Sex Differences in Endothelial-to-Mesenchymal Transition in Chronic Thromboembolic Pulmonary Hypertension

Abstract

<h3>Purpose</h3> Chronic Thromboembolic Pulmonary Hypertension (CTEPH) results from thrombus organization and obstruction of pulmonary arteries. Population studies suggest sex differences in outcomes. Yet, the mechanisms contributing to sex differences in CTEPH remain poorly understood. We propose that endothelial cells present in the organized thrombi undergo endothelial-to-mesenchymal transition (EndoMT); a process in which endothelial cells lose polarity, cell-to-cell contacts, and gradually adopt mesenchymal cells characteristics. Here, we find that markers of EndoMT are significantly higher in female vs male patients, which could contribute to sex differences in CTEPH pathophysiology. <h3>Methods</h3> A retrospective cohort of ten male and ten female CTEPH patients was studied. Pulmonary endarterectomy specimens from these patients were separated into lobar and segmental sections. Two samples (lobar and segmental) from each patient were paraffin embedded and used for Immunohistochemistry (IHC) analysis. IHC staining for markers for EndoMT, including endothelin-1 (ET-1), Transforming growth factor beta-1 (TGF beta-1), vimentin and alpha smooth muscle cell actin (alpha SMA), was performed. Quantitative tissue area analysis for each marker was performed using the HALO image analysis platform. <h3>Results</h3> We found that females have significantly higher total expression of vimentin and TGF beta-1 (Figure A). There was a trend towards increased total expression of ET-1 and alpha SMA in females that is not significantly different from males (Figure B). However, we found that female segmental sections have higher expression levels for vimentin, TGF beta-1, ET-1 and alpha SMA than male segmental sections (Figure C). <h3>Conclusion</h3> Increased expression of EndoMT markers may account for sex differences in the pathophysiology and outcomes of CTEPH. We will validate these findings and further explore EndoMT in the pathogenesis of CTEPH.