ATF6-DGAT pathway is involved in TLR7-induced innate immune response in Ctenopharyngodon idellus kidney cells

DGAT1 and DGAT2 are two acyl-CoA:diacylglycerol O-acyltransferase (DGAT) enzymes that catalyze the final step in triglyceride (TG) synthesis. TGs are the primary constituents of lipid droplets (LDs). Although it has been demonstrated that LDs modulate immune and inflammatory responses in CIK cells, little is known about whether DGAT1 and DGAT2 involve in this process. Firstly, grass carp DGAT2 was isolated and characterized, encoding 361 amino acids, and all DGAT2 proteins in genomic structures are conserved in vertebrates. Then, using TLR7 agonist, we induced LDs accumulation in CIK cells. Only DGAT1b and DGAT2 were upregulated in forming TLR7 agonist induced-LDs. Next, we utilized small-molecule inhibitors of DGAT1 and DGAT2. The results indicated that DGAT1 inactivation attenuated TG content and the relative expressions of IFNα3, NF-κB, IL-1β, and TNFα genes, whereas DGAT2 inhibition decreased TG content and the relative expressions of MyD88, IRF7, IFNα3, NF-κB, IL-1β, and TNFα genes, implying that DGAT1-generated LDs and DGAT2-generated LDs contribute to TLR7-induced immune response via different signaling pathways. Finally, inhibiting ATF6 effectively decreased DGAT-generated LDs accumulation and the expression of TLR7 signaling-related genes induced by TLR7 agonist, implying that ATF6 UPR pathway may mediate the role of DGAT-generated LDs in TLR7 signaling. Overall, we demonstrate that DGAT1 and DGAT2-catalyzed TAG synthesis may generate different LDs to provide distinct signaling platforms for innate TLR7 signaling.