Nucleic acids from bacteria or viruses induce potent immune responses in infected cells1–4. The detection of pathogen-derived nucleic acids is a central strategy by which the host senses infection and initiates protective immune responses5,6. Cyclic GMP-AMP synthase (cGAS) is a double-stranded DNA sensor7,8. It catalyzes the synthesis of cyclic GMP-AMP (cGAMP)9–12, which stimulates the induction of type I interferons (IFN-Is) through the STING-TBK1-IRF-3 signaling axis13–15. Stimulator of interferon genes (STING) oligomerizes upon cGAMP binding, leading to the recruitment and activation of tank-binding kinase 1 (TBK1)8,16. Interferon regulatory factor 3 (IRF-3) is then recruited to the signaling complex and activated by TBK18,17–20. Phosphorylated IRF-3 translocates to the nucleus and initiates the expression of IFN-Is21. However, the precise mechanisms governing STING activation by cGAMP and subsequent TBK1 activation by STING remained poorly understood. Here we show that a conserved PLPLRT/SD motif within the C-terminal tail of STING mediates the recruitment and activation of TBK1. Crystal structures of TBK1 bound to STING reveal that the PLPLRT/SD motif binds to the dimer interface of TBK1. Cell-based studies confirm that the direct interaction between TBK1 and STING is essential for IFN-β induction upon cGAMP stimulation. Moreover, we show that full-length STING oligomerizes upon cGAMP binding and highlight this as an essential step in the activation of STING-mediated signaling.

Pathogen-derived nucleic acids induce potent innate immune responses 1 - 6 . Cyclic GMP-AMP synthase (cGAS) is a dsDNA sensor that catalyzes the synthesis of a cyclic dinucleotide cGAMP, which mediates the induction of type I interferons through the STING-TBK1-IRF3 signaling axis 7 - 11 . It was widely accepted that cGAS is not reactive to self-DNA due to its cytosolic localization 2 , 12 , 13 . However, recent studies revealed that cGAS is mostly localized in the nucleus and tight nuclear tethering keeps cGAS inactive 14 - 18 . Here we show that cGAS binds to nucleosomes with nanomolar affinity and nucleosome binding potently inhibits the catalytic activity of cGAS. To elucidate the molecular basis of cGAS inactivation by nuclear tethering, we have determined the structure of mouse cGAS bound to human nucleosome by cryo-EM. The structure shows that cGAS binds to a negatively charged acidic patch formed by histone H2A and H2B via its second DNA binding site 19 . High affinity nucleosome binding blocks dsDNA binding and keeps cGAS in an inactive conformation. Mutations of cGAS that disrupt nucleosome binding dramatically affect cGAS mediated signaling in cells.

Background:The mechanisms of transcriptional regulation of TNFRSF10A and TNFRSF10B are not well described. Results: DDIT3 and KAT2A cooperatively up-regulated TNFRSF10A and TNFRSF10B. Conclusion: DDIT3 and KAT2A promote the transcription of TNFRSF10A and TNFRSF10B via the AP-1 and DDIT3 binding sites, respectively. Significance: Our findings offer new insights on the mechanisms of ER stress-mediated apoptosis.

Mitochondrial dysfunction is a key driver of inflammatory responses in human disease. However, it remains unclear whether alterations in mitochondria-innate immune cross-talk contribute to the pathobiology of mitochondrial disorders and aging. Using the polymerase gamma (POLG) mutator model of mitochondrial DNA instability, we report that aberrant activation of the type I interferon (IFN-I) innate immune axis potentiates immunometabolic dysfunction, reduces health span, and accelerates aging in mutator mice. Mechanistically, elevated IFN-I signaling suppresses activation of nuclear factor erythroid 2–related factor 2 (NRF2), which increases oxidative stress, enhances proinflammatory cytokine responses, and accelerates metabolic dysfunction. Ablation of IFN-I signaling attenuates hyperinflammatory phenotypes by restoring NRF2 activity and reducing aerobic glycolysis, which combine to lessen cardiovascular and myeloid dysfunction in aged mutator mice. These findings further advance our knowledge of how mitochondrial dysfunction shapes innate immune responses and provide a framework for understanding mitochondria-driven immunopathology in POLG-related disorders and aging.

Caseinolytic mitochondrial matrix peptidase proteolytic subunit, CLPP, is a serine protease that degrades damaged or misfolded mitochondrial proteins. CLPP null mice exhibit growth retardation, deafness, and sterility, resembling human Perrault syndrome (PS), but also display immune system alterations. However, the molecular mechanisms and signaling pathways underlying immunological changes in CLPP null mice remain unclear. Here we report the steady state activation of type I interferon (IFN-I) signaling and antiviral gene expression in CLPP deficient cells and tissues. Depletion of the cyclic GMP-AMP (cGAS)-Stimulator of Interferon 1

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The age of incidence of spinal cord injury (SCI) and the average age of people living with SCI is continuously increasing. However, SCI is extensively modeled in young adult animals, hampering translation of research to clinical applications. While there has been significant progress in manipulating axon growth after injury, the impact of aging is still unknown. Mitochondria are essential to successful neurite and axon growth, while aging is associated with a decline in mitochondrial functions. Using isolation and culture of adult cortical neurons, we analyzed mitochondrial changes in 2-, 6-, 12- and 18-month-old mice. We observed reduced neurite growth in older neurons. Older neurons also showed dysfunctional respiration, reduced membrane potential, and altered mitochondrial membrane transport proteins; however, mitochondrial DNA (mtDNA) abundance and cellular ATP were increased. Taken together, these data suggest that dysfunctional mitochondria in older neurons may be associated with the age-dependent reduction in neurite growth. Both normal aging and traumatic injury are associated with mitochondrial dysfunction, posing a challenge for an aging SCI population as the two elements can combine to worsen injury outcomes. The results of this study highlight this as an area of great interest in CNS trauma.

Human RNF213, which encodes the protein mysterin, is a known susceptibility gene for moyamoya disease (MMD), a cerebrovascular condition with occlusive lesions and compensatory angiogenesis. Mysterin mutations, together with exposure to environmental trigger factors, lead to an elevated stroke risk since childhood. Mysterin is induced during cell stress, to function as cytosolic AAA+ ATPase and ubiquitylation enzyme. Little knowledge exists, in which context mysterin is needed. Here, we found that genetic ablation of several mitochondrial matrix factors, such as the peptidase ClpP, the transcription factor Tfam, as well as the peptidase and AAA+ ATPase Lonp1, potently induces Rnf213 transcript expression in various organs, in parallel with other components of the innate immune system. Mostly in mouse fibroblasts and human endothelial cells, the Rnf213 levels showed prominent upregulation upon Poly(I:C)-triggered TLR3-mediated responses to dsRNA toxicity, as well as upon interferon gamma treatment. Only partial suppression of Rnf213 induction was achieved by C16 as an antagonist of PKR (dsRNA-dependent protein kinase). Since dysfunctional mitochondria were recently reported to release immune-stimulatory dsRNA into the cytosol, our results suggest that mysterin becomes relevant when mitochondrial dysfunction or infections have triggered RNA-dependent inflammation. Thus, MMD has similarities with vasculopathies that involve altered nucleotide processing, such as Aicardi-Goutières syndrome or systemic lupus erythematosus. Furthermore, in MMD, the low penetrance of RNF213 mutations might be modified by dysfunctions in mitochondria or the TLR3 pathway.