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Journal of Lipid Research, Vol. 42, 686-696, May 2001
Copyright © 2001 by Lipid Research, Inc.
A lipoprotein-containing particle is transferred from the serum across the mammary epithelium into the milk of lactating mice
Jenifer Monksa,
Patricia Uelmen Hueyb,
Linda Hansona,
Robert H. Eckelb,
Margaret C. Nevillea, and
Sean Gavigana
a Department of Physiology and Biophysics, Division of Endocrinology, Metabolism and Diabetes, University of Colorado Health Sciences Center, Denver, CO 80262
b University of Colorado Health Sciences Center, Denver, CO 80262 and Department of Medicine, Division of Endocrinology, Metabolism and Diabetes, University of Colorado Health Sciences Center, Denver, CO 80262
Correspondence to:
Margaret C. Neville, at Department of Physiology and Biophysics, 4200 East Ninth Avenue, C-240, University of Colorado Health Sciences Center, Denver, CO 80262., Peggy.Neville{at}UCHSC.edu (E-mail)
To investigate the role of low-density lipoprotein (LDL) in the delivery of cholesterol to the mammary gland during pregnancy and lactation, we examined the distribution of radioactivity from 125I-tyramine cellobiose-LDL injected into the tail vein of female mice at various stages of the reproductive cycle. Changes in the proportion of isotope taken up by the mammary gland largely reflected the increased weight of the gland in pregnancy and lactation. In addition, during lactation, radioactivity was found in the milk and was associated with a protein of the molecular weight of apoB-100. Quantitatively similar results were obtained with mice homozygous for disruption of the LDL receptor gene (LDLR null). Analysis of endogenous lipoproteins showed that the milk lipoprotein particles were denser than the corresponding serum lipoproteins and largely depleted of triglyceride and cholesterol. Using fluorescence microscopy we visualize the sorting of apoB protein from the LDL lipid phase at the basal surface of the mammary epithelial cell of both wild-type and LDLR-null mice.
Our findings provide evidence that the mammary epithelium of the lactating mouse is able to take up LDL from the plasma by a non-LDLR-mediated process. An apoB-containing particle from which the cholesterol has been removed is transferred into milk.Monks, J., P. U. Huey, L. Hanson, R. H. Eckel, M. C. Neville, and S. Gavigan. A lipoprotein-containing particle is transferred from the serum across the mammary epithelium into the milk of lactating mice. J. Lipid Res. 2001. 42: 686696.
Supplementary key words:
mammary gland, cholesterol, epithelium, LDL, LDLR-null mice, transcytosis, lipoprotein metabolism, milk secretion

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Copyright © 2001 by the American Society for Biochemistry and Molecular Biology.
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