The DNA sensor, cyclic GMP-AMP synthase (cGAS) is essential for induction of IFN beta during Chlamydia trachoma tis infection (INM6P.407)

IFNβ has been implicated as an effector of oviduct pathology resulting from genital Chlamydia infection in the mouse model. In this study, we investigated the role of cytosolic DNA and engagement of DNA sensors in IFNβ expression during Chlamydia infection. Using siRNA technique and gene knock out fibroblasts, we determined that TREX-1, a host 3’exonuclease reduced IFNβ expression significantly during Chlamydia infection, implicating cytosolic DNA as a ligand for this response. STING is a signaling adaptor required for IFNβ expression and the DNA sensor, cGAS binds cytosolic DNA to generate the STING ligand cGAMP. We establish that cGAS is required for IFNβ expression during Chlamydia infection in multiple cell types. Infected cells knocked down for STING or cGAS alone failed to induce IFNβ. Interestingly, IFNβ expression was rescued by co-culture of cells depleted for either STING or cGAS suggesting that cGAMP produced in cGAS+STING- cells migrated to adjacent cells via gap junctions to bind to STING in cGAS-STING+ cells. Further, cGAS was localized in punctate regions on the cytosolic side of the chlamydial inclusion membrane, indicating that chlamydial DNA is likely sensed outside the inclusion as infection progresses. These novel data provides evidence that cGAS-mediated-DNA sensing directs IFNβ expression during C.trachomatis infection and suggest that uninfected cells adjacent to infected cells can also induce IFNβ during in vivo infection, leading to oviduct pathology.