Abstract 12433: Distinct Immune and Mesenchymal Populations Identified by Single Cell RNA Sequencing Contribute to Chronic Thromboembolic Pulmonary Hypertension

Chronic thromboembolic pulmonary hypertension (CTEPH) is a sequelae of acute pulmonary embolism (PE) in which the PE remodels into a chronic scar in the pulmonary arterial system. This results in vascular obstruction, small vessel arteriopathy and pulmonary hypertension. Previous studies have attempted to identify cells that contribute to CTEPH thrombus but have been limited by the use of specific cell markers or phenotypic modulation after cell growth in culture. Here we have used single cell RNA sequencing (scRNAseq) of samples of CTEPH thrombus removed at the time of pulmonary thromboendarterectomy (PTE) surgery to identify clusters of macrophages, T cells, smooth muscle cells and endothelial cells in CTEPH thrombus. We identified that multiple macrophage subclusters, many of which have an inflammatory phenotype. T cells were a heterogeneous population consisting of CD4+ and CD8+ T cells that are predicted to be inflammatory and also promote vascular remodeling. In the smooth muscle cell cluster, a subcluster of myofibroblasts are predicted to arise from smooth muscle cells based on pseudotime analysis. Notably, cultured endothelial, smooth muscle and myofibroblast cells isolated from CTEPH thrombus have distinct phenotypes from control cells. For example, endothelial cells had reduced angiogenic potential, were proliferative and anti-apoptotic. Lastly, gene expression data identified protease-activated receptor 1 (PAR1) as a potential therapeutic target that links thrombosis to chronic PE in CTEPH. Together, these studies suggest a model in which chronic inflammation drives vascular remodeling and mesenchymal senescence in CTEPH pathogenesis and suggest new approaches for targeting this disease.