May 2021

Eur Respir J

Identification of a novel subset of alveolar type 2 cells enriched in PD-L1 and expanded following pneumonectomy.

Ahmadvand N, Khosravi F, Lingampally A, Wasnick R, Vazquez-Armendariz I, Carraro G, Heiner M, Rivetti S, Lv Y, Wilhelm J, Gunther A, Herold S, Al Alam D, Chen C, Minoo P, Zhang JS,Bellusci S.

Abstract:

Alveolar type 2 (AT2) cells are heterogeneous cells; where specialised AT2 subpopulations within this lineage exhibit stem cell properties. However, the existence of quiescent, immature cells within the AT2 lineage, which are activated during lung regeneration, is unknown.Sftpc^CreERT2/+; tdTomato^flox/flox mice were used for the labelling of AT2 cells and labeled subpopulations were analysed by flow cytometry, qPCR, ATAC-seq, gene arrays, pneumonectomy, and culture of precision-cut lung slides. ScRNA-seq data from human lungs were analysed.In mice, we detected two distinct AT2 subpopulations with low tdTomato level (Tom^Low) and high tdTomato level (Tom^High). Tom^Low express lower level of AT2 differentiation markers, Fgfr2b and Etv5, while Tom^High, as bona fide mature AT2 cells, show higher levels of Sftpc, Sftpb, Sftpa1, Fgfr2b and Etv5expression. ATAC-seq analysis indicates that Tom^Low and Tom^High constitute two distinct cell populations with specific silencing of Sftpc, Rosa26 and cell cycle gene loci in Tom^Low Upon pneumonectomy, the number of Tom^Low but not Tom^High cells increases and Tom^Low upregulate the expression of Fgfr2b, Etv5, Sftpc, Ccnd1 and Ccnd2 compared to sham. Tom^Low cells overexpress PD-L1, an immune inhibitory membrane receptor ligand, which is used by flow cytometry to differentially isolate these two sub-populations. In the human lung, data mining of a recent scRNA-seq AT2 dataset demonstrates the existence of a PD-L1 ^Pos population. Therefore, we have identified a novel population of AT2 quiescent, immature progenitor cells in mouse that expand upon pneumonectomy and provided evidence for the existence of such cells in human.