The miR-15/16 Cluster Is Involved in the Regulation of Vertebrate LC-PUFA Biosynthesis by Targeting pparγ as Demonostrated in Rabbitfish Siganus canaliculatus

Post-transcriptional regulatory mechanisms play important roles in the regulation of long-chain (≥ C20) polyunsaturated fatty acid (LC-PUFA) biosynthesis. Here, we address a potentially important role of the miR-15/16 cluster in the regulation of LC-PUFA biosynthesis in rabbitfish Siganus canaliculatus. In rabbitfish, miR-15 and miR-16 were both highly responsive to fatty acids affecting LC-PUFA biosynthesis and displayed a similar expression pattern in a range of rabbitfish tissues. A common potential binding site for miR-15 and miR-16 was predicted in the 3′UTR of peroxisome proliferator-activated receptor gamma (pparγ), an inhibitor of LC-PUFA biosynthesis in rabbitfish, and luciferase reporter assays revealed that pparγ was a potential target of miR-15/16 cluster. In vitro individual or co-overexpression of miR-15 and miR-16 in rabbitfish hepatocyte line (SCHL) inhibited both mRNA and protein levels of Pparγ, and increased the mRNA levels of Δ6Δ5 fads2, Δ4 fads2, and elovl5, key enzymes of LC-PUFA biosynthesis. Inhibition of pparγ was more pronounced with co-overexpression of miR-15 and miR-16 than with individual overexpression in SCHL. Knockdown of miR-15/16 cluster gave opposite results, and increased mRNA levels of LC-PUFA biosynthesis enzymes were observed after knockdown of pparγ. Furthermore, miR-15/16 cluster overexpression significantly increased the contents of 22:6n-3, 20:4n-6 and total LC-PUFA in SCHL with higher 18:4n-3/18:3n-3 and 22:6n-3/22:5n-3 ratio. These suggested that miR-15 and miR-16 as a miRNA cluster together enhanced LC-PUFA biosynthesis by targeting pparγ in rabbitfish. This is the first report of the participation of miR-15/16 cluster in LC-PUFA biosynthesis in vertebrates