SIRT1 overexpression in the rheumatoid arthritis synovium contributes to proinflammatory cytokine production and apoptosis resistance

Abstract

ObjectiveTo analyse the expression of SIRT1 in synovial tissues and cells of patients with rheumatoid arthritis (RA) and to study the function of SIRT1 in inflammation and apoptosis in RA.MethodsLevels of SIRT1 expression were analysed in synovial tissues and cells from patients with RA by real-time PCR and western blotting before and after stimulation with toll-like receptor ligands, tumour necrosis factor α (TNFα) and interleukin 1β (IL-1β). Immunohistochemistry was used to study the localisation of SIRT1. Fluorescence activated cell sorting analysis was performed to investigate the effect of SIRT1 on apoptosis. Peripheral blood monocytes and rheumatoid arthritis synovial fibroblasts (RASFs) were transfected with wild-type or enzymatically inactive SIRT1 expression vectors or with siRNA targeting SIRT1. Cytokine analysis of IL-6, IL-8 and TNFα were performed by ELISA to study the role of SIRT1 on proinflammatory mediators of RA.ResultsSIRT1 was found to be constitutively upregulated in synovial tissues and cells from patients with RA compared to osteoarthritis. TNFα stimulation of RASFs and monocytes resulted in further induced expression levels of SIRT1. Silencing of SIRT1 promoted apoptosis in RASFs, whereas SIRT1 overexpression protected cells from apoptosis. Inhibition of SIRT1 enzymatic activity by inhibitors, siRNA and overexpression of an enzymatically inactive form of SIRT1 reduced lipopolysaccharide-induced levels of TNFα in monocytes. Similarly, knockdown of SIRT1 resulted in a reduction of proinflammatory IL-6 and IL-8 in RASFs.ConclusionThe TNFα-induced overexpression of SIRT1 in RA synovial cells contributes to chronic inflammation by promoting proinflammatory cytokine production and inhibiting apoptosis.

Sirtuin 1 Is a Negative Regulator of Parathyroid Hormone Stimulation of Matrix Metalloproteinase 13 Expression in Osteoblastic Cells

“…Sirt1 overexpression significantly inhibited the up-regulation of MMP13 caused by IL-1␤ (53). Conversely, reduced SIRT1 protein levels are associated with increased protein levels of MMP13 in osteoarthritic cartilage (53)(54)(55)(56). MMP13 preferentially degrades type II collagen in cartilage but also degrades type I collagen in bone.…”

Regulation and function of SIRT1 in rheumatoid arthritis synovial fibroblasts

“…Down regulation of SIRT1 or inhibition of sirtuin activities in synovial cells of RA patients was found to reduce the expression of inflammatory mediators [13,14], and overexpression of SIRT1 increased production of pro-inflammatory cytokines in rheumatoid arthritis synovial fibroblasts (RASF) and monocytes from healthy persons [13]. In contrast, levels of SIRT1 were diminished in joint tissues of mice with collagen-induced arthritis [15].…”

“…In silencing experiments, 100 µM of validated siRNA for SIRT1 or control siRNA (Invitrogen) were used. For overexpression of SIRT1, 1 μg of SIRT1 wild-type or empty pcDNA3.1(-) (mock) expression vectors were used as previously described [13]. Silencing and overexpression of SIRT1 were verified by Western blot analysis or real-time PCR (Supplementary Fig.1).…”

“…Expression of SIRT1 was shown to be increased in the synovium of RA patients [13]. Down regulation of SIRT1 or inhibition of sirtuin activities in synovial cells of RA patients was found to reduce the expression of inflammatory mediators [13,14], and overexpression of SIRT1 increased production of pro-inflammatory cytokines in rheumatoid arthritis synovial fibroblasts (RASF) and monocytes from healthy persons [13].…”

Roles of Reactive Oxygen Species in Rheumatoid Arthritis Pathogenesis

“…The rate of apoptosis of peripheral blood mononuclear cells (PBMCs) in patients with RA was increased and negatively correlated with SIRT1 expression levels. SIRT1 is required to maintain T-cell tolerance [61]. And the lack of SIRT1 resulted in hyperacetylation of c-Jun and the breakdown of T cell tolerance [62].…”