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Transcriptional profiling of CD44hi AT2 cells under homeostasis and after lung injury [II]

ABSTRACT: The epithelium of alveoli is composed of alveoli type I cells (AT1) that cover ~95% of the surface area and alveoli type II cells (AT2) that secret surfactant as well as function as adult stem cells. CD44hi subpopulation of AT2 cells exhibits higher potential to proliferate and differentiate under steady state conditions. To understand the CD44hi subpopulation of AT2 cells after lung injury, we assessed those cells in a Pseudomonas aeruginosa (PA) induced mouse model of lung injury. CD44hi and CD44low AT2 cells were FACS sorted from untreated and 3d PA treated mice. In addition, since Sca1+ AT2 cells were shown to emerge during the repair phase of the PA induced injury in our earlier studies, we also isolated Sca1+ AT2 cells at 3d post PA injury to compare with the CD44hi subpopulation. RNA-seq was used to compare the expression profile of the different subgroups of AT2 cells.

ORGANISM(S): Mus musculus

PROVIDER: GSE267236 | GEO | 2024/05/23

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.

Project description:Chronic liver injury promotes fibrosis, which can progress to cirrhosis, a major cause of morbidity and mortality worldwide. Resolving the cell-type-specific transcriptional changes orchestrating this transformation remains challenging. Recent advances in differentiation protocols allow the generation of multi-lineage human liver organoids (HLOs) from human pluripotent stem cells (hPSCs), providing a new model system to study evolving liver injury. We differentiated hPSCs into HLOs and defined optimal 3D culture conditions for liver injury induction. We modeled steatohepatitis through treatment with palmitic acid (PA) and fibrotic injury through treatment with transforming growth factor beta 1 (TGF-β1). For each injury type, we evaluated the development of fibrosis and inflammation by monitoring changes in morphology, gene expression, and histology. We then performed single-cell RNA-sequencing (scRNA-seq) to investigate cell-type diversity in healthy organoids at different time-points and to understand how TGF-β1- and PA-mediated injury affects each cell type. We observed transcriptional response signatures in injured HLOs to be both cell-type- and injury-specific. TGF-β1 treatment expanded hepatic stellate cell (HSC)-like populations and remodeled cell-cycle patterning. Gene set scoring revealed increased fibroblast activity with TGF-β1 treatment, while PA treatment was associated with inflammatory activity. Differential gene expression analysis at the subpopulation level showed induced profibrotic and extracellular matrix-remodeling pathways with TGF-β1 and non-alcoholic fatty liver disease (NAFLD) expression signatures with PA treatment. Evaluation of receptor and ligand expression defined hepatocyte-, cholangiocyte-, and HSC-like cell-cell interactions induced upon TGF-β1 treatment, an effect not observed with PA treatment. Tracing the changes at receptor-ligand pair resolution revealed specific COL1A1-Integrin complex interactions with TGF-β1 treatment and inflammation-specific interactions including CXCR7 and HLA-C with PA treatment. Treatment of HLOs with PA and TGF-β1 also demonstrated a sequential increase in expression of gene sets that predict clinical disease progression in non-alcoholic steatohepatitis (NASH). Our results demonstrate the applicability of hPSC-derived HLOs as a dynamic in vitro 3D human liver model system for the study of fibrotic and inflammatory liver injury.

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Transcriptional profiling of CD44hi AT2 cells under homeostasis and after lung injury [II]

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