Differential proteomic profiling of endometrium and plasma indicate the importance of hydrolysis in bovine endometritis

Endometritis is an important disease of dairy cows that leads to significant economic losses in the dairy cattle industry. To investigate the alteration of proteins associated with endometritis in the dairy cow, the isobaric tags for relative and absolute quantification (iTRAQ) technique was applied to quantitatively identify differentially expressed proteins (DEP) in the endometrium and peripheral plasma of Chinese Holstein cows with endometritis. Compared with the normal (control) group, 159 DEP in the endometrium and 137 DEP in the plasma were identified in cows with endometritis. Gene ontology analysis demonstrated that the predominant endometrial DEP were primarily involved in responses to stimulus and stress processes and mainly played a role in hydrolysis in the extracellular region. The predominant plasma DEP were mainly components of the cytosol and non-membrane-bound organelles, and they were involved in the response to stress and regulation of enzyme activity. Protein-protein interaction of tissue DEP revealed that some core seed proteins, such as RAC2, ITGB2, and CDH1 in the same network as CD14, MMP3, and MMP9, had important functions in the cross-talk of pathways related to extracellular proteolysis. In summary, significant enzymatic hydrolase activity in the extracellular region is proposed as a molecular mechanism by which altered proteins may promote inflammation and hence endometritis.