SAT0023 Control of cytokine mrna degradation by the histone deacetylase inhibitor itf2357 in rheumatoid arthritis fibroblast-like synoviocytes
Authors: C. Angiolilli, P. Kabala, A. Grabiec, M. Rossato, W. Lai, P. Blackshear, K. Reedquist, D. Baeten, T. Radstake
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> Control of cytokine mRNA degradation acts as an essential check-point to limit the overproduction of inflammatory proteins.<sup>1</sup> In rheumatoid arthritis (RA), altered expression of the mRNA-degrading protein TTP (tristetraprolin, <i>ZFP36</i>) has been recently reported in synovial tissue, possibly contributing to the perpetuating inflammatory loop in the synovium.<sup>2</sup> Histone deacetylase inhibitors (HDACi) are small molecule drugs suppressing cytokine production <i>in vitro</i> and <i>in vivo</i> and displaying initial safety and efficacy in the treatment of systemic onset juvenile idiopathic arthritis.<sup>3,4</sup> However, their transcriptional and post-transcriptional mechanisms of action are not yet completely characterised. <h3>Objectives</h3> We aimed to investigate the mRNA degrading properties of the HDACi ITF2357 on a panel of inflammatory mediators in RA fibroblast-like synoviocytes (FLS). <h3>Methods</h3> The effects of ITF2357 on the expression and mRNA stability of IL-1β-inducible genes in FLS were analysed using array-based qPCRs and Luminex. The expression of primary and mature cytokines transcripts, the mRNA levels of TTP and other AU-rich element binding proteins (ARE-BP) and the cytokine profile of fibroblasts derived from <i>ZFP36<sup>+/+</sup></i> and<i> ZFP36<sup>-/-</sup></i> mice was measured by qPCR. ARE-BP silencing was performed by siRNA-mediated knockdown, and TTP post-translational modifications analysed by immunoblotting. <h3>Results</h3> ITF2357 reduced the expression of 85% of the analysed IL-1β-inducible transcripts, including cytokines (<i>IL6</i>, <i>IL8</i>), chemokines (<i>CXCL2</i>, <i>CXCL5</i>, <i>CXCL6</i>, <i>CXCL10</i>), matrix-degrading enzymes (<i>MMP1</i>, <i>ADAMTS1</i>) and other inflammatory mediators. Analyses of mRNA stability demonstrated that ITF2357 accelerates <i>IL6</i>, <i>IL8</i>, <i>PTGS2</i>, and <i>CXCL2</i> mRNA degradation, a phenomenon associated with the enhanced transcription of TTP, but not other ARE-BP, and the altered post-translational status of TTP protein. TTP knockdown potentiated cytokine production in RA FLS and murine fibroblasts. <h3>Conclusions</h3> Our study identifies that regulation of cytokine mRNA stability is a predominant mechanism underlying ITF2357 anti-inflammatory properties, occurring via regulation of TTP. These results highlight the therapeutic potential of ITF2357 in the treatment of RA. <h3>References</h3> [1] Turner M, Diaz-Munoz MD. RNA-binding proteins control gene expression and cell fate in the immune system. Nat Immunol2018. [2] Ross EA, Naylor AJ, O'Neil JD, et al. Treatment of inflammatory arthritis via targeting of tristetraprolin, a master regulator of pro-inflammatory gene expression. Ann Rheum Dis2016. [3] Joosten LA, Leoni F, Meghji S, Mascagni P. Inhibition of HDAC activity by ITF2357 ameliorates joint inflammation and prevents cartilage and bone destruction in experimental arthritis. Mol Med2011. [4] Vojinovic J, Damjanov N, D'Urzo C, et al. Safety and efficacy of an oral histone deacetylase inhibitor in systemic-onset juvenile idiopathic arthritis. Arthritis Rheum2011. <h3>Disclosure of Interest</h3> None declared