LAUSR

The gain-of-function minor allele of the MUC5B 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 following 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 and ATF6 co-express with MUC5B in epithelia of the distal IPF airway and honeycomb cyst, and 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 (scRNA-seq) in bleomycin-exposed mice, we found that pathologic ER-stress associated transcripts Atf4 and Ddit3 were elevated in alveolar epithelia of SFTPC-Muc5b transgenic (SFTPC-Muc5bTg) mice relative to wild type mice. Activation of the ER stress response inhibits protein translation for most genes by phosphorylation of Eif2α, 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 translation. We found that a single dose of ISRIB diminished Atf4 translation in SFTPC-Muc5bTg mice following bleomycin injury. Moreover, ISRIB resolved the exaggerated fibrotic response of SFTPC-Muc5bTg mice to bleomycin. In summary, we demonstrate that MUC5B/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.