Betaine supplementation in maternal diet modulates the epigenetic regulation of hepatic gluconeogenic genes in neonatal piglets
Maternal gestational nutrition provides a critical window in which neonates are predisposed to metabolic syndrome in adult life. Betaine as a methyl-donor nutrient is critical for fetal development and it donates methyl donors for DNA and protein methylation through methionine metabolism which is critical for the epigenetic regulation of gene expression. However, direct evidence regarding the effects of betaine supplementation in maternal diet during gestation on hepatic gluconeogenic genes in neonatal offspring are lacking. In this study, gestational sows were fed control or betaine-supplemented diets (0.3% w/w) throughout the pregnancy, and we are aiming to elucidate if maternal dietary betaine affects offspring hepatic gluconeogenic genes through epigenetic mechanisms. Neonatal piglets born to betaine-supplemented sows had significantly higher serum and hepatic betaine contents (p < 0.05), together with significantly enhanced expression of methionine metabolic enzymes (p < 0.05) in the liver. Interestingly, significantly higher serum concentrations of lactic acid (p < 0.05) and glucogenic amino acids, including serine (p < 0.05), glutamate (p < 0.05), methionine (p < 0.05) and histidine (p < 0.05) were detected in betaine-exposed piglets, which coincided with higher hepatic glycogen content (p < 0.05) and greater protein expression of gluconeogenic enzymes, pyruvate carboxylase (PC) (p < 0.05), cytoplasmic phosphoenolpyruvate carboxykinase (PEPCK1) (p < 0.05), mitochondrional phosphoenolpyruvate carboxykinase (PEPCK2) (p < 0.05) and fructose-1, 6-bisphosphatase (FBP1) (p < 0.05). Moreover, maternal betaine significantly changed the methylation status of both CpGs and histones on the promoter of gluconeogenic genes. The decreased PEPCK1 mRNA was associated with DNA hypermethylation (p < 0.05) and increased repression histone mark H3K27me3 (p < 0.05), while the up-regulated PEPCK2 and FBP1 mRNA was associated with DNA hypomethylation (p < 0.05) and increased activation histone mark H3K4me3 (p < 0.05). Furthermore, hepatic expression of miRNAs predicted to target PC and PEPCK1 was also affected by maternal betaine supplementation. Two out of 7 miRNAs targeting PC and 6 out of 7 miRNAs targeting PEPCK1 were detected to be dramatically suppressed (p < 0.05) in the liver of betaine-exposed piglets. Our results provide the first evidence that maternal betaine supplementation affects hepatic gluconeogenic genes expression in newborn piglets through enhanced hepatic methionine metabolism and epigenetic regulations which involve DNA and histone methylations, as well as miRNAs-mediated post-transcriptional mechanism.
Keywords: betaine; epigenetic regulation; gluconeogenic genes expression