Submitted to: Journal of Proteomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 15, 2011
Publication Date: February 16, 2012
Citation: Reinhardt, T.A., Lippolis, J.D., Nonnecke, B.J., Sacco, R.E. 2012. Bovine milk exosome proteome. Journal of Proteomics. 75(5):1486-1492. Interpretive Summary: A complete understanding of the components and proteins that make up milk is important for understanding neonatal calf nutrition as well as intra-mammary health. Exosomes are a recent discovery in bodily fluids. They are very small membrane vesicles secreted by cells and they function as non-cellular communicators between cells. They also can participate in immune functions during an infection. Therefore, it is important to gather initial data on their component proteins prior to studies examining their potential role in mammary infections. This study examined the protein composition of bovine milk exosomes. The result was the identification of 2107 proteins important for understanding milk production and mammary gland immune functions. Examination of the proteins associated with exosomes highlighted a dozen significant disease-fighting pathways that need to be examined in real world mammary infections. These findings may result in a new and better understanding of the economical important dairy production disease, mastitis.
Technical Abstract: Exosomes are 40-100 nm membrane vesicles of endocytic origin and are found in blood, urine, amniotic fluid, bronchoalveolar lavage (BAL) fluid, as well as human and bovine milk. Exosomes are extracellular organelles important in intracellular communication/signaling, immune function, and biomarkers for disease. Therefore, the proteome of bovine mammary-derived exosomes in milk is of considerable interest as milk exosomes have potential immune functions important in intramammary infections. Furthermore, these milk exosomes may provide insight into the complex processes of milk production. Triplicate exosome isolations from the milk of 2 mid-lactation cows were trypsin digested, subjected offline high pH reverse phase chromatography further fractionated on a nanoLC connected to tandem mass spectrometer. Analysis of the data resulted in identification of 2107 proteins in milk exosomes. The major milk fat globule membrane (MFGM) proteins (Butyrophilin, Xanthine oxidase, Adipophilin and Lactaherin) were among the most abundant proteins found in milk exosomes. They represented only 0.4-1.2% of the total spectra collected compared to 15-28% of the total spectra collected in the MFGM proteome. This indicates that the milk exosome pathway through the secretory cell apical plasma membrane into milk differs significantly from that of the MFGM. The protein composition of milk exosomes provides new information as to the potential physiological significance of exosomes to mammary physiology, health, and calf nutrition.