Genes involved in carnitine synthesis and carnitine uptake are up-regulated in the liver of sows during lactation
BACKGROUND:Convincing evidence exist that carnitine synthesis and uptake of carnitine into cells is regulated by peroxisome proliferator-activated receptor alpha (PPARA), a transcription factor which is physiologically activated during fasting or energy deprivation. Sows are typically in a negative energy balance during peak lactation. We ... investigated the hypothesis that genes involved in carnitine synthesis and uptake in the liver of sows are up-regulated during peak lactation. FINDINGS:Transcript levels of several PPARalpha target genes involved in fatty acid uptake (FABP4, SLC25A20), fatty acid oxidation (ACOX1, CYP4A24) and ketogenesis (HMGCS2, FGF21) were elevated in the liver of lactating compared to non-lactating sows (P < 0.05). In addition, transcript levels of genes involved in carnitine synthesis (ALDH9A1, TMLHE, BBOX1) and carnitine uptake (SLC22A5) in the liver were greater in lactating than in non-lactating sows (P < 0.05). Carnitine concentrations in liver and plasma were about 20% and 50%, respectively, lower in lactating than in non-lactating sows (P < 0.05), which is likely due to an increased loss of carnitine via the milk. CONCLUSIONS:The results of the present study show that PPARalpha is activated in the liver of sows during lactation which leads to an up-regulation of genes involved in carnitine synthesis and carnitine uptake. The PPARalpha mediated up-regulation of genes involved in carnitine synthesis and uptake in the liver of lactating sows may be regarded as an adaptive mechanism to maintain hepatic carnitine levels at a level sufficient to transport excessive amounts of fatty acids into the mitochondrion.