Abstract
The mechanisms that control fibroproliferation and matrix deposition in lung fibrosis remain unclear. We speculate that vitamin D deficiency may contribute to pulmonary fibrosis since vitamin D deficiency has been implicated in several diseases. First, we confirmed the presence of vitamin D receptors (VDRs) in cultured NIH/3T3 and lung fibroblasts. Fibroblasts transfected with a vitamin D response element–reporter construct and exposed to the active vitamin D metabolite, 1,25(OH) 2D 3, showed increased promoter activity indicating VDR functionality in these cells. Testing the effects of 1,25(OH) 2D 3 on fibroblasts treated with transforming growth factor β1 (TGFβ1), considered a driver of many fibrotic disorders, we found that 1,25(OH) 2D 3 inhibited TGFβ1-induced fibroblast proliferation in a dose-dependent fashion. 1,25(OH) 2D 3 also inhibited TGFβ1 stimulation of α-smooth muscle actin expression and polymerization and prevented the upregulation of fibronectin and collagen in TGFβ1-treated fibroblasts. Finally, we examined how 1,25(OH) 2D 3 affects epithelial–mesenchymal transformation of lung epithelial cells upon exposure to TGFβ1. We showed that the TGFβ1-induced upregulation of mesenchymal cell markers and abnormal expression of epithelial cell markers were blunted by 1,25(OH) 2D 3. These observations suggest that under TGFβ1 stimulation, 1,25(OH) 2D 3 inhibits the pro-fibrotic phenotype of lung fibroblasts and epithelial cells.
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