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

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.SftpcCreERT2/+; tdTomatoflox/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 (TomLow) and high tdTomato level (TomHigh). TomLow express lower level of AT2 differentiation markers, Fgfr2b and Etv5, while TomHigh, as bona fide mature AT2 cells, show higher levels of Sftpc, Sftpb, Sftpa1, Fgfr2b and Etv5 expression. ATAC-seq analysis indicates that TomLow and TomHigh constitute two distinct cell populations with specific silencing of Sftpc, Rosa26 and cell cycle gene loci in TomLow. Upon pneumonectomy, the number of TomLow but not TomHigh cells increases and TomLow upregulate the expression of Fgfr2b, Etv5, Sftpc, Ccnd1 and Ccnd2 compared to sham. TomLow 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-L1Pos 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.

Cross-Talk Between Inflammation and Fibroblast Growth Factor 10 During Organogenesis and Pathogenesis: Lessons Learnt From the Lung and Other Organs

“…In Choi's paper, the authors, using as a model the bleomycin-treated mice, confirmed interleukin 1β (Il-1β) as a possible inducer of the transitional state. The gene signature of primed AT2 cells corresponded to an activated immune state, similar to what is reported in Ahmadvand's paper more recently (Ahmadvand et al, 2021). In Choi's paper, they identified IM as the source of Il-1β.…”

“…It is therefore extremely difficult to identify a specific role for each player. For the AT2 cells, our recently published work suggests that a subpopulation of quiescent and relatively undifferentiated AT2 cells, positive for the immune marker PD-L1, could be a major partner for the immune cells (Ahmadvand et al, 2021). In addition, Fgf10 signaling via Fgfr2b in AT2 cells appears to control the expression of immune markers (Chao et al, 2017).…”

“…Like the LIFs, the AT2s are heterogeneous and contain a population of Wnt-responding cells displaying enhanced selfrenewal capabilities in vitro, both in mice (Nabhan et al, 2018;Zacharias et al, 2018) and in humans (Travaglini et al, 2020). In addition, our group has recently identified a subpopulation of AT2 cells, distinct from these Wnt-responding cells, which are normally quiescent in homeostasis, but which can proliferate upon injury (Ahmadvand et al, 2021). Of note, this subpopulation of AT2 cells preferentially express some genes related to the immune system.…”

Anomalous epithelial variations and ectopic inflammatory response in chronic obstructive pulmonary disease

“…The physiological involvement of iAT2 cell-mediated inflammation in the loss of parenchymal structure may be further strengthened by a recent report, which showed that the existence of β1 integrin-deficient AT2 with upregulation of NF-κB-dependent chemokines was sufficient for developing accelerated inflammation 42 . A recent paper suggested the existence of a novel subpopulation of AT2 with high PD-L1 but low SFTPC expression in IPF 43 . Despite the common characteristic of high PD-L1 expression, we recognize substantial differences between our iAT2 and AT2 subpopulations.…”

Fgfr2b signaling is essential for the maintenance of the alveolar epithelial type 2 lineage during lung homeostasis in mice

“…Despite these diverse biological activities during development and repair after injury, Fgfr2b signaling in AT2s has been deemed dispensable during homeostasis [14, 18]. Notably, the respective function of Fgfr2b signaling in our recently described, lineage-traced, AT2 subpopulations has not been defined [19].…”