Maternal influence on blood pressure suggests involvement of mitochondrial DNA in the pathogenesis of hypertension: the Framingham Heart Study

The Role of Mitochondrial DNA Mutations in Cardiovascular Diseases

Cardiovascular diseases (CVD) are one of the leading causes of morbidity and mortality worldwide. mtDNA (mitochondrial DNA) mutations are known to participate in the development and progression of some CVD. Moreover, specific types of mitochondria-mediated CVD have been discovered, such as MIEH (maternally inherited essential hypertension) and maternally inherited CHD (coronary heart disease). Maternally inherited mitochondrial CVD is caused by certain mutations in the mtDNA, which encode structural mitochondrial proteins and mitochondrial tRNA. In this review, we focus on recently identified mtDNA mutations associated with CVD (coronary artery disease and hypertension). Additionally, new data suggest the role of mtDNA mutations in Brugada syndrome and ischemic stroke, which before were considered only as a result of mutations in nuclear genes. Moreover, we discuss the molecular mechanisms of mtDNA involvement in the development of the disease.

Co-occurrence of m.15992A>G and m.15077G>A Is Associated With a High Penetrance of Maternally Inherited Hypertension in a Chinese Pedigree

BACKGROUND

Mitochondrial DNA (mtDNA) pathogenic variants have been identified to be associated with maternally inherited essential hypertension (MIEH). However, the distinctive clinical features and molecular pathogenesis of MIEH are not fully understood.

METHODS

In this study, we collected a Chinese MIEH family with extraordinary higher penetrance of essential hypertension (88.89%) and early ages of onset (31-40 years old), and performed clinical and genetic characterization for this family. The complete mitochondrial genome of the proband was sequenced and analyzed.

RESULTS

The maternally related members in this family were presented with severe increased blood pressure, left ventricular remodeling, and metabolic abnormalities. Through sequencing the entire mtDNA of the proband and performing systematic analysis of the mtDNA variants with a phylogenic approach, we identified a potentially pathogenic tRNA variant (m.15992A>G in the MT-TP gene) that may account for the MIEH in this family. One nonsynonymous variant (m.15077G>A in the MT-CYB gene) was identified to play a synergistic role with m.15992A>G to cause a high penetrance of MIEH.

CONCLUSIONS

Our results, together with previous findings, have indicated that tRNA pathogenic variants in the mtDNA could act important roles in the pathogenesis of MIEH through reducing mitochondrial translation and disturbing mitochondrial function.

mtDNA in the Pathogenesis of Cardiovascular Diseases

The incidence rate of cardiovascular disease (CVD) has been increasing year by year and has become the main cause for the increase of mortality. Mitochondrial DNA (mtDNA) plays a crucial role in the pathogenesis of CVD, especially in heart failure and ischemic heart diseases. With the deepening of research, more and more evidence showed that mtDNA is related to the occurrence and development of CVD. Current studies mainly focus on how mtDNA copy number, an indirect biomarker of mitochondrial function, contributes to CVD and its underlying mechanisms including mtDNA autophagy, the effect of mtDNA on cardiac inflammation, and related metabolic functions. However, no relevant studies have been conducted yet. In this paper, we combed the current research status of the mechanism related to the influence of mtDNA on the occurrence, development, and prognosis of CVD, so as to find whether these mechanisms have something in common, or is there a correlation between each mechanism for the development of CVD?

Mitochondrial tRNA Mutations Associated With Essential Hypertension: From Molecular Genetics to Function

Essential hypertension (EH) is one of the most common cardiovascular diseases worldwide, entailing a high level of morbidity. EH is a multifactorial disease influenced by both genetic and environmental factors, including mitochondrial DNA (mtDNA) genotype. Previous studies identified mtDNA mutations that are associated with maternally inherited hypertension, including tRNA^Ile m.4263A>G, m.4291T>C, m.4295A>G, tRNA^Met m.4435A>G, tRNA^Ala m.5655A>G, and tRNA^Met/tRNA^Gln m.4401A>G, et al. These mtDNA mutations alter tRNA structure, thereby leading to metabolic disorders. Metabolic defects associated with mitochondrial tRNAs affect protein synthesis, cause oxidative phosphorylation defects, reduced ATP synthesis, and increase production of reactive oxygen species. In this review we discuss known mutations of tRNA genes encoded by mtDNA and the potential mechanisms by which these mutations may contribute to hypertension.

Mitochondrial tRNA Mutation and Regulation of the Adiponectin Pathway in Maternally Inherited Hypertension in Chinese Han

Some essential hypertension (EH) patients show maternal inheritance, which is the mode of mitochondrial DNA inheritance. This study examines the mechanisms by which mitochondrial mutations cause EH characterized by maternal inheritance. The study enrolled 115 volunteers, who were divided into maternally inherited EH (group A, n = 17), non-maternally inherited EH (group B, n = 65), and normal control (group C, n = 33) groups. A mitochondrial tRNA (15910 C>T) gene mutation was significantly correlated with EH and may play an important role in the pathogenesis of maternally inherited EH. Examining two families carrying the mitochondrial tRNA 15910 C>T mutation, which disrupted base pairing and may affect the stability and function of mitochondrial tRNA^Thr, we find that the overall incidence of EH was 59.3% in the maternal family members and 90% in males, significantly higher than in the general population in China (23.2%), and that the EH began at a younger age in those carrying mitochondrial tRNA 15910 C>T. To reveal the mechanism through which mitochondrial tRNA 15910 C>T causes maternally inherited EH, we cultured human peripheral blood mononuclear cells from family A2 in vitro. We find that cells carrying mitochondrial tRNA 15910 C>T were more viable and proliferative, and the increased ATP production resulted in raised intracellular reactive oxygen species (ROS). Moreover, the mitochondrial dysfunction resulted in reduced APN levels, causing hypoadiponectinemia, which promoted cell proliferation, and produced more ROS. This vicious cycle promoted the occurrence of EH with maternally inherited mitochondrial tRNA 15910 C>T. The mitochondrial tRNA 15910 C>T mutation may induce hypertension by changing the APN, AdipoR1, PGC-1α, and ERRα signaling pathways to elevate blood pressure. We discover a new mitochondrial mutation (tRNA 15910 C>T) related to EH, reveal part of the mechanism by which mitochondrial mutations lead to the occurrence and development of maternally inherited EH, and discuss the role of APN in it.

Microbial Peer Pressure: The Role of the Gut Microbiota in Hypertension and Its Complications

There is increasing evidence of the influence of the gut microbiota on hypertension and its complications, such as chronic kidney disease, stroke, heart failure, and myocardial infarction. This is not surprising considering that the most common risk factors for hypertension, such as age, sex, medication, and diet, can also impact the gut microbiota. For example, sodium and fermentable fiber have been studied in relation to both hypertension and the gut microbiota. By combining second- and, now, third-generation sequencing with metabolomics approaches, metabolites, such as short-chain fatty acids and trimethylamine N-oxide, and their producers, have been identified and are now known to affect host physiology and the cardiovascular system. The receptors that bind these metabolites have also been explored with positive findings-examples include known short-chain fatty acid receptors, such as G-protein coupled receptors GPR41, GPR43, GPR109a, and OLF78 in mice. GPR41 and OLF78 have been shown to have inverse roles in blood pressure regulation, whereas GPR43 and GPR109A have to date been demonstrated to impact cardiac function. New treatment options in the form of prebiotics (eg, dietary fiber), probiotics (eg, Lactobacillus spp.), and postbiotics (eg, the short-chain fatty acids acetate, propionate, and butyrate) have all been demonstrated to be beneficial in lowering blood pressure in animal models, but the underlying mechanisms remain poorly understood and translation to hypertensive patients is still lacking. Here, we review the evidence for the role of the gut microbiota in hypertension, its risk factors, and cardiorenal complications and identify future directions for this exciting and fast-evolving field.

A high prevalence of arterial hypertension in patients with mitochondrial diseases

The prevalence of arterial hypertension in mitochondrial diseases remains unknown. Between January 2000 and May 2014, we retrospectively included patients with genetically proven mitochondrial diseases. We recorded clinical, genetic and cardiac exploration data, including the measure of arterial pressure. Among the 260 patients included in the study (mean age = 44 ± 15 years, women = 158), 108 (41.5%) presented with arterial hypertension. The prevalence of hypertension by sex and age was higher than that observed in the general population for all groups. The prevalence of hypertension was significantly higher in patients with MELAS (mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes) mutations (66%) and MERRF (myoclonus, epilepsy, ataxia with ragged ref fibres) mutations (61%). In patients with MELAS mutation, the presence of hypertension was significantly associated with age and mutation rate in the blood (odds ratio = 1.12; P = .02) in multivariate analysis. The prevalence of hypertension was more important in patients having a mitochondrial disease. The increased risk was more important in patient with MELAS or MERRF and depended on the rate of heteroplasmy.

Mitochondrial outer membrane voltage-dependent anion channel is involved in renal dysfunction in a spontaneously hypertensive rat carrying transfer RNA mutations

Mitochondrial DNA mutations promote hypertensive renal dysfunction, but the molecular mechanism remains unclear. This study compared renal damage between spontaneously hypertensive rats (SHR) and SHR with mitochondrial transfer (t)RNA mutations. To investigate the role of mitochondrial outer membrane voltage-dependent anion channel 1 (VDAC1) in the process of tRNA-promoting mitochondrial dysfunction, we treated HK-2 cells with H₂O₂, cyclosporine (CsA), or atractylodin (Atr) to observe the association between VDAC1 and mitochondrial function. Intriguingly, the mitochondrial structure of SHR carrying tRNA mutations was obviously disordered, and reactive oxygen species production and VDAC1 and Bax expression and binding were increased, which was associated with marked renal dysfunction. The expression of VDAC1 and Bax was also up-regulated in HK-2 cells by H₂O₂ treatment. However, CsA and Atr had no significant effect on the expression of VDAC1 and Bax. H₂O₂ caused mitochondrial membrane potential collapse, while CsA could increase the mitochondrial membrane potential and Atr had the opposite effect. Treatment with H₂O₂ significantly decreased ATP synthesis, which was improved by intervention with Atr. H₂O₂ also decreased the maximum oxygen consumption rate, while CsA and Atr had no significant effect. We found that H₂O₂ promoted the colocalization of VDAC1 and Bax, which was partially inhibited by intervention with CsA or Atr. In conclusion, we found that tRNA mutations promoted hypertensive renal insufficiency. Increased reactive oxygen species was an important associated mechanism, which inhibited mitochondrial function by affecting VDAC1 expression and function.

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.

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

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.

Mitochondrial tRNA mutation with high-salt stimulation on cardiac damage: underlying mechanism associated with change of Bax and VDAC

Mitochondrial transfer RNA (tRNA) mutation with high-salt stimulation can cause high blood pressure. However, the underlying mechanisms remain unclear. In the present study, we examined the potential molecular mechanisms of cardiac damage caused by mitochondrial tRNA mutation with high-salt stimulation in spontaneously hypertensive rats (SHR). Unanesthetized, 44-wk-old, male, SHR were divided into four groups: SHR, SHR with high-salt stimulation for 8 wk (SHR + NaCl), SHR carrying tRNA mutations (SHR + M), and SHR + M with high-salt stimulation for 8 wk (SHR + M + NaCl). Healthy Wistar-Kyoto (WKY) rats were used as controls. Left ventricular mass and interventricular septum were highest in the SHR + M + NaCl group ( P < 0.05), while ejection fraction was lowest in the SHR + M + NaCl group ( P < 0.05). Hematoxylin and eosin staining showed myocardial cell hypertrophy with interstitial fibrosis and localized inflammatory cell infiltration, in the hypertensive groups, particularly in the SHR + M + NaCl group. Electron microscopy showed different degrees of mitochondrial cavitation in heart tissue of the hypertensive groups, which was highest in the SHR + M + NaCl group. In hypertensive animals, levels of reactive oxygen species were highest in the SHR + M + NaCl group ( P < 0.05). Expression of the voltage-dependent anion channel (VDAC) and the apoptosis regulator Bax were highest in the SHR + M + NaCl group ( P < 0.05), which also showed evidence of VDAC and Bax colocalization ( P < 0.05). Overall, these data suggest that mitochondrial tRNA mutation with high-salt stimulation can aggravate cardiac damage, potentially because of increased expression and interaction between Bax and VDAC and increased reactive oxygen species formation and initiation of apoptosis.

The possible role of chromosome X variability in hypertensive familiarity

Familiarity participates in the pathogenesis of hypertension, although only recently, whole genome studies have proposed regions of the human genome possibly involved in the transmission of the hypertensive phenotype. Although studies have mainly focused on autosome, hitherto the influence of sex on familial transmission of hypertension has not been considered. We analysed the database of the Campania Salute Network of Hypertension center of the Federico II University Hospital of Naples (Italy), using dichotomous variables for paternal and maternal familiarity and gender (male and female) of 12 504 hypertensive patients (6868 males and 5636 females) and 6352 controls (3484 males and 2868 females), totaling 18 856 subjects. In the hypertensive group, familiarity was present in 75% of cases with odds of 3.77 and in only 26% of the normotensives with odds of 0.94. The odds ratio (OR) indicated that familiarity increases the risk of developing hypertension by 2.91 (95% confidence interval (CI)=2.67-3.17, P<0.001) times. Additionally, maternal familiarity was 37% (OR=3.01, 95% CI=2.66-3.41, P<0.001), paternal familiarity was 21% (OR=2.31, 95% CI=2.01-2.68, P<0.001) and the double familiarity was 17% (OR=3.45, 95% CI=2.87-4.01, P<0.001), thus suggesting a plausible association between maternal familiarity and development of hypertension; this finding was observed both in male and in female patients, although the phenomenon was larger in males. Given the dominance of maternal transmission in males, by genome-wide analysis of the X chromosome, we found two regions that were differently distributed in male hypertensives with maternal hypertension. Our data highlight the importance of genetic variants in the X chromosome to the maternal transmission of the hypertensive phenotype.

Disentangling the associations between parental BMI and offspring body composition using the four-component model

Objectives

This study sets out to investigate the intergenerational associations between the body mass index (BMI) of parents and the body composition of their offspring.

Methods

The cross‐sectional data were analyzed for 511 parent–offspring trios from London and south‐east England. The offspring were aged 5–21 years. Parental BMI was obtained by recall and offspring fat mass and lean mass were obtained using the four‐component model. Multivariable regression analysis, with multiple imputation for missing paternal values was used. Sensitivity analyses for levels of non‐paternity were conducted.

Results

A positive association was seen between parental BMI and offspring BMI, fat mass index (FMI), and lean mass index (LMI). The mother's BMI was positively associated with the BMI, FMI, and LMI z‐scores of both daughters and sons and of a similar magnitude for both sexes. The father's BMI showed similar associations to the mother's BMI, with his son's BMI, FMI, and LMI z‐scores, but no association with his daughter. Sensitivity tests for non‐paternity showed that maternal coefficients remained greater than paternal coefficients throughout but there was no statistical difference at greater levels of non‐paternity.

Conclusions

We found variable associations between parental BMI and offspring body composition. Associations were generally stronger for maternal than paternal BMI, and paternal associations appeared to differ between sons and daughters. In this cohort, the mother's BMI was statistically significantly associated with her child's body composition but the father's BMI was only associated with the body composition of his sons. Am. J. Hum. Biol. 28:524–533, 2016. © 2016 The Authors American Journal of Human Biology Published by Wiley Periodicals, Inc.

Cardiovascular Disease, Mitochondria, and Traditional Chinese Medicine

Recent studies demonstrated that mitochondria play an important role in the cardiovascular system and mutations of mitochondrial DNA affect coronary artery disease, resulting in hypertension, atherosclerosis, and cardiomyopathy. Traditional Chinese medicine (TCM) has been used for thousands of years to treat cardiovascular disease, but it is not yet clear how TCM affects mitochondrial function. By reviewing the interactions between the cardiovascular system, mitochondrial DNA, and TCM, we show that cardiovascular disease is negatively affected by mutations in mitochondrial DNA and that TCM can be used to treat cardiovascular disease by regulating the structure and function of mitochondria via increases in mitochondrial electron transport and oxidative phosphorylation, modulation of mitochondrial-mediated apoptosis, and decreases in mitochondrial ROS. However further research is still required to identify the mechanism by which TCM affects CVD and modifies mitochondrial DNA.

Sex-related clustering of intracranial aneurysms within families

BACKGROUND AND PURPOSE

Family history is important risk factor for intracranial aneurysms (ICA), but the pattern of inheritance is unsettled. If ICA within families would cluster according to sex, this may have implications for risk prediction and screening advice within families. We assessed the relationship between the sex of probands and their affected first-degree relatives (FDRs) within families with ICA.

METHODS

We used data from our prospectively collected database of families with known familial ICA. We calculated relative risks for a female affected proband having a female affected FDR as compared with a male affected proband having female affected FDR with corresponding 95% confidence intervals.

RESULTS

We included 148 families with 376 affected FDR. For a female proband the relative risk for having a female affected FDR compared with a male proband having an affected female FDR was 1.2 (95% confidence interval, 1.0-1.6).

CONCLUSIONS

The clustering of ICA within families is greater in women than in men, with an excess of affected female FDR in female probands. However, because this excess is modest, our findings indicate that sex is not a relevant factor in risk prediction or screening advice in families with ICA.

Revisiting heritability accounting for shared environmental effects and maternal inheritance

Heritability measures the proportion of phenotypic variation attributable to genetic factors. In addition to a shared nuclear genetic component, a number of additional variance components, such as spousal correlation, sibship, household and maternal effects, may have strong contributions to inter-individual phenotype variation. In humans, the confounding effects of these components on heritability have not been studied thoroughly. We sought to obtain unbiased heritability estimates for complex traits in the presence of multiple variance components and also to estimate the contributions of these variance components to complex traits. We compared regression and variance component methods to estimate heritability in simulations when additional variance components existed. We then revisited heritability for several traits in Framingham Heart Study (FHS) participants. Using simulations, we found that failure to account for or misclassification of necessary variance components yielded biased heritability estimates. The direction and magnitude of the bias varied depending on a variance structure and an estimation method. Using the best fitted models to account for necessary variance components, we found that heritability estimates for most FHS traits were overestimated, ranging from 4 to 47 %, when we compared models that considered necessary variance components to models that only considered familial relationships. Spousal correlation explained 14-36 % of phenotypic variation in several anthropometric and lifestyle traits. Maternal and sibling effects also contributed to phenotypic variation, ranging from 3 to 5 % and 4 to 7 %, respectively, in several anthropometric and metabolic traits. Our findings may explain, in part, the missing heritability for some traits.

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

BACKGROUND

Mitochondrial DNA mutations may be associated with cardiovascular disease, including the common cardiac vascular disease, hypertension.

METHODS

In 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.

RESULTS

In 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 (P < 0.01), while no differences were observed in fasting blood glucose (FBG), total cholesterol (TC), triglyceride, low density lipoprotein cholesterol (LDL-c) and creatinine levels (P > 0.05). The high density lipoprotein cholesterol (HDL-c) level of the maternally inherited members was lower than that of the control group (P = 0.04). 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, tRNA(Ser(UCN)) 7492 T > C was absent in controls and was present in <1% of 2704 mtDNAs, indicating potential functional significance.

CONCLUSIONS

This 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.

Effect of mitochondrial tRNA(Lys) 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.

The molecular basis of blood pressure variation

Advances in genetic mapping and sequencing techniques have led to substantial progress in the study of rare monogenic (Mendelian) forms of abnormal blood pressure. Many disease-defining pathways for hypertension have been identified in the past two decades. Perturbations in renal salt handling appear to be a common mechanism underlying these rare syndromes of hypertension. Excess activation at various points in the mineralocorticoid signaling pathway and malfunctioning of the autonomic (specifically sympathetic) nervous system have both been implicated in inducing hypertension, while complementary studies examining low blood pressure phenotypes have identified novel pathways exclusively linked to renal salt wasting in either the thick ascending limb or the distal nephron. The genetic defects and the physiological and cellular pathways affected in these various disorders are reviewed here. Importantly, studies have suggested that genetic variation affecting these same genes and pathways may play an important role in explaining the variation of blood pressure levels in the general population. The investigation of rare syndromes of human blood pressure variation has important implications for improving the diagnosis and treatment of hypertension.

Association of genetic variation in the mitochondrial genome with blood pressure and metabolic traits

Elevated blood pressure (BP) is a major risk factor for cardiovascular disease. Several studies have noted a consistent maternal effect on BP; consequently, mitochondrial DNA variation has become an additional target of investigation of the missing BP heritability. Analyses of common mitochondrial DNA polymorphisms, however, have not found evidence of association with hypertension. To explore associations of uncommon (frequency>5%) mitochon drial DNA variants with BP, we identified uncommon/rare variants through sequencing the entire mitochondrial genome in 32 unrelated individuals with extreme-high BP in the Framingham Heart Study and genotyped 40 mitochondrial single nucleotide polymorphisms in 7219 Framingham Heart Study participants. The nonsynonymous mitochondrial single nucleotide polymorphism 5913G>A (Asp4Asn) in the cytochrome c oxidase subunit 1 of respiratory complex IV demonstrated significant associations with BP and fasting blood glucose (FBG) levels. Individuals with the rare 5913A allele had, on average, 7-mm Hg higher systolic BP at baseline (Pempirical=0.05) and 17-mg/dL higher mean FBG over 25 years of follow-up (Pempirical=0.009). Significant associations with FBG levels were also detected for nonsynonymous mitochondrial single nucleotide polymorphism 3316G>A (Ala4Thr) in the NADH dehydrogenase subunit 1 of complex I. On average, individuals with rare allele 3316A had 17- and 25-mg/dL higher FBG at baseline (Pempirical=0.01) and over 25 years of follow-up (Pempirical=0.007). Our findings provide the first evidence of putative association of variants in the mitochondrial genome with systolic BP and FBG in the general population. Replication in independent samples, however, is needed to confirm these putative associations.

Superoxide dismutases: role in redox signaling, vascular function, and diseases

Excessive reactive oxygen species Revised abstract, especially superoxide anion (O₂•-), play important roles in the pathogenesis of many cardiovascular diseases, including hypertension and atherosclerosis. Superoxide dismutases (SODs) are the major antioxidant defense systems against (O₂•-), which consist of three isoforms of SOD in mammals: the cytoplasmic Cu/ZnSOD (SOD1), the mitochondrial MnSOD (SOD2), and the extracellular Cu/ZnSOD (SOD3), all of which require catalytic metal (Cu or Mn) for their activation. Recent evidence suggests that in each subcellular location, SODs catalyze the conversion of (O₂•-), H2O2, which may participate in cell signaling. In addition, SODs play a critical role in inhibiting oxidative inactivation of nitric oxide, thereby preventing peroxynitrite formation and endothelial and mitochondrial dysfunction. The importance of each SOD isoform is further illustrated by studies from the use of genetically altered mice and viral-mediated gene transfer. Given the essential role of SODs in cardiovascular disease, the concept of antioxidant therapies, that is, reinforcement of endogenous antioxidant defenses to more effectively protect against oxidative stress, is of substantial interest. However, the clinical evidence remains controversial. In this review, we will update the role of each SOD in vascular biologies, physiologies, and pathophysiologies such as atherosclerosis, hypertension, and angiogenesis. Because of the importance of metal cofactors in the activity of SODs, we will also discuss how each SOD obtains catalytic metal in the active sites. Finally, we will discuss the development of future SOD-dependent therapeutic strategies.

[Mitochondrial tRNAMet mutation in Chinese Han essential hypertensive individuals]

The objective of the present study was to explore the relationship between mitochondrial tRNAMet mutation and development of essential hypertension in Chinese Han individuals. A total of 990 patients with essential hypertension were involved. The general data (sex, age, body mass index, onset age, and family history) and information on routine blood test, blood biochemical examination, and color Doppler echocardiography of these patients were collected. All subjects under-went venous blood drawing for seperating white blood cells and DNA extraction. Then, mitochondrial tRNAMet was amplified and sequenced after purification. The patients who carried the tRNAMet mutation were taken as the indicative cases and the controls were the patients with essential hypertension who did not carry the mutation. We performed a comparative analysis on the routine blood test, blood biochemical examination, color Doppler echocardiography, and other data between the indicative cases and control cases. Among the 990 essential hypertensive patients, there were 8 who carried the tRNAMet mutation, and 6 mutation sites were confirmed, including A4401G, C4410A, U4418C, A4435G, U4454C, and C4456U. Compared with the control cases, the indicative cases developed essential hypertension at earlier ages. The average levels of high density of lipoprotein cholesterol, left ventricular end diastolic diameter, stroke volume, and cardiac index were higher in the indicative cases than in the controls. While the average levels of hemoglobin and left ventricular ejection fraction were lower in the indicative cases than in the control cases. Among the 8 indicative cases, 5 had maternally inherited hyper-tension; one had paternally inherited hypertension; and two denied any family history of hypertension. These results indicated that the mitochondrial tRNAMet mutations might induce the changes in structure and function, which was involved in the progress of the essential hypertension by disturbing the blood metabolism, the steady-state of the blood cells, and the cardiac structure and function.

Reactive oxygen species and vascular biology: implications in human hypertension

Increased vascular production of reactive oxygen species (ROS; termed oxidative stress) has been implicated in various chronic diseases, including hypertension. Oxidative stress is both a cause and a consequence of hypertension. Although oxidative injury may not be the sole etiology, it amplifies blood pressure elevation in the presence of other pro-hypertensive factors. Oxidative stress is a multisystem phenomenon in hypertension and involves the heart, kidneys, nervous system, vessels and possibly the immune system. Compelling experimental and clinical evidence indicates the importance of the vasculature in the pathophysiology of hypertension and as such much emphasis has been placed on the (patho)biology of ROS in the vascular system. A major source for cardiovascular, renal and neural ROS is a family of non-phagocytic nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (Nox), including the prototypic Nox2 homolog-based NADPH oxidase, as well as other Noxes, such as Nox1 and Nox4. Nox-derived ROS is important in regulating endothelial function and vascular tone. Oxidative stress is implicated in endothelial dysfunction, inflammation, hypertrophy, apoptosis, migration, fibrosis, angiogenesis and rarefaction, important processes involved in vascular remodeling in hypertension. Despite a plethora of data implicating oxidative stress as a causative factor in experimental hypertension, findings in human hypertension are less conclusive. This review highlights the importance of ROS in vascular biology and focuses on the potential role of oxidative stress in human hypertension.

Genome-wide discovery of maternal effect variants

Many phenotypes may be influenced by the prenatal environment of the mother and/or maternal care, and these maternal effects may have a heritable component. We have implemented in the computer program SOLAR a variance components-based method for detecting indirect effects of maternal genotype on offspring phenotype. Of six phenotypes measured in three generations of the Framingham Heart Study, height showed the strongest evidence (P = 0.02) of maternal effect. We conducted a genome-wide association analysis for height, testing both the direct effect of the focal individual's genotype and the indirect effect of the maternal genotype. Offspring height showed suggestive evidence of association with maternal genotype for two single-nucleotide polymorphisms in the trafficking protein particle complex 9 gene TRAPPC9 (NIBP), which plays a role in neuronal NF-κB signalling. This work establishes a methodological framework for identifying genetic variants that may influence the contribution of the maternal environment to offspring phenotypes.

Voltage-dependent anion channel (VDAC) is involved in apoptosis of cell lines carrying the mitochondrial DNA mutation

BACKGROUND

The mitochondrial voltage-dependent anion channel (VDAC) is increasingly implicated in the control of apoptosis. We have studied the effects the mitochondrial DNA (mtDNA) tRNAIle mutation on VDAC expression, localization, and apoptosis.

METHODS

Lymphoblastoid cell lines were derived from 3 symptomatic and 1 asymptomatic members of a family with hypertension associated with the A4263G tRNAIle mutation as well as from control subjects. Mitochondrial potential (DeltaPsim) and apoptosis were measured by flow cytometry; co-localization of VDAC and Bax was evaluated by confocal microscopy.

RESULTS

Expression of VDAC and Bax in mtDNA cell lines was found to be increased compared to controls, while expression of the small conductance calcium-dependant potassium channel (sKCa) was unchanged. Confocal imaging revealed co-localization of VDAC/Bax on the outer mitochondrial membrane of A4263G cell lines but not from controls. Flow cytometry indicated that the mitochondrial potential was decreased by 32% in mutated cells versus controls while rates of apoptosis were increased (P < 0.05). The difference was attenuated by Cyclosporin A (CsA, 2 muM), a blocker of VDAC.

CONCLUSION

We conclude that increased expression of mitochondrial VDAC and subcellular co-localization of VDAC/Bax increases mitochondrial permeability and apoptosis in cell lines carrying the mtDNA tRNAIle A4263G mutation.

Genetic variants in mitochondrial tRNA genes are associated with essential hypertension in a Chinese Han population

BACKGROUND

Of multiple factors contributing to essential hypertension, mitochondrial variants exhibited the trends for serving as molecular and genetic markers for the disease in last five years. However, previous studies focused on African-American or Caucasian pedigrees, knowledge of mitochondrial tRNA genes and population-based Chinese hypertensives were limited.

METHODS

We performed sequence analysis in tRNA genes, hot spots for cardiovascular diseases, in 270 Chinese Han essential hypertensives and 270 controls. Lymphoblastoid cell lines were immortalized by transformation with the Epstein-Barr virus. Rates of oxygen consumption in intact cells were determined with a YSI 5300 oxygraph (Yellow Springs Instruments) on samples, harboring variants in tRNA genes.

RESULTS

There were 26 variants in tRNA genes that were found in hypertensives and these variants were not in controls. Functional analysis found that these variants may lead to deficiencies in tRNA 3' end metabolism and/or impairment of critical subunits of the respiratory chain. Most importantly, the oxygen consumption rate in cells harboring variants T4454C (P=0.0010) and A4263G (P=0.0001) decreased as compared to the average level of control cell lines.

CONCLUSIONS

Variants located in mitochondrial tRNA genes may have biologic plausibility to implicate in the pathogenesis of Chinese essential hypertension.

The role of mitochondrial genome in essential hypertension in a Chinese Han population

Earlier genetic studies of essential hypertension have focused on nuclear genes or family-based mitochondrial screening in Caucasian and African-American pedigrees. The role of mitochondria in sporadic Chinese hypertensives is unknown. We sequenced mitochondrial genomes in 306 age- and gender-balanced Chinese Han hypertensives and controls. In 153 hypertensives, putative functional changes included 4 changes in rRNA genes, 11 changes in tRNA genes and 25 amino-acid substitutions. The remaining variants were synonymous changes or non-coding regions. In the 153 controls, 2 base changes in the tRNA genes and 13 amino-acid substitutions were found. A8701G in ATP6 gene (belongs to haplogroup M; P=0.0001) and C8414T in ATP8 gene (belongs to haplogroup D; P=0.01) were detected significantly different in the cases and controls. Interestingly, the cases were more likely to have two or more amino-acid changes and RNA variants compared with the controls (57.43 versus 23.81%, P=0.0001). In addition, several variants we found were highly conserved and/or specifically located at the 3' end adjacent to the anticodon, which may contribute to the stabilization of structure, and thus lead to the decrease of tRNA metabolism. In conclusion, mitochondrial SNPs (mtSNPs) may affect the course of hypertension in sporadic Chinese hypertensives. Some specific mtSNP within mitochondria may have potential role in the Chinese hypertensives due to their function. Synergetic interaction between mitochondrial mtSNPs and/or haplogroups is needed to be investigated in the future.

What are maternal effects (and what are they not)?

Maternal effects can play an important role in a diversity of ecological and evolutionary processes such as population dynamics, phenotypic plasticity, niche construction, life-history evolution and the evolutionary response to selection. However, although maternal effects were defined by quantitative geneticists well over half a century ago, there remains some confusion over exactly what phenomena should be characterized as maternal effects and, more importantly, why it matters and how they are defined. We suggest a definition of maternal effects as the causal influence of the maternal genotype or phenotype on the offspring phenotype. This definition differs from some definitions in that it treats maternal effects as a phenomenon, not as a statistical construct. The causal link to maternal genotype or phenotype is the critical component of this definition providing the link between maternal effects and evolutionary and ecological processes. We show why phenomena such as maternal cytoplasmic inheritance and genomic imprinting are distinct genetically from and have different evolutionary consequences than true maternal effects. We also argue that one should consider cases where the maternal effect is conditional on offspring genotype as a class of maternal effects.