Interferon regulatory factor 2 of red-spotted grouper (Epinephelus akaara): insights into its transcriptional profiling, antiviral potential, and function in macrophage polarization.

Interferon regulatory factor 2 (IRF2) is a member of the IRF family that is specifically involved in diverse immune responses via interferon (IFN)/IRF-dependent signaling pathways. In this study, IRF2 of Epinephelus akaara (EAIRF2) was identified and characterized by evaluating its structural and functional properties. EAIRF2 showed the highest homology with IRF2 of Epinephelus coioides and clustered with teleosts in the phylogenetic tree. The highest level of EAIRF2 mRNA was found in the blood under normal physiological conditions. In the immune challenge experiment, significant transcriptional modulation of EAIRF2 upon lipopolysaccharide (LPS), polyinosinic: polycytidylic acid (poly I:C), and nervous necrosis virus (NNV) challenge were observed. The subcellular localization assay confirmed the role of EAIRF2 as a transcription factor by revealing its specific nuclear localization. To elucidate its functional implications in antiviral defense, EAIRF2 was overexpressed in fathead minnow cells, which were subsequently infected with viral hemorrhagic septicemia virus (VHSV). Notably, cells overexpressing EAIRF2 exhibited a significant reduction in the transcription of VHSV genes. Concurrently, the genes associated with the IFN/IRF signaling pathway were upregulated. Furthermore, the Hoechst and propidium iodide dual staining assay, water-soluble tetrazolium-1 (WST-1) assay, and transcriptional analysis of B-cell lymphoma 2-associated X protein (Bax)/B-cell lymphoma 2 (Bcl-2) indicated that EAIRF2 possesses anti-apoptotic properties during viral infection and poly I:C treatment. Additionally, EAIRF2 overexpression in murine macrophages induced M1 polarization and augmented relative marker gene expression. Collectively, these findings suggest that EAIRF2 is a pivotal immune-related gene, specifically implicated in the IFN/IRF-mediated antiviral defense mechanism, apoptotic signaling pathway, and activation of macrophage-mediated immune responses in Epinephelus akaara. The finding of this study enhances our understanding of IRF2's function in teleost immunity and presents potential avenues for developing therapeutic strategies against viral infections and other immune-related conditions in aquaculture species.