P126 Epigenetic control of distally expressed hoxd genes in synovial fibroblasts
Authors: K Klein, M Frank-Bertoncelj, G Lee, C Kolling, O Distler, C Ospelt
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Introduction</h3> Synovial fibroblasts (SF) from different joint localizations exhibit profound differences in their expression profiles that might predispose specific joints for certain forms of arthritis.<sup>1</sup> Homeobox (<i>HOX</i>) genes were shown to play important roles in limb development and might influence the site-specific development of various diseases. <h3>Objectives</h3> To analyse the expression of distally expressed <i>HOXD</i> genes in SF from hands and to investigate their epigenetic regulation. <h3>Methods</h3> The expression of HOXD10, HOXD11 and HOXD13 was analysed by quantitative Real-time PCR. The histone marks H3K4me1 (enhancers), H3K4me3 (transcriptional starts of transcribed genes), H3K27me3 (inactive gene promoters) and H3K27ac (active enhancers) in SF from one RA (finger) and one osteoarthritis (OA; thumb) patient were analysed by ChIP DNA sequencing (ChIPseq). Hand SF (n=7) were treated for 24 hour with the bromodomain inhibitor I-BET151 (1 µM), targeting the bromodomain and extra-terminal domain (BET) proteins. The expression of the histone-acetyltransferases CREBBP-binding protein (CBP) and p300 was silenced by transfection of antisense LNA gapmeRs in hand SF (n=4). <h3>Results</h3> HOXD10, HOXD11 and HOXD13 transcripts were significantly increased in SF from RA and OA patients in digits II-IV and wrists compared to SF from digit I (thumb). Accordingly, ChIPseq showed an increase of H3K27ac and H3K4me3 marks in the genomic region between <i>HOXD9</i> and <i>HOXD13</i> in SF from a RA finger compared to SF from an OA thumb, paralleled by a loss of the repressive histone marks H3K27me3 between <i>HOXD12</i> and <i>MIR10B</i>. Treatment of SF with I-BET151 reduced the expression of HOXD10, HOXD11 and HOXD13 by 50% (±23; p&lt;0.001), 29% (±29; p&lt;0.05), and 27% (±27; p&lt;0.05) respectively. Silencing of CBP reduced the expression of HOXD10 by 47% (±10; p&lt;0.01) and HOXD11 by 22% (±19; p=0.1) but not HOXD13. Also silencing of p300 reduced the expression of HOXD10 by 47% (±24; p=0.06) and HOXD11 by 55% (±10; p&lt;0.01) but not HOXD13. <h3>Conclusions</h3> Distally expressed <i>HOXD</i> genes exhibit site-specific expression between digits II-IV and the thumb. The site-specific expression is maintained by a specific set of histone modifications and regulated by epigenetic writer (CBP, p300) and reader proteins (BET proteins). This epigenetically regulated expression of <i>HOXD</i> genes might influence the different occurrence of RA and OA in the small joints of the digits II-IV and the thumb. <h3>Reference</h3> . Frank-Bertoncelj, et al. Nat Commun2017. <h3>Acknowledgements</h3> Swiss National Fund (PMPDP3-171315/1), Institute of Rheumatology Research (IRR), Stiftung für wissenschaftliche Forschung, Opo-Stiftung, Hartmann Müller Stiftung <h3>Disclosure of interest</h3> K. Klein Grant/research support from: Swiss National Fund (PMPDP3-171315/1), Hartmann Müller Stiftung, M. Frank-Bertoncelj: None declared, G. Lee: None declared, C. Kolling: None declared, O. Distler Grant/research support from: Stiftung für wissenschaftliche Forschung, C. Ospelt Grant/research support from: Opo Stiftung