Chao Zhu

Mitochondrial tRNA mutations in Chinese hypertensive individuals.

PURPOSE Hypertension 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. METHODS In 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. RESULTS This 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. CONCLUSIONS These 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.

Characterization of a Chinese KCNQ1 mutation (R259H) that shortens repolarization and causes short QT syndrome 2

Objectives To evaluate the association between a KCNQ1 mutation, R259H, and short QT syndrome (SQTS) and to explore the electrophysiological mechanisms underlying their association. Methods We performed genetic screening of SQTS genes in 25 probands and their family members (63 patients). We used direct sequencing to screen the exons and intron-exon boundaries of candidate genes that encode ion channels which contribute to the repolarization of the ventricular action potential, including KCNQ1, KCNH2, KCNE1, KCNE2, KCNJ2, CACNA1c, CACNB2b and CACNA2D1. In one of the 25 SQTS probands screened, we discovered a KCNQ1 mutation, R259H. We cloned R259H and transiently expressed it in HEK-293 cells; then, currents were recorded using whole cell patch clamp techniques. Results R259H-KCNQ1 showed significantly increased current density, which was approximately 3-fold larger than that of wild type (WT) after a depolarizing pulse at 1 s. The steady state voltage dependence of the activation and inactivation did not show significant differences between the WT and R259H mutation (P > 0.05), whereas the time constant of deactivation was markedly prolonged in the mutant compared with the WT in terms of the test potentials, which indicated that the deactivation of R259H was markedly slower than that of the WT. These results suggested that the R259H mutation can effectively increase the slowly activated delayed rectifier potassium current (IKs) in phase 3 of the cardiac action potential, which may be an infrequent cause of QT interval shortening. Conclusions R259H is a gain-of-function mutation of the KCNQ1 channel that is responsible for SQTS2. This is the first time that the R259H mutation was detected in Chinese people.

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 4329C > G 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.

Effects of allocryptopine on outward potassium current and slow delayed rectifier potassium current in rabbit myocardium.

Objective Allocryptopine (ALL) is an effective alkaloid of Corydalis decumbens (Thunb.) Pers. Papaveraceae and has proved to be anti-arrhythmic. The purpose of our study is to investigate the effects of ALL on transmural repolarizing ionic ingredients of outward potassium current (Ito) and slow delayed rectifier potassium current (IKs). Methods The monophasic action potential (MAP) technique was used to record the MAP duration of the epicardium (Epi), myocardium (M) and endocardium (Endo) of the rabbit heart and the whole cell patch clamp was used to record Ito and IKs in cardiomyocytes of Epi, M and Endo layers that were isolated from rabbit ventricles. Results The effects of ALL on MAP of Epi, M and Endo layers were disequilibrium. ALL could effectively reduce the transmural dispersion of repolarization (TDR) in rabbit transmural ventricular wall. ALL decreased the current densities of Ito and IKs in a voltage and concentration dependent way and narrowed the repolarizing differences among three layers. The analysis of gating kinetics showed ALL accelerated the channel activation of Ito in M layers and partly inhibit the channel openings of Ito in Epi, M and Endo cells. On the other hand, ALL mainly slowed channel deactivation of IKs channel in Epi and Endo layers without affecting its activation. Conclusions Our study gives partially explanation about the mechanisms of transmural inhibition of Ito and IKs channels by ALL in rabbit myocardium. These findings provide novel perspective regarding the anti-arrhythmogenesis application of ALL in clinical settings.

Mitochondrial biogenesis dysfunction and metabolic dysfunction from a novel mitochondrial tRNA Met 4467 C>A mutation in a Han Chinese family with maternally inherited hypertension

To investigate the relationship between mitochondrial DNA (mtDNA) and hypertension as well as the mechanism involved in mitochondrial metabolic dysfunction. We identified a novel tRNAMet C4467A mutation in a Han Chinese family with hypertension. The maternal members presented with increased glucose, total cholesterol, low-density lipoprotein, and serum sodium as well as decreased potassium compared with non-maternal members (P < 0.05). Segregation analysis showed this mutation was maternally inherited. We analyzed lymphocyte cell lines derived from three maternal and three non-maternal family members. Reactive oxygen species production in the mutant cell lines was 114.5% higher compared with that in controls (P < 0.05) while ATP was 26.4% lower. The mitochondrial membrane potential of the mutated cell lines was 26.2% lower than that in controls (P < 0.05). Oxygen consumption rates were decreased in the mutant cell lines (P < 0.05). The activation of caspase-3/7 was 104.1% higher in the mutant cell lines compared with controls (P < 0.05). The expression of voltage-dependent anion channel (VDAC), Bax and apoptosis-inducing factor (AIF) in the mutant cell lines was higher compared with that in controls, with the increased colocalization of VDAC and Bax. Therefore, this mutation contributes to oxidative stress and mitochondrial biogenesis dysfunction, which may be involved in the pathogenesis of hypertension.

Kv4.3 Modulates the Distribution of hERG

This study examines the interaction between hERG and Kv4.3. The functional interaction between hERG and Kv4.3, expressed in a heterologous cell line, was studied using patch clamp techniques, western blot, immunofluorescence, and co-immunoprecipitation. Co-expression of Kv4.3 with hERG increased hERG current density (tail current after a step to +10 mV: 26 ± 3 versus 56 ± 7 pA/pF, p < 0.01). Kv4.3 co-expression also increased the protein expression and promoted the membrane localization of hERG. Western blot showed Kv4.3 increased hERG expression by Hsp70. hERG and Kv4.3 co-localized and co-immunoprecipitated in cultured 293 T cells, indicating physical interactions between hERG and Kv4.3 proteins in vitro. In addition, Hsp70 interacted with hERG and Kv4.3 respectively, and formed complexes with hERG and Kv4.3. The α subunit of Ito Kv4.3 can interact with and modify the localization of the α subunit of IKr hERG, thus providing potentially novel insights into the molecular mechanism of the malignant ventricular arrhythmia in heart failure.

Electrophysiological Characteristics of the LQT2 Syndrome Mutation KCNH2-G572S and Regulation by Accessory Protein KCNE2

Mutations in hERG cause long QT syndrome type 2 which is characterized by a prolonged QT interval on electrocardiogram and predisposition to life-threatening ventricular tachyarrhythmia, syncope, and sudden death. hERG-G572S induces trafficking defects of hERG channel protein from Golgi to the plasma membrane and results in a dominant negative suppression of hERG current density. As an accessory β subunit, KCNE2 promotes hERG migration from Golgi to cellular membrane. In this study, we investigated the rescue effect of KCNE2 in a G572S mutation of hERG. Transfection was performed into HEK293 cells. Patch clamp technique, western blotting analyses and confocal microscopic examination were used. Results showed that KCNE2 had a significantly enhanced effect on G572S mutation current. The increase of current was largest at KCNH2:KCNE2 of 1:3. Confocal images showed co-expressing G572S and KCNE2 could cause a substantial up-regulated membrane protein (155 kDa) expression. Expression of membrane protein accumulated markedly with increasing ratio of KCNH2:KCNE2. G572S defective mutant could be restored by both KCNE2 and lower temperature (27°C), which suggested that the lower temperature could be the favorable circumstances for the rescue function of KCNE2. In this study, we successfully set up “the action potential” on the HEK 293 cells by genetically engineered to express Kir2.1, Nav1.5, and Kv11.1, wherein on reaching over an excitation threshold by current injection. The results suggested that KCNE2 could shorten action potential duration which was prolonged by G572S. These findings described electrophysiological characteristics of the LQT2 syndrome mutation KCNH2-G572S and regulation by accessory protein KCNE2, and provided a clue about LQT2 and relative rescue mechanism.

Electrophysiological and trafficking defects of the SCN5A T353I mutation in Brugada syndrome are rescued by alpha-allocryptopine

Brugada syndrome (BrS), which causes arrhythmias that lead to sudden cardiac death, is linked to loss-of-function mutations that affect sodium channels. Here, we investigate the rescue effect of alpha-allocryptopine (All) from Chinese herbal medicine in a T353I mutation of SCN5A, which combines trafficking abnormalities with Brugada syndrome. SCN5A-T353I expressed in HEK293 cells showed a small peak current (I(peak)) of only 59.6% of WT and an observably sustained current (I(sus)). We found that All strongly enhanced the I(peak) of the T353I channel by enhancing the plasma membrane (PM) expression of Nav1.5 and rescued defective trafficking after co-incubation with HEK293 cells that carry mutation channel 24 h. It is also beneficial to increase the I(peak) of the T353I mutation by All by prolonging the closed-state inactivation (CSI) process and shortening the recovery from inactivation of the T353I mutation. Interestingly, the I(sus) of T353I was significantly inhibited by All, which reduces the occurrence of LQT syndrome 3 (LQT3). We provide evidence that All can rescue the trafficking deficiencies and restore the cellular electrophysiological characteristics of SCN5A-T353I. This feature of All may benefit patients with the BrS-associated Nav1.5 channel and might have other potential therapeutic effects.

Mitochondrial genome mutations in 13 subunits of respiratory chain complexes in Chinese Han and Mongolian hypertensive individuals

Abstract Mitochondrial DNA (mtDNA) mutations are associated with cardiovascular disease, including hypertension (HTN). Here we performed a genetic and molecular analysis of 13 mtDNA-encoded subunits of respiratory chain complexes in 100 Chinese Han and 80 Mongolian HTN cases, and 100 Han and 42 Mongolian normotension subjects. The total cholesterol of the Mongolian normotensive subjects was higher than that of the Han normotensive group (p < .05). Sequence analysis identified 636 point mutations in the 13 mtDNA-encoded subunits in the Han and Mongolian hypertensive individuals, including 66 in NADH dehydrogenase subunit 1(ND1), 62 in ND2, 71 in COI, 29 in COII, 17 in ATP8, one in ATP6/8, 49 in ATP6, 27 in COIII, 27 in ND3, 14 in ND4L, 74 in ND4, 97 in ND5, 24 in ND6, and 78 in CYTB. Eight of these point mutations were present at significantly different frequencies in Han and Mongolian hypertensive individuals. Thirty-one point mutations were present only in Mongolian hypertensive individuals, while 73 were present only in Han hypertensive individuals. The relation between point mutations in 13 mtDNA-encoded subunits of respiratory chain complexes and HTN is worth to further research in future; however, the functional effects of these mutations require elucidation.

Key Role of the Membrane Trafficking of Nav1.5 Channel Protein in Antidepressant-Induced Brugada Syndrome

Anti-depressant treatment has been found to be associated with the development of Brugada syndrome (BrS) through poorly defined mechanisms. Herein, this study aimed to explore the molecular basis for amitriptyline-induced BrS. The effects of long-term treatments of amitriptyline on Nav1.5 were investigated using neonatal rat ventricular myocytes. The electrophysiological properties, expression and distribution of Nav1.5 were studied using the patch clamp, Western blot and confocal laser microscopy assays. Interactions between Nav1.5 and its interacting proteins, including ankyrin-G and dystrophin, were evaluated by co-immunoprecipitation. A larger decrease in the peak INa occurred after long-term treatments to amitriptyline (56.64%) than after acute exposure to amitriptyline (28%). Slow recovery from inactivation of Nav1.5 was observed after acute or long-term treatments to amitriptyline. The expression of Nav1.5 on the cell membrane showed a larger decrease by long-term treatments to amitriptyline than by acute exposure to amitriptyline. After long-term treatments to amitriptyline, we observed reduced Nav1.5 proteins on the cell membrane and the disrupted co-localization of Nav1.5 and ankyrin-G or dystrophin. Co-immunoprecipitation experiments further testified that the combination of Nav1.5 and ankyrin-G or dystrophin was severely weakened after long-term treatments to amitriptyline, implying the failed interaction between Nav1.5 and ankyrin-G or dystrophin. Our data suggest that the long-term effect of amitriptyline serves as an important contribution to BrS induced by amitriptyline. The mechanisms of BrS induced by amitriptyline were related to Nav1.5 trafficking and could be explained by the disrupted interaction of ankyrin-G, dystrophin and Nav1.5.