1864: Mitochondrial Dysfunction Drives cGAS-STING–Mediated Type I Interferon Production and Fibrosis in Systemic Sclerosis

Background/Purpose: Systemic sclerosis (SSc) is an autoimmune disease characterized by type I interferon (IFN-I) production and mitochondrial dysfunction. Emerging evidence suggests that activation of the stimulator of interferon genes (STING) pathway in SSc is triggered by cytosolic mitochondrial DNA (mtDNA) released during mitochondrial stress. This link is further supported by the similarities between SSc and SAVI (STING-associated vasculopathy with onset in infancy) syndrome, a condition caused by a gain-of-function mutation in TMEM173 (which encodes STING) that phenocopies many key features of SSc. Nevertheless, the role of mitochondrial damage in activating cGAS-STING and driving IFN-I production in SSc remains poorly understood.


This study aims to investigate whether mitochondrial dysfunction activates the cGAS-STING pathway and drives IFN-I production and fibrosis in SSc.





Methods: Transcriptomic analysis was performed on RNA-seq data (GSE231692, FaSScinate trial) to assess mitochondrial, cGAS-STING, and interferon-related gene expression. Skin biopsies from SSc patients and healthy controls (n=10 per group) were analyzed by RT-PCR and immunohistochemistry (IHC) for cGAS, STING, IRF3, and IFN-I. Mitochondrial dysfunction was evaluated through TFAM and MTND1 expression, Seahorse metabolic profiling, and ATP quantification in fibroblasts. To examine STING activation, fibroblasts were treated with the mitochondrial uncoupler FCCP, followed by confocal microscopy and IFNB1 quantification. In vivo relevance was tested in bleomycin-induced fibrosis (BIF) mice, with or without treatment with the selective STING inhibitor H-151.

Results: SSc skin exhibited upregulation of STING1, cGAS, TBK1, IFI16, and STAT1 compared to controls, with overexpression of STING, cGAS, and IFNB1 confirmed by RT-PCR (p < 0.01) and IHC. Mitochondrial dysfunction was evident in SSc fibroblasts, with significantly reduced TFAM expression (p < 0.01), impaired oxidative phosphorylation, decreased ATP levels, and increased glycolytic activity. FCCP-induced mitochondrial stress promoted STING nuclear translocation and IFNB1 induction, more pronounced in SSc than in control fibroblasts supporting the idea of a direct link between mitochondrial dysfunction, STING activation, and IFNβ production. Bleomycin-treated mouse models mirrored these findings, with STING-related genes (Irf3, Tmem173) being upregulated, and antioxidant defenses (Sod1, Prdx3) diminished. Treatment with H-151 significantly reduced dermal thickness and collagen deposition, underscoring the role of STING in fibrosis and the possible therapeutic potential of targeting the STING pathway in SSc.

Conclusion: Mitochondrial dysfunction in SSc promotes activation of the cGAS-STING pathway and IFN-I production, contributing to fibrotic remodeling. Pharmacologic inhibition of STING attenuates skin fibrosis in vivo, supporting STING as a novel therapeutic target in systemic sclerosis.