Mani, O3; Sørensen, M T6; Sejrsen, K6; Bruckmaier, R M5; Albrecht, C3
1 Department of Animal Health and Bioscience, Faculty of Agricultural Sciences, Aarhus University, Aarhus University2 Disease Mechanisms, -Markers and -Prevention, Faculty of Agricultural Sciences, Aarhus University, Aarhus University3 Institute of Biochemistry and Molecular Medicine, University of Bern4 Department of Animal Science - Animal nutrition and physiology, Department of Animal Science, Science and Technology, Aarhus University5 Veterinary Physiology, Vetsuisse Faculty, University of Bern6 Department of Animal Science - Animal nutrition and physiology, Department of Animal Science, Science and Technology, Aarhus University
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 , and PPAR 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.
Journal of Dairy Science, 2009, Vol 92, Issue issue 8, p. 3744-3756