Idiopathic pulmonary fibrosis/usual interstitial pneumonia (IPF/UIP) is a devastating interstitial lung disease of unknown etiology, characterized by (myo)fibroblast activation/proliferation, extracellular matrix (ECM) deposition and progressive lung destruction. A central role for alveolar epithelium in IPF/UIP pathogenesis has recently been postulated. In this paradigm, injured alveolar epithelial cells (AEC) actively participate in fibrogenesis by releasing fibroproliferative mediators that promote proliferation an differentiation of fibroblasts that in turn induce AEC apoptosis and/or giving rise directly to fibroblasts through epithelial-mesenchymal transition (EMT). However, mechanisms underlying AEC injury/activation and downstream molecular pathways linking epithelial abnormalities to fibrosis remain unclear. Association between endoplasmic reticulum (ER) stress and both sporadic and familial pulmonary fibrosis associated with surfactant protein (SP) mutations has been reported. We recently found that ER stress triggers protective signaling known as the unfolded protein response (UPR) and induces both apoptosis and EMT in AEC in vitro via activation of the non-receptor membrane-associated tyrosine kinase Src, supporting a causal role for ER stress in the dysfunctional AEC phenotype in pulmonary fibrosis. Preliminary data suggest that reactive oxygen species (ROS) and b-catenin activation/interaction with the co-activator CBP are involved in Src-dependent signaling. The ER chaperone glucose-regulated protein 78 (GRP78) is a master regulator of ER homeostasis and thus represents an ideal target with which to modulate ER stress responses in alveolar epithelium. The overall goals of this proposal are to investigate mechanisms underlying ER stress-induced epithelial abnormalities implicated in the pathogenesis of fibrosis by modulating GRP78 utilizing mice with lung epithelial cell-specific deletion of Grp78. We hypothesize that (1) loss of Grp78 induces and/or exacerbates experimental fibrosis in vivo; (2) GRP78 insufficiency-induced epithelial injury contributes to fibrosis via direct effects on the epithelium (e.g., apoptosis/EMT) and/or abnormal epithelial-fibroblast crosstalk; and, (3) effects of GRP78 insufficiency on EMT/fibrosis are mediated via Src and/or ROS-dependent -catenin/CBP signaling. We will use AEC-specific Grp78 knockout mice, in conjunction with clinically relevant mutant SP-Cexon4, our well- established primary AEC in vitro monolayer model, and ICG-001, a novel inhibitor of -catenin/CBP interaction, to address the following Specific Aims: 1. Evaluate effects of ER stress mediated by loss of Grp78 on pulmonary fibrosis in inducible AEC-specific Grp78 knockout mice; 2. Investigate the role of ER stress in AEC abnormalities (apoptosis vs EMT vs aberrant epithelial-fibroblast crosstalk) implicated in fibrosis in inducible AEC-specific Grp78 knockout mice; and 3. Determine mechanisms underlying ER stress-induced AEC injury/fibrosis. These studies will provide insights into mechanisms underlying the pathogenesis of IPF and facilitate identification of novel therapeutic targets for this incurable disease.