The Notch1 signalling pathway promotes Silicotic fibrosis by modulating macrophage polarization in response to crystalline silica.

Silicosis, a fibrotic lung disorder triggered by inhalation of respirable crystalline silica (silicon dioxide, SiO₂) dust exposure, involves chronic inflammation, oxidative stress, and immune dysregulation as key pathogenic mechanisms. Evidence has identified Notch1 signalling as a determinant in disease progression through its regulatory influence on inflammatory activity, fibrotic remodeling, and immune cell function. The present study integrated animal models, cellular assays, and coculture systems to delineate the regulatory impact of Notch1 signalling on macrophage polarization and fibrosis. In vivo, silica exposure provoked fibrotic lesions, markedly enhanced pulmonary M1/M2 macrophage marker expression (iNOS, IL-1β, Arg1, and CD206), and activated Notch1 signalling. In vitro, silica displayed dual effects dependent on concentration and duration. At low doses (<50 μg/mL), M2 polarization predominated, whereas higher doses (≥200 μg/mL) primarily induced M1 polarization accompanied by reduced viability. Regarding temporal dynamics, short exposure (6h) triggered Notch1 activation and acute M1 polarization, while longer exposure (>6 h) shifted the balance toward M2 dominance. Pharmacological modulation with DAPT (Notch inhibitor) and valproic acid (VPA, Notch activator) demonstrated a direct correlation between Notch1 activity and M1 polarization intensity. Coculture assays further indicated that Notch1 activation synergistically reduced fibrotic marker expression (Vimentin, α-SMA) in epithelial cells, pointing to suppression of fibrosis through immune-stromal crosstalk. Collectively, the findings define a dynamic Notch1-macrophage polarization axis in silicotic fibrosis and provide a conceptual framework for stage-specific therapeutic strategies directed at this pathway.