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Deoxyguanosine Kinase Deficiency Couples Purine Metabolism to Innate Immune Activation and Lipid Accumulation in Hepatocytes

ABSTRACT: Mitochondrial DNA depletion syndromes (MDS) encompass a heterogeneous set of metabolic disorders caused by defects in enzymes responsible for maintaining mitochondrial nucleotide pools and genome integrity. Among these, deoxyguanosine kinase (DGUOK) acts within the mitochondrial purine-salvage pathway and loss-of-function mutations give rise to DGUOK deficiency, a severe hepatocerebral form of MDS marked by liver failure, neurodevelopmental impairment, and systemic metabolic inflammation. Although the clinical manifestations of DGUOK deficiency have been primarily ascribed to defective mitochondrial DNA (mtDNA) replication, some patients exhibit hepatic steatosis and inflammation despite preserved mtDNA content, suggesting that DGUOK deficiency may deregulate additional metabolic and immune pathways. Here we show that DGUOK depletion reprograms hepatocellular metabolism and innate immune signaling through a purine-dependent mechanism operating independently of mtDNA depletion. In Human hepatocellular carcinoma (HEPG2) hepatocytes subjected to siRNA-mediated DGUOK silencing, mitochondrial architecture and respiration remained intact but cells exhibited pronounced lipid droplet accumulation and a robust cell-intrinsic innate immune type I interferon response. Bulk RNA sequencing revealed widespread transcriptional reprogramming, including upregulation of human endogenous retroviruses (HERVs) and interferon-stimulated genes (ISGs), suppression of lipid metabolic pathways, and changes in purine, methionine, and methylation-associated gene networks. Perturbing purine homeostasis through deoxyadenosine (dAdo) supplementation in wild-type cells phenocopied DGUOK disruption, causing cellular DNA hypomethylation and activation of viral mimicry pathways. Together, these findings identify DGUOK as a central regulator of the purine-regulated lipid-immune axis in hepatocytes, demonstrating that mitochondrial nucleotide salvage preserves hepatic immune and metabolic homeostasis beyond its canonical role in mtDNA synthesis. By linking purine imbalances to steatosis and type I interferon activation, this study establishes a mechanistic framework for immunometabolic pathology in DGUOK deficiency.

ORGANISM(S): Homo sapiens

PROVIDER: GSE309813 | GEO | 2025/11/18

REPOSITORIES: GEO

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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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Deoxyguanosine Kinase Deficiency Couples Purine Metabolism to Innate Immune Activation and Lipid Accumulation in Hepatocytes

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