Regulation of epithelial, pro-apoptotic Endoplasmic Reticulum (ER) stress in Idiopathic Pulmonary Fibrosis (IPF).

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Idiopathic Pulmonary Fibrosis (IPF) is a rare and lethal disease, for which no curative therapy exists to date. Endoplasmic Reticulum (ER) stress, caused by the accumulation of unfolded or misfolded proteins in the ER, is a prominent finding in injured, apoptotic type-II alveolar epithelial cells (AECII) of patients with IPF. ER stress is signalled through the unfolded protein response (UPR) pathways PERK, ATF6, and IRE1alpha. If not resolved, the UPR may induce a variety of ER stress-mediated apoptosis pathways, amongst others via induction of the pro-apoptotic transcription factor CHOP, or through those activated by phosphorylated IRE1alpha-oligomers (p-IRE1a), involving 1) the degradation of microRNAs controlling the levels of caspase family cell death substrates and other pro-apoptotic factors and 2) the activation of the Apoptosis Signal-regulating Kinase-1 (ASK1), which causes downstream activation of stress kinases c-Jun-N-terminal kinases (JNK1/2) and p38 MAPK that promote apoptosis.We hypothesize that ER stress-induced apoptosis, largely driven by CHOP, IRE1alpha and ASK1, is the major reason for death of IPF-AECII, and that this process represents a common pathomechanistic principle of sporadic and familial IPF, including gene mutations affecting telomere maintenance. We also hypothesize that IPF reflects an aberrant reparative response to repetitive alveolar epithelial injury in a (genetically) susceptible individual, and that second hits such as oxidative stress, noxious fumes, or respiratory infections are required for a full-blown activation of a pro-apoptotic ER stress-response and high level AECII apoptosis, and consequent development of lung fibrosis. Based on these hypotheses, we will address the following questions:1) Does AECII-specific conditional overexpression of Chop in transgenic mice predispose to development of pulmonary fibrosis in response to second hits (such as herpesvirus-infection and ROS exposure) or ageing?2) Does ER stress-induced AECII apoptosis involving CHOP and/or the p-IRE1a/ASK1-signalling pathway play a role in familial IPF caused by SFTPA2 mutations or gene mutations in the Telomerase-complex?3) Are adaptive, pro-survival ER stress signalling pathways activated in Clara cells of patients with SFTPA2 mutations, thereby providing one possible explanation for the concomitant development of adenocarcinoma in these families? 4) Can ER stress-mediated apoptosis induced by mutant SP-A2, SP-C, or telomere-related proteins be prevented in ASK1 or CHOP deficient alveolar epithelial cells?5) Does ASK1 offer as novel therapeutic target for IPF? We aim to evaluate therapeutic blockade of ER stress-signalling on development of lung fibrosis in vivo by using Ask1(-/-) knockout mice or the small-molecule Ask1 inhibitor selonsertib in mouse models of lung fibrosis (bleomycin, amiodarone), as well as assessing the effects of ASK1 inhibition in precision cut lung slices from IPF-patients cultured ex vivo.