Background and aim Hepatic stellate cells (HSCs) are key participants in liver fibrosis development. 1,25(OH)₂D₃, the active form of vitamin D, has antiproliferative properties and antifibrotic potential, as well as a role in extracellular matrix and matrix metalloproteinase (MMP) regulation in renal and lung fibrosis. Little is known about the role of 1,25(OH)₂D₃ in liver and its involvement in liver fibrosis. Therefore, we investigated the antiproliferative and antifibrotic effects of 1,25(OH)₂D₃ in primary cultured HSCs and in a rat model of liver fibrosis induced by thioacetamide (TAA).

Methods Primary HSCs were isolated from rats' livers and treated with 1,25(OH)₂D₃. Proliferation was examined by bromodeoxyuridine. Vitamin D receptor (VDR) expression and several fibrotic markers were detected by western blot analysis and real-time PCR. Collagen Iα1 and MMP-9 promoter activity were measured by luciferase assay. MMP-9 enzymatic activity was investigated by zymography. VDR silencing was performed by sh-RNA. An in vivo study was performed on TAA-induced liver fibrosis model in rats treated with or without 1,25(OH)₂D₃. The fibrotic score and collagen deposition were determined by Masson and by Sirius red staining.

Results While VDR was highly expressed in quiescent HSCs, its expression decreased up to 40% during activation. Addition of 1,25(OH)₂D₃ to activated HSCs stimulated VDR expression. 1,25(OH)₂D₃ suppressed HSC proliferation and cyclin D1 expression by ∼50% and tissue inhibitor of metalloproteinase 1 (TIMP-1) by 60% and led to a 40% downregulation of collagen Iα1 expression. Moreover, 1,25(OH)₂D₃ increased MMP-9 activity by 30%. Silencing VDR by sh-RNA demonstrated that suppression of cyclin D1 and collagen Iα1 protein expression was VDR dependent. Treatment with 1,25(OH)₂D₃ significantly reduced extracellular matrix deposition and lowered the fibrotic score in TAA-induced liver fibrosis.

Conclusion 1,25(OH)₂D₃ has antiproliferative and antifibrotic effects on liver fibrosis in in vitro and in vivo models and may be considered as having potential therapeutic value.