Background SIRT1 is an NAD-dependent protein deacetylase that targets both histones and non-histone proteins including transcription factors. It has been shown to play an important role in a variety of age-related diseases demonstrating a broad anti-inflammatory function in different tissues (1).
Naturally occurring dietary polyphenols, such as catechins, have antioxidant and anti-inflammatory properties via modulating different signaling pathways and have been shown to activate SIRT1 directly or indirectly.
Little is known of the role that SIRT1 plays in osteoarthritis (OA) and in particular there is no evidence suggesting that mediators or modulators of inflammation can interfere with SIRT1 function in OA.
Objectives In this study, we explored the idea that the epigallocatechin-3-gallate (EGCG), the most active catechin found in green tea, modulates the expression of SIRT1 in an in vitro model which use synthetic calcium pyrophosphate (CPP) crystals to reproduce some inflammatory aspects of OA.
Methods Synthetic CPP crystals were used at 0.025mg/ml to stimulate a monocytic cell line (THP-1) in presence or absence of EGCG (10-50μM) and 2% of fetal calf serum. The IkappaB kinase (IKK) inhibitor, EF-24, was used to suppress NFkB activity. The production of IL-1β and IL-8 were determined in the supernatants along with the chemoattractant activity on polymorphonuclear cells. SIRT1 expression was determined by real-time quantitative PCR after 24 and 48h stimulation.
Results IL-8 and IL-1β production induced by crystals was suppressed in presence of the IKK inhibitor confirming the activation of NFkB in CPP crystal-induced inflammation. EGCG inhibited both cytokines production and the chemoattractant activity of culture supernatants in a dose dependent manner (e.g. IL-8 from 500 pg/ml to 100 and 45 pg/ml). The modulation of SIRT1 expression was more pronounced after 48h treatment and its trend corresponded to that observed for cytokine production. While CPP crystals provoked a slight diminution of SIRT1, in presence of EGCG SIRT1 expression was 1.6 time higher respect to control values. EGCG alone activated SIRT1 even if to a smaller extent.
Conclusions With this study we showed, for the first time, evidence that SIRT1 expression is affected by CPP crystals and is modulated by EGCG. It has been demonstrated that SIRT1 is able to deacetylate the p65 subunit of NF-kB, blocking its ability to bind DNA, thereby inhibiting transcription of proinflammatory genes (2). As CPP crystal stimulation acts through the activation of NFkB and EGCG inhibits cytokines release and lead to enhanced SIRT1 mRNA, it is possible that EGCG inhibits CPP crystal-induced inflammation through the activation of SIRT1. To explore this hypothesis activity of SIRT1 in presence of EGCG will be evaluated as well as cytokine production after inhibition of SIRT1 by means of nicotinamide or RNA silencing.
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Disclosure of Interest None Declared