Iron-induced oxidative stress alters the transcriptome of bronchoalveolar lavage cells in silicosis

Elevated iron levels are observed in silicosis patients, leading alveolar macrophages to increase ferritin production in response to this cellular stress. Our study employed a multi-omic approach to investigate how excess iron/ferritin influences the molecular profile of bronchoalveolar lavage (BAL) cells. Thirty-one participants were included, with RNA sequencing conducted on BAL cells from stone benchtop industry workers diagnosed with simple or complicated silicosis, compared to a cohort with no disease. BAL fluid (BALF) was analysed using gas chromatography-mass spectrometry (GC-MS) to screen for 498 volatile organic compounds (VOCs). Compared to no disease, simple silicosis showed 172 differentially expressed genes (DEGs), while complicated silicosis displayed 531 DEGs. Spearman correlation analysis revealed 1072 genes significantly positively association with BALF ferritin. Gene set variation analysis revealed upregulation in glutathione metabolism pathways in BAL cells, including ferroptosis repressor genes (GCLC/GCLM, GSR, SLC7A11, TXNRD1, and AIFM2). In the BALF, 116 VOCs were detected, with 4 showing reduced levels in silicosis patients, independent of smoking status. Notably, the abundance of these VOCs exhibited an inverse association with ferritin levels. In summary, antioxidant defence pathways, incorporating genes that encode proteins to prevent ferroptosis, an iron-dependent non-apoptotic form of cell death, are upregulated in BAL from silicosis patients. Excess iron/ferritin was also associated with a reduction in multiple VOCs present in BALF, which may reflect their oxidative metabolism. We propose that BAL macrophages loaded with iron experience oxidative stress, leading to the activation of an anti-ferroptotic gene network that prolongs the survival of this dysfunctional BAL cell population.