OP0166 SKIN RETICULARIZATION IN SYSTEMIC SCLEROSIS - POTENTIAL MEDIATORS
Authors: S. Chenguiti Fakhouri, H. Zhu, M. Ronicke, C. Dees, L. Konstantinidis, A. Rius Rigau, A. E. Matei, Y. N. LI, M. Eckstein, C. Geppert, I. Ludolph, A. Kreuter, M. Sticherling, C. Berking, G. Schett, R. Horch, J. Distler, C. Bergmann
Journal: Annals of the Rheumatic Diseases (2024)

<h3>Background:</h3> Systemic Sclerosis (SSc) is characterized by a significant alteration in skin structure. In normal adult human skin, the dermis consists of a papillary layer containing papillae, nerves, mechanoreceptors, vessels and lose collagen bundles, as well as a reticular dermis with coarse collagen bundles. In SSc, the skin morphology is disturbed, adopting a distinctive "reticularized" phenotype marked by the loss of dermal papillae and excessive collagen deposition. The mechanisms maintaining the physiological morphology of adult human skin remain poorly understood. Murine experiments suggest that short-distance morphogen gradients play a crucial role in three-dimensional pattern formation during embryonic skin morphogenesis in rodents [1]. <h3>Objectives:</h3> 1)To analyze if spatial WNT/β-catenin activation is observed in adult healthy human skin and investigate potential alterations in fibrosing skin disorders such as SSc. 2)To evaluate whether perturbations in spatial WNT/β-catenin activation correlate with disruptions in the physiological structure of the skin in SSc. 3)To assess whether changes in the spatial WNT/β-catenin activation correlate with an alteration of reticular markers in SSc skin. <h3>Methods:</h3> Skin morphology was quantitatively evaluated in 40 SSc patients and 18 healthy controls through HE and trichrome staining of skin sections. The transcriptome of healthy and SSc skin was assessed to identify an enrichment of papillary and reticular marker genes and WNT target genes by gene set enrichment analysis using prepublished datasets [2],[3]. Spatial activation of WNT/β-catenin was analyzed through RNAscope®-in situ hybridization detection of AXIN2. Immunofluorescence (IF) staining was performed to visualize β-catenin distribution. Enrichment of reticular marker genes in predefined fibroblast subpopulations was assessed using Gene Ontology (GO) and gene set enrichment analysis (GSEA). <h3>Results:</h3> We describe a significant reduction in number, area and height of papillary structures in SSc compared to healthy controls. Consistently, we found that the expression of papillary/reticular marker genes in SSc skin shifts towards a reticular profile compared to controls. Investigating the expression of WNT3A target genes, we observed an enrichment of WNT3A-regulated genes in papillary gene sets of healthy skin. The spatial distribution of β-catenin-positive fibroblasts in healthy skin, predominantly in the papillary dermis, contrasts with SSc skin, where a 2-fold increase in observed throughout the dermis. A gradient with enrichment of β-catenin-expressing fibroblasts in the papillary layer of healthy skin is no longer observed in SSc. Confocal imaging showed an increased nuclear staining pattern of β-catenin in the reticular dermis compared to the papillary dermis in SSc skin. The loss of spatial WNT activation in SSc was further confirmed at the transcriptional level. Notably, an enrichment of WNT/β-catenin-related genes was found in the Pl16+-population, which also relocates from the reticular to the papillary dermis in SSc. <h3>Conclusion:</h3> Our study provides first evidence of the disrupted physiological WNT/β-catenin gradient in SSc, linked to the loss of papillary dermal structure. Further investigations into the spatial distribution of WNT agonists and antagonists, along with advanced in vitro models simulating a papillary skin structure, will be essential for a more comprehensive understanding of the mechanisms maintaining the skin structure in healthy adult human skin. <h3>REFERENCES:</h3> [1] Matos et al. Elife 2020. [2] Skaug, Khanna et al. Ann Rheum Dis. 2020. [3] Zhu et al. J Invest Dermatol. 2023. <h3>Acknowledgements:</h3> <b>NIL.</b> <h3>Disclosure of Interests:</h3> Sara Chenguiti Fakhouri: None declared, Honglin Zhu: None declared, Moritz Ronicke: None declared, Clara Dees: None declared, Laura Konstantinidis: None declared, Aleix Rius Rigau: None declared, Alexandru-Emil Matei: None declared, Yi-nan Li: None declared, Markus Eckstein: None declared, Carol Geppert: None declared, Ingo Ludolph: None declared, Alexander Kreuter: None declared, Michael Sticherling: None declared, Carola Berking: None declared, Georg Schett: None declared, Raymund Horch: None declared, Jörg Distler JHWD is stock owner of 4D Science and scientific lead of FibroCure, JHWD has consultancy relationships with Actelion, Active Biotech, Anamar, ARXX, Bayer Pharma, Boehringer Ingelheim, Celgene, Galapagos, GSK, Inventiva, Medac, Novartis, Pfizer, RuiYi and UCB, JHWD has received research funding from Anamar, Active Biotech, Array Biopharma, ARXX, aTyr, AstraZeneca, BMS, Bayer Pharma, Boehringer Ingelheim, Cantargia, Celgene, CSL Behring, Galapagos, GSK, Inventiva, Kiniksa, Sanofi-Aventis, RedX, UCB, Christina Bergmann CB has received consultancy fees from Pfizer and Boehringer-Ingelheim.