Synthesis and Regulation of Omega-3 and Omega-6 Long Chain Polyunsaturated Fatty Acids in Salmonids

Abstract

Omega-3 (n-3) and omega-6 (n-6) long-chain polyunsaturated fatty acids (LC-PUFA) are essential components of human nutrition, necessary for cellular function and overall health. However, Western diets often lack adequate n-3 LC-PUFA, altering the recommended n-3 to n-6 ratio. Salmonids are an important dietary source of n-3 LC-PUFA, but the transition in aquaculture diet from fish oils to plant oils has decreased their n-3 content. With rising global fish consumption, this reduction highlights the need for sustainable, nutrient-rich alternatives, like cultured fish meat. This review examines LC-PUFA biosynthesis and regulation in salmonids, identify existing knowledge gaps, and explores how these insights could benefit the cultured fish industry. LC-PUFA biosynthesis in salmonids involves a complex process of desaturation and elongation of dietary precursors, facilitated by two main enzyme families: fatty acyl desaturases (FADS) and elongases (ELOVL). Regulation of this pathway occurs primarily through transcription factors such as sterol regulatory element-binding proteins (SREBPs), liver X receptors (LXR), and peroxisome proliferator-activated receptors (PPARs). Additionally, hormonal influences, specifically insulin and estrogen, and factors like diet, developmental stage, and temperature, also influence LC-PUFA synthesis. LC-PUFA are vital for various physiological functions in salmonids, such as immune function, neural development, and cellular function, yet gaps remain in the understanding of the regulatory mechanisms of LC-PUFA biosynthesis. Key proteins and pathways, for instance the roles of SREBP1, and PPARβ, along with the β-oxidation process, require further research. Dietary strategies in aquaculture to enhance LC-PUFA content are ongoing, and the most effective methods remain debated in literature. Future research should focus on optimizing LC-PUFA content in lab-grown fish meat, considering factors like diet and life stage of the salmonid harvested, and utilizing alternative cell types to improve the n-3 LC-PUFA biosynthesis.