Role of ferroptosis in coal dust induced mouse models of coal workers' pneumoconiosis

Background  Coal workers' pneumoconiosis (CWP) is a serious occupational disease. Whether ferroptosis, a form of necrotic regulated cell death, is involved in coal dust induced mouse models of CWP needs further survey.

Objective  This experiment is designed to elucidate the role of ferroptosis in the formation of CWP induced by coal dust in mice.

Methods  C57BL/6J mice were randomly assigned to a saline group or a CWP group, with eight mice in each group. The mice were treated with 0.1 mL normal saline or 0.1 mL coal dust suspensions (50g·L^-1) via intra-tracheal instillation. HE staining and Masson staining were used to show lung injury and lung fibrosis. Iron concentration in mouse lung tissues was measured using iron assay kit. Lipid peroxidation was estimated in lung tissues by malondialdehyde (MDA) concentration and immunofluorescence intensity, and the ratio of glutathione (GSH) to L-glutathione oxidized (GSSG). Western blotting and real-time fluorescence-based quantitative PCR were used to test protein and mRNA expression levels of glutathione peroxidase 4 (GPX₄) and ferritin in mice.

Results  Coal dust injured pulmonary structure, thickened alveolar wall, and caused collagen deposition and infiltration of inflammatory cells in the CWP group. The iron concentration in the CWP group (10.75 ± 5.42) mg·L⁻¹ was higher than that in the saline group (1.14 ± 0.37) mg·L⁻¹ (P < 0.01). The MDA concentration in the CWP group (37.32 ± 12.18) μmol·L ⁻¹ was higher than that in the saline group (18.70 ± 8.22) μmol·L⁻¹ (P <0.01). The immunofluorescence intensity of MDA in the CWP group was stronger than that in the saline group. The GSH/GSSG ratio decreased in CWP treated mice (1.50 ± 1.70) compared with the normal saline treated ones (4.95 ± 2.86) ( P < 0.01). Compared with the saline group (38.84 ± 15.61 for GPX ₄, 225.90 ± 54.34 for ferritin), the relative expression levels of GPX₄ and ferritin mRNA in the CWP group were downregulated (14.29 ± 7.21 for GPX₄, 106.70 ± 36.70 for ferritin) (P < 0.01). Compared with the saline group (1.47 ± 0.54 for GPX ₄, 1.73 ± 0.34 for ferritin), the relative expression levels of GPX₄ and ferritin protein in the CWP group were also downregulated (0.92 ± 0.22 for GPX₄, 0.97 ± 0.09 for ferritin) (P < 0.05).

Conclusion  Ferroptosis may be involved in the formation of coal workers' pneumoconiosis induced by coal dust in mice.