Choline and methionine regulate lipid metabolism via the AMPK signaling pathway in hepatocytes exposed to high concentrations of nonesterified fatty acids

High concentrations of nonesterified fatty acids (NEFAs) and beta-hydroxybutyric acid (BHBA) induce lipid peroxidation, resulting in liver damage. Choline and methionine (Met) can promote energy balance and benefit liver health in transition dairy cows; however, the regulating mechanism remains unclear. In the present study, we established the hepatocyte damage model by 1.5mM NEFAs or BHBA treatment, and examined lipid metabolism in hepatocytes. The results showed that 1.5mM NEFAs and 1.5mM BHBA significantly decreased the messenger RNA (mRNA) expression of AMP-activated protein kinase (AMPK)-alpha as well as its target genes carnitine palmitoyltransferase-1 alpha (CPT-1 alpha), acetyl-CoA carboxylase, fatty acid synthetase, and Apolipoprotein B100 (ApoB100). Choline and Met upregulated the phosphorylation level of AMPK-alpha, which was blocked by BML (an AMPK-alpha inhibitor). The mRNA expression level of peroxisome proliferator-activated receptor-alpha (PPAR-alpha), CPT-1 alpha, and ApoB100 showed a similar trend. The expressions of liver X recptoer alpha (LXR-alpha) and sterol regulatory element-binding protein 1c (SREBP-1c) were decreased by choline and Met, while only the decrease of LXR-alpha was blocked by BML. These findings indicate that the high-level NEFAs and BHBA weaken the lipid metabolism by impairing the fatty acid oxidation, synthesis, and transport proteins. Choline and Met regulate PPAR-alpha and LXR-alpha transcriptional activity through AMPK-alpha phosphorylation and regulate SREBP-1c independently of AMPK-alpha to promote lipid oxidation and transport in NEFAs-treated hepatocytes.