Proteomic Analysis Reveals Proteins and Pathways Associated with Lactation in Bovine Mammary Epithelial Cell-Derived Exosomes

Milk-derived
exosomes have been reported, which are involved in
many biological processes. The exosomes derived from mammary glands
are not known yet, and their relationship with mammary gland lactation
and the origin of milk-derived exosomes are largely unclear. The present
study aimed to investigate the proteome of exosomes derived from bovine
mammary epithelial cells (BMECs) and compare them with milk-derived
exosomes in the database. BMEC-derived exosomes were successfully
separated from the culture supernatant of BMECs by a combined ultracentrifugation
approach, and the purity of exosomes was identified by western blot
analysis. Liquid chromatography with tandem mass spectrometry identified
638 proteins in BMEC-derived exosomes. The MS data were deposited
into the PUBLIC repository ProteomeXchange, dataset identifier(s): https://www.iprox.org/page/PSV023.html;?url=1590961453176tKpa. Gene Ontology annotation and Kyoto Encyclopedia of Genes and Genomes
(KEGG) pathway analysis showed that these proteins were associated
with specific biological processes and molecular functions of metabolism.
Cross comparison of these proteins with the protein database of milk
exosomes showed that 77 common expressed proteins (CEPs) were in both
BMEC- and milk-derived exosomes. The KEGG pathway analysis for these
CEPs showed that they were mainly involved in signaling pathways associated
with milk biosynthesis in BMECs. Among these CEPs, six proteins have
been previously reported to be associated with the lactation function.
The western blot analysis detected that expression of these six proteins
in BMEC-derived exosomes was increased after the stimulation of methionine
and β-estradiol on BMECs. In summary, the proteome of BMEC-derived
exosomes reveals that they are associated with milk biosynthesis in
BMECs and might be a source of milk-derived exosomes.