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Type II lung cells in young mice exposed to differing levels of oxygen

ABSTRACT: Alveolar epithelial type 2 (AT2) cells are an adult lung stem cell. Oxidative stress, mitogens, and cytokines affect their proliferation through poorly understood mechanisms. We previously showed in mice how neonatal hyperoxia between postnatal days (PND) 0-4 accelerates AT2 proliferation that normally takes place on PND7. Here, RNA-seq analysis of revealed neonatal hyperoxia stimulates expression of the mitochondrial-specific methylenetetrahydrofolate dehydrogenase (Mthfd) 2 and other genes involved in serine synthesis and one carbon-coupled folate metabolism. While MTHFD2 is important for embryonic development and proliferation of cancer cells, it is non-essential after birth. However, Mthf2 mRNA and other enzymes in serine and folate metabolism were highly expressed when AT2 cells proliferate on PND7. They were nearly undetectable in adult AT2 cells, but re-expressed when AT2 cells proliferated in response to fibroblast growth factor (FGF) 7 or during alveolar regeneration. Suppressing Mthfd2 or phosphoglycerate dehydrogenase (Phgdh) used to generate serine blocked FGF7-dependent proliferation of AT2 cells.

ORGANISM(S): Mus musculus

PROVIDER: GSE140915 | GEO | 2020/03/31

REPOSITORIES: GEO

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Project description:Alveoli are thin-walled sacs that serve as the gas exchange units of the lung. They are affected in devastating lung diseases including COPD, Idiopathic Pulmonary Fibrosis, and the major form (adenocarcinoma) of lung cancer, the leading cause of cancer deaths. The alveolar epithelium is composed of two morphologically distinct cell types: alveolar type (AT) 1 cells, exquisitely thin cells across which oxygen diffuses to reach the blood, and AT2 cells, specialized surfactant-secreting cells. Classical studies suggested that AT1 cells arise from AT2 cells during development and following injury, but more recent studies suggest other sources. Here we use histological and marker analysis, lineage tracing, and clonal analysis in mice to identify alveolar progenitor and stem cells and map their locations and potential in vivo. The results show that AT1 and AT2 cells arise independently during development from a bipotential progenitor. After birth, new AT1 cells derive from rare, long-lived, self-renewing AT2 cells, each producing a slowly expanding clonal focus of regenerated alveoli contiguous with the founder AT2 cell. This stem cell function of AT2 cells is broadly activated by diffuse AT1 cell injury, and AT2 self-renewal can be induced in vitro by EGF ligands and permanently activated in vivo by AT2 cell-specific targeting of the oncogenic KrasG12D allele, efficiently transforming AT2 cells into monoclonal adenomatous tumors that rapidly enlarge and prove fatal. Thus, there is a developmental switch in alveolar progenitor cells after birth, when mature AT2 cells function as facultative stem cells that contribute to local alveolar renewal, repair, and cancer. We propose that short-range signals from dying AT1 cells regulate AT2 stem cell activity: a signal transduced by EGFR-KRAS controls AT2 self-renewal and is hijacked during oncogenic transformation, and a separate signal controls reprogramming to AT1 cell fate. To compare expression between ATII and E18 BP populations, RNA was isolated from either population purified by FACS. Two populations are analyzed with 3 biological replicates per population.

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Type II lung cells in young mice exposed to differing levels of oxygen

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