A lipoprotein-containing particle is transferred from the serum across the mammary epithelium into the milk of lactating mice

Abstract

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 125 I-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.

Network analysis of the proteome and peptidome sheds light on human milk as a biological system

“…Cluster 13 shows an overrepresentation of lipoprotein particles as the cellular location of the proteins ( p = ). The cluster comprises 6 different apolipoproteins, including apolipoproteins A1, A2, A4, B100, D, and E. It was shown in a study with mice that lipoprotein particles could be transferred from serum, deliver cholesterol in the MEC, and be secreted into the milk 37 . Considering the overrepresentation of apolipoproteins, the associations found in Cluster 13 might be an indicator of this mechanism.…”

Relationship between Plasma Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Level and Proteome Profile of Cows

“…Besides apoA1, apoA4 is also a cofactor for lecithin cholesterol acyltransferase. The apolipoproteins could be secreted from blood to milk by transcytotic pathways in mammary epithelial cells, and Monks et al concluded they may play a role in milk lipid transport in the mammary gland [ 32 ].…”