MOE Joint International Research Laboratory of Animal Health & Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing 210095, P. R. China; Key Laboratory of Animal Physiology & Biochemistry, Ministry of Agriculture and Rural Affairs, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing 210095, P. R. China; College of Allied Medical Sciences, University of Nyala, Nyala, Sudan.
MOE Joint International Research Laboratory of Animal Health & Food Safety, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing 210095, P. R. China; Key Laboratory of Animal Physiology & Biochemistry, Ministry of Agriculture and Rural Affairs, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing 210095, P. R. China.
Poult Sci. 2020 Jun;99(6):3121-3132. doi: 10.1016/j.psj.2020.01.017. Epub 2020 Mar 18.
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.
在禽类中，肝脏脂质代谢在产卵性能中起着重要作用。先前的研究表明，蛋鸡补充甜菜碱可提高产蛋量。然而，甜菜碱是否通过影响肝脏脂质代谢来改善产蛋性能尚不清楚，也不清楚涉及哪些机制。我们给产蛋鸡喂食 0.5%的甜菜碱补充饲料 4 周，以研究其对体内肝脏脂质代谢的影响，并通过使用胚胎鸡肝细胞的体外实验来验证其机制。结果表明，与正常饮食相比，甜菜碱补充饮食使产蛋量提高了 4.3%，同时母鸡肝脏和血浆中的三酰甘油浓度也增加（P<0.05）。同时，肝脏脂质合成关键基因，如固醇调节元件结合蛋白 1（SREBP-1）、脂肪酸合酶、乙酰辅酶 A 羧化酶和硬脂酰辅酶 A 去饱和酶 1（SCD1），在 mRNA 水平上显著上调（P<0.05）。Western blot 结果表明，SREBP-1 和 SCD1 蛋白水平也增加（P<0.05）。此外，蛋黄靶向脂蛋白的主要载脂蛋白成分，载脂蛋白 B（ApoB）和载脂蛋白-V1（ApoV1）的 mRNA 表达，以及与极低密度脂蛋白合成和释放密切相关的微粒体甘油三酯转移蛋白，也显著升高（P<0.05）。甲基化 DNA 免疫沉淀结合 PCR 检测到上述基因启动子某些区域的甲基化水平降低。染色质免疫沉淀 PCR 检测显示，糖皮质激素受体（GR）与 SREBP1 和 ApoB 基因启动子的结合增加。用甜菜碱处理培养的肝细胞也得到了类似的 ApoV1 基因表达结果。此外，甜菜碱在体外增加了 GR 和一些参与蛋氨酸循环的基因的表达。这些结果表明，甜菜碱补充剂可以通过修饰其启动子上的甲基化状态和 GR 结合来改变肝脏脂质合成和转运相关基因的表达，从而促进肝脏中卵黄前体物质的合成和释放。
