1,25-(OH(2))D(3) alters the transforming growth factor beta signaling pathway in renal tissue.
BACKGROUND
1,25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) plays an important role in regulating immune responses, in addition to its effects on bone metabolism. The cytokine transforming growth factor beta (TGF-beta) regulates diverse biological processes, including cellular proliferation and differentiation, immune modulation, and modulation of extracellular matrix deposition. 1,25-(OH)(2)D(3) interacts in vitro with Smad proteins, important regulators of TGF-beta signal transduction. We hypothesized that exogenous 1,25-(OH)(2)D(3) would alter levels of TGF-beta(1) and TGF-beta(1) signaling proteins in renal tissue.


METHODS
C57BL6 mice and Lewis rats were placed on diets with or without 1,25-(OH)(2)D(3) for 14 days. Renal lysates were examined for TGF-beta(1), vitamin D receptor (VDR), and Smad3 protein levels using a cell proliferation assay and Western blot analysis. Coimmunoprecipitation was used to determine if any interaction between VDR and Smad3 proteins occurs in vivo. Reverse transcription-polymerase chain reaction (RT-PCR) was used to assess messenger RNA (mRNA) levels for all of these molecules.


RESULTS
Vitamin D supplementation decreased VDR and Smad3 protein levels. Coimmunoprecipitation of VDR and Smad3 revealed a Smad3-VDR interaction in vivo. Vitamin D-treated rats had a significant (P = 0.001) reduction in bioactive renal TGF-beta(1). RT-PCR demonstrated no difference in mRNA expression for either VDR or TGF-beta(1).


CONCLUSIONS
Our results suggest that vitamin D has a significant effect in regulating levels of bioactive TGF-beta(1) and appears to affect aspects of the TGF-beta(1) signaling system. These effects, in combination with the immunomodulatory actions of vitamin D, may alter the evolution of chronic rejection in renal transplants.
Aschenbrenner
J K
JK
Department of Surgery, University of Wisconsin, 600 Highland Avenue, Madison, WI 53792, USA.
Sollinger
H W
HW
Becker
B N
BN
Hullett
D A
DA
D000818:Animals; D015153:Blotting, Western; D002117:Calcitriol / Q000494:pharmacology*; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D015870:Gene Expression / Q000187:drug effects; D006084:Graft Rejection / Q000188:drug therapy; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D016030:Kidney Transplantation; D051379:Mice; D008810:Mice, Inbred C57BL; D008907:Mink; D011233:Precipitin Tests; D051381:Rats; D011917:Rats, Inbred Lew; D018167:Receptors, Calcitriol / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D020545:Respiratory Mucosa / Q000166:cytology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects*; D051900:Smad3 Protein; D015534:Trans-Activators / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*; D014184:Transplantation, Homologous
D002120:Calcium Channel Agonists; D004268:DNA-Binding Proteins; D018167:Receptors, Calcitriol; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; C497787:Smad3 protein, rat; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D002117:Calcitriol