Mechanism of Parathyroid Hormone-Related Protein Secretion on Three-Dimensional Culture of Bovine Mammary Cells

牛奶中含有多种激素和细胞因子。然而，关于乳腺中机制的确切信息仍不清楚。甲状旁腺激素相关蛋白（PTHrP）是由哺乳期乳腺产生的，并以生物活性形式存在于乳汁中。本研究通过体外三维培养牛乳腺细胞，观察表皮生长因子（EGF）和转化生长因子（TGF）-β对牛乳腺细胞分泌甲状旁腺相关蛋白的影响。从产犊后1-6周的泌乳奶牛的乳腺中分离乳腺腺泡。将新鲜或冷冻保存的乳腺腺泡在胶原凝胶内和胶原包被的培养插入物或塑料皿上培养。N-末端放射免疫法测定PTHrP的产生。用北方分析法测定培养的牛乳腺细胞PTHrP mRNA的表达。用EGF和TGF-β处理以剂量依赖性方式增加培养基中PTHrP的产生以及PTHrP mRNA的表达。总PTHrP分泌在顶端方向保持在水平，而分泌在基底方向保持在高水平，在膜插入培养系统。这些数据表明，泌乳奶牛乳腺细胞可以在体外培养，并以可调控的方式分泌PTHrP。这些结果还表明，EGF和TGF-β可能是调节乳腺PTHrP分泌的重要因素。PTHrP的病理生理作用尚不确定。肌上皮细胞位于乳腺腺泡的基底部，对腺泡的收缩起作用。PTHrP可能在调节乳汁或乳汁成分进入肺泡腔中发挥作用。总之，该体外模型将有助于研究PTHrP在泌乳乳腺中的功能和调节。

Various hormones and cytokines are present in milk. However, precise information on the mechanism in the mammary gland is still unclear. Parathyroid hormone-related protein (PTHrP) is produced by the lactating mammary gland and is present in milk in a biologically active form. This investigation was performed to determine the effect of epidermal growth factor (EGF) and transforming growth factor (TGF) -beta on parathyroid hormone-related protein secretion by three dimensional culture of bovine mammary cells in vitro. Mammary acini were isolated from lactating mammary glands of cows at 1-6 weeks after calving. Fresh or cryopreserved mammary acini were cultured within collagen gels and on collagen coated culture inserts or plastic dishes. PTHrP production was measured by N-terminal radioimmunoassay. PTHrP mRNA expression from cultured bovine mammary cells was determined by northern analysis. PTHrP production in the culture medium as well as PTHrP mRNA expression was increased by treatment with EGF and TGF-beta in dose dependent manner. Total PTHrP secretion in an apical direction remained at levels, whereas secretion in a basal direction remained at high levels in a membrane insert cultured system. These data demonstrated that the mammary cell from lactating cows could be cultured in vitro and secreted PTHrP in a regulated manner. These results also indicate that EGF and TGF-beta may be important factors in the regulation of PTHrP secretion in the mammary gland. The pathophysiological role of PTHrP is uncertain. Myoepithelial cells situated in the basal position of mammary alveoli act on the alveolar contraction. PTHrP could play a role in the regulation of milk or milk components into the alveolar lumen. In conclusion, this in vitro model will be useful to investigate the function and regulation of PTHrP in the lactating mammary gland.