Zongbin Li

Maternally Inherited Essential Hypertension Is Associated With the Novel 4263A>G Mutation in the Mitochondrial tRNAIle Gene in a Large Han Chinese Family

Rational: Despite maternal transmission of hypertension in some pedigrees, pathophysiology of maternally inherited hypertension remains poorly understood. Objective: To establish a causative link between mitochondrial dysfunction and essential hypertension. Method and Results: A total of 106 subjects from a large Chinese family underwent clinical, genetic, molecular, and biochemical evaluations. Fifteen of 24 adult matrilineal relatives exhibited a wide range of severity in essential hypertension, whereas none of the offspring of affected fathers had hypertension. The age at onset of hypertension in the maternal kindred varied from 20 years to 69 years, with an average of 44 years. Mutational analysis of their mitochondrial genomes identified a novel homoplasmic 4263A>G mutation located at the processing site for the tRNAIle 5′-end precursor. An in vitro processing analysis showed that the 4263A>G mutation reduced the efficiency of the tRNAIle precursor 5′-end cleavage catalyzed by RNase P. tRNA Northern analysis revealed that the 4263A>G mutation caused ≈46% reduction in the steady-state level of tRNAIle. An in vivo protein-labeling analysis showed ≈32% reduction in the rate of mitochondrial translation in cells carrying the 4263A>G mutation. Impaired mitochondrial translation is apparently a primary contributor to the reductions in the rate of overall respiratory capacity, malate/glutamate-promoted respiration, succinate/glycerol-3-phosphate-promoted respiration, or N,N,N′,N′-tetramethyl-p-phenylenediamine/ascorbate–promoted respiration and the increasing level of reactive oxygen species in cells carrying the 4263A>G mutation. Conclusions: These data provide direct evidence that mitochondrial dysfunction caused by mitochondrial tRNAIle 4263A>G mutation is involved in essential hypertension. Our findings may provide new insights into pathophysiology of maternally transmitted hypertension.

Mitochondrial Transfer RNAMet 4435A>G Mutation Is Associated With Maternally Inherited Hypertension in a Chinese Pedigree

Mitochondrial DNA mutations have been associated with cardiovascular disease. We report here the clinical, genetic, and molecular characterization of 1 Han Chinese family with suggestively maternally transmitted hypertension. Matrilineal relatives in this family exhibited the variable degree of hypertension at the age at onset of 44 to 55 years old. Sequence analysis of entire mitochondrial DNA in this pedigree identified the known homoplasmic 4435A>G mutation, which is located immediately at the 3 prime end to the anticodon, corresponding with the conventional position 37 of tRNAMet, and 35 other variants belonging to the Asian haplogroup B5a. The adenine (A37) at this position of tRNAMet is extraordinarily conserved from bacteria to human mitochondria. This modified A37 was shown to contribute to the high fidelity of codon recognition, the structural formation, and stabilization of functional tRNAs. In fact, a 40% reduction in the levels of tRNAMet was observed in cells carrying the 4435A>G mutation. As a result, a failure in mitochondrial tRNA metabolism, caused by the 4435A>G mutation, led to ≈30% reduction in the rate of mitochondrial translation. However, the homoplasmic form, mild biochemical defect, and late onset of hypertension in subjects carrying the 4435A>G mutation suggest that the 4435A>G mutation itself is insufficient to produce a clinical phenotype. The other modifier factors, such as nuclear modifier genes, environmental, and personal factors may also contribute to the development of hypertension in the subjects carrying this mutation. Our findings imply that the 4435A>G mutation may act as an inherited risk factor for the development of hypertension in this Chinese pedigree.

Failures in Mitochondrial tRNAMet and tRNAGln Metabolism Caused by the Novel 4401A>G Mutation Are Involved in Essential Hypertension in a Han Chinese Family

We report here on the clinical, genetic, and molecular characterization of 1 Han Chinese family with maternally transmitted hypertension. Three of 7 matrilineal relatives in this 4-generation family exhibited the variable degree of essential hypertension at the age at onset, ranging from 35 to 60 years old. Sequence analysis of the complete mitochondrial DNA in this pedigree identified the novel homoplasmic 4401A>G mutation localizing at the spacer immediately to the 5′ end of tRNAMet and tRNAGln genes and 39 other variants belonging to the Asian haplogroup C. The 4401A>G mutation was absent in 242 Han Chinese controls. Approximately 30% reductions in the steady-state levels of tRNAMet and tRNAGln were observed in 2 lymphoblastoid cell lines carrying the 4401A>G mutation compared with 2 control cell lines lacking this mutation. Failures in mitochondrial metabolism are apparently a primary contributor to the reduced rate of mitochondrial translation and reductions in the rate of overall respiratory capacity, malate/glutamate-promoted respiration, succinate/glycerol-3-phosphate–promoted respiration, or N,N,N′,N′-tetramethyl-p-phenylenediamine/ascorbate-promoted respiration in lymphoblastoid cell lines carrying the 4401A>G mutation. The homoplasmic form, mild biochemical defect, late onset, and incomplete penetrance of hypertension in this family suggest that the 4401A>G mutation itself is insufficient to produce a clinical phenotype. Thus, the other modifier factors, eg, nuclear modifier genes and environmental and personal factors, may also contribute to the development of hypertension in these subjects carrying this mutation. These data suggest that mitochondrial dysfunctions, caused by the 4401A>G mutation, are involved in the development of hypertension in this Chinese pedigree.

Maternally inherited hypertension is associated with the mitochondrial tRNAIle A4295G mutation in a Chinese family

Mutations in mitochondrial DNA have been associated with cardiovascular disease. We report here the clinical, genetic, and molecular characterization of one three-generation Han Chinese family with maternally transmitted hypertension. All matrilineal relatives in this family exhibited the variable degree of hypertension at the age at onset of 36 to 56 years old. Sequence analysis of the complete mitochondrial DNA in this pedigree revealed the presence of the known hypertension-associated tRNA(Ile) A4295G mutation and 33 other variants, belonging to the Asian haplogroup D4j. The A4295G mutation, which is extraordinarily conserved from bacteria to human mitochondria, is located at immediately 3 end to the anticodon, corresponding to conventional position 37 of tRNA(Ile). The occurrence of the A4295G mutation in several genetically unrelated pedigrees affected by cardiovascular disease but the absence of 242 Chinese controls strongly indicates that this mutation is involved in the pathogenesis of cardiovascular disease. Of other variants, the tRNA(Glu) A14693G and ND1 G11696A mutations were implicated to be associated with other mitochondrial disorders. The A14693G mutation, which is a highly conserved nucleoside at the TpsiC-loop of tRNA(Glu), has been implicated to be important for tRNA structure and function. Furthermore, the ND4 G11696A mutation was associated with Lebers hereditary optic neuropathy. Therefore, the combination of the A4295G mutation in the tRNA(Ile) gene with the ND4 G11696A mutation and tRNA(Glu) A14693G mutation may contribute to the high penetrance of hypertension in this Chinese family.

The mitochondrial ND1 T3308C mutation in a Chinese family with the secondary hypertension

Mutations in mitochondrial DNA have been associated with hypertension. We report here the clinical, genetic, and molecular characterization of one four-generation Han Chinese family with hypertension. Two matrilineal relatives in this family exhibited the variable degree of a secondary hypertension (renal hypertension) at the age-at-onset of 42 and 56years old, respectively. Sequence analysis of the complete mitochondrial DNA in this pedigree revealed the presence of the known hypertension-associated ND1 T3308C mutation and 42 other variants, belonging to the Asian haplogroup D4h. The T3308C mutation resulted in the replacement of the first amino acid, translation-initiating methionine with a threonine in ND1. Furthermore, the ND3 T3308C mutation also locates in two nucleotides adjacent to the 3 end of mitochondrial tRNA(Leu(UUR)). Thus, this T3308C mutation caused an alteration on the processing of the H-strand polycistronic RNA precursors or the destabilization of ND1 mRNA. The occurrence of the T3308C mutation in these genetically unrelated pedigrees affected by diseases but absence of 242 Chinese controls as well as the mitochondrial dysfunctions detected in cells carrying this mutation indicate that this mutation is involved in the pathogenesis of hypertension. However, the mild biochemical defects, the lower penetrance of hypertension in this Chinese family and the presence of some control populations suggested the involvement of other modifier factors in the pathogenesis of hypertension associated with this ND1 T3308C mutation.

Mitochondrial tRNA mutations in Chinese hypertensive individuals.

PURPOSEnHypertension is a very important risk factor for cardiac vascular disease. The previous studies showed that mitochondrial DNA mutations are associated with cardiovascular disease, including hypertension.nnnMETHODSnIn this study we did systematical analysis on the total 22 mitochondrial tRNAs and the clinical, genetic and molecular changes of 140 Chinese hypertension and 124 controls.nnnRESULTSnThis analysis identified 22 nucleotide changes among 15 different tRNA genes. There are 15 mutations with CI (Conservation index) larger than 75%. Of these, there are 26 patients with CI larger than 75% in the HTN group, higher than the 6 subjects in the control group (P=0.00). The tRNA(Phe) G586A, tRNA(Lys) G8313A and tRNA(His) G12147A mutations create highly conservative base-pairings on the D-stem, tRNA(Lys) G8342A on the T-stem, tRNA(Phe) T616C, tRNA(Ala) T5628C, tRNA(Tyr) G5856A and tRNA(Thr) A15924G on the AC stem, tRNA(Leu(CUN)) G12300A on the AC loop, tRNA(Met) C4467T, tRNA(Trp) T5578C, tRNA(Lys) A8296G, tRNA(Arg) T10463C and tRNA(Thr) C15891T on ACC stem, and tRNA(Ser(UCN)) C7492T on D-A junction, while the other tRNA variants were polymorphisms. The pedigrees of PLAH78 carrying the T5578C, PLAH84 carrying the C4467T, PLAH60 carrying the T5628C and PLAH118 carrying the C7492T mutation exhibited maternal transmission of essential hypertension. Sequence analysis of their mitochondrial genomes revealed the presence of T5578C, C4467T, T5628C or C7492T mutations but the absence of other functionally significant mutations in all matrilineal relatives of these families.nnnCONCLUSIONSnThese tRNAs mutations, associated with altered structures of tRNAs and mitochondrial dysfunction, may contribute to the hypertension in Chinese population. A lot of work still should be done for the mechanism and functional effect of the mtDNA mutation on hypertension.

Voltage-dependent anion channel involved in the mitochondrial calcium cycle of cell lines carrying the mitochondrial DNA A4263G mutation

In this study, we investigated the effects of the voltage-dependent anion channel (VDAC) on the mitochondrial calcium cycle in cell lines carrying the mitochondrial DNA A4263G mutation. We established lymphoblastoid cell lines from three symptomatic individuals and one asymptomatic individual from the large Chinese Han family carrying the A4263G mutation; these were compared with three control cell lines. The mitochondrial Ca(2+) concentration and membrane potential were detected by loading cells with Rhod-2 and JC-1, respectively. Confocal images showed the average Rhod-2 and JC-1 fluorescence levels of individuals carrying the tRNA(Ile) A4263G mutation were lower than those of the control group (P<0.05). The baseline Rhod-2 fluorescence in the control group increased after exposure to atractyloside (an opener of the adenine nucleotide translocator, P<0.05), but no significant change was detected in the cell line harboring the A4263G mutation (P>0.05). The baseline JC-1 fluorescence in both the mutated and control cell lines decreased after subsequent exposure to atractyloside (P<0.05), whereas this effect of atractyloside was inhibited by Cyclosporin A (CsA, a VDAC blocker). We conclude that the mitochondrial VDAC is involved in both the increase of mitochondrial permeability to Ca(2+) and the decrease of mitochondrial membrane potential in cell lines carrying the mtDNA A4263G mutation.

Effect of mitochondrial tRNALys mutation on the clinical and biochemical characteristics of Chinese essential hypertensive subjects

Mitochondrial dysfunction has been potentially implicated in both human and experimental hypertension. We performed the mutational analysis of tRNA(Lys) gene by PCR amplification and subsequent sequence analysis of the PCR fragments from 990 Chinese essential hypertensive subjects. We also made a comparative analysis of the collected data of the essential hypertension subjects who carried tRNA(Lys) mutation and those who did not carry the mutation using the methods of 1:1 case-control study. We totally found 7 mutation sites in 10 subjects. The onset ages of the individuals carrying the mutation were earlier than those who did not bear them. The level of blood urea nitrogen in hypertension subjects who carried tRNA(Lys) mutation was higher than the hypertension subjects who did not carried tRNA(Lys) mutation, while the serum potassium was significantly lower. The level of platelet count in hypertension subjects who carried tRNA(Lys) mutation was lower. The level of ventricular septal thickness in hypertension subjects who carried tRNA(Lys) mutation was higher and the level of left ventricular end diastolic diameter in hypertension subjects was significantly lower. Mitochondrial tRNA(Lys) mutations might result in the change of their structure and function, and then damaged the blood metabolism, the balance of the blood electrolyte, the steady-state of the blood cells and the heart structure and function, which were involved in the progress of the essential hypertension. Part of the essential hypertension patients clinically presented the characters of maternal inheritance, which might be associated with the tRNA(Lys) mutation.

Molecular characterization of a Chinese family carrying a novel C4329A mutation in mitochondrial tRNAIle and tRNAGln genes

BackgroundHypertension is a very common cardiovascular disease influenced by multiple genetic and environmental factors. More recently, there are some studies showed that mutations in mitochondrial DNA have been involved in its pathogenesis. In this study we did further investigations on this relationship.MethodsEpidemiological research found a Han Chinese family with probable maternally transmitted hypertension. Sequence analysis of the whole mitochondrial DNA was detected from all the family members. And evaluations of the clinical, genetic and molecular characterization were also performed.ResultsMatrilineal relatives within the family exhibited varying degrees of hypertension with an onset age of 48–55 years. Sequence analysis of this pedigree showed a novel homoplasmic 4329Cu2009>u2009G mutation located at the 3’ end of the tRNAIle and tRNAGln genes that was absent from 366 Chinese controls. The cytosine (C) at 4329 position was very important in the structural formation and stabilization of functional tRNAs, which was highly conserved in mitochondria of various organisms and also contributed to the high fidelity of the acceptor arm. Cells carrying this mutation were also shown to harbor mitochondrial dysfunctions.ConclusionsThe C4329G point mutation in tRNAIle and tRNAGln was involved in the pathogenesis of hypertension, perhaps in association with other modifying factors.

Systematic analysis of the clinical and biochemical characteristics of maternally inherited hypertension in Chinese Han families associated with mitochondrial

BackgroundMitochondrial DNA mutations may be associated with cardiovascular disease, including the common cardiac vascular disease, hypertension.MethodsIn this study we performed segregation analysis and systematically evaluated the entire mitochondrial genome in nine maternally inherited hypertension probands from Chinese Han families. We also performed clinical, genetic and molecular characterization of 74 maternally inherited members from these families and 216 healthy controls.ResultsIn the maternally inherited members, 12 had coronary heart disease (CHD), six had cerebrovascular disease, five had diabetes, nine had hyperlipidemia and three had renal disease. Laboratory tests showed that the sodium and potassium levels in blood of the maternally inherited members were higher than those of the control group (Pu2009<u20090.01), while no differences were observed in fasting blood glucose (FBG), total cholesterol (TC), triglyceride, low density lipoprotein cholesterol (LDL-c) and creatinine levels (Pu2009>u20090.05). The high density lipoprotein cholesterol (HDL-c) level of the maternally inherited members was lower than that of the control group (Pu2009=u20090.04). The whole mitochondrial DNA sequence analysis revealed a total of 172 base changes, including 17 in ribosomal RNA (rRNA) genes, four in transfer RNA (tRNA) genes, and 22 amino acid substitutions. The remainder were synonymous changes or were located in non-coding regions. We identified seven amino acid changes in the nine maternally inherited hypertension families, including four mutations in ATPase6 and three in Cytb. More interestingly, tRNASer(UCN) 7492xa0Tu2009>u2009C was absent in controls and was present in <1% of 2704 mtDNAs, indicating potential functional significance.ConclusionsThis study showed that mutations in mtDNA may contribute to the pathogenesis of hypertension in these Chinese Han families. In the near future, identification of additional mtDNA mutations may indicate further candidate genes for hypertension.