Systemic Sclerosis dermal fibroblast exosomes trigger a Type 1 interferon response in keratinocytes through the TBK/JAK/STAT signalling axis

Background Activation of Type I IFN response has been shown to correlates with disease activity in systemic sclerosis. It is currently unknown whether the tissue-specific Type I IFN activation is a consequence of the response observed in blood or rather its source. Exosomes from SSc fibroblasts have been recently shown to activate macrophages, in vitro. Here, we aimed to determine the source of Type I IFN signature in SSc skin biopsies and the potential role of exosomes from SSc dermal fibroblasts in the process. Methods Skin biopsies were obtained from healthy and SSc patients forearms and processed for dermal fibroblasts and keratinocytes. Exosomes were isolated from healthy and SSc dermal fibroblast supernatants by ultracentrifugation and added to human skin keratinocytes. Keratinocyte transcriptome was analysed by RNA-seq analysis. TANK-binding kinase (TBK) and JAK were inhibited using a small molecule inhibitor (GSK8612) and Tofacitinib, respectively. Results SSc skin biopsies showed highest levels of Type I IFN response in the epidermal layer. RNA-seq analysis of keratinocytes transcriptome following exposure to dermal fibroblast exosomes showed strong upregulation of IFN signature genes induced by SSc exosomes compared to Healthy control. Suppression of TBK or JAK activity suppressed the upregulation of the IFN signature induced by SSc exosomes. Conclusion IFN activation of SSc keratinocytes is dependent on their crosstalk with dermal fibroblasts and inducible by extracellular exosomes. Our data indicates that SSc fibroblasts exosomes may carry the signal zero of local Type I IFN activation through activation of pattern recognition receptors upstream of TBK. ### Competing Interest Statement The authors have declared no competing interest.