Farke Carolin, Meyer Heinrich H D, Bruckmaier Rupert M, Albrecht Christiane
Physiology Weihenstephan, Technical University Munich, 85354 Freising, Germany.
J Dairy Res. 2008 Nov;75(4):406-14. doi: 10.1017/S002202990800335X. Epub 2008 Aug 14.
ATP-binding cassette (ABC) transporters play a pivotal role in human physiology, and mutations in these genes often result in severe hereditary diseases. ABC transporters are expressed in the bovine mammary gland but their physiological role in this organ remains elusive. Based on findings in the context of human disorders we speculated that candidate ABC transporters are implicated in lipid and cholesterol transport in the mammary gland. Therefore we investigated the expression pattern of selected genes that are associated with sterol transport in lactating and nonlactating mammary glands of dairy cows. mRNA levels from mammary gland biopsies taken during lactation and in the first and second week of the dry period were analysed using quantitative PCR. Five ABC transporter genes, namely ABCA1, ABCA7, ABCG1, ABCG2 and ABCG5, their regulating genes LXRalpha, PPARgamma, SREBP1 and the milk proteins lactoferrin and alpha-lactalbumin were assessed. A significantly enhanced expression in the dry period was observed for ABCA1 while a significant decrease of expression in this period was detected for ABCA7, ABCG2, SREBP1 and alpha-lactalbumin. ABCG1, ABCG5, LXRalpha, PPARgamma and lactoferrin expression was not altered between lactation and dry period. These results indicate that candidate ABC transporters involved in lipid and cholesterol transport show differential mRNA expression between lactation and the dry period. This may be due to physiological changes in the mammary gland such as immigration of macrophages or the accumulation of fat due to the loss of liquid in the involuting mammary gland. The current mRNA expression analysis of transporters in the mammary gland is the prerequisite for elucidating novel molecular mechanisms underlying cholesterol and lipid transfer into milk.
ATP结合盒（ABC）转运蛋白在人体生理过程中起着关键作用，这些基因的突变常常导致严重的遗传性疾病。ABC转运蛋白在牛乳腺中表达，但其在该器官中的生理作用仍不清楚。基于人类疾病背景下的研究结果，我们推测候选ABC转运蛋白与乳腺中的脂质和胆固醇转运有关。因此，我们研究了与奶牛泌乳期和非泌乳期乳腺中甾醇转运相关的特定基因的表达模式。使用定量PCR分析了泌乳期以及干奶期第一周和第二周采集的乳腺活检组织中的mRNA水平。评估了五个ABC转运蛋白基因，即ABCA1、ABCA7、ABCG1、ABCG2和ABCG5，它们的调控基因LXRα、PPARγ、SREBP1以及乳蛋白乳铁蛋白和α-乳白蛋白。观察到ABCA1在干奶期表达显著增强，而ABCA7、ABCG2、SREBP1和α-乳白蛋白在此期间表达显著下降。ABCG1、ABCG5、LXRα、PPARγ和乳铁蛋白的表达在泌乳期和干奶期之间没有变化。这些结果表明，参与脂质和胆固醇转运的候选ABC转运蛋白在泌乳期和干奶期之间表现出不同的mRNA表达。这可能是由于乳腺中的生理变化，如巨噬细胞的迁入或由于退化期乳腺中液体流失导致的脂肪积累。目前对乳腺中转运蛋白的mRNA表达分析是阐明胆固醇和脂质转运到乳汁中的新分子机制的前提条件。
