Deoxyguanosine Kinase Deficiency Couples Purine Metabolism to Innate Immune Activation and Lipid Accumulation in Hepatocytes 2309176

Abstract

Abstract Introduction Mitochondrial DNA depletion syndromes (MDS) are fatal pediatric disorders with few treatment options. Deoxyguanosine kinase (DGUOK), a mitochondrial nucleoside salvage enzyme, is classically linked to impaired mtDNA replication. However, patients with DGUOK deficiency can develop hepatic inflammation and steatosis despite intact mtDNA, suggesting additional pathogenic mechanisms. As DGUOK regulates intracellular deoxyadenosine (dAdo) levels, we hypothesized that DGUOK deficiency initiates a purine-driven immunometabolic program contributing to liver pathology. Methods DGUOK was acutely depleted in human hepatocytes using siRNA to model early disease states prior to mtDNA loss. Innate immune activation and metabolic remodeling were assessed by RNA sequencing, hERV analysis, and RT-qPCR. Lipid accumulation was quantified by BODIPY and Oil Red O staining, flow cytometry, and electron microscopy. Global DNA methylation was measured by 5-mC ELISA, and purine imbalance was modeled by exogenous dAdo supplementation. Results Early DGUOK depletion preserved mtDNA copy number but induced robust type I interferon signaling, ISG expression, and hERV derepression. Transcriptomic analysis revealed suppression of lipid metabolic pathways alongside enrichment of purine and methylation-associated networks. DGUOK-deficient hepatocytes accumulated neutral lipid droplets prior to mitochondrial dysfunction, a phenotype recapitulated by dAdo treatment in wild-type cells and associated with global DNA hypomethylation. These immunometabolic signatures parallel interferon activation and steatosis in DGUOK deficient mice. Conclusion These data support a model in which DGUOK deficiency first triggers a purine-epigenetic axis that drives innate immune activation and lipid dysregulation, preceding mtDNA depletion. This framework links early hepatocyte dysfunction to inflammatory liver pathology in DGUOK-deficient mice, identifying purine metabolism and downstream interferon signaling as tractable preclinical targets in MDS. Funding Source This work was supported by philanthropic and institutional funding from the Kyowa Kirin Interactive Fund (award no. 18040-01-403), the National Institutes of Health grant R01 CA256133 (award no. 20071-04-403), and the University of California San Diego gr Topic Categories Innate Immune Responses and Host Defense: Molecular Mechanisms (INM)