Analysis of human breast milk cells: gene expression profiles during pregnancy, lactation, involution and mastitic infection.

The molecular processes underlying human milk production and the effects of mastitic infection are largely unknown because of limitations in obtaining tissue samples. Determination of gene expression in normal lactating women would be a significant step towards understanding why some women display poor lactation outcomes. Here we demonstrate the utility of RNA obtained directly from human milk cells to detect mammary epithelial cell (MEC)-specific gene expression. Milk cell RNA was collected from 5 time points (24 hours pre-partum during the colostrum period, mid lactation, two involution, and during a bout of mastitis) in addition to an involution series comprising three time points. Gene expression profiles were determined by use of human Affymetrix arrays. Milk cells collected during milk production showed that the most highly expressed genes were involved in milk synthesis (eg. CEL, OLAH, FOLR1, BTN1A1, ARG2), while milk cells collected during involution showed a significant down regulation of milk synthesis genes and activation of involution associated genes (eg. STAT3, NF-kB, IRF5, IRF7). Milk cells collected during mastitic infection revealed regulation of a unique set of genes specific to this disease state, whilst maintaining regulation of milk synthesis genes. Use of conventional epithelial cell markers was used to determine the population of MECs within each sample. This paper is the first to describe the milk cell transcriptome across the human lactation cycle and during mastitic infection, providing valuable insight into gene expression of the human mammary gland.

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Sharp JA, Lefèvre C, Watt A, Nicholas KR