Concentric pulmonary vascular remodelling driven by endothelial cells (EC) contributes to elevated pulmonary vascular resistance in PAH, and has previously shown pronounce cellular heterogeneity and implicated ROCK. Can we leverage the high heterogeneity for detailed lung cell characterizations? Are ROCK- and PAH-related pathways linked with emerging patterns in Smooth Muscle Cells (SMC) or EC?

Systems biology analyses of a single-cell RNA-Seq lung explant dataset showed 16 cell clusters including EC- and immune-specific clusters. While ECs organized into a distinct vascular cluster, SMC heterogeneously clustered with fibroblasts/pericytes. Vascular ECs further stratified into venous (vEC), capillary-venous (cvEC), and capillary-arterial (caEC) ECs, and displayed PAH- and ROCK-associated differences: caEC showed >77 times more PAH-altered gene expression differences than cvEC, and disrupted Slit/Robo and EIF2AK4 pathways. Despite negligible ROCK expression differences, caEC exclusively displayed ROCK- and PAH-associated pathway changes (e.g. cytoskeleton regulation, leukocyte migration, or RHO GTPase signalling). caEC showed strong evidence of crosstalk with immune clusters (e.g. CD4 T cells), not observed in other EC subtypes.

These observations suggest that a previously uncharacterized lung EC subtype is linked with remodelling, ROCK- and PAH-specific pathways, and points to crosstalk with specific immune cells.