Background Rheumatoid arthritis (RA) is characterized by proliferation of synovial fibroblasts (FLS), activation of these cells by synovial macrophages (Mϕ), and production of pro-inflammatory proteins. As genetic backgrounds do not completely explain the etiology of RA, a growing attention has focused on potential epigenetic contributions to inflammation.
Objectives Here we examined the role of the closely related epigenetic regulatory proteins sirtuin 1 (Sirt1) and sirtuin 2 (Sirt2), class III histone deacetylases, in the inflammatory activation of RA FLS and human macrophages.
Methods Sirt1 and Sirt2 mRNA and protein expression was measured in RA FLS following stimulation with IL-1β and TNF-α. RA-FLS production of IL-6, IL-8, MMP-1 and MMP-3 mRNA and protein expression in response to IL-1β, in the absence or presence of specific inhibitors for Sirt1 and Sirt2, was measured by quantitative PCR (qPCR) and ELISA. The expression of 84 genes regulated by IL-1β in RA FLS were analyzed by qPCR array in the presence or absence of Sirt2-specific inhibitor. Monocytes obtained from healthy volunteers were differentiated into either M1 or M2 macrophages with human recombinant IFN-γ or IL-10 for 7 days. Macrophage production of IL-6 and IL-8 in response to LPS stimulation in the absence or presence of Sirt inhibitors was assessed by ELISA.
Results The expression of Sirt1 was enhanced following RA FLS IL-1β stimulation, while Sirt2 expression was significantly reduced (p<0.05). Pharmacological inhibition of Sirt2, but not Sirt1, significantly reduced RA FLS expression of IL-6, IL-8, and MMP-3 mRNA, in response to IL-1β stimulation (p<0.05), an effect mimicked at the protein level. qPCR array analysis demonstrated that mRNA expression of 18 of 84 genes induced by IL-1β in RA FLS (n=3) were significantly reduced by 50% or more in the presence of Sirt2 inhibitor. Furthermore Sirt2 inhibitor reduced LPS-induced levels of IL-8 in IFN-γ–but not IL-10–differentiated macrophages.
Conclusions Our studies identify Sirt2 as a novel epigenetic regulator of inflammatory activation of macrophages and RA FLS.
Disclosure of Interest E. Mohammadi: None declared, C. Angiolilli: None declared, P. Kabala: None declared, P. Tak Shareholder of: GlaxoSmithKline, Employee of: GlaxoSmithKline, D. Baeten: None declared, F. Husseini Shirazi: None declared, K. Reedquist: None declared