Developmental changes in the milk fat globule membrane proteome during the transition from colostrum to milk

Shotgun proteomics, using amine-reactive isobaric tags (iTRAQ), was used to quantify protein changes in milk fat globule membranes (MFGM) that were isolated from d 1 colostrum and compared with MFGM from d 7 milk. Eight Holstein cows were randomly assigned to 2 groups of 4 cow sample pools for a simple replication of this proteomic analysis using iTRAQ. The iTRAQ labeled peptides from the experiment sample pools were fractionated by strong cation exchange chromatography followed by further fractionation on a microcapillary high performance liquid chromatograph connected to a nanospray-tandem mass spectrometer. Data analysis identified 138 bovine proteins in the MFGM with 26 proteins upregulated and 19 proteins downregulated in d 7 MFGM compared with colostrum MFGM. Mucin 1 and 15 were upregulated greater than 7-fold in MFGM from d 7 milk compared with colostrum MFGM. The tripartite complex of proteins of adipophilin, butyrophilin, and xanthine dehydrogenase were individually upregulated in d 7 MFGM 3.4-, 3.2-, and 2.6-fold, respectively, compared with colostrum MFGM. Additional proteins associated with various aspects of lipid transport synthesis and secretion such as acyl-CoA synthetase, lanosterol synthase, lysophosphatidic acid acyltransferase, and fatty acid binding protein were upregulated 2.6- to 5.1-fold in d 7 MFGM compared with colostrum MFGM. In contrast, apolipoproteins A1, C-III, E, and A-IV were downregulated 2.6- to 4.3-fold in d 7 MFGM compared with colostrum MFGM. These data demonstrate that quantitative shotgun proteomics has great potential to provide new insights into mammary development.