OP0267 Sirt1 Regulates Canonical Tgf-Beta Signaling to Control Fibroblast Activation and Tissue Fibrosis
Authors: P. Zerr, K. Palumbo-Zerr, J. Huang, A. Distler, O. Distler, G. Schett, J.H. Distler
Journal: Annals of the Rheumatic Diseases (2014)

<h3>Background</h3> SIRT1 is a member of the sirtuin family (SIRT1-7) of proteins, homologs of the Sir2 in yeast. Sirtuins are characterized by a sirtuin core domain and grouped into four classes. SIRT1 is a class III histone deacetylase with important regulatory roles in transcription, cellular differentiation, proliferation and metabolism. <h3>Objectives</h3> Considering that various epigenetic modifications have recently been linked to the pathogenesis of SSc, we aimed to investigate the role of SIRT1 in fibroblast activation and tissue fibrosis in SSc. <h3>Methods</h3> SIRT1 expression was analyzed by real-time PCR, Western Blot and immunohistochemistry in cultured human fibroblasts, in murine models of SSc and in skin samples from SSc patients. Collagen synthesis was quantified by real-time PCR, SirCol- and hydroxyproline assays. The effects of SIRT1 on canonical TGF-β signaling were evaluated by Smad reporter assays and analyses of TGF-β target genes. SIRT1 signaling was modulated by SIRT1 agonist resveratrol and by fibroblast-specific knockout. The role of SIRT1 was evaluated in bleomycin-induced skin fibrosis in mice overexpressing a constitutively active TGF-β receptor I (TBR). <h3>Results</h3> SIRT1 expression was decreased in the skin of SSc patients. IHC demonstrated a pronounced decrease of SIRT1 in fibroblasts in SSc skin. SIRT1 mRNA and protein levels were also decreased in bleomycin or TBR-induced skin fibrosis. TGF-β reduced mRNA and protein levels of SIRT1 in cultured fibroblasts. TBR overexpression reduced SIRT1 in murine skin, whereas treatment with the TBR inhibitor SD-208 prevented the downregulation of SIRT1 in experimental fibrosis. Activation of SIRT1 by treatment with resveratrol potentiated the stimulatory effects of TGF-β on cultured fibroblasts with more pronounced increases of Col1a1 mRNA and collagen protein. These effects were mediated by enhanced canonical TGF-β signaling as resveratrol induced SMAD-dependent transcription in reporter assays and increased the mRNA levels of CTGF of classical SMAD target genes. In contrast, knockdown of SIRT1 inhibited TGF-β/SMAD signaling and reduced release of collagen in fibroblasts. Consistent with a pro-fibrotic role of SIRT1, mice treated with resveratrol were more sensitive to bleomycin-induced dermal fibrosis with more pronounced dermal thickening (74%, p=0.006), increased myofibroblast counts and higher hydroxyproline levels. Mice with fibroblast-specific SIRT1 knockdown were less susceptible to bleomycin induced fibrosis. SIRT1 Inactivation also protected from fibrosis induced by overexpression of TBR. <h3>Conclusions</h3> We identify SIRT1 as a crucial regulator of TGF-β/Smad signaling in SSc. Although SIRT1 is downregulated, this decrease is not sufficient to counter-balance the excessive activation of TGF-β signaling in SSc. However, augmentation of this endogenous regulatory mechanism, e.g. by knockdown of SIRT1 can effectively inhibit TGF-β signaling and exerts potent anti-fibrotic effects. Although further studies are required, these findings provide first evidence that SIRT1 may be an interesting target for pharmacological intervention. <h3>Disclosure of Interest</h3> None declared <h3>DOI</h3> 10.1136/annrheumdis-2014-eular.2212