Systemic Sclerosis Dermal Fibroblast Exosomes Trigger Type 1 Interferon Responses in Keratinocytes via a TBK/JAK/STAT Signaling Axis

Abstract

Objective

Activation of type I interferon (IFN) response has been shown to correlate with disease activity in systemic sclerosis (SSc). 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 were 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 the forearms of healthy patients and of those with SSc 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 analyzed by RNA sequencing (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 the 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 up-regulation of IFN signature genes induced by SSc exosomes compared to healthy control. Inhibition of TBK or JAK activity suppressed the up-regulation 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 indicate that SSc fibroblast exosomes contribute to the type I IFN activation in SSc skin through activation of pattern recognition receptors upstream of TBK.