(The) role of mitochondria in STING-mediated type I IFN producing pathway

Abstract

The stimulator of interferon genes (STING)-mediated DNA sensing pathway plays an important role in the innate immune response to pathogen infection, autoimmunity, and cancer. However, its regulatory mechanism has not been fully elucidated, and I do not yet know whether the STING pathway is cross-regulated by other innate immune pathways. In this study, I present evidence that the mitochondria and the mitochondria-associated ER membrane (MAM) contribute to regulating the activation of the STING signaling pathway. More specifically, I found that the mitochondrial protonophore, carbonyl cyanide 3-chlorophenylhydrazone (CCCP), inhibited the activation of STING and its downstream signaling molecules, TBK1 and IRF3, which is coupled to DRP1-mediated mitochondrial fission. In addition, I found that deficiency of mitofusin (MFN) 1, a mitochondrial fusion regulator, inhibited STING pathway activation, thus phenocopying the effect of CCCP. Importantly, the NLRP3-activating agonists, ATP and nigericin, also induced mitochondrial fission and prevented STING pathway activation. Although this fission was dependent on DRP1 and TBC1D15, only knockdown of TBC1D15 could suppress NLRP3-agonist-induced inhibition of the STING pathway. Moreover, I show that paradoxically, both BAPTA-AM-mediated calcium depletion and ionomycin-induced elevation of intracellular calcium level suppressed the translocation of STING and STING-mediated IFN-β production. I demonstrated that the mitochondria fission mediator DRP1 is crucial for ionomycin-induced inhibition of IFN-β production. I found that knockout of DRP1 suppressed ionomycin-induced calcium rise as well as mitochondrial dynamics Finally, I found that knockout of the crucial MAM formation regulator MITOL inhibits STING-mediated IFN-β production, and activation of the IRF3 at the MAM. Collectively, my findings reveal that mitochondrial and MAM are crucial for the competency of the STING pathway, and that inflammasome-activating signals curtail STING pathway activation by disrupting mitochondrial dynamics.