Developing human mammary‐gland functions during the first year of lactation (II) (622.7)

Abstract

Proteomic analysis of human milk provides a non‐invasive means to explore the physiology of lactating mammary gland. We applied quantitative milk proteomic analysis (TMT labeling) over one year of lactation (n =10 women with samples at 1 week, 1, 3, 6, 9 and 12 months) as probes for the developing mammary‐gland function. Proteins involved in the processes of endoplasmic reticulum‐assisted degradation and proteasomal degradation are, in general, upregulated over lactation, suggesting increased activities in protein catabolism. Rab GTPases that control intracellular membrane trafficking in various endocytosis and secretion processes are typically present at highest abundance at 6 months of lactation. The extracellular domain of intercellular adhesion molecule 1 (ICAM‐1) is upregulated over lactation. The increased proteolytic shedding of ICAM‐1 may represent a means to suppress leukocyte recruitment into milk as lactation progresses. In contrast, the shedding of E‐cadherin decreases over lactation, suggesting increasing barrier integrity at the adherens junctions in lactating human mammary epithelium. These insights combining in‐depth determination of protein content in milk with bioinformatic analysis illustrate the large potential for advancing our understanding of the lactating mammary gland.