INTRODUCTION: The cGAS-STING pathway plays a major role in aberrant immune responses following recognition of cytosolic DNA seen it many diseases such as Parkinson’s disease, Myocardial infarction or Systemic Lupus. Critically, this pathway can be amplified through formation of direct cell: cell interactions, known as gap junctions. Naturally occurring flavonoid compounds have been suggested to impact the activity of gap junction, but whether this can alter propagation of cGAS-STING signalling is not known.
METHODS: Here we used in vitro co-culture methods to assess the activity of a small set of flavonoid compounds on the propagation of cyclic GMP-AMP, the product of cGAS, between cells forming gap junctions. Since cGAMP directly binds to activate STING, we also studied the effect of flavonoids on STING downstream signalling, in human and murine cell models.
RESULTS: In co-cultures of cGAMP donor cells with STING expressing recipient cells, Genistein was the only flavonoid tested to decrease adjacent cell transactivation. This effect was concurrent with a decreased gap junction intercellular communication. Critically, Genistein pre-treatment of STING expressing recipient cells abolished cellular transactivation, indicating a direct effect on STING signalling. Accordingly, Genistein significantly decreased STING signalling upon activation by its agonists in human and murine cell models. Short pre-treatment with Genistein impacted STING phosphorylation, along with that of IRF3 and IKKe, demonstrating a direct effect on STING signalling. These findings establish a converging inhibitory activity of Genistein on cGAS-STING signalling, acting on preventing cGAMP transfer between adjacent cells, and preventing STING activation.
CONCLUSION: Collectively these findings indicate that select flavonoid compounds may present novel therapeutic opportunities to inhibit the cGAS-STING pathway involved in a growing number of auto-inflammatory diseases.