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.