1,25-dihydroxyvitamin D₃ inhibits renal interstitial myofibroblast activation by inducing hepatocyte growth factor expression.

Vitamin D and its metabolites play an important role in calcium homeostasis, bone remodeling, hormone secretion, cell proliferation, and differentiation. Recent studies also suggest a beneficial role of vitamin D in slowing the progression of chronic renal glomerular diseases. This study investigated the effects and potential mechanism of 1,25-dihydroxyvitamin D₃ [1,25(OH)₂D₃] on the regulation of myofibroblast activation from interstitial fibroblast, a critical event in generating α-smooth muscle actin (αSMA)-positive, matrix-producing effector cells in renal interstitial fibrosis.

Normal rat renal interstitial fibroblast cell line (NRK-49F) was used as a model system. Myofibroblast activation was initiated by incubation with transforming growth factor (TGF)-β1. Expression of α-SMA, collagen I, thrombospondin-1, and hepatocyte growth factor (HGF) was assessed by reverse transcription-polymerase chain reaction (RT-PCR), Western blot, and immunostaining, respectively. HGF promoter activity was evaluated by using luciferase reporter assay.

Incubation of rat renal interstitial fibroblasts (NRK-49F) with 1,25(OH)₂D₃ suppressed TGF-β1-induced de novo α-SMA expression in a dose-dependent manner. 1,25(OH)₂D₃ also suppressed type I collagen and thrombospondin-1 expression induced by TGF-β1. Interestingly, 1,25(OH)₂D₃ induced HGF mRNA expression and protein secretion in renal interstitial fibroblasts. Transfection studies revealed that 1,25(OH)₂D₃ stimulated HGF gene promoter activity, which was dependent on the presence of vitamin D response element (VDRE). 1,25(OH)₂D₃ induced the binding of vitamin D receptor to the VDRE in HGF promoter region. Furthermore, 1,25(OH)₂D₃ was capable of stimulating HGF receptor phosphorylation in renal fibroblasts. Incubation with specific HGF neutralizing antibody largely abolished 1,25(OH)₂D₃-mediated suppression of myofibroblast activation.

These observations suggest that vitamin D analogue possesses renoprotective activity through suppression of the matrix-producing myofibroblast activation. This action of vitamin D is mediated, at least in part, by up-regulating antifibrotic HGF gene expression in renal interstitial fibroblasts.