The effect and underlying mechanism of yeast β-glucan on antiviral resistance of zebrafish against spring viremia of carp virus infection

Abstract

β-glucan has been used as immunostimulant for fish. However, the effect of yeast β-glucan on viral infections has been less studied in fish. In this study, we investigated the effects of β-glucan on the resistance of zebrafish against spring viraemia of carp virus (SVCV) and elucidated the underlying mechanisms. Zebrafish were fed with a control diet or diet supplemented with 0.01% and 0.025% β-glucan for 2 weeks, and were challenged by SVCV. Zebrafish embryonic fibroblast (ZF4) cells were treated with 5 μg/mL β-glucan and were infected by SVCV. We further investigated the effect of β-glucan on autophagy level post SVCV infection. The intestinal microbiota was evaluated by 16S rRNA gene pyrosequencing. Results showed that dietary supplementation of 0.025% β-glucan significantly increased survival rate of zebrafish compared with control group after SVCV challenge (P < 0.05). Dietary β-glucan significantly increased the expression of genes related to type I IFN antiviral immune pathway in the spleen of zebrafish after viral infection, including type I IFN genes (ifnφ1, ifnφ2, ifnφ3), IFN-stimulated genes (mxb, mxc), as well as other genes involved in the IFN signaling pathway, including tlr7, rig1, mavs, irf3 and irf7. Morpholino knockdown of type I IFN receptors dampened the antiviral effect of β-glucan in zebrafish larvae, indicating that β-glucan-mediated antiviral function was at least partially dependent on IFN immune response. Furthermore, β-glucan can inhibit the replication of SVCV in ZF4 cells. However, β-glucan did not stimulate type I IFN antiviral response in ZF4 cells, and the antiviral effect of β-glucan in ZF4 was independent of Myd88. Interestingly, β-glucan induced autophagy in ZF4 cells after SVCV infection. Inhibition of autophagy blocked the antiviral effect of β-glucan in ZF4 cells. Lastly, dietary β-glucan changed the composition of intestinal microbiota in zebrafish, with reduced abundance of Proteobacteria and an enrichment of Fusobacteria and Firmicutes. To sum up, our results indicate that the β-glucan enhanced resistance of zebrafish against SVCV and the mechanism involved stimulation of type I IFN antiviral immune response of fish after viral infection.

Zebrafish use conserved CLR and TLR signaling pathways to respond to fungal PAMPs in zymosan

“…Because our experiments utilized an EGFP reporter of NF-κB activation, it takes several hours to observe NF-κB activation but this likely due to the time it takes to transcribe, translate, and fold EGFP rather than a true delay in activation of this signaling pathway and transcription factor. While it was previously found that in larval zebrafish β-glucan can drive increased resistance to bacterial or viral infections (Darroch et al, 2022, Liang et al, 2022) and that zymosan particles or β-glucan-coated beads can be shuttled between phagocytes (Pazhakh et al, 2019), this the first characterization of the innate immune response to these PAMPs in larval zebrafish. The receptors and signaling pathways that zebrafish use to sense fungal PAMPs have been unclear.…”

“…Several lines of evidence further demonstrate that zebrafish can respond to β-glucan specifically. First, exposure of zebrafish to β-glucan triggers both trained immunity (Darroch et al, 2022) and increased resistance to viral infection (Liang et al, 2022). Second, phagocytes in larval zebrafish can shuttle fungal spores from one cell to another and a β-glucan signal was sufficient to instigate this shuttling (Pazhakh et al, 2019).…”

β-Glucan Induces Training Immunity to Promote Antiviral Activity by Activating TBK1

“…It has been demonstrated that β-glucan can improve the defense of experimental mice against pathogenic infections [ 3 , 28 ]. Glucan feeding significantly reduced the effects of influenza infection on total mortality by activating both cellular and humoral immune responses, resulting in a lower level of viral load [ 29 ].…”

Ornamental Fishes and Zoonotic Problems to Animals and Public Health

“…However, individuals who handle infected fish or consume raw or undercooked infected fish may be at a higher risk (Clouthier et al 2021). In fish, post mortem examination may reveal hemorrhages, congestion and abnormalities in the internal organs particularly the liver and spleen (Liang et al 2022).…”