Borrelia Burgdorferi mediated mitochondrial DNA release into the cytosol induces host inflammatory response via the activation of cGAS-STING signaling pathway

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Abstract Background: Mitochondrial DNA (mtDNA) is a potent ligand of inflammation when it leaks from stressed mt into the host cytosol during bacterial infections. In this study, we uncover mtDNA as one of the ligands involved in inflammatory response against B. burgdorferi (Bb) infection via the activation of cGAS-STING signaling pathway in Raw264.7 cells. Methods: Raw264.7 cells were infected with Bb & the mt stress was studied by measuring mt reactive oxygen species (mtROS) using MitoSOX dye & mt membrane potential (MMP) by JC-1 dye staining. The release of mtDNA was assessed by Immunofluorescence assay & q-RT-PCR. The co-localization of mtDNA & cGAS was determined by IP assay. To explore the requirement of mtDNA for Bb-induced inflammation, both WT & cGAS-KO cells were treated with Ethidium bromide (EtBr) to deplete the mtDNA & ELISA was done to detect the level of inflammatory cytokines. Results:Bb infection to Raw264.7 cells caused mt stress, that results in decrease of MMP, enhanced mtROS & promoted mtDNA leakage into the cytosol. Leaked mtDNA activates cGAS-STING signaling pathway & results in inflammation. Both stable knockdown of cGAS & depletion of mtDNA reduced Bb induced inflammation. Conclusions: We uncover a novel mechanism of Bb induced inflammation, which involved mtDNA leakage from stressed mt into the cytosol stimulating the cGAS-STING signaling pathway. The mtDNA-cGAS-STING pathway could be a therapeutic target to prevent Bb induced inflammatory disease.