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Epithelial endoplasmic reticulum stress and apoptosis in sporadic idiopathic pulmonary fibrosis.

ABSTRACT: The molecular pathomechanisms underlying idiopathic pulmonary fibrosis (IPF) are elusive, but chronic epithelial injury has recently been suggested as key event.We investigated the possible implication of endoplasmic reticulum (ER) stress-mediated apoptosis in sporadic IPF.We analyzed peripheral explanted lung tissues from patients with sporadic IPF (n = 24), chronic obstructive pulmonary disease (COPD) (n = 9), and organ donors (n = 12) for expression of major ER stress mediators and apoptosis markers by means of immunoblotting, semiquantitative reverse transcription-polymerase chain reaction, immunohistochemistry, and the TUNEL method.Compared with COPD and donor lungs, protein levels of ER stress mediators, such as processed p50 activating transcription factor (ATF)-6 and ATF-4 and the apoptosis-inductor CHOP (C/EBP-homologous protein), as well as transcript levels of spliced X-box binding protein (XBP)-1, were significantly elevated in lung homogenates and type II alveolar epithelial cells (AECIIs) of IPF lungs. Proapoptotic, oligomeric forms of Bax, which play a key role in ER stress-mediated apoptosis downstream of CHOP induction, as well as caspase-3 cleavage, could be detected in IPF lungs. By means of immunohistochemistry, exclusive induction of active ATF-6, ATF-4, and CHOP in AECIIs was encountered in IPF but not in COPD or donor lungs. Immunoreactivity was most prominent in the epithelium near dense zones of fibrosis and fibroblast foci, where these ER stress markers colocalized with markers of apoptosis (TUNEL, cleaved caspase-3).Severe ER stress response in the AECIIs of patients with sporadic IPF may underlie the apoptosis of this cell type and development of fibrosis in this disease.

SUBMITTER: Korfei M

PROVIDER: S-EPMC2566794 | biostudies-literature | 2008 Oct

REPOSITORIES: biostudies-literature

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Epithelial endoplasmic reticulum stress and apoptosis in sporadic idiopathic pulmonary fibrosis.

Korfei Martina M Ruppert Clemens C Mahavadi Poornima P Henneke Ingrid I Markart Philipp P Koch Miriam M Lang Gyoergy G Fink Ludger L Bohle Rainer-Maria RM Seeger Werner W Weaver Timothy E TE Guenther Andreas A

American journal of respiratory and critical care medicine 20080717 8

<h4>Rationale</h4>The molecular pathomechanisms underlying idiopathic pulmonary fibrosis (IPF) are elusive, but chronic epithelial injury has recently been suggested as key event.<h4>Objectives</h4>We investigated the possible implication of endoplasmic reticulum (ER) stress-mediated apoptosis in sporadic IPF.<h4>Methods</h4>We analyzed peripheral explanted lung tissues from patients with sporadic IPF (n = 24), chronic obstructive pulmonary disease (COPD) (n = 9), and organ donors (n = 12) for e ...[more]

PMID: 18635891

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Project description:BackgroundIdiopathic pulmonary fibrosis (IPF) is a chronic progressive interstitial lung disease. This study aimed to investigate the involvement of endoplasmic reticulum stress (ERS) in IPF and explore its correlation with immune infiltration.MethodsERS-related differentially expressed genes (ERSRDEGs) were identified by intersecting differentially expressed genes (DEGs) from three Gene Expression Omnibus datasets with ERS-related gene sets. Gene Set Variation Analysis and Gene Ontology were used to explore the potential biological mechanisms underlying ERS. A nomogram was developed using the risk signature derived from the ERSRDEGs to perform risk assessment. The diagnostic value of the risk signature was evaluated using receiver operating characteristics, calibration, and decision curve analyses. The ERS score of patients with IPF was measured using a single-sample Gene Set Enrichment Analysis (ssGSEA) algorithm. Subsequently, a prognostic model based on the ERS scores was established. The proportion of immune cell infiltration was assessed using the ssGSEA and CIBERSORT algorithms. Finally, the expression of ERSRDEGs was validated in vivo and in vitro via RT-qPCR.ResultsThis study developed an 8-ERSRDEGs signature. Based on the expression of these genes, we constructed a diagnostic nomogram model in which agouti-related neuropeptide had a significantly greater impact on the model. The area under the curve values for the predictive value of the ERSRDEGs signature were 0.975 and 1.000 for GSE70866 and GSE110147, respectively. We developed a prognostic model based on the ERS scores of patients with IPF. Furthermore, we classified patients with IPF into two subtypes based on their signatures. The RT-qPCR validation results supported the reliability of most of our conclusions.ConclusionWe developed and verified a risk model using eight ERSRDEGs. These eight genes can potentially affect the progression of IPF by regulating ERS and immune responses.

Project description:The gain-of-function minor allele of the MUC5B (mucin 5B, oligomeric mucus/gel-forming) promoter (rs35705950) is the strongest risk factor for idiopathic pulmonary fibrosis (IPF), a devastating fibrotic lung disease that leads to progressive respiratory failure in adults. We have previously demonstrated that Muc5b overexpression in mice worsens lung fibrosis after bleomycin exposure and have hypothesized that excess Muc5b promotes endoplasmic reticulum (ER) stress and apoptosis, stimulating fibrotic lung injury. Here, we report that ER stress pathway members ATF4 (activating transcription factor 4) and ATF6 coexpress with MUC5B in epithelia of the distal IPF airway and honeycomb cyst and that this is more pronounced in carriers of the gain-of-function MUC5B promoter variant. Similarly, in mice exposed to bleomycin, Muc5b expression is temporally associated with markers of ER stress. Using bulk and single-cell RNA sequencing in bleomycin-exposed mice, we found that pathologic ER stress-associated transcripts Atf4 and Ddit3 (DNA damage inducible transcript 3) were elevated in alveolar epithelia of SFTPC-Muc5b transgenic (SFTPC-Muc5bTg) mice relative to wild-type (WT) mice. Activation of the ER stress response inhibits protein translation for most genes by phosphorylation of Eif2α (eukaryotic translation initiation factor 2 alpha), which prevents guanine exchange by Eif2B and facilitates translation of Atf4. The integrated stress response inhibitor (ISRIB) facilitates interaction of phosphorylated Eif2α with Eif2B, overcoming translation inhibition associated with ER stress and reducing Atf4. We found that a single dose of ISRIB diminished Atf4 translation in SFTPC-Muc5bTg mice after bleomycin injury. Moreover, ISRIB resolved the exaggerated fibrotic response of SFTPC-Muc5bTg mice to bleomycin. In summary, we demonstrate that MUC5B and Muc5b expression is associated with pathologic ER stress and that restoration of normal translation with a single dose of ISRIB promotes lung repair in bleomycin-injured Muc5b-overexpressing mice.

Dataset Information

Epithelial endoplasmic reticulum stress and apoptosis in sporadic idiopathic pulmonary fibrosis.

Publications

Epithelial endoplasmic reticulum stress and apoptosis in sporadic idiopathic pulmonary fibrosis.

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