# FOXF1 and SHH participate in the regulation of iron signaling in pulmonary fibrosis

## TL;DR

This study shows how iron overload and specific signaling pathways contribute to the progression of pulmonary fibrosis.

## Contribution

The study identifies new iron/ROS–FOXF1 and SHH–iron signaling pathways that drive fibroblast activation in pulmonary fibrosis.

## Key findings

- Iron overload promotes fibroblast proliferation and collagen deposition in pulmonary fibrosis.
- FOXF1 overexpression reduces labile iron pool and ROS levels in fibroblasts.
- SHH signaling creates a self-promoting loop that increases intracellular iron and fibroblast activation.

## Abstract

Pulmonary fibrosis (PF) involves persistent activation of fibroblasts and excessive deposition of extracellular matrix, with limited therapeutic options. Pulmonary iron overload has been identified in PF and is associated with the progression of PF. However, the underlying signaling pathway remains unclear. This study demonstrated that iron accumulates in the mouse lung from day 7 post-bleomycin (BLM) instillation until harvest, coinciding with the activation of pulmonary fibroblasts and the onset of fibrogenesis. Iron supplementation promoted the G1/S cell cycle transition and proliferation of fibroblasts, and worsened PF, whereas iron deficiency demonstrated the opposite effects. Mechanistically, both iron and reactive oxygen species (ROS) suppress Forkhead box F1 (FOXF1) expression. FOXF1 overexpression upregulates the expression of antioxidant proteins, including ferredoxin 1 (FDX1) and heme oxygenase-1 (HO-1). Both FOXF1 overexpression and FDX1 overexpression reduced cellular labile iron pool (LIP), ROS levels, and collagen synthesis in human pulmonary fibroblasts. Sonic hedgehog (SHH) signaling elevated intracellular iron, fibroblast proliferation, and its own secretion, establishing a sustained SHH/iron amplifying loop. These findings identify an iron/ROS–FOXF1 positive feedback loop and an SHH–iron self-promoting pathway that drive sustained elevated iron levels and persistent fibroblast activation and fibrogenesis, thereby deepening our understanding of the iron signaling in PF.

•Iron overload drives fibroblast proliferation and collagen deposition in pulmonary fibrosis.•Iron/ROS–FOXF1 positive feedback and SHH–iron self-promotion sustain high iron in PF.•FOXF1 mediates iron/ROS signaling during lung fibrogenesis.•Iron contributes to the activation of fibroblasts by SHH signaling.

Iron overload drives fibroblast proliferation and collagen deposition in pulmonary fibrosis.

Iron/ROS–FOXF1 positive feedback and SHH–iron self-promotion sustain high iron in PF.

FOXF1 mediates iron/ROS signaling during lung fibrogenesis.

Iron contributes to the activation of fibroblasts by SHH signaling.