Single-cell transcriptomic analysis of human pleura reveals stromal heterogeneity and informs in vitro models of mesothelioma

Our plain-English summary of Single-cell transcriptomic analysis of human pleura reveals stromal heterogeneity and informs in vitro models of mesothelioma, by J. Obacz, J.A. Valer, R. Nibhani, et al (The European Respiratory Journal, 2024).

The study

• Authors: J. Obacz, J.A. Valer, R. Nibhani, T.S. Adams, J.C. Schupp, N. Veale, A. Lewis-Wade, J. Flint, J. Hogan, G. Aresu, A.S. Coonar, A. Peryt, G. Biffi, N. Kaminski, H. Francies, D.M. Rassl, M.J. Garnett, R.C. Rintoul, S.J. Marciniak
• Journal: The European Respiratory Journal
• Published: 2024;63(1)
• Cited by: 16 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The pleural lining of the thorax regulates local immunity, inflammation and repair. A variety of conditions, both benign and malignant, including pleural mesothelioma, can affect this tissue. A lack of knowledge concerning the mesothelial and stromal cells comprising the pleura has hampered the development of targeted therapies. Here, we present the first comprehensive single-cell transcriptomic atlas of the human parietal pleura and demonstrate its utility in elucidating pleural biology. We confirm the presence of known universal fibroblasts and describe novel, potentially pleural-specific, fibroblast subtypes. We also present transcriptomic characterisation of multiple in vitro models of benign and malignant mesothelial cells, and characterise these through comparison with in vivo transcriptomic data. While bulk pleural transcriptomes have been reported previously, this is the first study to provide resolution at the single-cell level. We expect our pleural cell atlas will prove invaluable to those studying pleural biology and disease. It has already enabled us to shed light on the transdifferentiation of mesothelial cells, allowing us to develop a simple method for prolonging mesothelial cell differentiation in vitro.

Copyright ©The authors 2024.

In plain English

This laboratory study built a map of gene activity in single cells from the parietal pleura, the lining of the chest wall. It did not study asbestos exposure. Pleura came from eight people (age range 16 to 50 years) having video-assisted surgery for spontaneous pneumothorax (collapsed lung). The atlas held 63 748 cells, including mesothelial cells, smooth muscle cells, pericytes and at least five fibroblast types. One rare type numbered 80 cells (0.2% of stromal cells). Computer analysis suggested that mesothelial cells change mainly into a fibroblast type lacking the markers PI16 and COL15A1, and it pointed to TGF-β1 as a possible signal. In culture, mesothelial cells lost their typical features, but cultures treated with TGF-β inhibitors kept them. Cultured mesothelial cells from five people matched the mesothelial cells in the atlas. Twenty-one early-passage mesothelioma cell lines split into two clusters. Cluster 2 resembled epithelioid and cluster 1 resembled sarcomatoid mesothelioma. The two lines from patients with proven sarcomatoid mesothelioma were both in cluster 1. The authors noted that the rare fibroblast type remains unconfirmed.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory study: single-cell RNA-sequencing atlas of human parietal pleura, with cell-culture experiments and bulk RNA-sequencing of primary mesothelial cultures and mesothelioma cell lines
• Who was studied: Parietal pleura from eight donors (median age 28.5 years, range 16 to 50; six male) having video-assisted thoracoscopic pleurectomy for spontaneous pneumothorax at Royal Papworth Hospital, UK. Also primary mesothelial cultures from five individuals and 21 early-passage mesothelioma cell lines from Mesobank UK. Dates not given.
• Exposure: No asbestos or other environmental exposure was studied. Asbestos is mentioned only in the introduction as a cause of pleural mesothelioma. The experimental treatment was the TGF-β type I receptor inhibitor SB431542 (with Noggin) added to cultured mesothelial cells.
• Main results:
  • The pleural atlas comprised 63 748 cells from the eight donors.
  • Among 32 750 stromal and mesothelial cells, subclusters were mesothelial (n=11 535), smooth muscle (n=4245), pericyte (n=1194) and at least five fibroblast populations.
  • A rare PI16-positive fibroblast subpopulation (expressing ANGPTL7) was detected: 80 cells, 0.2% of stromal cells.
  • Pseudotime analysis suggested mesothelial cells transition preferentially to PI16-negative COL15A1-negative fibroblasts.
  • Media from mesothelial cell cultures contained 10 ng per mL TGF-β, reduced by TGF-β inhibitor; inhibitor-treated cultures kept mesothelial morphology and marker gene expression.
  • All five primary benign mesothelial cultures (N1 to N5) clustered together, as did the mesothelioma cell lines.
  • The 21 mesothelioma cell lines formed two clusters: cluster 2 resembled mesothelial cells in vivo; cluster 1 was dissimilar to all healthy pleural cell populations.
  • BAP1 and NF2 pathogenic variants were detected only in cluster 2 mesothelioma lines.
  • Of the 21 mesothelioma cultures, two came from individuals with proven sarcomatoid mesothelioma; both were in cluster 1.
• The authors' conclusion: The authors concluded that early-passage mesothelioma cell lines adopt two main phenotypes resembling epithelioid and sarcomatoid mesothelioma, which do not always match the donor's diagnostic label. They also concluded that trypsin-isolated mesothelial cells model benign mesothelial cells.
• Limitations the authors state:
  • The rare PI16-positive ANGPTL7-positive fibroblast population remains a putative cell type without further validation.
  • Ambient RNA contamination may confound the finding of MHC class II gene expression in some fibroblasts.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Pleura, Mesothelioma, Thorax, Inflammation, Pleural Mesothelioma, Parietal Pleura, Fibroblast, Mesothelial Cells.

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