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

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.