Dietary betaine improves egg-laying rate in hens through hypomethylation and glucocorticoid receptor–mediated activation of hepatic lipogenesis-related genes

Abstract

In avian species, liver lipid metabolism plays an important role in egg laying performance. Previous studies indicate that betaine supplementation in laying hens improves egg production. However, it remains unclear if betaine improves laying performance by affecting hepatic lipid metabolism and what mechanisms are involved. We fed laying hens a 0.5% betaine-supplemented diet for 4 wks to investigate its effect on hepatic lipids metabolism in vivo and confirmed its mechanism via in vitro experiments using embryonic chicken hepatocytes. Results showed that betaine supplemented diet enhanced laying production by 4.3% compared with normal diet, accompanied with increased liver and plasma triacylglycerol concentrations ( P < 0.05) in hens. Simultaneously, key genes involved in hepatic lipid synthesis, such as sterol regulatory element binding protein 1 (SREBP-1), fatty acid synthase, acetyl-CoA carboxylase, and stearoyl-CoA desaturase 1 (SCD1) were markedly upregulated at the mRNA level ( P < 0.05). Western blot results showed that SREBP-1 and SCD1 protein levels were also increased ( P < 0.05). Moreover, mRNA expression of main apolipoprotein components of yolk-targeted lipoproteins, apolipoprotein B (ApoB) and apolipoprotein-V1 (ApoV1), in addition to microsomal triglyceride transfer proteins, which is closely related to the synthesis and release of very-low density lipoprotein, were also markedly elevated ( P < 0.05). Methylated DNA immunoprecipitation combined with PCR detects reduction of methylation levels in certain regions of the above gene promoters. Chromatin immunoprecipitation PCR assays showed increased binding of glucocorticoid receptor (GR) to SREBP1 and ApoB gene promoters. Similar results of ApoV1 gene expression were obtained from cultured hepatocytes treated with betaine. Additionally, betaine increased the expression of GR and some genes involved in methionine cycle in vitro. These results suggest that betaine supplementation could alter the expression of liver lipid synthesis and transport-related genes by modifying the methylation status and GR binding on their promoter and hence promote the synthesis and release of yolk precursor substances in the liver.

GR-mediated transcriptional regulation of m6A metabolic genes contributes to diet-induced fatty liver in hens

“…GR can be activated via both ligand-dependent [ 48 ] and ligand-independent manners [ 49 ]. Previously, we reported CORT-dependent GR activation in the liver of CORT-treated chickens [ 16 , 50 ]. In this study, chickens are not treated with CORT and the plasma CORT level was not determined.…”

Parental methyl-enhanced diet and in ovo corticosterone affect first generation Japanese quail (Coturnix japonica) development, behaviour and stress response

“…Moreover, considering the higher percentage of sexually regressed females and lower yield per bird from control fed parents, there are very likely to be positive downstream methylation implications for sexual maturity and productivity from the HiBET diet 51 , 52 . Indeed, other studies have demonstrated that 1-carbon-metabolic essential nutrient diet supplementation can heighten reproductive performance 23 , 46 , 47 . It is plausible that these effects are again due to increased hepatic enzyme activity that has been transmitted via transgenerational mechanisms to the G 1 , resulting in (at least) enhanced reproductive performance.…”

Impacts of Epigenetic Processes on the Health and Productivity of Livestock

“…Supplemental betaine potentially caused hypomethylation of the promoter of GR , followed by enhanced expression of GR and GR/ER α interaction (contributed to increase VTGII expression in the liver), which partly supported improved egg production in betaine-supplemented laying hens ( Omer et al, 2018 ). Furthermore, promoter region methylation could be the possible regulatory mechanism underlying altered expression of liver lipid synthesis and transport-related genes in response to betaine supplementation, which supported the synthesis and release of yolk precursor substances in the liver and consequently promoted egg laying performance ( Omer et al, 2020 ).…”