P127 S100A4 regulated genes are differentially activated in systemic sclerosis skin across limited and diffuse cutaneous subsets

Abstract Background/Aims S100A4 is one of a family of damage-associated molecular peptide proteins causing downstream intracellular and extracellular fibrotic effects. Pre-clinical animal and functional studies have shown that S100A4 is implicated in skin and lung fibrosis in systemic sclerosis (SSc). Previous work Denton et al, 2023 demonstrated that recombinant S100A4 protein promotes a fibrotic phenotype in normal fibroblasts whilst anti-S100A4 neutralising monoclonal antibody (AX-202) attenuated the profibrotic phenotype of SSc fibroblasts (SScF). Integrated analysis determined a set of 475 genes (the ‘‘S100A4 signature’’) that are differentially expressed between normal (NDF) and SScF, induced in NDF by recombinant S100A4, and significantly attenuated in SScF by AX-202. Methods Gene set enrichment analysis interrogated the S100A4 signature gene expression in whole skin in 68 well characterised SSc patients or healthy controls prospectively from a large tertiary centre over the course of 24 months (BIOPSY cohort). These included early diffuse cutaneous (dc)SSc (n = 21), limited cutaneous (lc)SSc (n = 15) and established dcSSc (n = 14) with 16 matched healthy controls. Bulk RNA sequencing assessed genome-wide gene expression of whole skin samples to obtain normalised gene expression values for each sample. Results 460 of the 475 S100A4 signature genes were also identified in the BIOPSY cohort. 191 of the 460 genes showed statistically significant expression (p value 0.01) across all subsets of SSc compared to healthy controls. Of the top 50 differentially expressed genes the early diffuse subset scatter more widely and overlap with the established subset suggesting transitional heterogeneity. Supervised hierarchical clustering by samples and genes revealed distinct genetic signatures. Expression values of each gene are calculated using normalised z scores to highlight relative over and under expression of the gene in each sample. Conclusion Our findings confirm differential activation of S100A4 regulated genes across the spectrum of SSc subsets that is not present in healthy skin. Since S100A4 is a potential molecular marker and target in different SSc subgroups our findings may inform future clinical study design to help understand differential treatment response. Disclosure M. Kanitkar: None. P. Yee: None. K.E. Clark: None. V. Ong: None. C. Denton: None.