Resident cell lineages are preserved in pulmonary vascular remodeling

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.

PDGFRα and αSMA mark two distinct mesenchymal cell populations involved in parenchymal and vascular remodeling in pulmonary fibrosis

“…This is further supported by the exclusive expression of the contractile marker DES on ␣SMAϩ cells. This is in line with our previous study where similar results were obtained by using different remodeling stimuli such as hypoxia or allergen challenge (7,19). Additionally, in both our murine models we could show that the percentage of ␣SMAϩ cells expressing DES decreased, while those positive for COL1 increased, suggesting either a shift from a contractile to a synthetic phenotype in ␣SMAϩ cells or expansion of the COL1ϩ/␣SMAϩ population in fibrotic conditions.…”

“…Expansion of ␣-smooth muscle actin (␣SMA)expressing cells, termed myofibroblasts, is thought to be the major pathomechanism responsible for vascular and parenchymal remodeling. While resident ␣SMAϩ cells are indeed a major pathological cell type that expands and contributes to pulmonary vascular remodeling (7,28), neither vascular nor airway smooth muscle cells represent the major source of interstitial myofibroblasts in lung parenchymal remodeling (10). Furthermore, the simplistic paradigm of myofibroblasts as the single most important cell type in lung fibrosis has been questioned by a recent fate-mapping approach, which showed that ␣SMAϩ cells are not the main source of collagen production (29).…”

“…However, in adult animals there are strong compartmental differences in PDGFR␣ and ␣SMA expression. We have recently demonstrated that PDGFR␣ expression marks a population of ␣SMA negative perivascular (adventitial) fibroblasts (7). Furthermore, after bleomycin challenge, interstitial PDGFR␣ϩ cells are ␣SMA negative, while perivascular and peribronchial PDGFR␣ϩ cells express variable amounts of ␣SMA (27).…”

Basement Membrane Remodeling Controls Endothelial Function in Idiopathic Pulmonary Arterial Hypertension

“…Sample preparation and processing were adapted from Crnkovic and colleagues (16). In brief, fresh human lung tissue and isolated PA samples were fixed in 2.5% glutaraldehyde and postfixed in osmium tetroxide.…”

Targeting Bronchopulmonary Dysplasia-Associated Pulmonary Hypertension (BPD-PH): Potential Role of the FGF Signaling Pathway in the Development of the Pulmonary Vascular System

“…Consistent with previous results, we and others, utilizing BPD animal models, established by hyperoxia exposure, also showed a decrease of endothelial cells in capillaries and blood vessel numbers and an increase of α-Sma positive cells (VSMC) in the tunica media of pulmonary arterioles and normally non-muscularized precapillary arterioles [ 79 , 80 , 81 ]. A lineage tracing study indicated that the expansion of resident SMCs was the major source related to the thickening of the smooth muscle layer in adult PH [ 82 ]. An increased collagen and elastin expression associated with increased α-SMA-positive myofibroblasts, possibly due to endothelial to mesenchymal transition (EndMT), has also been proposed as a mechanism for the accumulation of myofibroblats in the adventitia of pulmonary arteries ( Figure 2 ) [ 83 , 84 ].…”