Biosynthesis of LC-PUFAs and VLC-PUFAs in Pampus argenteus: Characterization of ElovI4 Elongases and Regulation under Acute Salinity

Salinity has been demonstrated to influence the biosynthesis of long-chain (C20-24) polyunsaturated fatty acids (LC-PUFAs) in teleost fish. Since LC-PUFAs are essential nutrients for vertebrates, it is central to understand how fish cope with an acute change in salinity associated with natural events. We herein report on the cloning and functional characterization of two elongation of very-long-chain fatty acid (ElovI)4 proteins, namely, ElovI4a and Elovl4b, and study the roles that these enzymes play in the biosynthesis of LC-PUFAs and very-long-chain (>C-24) polyunsaturated fatty acids (VLC-PUFAs) in marine teleost Pampus argenteus. The P. argenteus ElovI4 displayed all of the typical features of Elovl-like enzymes and have eyes and brain as major sites through which they exert their functions. Moreover, functional studies showed that the P. argenteus Elovl4 can effectively elongate C18-22 substrates to C-36 VLC-PUFA. Because both P. argenteus ElovI4 are able to produce 24:5n - 3 from shorter precursors, we tested whether the previously reported Delta 6 Fads2 from P. argenteus was able to desaturate 24:5n - 3 to 24:6n - 3, a key step for docosahexaenoic acid (DHA) synthesis. Our results showed that P. argenteus can indeed bioconvert 24:5n - 3 into 24:6n - 3, suggesting that P. argenteus has the enzymatic capacity required for DHA biosynthesis through the coordinated action of both Elovl4 and Fads2. Furthermore, an acute salinity test indicated that low-salinity stress (12 ppt) upregulated genes involved in LC-PUFA biosynthesis, with 12 ppt salinity treatment showing the highest hepatic LC-PUFA content. Overall, our results unveiled that the newly characterized Elovl4 enzymes have indispensable functions in LC- and VLC-PUFA biosynthesis. Moreover, acute salinity change influenced the biosynthesis of LC-PUFA in P. argenteus. This study provided new insight into the biosynthesis of LC- and VLC-PUFAs in vertebrates and the physiological responses that teleosts have under acute salinity stress.

Automated summary

The study demonstrates that Elovl4 enzymes in silver pomfret play crucial roles in the biosynthesis of long-chain and very-long-chain polyunsaturated fatty acids. Acute salinity changes influence the biosynthesis of LC-PUFAs in silver pomfret, with low salinity stress potentially enhancing this process.