Online

Elko, Evan

Cellular, Molecular, and Biomedical Sciences Graduate Program

2021

Ph. D.

Idiopathic Pulmonary Fibrosis (IPF) is a disease that is characterized by excessive scar formation in the lung. IPF is a disease associated with aging and is believed to be the manifestation of repeated micro-injuries and lack of adequate repair over time. Notably increases in endoplasmic reticulum (ER) stress of epithelial cells and excessive epithelial cell death have been identified as processes that drive the progression of fibrosis. Every year 34,000 people in the United States are diagnosed with Idiopathic Pulmonary Fibrosis (IPF). The average survival time for these patients is only 3-5 years after diagnosis. Two available drugs stabilize patients for some time but not influence overall survival, pointing to a strong need for development of new treatment modalities. ER stress has come to the forefront of IPF research. ER stress occurs in familial and sporadic IPF, and pharmacological inducers of ER stress augment bleomycin-induced fibrosis in mice. Recent studies have shown that triggering of the ER stress response or epithelial cell death are sufficient to induce pulmonary fibrosis in mouse models. The ER is an oxidizing environment that allows disulfide bridge formation in proteins that are localized to the cell surface or secreted, in order to provide structural stability. Therefore, the ER has a unique complement of oxidoreductases required to maintain redox homeostasis. Peroxiredoxin 4 (PRDX4) is amongst the highest expressed ER oxidoreductases in the lung. Little information is known about the role of PRDX4 in the pathogenesis of pulmonary fibrosis or in epithelial cell responses to pro-fibrotic insults. In this thesis, I demonstrated that with age there is a significant decrease in the mRNA expression of a large subset of oxidoreductase genes in the lung, one of which is PRDX4. Interestingly there was also a significant increase in genes associated with the extracellular matrix and the expression of the profibrotic growth factor, transforming growth factor beta 1 (TGFB1), which has been shown to play an important role in IPF. I identified an increase in the oligomerization of PRDX4 in IPF patient samples, which points to an alteration in ER redox homeostasis in the lungs of IPF patients compared to normal controls. The stabilization of high molecular weight (HMW) species of PRDX4 in response to an increased oxidative burden was confirmed and the mechanism by which PRDX4 oligomerizes was unraveled via mutagenesis studies. Treatment of mouse lung epithelial cells with TGFB1 caused the formation of HMW species of PRDX4, induced the unfolded protein response (UPR), and led to apoptosis. I also demonstrated that TGFB1 induced PRDX4 HMW species formation via the increased expression of ER oxidoreductin 1 alpha (ERO1A). Furthermore, the overexpression of PRDX4 alleviated TGFB1 induced ER stress, and the inhibition of ERO1A decreased lung epithelial cell death in response to TGFB1. Overall, these findings point to the importance of the ER oxidative environment in modulating epithelial cell fate in settings of pulmonary fibrosis.