Lack of ∆5 Desaturase Activity Impairs EPA and DHA Synthesis in Fish Cells from Red Sea Bream and Japanese Flounder

Abstract

Long-chain (≥ C 20 ) polyunsaturated fatty acids (LC-PUFA), such as eicosapentaenoic acid (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA), are necessary for human health and are obtained from marine fish-derived oils. Marine fish are LC-PUFA-rich animals; however, many of them require LC-PUFA for growth. Therefore, it is suggested that they do not have sufficient ability to biosynthesize LC-PUFA. To evaluate in vivo LC-PUFA synthetic activity in fish cells, fishderived cell lines from red sea bream (Pagrus major, PMS and PMF), Japanese flounder (Paralichthys olivaceus, HINAE), and zebrafish (Danio rerio, BRF41) were incubated with n-3 fatty acids labeled by radioisotopes or stable isotopes, and then, n-3 PUFA were analyzed by thin-layer chromatography or liquid chromatography-mass spectrometry. Labeled EPA and DHA were biosynthesized from labeled α-linolenic acid (18:3n-3) in BRF41, whereas they were not detected in PMS, PMF, or HINAE cells. We next cloned the fatty acid desaturase 2 (Fads2) cDNAs from PMF cells and zebrafish, expressed in budding yeasts, and then analyzed the substrate specificities of enzymes. As a result, we found that Fads2 from PMF cells was a ∆6/∆8 desaturase. Collectively, our study indicates that cell lines from red sea bream and Japanese flounder were not able to synthesize EPA or DHA by themselves, possibly due to the lack of ∆5 desaturase activity. Furthermore, this study provides a sensitive and reproducible non-radioactive method for evaluating LC-PUFA synthesis in fish cells using a stable isotope and liquid chromatography-mass spectrometry. KeywordsFatty acid desaturase 2 • Japanese flounder • LC-ESI MS • n-3 polyunsaturated fatty acids • Red sea bream * Nozomu Okino

Enhancing Reproductive Performance of Freshwater Finfish Species through Dietary Lipids

“…In addition, significant findings have been made in identifying genes involved in fatty acid metabolism at molecular level [47] and enzymes that possess function capacity in biosynthesis of EPA, DHA, and ARA [25] in freshwater species. In comparison, marine fishes exhibit lack of delta-5 desaturase activity characterized by loss of Fads1 gene, consequently, impairing EPA and DHA synthesis [48][49][50].…”

Depletion of <i>stearoyl-CoA desaturase</i> (<i>scd</i>) leads to fatty liver disease and defective mating behavior in zebrafish

“…Nutritional manipulation of laying hen diets to include sources of n-3 fatty acids promotes the deposition of these nutrients into egg yolk, with n-3 fatty acid-rich eggs potentially providing an alternative food source to enhance consumer intake of these proposed healthful fatty acids ( Van Elswyk, 1997 ). Previous research has indicated that a lack of ∆5 desaturase activity impairs eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) synthesis in Red Sea bream and Japanese flounder cells ( Nyunoya et al, 2021 ). Transgenic zebrafish and common carp enriched in n-3 fatty acids are protected from abnormal lipid deposition in the liver ( Pang et al, 2014 ; Sun et al, 2020a ; Zhang et al, 2019 ).…”