Cyclic GMP-AMP synthase expression is enhanced in systemic sclerosis-associated interstitial lung disease and stimulates inflammatory myofibroblast activation

Objective The lungs of patients with systemic sclerosis-associated interstitial lung disease (SSc-ILD) contain inflammatory myofibroblasts that arise in association with fibrotic stimuli and perturbed innate immunity. The cytosolic DNA-binding receptor cyclic GMP-AMP synthase (cGAS) is implicated in inflammation and fibrosis, but its involvement in SSc-ILD remains unknown. We examined cGAS expression, activity and therapeutic potential in SSc-ILD using human biospecimens, cultured fibroblasts, precision-cut lung slices and a well-accepted animal model. Methods Expression and localisation of cGAS, cytokines and type 1 interferons were evaluated in SSc‑ILD lung tissues, bronchoalveolar lavage fluid and isolated lung fibroblasts. CGAS activation was assessed in a publicly available SSc-ILD single-cell RNA-sequencing dataset. Production of cytokines, type 1 interferons and α-smooth muscle actin elicited by transforming growth factor-β1 or local substrate stiffness was measured in normal human lung fibroblasts via quantitative reverse transcription PCR, ELISA and immunofluorescence. Small molecule cGAS inhibition was tested in cultured fibroblasts, human precision-cut lung slices and the bleomycin pulmonary fibrosis model. Results SSc-ILD lung tissue and bronchoalveolar lavage fluid were enriched for cGAS, cytokines and type 1 interferons. The cGAS pathway showed constitutive activation in SSc-ILD fibroblasts and was inducible in normal human lung fibroblasts by transforming growth factor-β1 or mechanical stimuli. In these settings, and in precision-cut lung slices, cGAS expression was paralleled by the production of cytokines, type 1 interferons and α-smooth muscle actin, which was mitigated by a small molecule cGAS inhibitor. These findings were recapitulated in the bleomycin mouse model. Conclusion cGAS signalling contributes to pathogenic inflammatory myofibroblast phenotypes in SSc‑ILD. Inhibiting cGAS or its downstream effectors represents a novel therapeutic approach.