Resident cell lineages are preserved in pulmonary vascular remodeling.

Slaven Crnkovic,Leigh M Marsh,Grazyna Kwapiszewska,Elie El Agha,Elvira Stacher‐Priehse,Walter Klepetko,Saverio Bellusci,Andrea Olschewski,Wilhelm Bloch,Robert Voswinckel,Bahil Ghanim,Horst Olschewski

doi:10.1002/path.5044

Abstract

Pulmonary vascular remodeling is the main pathological hallmark of pulmonary hypertension disease. We undertook a comprehensive and multilevel approach to investigate the origin of smooth muscle actin‐expressing cells in remodeled vessels. Transgenic mice that allow for specific, inducible, and permanent labeling of endothelial (Cdh5‐tdTomato), smooth muscle (Acta2‐, Myh11‐tdTomato), pericyte (Cspg4‐tdTomato), and fibroblast (Pdgfra‐tdTomato) lineages were used to delineate the cellular origins of pulmonary vascular remodeling. Mapping the fate of major lung resident cell types revealed smooth muscle cells (SMCs) as the predominant source of cells that populate remodeled pulmonary vessels in chronic hypoxia and allergen‐induced murine models. Combining in vivo cell type‐specific, time‐controlled labeling of proliferating cells with a pulmonary artery phenotypic explant assay, we identified proliferation of SMCs as an underlying remodeling pathomechanism. Multicolor immunofluorescence analysis showed a preserved pattern of cell type marker localization in murine and human pulmonary arteries, in both donors and idiopathic pulmonary arterial hypertension (IPAH) patients. Whilst neural glial antigen 2 (chondroitin sulfate proteoglycan 4) labeled mostly vascular supportive cells with partial overlap with SMC markers, PDGFRα‐expressing cells were observed in the perivascular compartment. The luminal vessel side was lined by a single cell layer expressing endothelial markers followed by an adjacent and distinct layer defined by SMC marker expression and pronounced thickening in remodeled vessels. Quantitative flow cytometric analysis of single cell digests of diverse pulmonary artery layers showed the preserved separation into two discrete cell populations expressing either endothelial cell (EC) or SMC markers in human remodeled vessels. Additionally, we found no evidence of overlap between EC and SMC ultrastructural characteristics using electron microscopy in either donor or IPAH arteries. Lineage‐specific marker expression profiles are retained during pulmonary vascular remodeling without any indication of cell type conversion. The expansion of resident SMCs is the major underlying and evolutionarily conserved paradigm of pulmonary vascular disease pathogenesis. © 2018 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Highlights

Pulmonary vascular remodeling is a ubiquitous pathologic finding in patients with pulmonary hypertension (PH), a condition associated with impaired quality of life and decreased life expectancy [1]
The coverage of pulmonary vessels with alpha smooth muscle actin (αSMA)+ cells was investigated on lung sections stained for vWF and αSMA in chronic hypoxia and allergen-driven-induced pulmonary vascular remodeling
Pulmonary vascular remodeling in idiopathic pulmonary arterial hypertension (IPAH) patients is a hallmark of disease pathology, has a variable progression, and is mostly unresponsive to current therapies [2]

Summary

Introduction

Pulmonary vascular remodeling is a ubiquitous pathologic finding in patients with pulmonary hypertension (PH), a condition associated with impaired quality of life and decreased life expectancy [1]. Despite treatment with potent vasodilating agents, pulmonary arterial hypertension (PAH) patients have a progressive disease course and extensive pulmonary vascular remodeling [1,2]. The proposed repertoire of cell types that directly contribute to the neomuscularization has expanded to include major vascular resident cells from all three vessel layers, and bone marrow-derived cells. Adventitial fibroblasts, either directly through transdifferentiation into myofibroblasts or indirectly by recruitment of circulating inflammatory cells, were postulated as a contributing cell type to pulmonary vascular remodeling [12]. One study using a lineage tracing approach did indicate a structural contribution of bone marrow-derived cells [13]; follow-up studies did not replicate these findings [14,15]. Lung resident mesenchymal stem and progenitor cells were described to structurally contribute to neomuscularization [16,17]

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