Polyunsaturated fatty acids synthesized by freshwater fish: A new insight to the roles of elovl2 and elovl5 in vivo

At present, fish provide an important supply of long-chain polyunsaturated fatty acids (LC-PUFAs) for human consumption. Previous studies have shown that fatty acyl elongase 2 (elovl2) and elovl5 play important roles in fish LC-PUFA synthesis. Generally, freshwater fish have a stronger ability to synthesize LC-PUFAs than marine fish. However, the roles of elovl2, elovl5 and elovl2 + elovl5 in LC-PUFA synthesis of freshwater fish in vivo are not very clear. In this study, the elovl2 knockout zebrafish (elovl2(-/-)), elovl5 knockout zebrafish (elovl5(-/-)) and the double gene knockout zebrafish (DKO) were generated by CRISPR/Cas9 technology for the first time. Compared with wild type zebrafish (WT), elovl5-deletion zebrafish showed a significant increase in C22 PUFA content, which might be due to the up-regulation expressions of elovl4b and elovl2. elovl5 expressed at very low levels in livers of elovl2(-/- )relative to WT, indicating that elovl5 may be an "assistant attacker" of elovl2 in LC-PUFA synthesis of zebrafish. Moreover, there were no significant differences in levels of C18-C22 PUFAs between DKO and WT, indicating that besides elovl2 + elovl5 path, LC-PUFA synthesis in zebrafish could be performed by other paths. In addition, the hepatic lipidomic analysis results revealed that the contents of C22:6n-3 in phosphatidyl ethanolamine (PE-DHA) and PE-C22 PUFAs were more easily affected by the absence of elovl2 and elovl5. Our results suggest that the elovl2+elovl5 path is not the only path for LC-PUFA synthesis in zebrafish, and provide novel insights into the roles of elovl2 and elovl5 in LC-PUFA synthesis of freshwater fish. (C) 2020 Elsevier Inc. All rights reserved.

目前，鱼类为人类消费提供了长链多不饱和脂肪酸（LC - PUFAs）的重要来源。先前的研究表明，脂肪酸延长酶2（elovl2）和elovl5在鱼类LC - PUFA合成中起重要作用。一般来说，淡水鱼合成LC - PUFAs的能力比海水鱼强。然而，elovl2、elovl5以及elovl2 + elovl5在淡水鱼体内LC - PUFA合成中的作用尚不十分清楚。在本研究中，首次利用CRISPR/Cas9技术构建了elovl2基因敲除斑马鱼（elovl2（-/-））、elovl5基因敲除斑马鱼（elovl5（-/-））以及双基因敲除斑马鱼（DKO）。与野生型斑马鱼（WT）相比，elovl5缺失的斑马鱼C22 PUFA含量显著增加，这可能是由于elovl4b和elovl2表达上调所致。相对于WT，elovl5在elovl2（-/-）斑马鱼肝脏中的表达水平极低，这表明在斑马鱼LC - PUFA合成中elovl5可能是elovl2的“辅助因子”。此外，DKO与WT之间C18 - C22 PUFAs水平没有显著差异，这表明除了elovl2 + elovl5途径外，斑马鱼的LC - PUFA合成还可通过其他途径进行。此外，肝脏脂质组学分析结果显示，磷脂酰乙醇胺（PE - DHA）中C22:6n - 3以及PE - C22 PUFAs的含量更容易受到elovl2和elovl5缺失的影响。我们的研究结果表明，elovl2 + elovl5途径不是斑马鱼LC - PUFA合成的唯一途径，并为elovl2和elovl5在淡水鱼LC - PUFA合成中的作用提供了新的见解。（C）2020爱思唯尔公司。保留所有权利。