Abstract Rationale Alveolar type II (AT2) cells function as facultative progenitors that sustain and regenerate the alveolar epithelium after injury. Under endoplasmic reticulum (ER) stress, AT2s can enter a transitional state—an intermediate phenotype observed across multiple models of lung fibrosis and repair failure. Persistent activation of proteostatic stress pathways, including the unfolded protein response (UPR), has been implicated in driving this maladaptive AT2 reprogramming, and modulation of the UPR has been proposed by our group and others as a potential therapeutic strategy. However, the molecular circuitry linking proteostatic stress to AT2 cell-state transitions remains less defined. TRIB3, a stress-inducible pseudokinase, has been shown to modulate expression of CEBPα, a transcription factor recently demonstrated as essential for a homeostatic AT2 program through recruitment of the lung lineage transcription factor Nkx-2.1. The goal of this study was to assess the role of TRIB3 as a downstream effector of ER stress signaling regulating AT2 cell fate. Methods To address this, we generated an AT2-specific Atf6 knockout (KO) mouse challenged with exogenous bleomycin. Sorted AT2 cells from the in vivo model were subjected to bulk RNA-seq and used in feeder-free organoid assays to assess regenerative capacity. Lung sections were analyzed by immunofluorescence for expression of AT2 and AT2-transitional markers. Results AT2-specific Atf6 knockout (KO) mice demonstrated increased lung injury to intratracheal bleomycin. RNA-seq of Atf6-deficient AT2s revealed enrichment of stress-apoptotic pathways with marked Ddit3 and Trib3 upregulation. In vivo, ATF6 loss coincided with increased Trib3 expression in AT2 cells during bleomycin injury, spatially localized in areas also containing KRT8+ transitional cells. Organoids containing Atf6 null AT2 cells showed reduced colony-forming efficiency and smaller organoid size, indicating compromised progenitor fitness. To assess Trib3 kinetics in vitro, induction of mutant SFTPC isoforms in MLE12 cells caused increased CHOP expression which preceded TRIB3 expression and was blunted by ATF6 agonism using AA147. Conclusions Our results highlight a role for TRIB3 as a pivotal stress-responsive effector within the ATF6-CHOP network that links proteostasis to alveolar epithelial fate by serving as a tunable axis that shapes AT2 cell plasticity and repair capacity after injury. This abstract is funded by: NIH
Bui et al. (Fri,) studied this question.