NF-κB pathway affects silica nanoparticle-induced fibrosis via inhibited inflammatory response and epithelial-mesenchymal transition in 3D co-culture

Long-term inhalation of silica nanoparticles (SiNPs) can induce pulmonary fibrosis (PF), nevertheless, the potential mechanisms remain elusive. Herein, we constructed a three-dimensional (3D) co-culture model by using Matrigel to investigate the interaction among different cells and potential regulatory mechanisms after SiNPs exposure. Methodologically, we dynamically observed the changes in cell morphology and migration after exposure to SiNPs by co-culturing mouse monocytic macrophages (RAW264.7), human non-small cell lung cancer cells (A549), and medical research council cell strain-5 (MRC-5) in Matrigel for 24 h. Subsequently, we detected the expression of nuclear factor kappa B (NF-κB), inflammatory factor and epithelial-mesenchymal transition (EMT) markers. The results showed that SiNPs produced toxic effects on cells. In the 3D co-culture state, the cell's movement velocity and displacement increased, and the cell migration ability was enhanced. Meanwhile, the expression of inflammatory factor tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) were upregulated, the epithelial marker E-cadherin (E-cad) was downregulated, the mesenchymal marker N-cadherin (N-cad) and myofibroblast marker alpha-smooth muscle actin (α-SMA) expression were upregulated, while NF-κB expression was also upregulated after SiNPs exposure. We further found that cells were more prone to transdifferentiate into myofibroblasts in the 3D co-culture state. Conversely, utilizing the NF-κB-specific inhibitor BAY 11–7082 effectively downregulated the expression of TNF-α, IL-6, interleukin-1β (IL-1β), N-cad, α-SMA, collagen-I (COL I), and fibronectin (FN), the expression of E-cad was upregulated. These findings suggest that NF-κB is involved in regulating SiNPs-induced inflammatory, EMT, and fibrosis in the 3D co-culture state.