IRE1α drives lung epithelial progenitor dysfunction to establish a niche for pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a disease of progressive interstitial fibrosis, which leads to severe debilitation, respiratory failure, and death. In IPF, environmental exposures interact with genetic risk factors to engender critical patho-etiological events in lung epithelial cells, including endoplasmic reticulum (ER) stress and TGF{beta} signaling, but the interactions between these disparate pathways are not well understood. We previously showed that kinase inhibitors of the IRE1 bifunctional kinase/RNase--a central mediator of the unfolded protein response (UPR) to ER stress--protected mice from bleomycin-induced pulmonary fibrosis. Here we show that a nanomolar-potent, mono-selective kinase inhibitor of IRE1 (KIRA8) decreases ER-stress induced TGF{beta} signaling and the senescence-associated secretory phenotype (SASP) in the lung epithelium after bleomycin exposure. A recently-described subset of "damage-associated transient progenitors" (DATPs) display IRE1-regulated pathological gene signatures that are quelled by KIRA8, in vivo. After injury, these cells uniquely express integrin v{beta}6, a key activator of TGF{beta} in pulmonary fibrosis. KIRA8 inhibition of IRE1 decreases both DATP number and Itgb6 expression in remaining cells, with a decrease in local collagen accumulation. Single-cell RNA sequencing from IPF lungs revealed an analogous Itgb6+ cell population that may also be regulated by IRE1. These findings suggest that lung epithelial progenitor cells sit at the center of the fibrotic niche, and IRE1 signaling locks them into a dysfunctional state that establishes and perpetuates pathological fibrosis.