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Comparative 2D-DIGE Proteomic Analysis of Mammary Epithelial Cells during Lactation reveals Protein Signatures for Lactation Persistency and Milk Yield
Mammary gland is made up of a branching network of ducts that end with alveoli which surrounds the lumen. These alveolar mammary epithelial cells (MEC) reflect the milk producing ability of farm animals. In our previous study, we reported the proteome profile of functionally differentiated mammary epithelial cells isolated from milk.1 In this study, we have used 2-D DIGE and mass spectrometry to identify and relatively quantify protein expression changes in MEC during early, peak and late stages of lactation and also compared differentially expressed proteins in MEC isolated from high and low milk yielding animals. All the animals selected for these studies were in their 3rd or 4th parity. For the comparative proteomic analysis at different stages of lactations, we selected four animals (Sahiwal cows) in each group of immediate early (E, days 15-30 post-parturition), peak (P, days 75-100 post-parturition) and late stage (L, days 210 – 250 post-parturition) of lactation. For the comparative proteomic analysis of high and low milk yield samples, we selected four animals each of indigenous Sahiwal cows with high yielding (Hy, ~15 liters/day) and low-yielding (Ly, ~5 liters/day) breeds and four high-yielding cross bred cows (Karan Fries: KF, ~22 liters/day) were selected which were at peak stage of their lactation. We have identified 44 differentially expressed proteins during lactation stages and 28 proteins in high and low milk yielding animals. Bioinformatics analysis showed, a majority of the differentially expressed proteins are associated in metabolic process, catalytic and binding activity. The differentially expressed proteins were mapped to the available biological pathways and networks involved in lactation. The proteins up-regulated during late stage of lactation are associated with NF-kB stress induced signaling pathways and whereas Akt, PI3K and p38/MAPK signaling pathways are associated with high milk production mediated through insulin hormone signaling. The differentially expressed proteins reported in our present study could be potential biomarkers associated with lactation persistency and secretory diminution. The findings reported in the present study could benefit to the field of lactation biology.
Keywords: Lactation, Mammary epithelial cells, Proteomics
1. Janjanam et al., (2013). Proteome analysis of functionally differentiated bovine (Bos indicus) mammary epithelial cells isolated from milk. Proteomics, 13: 3189–3204.