Betaine is reported to regulate hepatic
cholesterol metabolism in mammals. Chicken eggs contain considerable amount of
betaine, yet it remains unknown whether and how
betaine in the egg affects hepatic
cholesterol metabolism in chicks. In this study, eggs were injected with
betaine at 2.5 mg/egg and the hepatic
cholesterol metabolism was investigated in newly hatched chicks.
Betaine did not affect
body weight or liver weight, but significantly increased the serum concentration (P < 0.05) and the hepatic content (P < 0.01) of
cholesterol. Accordingly, the
cholesterol biosynthetic
enzyme HMGCR was up-regulated (P < 0.05 for both
mRNA and
protein), while CYP7A1 which converts
cholesterol to
bile acids was down-regulated (P < 0.05 for
mRNA and P = 0.07 for
protein). Moreover, hepatic
protein content of the
sterol-regulatory element binding protein 1 which regulates
cholesterol and
lipid biosynthesis, and the
mRNA abundance of
ATP binding cassette sub-family A member 1 (ABCA1) which mediates
cholesterol counter transport were significantly (P < 0.05) increased in
betaine-treated chicks. Meanwhile, hepatic
protein contents of
DNA methyltransferases 1 and
adenosylhomocysteinase-like 1 were increased (P < 0.05), which was associated with global genomic
DNA hypermethylation (P < 0.05) and diminished gene repression mark histone H3
lysine 27 trimethylation (P < 0.05). Furthermore, CpG methylation level on gene promoters was found to be increased (P < 0.05) for CYP7A1 yet decreased (P < 0.05) for ABCA1. These results indicate that in ovo
betaine injection regulates hepatic
cholesterol metabolism in chicks through epigenetic mechanisms including
DNA and
histone methylations.