RNA-sequencing comparison of pneumonectomy and bleomycin reveals anti-fibrotic mechanisms of lung fibroblasts

Abstract

Background Idiopathic pulmonary fibrosis (IPF) is characterized by pathological accumulation of scar tissue in the lung parenchyma. Many of the processes that are implicated in fibrosis, such as matrix deposition also occur following pneumonectomy (PNX). However, fibrosis does not occur. Since fibroblasts are the major cell type responsible for extracellular matrix production, we hypothesized that comparing their responses to PNX and bleomycin (BLM) would unveil key differences in the role they play during regulated and fibrotic lung growth. Methods RNA-sequencing was performed on flow cytometry-sorted fibroblasts from mouse lungs 14 days after bleomycin challenge, PNX, or sham. Pathway and transcription factor binding motif enrichment analysis were performed to characterize RNA-sequencing data. Normal human lung fibroblasts (NHLFs) were used as a cell culture model to validate targets. Results RNA-sequencing analysis revealed similar biological processes to be involved in both responses, including signaling by transforming growth factor-β (TGF-β1) and tumor necrosis factor-α. Transcription factor binding motif enrichment predicted erythroid transformation specific (ETS) superfamily members to play a key role in the response to BLM, whereas nuclear factor-κB (NF-κB) and activator protein-1 (AP-1) were predicted to orchestrate much of the response to PNX. Itpkc, encoding inositol triphosphate kinase C, was a gene uniquely up-regulated by PNX and a likely AP-1 target. ITPKC overexpression in NHLFs antagonized the fibrotic effect of TGF-β1. RNA-sequencing analysis of primary NHLFs overexpressing ITPKC further supported its role in repressing collagen production and predicted it as an activator of canonical NF-κB signaling. ITPKC overexpression showed considerable overlap with the innate immune signaling seen following PNX. Conclusion Taken together, our RNA-sequencing analysis suggests that during post-PNX lung growth, AP-1 activates ITPKC to promote canonical NF-κB signaling to prevent fibrogenesis. Future studies to understand this lack of ITPKC induction during fibrotic injury may identify attractive therapeutic targets.