Project description:Mitochondria are arising as critical modulators of antiviral tolerance by releasing mtDNA/mtRNA fragments to cytoplasm upon infection, activating virus sensors and type-I interferon response. The relevance of these mechanisms for mitochondrial diseases remains understudied. Here, we investigated mitochondrial recessive ataxia syndrome (MIRAS), caused by a common European founder mutation in DNA polymerase gamma (POLG1). The patients homozygous for the MIRAS variant p.W748S show exceptionally variable ages-of-onset and symptoms, indicating unknown modifying factors contributing to disease manifestation. We report that the mitochondrial DNA (mtDNA) replicase POLG1 has a role in antiviral defence mechanisms to double-stranded DNA and positive-strand RNA virus infections (HSV-1, TBEV, SARS-CoV-2) and its p.W748S variant dampens innate immune responses. Our patient and knock-in mouse data show that p.W748S compromises mtDNA replisome stability, causing mtDNA depletion, aggravated by virus infection. Low mtDNA and mtRNA release to cytoplasm and slow interferon response in MIRAS allow an early replicative advantage for viruses, leading to augmented pro-inflammatory response, subacute loss of GABAergic neurons, liver inflammation and necrosis. A population databank of ~300,000 Finns demonstrates enrichment of immunodeficient traits in p.W748S carriers. Our evidence suggests that POLG1 defects compromise antiviral tolerance, triggering epilepsy and liver disease. The finding has important implications to mitochondrial disease spectrum, including epilepsy, ataxia, and parkinsonism. In this metabolomic dataset: To investigate the in vivo response of MIRAS to viral infection, we generated a MIRAS-knock-in mouse model and subjected the mice to TBEV infection. These animals carry a homozygous knock-in mutation and the accompanying polymorphic variant homologous to the human ancestral MIRAS allele (p.W726S+E1121G in mice and p.W748S+E1143G in humans). We performed metabolomic analyses on the mouse brain (cerebral cortex) isolated from the control (wildtype) and MIRAS mice at 4 days post TBEV infection (n=5 mice per condition).

Project description:The goal of this analysis was to utilize microarray profiling to identify basal alterations in gene expression in response to TFAM depletion and mtDNA stress. Mitochondrial DNA (mtDNA) is normally present at thousands of copies per cell and is packaged into several hundred higher-order structures termed nucleoids. The abundant mtDNA-binding protein, TFAM (transcription factor A,mitochondrial), regulates nucleoid architecture, abundance and segregation. Complete mtDNA depletion profoundly impairs oxidative phosphorylation, triggering calcium-dependent stress signalling and adaptive metabolic responses. However, the cellular responses to mtDNA instability, a physiologically relevant stress observed in many human diseases and ageing, remain poorly defined. 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 signaling and suggest that cellular monitoring of mtDNA homeostasis cooperates with canonical virus sensing mechanisms to fully engage antiviral innate immunity. Murine embryonic fibroblasts were isolated from wild-type or Tfam+/- E13.5 littermate embryos. RNA from passage-matched wild-type and Tfam+/- MEF lines was extracted in duplicate and hybridized onto Affymetrix microarrays. Four arrays were performed in total with two technical replicates per genotype.

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Ancestral allele of DNA polymerase gamma modifies antiviral tolerance

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