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 β-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 1.5 mM NEFAs or BHBA treatment, and examined lipid metabolism in hepatocytes. The results showed that 1.5 mM NEFAs and 1.5 mM BHBA significantly decreased the messenger RNA (mRNA) expression of AMP-activated protein kinase (AMPK)-α as well as its target genes carnitine palmitoyltransferase-1α (CPT-1α), acetyl-CoA carboxylase, fatty acid synthetase, and Apolipoprotein B100 (ApoB100). Choline and Met upregulated the phosphorylation level of AMPK-α, which was blocked by BML (an AMPK-α inhibitor). The mRNA expression level of peroxisome proliferator-activated receptor-α (PPAR-α), CPT-1α, and ApoB100 showed a similar trend. The expressions of liver X recptoer α (LXR-α) and sterol regulatory element-binding protein 1c (SREBP-1c) were decreased by choline and Met, while only the decrease of LXR-α 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-α and LXR-α transcriptional activity through AMPK-α phosphorylation and regulate SREBP-1c independently of AMPK-α to promote lipid oxidation and transport in NEFAs-treated hepatocytes.