Abstract
Simple SummaryThe current work evaluates the liver-blood-ovary signal axis in relation to age changes involved in regulating egg yolk precursor synthesis in chickens. In this study, we observe the morphology and histology of the liver and ovary and determine the serum biochemical parameters and the expression abundance of the critical genes from the age of 90 days (d90) to d153. The mRNA and protein expressions of estrogen receptor-alpha (ER-α) and E2 levels in the liver and serum, respectively, showed similar changes. Moreover, with reference to an increased serum E2 level, the mRNA expression of genes related to yolk precursor synthesis (very low density apolipoprotein-II (ApoVLDL-II) and vitellogenin-II (VTG-II)), lipogenesis (fatty acid synthase (FAS)), and lipid transport (microsomal triglyceride transport protein (MTTP)) in the liver showed up-regulation.Several reproductive hormones were reported to be involved in regulating egg yolk precursor synthesis in chickens; however, the mechanism that shows how the liver-blood-ovary signal axis works in relation to age changes has not been reported yet. Therefore, in this study, we observe the morphology and histology of the liver and ovary and determine the serum biochemical parameters and the expression abundance of the critical genes from d90 to 153. Results show that the body weight and liver weight were significantly increased from d132, while the ovary weight increased from d139. Aside from the increase in weight, other distinct changes such as the liver color and an increased deposition of large amounts of yolk precursors into the ovarian follicles were observed. On d139, we observed small fatty vacuoles in the hepatocytes. The results of serum biochemical parameters showed a significant increase in the estradiol (E2) level, first on d125, and then it reached its peak on d132. Meanwhile, the levels of follicle-stimulating hormone (FSH) increased initially and then remained at a high level from d146 to d153, while the levels of luteinizing hormone (LH) increased significantly on d132 and reached the top level on d153. Moreover, the levels of lecithin (LEC), vitellogenin (VTG), very low density lipoprotein y (VLDLy), triglyceride (TG), and total cholesterol (TC) were significantly increased at d125 and were close from d146 to d153. The mRNA and protein expression of estrogen receptor-alpha (ER-α) and E2 levels in the liver and serum, respectively, showed similar changes. Moreover, with reference to an increase in serum E2 level, the mRNA expression of genes related to yolk precursor synthesis (very low density apolipoprotein-II, ApoVLDL-II) and vitellogenin-II (VTG-II), lipogenesis (fatty acid synthase, FAS), and lipid transport (microsomal triglyceride transport protein, MTTP) in the liver showed up-regulation. These results suggest that the correlation between liver-blood-ovary alliances regulate the transport and exchange of synthetic substances to ensure synchronous development and functional coordination between the liver and ovary. We also found that E2 is an activator that is regulated by FSH, which induces histological and functional changes in the hepatocytes through the ER-α pathway.
Highlights
The poultry egg is an important nutritional source that contains rich proteins, lipids, vitamins, and minerals [1,2]
After the synthesis of these yolk precursors in the liver, APoB is packaged into very low density lipoprotein (VLDL) particles for transportation while VTG is released into the blood to be transported into the oocyte [18]
Our results showed that the body and liver weights increased dramatically from d132, while the ovary weight increased sharply from d139 (Table 2)
Summary
The poultry egg is an important nutritional source that contains rich proteins, lipids, vitamins, and minerals [1,2]. The major constituents of the egg yolk are proteins and lipids, which are present mainly in the form of lipoproteins and have several beneficial functions. Egg yolk lipoproteins have been found to possess numerous nutritional and health benefits, such as antimicrobial immunoglobulin Y [4,5,6], antioxidant properties [7,8], and the provision of the required nutrients for infant brain development [9,10,11]. After the synthesis of these yolk precursors in the liver, APoB is packaged into very low density lipoprotein (VLDL) particles for transportation while VTG is released into the blood to be transported into the oocyte [18]. VLDL and VTG are the key yolk precursors to transport and deposit additional nutrients into the ovary. VTG, as a glycophospholipoprotein, is responsible for supplying glucose, phosphorus, and fat and binds metal ions such as calcium, zinc, and iron and transports them into the oocyte [19]
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