Long-chain polyunsaturated fatty acid biosynthesis and its response to cadmium exposure in silver pomfret

Despite a close interaction between cadmium (Cd) and long-chain polyunsaturated fatty acid (LC-PUFA) metabolism, the influence of Cd exposure on the endogenous synthesis of LC-PUFA has received little attention. In the present study, we hypothesized that Cd exposure would affect the synthesis of LC-PUFA in the marine fish silver pomfret (Pampus argenteus). Therefore, the molecular basis of LC-PUFA biosynthesis and regulation was investigated as the first step to understanding the mechanisms underpinning the effects of Cd exposure. Thereafter, transcriptional regulation of the genes that participate in LC-PUFA biosynthesis and regulation by Cd exposure were also explored. Our results showed that fatty acyl desaturase 2 (Fads2) and elongases of very long-chain fatty acids 5 (Elovl5), two key enzymes involved in LC-PUFA biosynthesis, enabled silver pomfret to biosynthesize 20:3n-6 and 20:4n-3 from 18:2n-6 and 18:3n-3. The results also raise the possibility that silver pomfret may have the ability to produce docosahexaenoic acid (DHA, 22:6n-3) from endogenous eicosapentaenoic acid (EPA, 20:5n-3). The expression of silver pomfret fads2 and elovl5 was transcriptionally regulated by the peroxisome proliferator activated receptor alpha (Ppar alpha). The expression of fads2, elovl5 and ppar alpha in the brain was significantly increased in response to Cd exposure. In addition, Cd exposure significantly reduced the DHA concentration and significantly increased the malondialdehyde concentration in the brain of silver pomfret. Cd exposure likely increases brain-specific DHA synthesis from EPA by transcriptionally activating fads2 and elovl5 via Ppar alpha in silver pomfret. This regulation may be a coping mechanism for the reduction of DHA caused by Cd-oxidative stress in the brains of silver pomfret.