Background Mutations in mitochondrial tRNA (mt‐tRNA) genes are associated with hypertension, although their pathogenic mechanisms remain poorly understood. Methods In the present study, two Han Chinese families with maternally transmitted hypertension were interviewed. The mtDNA mutations of matrilineal relatives were screened by polymerase chain reaction‐Sanger sequencing. Mitochondrial ATP, membrane potential and reactive oxygen species (ROS) were also analyzed in polymononuclear leukocytes carrying these mt‐tRNA mutations. Additionally, the levels of oxidative stress‐related biomarkers [malondialdehyde (MDA), superoxide dismutase (SOD) and glutathione peroxidase (GSH‐Px) and 8‐hydroxy‐2‐deoxyguanosine (8‐OHdG)] were analyzed. Results Nine of 13 adult matrilineal relatives of these pedigrees exhibited a wide range of severity of hypertension. The age at onset of hypertension was 30–62 years (average 46 years). Mutational screening of mitochondrial genomes revealed tRNAArg T10410C and T10454C mutations. Indeed, the m.T10454C and m.T10410C mutations occurred at conserved bases of TΨC‐loop and acceptor arm of tRNAArg (positions 55 and 6), which are critical for tRNAArg post‐transcriptional modification. Thus, the defects in tRNA modification may cause failure in tRNA metabolism, impairing mitochondrial translation. Biochemical analysis revealed that m.T10454C or m.T10410C mutation significantly reduced mitochondrial ATP and membrane potential and also increased ROS production in mutant cell lines (all p < 0.05). In addition, the levels of MDA and 8‐OHdG in hypertensive patients markedly increased, whereas those of SOD and GSH‐Px decreased (all p < 0.05). Conclusions These findings demonstrate that m.T10410C and m.T10454C mutations affect the structure and function of tRNAArg and consequently alter mitochondrial function and lead to oxidative stress, which are involved in the pathogenesis of maternally inherited hypertension.

Background Mitochondrial dysfunctions caused by mitochondrial DNA (mtDNA) pathogenic mutations play putative roles in type 2 diabetes mellitus (T2DM) progression. But the underlying mechanism remains poorly understood. Methods A large Chinese family with maternally inherited diabetes and deafness (MIDD) underwent clinical, genetic, and molecular assessment. PCR and sequence analysis are carried out to detect mtDNA variants in affected family members, in addition, phylogenetic conservation analysis, haplogroup classification, and pathogenicity scoring system are performed. Moreover, the GJB2, GJB3, GJB6, and TRMU genes mutations are screened by PCR‐Sanger sequencing. Results Six of 18 matrilineal subjects manifested different clinical phenotypes of diabetes. The average age at onset of diabetic patients is 52 years. Screening for the entire mitochondrial genomes suggests the co‐existence of two possibly pathogenic mutations: tRNATrp A5514G and tRNASer(AGY) C12237T, which belongs to East Asia haplogroup G2a. By molecular level, m.A5514G mutation resides at acceptor stem of tRNATrp (position 3), which is critical for steady‐state level of tRNATrp. Conversely, m.C12237T mutation occurs in the variable region of tRNASer(AGY) (position 31), which creates a novel base‐pairing (11A‐31T). Thus, the mitochondrial dysfunctions caused by tRNATrp A5514G and tRNASer(AGY) C12237T mutations, may be associated with T2DM in this pedigree. But we do not find any functional mutations in those nuclear genes. Conclusion Our findings suggest that m.A5514G and m.C12337T mutations are associated with T2DM, screening for mt‐tRNA mutations is useful for molecular diagnosis and prevention of mitochondrial diabetes.

Background Mutations in mitochondrial DNA (mtDNA) are associated with type 2 diabetes mellitus (T2DM). In particular, m.A3243G is the most common T2DM-related mtDNA mutation in many families worldwide. However, the clinical features and pathophysiology of m.A3243G-induced T2DM are largely undefined. Methods Two pedigrees with maternally inherited T2DM were underwent clinical, molecular and biochemical assessments. The mtDNA genes were PCR amplified and sequenced. Mitochondrial adenosine triphosphate (ATP) and reactive oxygen species (ROS) were measured in polymononuclear leukocytes derived from three patients with both the m.A3243G and m.T14502C mutations, three patients with only the m.A3243G mutation and three controls without these mutations. Moreover, GJB2, GJB3 and GJB6 mutations were screened by PCR-Sanger sequencing. Results Members of the two pedigrees manifestated variable clinical phenotypes including diabetes and hearing and vision impairments. The age at onset of T2DM varied from 31 to 66 years, with an average of 41 years. Mutational analysis of mitochondrial genomes indicated the presence of the m.A3243G mutation in both pedigrees. Matrilineal relatives in one of the pedigrees harbored the coexisting of m.A3243G and m.T14502C mutations. Remarkably, the m.T14502C mutation, which causes the substitution of a conserved isoleucine for valine at position 58 in ND6 mRNA, may affect the mitochondrial respiratory chain functions. Biochemical analysis revealed that cell lines bearing both the m.A3243G and m.T14502C mutations exhibited greater reductions in ATP levels and increased ROS production compared with those carrying only the m.A3243G mutation. However, we did not find any mutations in the GJB2, GJB3 and GJB6 genes. Conclusion Our study indicated that mitochondrial diabetes is associated with the tRNA Leu(UUR) A3243G and ND6 T14502C mutations.