Betaine Promotes Fat Accumulation and Reduces Injury in Landes Goose Hepatocytes by Regulating Multiple Lipid Metabolism Pathways

SIMPLE SUMMARY: Betaine is a safe, effective, naturally occurring trimethylglycine, which is widely used as a nutritional supplement in animal husbandry. Early research showed betaine redistributes body fat by regulating systemic fatty acid metabolism. We previously found that betaine reduces sebum thickness and abdominal fat, and increases liver weight and triglyceride content, in Landes geese fed with high-energy carbohydrates. However, the mechanism underlying these effects remained unclear. Here, we present an in vitro Landes goose fatty liver model, which was developed using primary hepatocytes and a high-glucose medium simulating the conditions of high-energy carbohydrate feeding in vivo. We used this model to investigate the effects of betaine supplementation. Our results suggest that betaine increases lipid deposition, reduces lipid droplet size, and restores mitochondrial membrane potential (β-oxidation) and the expression of genes involved in lipid hydrolysis transfer genes. By contrast, the expression of fatty acid synthesis genes was down-regulated. The comprehensive effect led to an increase in total triglyceride in the liver, but a healthier steatosis phenotype. Overall, these results show that betaine could improve the quality of foie-gras while decreasing the injury to geese that results from overfeeding. ABSTRACT: Betaine is a well-established supplement used in livestock feeding. In our previous study, betaine was shown to result in the redistribution of body fat, a healthier steatosis phenotype, and an increased liver weight and triglyceride storage of the Landes goose liver, which is used for foie-gras production. However, these effects are not found in other species and strains, and the underlying mechanism is unclear. Here, we studied the underpinning molecular mechanisms by developing an in vitro fatty liver cell model using primary Landes goose hepatocytes and a high-glucose culture medium. Oil red-O staining, a mitochondrial membrane potential assay, and a qRT-PCR were used to quantify lipid droplet characteristics, mitochondrial β-oxidation, and fatty acid metabolism-related gene expression, respectively. Our in vitro model successfully simulated steatosis caused by overfeeding. Betaine supplementation resulted in small, well-distributed lipid droplets, consistent with previous experiments in vivo. In addition, mitochondrial membrane potential was restored, and gene expression of fatty acid synthesis genes (e.g., sterol regulatory-element binding protein, diacylglycerol acyltransferase 1 and 2) was lower after betaine supplementation. By contrast, the expression of lipid hydrolysis transfer genes (mitochondrial transfer protein and lipoprotein lipase) was higher. Overall, the results provide a scientific basis and theoretical support for the use of betaine in animal production.