Mitochondrial DNA stress primes the antiviral innate immune response

Mitochondrial DNA stress potentiates type I interferon responses via activation of the cGAS–STING–IRF3 pathway. Accumulating evidence suggests that mitochondria, the organelles primarily responsible for cellular respiration and energy production, are also critical centres for antibacterial and antiviral innate immune responses. This study describes a link between mitochondrial stress and antiviral innate immunity. Specifically, mitochondrial DNA stress in herpes virus infected mice is shown to elevate interferon-stimulated gene expression, potentiate type I interferon responses and confer broad viral resistance through activation of the DNA sensor cGAS and the STING–IRF3 stress pathway. Mitochondrial DNA (mtDNA) is normally present at thousands of copies per cell and is packaged into several hundred higher-order structures termed nucleoids1. The abundant mtDNA-binding protein TFAM (transcription factor A, mitochondrial) regulates nucleoid architecture, abundance and segregation2. Complete mtDNA depletion profoundly impairs oxidative phosphorylation, triggering calcium-dependent stress signalling and adaptive metabolic responses3. However, the cellular responses to mtDNA instability, a physiologically relevant stress observed in many human diseases and ageing, remain poorly defined4. Here we show that moderate mtDNA stress elicited by TFAM deficiency engages cytosolic antiviral signalling to enhance the expression of a subset of interferon-stimulated genes. Mechanistically, we find that aberrant mtDNA packaging promotes escape of mtDNA into the cytosol, where it engages the DNA sensor cGAS (also known as MB21D1) and promotes STING (also known as TMEM173)–IRF3-dependent signalling to elevate interferon-stimulated gene expression, potentiate type I interferon responses and confer broad viral resistance. Furthermore, we demonstrate that herpesviruses induce mtDNA stress, which enhances antiviral signalling and type I interferon responses during infection. Our results further demonstrate that mitochondria are central participants in innate immunity, identify mtDNA stress as a cell-intrinsic trigger of antiviral signalling and suggest that cellular monitoring of mtDNA homeostasis cooperates with canonical virus sensing mechanisms to fully engage antiviral innate immunity.