Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2008
Publication Date: 6/20/2008
Citation: Reinhardt, T.A., Lippolis, J.D. 2008. Developmental changes in the milk fat globule membrane proteome during the transition from colostrum to milk. Journal of Dairy Science. 91(6):2307-2318. Interpretive Summary: Proteomics is a technology that allows one to survey and quantitate proteins in tissue of interest. The milk fat globule membrane is the membrane that covers secreted milk fat and is derived from the apical membrane of the secretory epithelium of the mammary gland. The proteins that make up this membrane were identified by mass spectroscopy. The bulk of the proteins identified have functions associated with milk secretion mechanisms, milk fat and protein synthesis and transport. The identity and quantitation of protein changes in lactation will provide important information needed to more fully understand milk secretion and production. Functional immune proteins, such as CD14, Toll like receptors 2 and 4 were also identified. This suggests a direct role for the mammary gland in detecting an infection. These findings may result in a new and better understanding of the economical important dairy production disease mastitis.
Technical Abstract: Shotgun Proteomics, using amine-reactive isobaric tags (iTRAQ) was used to quantify protein changes in milk fat globule membranes (MFGM) that were isolated from day 1 colostrum and compared to MFGM from day 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. iTRAQ labeled peptides from the experiment sample pools were fractionated by strong cation exchange chromatography followed by further fractionation on a micro-capillary high performance liquid chromatograph connected to a nanospray-tandem mass spectrometer. Data analysis identified 138 bovine proteins in the MFGM with 26 proteins up-regulated and 19 proteins down-regulated in day 7 MFGM compared to colostrum MFGM. Mucin 1 and 15 were up-regulated greater than 7 fold in MFGM from day 7 milk compared to colostrum MFGM. The tripartite complex of proteins of adipophilin, butyrophilin, and xanthine dehydrogenase were individually up-regulated in day 7 MFGM 3.4, 3.2, and 2.6 fold, respectively, compared to 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 up-regulated 2.6-5.1 fold in day 7 MFGM compared to colostrum MFGM. In contrast, apolipoproteins A1, C-III, E, and A-IV were down-regulated 2.6-4.3 fold in day 7 MFGM compared to colostrum MFGM. These data demonstrate that quantitative shotgun proteomics has great potential to provide new insights into mammary development.