1,25-dihydroxyvitamin D 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 (alphaSMA)-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)-beta1. 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-beta1-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-beta1. 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.


CONCLUSIONS
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.
Li
Yingjian
Y
Division of Cellular and Molecular Pathology, Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
Spataro
Bradley C
BC
Yang
Junwei
J
Dai
Chunsun
C
Liu
Youhua
Y
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D002117:Calcitriol / Q000494:pharmacology*; D002478:Cells, Cultured; D024042:Collagen Type I / Q000235:genetics; D005347:Fibroblasts / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D015870:Gene Expression / Q000187:drug effects; D017228:Hepatocyte Growth Factor / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D007668:Kidney / Q000166:cytology*; D010766:Phosphorylation / Q000187:drug effects; D011401:Promoter Regions, Genetic / Q000502:physiology; D019859:Proto-Oncogene Proteins c-met / Q000378:metabolism; D051381:Rats; D019700:Thrombospondin 1 / Q000235:genetics; D016212:Transforming Growth Factor beta / Q000378:metabolism; D053773:Transforming Growth Factor beta1; D015854:Up-Regulation / Q000187:drug effects; D014815:Vitamins / Q000494:pharmacology*
D000906:Antibodies; D024042:Collagen Type I; C508962:Tgfb1 protein, rat; D019700:Thrombospondin 1; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D014815:Vitamins; D017228:Hepatocyte Growth Factor; D019859:Proto-Oncogene Proteins c-met; D002117:Calcitriol