Platelets induce endothelial-mesenchymal transition and subsequent fibrogenesis in endometriosis

Research question: Do endometriotic lesions undergo endothelial-mesenchymal transition (EndoMT)? Design: Lesion samples from 30 patients with ovarian endometriomas and deep endometriosis, and control endometrial tissue samples from 30 women without endometriosis, were analysed. In-vitro experimentation using the human umbilical vein endothelial cell (HUVEC) line were conducted. Immunofluorescence staining and immunohistochemistry analysis using antibodies against endothelial cell and mesenchymal cell markers were conducted. The HUVEC cells were co-cultured with activated platelets or control medium with and without neutralization of TGF-beta 1 PDGFR, or both. Their morphology, proliferation and expression levels of genes and proteins known to be involved in EndoMT were evaluated, along with their migratory and invasive propensity, contractility and collagen production capability. Results: The proportion of CD31 and FSP-1 dual-positive cells in FSP-1+ fibroblasts was 74.7% (+/- 5.4%) in ovarian endometrioma lesions, significantly higher than that in deep endometriosis lesions (26.8% +/- 26.0%; P = 5.7 x 10(-5)), and was zero in normal endometrium. The extent of lesional fibrosis correlated positively with staining levels of the lesional mesenchymal markers FSP-1 and alpha-SMA (r = 0.91; P < 2.2 x 10(-16), r = 0.81; P = 5.8 x 10(-15), respectively). Human endothelial cells co-cultured with activated platelets acquire a morphology suggestive of EndoMT, concomitant with increased proliferation, loss of CD31 but marked increase in expression of mesenchymal markers. Morphological and gene and protein expression changes are accompanied by functional differentiation reflected by increased migratory and invasive capacity, contractility and collagen production. Neutralization of TGF-beta 1 and PDGFR signalling abolished platelet-induced EndoMT in human endothelial cells. Conclusions: Multiple sources of myofibroblasts exist in endometriotic lesions, and implicates platelets, EndoMT, or both, as potential therapeutic targets for treating endometriosis.