Omega-3 fatty acid deficiency selectively up-regulates delta6-desaturase expression and activity indices in rat liver: prevention by normalization of omega-3 fatty acid status.

This study investigated the effects of perinatal dietary omega-3 (n-3) fatty acid depletion and subsequent repletion on the expression of genes that regulate long-chain (LC) polyunsaturated fatty acid biosynthesis in rat liver and brain. It was hypothesized that chronic n-3 fatty acid deficiency would increase liver Fads1 and Fads2 messenger RNA (mRNA) expression/activity and that n-3 fatty acid repletion would normalize this response. Adult rats fed the n-3-free diet during perinatal development exhibited significantly lower erythrocyte, liver, and frontal cortex LCn-3 fatty acid composition and reciprocal elevations in LC omega-6 (n-6) fatty acid composition compared with controls (CONs) and repleted rats. Liver Fads2, but not Fads1, Elovl2, or Elovl5, mRNA expression was significantly greater in n-3-deficient (DEF) rats compared with CONs and was partially normalized in repleted rats. The liver 18:3n-6/18:2n-6 ratio, an index of delta6-desturase activity, was significantly greater in DEF rats compared with CON and repleted rats and was positively correlated with Fads2 mRNA expression among all rats. The liver 18:3n-6/18:2n-6 ratio, but not Fads2 mRNA expression, was also positively correlated with erythrocyte and frontal cortex LCn-6 fatty acid compositions. Neither Fads1 or Fads2 mRNA expression was altered in brain cortex of DEF rats. These results confirm previous findings that liver, but not brain, delta6-desaturase expression and activity indices are negatively regulated by dietary n-3 fatty acids.