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Isoleucyl-tRNA synthetase levels modulate the penetrance of a homoplasmic m.4277T > C mitochondrial tRNA(Ile) mutation causing hypertrophic cardiomyopathy

Lookup NU author(s): Dr Helen Tuppen, Dr Arianna Montanari, Martina Leopizzi, Professor Robert Taylor


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The genetic and epigenetic factors underlying the variable penetrance of homoplasmic mitochondrial DNA mutations are poorly understood. We investigated a 16-year-old patient with hypertrophic cardiomyopathy harboring a homoplasmic m.4277T>C mutation in the mt-tRNA(Ile) (MTTI) gene. Skeletal muscle showed multiple respiratory chain enzyme abnormalities and a decreased steady-state level of the mutated mt-tRNA(Ile). Transmitochondrial cybrids grown on galactose medium demonstrated a functional effect of this mutation on cell viability, confirming pathogenicity. These findings were reproduced in transmitochondrial cybrids, harboring a previously described homoplasmic m.4300A>G MTTI mutation. The pathogenic role of the m.4277T>C mutation may be ascribed to misfolding of the mt-tRNA molecule, as demonstrated by the altered electrophoretic migration of the mutated mt-tRNA. Indeed, structure and sequence analyses suggest that thymidine at position 4277 of mt-tRNA(Ile) is involved in a conserved tertiary interaction with thymidine at position 4306. Interestingly, the mutation showed variable penetrance within family members, with skeletal muscle from the patient's clinically unaffected mother demonstrating normal muscle respiratory chain activities and steady-state levels of mt-tRNA(Ile), while homoplasmic for the m.4277T>C mutation. Analysis of mitochondrial isoleucyl-tRNA synthetase revealed significantly higher expression levels in skeletal muscle and fibroblasts of the unaffected mother when compared with the proband, while the transient over-expression of the IARS2 gene in patient transmitochondrial cybrids improved cell viability. This is the first observation that constitutively high levels of aminoacyl-tRNA synthetases (aaRSs) in human tissues prevent the phenotypic expression of a homoplasmic mt-tRNA point mutation. These findings extend previous observations on aaRSs therapeutic effects in yeast and human.

Publication metadata

Author(s): Perli E, Giordano C, Tuppen HAL, Montopoli M, Montanari A, Orlandi M, Pisano A, Catanzaro D, Caparrotta L, Musumeci B, Autore C, Morea V, Di Micco P, Campese AF, Leopizzi M, Gallo P, Francisci S, Frontali L, Taylor RW, d'Amati G

Publication type: Article

Publication status: Published

Journal: Human Molecular Genetics

Year: 2012

Volume: 21

Issue: 1

Pages: 85-100

Print publication date: 26/09/2011

ISSN (print): 0964-6906

ISSN (electronic): 1460-2083

Publisher: Oxford University Press


DOI: 10.1093/hmg/ddr440


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Funder referenceFunder name
Associazione Serena Talarico per i Giovani nel Mondo
UK NHS Specialised Services
074454/Z/04/ZWellcome Trust
C26A1089SWFondazione Giuseppe Tomasello Onlus, Sapienza University of Rome