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Cross-species transcriptome profiling identifies new alveolar epithelial type I cell-specific genes

ABSTRACT: Diseases involving the distal lung alveolar epithelium include chronic obstructive pulmonary disease (COPD), idiopathic pulmonary fibrosis (IPF) and lung adenocarcinoma. Accurate labeling of specific cell types is critical for determining the contribution of each to pathogenesis of these diseases. The distal lung alveolar epithelium is comprised of two cell types, alveolar epithelial type 1 (AT1) and type 2 (AT2) cells. While cell type-specific markers, most prominently surfactant protein C (SFTPC), have allowed detailed studies of AT2 cell differentiation and their roles in disease, studies of AT1 cells have been hampered by lack of genes with expression unique to AT1 cells. To address this, we performed genome-wide expression profiling of multiple rat organs alongside purified rat AT2, AT1 and in vitro differentiated AT1-like cells, resulting in identification of 54 candidate AT1 cell markers. Cross-referencing with genes upregulated in human in vitro differentiated AT1-like cells narrowed the potential list to 18 candidate genes. Testing the top four candidate genes at RNA and protein levels revealed GRAM domain 2 (GRAMD2), a protein of unknown function, as unique to AT1 cells, while SCNN1G within lung is restricted to AT1 cells. RNAseq confirmed that GRAMD2 is transcriptionally silent in human AT2 cells. Immunofluorescence of mouse alveoli verified that GRAMD2 expression is restricted to the plasma membrane of AT1 cells. These new AT1 cell-specific genes, with GRAMD2 as a leading candidate, will enhance AT1 cell isolation, investigation of alveolar epithelial cell differentiation potential, and contribution of AT1 cells to distal lung diseases.

ORGANISM(S): Homo sapiens

PROVIDER: GSE66627 | GEO | 2016/11/03

SECONDARY ACCESSION(S): PRJNA277526

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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Cross-species transcriptome profiling identifies new alveolar epithelial type I cell-specific genes

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