LAUSR

Background/Aims  The major antinuclear autoantibodies of systemic sclerosis (SSc) associate with different skin score trajectories and risk of internal organ manifestations. To elucidate molecular differences between ANA-defined subgroups, we utilised the prospective BIOPSY cohort of well-characterised SSc patients. Methods  The prospectively collected BIOPSY cohort recruited 52 SSc patients (21 early dcSSc, 15 established dcSSc, 16 lcSSc) and 16 healthy controls (HC). 36 (69%) of the SSc patients are female. Mean disease duration in the early dcSSc cohort was 24 months (sd 12 months), and in established dcSSc was 11.3 years. ANA frequency in BIOPSY reflected the overall dcSSc population: anti-topoisomerase-1 (ATA) n = 14 (27%), anti-RNA pol III (ARA) n = 12 (23%) and other n = 26 (50%). Mean baseline skin score (MRSS) for early dcSSc was 21 (sd 11.2). At a group level mRSS peak was 21.9 (11.8) at 3 months and fell to 19.1(10.5) at 12 months. Serum biomarkers of ECM turnover and fibrosis were measured three monthly and genome-wide transcriptomic profiling of whole skin and whole blood performed by RNA-Seq. Statistical analysis used RStudio with ANOVA, and Tukey post-hoc test. Differential gene expression used the Bioconductor limma software, with standard thresholds for significance. Results  At baseline, there were differences in soluble markers between clinical SSc sugroups and HC but not for major ANA subgroups. However, we found clear differences in early dcSSc analysed by major ANA subset for longitudinal change in serum markers of fibrosis and in whole skin gene expression, suggesting a mechanistic basis for the distinct clinical phenotypes associated with hallmark ANAs. During follow-up, significant differences were observed in HA, TIMP1, and PIIINP at 6 and 12 months (p < 0.05), with stable levels in ATA+ patients compared to progressively increased levels in the other subgroups. There were 564 significantly differentially expressed genes in skin between early dcSSc and HC. Unsupervised clustering differentiated patients with ARA and ATA positivity with early dcSSc. 54 genes were significantly differentially expressed in skin between ATA and ARA patients. Whilst 179 genes were differentially expressed in whole blood between early dcSSc compared with HC, no genes could significantly differentiate ATA from ARA. Functional analysis using HALLMARK pathway analysis identified both shared pathways associated with SSc across ANA groups (e.g. TGF beta signaling, IL6 JAK STAT3 signalling, inflammatory response), and pathways only upregulated in patients with ATA (e.g. Wnt beta catenin signaling, Notch signaling), and ARA (e.g. interferon gamma response, adipogenesis). Conclusion  We have found significant differences in skin gene expression and longitudinal change in serum markers by autoantibody specificity in dcSSc. Our findings have implications for SSc pathogenesis and support stratification by ANA subgroup in clinical studies. Disclosure  K.E. Clark: None. C. Campochiaro: None. E. Csomor: Corporate appointments; employee of GSK. A. Taylor: Corporate appointments; employee of GSK. K. Nevin: Corporate appointments; employee of GSK. N. Galwey: Corporate appointments; employee of GSK. M.A. Morse: Corporate appointments; employee of GSK. V.H. Ong: None. E. Derrett-Smith: None. N. Wisniacki: Corporate appointments; employee of GSK. S. Flint: Corporate appointments; employee of GSK. C.P. Denton: Consultancies; Actelion, GlaxoSmithKline, Bayer, Sanofi, lnventiva, Boehringer Ingelheim, Roche, Bristol Myers Squibb, CSL Behring, UCB, Leadiant Biosciences, Corbus, Servier, Arxx Therapeutics.