Epithelial Endoplasmic Reticulum Stress Enhances the Risk of Muc5b-associated Lung Fibrosis

The gain-of-function minor allele of the (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 in epithelia of the distal IPF airway and honeycomb cyst and that this is more pronounced in carriers of the gain-of-function promoter variant. Similarly, in mice exposed to bleomycin, 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 and (DNA damage inducible transcript 3) were elevated in alveolar epithelia of -Muc5b transgenic (-Muc5b) 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 . The integrated stress response inhibitor (ISRIB) facilitates interaction of phosphorylated Eif2α with Eif2B, overcoming translation inhibition associated with ER stress and reducing . We found that a single dose of ISRIB diminished translation in -Muc5b mice after bleomycin injury. Moreover, ISRIB resolved the exaggerated fibrotic response of -Muc5b 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.