Molecular pathogenesis and gene therapy-based intervention of GTPBP3-related mitochondrial disease

Mitochondrial transfer RNA (mt-tRNA) modification determines organelle translation and function. GTPBP3 and MTO1 catalyze 5-taurinomethyluridine (τm5U) modification at wobble uridine of five mt-tRNAs. τm5U hypomodification causes mitochondrial encephalomyopathy, but the underlying pathogenesis and intervention strategy due to GTPBP3 mutations are lacking. In this study, we identify two genetic variants (c.689 A > C (p.Q230P) and c.1120 A > G (p.N374D)) of GTPBP3 in a Chinese proband with metabolic disorders and multisystem dysfunction. Mechanistically, Q230P and N374D mutations induce protein multimerization/aggregation, protease degradation, decreased GTPase activity, and tRNA modification to varying degrees, affecting mitochondrial translation, respiration, dynamics, and function. Homozygous N374D mutations in mice cause embryonic lethality; homozygous E230P or compound heterozygous E230P/N374D knock-in mice develop cardiac and muscular dysfunction due to altered mitochondrial translation. Mitochondrial dysfunction and pathology are efficiently reversed by virus-mediated GTPBP3 expression in cells and animals. This study provides valuable insights into the etiology of and promising intervention strategies for GTPBP3-related diseases. The manuscript describes two pathogenic mutations in GTPBP3 that cause defects in mitochondrial tRNA taurine modification, mitochondrial translation, structure and function. Mutant mice reproduce certain clinical features seen in patients and this can be reversed by virus-mediated exogenous expression of Gtpbp3.