AB0044 PHARMACOLOGICAL MANIPULATION OF SIRTUIN 1 ACTIVITY IN EXPERIMENTALLY INDUCED ARTHRITIS
Authors: Milena Leseva, Kalin Stoyanov, Petya Dimitrova
Journal: Annals of the Rheumatic Diseases (2019)

<h3>Background:</h3> Sirtuin 1 (Sirt1) is a member of the sirtuin family of NAD+ dependent protein deacylases. This nuclear enzyme with deacetylase activity serves as a metabolic sensor and transcriptional regulator, and exerts its beneficial effects by promotion of cell viability, tissue regeneration, and inhibition of inflammation. <h3>Objectives:</h3> 1) To investigate the effect of pharmacological modulation of Sirt1 enzymatic activity on disease outcomes of experimental rheumatoid arthritis in mice; and 2) To characterize surface marker and pro-inflammatory cytokine expression in neutrophils following Sirt1 activation or inhibition. <h3>Methods:</h3> Arthritis was induced by intra-peritoneal administration of a cocktail of monoclonal antibodies against collagen type II in Balb/c mice (CAIA). We utilized synthetic compounds which specifically activate or inhibit Sirt1 activity - SRT2183 and EX527, respectively. We investigated the effect of Sirt1 activity modulation on clinical scores of arthritic mice after subcutaneous seven-day treatment initiated at Day 7 of CAIA. We used flow-cytometry for phenotyping and functional analysis of blood, and bone marrow (BM) derived neutrophils stimulated <i>in vivo</i>, and <i>in vitro</i>. The effects of the two compounds on Sirt1 activity and on cell viability were assessed using ELISA-based colorimetric assays. <h3>Results:</h3> Activation and inhibition of Sirt1 activity led to CD11b down-regulation and CXCR2 up-regulation on healthy blood and BM neutrophils, suggestive of neutrophil mobilization from the BM to the periphery following treatment <i>in vivo</i>. Both SRT2183 and EX527 had a positive effect on clinical scores in CAIA mice. However, in EX527-treated mice the re-emergence of signs of joint inflammation was observed 14 days after cessation of treatment. Administration of SRT2183 was able to up-regulate IL-1beta in healthy and CAIA mice, which we also observed in un-stimulated neutrophils<i> in vitro</i>. Iso-nicotinamide, a compound which activates sirtuins via an alternative mechanism, had a similar effect on IL-1beta expression <i>in vitro</i>. Finally, Parp1 cleavage, a marker for cell death, was reduced in purified BM neutrophils following Sirt1 activation. <h3>Conclusion:</h3> Sirt1 activity modulation, whether activation or inhibition, improved clinical scores in arthritis. This corresponds to the mobilization of neutrophils from the BM to the periphery. The selective increase of IL-1beta following Sirt1 activation indicates that while activation or inhibition achieves a similar outcome, this is done through different molecular pathways. Our results underscore that systemic pharmacological modulation of Sirt1 activity for a complex disease, such as rheumatoid arthritis, is complicated and attention should be paid to the schedule and duration of treatment, as well as to the progressive involvement of various cell types, in order to maximize the beneficial effects. <h3>Acknowledgement:</h3> This study was funded by the Bulgarian National Science Fund (DN 5/11-2017 to P.D). <h3>Disclosure of Interests:</h3> None declared