1,25-Dihydroxyvitamin D₃ reduces TGF-β3-induced fibrosis-related gene expression in human uterine leiomyoma cells

Background: Uterine leiomyomas (fibroids) are the most common benign estrogen-dependent tumors of premenopausal women. TGF-β3 up-regulates the synthesis of many of extracellular matrix proteins that are associated with tissue fibrosis. Objective: To examine the effect of 1,25-dihydroxyvitamin D₃ (vitamin D₃) on TGF-β3-induced fibrosis-related protein expression in immortalized human uterine leiomyoma (HuLM) cells. Methods: HuLM cells were treated with TGF-β3 with or without vitamin D ₃. Western blot analyses were employed to test the effect of vitamin D₃ on TGF-β3-induced protein expression of collagen type 1, fibronectin, and plasminogen activator inhibitor-1 proteins. Western blots as well as immunofluorescence analyses were used to verify the effect of vitamin D₃ on TGF-β3-induced Smad activation involved in extracellular matrix protein synthesis and deposition, which ultimately lead to tissue fibrosis. Results: We observed that TGF-β3 induced fibronectin and collagen type 1 protein expression in HuLM cells, and that effect was suppressed by vitamin D₃. TGF-β3 also induced protein expression of plasminogen activator inhibitor-1, an important TGF-β target, in HuLM cells, which was also inhibited by vitaminD₃. Additionally, TGF-β3 induced phosphorylation of Smad2 as well as nuclear translocation of Smad2 and Smad3 in HuLM cells, whereas vitamin D significantly reduced all these TGF-β3-mediated effects. Therefore, our results suggest that vitamin D₃ has consistently reduced TGF-β3 effects that are involved in the process of fibrosis in human leiomyoma cells. Conclusion: Vitamin D ₃ is an antifibrotic factor that might be potentially useful as a novel therapeutic for nonsurgical treatment of benign uterine fibroids.