Molecular characterization of mitochondrial transferRNAGln and transferRNAMet A4401G mutations in a Chinese family with hypertension

Maternally Inherited Essential Hypertension May Be Associated with the Mutations in Mitochondrial tRNAGlu Gene

Background

Mitochondrial DNA (mtDNA) mutations are associated with essential hypertension (EH), but the molecular mechanism remains largely unknown.

Objective

The aim of this study is to explore the association between mtDNA mutations and EH.

Methods

Two maternally inherited families with EH are underwent clinical, genetic and biochemical assessments. mtDNA mutations are screened by PCR-Sanger sequencing and phylogenetic, and bioinformatics analyses are performed to evaluate the pathogenicity of mtDNA mutations. We also generate cytoplasmic hybrid (cybrid) cell lines to analysis mitochondrial functions.

Results

Matrilineal relatives exhibit variable degree of clinical phenotypes. Molecular analysis reveals the presence of m.A14693G and m.A14696G mutations in two pedigrees. Notably, the m.A14693G mutation occurs at position 54 in the TψC loop of tRNAGlu, a position which is critical for post-transcriptionally modification of tRNAGlu. While the m.A14696G mutation creates a novel base-pairing (51C-64G). Bioinformatic analysis shows that these mutations alter tRNAGlu secondary structure. Additionally, patients with tRNAGlu mutations exhibit markedly decreased in mtDNA copy number, mitochondrial membrane potential (MMP) and ATP, whereas the levels of reactive oxygen species (ROS) increase significantly.

Conclusion

The m.A14696G and m.A14693G mutations lead to failure in tRNAGlu metabolism and cause mitochondrial dysfunction that is responsible for EH.

Premature ovarian insufficiency may be associated with the mutations in mitochondrial tRNA genes

Premature ovarian insufficiency (POI) is a common endocrine disorder featured by the triad constituting of amenorrhea for at least four months, to date, the molecular pathogenesis of POI is largely undetermined. Despite several investigations have reported an increase in reactive oxygen species (ROS) content in idiopathic POI, the role of mitochondrial DNA (mtDNA) mutations/variants in the progression of POI has not been widely investigated. The current study aimed to explore the association between mt-tRNA mutations/variants and POI; we first used the PCR-Sanger sequencing to detect the mutations/variants in mt-tRNA genes from 50 POI patients and 30 healthy subjects. In addition, we evaluated the mitochondrial functions by using trans-mitochondrial cybrid cells containing these potential pathogenic mt-tRNA mutations. Consequently, five mutations: tRNA^Leu(UUR) C3303T, tRNA^Met A4435G, tRNA^Gln T4363C, tRNA^Cys G5821A and tRNA^Thr A15951G were identified. Notably, these mutations occurred at the extremely conserved nucleotides of the corresponding mt-tRNAs and may result the failure in mt-tRNA metabolism and subsequently lead to the impairment in mitochondrial protein synthesis. Furthermore, biochemical and molecular analyses of the cybrid cells containing these mutations showed a significantly lower level of ATP production when compared with the controls, whereas the ROS levels were much higher in POI patients carrying these mt-tRNA mutations, strongly indicated that these mt-tRNA mutations may cause the mitochondrial dysfunction, and play active roles in the progression and pathogensis of POI. Together, this study shaded additional light on the molecular mechanism of POI that was manifestated by mt-tRNA mutations.

Mitochondrial tRNAAla C5601T mutation may modulate the clinical expression of tRNAMet A4435G mutation in a Han Chinese family with hypertension

Mutations in mitochondrial DNA, especially in mitochondrial tRNA (mt-tRNA) genes, are the important causes for maternally inherited hypertension. In this study, we reported the clinical, genetic, and molecular characterization of a Han Chinese family with hypertension. Most strikingly, this family exhibited a high penetrance and expressivity of hypertension. Sequence analysis of the complete mt-tRNA genes showed the presence of tRNA^Met A4435G and tRNA^Ala C5601T mutations. The A4435G had already been reported as a pathogenic mutation associated with hypertension; in addition, the C5601T mutation, which was located at the highly conserved nucleotide of T arm of tRNA^Ala, created a novel Watson-Crick base pairing and may result in failure of tRNA metabolism. Moreover, bioinformatics analysis indicated that the C5601T mutation altered the secondary structure of tRNA^Ala. Thus, the mitochondrial dysfunction, caused by the A4435G mutation, may be worsened by the C5601T mutation. Taken together, our data indicated that the co-occurrence of the A4435G and C5601T mutations may account for the high penetrance and expressivity of hypertension in this family. Therefore, our study provided novel insight into the pathophysiology of maternally inherited hypertension.