Vitamin D alleviates silica-induced pulmonary fibrosis partly by inhibiting STAT3/hexokinase 2-mediated fibroblast glycolysis.

Pulmonary fibrosis is defined by the excessive accumulation of extracellular matrix proteins, with few treatment options currently available. Notably, emerging evidence indicates that vitamin D may provide benefits for fibrotic lesions across various tissues. However, the underlying molecular mechanisms have not yet been fully elucidated. In our study, we observed that glycolysis levels increased during the fibroblast-to-myofibroblast transition (FMT) in both MRC-5 cells and mouse primary lung fibroblasts, however, vitamin D treatment inhibited fibroblasts' activation, proliferation, and glycolysis in vitro. We further identified signal transducer and activator of transcription 3 (STAT3) as a crucial downstream effector of vitamin D, with the expression of phosphorylated STAT3 (p-STAT3) being negatively regulated by vitamin D. In MRC-5 cells and mouse primary lung fibroblasts, ectopic expression of STAT3 enhanced fibroblast activation and blocked the anti-fibrotic effects of vitamin D. Mechanistic studies revealed that vitamin D reduces p-STAT3 levels, which inhibits the expression of hexokinase-II (HK2), a key enzyme in the glycolytic pathway, consequently blocking fibroblast glycolysis and activation. In vivo experiments demonstrated that vitamin D administration significantly mitigated silica-induced fibrogenesis, while a deficiency in vitamin D exacerbated the progression of pulmonary fibrosis. Collectively, our findings suggest that vitamin D alleviates silica-induced pulmonary fibrosis by inhibiting fibroblast glycolysis in a STAT3/HK2-dependent manner, indicating that vitamin D supplementation may serve as a promising antifibrotic agent.