CRISPR‐Induced Mutations of <i>mk2b</i> and <i>mk3</i> Host Proteins Enhance Chikungunya Virus Susceptibility and Modulate Host Immune Responses in Zebrafish

Host factors are essential at every stage of the viral life cycle and therefore represent attractive and potentially effective targets for the development of antiviral therapeutics. This study highlights the crucial roles of host factors, specifically mitogen-activated protein kinase 2 (mk2) and mitogen-activated protein kinase 3 (mk3), both of which are stress-stimulated serine/threonine kinases. The roles of mk2 and mk3 were investigated by generating single (mk2b-/- and mk3-/-) and double knockouts (mk2b-/-mk3-/-) in a zebrafish model using the CRISPR-Cas9 technique, followed by chikungunya virus (CHIKV) infection. All knockout lines exhibited significantly higher CHIKV titers and severe phenotypes compared to the WT control, with mk3^-/^- showing the greatest susceptibility. After CHIKV infection, expression levels of TNF-α changed across all knockout models. Notably, mk2b^-/^- and mk2b^-/^-mk3^-/^- double knockout larvae exhibited reduced TNF-α expression, suggesting that higher levels of TNF-α may be associated with viral clearance via the p38-MK2-TNF-α signaling axis. In contrast, mk3-/- zebrafish exhibited increased vulnerability to CHIKV through alternative, yet unidentified, pathways. Furthermore, an increase in viral titer corresponded with an enhanced host immune response, as indicated by significantly higher expression levels of ifnɸ1 and rsad2 in all knockout groups. In conclusion, this study confirms that the mk2b and mk3 host proteins are essential in controlling CHIKV infection at the organism level. These findings might have implications towards designing strategies for future antiviral therapeutics. Furthermore, the knockout model of mk2b and mk3 in zebrafish could serve as a valuable tool for studying their roles in other viral infections.