title: Isoleucyl-tRNA synthetase levels modulate the penetrance of a homoplasmic m.4277T>C mitochondrial tRNA(Ile) mutation causing hypertrophic cardiomyopathy.
abstract: 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.
authors.affiliation: Department of Internal Medicine and Medical Specialities, Sapienza University of Rome, 00161 Roma, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Perli
authors.forename: Carla
authors.initials: C
authors.lastname: Giordano
authors.forename: Helen A L
authors.initials: HA
authors.lastname: Tuppen
authors.forename: Monica
authors.initials: M
authors.lastname: Montopoli
authors.forename: Arianna
authors.initials: A
authors.lastname: Montanari
authors.forename: Maurizia
authors.initials: M
authors.lastname: Orlandi
authors.forename: Annalinda
authors.initials: A
authors.lastname: Pisano
authors.forename: Daniela
authors.initials: D
authors.lastname: Catanzaro
authors.forename: Laura
authors.initials: L
authors.lastname: Caparrotta
authors.forename: Beatrice
authors.initials: B
authors.lastname: Musumeci
authors.forename: Camillo
authors.initials: C
authors.lastname: Autore
authors.forename: Veronica
authors.initials: V
authors.lastname: Morea
authors.forename: Patrizio
authors.initials: P
authors.lastname: Di Micco
authors.forename: Antonio F
authors.initials: AF
authors.lastname: Campese
authors.forename: Martina
authors.initials: M
authors.lastname: Leopizzi
authors.forename: Pietro
authors.initials: P
authors.lastname: Gallo
authors.forename: Silvia
authors.initials: S
authors.lastname: Francisci
authors.forename: Laura
authors.initials: L
authors.lastname: Frontali
authors.forename: Robert W
authors.initials: RW
authors.lastname: Taylor
authors.forename: Giulia
authors.initials: G
authors.lastname: d'Amati
mesh_terms: D000293:Adolescent; D001483:Base Sequence; D002312:Cardiomyopathy, Hypertrophic / Q000201:enzymology* / Q000235:genetics*; D004272:DNA, Mitochondrial / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007533:Isoleucine-tRNA Ligase / Q000235:genetics / Q000378:metabolism*; D008297:Male; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D019683:Penetrance; D017354:Point Mutation; D012355:RNA, Transfer, Ile / Q000235:genetics* / Q000378:metabolism
chemical_list: D004272:DNA, Mitochondrial; D012355:RNA, Transfer, Ile; D007533:Isoleucine-tRNA Ligase