Dietary betaine activates hepatic VTGⅡexpression in laying hens associated with hypomethylation of GR gene promoter and enhanced GR expression

Background: Vitellogenin(VTG) is a precursor of egg yolk proteins synthesized within the liver of oviparous vertebrates. Betaine is an important methyl donor that is reported to improve egg production of laying hens with an unclear mechanism. In the present study, we fed betaine-supplemented diet(0.5%) to laying hens for 4 wk and investigated its effect on VTGII expression in the liver.Results: Betaine did not affect chicken weight, but significantly(P < 0.05) increased egg laying rate accompanied with a significant(P < 0.05) increase in hepatic concentration and plasma level of VTGI. Plasma estrogen level did not change,but the hepatic expression of estrogen receptor α(ERα) mR NA was significantly(P < 0.05) up-regulated. Betaine did not affect the protein content of ERα, but significantly(P < 0.05) increased hepatic expression of glucocorticoid receptor(GR)at both mR NA and protein levels. Also, ERα/GR interaction tended to be enhanced in the liver nuclear lysates of betainesupplemented hens as determined by co-immunoprecipitation. Furthermore, dietary betaine supplementation significantly increased(P < 0.05) the hepatic expression of methyl-transfer enzymes, such as BHMT, GNMT, and DNMT1,which was associated with higher SAM/SAH ratio and hypomethylation of GR promoter regions.Conclusions: Betaine activates hepatic VTGII expression in association with modified DNA methylation of GR gene promoter, GR expression and ERα/GR interaction. Activation of hepatic VTGII expression may contribute, at least partly, to improved egg production in betaine-supplemented hens.

Maternal betaine suppresses adrenal expression of cholesterol trafficking genes and decreases plasma corticosterone concentration in offspring pullets

Background:Laying hens supplemented with betaine demonstrate activated adrenal steroidogenesis and deposit higher corticosterone(CORT)in the egg yolk.Here we further investigate the effect of maternal betaine on the plasma CORT concentration and adrenal expression of steroidogenic genes in offspring pullets.Results:Maternal betaine significantly reduced(P<0.05)plasma CORT concentration and the adrenal expression of vimentin that is involved in trafficking cholesterol to the mitochondria for utilization in offspring pullets.Concurrently,voltage-dependent anion channel 1 and steroidogenic acute regulatory protein,the two mitochondrial proteins involved in cholesterol influx,were both down-regulated at m RNA and protein levels.However,enzymes responsible for steroid syntheses,such as cytochrome P450 family 11 subfamily A member 1 and cytochrome P450 family 21 subfamily A member 2,were significantly(P<0.05)up-regulated at m RNA or protein levels in the adrenal gland of pullets derived from betaine-supplemented hens.Furthermore,expression of transcription factors,such as steroidogenic factor-1,sterol regulatory element-binding protein 1 and c AMP response element-binding protein,was significantly(P<0.05)enhanced,together with their downstream target genes,such as 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase,LDL receptor and sterol regulatory element-binding protein cleavage-activating protein.The promoter regions of most steroidogenic genes were significantly(P<0.05)hypomethylated,although methyl transfer enzymes,such as AHCYL,GNMT1 and BHMT were up-regulated.Conclusions:These results indicate that the reduced plasma CORT in betaine-supplemented offspring pullets is linked to suppressed cholesterol trafficking into the mitochondria,despite the activation of cholesterol and corticosteroid synthetic genes associated with promoter hypomethylation.