Department of Animal Science, University of Vermont, Burlington, VT 05405, USA.
Domest Anim Endocrinol. 2013 Feb;44(2):57-69. doi: 10.1016/j.domaniend.2012.09.001. Epub 2012 Sep 29.
During the onset of lactation, there is a dramatic increase in the expression of glucose transporters (GLUT) and a group of enzymes involved in milk fat synthesis in the bovine mammary gland. The objective of this study was to investigate whether the lactogenic hormones mediate both of these increases. Bovine mammary explants were cultured for 48, 72, or 96 h with the following hormone treatments: no hormone (control), IGF-I, insulin (Ins), Ins + hydrocortisone + ovine prolactin (InsHPrl), or Ins + hydrocortisone + prolactin + 17β-estradiol (InsHPrlE). The relative expression of β-casein, α-lactalbumin, sterol regulatory element binding factor 1 (SREBF1), fatty acid synthase (FASN), acetyl-CoA carboxylase α (ACACA), stearyol-CoA desaturase (SCD), GLUT1, GLUT8, and GLUT12 were measured by real-time PCR. Exposure to the lactogenic hormone combinations InsHPrl and InsHPrlE for 96 h stimulated expression of β-casein and α-lactalbumin mRNA by several hundred-fold and also increased the expression of SREBF1, FASN, ACACA, and SCD genes in mammary explants (P < 0.01). However, those hormone combinations had no effect on GLUT1 or GLUT8 expression and inhibited GLUT12 expression by 50% after 72 h of treatment (P < 0.05). In separate experiments, the expression of GLUTs in the mouse mammary epithelial cell line HC11 or in bovine primary mammary epithelial cells was not increased by lactogenic hormone treatments. Moreover, treatment of dairy cows with bovine prolactin had no effect on GLUT expression in the mammary gland. In conclusion, lactogenic hormones clearly stimulate expression of milk protein and lipogenic genes, but they do not appear to mediate the marked up-regulation of GLUT expression in the mammary gland during the onset of lactation.
在泌乳开始时，牛乳腺中葡萄糖转运体 (GLUT) 和一组参与乳脂肪合成的酶的表达显著增加。本研究的目的是探讨泌乳激素是否介导这两种增加。将牛乳腺外植体用以下激素处理培养 48、72 或 96 小时：无激素（对照）、IGF-I、胰岛素（Ins）、Ins+hydrocortisone+牛催乳素（InsHPrl）或 Ins+hydrocortisone+催乳素+17β-雌二醇（InsHPrlE）。通过实时 PCR 测量 β-酪蛋白、α-乳白蛋白、固醇调节元件结合蛋白 1 (SREBF1)、脂肪酸合酶 (FASN)、乙酰辅酶 A 羧化酶 α (ACACA)、硬脂酰辅酶 A 去饱和酶 (SCD)、GLUT1、GLUT8 和 GLUT12 的相对表达。暴露于泌乳激素组合 InsHPrl 和 InsHPrlE 96 小时可刺激 β-酪蛋白和 α-乳白蛋白 mRNA 的表达增加数百倍，并增加乳腺外植体中 SREBF1、FASN、ACACA 和 SCD 基因的表达（P<0.01）。然而，这些激素组合对 GLUT1 或 GLUT8 的表达没有影响，并在处理 72 小时后抑制 GLUT12 的表达 50%（P<0.05）。在单独的实验中，泌乳激素处理不会增加 HC11 小鼠乳腺上皮细胞系或牛原代乳腺上皮细胞中 GLUTs 的表达。此外，给奶牛注射牛催乳素对乳腺中 GLUT 的表达没有影响。总之，泌乳激素显然刺激乳蛋白和脂肪生成基因的表达，但它们似乎不介导泌乳开始时乳腺中 GLUT 表达的显著上调。
