Knockout of elovl5 increases n-3/n-6 PUFA ratio and attenuates inflammation in grass carp (Ctenopharyngodon idella)

The balance between n-3 and n-6 polyunsaturated fatty acids (PUFAs) is a critical determinant of lipid homeostasis and inflammatory status in aquaculture species and human being. However, the regulatory mechanisms governing n-3/n-6 PUFA balance in freshwater fish remain incompletely understood. Here, we generated an elovl5 knockout (KO) grass carp ( Ctenopharyngodon idella ) using CRISPR/Cas9 technology to investigate the role of this elongase in PUFA homeostasis. Fatty acid profiling revealed that deletion of elovl5 significantly increased n-3 PUFAs, particularly DHA, while reducing n-6 PUFAs, resulting in an elevated n-3/n-6 ratio. Transcriptomic analysis of the liver suggest that this phenotype arose from markedly increased oxidative utilization of n-6 PUFAs for energy, together with feedback upregulation of desaturase genes including fads2 , which further promoted n-3 PUFA biosynthesis. The altered n-3/n-6 balance further attenuated the activity and expression of pro-inflammatory pathways in elovl5 KO fish, which contributes to an anti-inflammatory metabolic state. Taken together, this study generated a novel grass carp strain exhibiting enhanced resilience to inflammation, which could serve as a healthier dietary fatty acid source for humans.