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Stat3-Bdnf-TrkB axis promotes alveolar regeneration [ATAC-seq]

ABSTRACT: Regenerating new alveolar epithelium is essential for recovery from many lung diseases. This multi-cellular regenerative process occurs when type II alveolar pneumocytes (AT2), with support from mesenchymal niche cells, proliferate to generate more AT2 cells and transdifferentiate in type I pneumocytes. To elucidate how coordinated events between AT2 cells and mesenchyme restore alveolar epithelium we used unbiased genome-wide analysis of chromatin accessibility and gene expression in both cell types following acute lung injury. We observed that chromatin acessability in AT2 cells changes signficantly following acute lung injury. Newly accessible chromatin reveals new STAT3 binding motifs adjacent to genes that regulate essential regenerative pathways in AT2 cells. Restoration of alveolar structures following both sterile and infectious lung injuries was inhibited when STAT3 signaling was lost in AT2 cells. Single-cell transcriptome analysis of regenerating AT2 cells identified brain neurotrophic factor (Bdnf) as the sole STAT3 target gene whose chromatin becomes newly accessible in a regenerating population of AT2 cells. BDNF increased alveolar organoid size and forming efficiency in murine and human models. The receptor for BDNF, TrkB, is uniquely? expressed on mesenchymal alveolar niche cells (MANC). Exposure of BDNF to TrkB increases expression of fibroblast growth factor 7 (Fgf7), an essential regenerative cytokine, in MANCs. Blocking Bdnf signaling with a TrkB receptor antagonist abrogated murine and human alveolar organoid formation. Finally, a small molecule TrkB agonist improved functional and histological outcomes in vivo following sterile and infectious lung injuries. Collectively, these data highlight the biological and therapeutic importance of the Stat3-Bdnf-TrkB axis in orchestrating alveolar epithelial regeneration

ORGANISM(S): Mus musculus

PROVIDER: GSE132534 | GEO | 2020/06/01

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.