Molecular characterization of ER Stress sensor IRE1α and IRE1β and their expression analysis in response to different fatty acid in grass carp (Ctenopharyngodon idellus)

Abstract Inositol-requiring enzyme 1 (IRE1) is the most evolutionarily conserved endoplasmic reticulum (ER) membrane protein. Here, we identified and analyzed two IRE isoforms (IRE1α and IRE1β) in grass carp ( Ctenopharyngodon idellus ). The coding sequences of IRE1α and IRE1β were 3096 and 2835 nucleotides, and they encoded proteins of 1031 and 944 amino acids, respectively. Each of the two IRE1s proteins had four PPQ domains, a transmembrane helix region, an S_TKc and a PUG domain, which were relatively conserved in comparison to mammals. qRT-PCR revealed that IRE1α was the highest in liver and brain, whereas the highest expression of IRE1β expressed was found in the hindgut, which may be closely related with their role. Moreover, we have compared the effect of saturated (palmitic acid, PA) , monounsaturated fatty acid (oleic acid, OA) and polyunsaturated fatty acids (Docosahexaenoic acid, DHA) on ER stress in CIK cells, and found that PA and DHA induced UPR-related gene expression in dose-dependent , and OA increased expression of IRE1α and decreased expression of IRE1β, ATF4 and ATF6 at lower doses. Additionally, our studies revealed that blocking IRE1α pathway using specific inhibitor 4μ8c, subsequently reversed PA-induced autophagy and inflammation, indicating the role of IRE1α in mediating PA-induced CIK cells. Taken together, the study demonstrated the IRE1α and IRE1β that likely have an important role in physiological processes induced by fatty acids in grass carp.