<i>Pten</i> Regulates Development and Lactation in the Mammary Glands of Dairy Cows

<div><p><i>Pten</i> is a tumor suppressor gene regulating many cellular processes, including growth, adhesion, and apoptosis. In the aim of investigating the role of <i>Pten</i> during mammary gland development and lactation of dairy cows, we analyzed <i>Pten</i> expression levels in the mammary glands of dairy cows by using western blotting, immunohistochemistry, and quantitative polymerase chain reaction (qPCR) assays. Dairy cow mammary epithelial cells (DCMECs) were used to study the function of <i>Pten in vitro</i>. We determined concentrations of β-casein, triglyceride, and lactose in the culture medium following <i>Pten</i> overexpression and siRNA inhibition. To determine whether <i>Pten</i> affected DCMEC viability and proliferation, cells were analyzed by CASY-TT and flow cytometry. Genes involved in lactation-related signaling pathways were detected. <i>Pten</i> expression was also assessed by adding prolactin and glucose to cell cultures. When <i>Pten</i> was overexpressed, proliferation of DCMECs and concentrations for β-casein, triglyceride, and lactose were significantly decreased. Overexpression of <i>Pten</i> down-regulated expression of MAPK, CYCLIN D1, AKT, MTOR, S6K1, STAT5, SREBP1, PPARγ, PRLR, and GLUT1, but up-regulated 4EBP1 in DCMECs. The <i>Pten</i> siRNA inhibition experiments revealed results that opposed those from the gene overexpression experiments. Introduction of prolactin (PRL) increased secretion of β-casein, triglyceride, and lactose, but decreased <i>Pten</i> expression levels. Introduction of glucose also increased β-casein and triglyceride concentrations, but did not significantly alter <i>Pten</i> expression levels. The <i>Pten</i> mRNA and protein expression levels were decreased 0.3- and 0.4-fold in mammary glands of lactating cows producing high quality milk (milk protein >3.0%, milk fat >3.5%), compared with those cows producing low quality milk (milk protein <3.0%, milk fat <3.5%). In conclusion, <i>Pten</i> functions as an inhibitor during mammary gland development and lactation in dairy cows. It can down-regulate DCMECs secretion of β-casein, triglyceride, and lactose, and plays a critical role in lactation related signaling pathways.</p>