Abstract Background Factors contributing to non-response to targeted immune therapies for IBD are not well understood. Activation of cGAS-STING in macrophages culminates in the release of vast amounts of interferon (IFN) and chemokines and likely negatively impacts responsiveness to therapy. Evidence shows that IFN responses are heightened in myeloid cells of non-responders to anti-TNF therapy for Ulcerative colitis1. Furthermore, ablation of STING has been encouraging at relieving inflammation in mouse models of IBD2. We aimed to quantify markers of cGAS-STING driven inflammation in responder and non-responder IBD cohorts and explore pharmacological and microbiome-driven influence on these using in-vitro models. Methods IBD patient cohorts were stratified by response (n = 20) and non-response (n = 20) to targeted immune therapies—and plasma proteomic analysis was conducted to search for markers of cGAS-STING activation. Using an in-vitro monocyte-derived macrophage (MDM) model, cells were delivered with STING agonists 2’3’cGAMP (3μg/ml) or dsDNA (1μg/ml). STING-driven responses were assessed following treatments with butyrate (1mM), a pan-histone deacetylase (HDAC) inhibitor SAHA (1μM) or a specific inhibitor of HDAC3 RGFP966 (10μM). Phosphorylation of critical cGAS-STING signalling proteins Tank-binding Kinase 1 (TBK1) and Interferon Regulatory Factor 3 (IRF3) were monitored by Western Blot. Interferon and chemokine responses were assessed using RT-PCR and ELISA. Results Proteomic analysis revealed strong trends of heightened plasma levels of IFN-β (p = 0.123), TBK1 (p = 0.355) and IRF3 (p = 0.053) in non-responders. Intracellular delivery of either 2’3’cGAMP or dsDNA into macrophages led to sharp upregulation in expression of IFN-β1 and CXCL10 in MDMs— an effect that was repressed by butyrate exposure. Likewise, butyrate limited supernatant levels IFN-β and CXCL10. To further dissect this mechanism of butyrate-mediated suppression, macrophages were pre-treated with pan-HDAC inhibitor SAHA or RGFP966. SAHA strongly mirrored responses mediated by butyrate, shown by suppressed secretion of IFN-β and CXCL10—pointing toward a shared mechanism between these by inhibition of specific signalling pathways. Conclusion cGAS-STING activation can be detrimental during chronic inflammation, and we have identified markers of this pathway in IBD non-responders. In-vitro models of cGAS-STING show muted IFN and chemokine secretion in the presence of microbiome-derived butyrate—likely though a HDAC-mediated mechanism. Together, these findings highlight cGAS-STING as a target for therapeutic modulation, especially mediated by butyrate —and suggest microbial metabolites could be a complementary strategy for reducing inflammation in treatment-refractory patients. References: 1.Thomas T, Friedrich M, Rich-Griffin C, et al. A longitudinal single-cell atlas of anti-tumour necrosis factor treatment in inflammatory bowel disease. Nature Immunology. Published online 2024:1-14. 2.Xu S, Peng Y, Yang K, et al. PROTAC based STING degrader attenuates acute colitis by inhibiting macrophage M1 polarization and intestinal epithelial cells pyroptosis mediated by STING-NLRP3 axis. International Immunopharmacology. 2024;141:112990. Conflict of interest: Mr. O Mahony, Cian: No conflict of interest Toman, Jan: No conflict of interest Deery, Alan: No conflict of interest Ghosh, Subrata: No conflict of interest Amamou, Asma: No conflict of interest
Mahony et al. (Thu,) studied this question.