Endoplasmic Reticulum Stress-Induced Apoptosis Resistance Mechanisms in Idiopathic Pulmonary Fibrosis-Derived Fibroblasts

Abstract

Idiopathic pulmonary fibrosis (IPF) is a devastating fatal interstitial lung disease that is the result of an accumulation of highly secretory senescent fibroblasts. Our group has previously demonstrated that IPF fibroblasts (IPF-F) are resistant to the apoptotic pressures initiated by the unfolded protein response (UPR) during times of ER stress. IPF-F show an upregulation of BAX Inhibitor-1 (BI-1), which has been shown to negatively regulate the dimerization of IRE1α and inhibit BAX-mediated apoptosis. We hypothesize that IPF-F can evade ER stress-induced apoptosis through an upregulation of BI-1, but it is uncertain whether this is primarily through an IRE1α or BAX-driven pathway. IPF-F and normal human lung fibroblasts (NHLF) were transfected with siRNAs targeting BI-1, IRE1α, and BAX. ER stress was generated through a 0.1 μg/mL tunicamycin challenge. Activation of ER stress-driven apoptosis was assayed through a western blot of apoptosis signaling molecules CHOP and Caspase 3. Cell survival was measured through a CCK-8 cytotoxicity assay. We demonstrate that both the IRE1α and BAX pathways are important to the cell’s ability to undergo ER stress-driven apoptosis. Silencing each pathway individually did not rescue the cell from tunicamycin-induced apoptosis. This suggests that BI-1 is a multifaceted inhibitor of ER stress-mediated apoptosis. Further characterization of UPR and BAX-driven apoptosis via western blot will be required to better understand the mechanisms by which BI-1 prevents apoptosis.