Iron dysregulation and ferroptosis are associated with pulmonary fibrosis: Insight from idiopathic pulmonary fibrosis, systemic sclerosis, and COVID-19 patients.

BACKGROUND

Pulmonary fibrosis (PF) is the leading cause of death in many lung diseases due to inflammation, tissue damage, infection, or other contributing factors. Iron metabolism and ferroptosis have been reported to participate in some PF diseases, but the universality remains elusive.

METHODS

Herein, comparative studies were conducted among idiopathic pulmonary fibrosis (IPF), immune-associated systemic sclerosis (SSc), and infectious COVID-19. The iron level was evaluated by Perls' staining and ferritin level. Ferroptosis was detected by immunohistochemistry (malondialdehyde, oxidizing lipids, GPX4, and FSP1) and transmission electron microscopy. The results were also validated by public datasets analysis. Furthermore, the iron homeostasis and ferroptosis signatures were studied in the SARS-Cov-2 spike protein-induced PF cell model. The iron-mediated inflammation and fibrosis in PF were evaluated both in vitro and in vivo.

RESULTS

We found that COVID-19 patients showed the most severe pulmonary damage and fibrosis signature. COVID-19 and SSc-PF patients have more obvious immune cell infiltration with CD11c+ monocytes and CD68 + macrophages. Iron overload and ferroptosis were common in PF, while COVID-19 patients showed distinct iron metabolism signatures with higher expression of HO-1. Among all ferroptosis markers, IPF patients showed the highest E06 level, COVID-19 and SSc-PF had both higher levels of MDA and 4HNE. Further studies showed iron overload and ferroptosis occurred mainly in alveolar type II cells and macrophages. Deferoxamine (DFO) and Ferrostatin-1 (Fer1) effectively prevented malondialdehyde production and IL-6 upregulation. DFO and Fer1 alleviated fibrosis in mice.

CONCLUSIONS

Our study demonstrates that iron overload and ferroptosis are common signatures in PF and represent potential therapeutic targets.