Distinct Endothelial Cell Populations Characterize the Pulmonary Endarterectomy Specimen in Chronic Thromboembolic Pulmonary Hypertension

Abstract

<h3>Purpose</h3> Misguided vascular repair is thought to contribute to the pathophysiology of chronic thromboembolic pulmonary hypertension (CTEPH), yet little is known about endothelial cell (EC) phenotypes in the organized thromboembolic material of patients with CTEPH. Therefore, we sought to characterize ECs from pulmonary endarterectomy (PEA) specimens. <h3>Methods</h3> Human PEA specimens from proximal pulmonary arteries were collected from five CTEPH patients and dissociated for droplet-based single-cell RNA sequencing. Data from three control human lungs was obtained from the Human Lung Cell Atlas (https://hlca.ds.czbiohub.org accessed Sept. 9, 2021). <h3>Results</h3> From the PEA specimens of five CTEPH patients, we obtained transcriptional profiles for 11068 cells representing 20 clusters and 9 cell types. From those, 4 clusters displayed markers of ECs. To identify appropriate control ECs, we assessed markers of endothelial subtype from the Human Lung Cell Atlas and identified markers of pulmonary and bronchial artery ECs. Therefore, we obtained the transcriptional profiles of pulmonary and bronchial artery ECs from the Human Lung Cell Atlas as controls. After standardizing quality control metrics, we merged the data from 2174 control and 1772 CTEPH ECs. Dimension reduction of the merged dataset revealed 12 endothelial clusters (Figure). We note disproportionate distribution of control vs CTEPH ECs across clusters, with a majority of clusters biased towards one condition. Between and within clusters, CTEPH ECs displayed greater expression of TGFβ1, a marker of endothelial-mesenchymal transition (EMT), and P-selectin, a marker of endothelial activation. <h3>Conclusion</h3> Significant endothelial heterogeneity exists in both control and CTEPH ECs. However, we find differences in the composition of EC phenotypes between these two groups. We identify marker genes for CTEPH ECs that contribute to our understanding of EC phenotypes and misguided vascular repair in CTEPH.