# Effects of Betaine on DNA Methylation Level, Expression Level, and Fat Synthesis of VNN1 in Goose Hepatocytes

## TL;DR

This study shows that betaine reduces fat buildup in goose liver cells by increasing DNA methylation and lowering gene activity linked to fat production.

## Contribution

The study reveals a novel epigenetic mechanism by which betaine reduces lipid synthesis in goose hepatocytes through VNN1 gene hypermethylation.

## Key findings

- Betaine significantly reduced triglyceride and LDL levels in steatotic goose hepatocytes.
- Betaine increased DNA methylation in the VNN1 promoter and downregulated VNN1 and lipogenic gene expression.
- Lipid droplet accumulation was most reduced at 50 mM betaine concentration.

## Abstract

This study demonstrates for the first time in goose hepatocytes that betaine ameliorates fat accumulation by epigenetically modulating the VNN1 gene. The novel mechanism involves betaine’s ability to increase DNA methylation levels in the VNN1 promoter region, which is associated with the downregulation of VNN1 expression. This epigenetic regulation occurs alongside the suppression of key lipogenic genes (FAS, SCD, SREBPQ), establishing a direct link between betaine-induced hypermethylation of VNN1 and the reduction of hepatic lipid synthesis in a waterfowl model of steatosis.

This experiment was conducted to explore the effects of betaine on the DNA methylation level, expression level, and fat synthesis of VNN1 in goose hepatocytes by isolating the primary hepatocytes of goose at the cellular level and constructing a fatty degeneration model of goose hepatocytes. In the study, 23-day-old Taizhou goose embryos were used as the research object, and free fatty acid (PA:OA = 2:1) was used to induce steatosis of goose primary hepatocytes. The experiment was randomly divided into seven groups: control group, steatosis model group, and betaine (2, 10, 25, 50, 100mM) group. After 24 h of cell culture, cell viability, oil red O staining, and lipid metabolism-related indicators in cell supernatant were measured, and cells were collected to determine VNN1, FAS, ACC, SCD, SREBPQ gene expression and VNN1 promoter region DNA methylation level. (1) The addition of 0.5 mM fatty acids successfully determined the degeneration of goose hepatocytes. The levels of TG and LDL were significantly increased (p < 0.05), and the level of HDL was significantly decreased. (2) The addition of 100 mM betaine significantly reduced TG levels, and 10, 25, 50, and 100 mM betaine significantly reduced LDL levels. The addition of betaine had no significant effect on HDL level compared to the FFA group (p > 0.05), although a significant overall model effect was observed. Oil red O staining showed that the area of lipid droplets in cells with 50 mM betaine decreased most significantly. (3) The expression levels of VNN1, FAS, ACC, SCD, and SREBPQ genes in the fat model group were significantly higher compared to the control group (p < 0.05), and the DNA methylation level in the promoter region of the VNN1 gene decreased. (4) The addition of 2, 10, 25, 50, and 100 mM betaine significantly reduced the expression of VNN1. The expression of FAS in 2, 10, and 25 mM betaine groups significantly decreased. Betaine at 10 and 100 mM significantly reduced the expression of SREBPQ, but it showed no significant effect on ACC expression. Addition of 2, 50, and 100 mM betaine led to an increased DNA methylation status at the VNN1 gene promoter region. In summary, the addition of betaine can reduce the expression of fatty acid synthesizing genes such as FAS, SCD, and SREBPQ, down-regulate the expression level of the VNN1 gene, increase the DNA methylation level of the VNN1 promoter region, and reduce lipid deposition in goose liver steatosis cells.