Time‐resolved quantitative analysis of human milk proteome reveals developing milk and mammary‐gland functions during the first year of lactation

Abstract

In‐depth understanding of the developing function of human milk (HM) proteins and the corresponding physiological adaptions of the lactating mammary gland has been inhibited by incomplete knowledge of HM proteome. We analyzed the HM proteome (n =10 women with samples at 1, 4, 12, 24, 36 and 52 weeks) using a quantitative proteomic approach. 1147 proteins were identified with 580 being quantified. Principle component analysis showed that HM proteomes transition throughout the first year of lactation. Abundance changes of IgG, sIgA and IgM display distinct features during the first year. Complement components and other acute‐phase proteins are generally at higher levels in early lactation. Proteomic analysis further suggests that milk fatty‐acid (FA) metabolism shifts from more direct blood intake to more de novo mammary synthesis, which may alter the lipoprotein profile in lactating women and the composition of milk FAs. Glycoprotein metabolism transitions to catabolism in late lactation, which may increase the presence of free anti‐pathogenic HM oligosaccharides and peptides. Increased metabolic activity in late lactation can lead to a larger amount of deleterious by‐products. Cellular detoxification machinery is also transformed, thereby accommodating increased metabolic activities in late lactation. The multiple functions of the HM proteins become more apparent from this study.