Enoyl-CoA hydratase/3-hydroxyacyl CoA dehydrogenase is essential for the production of DHA in zebrafish

Compared with other species, freshwater fish are more capable of synthesizing DHA via same biosynthetic pathways. Freshwater fish have a Sprecher pathway to biosynthesize DHA in a peroxisome-dependent manner. Enoyl-CoA hydra-tase/3-hydroxyacyl CoA dehydrogenase (Ehhadh) is involved in the hydration and dehydrogenation re-actions of fatty acid beta-oxidation in peroxisomes. However, the role of Ehhadh in the synthesis of DHA in freshwater fish remains largely unclear. In this study, the knockout of Ehhadh significantly inhibited DHA synthesis in zebrafish. Liver transcriptome analysis showed that Ehhadh deletion significantly inhibited SREBF and PPAR signaling pathways and decreased the expression of PUFA synthesis-related genes. Our results from the analysis of transgenic zebrafish (Tg:Ehhadh) showed that Ehhadh over-expression significantly increased the DHA content in the liver and significantly upregulated the expression of genes related to PUFA synthesis. In addition, the DHA content in the liver of Tg:Ehhadh fed with linseed oil was significantly higher than that of wildtype, but the expression of PUFA synthesis-related genes fads2 and elovl2 were significantly lower, indicating that Ehhadh had a direct effect on DHA synthesis. In conclusion, our results showed that Ehhadh was essential for DHA synthesis in the Sprecher pathway, and Ehhadh overexpression could promote DHA synthesis. This study provides insight into the role of Ehhadh in freshwater fish.

Automated summary

Compared with other species, freshwater fish have a more efficient biosynthetic pathway for synthesizing DHA. This study investigated the role of Ehhadh in the synthesis of DHA in zebrafish. The results showed that knockout of Ehhadh inhibited DHA synthesis, while overexpression of Ehhadh increased DHA content in the liver. Additionally, Ehhadh was found to affect the expression of genes related to PUFA synthesis and SREBF and PPAR signaling pathways.