Emergence of disease-specific endothelial and stromal cell populations responsible for arterial remodeling during development of pulmonary arterial hypertension

AbstractPulmonary arterial hypertension (PAH) is a severe and lethal pulmonary vascular disease characterized by arteriolar pruning and occlusive vascular remodeling leading to increased pulmonary vascular resistance and eventually right heart failure. While endothelial cell (EC) injury and apoptosis are known triggers for this disease, the mechanisms by which they lead to complex arterial remodeling remain obscure. We employed multiplexed single-cell RNA sequencing (scRNA-seq) at multiple timepoints during the onset and progression of disease in a model of severe PAH to identify mechanisms involved in the development of occlusive arterial lesions. There was significant loss of arterial volume as early as 1-week by microCT, preceding any evidence of occlusive arteriopathy, consistent with early arteriolar dropout. Maximal arterial pruning was seen by 5 to 8 weeks, with signs of progressive occlusive remodeling. Analysis of the scRNA-seq data resolved 44 lung cell populations, with widespread early transcriptomic changes at 1 week affecting endothelial, stromal and immune cell populations. Notably, this included emergence of a relatively dedifferentiated (dD) EC population that was enriched for Cd74 expression compared to general capillary (gCap) ECs which were primed to undergo endothelial-mesenchymal transition, as evidenced by RNA velocity analysis. However, at late timepoints (5 and 8 weeks), activated arterial ECs (aAECs) were the only cell population exhibiting persistent differential gene expression. This was characterized by a growth regulated state, including high expression of Tm4sf1, a gene implicated in cancer cell growth, which was also expressed by a smooth muscle (SM)-like pericyte cluster. Both these populations were localized to regions of arterial remodeling in the rat model and PAH patients, with aAECs contributing to intimal occlusive lesions and SM-like pericytes forming bands of medial muscularization. Together these findings implicate disease-specific vascular cells in PAH progression and suggest that TM4SF1 may be a novel therapeutic target for arterial remodeling.