Nuclear background determines biochemical phenotype in the deafness-associated mitochondrial 12S rRNA mutation

TLDR

The study aimed to investigate the pathogenic mechanism of the A1555G mitochondrial 12S rRNA mutation associated with non‑syndromic and aminoglycoside‑induced deafness. The authors generated 33 transmitochondrial cybrids by transferring mitochondria from patient lymphoblastoid cells into mtDNA‑less ρ°206 cells to isolate the effect of the mutation in a uniform nuclear background. In the uniform nuclear background, transformants from both symptomatic and asymptomatic carriers showed similar reductions in growth on galactose, mitochondrial protein synthesis, and respiration, whereas the original lymphoblastoid lines displayed marked differences, indicating that nuclear background determines the phenotypic manifestation of the A1555G mutation.

Abstract

The pathogenetic mechanism of the human mitochondrial 12S rRNA gene mutation at position 1555, associated with non-syndromic deafness and aminoglycoside-induced deafness, has been investigated in 33 transformants obtained by transferring mitochondria from lymphoblastoid cell lines into human mitochondrial DNA (mtDNA)-less (ρ°206) cells. In this nearly constant nuclear background, 15 transformants derived from five symptomatic individuals from a large Arab-Israeli family, carrying this mutation in homoplasmic form, exhibited significant decreases compared with nine control transformants in the rate of growth in a medium containing galactose instead of glucose, as well as in the rates of mitochondrial protein synthesis and of substrate-dependent respiration. Most significantly, these decreases were very similar to those observed in nine transformants derived from three asymptomatic members of the family. This result in transmitochondrial cybrids is in contrast to the differences in the same parameters previously demonstrated between the original lymphoblastoid cell lines derived from the symptomatic and asymptomatic members of the Arab-Israeli family. In addition, the intragroup variability in biochemical dysfunction among the lymphoblastoid cell lines from different symptomatic or asymptomatic or control individuals was significantly reduced in the derived mitochondrial transformants carrying the same nuclear background. These observations provide strong genetic and biochemical evidence in support of the idea that the nuclear background plays a determinant role in the phenotypic manifestation of the non-syndromic deafness associated with the A1555G mutation.