Queuine ameliorates impaired mitochondrial function caused by mt-tRNAAsn variants

Background Mitochondrial tRNA (mt-tRNA) variants have been found to cause disease. Post-transcriptional queuosine (Q) modifications of mt-tRNA can promote efficient mitochondrial mRNA translation. Q modifications of mt-tRNA.sup.Asn have recently been identified. Here, the therapeutic effectiveness of queuine was investigated in cells from patients with mt-tRNA.sup.Asn variants. Methods Six patients (from four families) carrying mt-tRNA.sup.Asn variants were included in the study. Queuine levels were quantified by mass spectrometry. Clinical, genetic, histochemical, biochemical, and molecular analysis was performed on muscle tissues and lymphoblastoid cell lines (LCLs) from patients to investigate the pathogenicity of the novel m.5708 C > T variant. The use of queuine in mitigating mitochondrial dysfunction resulting from the mt-tRNA.sup.Asn variants was evaluated. Results The variants included the m.5701 delA, m.5708 C > T, m.5709 C > T, and m.5698 G > A variants in mt-tRNA.sup.Asn. The pathogenicity of the novel m.5708 C > T variant was confirmed, as demonstrated by a decreased steady-state level of mt-tRNA.sup.Asn, mtDNA-encoded protein levels, oxygen consumption rate (OCR), and the respiratory complex activity. Notably, the serum queuine level was significantly reduced in these patients and in vitro queuine supplementation was found to restore the reductions in mitochondrial protein activities, mitochondrial membrane potential, OCR, and increases in reactive oxygen species. Conclusions The study not only confirmed the pathogenicity of the m.5708 C > T variant but also explored the therapeutic potential of queuine in individuals with mt-tRNA.sup.Asn variants. The recognition of the novel m.5708 C > T variant's pathogenic nature contributes to our comprehension of mitochondrial disorders. Furthermore, the results emphasize queuine supplementation as a promising approach to enhance the stability of mt-tRNA.sup.Asn and rescue mitochondrial dysfunction caused by mt-tRNA.sup.Asn variants, indicating potential implications for the development of targeted therapies for patients with mt-tRNA.sup.Asn variants. Keywords: Mitochondrial disease, mt-tRNA.sup.Asn, m.5708C > T, Queuine, Therapy