Emergence of disease specific endothelial and stromal cell populations involved in arterial remodeling during development of pulmonary arterial hypertension

Pulmonary 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 the SU/CH model of 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 transcriptional changes at 1 week affecting endothelial, stromal, and immune cell populations. Notably, this included emergence of a relatively dedifferentiated general capillary (gCap) EC population (dCap ECs) that expresses Cd74 and appears to undergo endothelial-mesenchymal transition by RNA velocity analysis. However, at late timepoints (5 and 8 weeks), only the activated arterial EC (aAEC) population exhibited persistent differential gene expression characterized by a dysfunctional growth regulated state. This included high expression of Tm4sf1, implicated in cancer cell growth, which was also found in a smooth muscle (SM)-like pericyte population. Both aAECs and SM-like pericytes were found to be spatially localized to regions of occlusive arterial remodeling in lungs of SU/CH rats and PAH patient samples. Together these findings implicate disease specific vascular cells in PAH progression and suggest that TM4SF1 may be a novel therapeutic target for arterial remodeling. ### Competing Interest Statement The authors have declared no competing interest.