College of Marine Science, South China Agricultural University & Guangdong Laboratory for Lingnan Modern Agriculture, Guangzhou510642, People's Republic of China.
Pearl River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou510380, People's Republic of China.
Br J Nutr. 2022 Jan 14;127(1):3-11. doi: 10.1017/S0007114521000775. Epub 2021 Mar 5.
N-3 long-chain (≥C20) PUFA (LC-PUFA) are vital fatty acids for fish and humans. As a main source of n-3 LC-PUFA for human consumers, the n-3 LC-PUFA content of farmed fish is important. Previously, we identified fatty acid-binding protein (fabp)-4 as a candidate gene for regulating the n-3 LC-PUFA content. Herein, we further assessed the role of fabp4 in this process. First, a 2059 bp promoter sequence of fabp4 in Trachinotus ovatus was cloned and, using progressive deletion, determined -2006 bp to -1521 bp to be the core promoter sequence. The PPAR-γ binding sites were predicted to occur in this region. A luciferase reporter assay showed that the promoter activity of fabp4 decreased following mutation of the PPARγ binding site and that PPARγ increased the fabp4 promoter activity in a dose-dependent manner, implying that T. ovatus fabp4 is a target of PPARγ. The overexpression of fabp4 or PPARγ increased the DHA content in hepatocytes, whereas suppression of their expression diminished this effect, suggesting that both fabp4 and PPARγ play an active role in regulating DHA content. Moreover, the inhibition of fabp4 attenuated the increase in PPARγ-mediated DHA content, and the overexpression of fabp4 alleviated this effect. Collectively, our findings indicated that fabp4, which is controlled by PPARγ, plays an important role in DHA content regulation. The new regulation axis can be considered a promising novel target for increasing the n-3 LC-PUFA content in T. ovatus.
N-3 长链（≥C20）多不饱和脂肪酸（LC-PUFA）是鱼类和人类必需的脂肪酸。作为人类消费者 n-3 LC-PUFA 的主要来源，养殖鱼类的 n-3 LC-PUFA 含量很重要。此前，我们已将脂肪酸结合蛋白（fabp）-4 鉴定为调节 n-3 LC-PUFA 含量的候选基因。在此，我们进一步评估了 fabp4 在这一过程中的作用。首先，克隆了卵形鲳鲹 fabp4 的 2059 bp 启动子序列，并通过逐步缺失，确定-2006 bp 至-1521 bp 为核心启动子序列。预测该区域存在 PPAR-γ 结合位点。荧光素酶报告基因检测显示，fabp4 启动子活性在 PPARγ 结合位点突变后降低，PPARγ 以剂量依赖的方式增加 fabp4 启动子活性，这表明卵形鲳鲹 fabp4 是 PPARγ 的靶基因。fabp4 或 PPARγ 的过表达增加了肝细胞中的 DHA 含量，而抑制其表达则减弱了这种作用，这表明 fabp4 和 PPARγ 都在调节 DHA 含量方面发挥了积极作用。此外，fabp4 的抑制减弱了 PPARγ 介导的 DHA 含量的增加，而过表达 fabp4 则缓解了这种作用。综上，我们的研究结果表明，fabp4 受 PPARγ 调控，在 DHA 含量调节中发挥重要作用。该新的调控轴可被视为增加卵形鲳鲹 n-3 LC-PUFA 含量的有前途的新靶点。
