A DHA-Deficient Diet Affects the n-3 LC PUFA Molecular Synthesis Pathway and Fatty Acid Composition in European Sardine (Sardina pilchardus).

Climate change is expected to alter the phytoplankton production of n-3 long-chain polyunsaturated fatty acids (n-3 LC PUFA), including DHA (docosahexaenoic acid), impacting their transfer toward marine consumers. European sardine (Sardina pilchardus) is a major source of n-3 LC PUFA for human populations and is considered to be unable to synthesize sufficient quantities of n-3 LC PUFA to meet their physiological needs. This study aimed to understand the effect of a dietary DHA deficiency on the n-3 LC PUFA metabolism of sardine by investigating their fatty acid composition in three tissues (muscle, brain, and liver) and the hepatic expression of genes involved in the LC PUFA synthesis pathway. Wild-caught fish were fed either a DHA-deficient diet or a control diet for 2 months. The dietary DHA deficiency led to a lower DHA content in muscle reserves and liver membranes but did not change the brain fatty acid composition in sardines. In both dietary groups, the hepatic expressions of genes encoding elongase (elovl2, elovl5) and desaturase (fads2) enzymes were similar, but the expression levels of elovl2 and fads2 were negatively correlated to the DHA percentage in hepatic reserve lipids. The relative expressions of elovl5 and fads2 genes were positively correlated but only in DHA-deficient individuals. Besides, the individuals fed the DHA-deficient diet showed a higher expression of the phospholipase A2 gene (pla2g12b), suggesting a mobilization of n-3 LC PUFA from phospholipids. These results may suggest the activation of compensatory mechanisms at the molecular level in sardines to offset the dietary DHA deficiency.