Background/Purpose: Vitamin D receptor (VDR) is a member of the nuclear receptor superfamily. Its ligand, 1,25-(OH)2D, is a metabolically active hormone derived from vitamin D3. Activated VDR binds to specific VDR elements in the promoters of target genes to regulate their expression. The levels of vitamin D3 have been shown to be significantly decreased in patients with systemic sclerosis (SSc). However, the functional consequences remain unknown. Our aim was to find a potential link between impaired VDR signaling and fibrosis.
Methods: VDR expression was analyzed by real-time PCR, Western Blot and IF. VDR agonist paricalcitol was used in in vitro and in vivo experiments. Collagen synthesis was quantified in fibroblasts overexpressing or lacking VDR. Interaction of VDR and Smad3 was shown by Co-IP. VDR was analyzed in two different mouse models of SSc: bleomycin-induced dermal fibrosis and mice overexpressing a constitutively active TGFβ receptor I (TBR).
Results: VDR mRNA levels were reduced by 78 % in skin of SSc patients compared to healthy individuals (p = 0.02). Similar decreases were observed on the protein level. VDR mRNA and protein levels were also decreased in the bleomycin-induced (33 %; p = 0.01) and the TBR-induced fibrosis (45 %; p = 0.03). Chronic stimulation with TGFβ strongly decreased VDR mRNA and protein levels in fibroblasts. VDR knockdown fibroblasts showed significantly increased levels of Col1a1 mRNA (+216 %; p = 0.002) and collagen protein (+165 %; p = 0.01) compared to TGFβ stimulated controls. In contrast, VDR overexpression inhibited the pro-fibrotic effects of TGFβ with decreased Col1a1 mRNA levels, collagen release and prevented differentiation into myofibroblasts. Co-IP showed that paricalcitol stimulated the formation of high affinity complexes of VDR and active, phosphorylated Smad3 in fibroblasts. Reporter assays confirmed that binding of VDR to phosphorylated Smad3 impaired the transcriptional activity of phosphorylated Smad3. Moreover, potent anti-fibrotic effects of paricalcitol were observed in different mouse models of SSc. Mice treated with paricalcitol were less sensitive to TBR induced dermal fibrosis with reduced dermal thickening (-46%, p = 0.01), myofibroblast counts (-69%, p = 0.001) and hydroxyproline content (-77%, p = 0.02). Paricalcitrol also significantly ameliorated bleomycin-induced fibrosis.
Conclusion: We demonstrate that VDR is a crucial regulator of TGFβ / Smad signaling. Pharmacological activation of VDR inhibits TGFβ signaling and reduces fibrosis. Impaired VDR signaling with reduced levels of its ligand vitamin D3 may thus contribute to hyper-active TGFβ signaling and aberrant fibroblast activation in SSc. These findings may have direct clinical implications, considering the higher binding affinity and the less calcaemic effects with more prolonged administration of paricalcitol compared to the natural ligand and the potent anti-fibrotic effects, the good tolerability and the availability of VDR agonists in clinical trials.
Disclosure:
P. Zerr,
None;
S. Vollath,
None;
K. Palumbo-Zerr,
None;
M. Tomcik,
None;
J. Huang,
None;
A. Distler,
None;
C. Beyer,
None;
C. Dees,
None;
O. Distler,
Sanofi, Active Biotech, Pfizer, Actelion, and Novartis,
2,
Actelion, Sanofi-Aventis, Roche, Genentech, Active Biotec, medac, Novartis, Sinoxa, 4D Science,
5;
G. Schett,
Celgene,
2,
Abbott Laboratories, UCB, Roche,
5;
J. H. W. Distler,
None.
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ACR Meeting Abstracts - https://acrabstracts.org/abstract/impaired-vitamin-d-receptor-signaling-upregulates-transforming-growth-factor-beta-tgf%ce%b2-signaling-in-systemic-sclerosis/