrane potential (ΔΨm) was protected from copper exposure by β-glucan treatment. Furthermore, the inhibition on phagocytic abilities of IgM⁺ B cells caused by copper exposure could be enhanced with β-glucan treatment via evaluation of microspheres and bioparticles uptake and LPS-induced NO production. Importantly, β-glucan might participate in immunomodulation in IgM⁺ B cells through B cell antigen receptor (BCR) to suppress toxicological effect derived from copper exposure. Taken together, this study provides more information on the toxicological damages in IgM⁺ B cells upon copper exposure and explains the molecular mechanism to reverse adverse effects caused by copper exposure with β-glucan administration.

IFN-γ Manipulates NOD1-Mediated Interaction of Autophagy and Edwardsiella piscicida to Augment Intracellular Clearance in Fish

Edwardsiella piscicida is an intracellular pathogenic bacterium accounting for significant losses in farmed fish. Currently, cellular and molecular mechanisms underlying E. piscicida-host cross-talk remain obscure. In this study, we revealed that E. piscicida could increase microtubule-associated protein L chain 3 (LC3) puncta in grass carp (Ctenopharyngodon idella) monocytes/macrophages and a carp cell line, Epithelioma papulosum cyprini The autophagic response was confirmed by detecting the colocalization of E. piscicida with LC3-positive autophagosomes and LysoTracker-probed lysosomes in the cells. Moreover, we unveiled the autophagic machinery targeting E. piscicida by which the nucleotide-binding oligomerization domain receptor 1 (NOD1) functioned as an intracellular sensor to interact and recruit autophagy-related gene (ATG) 16L1 to the bacteria. Meanwhile, E. piscicida decreased the mRNA and protein levels of NOD1 and ATG16L1 in an estrogen-related receptor-α-dependent manner, suggesting a possible mechanism for this bacterium escaping autophagy. Subsequently, we examined the effects of various E. piscicida virulence factors on NOD1 expression and found that two of them, EVPC and ESCB, could reduce NOD1 protein expression via ubiquitin-dependent proteasomal degradation. Furthermore, an intrinsic regulator IFN-γ was found to enhance the colocalization of E. piscicida with NOD1 or autophagosomes, suggesting its involvement in the interaction between autophagy and E. piscicida Along this line, a short-time treatment of IFN-γ caused intracellular E. piscicida clearance through an autophagy-dependent mechanism. Collectively, our works demonstrated NOD1-mediated autophagy-E. piscicida dialogues and uncovered the molecular mechanism involving autophagy against intracellular bacteria in fish.