Department of Physiology and Biophysics, University of Colorado School of Medicine, Aurora, Colorado;
Am J Physiol Endocrinol Metab. 2013 Nov 1;305(9):E1103-14. doi: 10.1152/ajpendo.00337.2013. Epub 2013 Aug 27.
Insulin is known to be an important regulator of milk secretion in the lactating mammary gland. Here we examine the role of insulin signaling in mammary development in pregnancy using a mouse with a floxed insulin receptor (IR) crossed with a mouse expressing Cre specifically in the mammary gland. In the mammary glands of these IR(fl/fl) Cre(+) mice, expression of IR is significantly diminished throughout development. Glands from these mice had 50% fewer alveoli at midpregnancy; casein and lipid droplets were diminished by 60 and 75%, respectively, indicating a role for IR both in alveolar development and differentiation. In an acinar preparation from mammary epithelial cells (MEC) isolated from pregnant mice, insulin stimulated lumen formation, mammary cell size, acinar size, acinar casein content, and the formation of lipid droplets with a Km of ∼1.7 nM. IGF-I and IGF-II had no effect at concentrations below 50 nM, and a function blocking antibody to the IGF type 1 receptor did not alter the response to insulin. We conclude that insulin interacting with IR is essential for mammary differentiation during murine pregnancy. Using array analysis, we then examined the expression of genes up- or downregulated >1.5-fold in the IR(fl/fl) Cre(+) MECs, finding significant downregulation of differentiation specific genes and upregulation of cell cycle and extracellular matrix genes. We conclude that insulin fosters differentiation and may inhibit cell proliferation in the mammary gland of the midpregnant mouse.
胰岛素是已知的哺乳乳腺中乳汁分泌的重要调节剂。在这里，我们使用一种在乳腺中特异性表达 Cre 的 floxed 胰岛素受体（IR）的小鼠，研究了胰岛素信号在妊娠期间乳腺发育中的作用。在这些 IR(fl/fl) Cre(+) 小鼠的乳腺中，IR 的表达在整个发育过程中显著减少。这些小鼠的乳腺在妊娠中期的腺泡数量减少了 50%；酪蛋白和脂滴分别减少了 60%和 75%，表明 IR 在腺泡发育和分化中都有作用。在从妊娠小鼠分离的乳腺上皮细胞（MEC）的腺泡制剂中，胰岛素刺激腔形成、乳腺细胞大小、腺泡大小、腺泡酪蛋白含量和脂滴形成，Km 值约为 1.7 nM。IGF-I 和 IGF-II 在低于 50 nM 的浓度下没有作用，并且 IGF 型 1 受体的功能阻断抗体也不会改变对胰岛素的反应。我们得出结论，胰岛素与 IR 相互作用对于小鼠妊娠期间的乳腺分化是必不可少的。然后，我们使用阵列分析检查了在 IR(fl/fl) Cre(+) MEC 中上调或下调 >1.5 倍的基因的表达，发现分化特异性基因显著下调，细胞周期和细胞外基质基因上调。我们得出结论，胰岛素促进分化，并可能抑制妊娠中期乳腺中的细胞增殖。
