Tissue-specific, nutritional, and developmental regulation of rat fatty acid elongases.

Of the six fatty acid elongase (Elovl) subtypes expressed in mammals, adult rat liver expresses four subtypes: Elovl-5 > Elovl-1 = Elovl-2 = Elovl-6. Overnight starvation and fish oil-enriched diets repressed hepatic elongase activity in livers of adult male rats. Diet-induced changes in elongase activity correlate with Elovl-5 and Elovl-6 mRNA abundance. Adult rats fed the peroxisome proliferator-activated receptor alpha (PPARalpha) agonist WY14,643 have increased hepatic elongase activity, Elovl-1, Elovl-5, Elovl-6, Delta5, Delta6, and Delta9 desaturase mRNA abundance, and mead acid (20:3,n-9) content. PPARalpha agonists affect both fatty acid elongation and desaturation pathways leading to changes in hepatic lipid composition. Elovl activity is low in fetal liver but increases significantly after birth. Developmental changes in hepatic elongase activity paralleled the postnatal induction of Elovl-5 mRNA and mRNAs encoding the PPARalpha-regulated transcripts, Delta5 and Delta6 desaturase, and cytochrome P450 4A. In contrast, Elovl-6, Delta9 desaturase, and FAS mRNA abundance paralleled changes in hepatic sterol regulatory element binding protein 1c (SREBP-1c) nuclear content. SREBP-1c is present in fetal liver nuclei, absent from nuclei immediately after birth, and reappears in nuclei at weaning, 21 days postpartum. In conclusion, changes in Elovl-5 expression may account for much of the nutritional and developmental control of fatty acid elongation activity in the rat liver.