MiR-26a mediates LC-PUFA biosynthesis by targeting the Lxrα–Srebp1 pathway in the marine teleost Siganus canaliculatus

Cuiying Chen,Shuqi Wang,Yu Hu,Mei Zhang,Xianda He,Cuihong You,Xiaobo Wen,Óscar Monroig,Douglas R Tocher,Yuanyou Li

doi:10.1074/jbc.ra120.014858

Abstract

MicroRNAs have been recently shown to be important regulators of lipid metabolism. However, the mechanisms of microRNA-mediated regulation of long-chain polyunsaturated fatty acid (LC-PUFA) biosynthesis in vertebrates remain largely unknown. Herein, we for the first time addressed the role of miR-26a in LC-PUFA biosynthesis in the marine rabbitfish Siganus canaliculatus The results showed that miR-26a was significantly down-regulated in liver of rabbitfish reared in brackish water and in S. canaliculatus hepatocyte line (SCHL) incubated with the LC-PUFA precursor α-linolenic acid, suggesting that miR-26a may be involved in LC-PUFA biosynthesis because of its abundance being regulated by factors affecting LC-PUFA biosynthesis. Opposite patterns were observed in the expression of liver X receptor α (lxrα) and sterol regulatory element-binding protein-1 (srebp1), as well as the LC-PUFA biosynthesis-related genes (Δ4 fads2, Δ6Δ5 fads2, and elovl5) in SCHL cells incubated with α-linolenic acid. Luciferase reporter assays revealed rabbitfish lxrα as a target of miR-26a, and overexpression of miR-26a in SCHL cells markedly reduced protein levels of Lxrα, Srebp1, and Δ6Δ5 Fads2 induced by the agonist T0901317. Moreover, increasing endogenous Lxrα by knockdown of miR-26a facilitated Srebp1 activation and concomitant increased expression of genes involved in LC-PUFA biosynthesis and consequently promoted LC-PUFA biosynthesis both in vitro and in vivo These results indicate a critical role of miR-26a in regulating LC-PUFA biosynthesis through targeting the Lxrα-Srebp1 pathway and provide new insights into the regulatory network controlling LC-PUFA biosynthesis and accumulation in vertebrates.

Highlights

Long-chain polyunsaturated fatty acids (LC-PUFA), arachidonic acid (ARA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3), and docosahexaenoic acid (DHA, 22:6n-3), are major components of complex lipid molecules that are involved in numerous critical biological processes and play physiologically important roles essential to human health [1,2,3]
Most marine teleosts have no or very limited ability to convert C18 PUFA precursors into C20/22 LCPUFA because of the absence of certain enzymes activities required in one or more steps of the LC-PUFA biosynthetic pathways, and little is known about how these processes occur in vivo and how they are regulated [1, 13]
With increasing use of vegetable oil (VO) sources in feeds used in fish farming, it is critical to understand the regulatory mechanisms of LC-PUFA biosynthesis to enable fish to make effective use of dietary C18 PUFA supplied in the diet to produce LC-PUFA that both satisfies the physiological demands of the fish itself and guarantees a healthy food item for humans

Summary

Introduction

Long-chain polyunsaturated fatty acids (LC-PUFA), arachidonic acid (ARA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3), and docosahexaenoic acid (DHA, 22:6n-3), are major components of complex lipid molecules that are involved in numerous critical biological processes and play physiologically important roles essential to human health [1,2,3]. Our recent studies in rabbitfish Siganus canaliculatus demonstrated that miR-17 and miR-146a regulate LC-PUFA biosynthesis by negative regulating the liver expression of D4 fads and elovl, respectively [34, 35], whereas miR-24 and miR-33 can enhance LC-PUFA biosynthesis through activating the Srebp pathway by targeting Insig (insulin-induced gene protein 1) [22, 23] These new data highlight the important roles of miRNAs in the regulation of LC-PUFA biosynthesis at a post-transcriptional level in vertebrates. Because the activation of Lxra can increase expression of srebp and its downstream fads and elovl genes involved in LC-PUFA biosynthesis [29,30,31, 41, 42], the present study aimed to validate and characterize the potential roles of miR-26a in the regulation of LC-PUFA biosynthesis by targeting Lxra in rabbitfish S. canaliculatus

Methods

Results

Conclusion