Preliminary Study of the Mechanism of Non-Syndromic Hearing Loss Carrying Mitochondrial tRNA^Thr 15943T>C and 12S rRNA 1555A>G Mutations

This study aims to explore the relationship between mitochondrial tRNA^Thr 15943T>C and 12S rRNA 1555A>G mutations and non-syndromic hearing loss, and the molecular mechanism of mitochondrial mutations in deafness. Immortalized lymphoblastic cell lines carrying mitochondrial tRNA^Thr 15943T>C and 12S rRNA 1555A>G mutations (double mutation group), the same haplotype (R9) with only 12S rRNA 1555A>G mutation (single mutation group), and a normal control group were established. Analysis of the clinical data of this family showed that when the family members of the drug-induced deafness using AmAn (aminoglycoside antibiotic) were included, the penetrance rate of deafness in this family was 26.3%; when the deaf members who used the medicine were excluded, the penetrance rate of deafness was 10%; in contrast, in the reported 14 deaf families with m.1555A>G, the average penetrance rates were only 13% and 6% separately in the treated and untreated conditions. Northern blot and Western blot separately were used to detect the expression of mitochondrial tRNA and polypeptide. Compared with the normal control group, the steady-state level of tRNA^Thr was significantly lower in the double-mutation group, but there was no significant change in the single-mutation group. Meanwhile, there was no significant difference in the steady-state level of other tRNAs in the three groups. The expression of CO2, CO3, and A6 in the double-mutation group was significantly reduced, but their expression had no significant difference in the single-mutation group. The expression levels of other protein polypeptides had no significant difference in the three groups. The m.15943T>C mutation reduces the steady-state level of tRNA^Thr. It results in a decrease in the expression of some mitochondrial polypeptides, which affects the function and stability of the mitochondrial respiratory chain complex. Eventually, it leads to mitochondrial metabolism disorders, suggesting that mitochondrial tRNA^Thr 15943T>C may be related to the deafness with m.1555A>G.

CSTR: 32200.14.cjcb.2021.08.0008