Abstract Rationale Pulmonary hypertension (PH) is frequently associated with idiopathic pulmonary fibrosis (IPF), affecting 5-15% of early-stage patients and up to 80% at the time of lung transplantation. In these patients, pulmonary vascular resistance (PVR) is the strongest hemodynamic predictor of mortality, with risk rising sharply above 5 Wood Units (WU). Interestingly, even in the absence of PH, modest increases in PVR (2 WU), identify patients at risk of mortality. Evidence suggests that vascular remodeling contributes to fibrotic progression through crosstalk with the extracellular matrix, yet the cellular and molecular mechanisms linking elevated PVR to fibrosis remain unclear. We sought to explore how pulmonary vascular remodeling, as reflected by PVR, contributes to IPF pathogenesis. Methods We performed a comparative single-cell RNA sequencing analysis of 57 IPF lung explants (29 with PH and 28 without PH) stratified by PVR (normal ≤2 WU, intermediate 2-5 WU, severe ≥5 WU) and 19 healthy controls. Cell types were annotated using the Human Lung Cell Atlas, and differential gene expression was assessed with MAST (fold change ≥1.5, FDR 0.05) Regulatory network analysis was performed on high-confidence gene intersections. Results Comparison of IPF lungs with normal PVR vs controls revealed extensive transcriptional regulation within the vascular niche. Adventitial fibroblasts emerged as the most strongly regulated cell type, with several profibrotic genes, including COL1A1, ADAM17, CXCL12, and MMP16, differentially expressed. Gene Ontology analysis highlighted enrichment in biological processes related to extracellular matrix organization, collagen fibril formation, cell-matrix adhesion, and wound healing. Regulatory network analysis identified key transcriptional nodes, specifically NR3C1, SS18, and STAT3, as potential drivers of the profibrotic signature across the vascular niche. Notably, alveolar fibroblasts exhibited a similar transcriptional profile, further supporting the profibrotic role of adventitial fibroblast in IPF. In subjects with severe PVR, adventitial fibroblasts showed upregulated genes enriched in extracellular matrix organization and mesenchymal differentiation, alongside downregulated genes that included negative regulators of Wnt and TGF-β signaling. These findings underscore the role of adventitial fibroblasts within the pulmonary vasculature in fostering a profibrotic environment, positioning them as critical mediators of vascular remodeling and fibrosis in IPF. Conclusions Adventitial fibroblasts are central mediators of vascular remodeling and fibrosis in IPF, exhibiting a profibrotic, extracellular matrix-producing phenotype that is further amplified in subjects with elevated PVR. These results provide a potential link between pulmonary vascular remodeling and the increased mortality associated with elevated PVR in IPF patients. Future research will validate these findings. This abstract is funded by: NIH, Alfonso Martin Escudero Foundation
Fernandez et al. (Fri,) studied this question.