miR-17 is involved in the regulation of LC-PUFA biosynthesis in vertebrates: Effects on liver expression of a fatty acyl desaturase in the marine teleost Siganus canaliculatus

Biosynthesis in vertebrates of long-chain polyunsaturated fatty acids (LC-PUFA) such as arachidonic (ARA; 20:4n - 6), eicosapentaenoic (EPA; 20:5n - 3) and docosahexaenoic (DHA; 22:6n - 3) acids requires the catalysis by fatty acyl desaturases (Fads). A vertebrate Fad with Delta 4 activity catalyzing the direct conversion of 22:5n - 3 to DHA was discovered in the marine teleost rabbitfish Siganus canaliculatus. Recent studies in vertebrates have shown that miRNAs may participate in the regulation of lipid metabolism at post-transcription level. However, their roles in LC-PUFA biosynthesis were not known. In the present study, in silico analysis predicts that the rabbitfish Delta 4 Fad may be a target of miR-17 and thus we cloned miR-17, which is located at the forepart of the miR-17-92 cluster. Dual luciferase reporter assays demonstrated that miR-17 targeted the 3 ' UTR of M Fad directly. Furthermore, the expression level of miR-17 displayed an inverse pattern with that of Delta 4 Fad mRNA in gill, liver and eyes, and also the M Fad protein quantity in rabbitfish liver. Incubation of rabbitfish primary hepatocytes with linoleic acid (LA; 18:2n - 6), alpha-linolenic acid (LNA; 18:3n - 3), EPA or DHA showed differential effects on miR-17, Delta 4 Fad and Delta 6/Delta 5 Fad expression. LNA promoted the expression of miR-17 and Delta 6/Delta 5 Fad, but suppressed the expression of Delta 4 Fad. In contrast, LA and EPA decreased the expression of miR-17 and Delta 6/Delta 5 Fad, but had no effect on Delta 4 Fad. However, all the above were down-regulated by DHA. These data indicate that miR-17 was involved in the regulation of LC-PUFA biosynthesis in rabbitfish liver by targeting M Fad. (C) 2014 Elsevier B.V. All rights reserved.