Proteomic profiling of endometrial tissue and plasma from mares with endometrial fibrosis†

Endometrial fibrosis leads to subfertility when periglandular fibrosis impairs endometrial gland function. Identifying distinct protein expressions in mares suffering from this condition is essential for understanding the pathogenesis and developing treatments to delay fibrotic progression. To gain a better understanding of protein dynamics underlying this condition, Data-Independent Acquisition Mass Spectrometry was utilized to comprehensively characterize and compare the equine endometrial and plasma proteome from mares with different severities of endometrial fibrosis. Mares in diestrus were selected as controls (n = 9), moderate endometrial fibrosis (n = 9), and severe endometrial fibrosis (n = 9), based on examination of tissue sections stained with hematoxylin and eosin and immunohistochemically marked for alpha-smooth muscle actin. Approximately 10,000 proteins were identified in endometrial tissue and 500 in plasma. Between moderate fibrosis and controls, 310 and 75 differed in endometrial tissue and plasma, respectively, and between severe fibrosis and controls, 585 and 71 differed, respectively. Extracellular matrix-related pathways were over-represented among upregulated proteins in endometrial tissue from mares with moderate and severe fibrosis. Several of the proteins involved appear to promote development or progression of fibrosis. Immune-related pathways were over-represented among downregulated proteins in mares with moderate fibrosis, and among upregulated proteins in mares with severe fibrosis. Several of the proteins highlighted by our analysis have both immunologic and fibrotic properties. We anticipate that the extensive profiling of endometrial and plasma proteome paves the way for identification of potential diagnostic biomarkers and targets for therapeutic use in equine endometrial fibrosis.