Submitted to: Physiological Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2008
Publication Date: 3/25/2009
Citation: Maningat, P.D., Sen, P., Rijnkels, M., Sunehag, A.L., Hadsell, D.L., Bray, M., Haymond, M.W. 2009. Gene expression in the human mammary epithelium during lactation: The milk fat globule transcriptome. Physiological Genomics. 37(1):12-22. Interpretive Summary: In vivo human gene expression studies and the response to hormonal and metabolic manipulations may be hindered by the availability of tissue samples. Utilizing RNA isolated from breast milk fat enabled us to obtain repeated samples from 5 women in a non-invasive manner. In this paper, we describe the gene expression profile, and the changes that occur casually within a 24th period, of mRNA isolated from the milk fat globule through microarray studies. The pathways and functions associated with the expressed genes were analyzed. Because of the lack of human data, we compared our gene expression data to published mice data. We found that milk protein genes as well as genes involved in various metabolic processes are expressed and may be studied using this novel RNA source. This is the first report of data gathered from the milk fat globule and may be used in future studies to determine the changes that occur in response to hormonal or other pharmacologic interventions.
Technical Abstract: The molecular physiology underlying human milk production is largely unknown because of limitations in obtaining tissue samples. Determining gene expression in normal lactating women would be a potential step toward understanding why some women struggle with or fail at breastfeeding their infants. Recently, we demonstrated the utility of RNA obtained from breast milk fat globule (MFG) to detect mammary epithelial cell (MEC)-specific gene expression. We used MFG RNA to determine the gene expression profile of human MEC during lactation. Microarray studies were performed using Human Ref-8 BeadChip arrays (Illumina). MFG RNA was collected every 3 h for 24 h from five healthy, exclusively breastfeeding women. We determined that 14,070 transcripts were expressed and represented the MFG transcriptome. According to GeneSpring GX 9, 156 ontology terms were enriched (corrected P < 0.05), which include cellular (n = 3,379 genes) and metabolic (n = 2,656) processes as the most significantly enriched biological process terms. The top networks and pathways were associated primarily with cellular activities most likely involved with milk synthesis. Multiple sampling over 24 h enabled us to demonstrate core circadian clock gene expression and the periodicity of 1,029 genes (7%) enriched for molecular functions involved in cell development, growth, proliferation, and cell morphology. In addition, we found that the MFG transcriptome was comparable to the metabolic gene expression profile described for the lactating mouse mammary gland. This paper is the first to describe the MFG transcriptome in sequential human samples over a 24 h period, providing valuable insights into gene expression in the human MEC.