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

1,25-dihydroxyvitamin D-3 inhibits renal interstitial myofibroblast activation by inducing hepatocyte growth factor expression. Background. 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 D-3[1,25(OH)(2)D-3] on the regulation of myofibroblast activation from interstitial fibroblast, a critical event in generating alpha-smooth muscle actin (alpha SMA)-positive, matrix-producing effector cells in renal interstitial fibrosis. Methods. 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)-beta 1. Expression of alpha-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. Results. Incubation of rat renal interstitial fibroblasts (NRK-49F) with 1,25(OH)(2)D-3 suppressed TGF-beta 1-induced de novo alpha-SMA expression in a dose-dependent manner. 1,25(OH)(2)D-3 also suppressed type I collagen and thrombospondin-1 expression induced by TGF-beta 1. Interestingly, 1,25(OH)(2)D-3 induced HGF mRNA expression and protein secretion in renal interstitial fibroblasts. Transfection studies revealed that 1,25(OH)(2)D-3 stimulated HGF gene promoter activity, which was dependent on the presence of vitamin D response element (VDRE). 1,25(OH)(2)D-3 induced the binding of vitamin D receptor to the VDRE in HGF promoter region. Furthermore, 1,25(OH)(2)D-3 was capable of stimulating HGF receptor phosphorylation in renal fibroblasts. Incubation with specific HGF neutralizing antibody largely abolished 1,25(OH)(2)D-3-mediated suppression of myofibroblast activation. Conclusion. 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.