Mani O, Sorensen M T, Sejrsen K, Bruckmaier R M, Albrecht C
Institute of Biochemistry and Molecular Medicine, University of Bern, CH-3012 Bern, Switzerland.
J Dairy Sci. 2009 Aug;92(8):3744-56. doi: 10.3168/jds.2009-2063.
The transport of lipids across mammary gland epithelial cells (MEC) determines milk lipid content and composition. We investigated the expression of lipid transporters and their regulators in comparison to blood metabolites during lactation and dry period (DP) in dairy cows. Repeated mammary gland biopsies and blood samples were taken from 10 animals at 7 stages of the pregnancy-lactation cycle. Expression levels of the specific mRNAs were determined by quantitative reverse transcription-PCR, whereas ABCA1 was localized by immunohistochemistry. Blood serum metabolites were determined by common enzymatic chemistries. Elevated mRNA profiles of ABCA1 and ABCA7 were found during DP as compared with lactation and were inversely associated with blood cholesterol levels. Elevated levels of ABCG2, NPC1, SREBP1, SREBP2, LXR alpha, and PPAR gamma were found postpartum, whereas ABCG1 did not differ between the functional stages of the mammary gland. The ABCA1 protein was localized in MEC and showed differential activity between DP and lactation suggesting a role of ABCA1 in the removal of excess cellular cholesterol from MEC during the DP. The expression profiles of ABCA7 and NPC1 may reflect a role of these transporters in the clearance of apoptotic cells and the intracellular redistribution of cholesterol, respectively. Regulation of lipid transporters in the mammary gland is partially associated with transcription factors that control lipid homeostasis.
脂质跨乳腺上皮细胞（MEC）的转运决定了乳脂的含量和组成。我们研究了奶牛在泌乳期和干奶期（DP）时脂质转运蛋白及其调节剂的表达，并与血液代谢物进行了比较。在妊娠-泌乳周期的7个阶段，从10头动物身上重复采集乳腺活检组织和血样。通过定量逆转录PCR测定特定mRNA的表达水平，而ABCA1则通过免疫组织化学进行定位。血清代谢物通过常规酶促化学方法测定。与泌乳期相比，在干奶期发现ABCA1和ABCA7的mRNA水平升高，且与血液胆固醇水平呈负相关。产后发现ABCG2、NPC1、SREBP1、SREBP2、LXRα和PPARγ水平升高，而ABCG1在乳腺的不同功能阶段没有差异。ABCA1蛋白定位于MEC，并且在干奶期和泌乳期表现出不同的活性，表明ABCA1在干奶期从MEC清除多余细胞胆固醇中发挥作用。ABCA7和NPC1的表达谱可能分别反映了这些转运蛋白在凋亡细胞清除和胆固醇细胞内再分布中的作用。乳腺中脂质转运蛋白的调节部分与控制脂质稳态的转录因子有关。
