Transcriptional Expression Profiles of Olive Flounder (Paralichthys olivaceus) Toll-like Receptor 3 (TLR3) and TLR22 in Response to Extracellular Poly I:C Stimuli

Abstract

Toll-like receptors (TLRs) recognize extracellular and intracellular double-stranded RNA (dsRNA) and play crucial roles in innate and adaptive immune systems. Here, we aimed to investigate the changes in the transcriptional profile of TLR3 and TLR22 genes of olive flounder (Paralichthys olivaceus) in response to polyinosinic:polycytidylic acid (poly I:C; a dsRNA analog) stimuli in vivo, using healthy olive flounders and in vitro, using Hirame natural embryonic (HINAE) cells. The role of JfTLR3 and JfTLR22 in inducing type I interferon response in HINAE cells was analyzed through construction and transfection of short-hairpin RNA (shRNA)-producing vector targeting the JfTLR22 and JfTLR3. Poly I:C stimuli upregulated the JfTLR3 and JfTLR22 genes both in vivo and in vitro, and JfTLR22 showed an earlier (at 6 and 12 h post-stimulation) response than JfTLR3, suggesting that JfTLR22 is a more sensitive receptor and recognizes the extracellular dsRNA more quickly than JfTLR3. After 12 h of poly I:C stimulation, the expression of ISG15 and Mx genes in HINAE cells harboring TLR22-targeting shRNA vector was markedly reduced, wherein the reduction in expression of these genes was weakly reduced in HINAE cells carrying TLR3-targeting shRNA vector. These results suggested that JfTLR22 plays an important role, wherein JfTLR3 partially induces type I interferon response to extracellular dsRNA at 12 h after poly I:C stimulation.