p63+Krt5+ distal airway stem cells are essential for lung regeneration

Abstract

Lung diseases such as chronic obstructive pulmonary disease and pulmonary fibrosis involve the progressive and inexorable destruction of oxygen exchange surfaces and airways, and have emerged as a leading cause of death worldwide. Mitigating therapies, aside from impractical organ transplantation, remain limited and the possibility of regenerative medicine has lacked empirical support. However, it is clinically known that patients who survive sudden, massive loss of lung tissue from necrotizing pneumonia or acute respiratory distress syndrome often recover full pulmonary function within six months. Correspondingly, we recently demonstrated lung regeneration in mice following H1N1 influenza virus infection, and linked distal airway stem cells expressing Trp63 (p63) and keratin 5, called DASC(p63/Krt5), to this process. Here we show that pre-existing, intrinsically committed DASC(p63/Krt5) undergo a proliferative expansion in response to influenza-induced lung damage, and assemble into nascent alveoli at sites of interstitial lung inflammation. We also show that the selective ablation of DASC(p63/Krt5) in vivo prevents this regeneration, leading to pre-fibrotic lesions and deficient oxygen exchange. Finally, we demonstrate that single DASC(p63/Krt5)-derived pedigrees differentiate to type I and type II pneumocytes as well as bronchiolar secretory cells following transplantation to infected lung and also minimize the structural consequences of endogenous stem cell loss on this process. The ability to propagate these cells in culture while maintaining their intrinsic lineage commitment suggests their potential in stem cell-based therapies for acute and chronic lung diseases.

Single-cell RNA sequencing identifies diverse roles of epithelial cells in idiopathic pulmonary fibrosis

“…The respiratory epithelium is capable of robust regeneration from rapid amplifying progenitor cells and various other progenitor cell types, including basal cells in conducting airways and AT2 cells in the alveoli (22). Recent studies support the activation and/or migration of p63/Sox2-expressing basal cells in the alveoli after severe, chronic epithelial cell injury caused by bleomycin and influenza viruses (8,9). Our present single-cell data support the concept that an abnormal differentiation program has been initiated in the tissue microenvironment of IPF in which the proximal-peripheral patterns of cell differentiation are disrupted, with many respiratory epithelial cells acquiring aberrant, multilineage-like states and some individual cells sharing the characteristics of both conducting airway and alveolar epithelial cells.…”

“…Basal cells in conducting airways, and AT2 cells in the alveoli, serve as progenitor cells, with critical roles in regeneration of the respiratory epithelium following both acute and chronic injury. In experimental models, severe injury to the respiratory epithelium is associated with pathological features of IPF, with alveolar remodeling and the presence of atypical basal-like cells in alveolar regions (8,9). Mutations in genes affecting AT2 cell function or survival, e.g., TEL, TERC, ABCA3, SFTPB, SFTPC, SFTPA, RTELI, and PARN are associated with ILD, further implicating alveolar cell injury and abnormal repair processes in these disorders (for review, see refs.…”

Influenza virus-induced lung injury: pathogenesis and implications for treatment

“…Within the alveoli, itgb4 + cells, "bipotent" type I and type II alveolar epithelial cell progenitors and alveolar type II cells have been attributed stem/progenitor cell functions during repair [158,159]. While all of these populations have been reported to expand in different models of lung injury, the emergence of p63-positive and keratin 5-positive epithelial pods in the alveolar space has only been observed after severe IAV-induced lung injury [160,161]. Whether this is accompanied by expansion of other progenitor pools or whether direct or immune-mediated damage to the more distal progenitor populations in response to viral infection necessitates the expansion of the airway stem cell pool is not known.…”

Plasticity in the lung: making and breaking cell identity

“…+ /KRT6 + cells that appear following influenza injury are essential for the regeneration of the damaged lung because they give rise to new alveolar epithelium sourced from the pod cells (Zuo et al, 2015). A second study suggested that pods may arise from both Krt5 + lineage-labeled basal cells and Scgb1a1 + lineagelabeled secretory cells (Zheng et al, 2013).…”

“…Recent studies in mice have also demonstrated the presence of small numbers of basal-like progenitor cells in the distal airways, even at steady state (Kumar et al, 2011;Vaughan et al, 2015). Remarkably, the number of such cells is increased in the small airways and alveoli following severe injury caused by H1N1 influenza injury or bleomycin (Vaughan et al, 2015;Zuo et al, 2015). Finally, it is likely that each of the cell types of the airway epithelium have additional functions beyond that Anatomical and cellular differences between murine and human lung.…”