Mitochondrial genome polymorphisms associated with type-2 diabetes or obesity

Association between mtDNA haplogroups and skeletal fluorosis in Han population residing in drinking water endemic fluorosis area of northern China

To investigate the association between mtDNA genetic information and the risk of SF, individuals were conducted in the drinking water endemic fluorosis area in northern China, sequenced the whole genome of mtDNA, identified the SNPs and SNVs, analyzed the haplogroups, and diagnosed SF, and then, the effect of mtDNA genetic information on the risk of SF was evaluated. We find that, D5 haplogroup and its specific SNPs reduced the risk, while the D4 haplogroup and its specific SNPs increased the risk of SF. The number of SNVs in coding regions of mitochondrial respiratory chain (MRC) is different between the controls and cases. This suggests that D5 haplogroup may play a protective role in the risk of SF, while the opposite is observed for the D4 haplogroup, this may relate to their specific SNPs. And SNVs that encode the MRC complex may also be associated with the risk of SF.

mtDNA Single-Nucleotide Variants Associated with Type 2 Diabetes

Type 2 diabetes (T2D) is a chronic systemic disease with a complex etiology, characterized by insulin resistance and mitochondrial dysfunction in various cell tissues. To explore this relationship, we conducted a secondary analysis of complete mtDNA sequences from 1261 T2D patients and 1105 control individuals. Our findings revealed significant associations between certain single-nucleotide polymorphisms (SNPs) and T2D. Notably, the variants m.1438A>G (rs2001030) (controls: 32 [27.6%], T2D: 84 [72.4%]; OR: 2.46; 95%CI: 1.64-3.78; p < 0.001), m.14766C>T (rs193302980) (controls: 498 [36.9%], T2D: 853 [63.1%]; OR: 2.57, 95%CI: 2.18-3.04, p < 0.001), and m.16519T>C (rs3937033) (controls: 363 [43.4%], T2D: 474 [56.6%]; OR: 1.24, 95%CI: 1.05-1.47, p = 0.012) were significantly associated with the likelihood of developing diabetes. The variant m.16189T>C (rs28693675), which has been previously documented in several studies across diverse populations, showed no association with T2D in our analysis (controls: 148 [13.39] T2D: 171 [13.56%]; OR: 1.03; 95%CI: 0.815-1.31; p = 0.83). These results provide evidence suggesting a link between specific mtDNA polymorphisms and T2D, possibly related to association rules, topological patterns, and three-dimensional conformations associated with regions where changes occur, rather than specific point mutations in the sequence.

Mitochondrial Dysfunction Associated with mtDNA in Metabolic Syndrome and Obesity

Metabolic syndrome (MetS) is a precursor to the major health diseases associated with high mortality in industrialized countries: cardiovascular disease and diabetes. An important component of the pathogenesis of the metabolic syndrome is mitochondrial dysfunction, which is associated with tissue hypoxia, disruption of mitochondrial integrity, increased production of reactive oxygen species, and a decrease in ATP, leading to a chronic inflammatory state that affects tissues and organ systems. The mitochondrial AAA + protease Lon (Lonp1) has a broad spectrum of activities. In addition to its classical function (degradation of misfolded or damaged proteins), enzymatic activity (proteolysis, chaperone activity, mitochondrial DNA (mtDNA)binding) has been demonstrated. At the same time, the spectrum of Lonp1 activity extends to the regulation of cellular processes inside mitochondria, as well as outside mitochondria (nuclear localization). This mitochondrial protease with enzymatic activity may be a promising molecular target for the development of targeted therapy for MetS and its components. The aim of this review is to elucidate the role of mtDNA in the pathogenesis of metabolic syndrome and its components as a key component of mitochondrial dysfunction and to describe the promising and little-studied AAA + LonP1 protease as a potential target in metabolic disorders.

ANALYSIS OF MITOCHONDRIAL DNA CYTOCHROME-B (CYB) and ATPase-6 GENE MUTATIONS IN COVID-19 PATIENTS

BACKGROUND

Coronavirus disease of 2019 (COVID-19) is a pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Mutations of mitochondrial DNA (mtDNA) are becoming increasingly common in various diseases. This study aims to investigate mutations in the cytochrome-b (CYB) and adenosine triphosphatase-6 (ATPase-6) genes of mtDNA in COVID-19 patients. The association between mtDNA mutations and clinical outcomes is investigated.

METHODS

In the present study, mutations of the mtDNA genes CYB and ATPase-6 were investigated in COVID-19(+) (n=65) and COVID-19 (-) patients (n=65). First, we isolated DNA from the blood samples. After the PCR analyses, the mutations were defined using Sanger DNA sequencing.

RESULTS

The age, creatinine, ferritin and CRP levels of the COVID 19 (+) patients were higher than those of the COVID-19 (-) patients (p=0.0036, p=0.0383, p=0.0305, p<0.0001, respectively). We also found 16 different mutations in the CYB gene and 14 different mutations in the ATPase-6 gene. The incidences of CYB gene mutations A15326G, T15454C and C15452A were higher in COVID-19 (+) patients than COVID-19 (-) patients (p<0.0001 (OR (95% CI): 4.966 (2.215-10.89)), p=0.0226 and p=0.0226, respectively). In contrast, the incidences of A8860G and G9055A ATPase-6 gene mutations were higher in COVID-19 (+) patients than COVID-19 (-) patients (p<0.0001 (OR (95%CI): 5.333 (2.359-12.16) and p=0.0121 respectively). Yet, no significant relationship was found between mtDNA mutations and patients' age and biochemical parameters (p> 0.05).

CONCLUSIONS

The results showed that the frequency of mtDNA mutations in COVID-19 patients is quite high and it is important to investigate the association of these mutations with other genetic mechanisms in larger patient populations. This article is protected by copyright. All rights reserved.

Influence of Nutritional Intakes in Japan and the United States on COVID-19 Infection

The U.S. and Japan are both democratic industrialized societies, but the numbers of COVID-19 cases and deaths per million people in the U.S. (including Japanese Americans) are 12.1-times and 17.4-times higher, respectively, than those in Japan. The aim of this study was to investigate the effects of diet on preventing COVID-19 infection. An analysis of dietary intake and the prevalence of obesity in the populations of both countries was performed, and their effects on COVID-19 infection were examined. Approximately 1.5-times more saturated fat and less eicosapentaenoic acid/docosahexaenoic acid are consumed in the U.S. than in Japan. Compared with food intakes in Japan (100%), those in the U.S. were as follows: beef 396%, sugar and sweeteners 235%, fish 44.3%, rice 11.5%, soybeans 0.5%, and tea 54.7%. The last four of these foods contain functional substances that prevent COVID-19. The prevalence of obesity is 7.4- and 10-times greater in the U.S. than in Japan for males and females, respectively. Mendelian randomization established a causal relationship between obesity and COVID-19 infection. Large differences in nutrient intakes and the prevalence of obesity, but not racial differences, may be partly responsible for differences in the incidence and mortality of COVID-19 between the U.S. and Japan.

Synthesis and properties of the anticodon stem-loop of human mitochondrial tRNAMet containing the disease-related G or m1G nucleosides at position 37

A single point mutation (A4435G) in the human mitochondrial tRNA^Met (hmt-tRNA^Met) gene causes severe mitochondrial disorders associated with hypertension, type 2 diabetes and LHON. This mutation leads to the exchange of A₃₇ in the anticodon loop of hmt-tRNA^Met for G₃₇ and 1-methylguanosine (m¹G₃₇). Here we present the first synthesis and structural/biophysical studies of the anticodon stem and loop of pathogenic hmt-tRNAs^Met.

Mitochondria and Antibiotics: For Good or for Evil?

The discovery and application of antibiotics in the common clinical practice has undeniably been one of the major medical advances in our times. Their use meant a drastic drop in infectious diseases-related mortality and contributed to prolonging human life expectancy worldwide. Nevertheless, antibiotics are considered by many a double-edged sword. Their extensive use in the past few years has given rise to a global problem: antibiotic resistance. This factor and the increasing evidence that a wide range of antibiotics can damage mammalian mitochondria, have driven a significant sector of the medical and scientific communities to advise against the use of antibiotics for purposes other to treating severe infections. Notwithstanding, a notorious number of recent studies support the use of these drugs to treat very diverse conditions, ranging from cancer to neurodegenerative or mitochondrial diseases. In this context, there is great controversy on whether the risks associated to antibiotics outweigh their promising beneficial features. The aim of this review is to provide insight in the topic, purpose for which the most relevant findings regarding antibiotic therapies have been discussed.

Placental mitochondrial DNA mutational load and perinatal outcomes: Findings from a multi-ethnic pregnancy cohort

Mitochondria fuel placental activity, with mitochondrial dysfunction implicated in several perinatal complications. We investigated placental mtDNA mutational load using NextGen sequencing in relation to birthweight and gestational length among 358 mother-newborn pairs. We found that higher heteroplasmy, especially in the hypervariable displacement loop region, was associated with shorter gestational length. Results were similar among male and female pregnancies, but stronger in magnitude among females. With regard to growth, we observed that higher mutational load was associated with lower birthweight-for-gestational age (BWGA) among females, but higher BWGA among males. These findings support potential sex-differential fetal biological strategies for coping with increased heteroplasmies.

Heterologous Inferential Analysis (HIA) and Other Emerging Concepts: In Understanding Mitochondrial Variation In Pathogenesis: There is no More Low-Hanging Fruit

Here we summarize our latest efforts to elucidate the role of mtDNA variants affecting the mitochondrial translation machinery, namely variants mapping to the mt-rRNA and mt-tRNA genes. Evidence is accumulating to suggest that the cellular response to interference with mitochondrial translation is different from that occurring as a result of mutations in genes encoding OXPHOS proteins. As a result, it appears safe to state that a complete view of mitochondrial disease will not be obtained until we understand the effect of mt-rRNA and mt-tRNA variants on mitochondrial protein synthesis. Despite the identification of a large number of potentially pathogenic variants in the mitochondrially encoded rRNA (mt-rRNA) genes, we lack direct methods to firmly establish their pathogenicity. In the absence of such methods, we have devised an indirect approach named heterologous inferential analysis (HIA ) that can be used to make predictions concerning the disruptive potential of a large subset of mt-rRNA variants. We have used HIA to explore the mutational landscape of 12S and 16S mt-rRNA genes. Our HIA studies include a thorough classification of all rare variants reported in the literature as well as others obtained from studies performed in collaboration with physicians. HIA has also been used with non-mammalian mt-rRNA genes to elucidate how mitotypes influence the interaction of the individual and the environment. Regarding mt-tRNA variations, rapidly growing evidence shows that the spectrum of mutations causing mitochondrial disease might differ between the different mitochondrial haplogroups seen in human populations.

Maternal transmission of mitochondrial diseases

Given the major role of the mitochondrion in cellular homeostasis, dysfunctions of this organelle may lead to several common diseases in humans. Among these, maternal diseases linked to mitochondrial DNA (mtDNA) mutations are of special interest due to the unclear pattern of mitochondrial inheritance. Multiple copies of mtDNA are present in a cell, each encoding for 37 genes essential for mitochondrial function. In cases of mtDNA mutations, mitochondrial malfunctioning relies on mutation load, as mutant and wild-type molecules may co-exist within the cell. Since the mutation load associated with disease manifestation varies for different mutations and tissues, it is hard to predict the progeny phenotype based on mutation load in the progenitor. In addition, poorly understood mechanisms act in the female germline to prevent the accumulation of deleterious mtDNA in the following generations. In this review, we outline basic aspects of mitochondrial inheritance in mammals and how they may lead to maternally-inherited diseases. Furthermore, we discuss potential therapeutic strategies for these diseases, which may be used in the future to prevent their transmission.

Genomic profiling of mitochondrial DNA reveals novel complex gene mutations in familial type 2 diabetes mellitus individuals from Mizo ethnic population, Northeast India

The variants reported for mitochondrial DNA (mtDNA) and type 2 diabetes (T2D) may not be accountable for the disease in certain other populations and the risk depends upon numerous factors which may include genetics, environment as well as ethnicity. This leads to a challenge in identifying, exploring and comparing the variants between diabetic cases and healthy controls in a remote unexplored tribal population. To study the possible contribution of mtDNA variants, we sequenced the entire mitochondrial genomes and the frequencies of mtSNPs, their association with familial T2D and the potential impact of non-synonymous substitutions on protein functions were determined. The mtSNP 8584 G > A (ATP6: A20T) was detected in 14.28% of the diabetic patients and none in the control groups. The mitochondrial ND3 variant 10398A > G was found to be significantly associated with the risk of T2D (OR = 9.489, 95% CI = 1.161-77.54, P value = 0.036). A novel Frame-shift substitution ND5: 81_81ins A at position 12,417 was observed in 53.57% of diabetic individuals. Majority of the variants lie in tRNA-Phe in the non-protein coding region of mtDNA for both diabetic cases and common cases. We concluded that mutations in the coding (synonymous or non-synonymous) and noncoding regions of the mitochondria might have contribution towards the development of T2D. Our study is the first to report the distinct mitochondrial variants which may be attributed to the susceptibility as well as development of type 2 diabetes in an ethnic tribe from northeast India.

Mitochondrial complex I deficiency and cardiovascular diseases: current evidence and future directions

Compelling evidence demonstrates the emerging role of mitochondrial complex I deficiency in the onset and development of cardiovascular diseases (CVDs). In particular, defects in single subunits of mitochondrial complex I have been associated with cardiac hypertrophy, ischemia/reperfusion injury, as well as diabetic complications and stroke in pre-clinical studies. Moreover, data obtained in humans revealed that genes coding for complex I proteins were associated with different CVDs. In this review, we discuss recent experimental studies that underline the contributory role of mitochondrial complex I deficiency in the etiopathogenesis of several CVDs, with a particular focus on those involving loss of function models of mitochondrial complex I. We also discuss human studies and potential therapeutic strategies able to rescue mitochondrial function in CVDs.

Relationships Between Adipose Mitochondrial Function, Serum Adiponectin, and Insulin Resistance in Persons With HIV After 96 Weeks of Antiretroviral Therapy

OBJECTIVE

Some antiretroviral therapy (ART) and HIV itself confer metabolic risk, perhaps through altered mitochondrial function and adipokines. In AIDS Clinical Trials Group study A5224s, adipose mitochondrial DNA (mtDNA) levels decreased on ART, and electron transport chain complex I (CI) and complex IV (CIV) activity decreased. Another study found decreased serum adiponectin on ART with mtDNA mutation m.10398A>G. We hypothesized that decreased adipose tissue mitochondrial function would be associated with lower adiponectin and insulin sensitivity on ART, and m.10398G would influence these changes.

DESIGN

Retrospective analysis of an ART-naive substudy population from A5224s.

METHODS

Analyses included adipose mtDNA levels, CI and CIV activity by immunoassay, visceral adipose tissue by computed tomography, and fasting serum glucose at week 0 and week 96 of ART. Fasting insulin and adiponectin were measured from cryopreserved serum using multiplex bead array. Homeostasis model assessment-2 (HOMA2)-IR and HOMA2-%B estimated insulin resistance and β-cell function, respectively. The m.10398A>G mtDNA variant was available from existing genetic data.

RESULTS

Thirty-seven participants had adipose biopsies at week 0 and week 96. Percent decreases in CIV activity and adiponectin were correlated (Spearman rho 0.41; P = 0.01); this association persisted after controlling for age, sex, body mass index, or visceral adipose tissue in single-covariate regression. HOMA2-IR correlated with decreased CIV (-0.44; P = 0.01) and CI (-0.34; P = 0.05) activity. Among 12 non-Hispanic white persons, m.10398G was associated with decreased adiponectin (P = 0.04).

CONCLUSIONS

Decreased adipose mitochondrial activity correlated with changes in adiponectin and glucose homeostasis on ART. Previous findings that a mtDNA mutation modulates adiponectin levels in persons with HIV were replicated.

Mitochondrial dysfunction in type 2 diabetes mellitus: an organ-based analysis

Type 2 diabetes mellitus (T2DM) is a systemic disease characterized by hyperglycemia, hyperlipidemia, and organismic insulin resistance. This pathological shift in both circulating fuel levels and energy substrate utilization by central and peripheral tissues contributes to mitochondrial dysfunction across organ systems. The mitochondrion lies at the intersection of critical cellular pathways such as energy substrate metabolism, reactive oxygen species (ROS) generation, and apoptosis. It is the disequilibrium of these processes in T2DM that results in downstream deficits in vital functions, including hepatocyte metabolism, cardiac output, skeletal muscle contraction, β-cell insulin production, and neuronal health. Although mitochondria are known to be susceptible to a variety of genetic and environmental insults, the accumulation of mitochondrial DNA (mtDNA) mutations and mtDNA copy number depletion is helping to explain the prevalence of mitochondrial-related diseases such as T2DM. Recent work has uncovered novel mitochondrial biology implicated in disease progressions such as mtDNA heteroplasmy, noncoding RNA (ncRNA), epigenetic modification of the mitochondrial genome, and epitranscriptomic regulation of the mtDNA-encoded mitochondrial transcriptome. The goal of this review is to highlight mitochondrial dysfunction observed throughout major organ systems in the context of T2DM and to present new ideas for future research directions based on novel experimental and technological innovations in mitochondrial biology. Finally, the field of mitochondria-targeted therapeutics is discussed, with an emphasis on novel therapeutic strategies to restore mitochondrial homeostasis in the setting of T2DM.

Human mitochondrial DNA haplogroup M8a influences the penetrance of m.8684C>T in Han Chinese men with non-obstructive azoospermia

RESEARCH QUESTION

What is the role of mitochondrial DNA (mtDNA) in the pathogenesis of non-obstructive azoospermia (NOA)?

DESIGN

mtDNA genome sequencing followed by an independent population validation were performed in 628 NOA cases and 584 healthy controls. Antioxidant capacity of serum was evaluated in 54 randomly selected cases out of 536 and 49 out of 489 controls.

RESULTS

In the screening stage, 13 mtDNA haplogroups (hg) were ascertained, and 10 susceptible variants were observed. In the validation stage, hg M8* in individuals was found to be associated with increased risk of NOA [odds ratio (OR) 2.61, 95% confidence interval (CI) 1.47-4.61] (P=0.001). Unexpectedly, the frequency of m.8684C>T, the defining marker for hg M8a, was also higher in NOA (OR 4.14, 95% CI 1.56-11.03) (P=0.002). Subsequently, the frequency distributions were compared among the sub-hg of hg M8* (including hg M8a, C and Z) and, intriguingly, no significance was found in hg C and Z. Additionally, the level of total antioxidant capacity was significantly decreased (P<0.05) compared with the control group.

CONCLUSIONS

hg M8a background in general played an active role in the penetrance of 8684C>T in NOA, and mtDNA genetic variants (causing low antioxidant levels) might increase mtDNA damage and impair normal spermatogenesis.

Mitochondrial DNA associations with East Asian metabolic syndrome

Mitochondrial dysfunction has repeatedly been reported associated with type 2 diabetes mellitus (T2DM) and metabolic syndrome (MS), as have mitochondrial DNA (mtDNA) tRNA and duplication mutations and mtDNA haplogroup lineages. We identified 19 Taiwanese T2DM and MS pedigrees from Taiwan, with putative matrilineal transmission, one of which harbored the pathogenic mtDNA tRNA^Leu(UUR) nucleotide (nt) 3243A>G mutation on the N9a3 haplogroup background. We then recruited three independent Taiwanese cohorts, two from Taipei (N = 498, mean age 52 and N = 1002, mean age 44) and one from a non-urban environment (N = 501, mean age 57). All three cohorts were assessed for an array of metabolic parameters, their mtDNA haplogroups determined, and the haplogroups correlated with T2DM/MS phenotypes. Logistic regression analysis revealed that mtDNA haplogroups D5, F4, and N9a conferred T2DM protection, while haplogroups F4 and N9a were risk factors for hypertension (HTN), and F4 was a risk factor for obesity (OB). Additionally, the 5263C>T (ND2 A165V) variant commonly associated with F4 was associated with hypertension (HTN). Cybrids were prepared with macro-haplogroup N (defined by variants m.ND3 10398A (114T) and m.ATP6 8701A (59T)) haplogroups B4 and F1 mtDNAs and from macro-haplogroup M (variants m.ND3 10398G (114A) and m.ATP6 8701G (59A)) haplogroup M9 mtDNAs. Additionally, haplogroup B4 and F1 cybrids were prepared with and without the mtDNA variant in ND1 3394T>C (Y30H) reported to be associated with T2DM. Assay of mitochondria complex I in these cybrids revealed that macro-haplogroup N cybrids had lower activity than M cybrids, that haplogroup F cybrids had lower activity than B4 cybrids, and that the ND1 3394T>C (Y30H) variant reduced complex I on both the B4 and F1 background but with very different cumulative effects. These data support the hypothesis that functional mtDNA variants may contribute to the risk of developing T2DM and MS.

Mitochondrial DNA Mutations Associated with Type 2 Diabetes Mellitus in Chinese Uyghur Population

A hospital-based case-control study was conducted to investigate potential association between mitochondrial DNA and Type 2 diabetes mellitus (T2DM) in Chinese Uyghur population. We sequenced mitochondrial DNA from 210 Uyghur individuals including 88 T2DM patients and 122 controls. Using haplogroup classification and association test, we found that haplogroup H (odds ratio [OR] = 1.40; 95% confidence interval [CI]: 1.20–1.64; P = 0.0005138) and D4 (odds ratio = 1.47; 95% CI: 1.22–1.77; P = 0.001064) were associated with an increased risk of T2DM in Chinese Uyghur population. Two markers of haplogroup D4 and H, MT-ATP8 m.8414 T > G (p.Leu17Phe) and m.2706 G > A encoding 16S rRNA in mitochondria, were predicted to affect the structure of MT-ATP8 and 16S RNA, respectively, and may be involved in the pathogenesis of T2DM. Our study provides a new clue for mitochondrial DNA in the etiology of T2DM in Chinese Uyghur population.

Endothelial Cell Bioenergetics and Mitochondrial DNA Damage Differ in Humans Having African or West Eurasian Maternal Ancestry

BACKGROUND

We hypothesized that endothelial cells having distinct mitochondrial genetic backgrounds would show variation in mitochondrial function and oxidative stress markers concordant with known differential cardiovascular disease susceptibilities. To test this hypothesis, mitochondrial bioenergetics were determined in endothelial cells from healthy individuals with African versus European maternal ancestries.

METHODS AND RESULTS

Bioenergetics and mitochondrial DNA (mtDNA) damage were assessed in single-donor human umbilical vein endothelial cells belonging to mtDNA haplogroups H and L, representing West Eurasian and African maternal ancestries, respectively. Human umbilical vein endothelial cells from haplogroup L used less oxygen for ATP production and had increased levels of mtDNA damage compared with those in haplogroup H. Differences in bioenergetic capacity were also observed in that human umbilical vein endothelial cells belonging to haplogroup L had decreased maximal bioenergetic capacities compared with haplogroup H. Analysis of peripheral blood mononuclear cells from age-matched healthy controls with West Eurasian or African maternal ancestries showed that haplogroups sharing an A to G mtDNA mutation at nucleotide pair 10398 had increased mtDNA damage compared with those lacking this mutation. Further study of angiographically proven patients with coronary artery disease and age-matched healthy controls revealed that mtDNA damage was associated with vascular function and remodeling and that age of disease onset was later in individuals from haplogroups lacking the A to G mutation at nucleotide pair 10398.

CONCLUSIONS

Differences in mitochondrial bioenergetics and mtDNA damage associated with maternal ancestry may contribute to endothelial dysfunction and vascular disease.

Effects of mitochondrial haplogroup N9a on type 2 diabetes mellitus and its associated complications

A case-control study was conducted with the aim of identifying the predominant haplogroups associated with type 2 diabetes mellitus (T2DM) and its complications. In addition, the role of N9a in T2DM risk and complications was analyzed. Sequencing of the entire mitochondrial DNA was conducted in 235 patients and 244 controls in cohort 1, and six haplogroups (F, B4, D4, D5, M8a and N9a) associated with T2DM were classified. The frequency of N9a was further determined in cohort 2 (440 patients and 244 controls) and examined in two combined cohorts, including 675 patients with T2DM and 649 non-diabetic controls. Multivariate logistic regression analysis and association analysis were performed to investigate the association between genotypes, T2DM and diabetic nephropathy. M8a [P=0.011; odds ratio (OR), 3.49; 95% confidence interval (CI), 1.26-9.69] and haplogroup N9a (P=0.023; OR, 2.60; 95% CI, 1.11-6.05) were associated with an increased risk of T2DM. The frequency of N9a was higher in T2DM patients compared with that in the controls (6.2% vs. 4.3%) and associated with a mild risk (P=0.10; OR, 1.51; 95% CI, 0.92-2.49). N9a was significantly associated with an increased risk of diabetic nephropathy (P=0.024; OR, 2.15; 95% CI, 1.11-4.19). Previous findings of N9a being protective against T2DM were not replicated in the present study, although this haplogroup was associated with an increased risk of diabetic nephropathy.

Mitochondrial dysfunction as a central event for mechanisms underlying insulin resistance: the roles of long chain fatty acids

Insulin resistance is characterized by hyperglycaemia, dyslipidaemia and oxidative stress prior to the development of type 2 diabetes mellitus. To date, a number of mechanisms have been proposed to link these syndromes together, but it remains unclear what the unifying condition that triggered these events in the progression of this metabolic disease. There have been a steady accumulation of data in numerous experimental studies showing the strong correlations between mitochondrial dysfunction, oxidative stress and insulin resistance. In addition, a growing number of studies suggest that the raised plasma free fatty acid level induced insulin resistance with the significant alteration of oxidative metabolism in various target tissues such as skeletal muscle, liver and adipose tissue. In this review, we herein propose the idea of long chain fatty acid-induced mitochondrial dysfunctions as one of the key events in the pathophysiological development of insulin resistance and type 2 diabetes. The accumulation of reactive oxygen species, lipotoxicity, inflammation-induced endoplasmic reticulum stress and alterations of mitochondrial gene subset expressions are the most detrimental that lead to the developments of aberrant intracellular insulin signalling activity in a number of peripheral tissues, thereby leading to insulin resistance and type 2 diabetes.

Characterization of proteins regulated by interleukin-4 in 3T3-L1 adipocytes

Obesity is closely associated with metabolic syndrome, type 2 diabetes mellitus (T2DM) and cardiovascular diseases. Our previous reports uncover the significant associations between interleukin-4 (IL-4)/IL-4 receptor genotypes and T2DM, as well as IL-4 genotypes and high density lipoprotein-cholesterol. Theses observations suggest that IL-4 harbors the capacity to regulate lipid metabolism. The present study is aimed at further elucidating regulatory roles of IL-4 to lipid metabolism by identifying putative proteins in 3T3-L1 adipocytes which are differentially expressed under IL-4 treatment. Proteins in mature 3T3-L1 adipocytes with altered expression levels under IL-4 treatment were identified by proteomic strategy. Our results revealed that IL-4 up-regulated levels of ATP synthase δ chain, Cytochrome c reductase, Pyrophsphatase and Vimentin, whereas, Alpha-enolase, Gelsolin, Vinculin and Valosin were down-regulated. These observations suggest that IL-4 promotes energy metabolism and inhibit lipid deposits in adipocytes by up-regulating proteins accelerating ATP synthesis. Our results suggest that IL-4 facilitates adipocytes metabolism to catabolism with a favorable condition for lipolysis. These catabolized lipids in adipocytes triggered by IL-4 might either be released into periphery or metabolized intracellularlly, and modulate systemic energy metabolism.

Alper Ö. Mitochondrial ATPase subunit 6 and cytochrome B gene variations in obese Turkish children

OBJECTIVE

Due to the importance of energy metabolism in mitochondria, mitochondrial genome variations are evaluated in energy-related diseases such as obesity. To date, several nuclear genes were found to be related to obesity. Our aim in this study was to investigate the presence of polymorphisms in mitochondrial ATPase subunit 6 (mt-ATP6) and cytochrome b (mt-CytB) genes that may be associated with childhood obesity.

METHODS

The mt-ATP6 and mt-CytB genes were amplified and entirely sequenced in a series of 100 obese and in an equal number of healthy Turkish children aged between 6-14 years.

RESULTS

A total of 118 synonymous and nonsynonymous variations were detected in the obese and control groups. Only two previously reported synonymous substitutions (mt.8614T>C and mt.8994G>A) in the mt-ATP6 gene were found to be significantly higher in the obese group compared to the control group (p<0.05). In the mt-ATP6 gene, one novel nonsynonymous substitution (mt.8726C>T) and one novel synonymous substitution (mt.9108A>T) were found. In the mt-CytB gene, one nonsynonymous substitution (mt.14880T>C) and two synonymous substitutions (mt.14891C>T and mt.15091C>T) were novel substitutions.

CONCLUSION

Two synonymous substitutions (mt.8614T>C and mt.8994G>A) in the mt-ATP6 gene may be associated with childhood obesity. Our study provides the first data about mitochondrial genome variations in a Turkish obese population and also the first in obese children. More cases should be screened in obese groups in order to understand the effects of mitochondrial polymorphisms in the development of obesity.

Disrupting mitochondrial-nuclear coevolution affects OXPHOS complex I integrity and impacts human health

The mutation rate of the mitochondrial DNA (mtDNA), which is higher by an order of magnitude as compared with the nuclear genome, enforces tight mitonuclear coevolution to maintain mitochondrial activities. Interruption of such coevolution plays a role in interpopulation hybrid breakdown, speciation events, and disease susceptibility. Previously, we found an elevated amino acid replacement rate and positive selection in the nuclear DNA-encoded oxidative phosphorylation (OXPHOS) complex I subunit NDUFC2, a phenomenon important for the direct interaction of NDUFC2 with the mtDNA-encoded complex I subunit ND4. This finding underlines the importance of mitonuclear coevolution to physical interactions between mtDNA and nuclear DNA-encoded factors. Nevertheless, it remains unclear whether this interaction is important for the stability and activity of complex I. Here, we show that siRNA silencing of NDUFC2 reduced growth of human D-407 retinal pigment epithelial cells, significantly diminished mitochondrial membrane potential, and interfered with complex I integrity. Moreover, site-directed mutagenesis of a positively selected amino acid in NDUFC2 significantly interfered with the interaction of NDUFC2 with its mtDNA-encoded partner ND4. Finally, we show that a genotype combination involving this amino acid (NDUFC2 residue 46) and the mtDNA haplogroup HV likely altered susceptibility to type 2 diabetes mellitus in Ashkenazi Jews. Therefore, mitonuclear coevolution is important for maintaining mitonuclear factor interactions, OXPHOS, and for human health.

Mitochondrial genetic variants identified to be associated with BMI in adults

It has been suggested that mitochondrial dysfunction plays a role in metabolic disorders including obesity, diabetes, and hypertension. The fact that mitochondrial defects can be accumulated over time as a normal part of aging may explain why some individuals can eat all sorts of foods and remain at normal weight while they are young. However, around the fourth decade of life there is a trend towards "middle-age spread" with weight gain and the body's decreasing ability to metabolize calories efficiently. To test the hypothesis that mitochondrial variants are associated with BMI in adults, we analyzed a total number of 984 mitochondrial single nucleotide polymorphisms (mtSNPs) in a sample of 6,528 individuals participating in the KORA studies. To assess mtSNP association while taking heteroplasmy into account we used the raw signal intensity values measured on the microarray and applied linear regression. Significant results were obtained for 2 mtSNPs located in the Cytochrome c oxidase subunit genes (MT-CO1: Padjusted = 0.0140 and MT-CO3: Padjusted = 0.0286) and 3 mtSNPs located in the NADH dehydrogenase subunit genes (MT-ND1, MT-ND2 and MT-ND4L: Padjusted = 0.0286). Polymorphisms located in the MT-CO3 and MT-ND4L genes have not been associated with BMI or related phenotypes in the past. Our results highlight the importance of the mitochondrial genome among the factors that contribute to the risk of high BMI. Focusing on mitochondrial variants may lead to further insights regarding effects of existing medications, or even to the development of innovative treatments.

Association study of mitochondrial DNA polymorphisms with type 2 diabetes in Tunisian population

Mitochondrial DNA (mtDNA) variation may play an important role in the pathogenesis of type 2 diabetes (T2Ds). In this study, we aimed to explore whether mtDNA variants contribute to the susceptibility to T2Ds in a Tunisian population. The hypervariable region 1 (HVS1) of the mtDNA of 64 T2Ds patients and 77 healthy controls was amplified and sequenced. Statistical analysis was performed using the STATA program. Analysis of the total screened variants (N = 88) from the HVS1 region showed no significant difference in the distribution of all polymorphisms between T2Ds and controls, except for the variant G16390A which was more frequent in T2Ds (15.9%) than in controls (5.4%) (p = 0.04). The association of G16390A was not detected after multivariate regression analysis. Similarly, analysis of the distribution of mitochondrial haplogroups within our dataset showed 18 distinct major haplogroups with no significant difference between T2Ds and controls. Except, the weakly association found for the G16390A variant, our results showed that none of the tested polymorphisms from the HVS1 region have a major role in T2Ds pathogenesis in the studied Tunisian population even when taking into account the population stratification.

Associations of mitochondrial haplogroups b4 and e with biliary atresia and differential susceptibility to hydrophobic bile Acid

Mitochondrial dysfunction has been implicated in the pathogenesis of biliary atresia (BA). This study aimed to determine whether a specific mitochondrial DNA haplogroup is implicated in the pathogenesis and prognosis of BA. We determined 40 mitochondrial single nucleotide polymorphisms in 15 major mitochondrial haplogroups by the use of 24-plex PCR and fluorescent beads combined with sequence-specific oligonucleotide probes in 71 patients with BA and in 200 controls in the Taiwanese population of ethnic Chinese background. The haplogroup B4 and E prevalence were significantly lower and higher respectively, in the patients with BA than in the controls (odds ratios, 0.82 [p = 0.007] and 7.36 [p = 0.032] respectively) in multivariate logistic-regression analysis. The 3-year survival rate with native liver was significantly lower in haplogroup E than the other haplogroups (P = 0.037). A cytoplasmic hybrid (cybrid) was obtained from human 143B osteosarcoma cells devoid of mtDNA (ρ⁰ cell) and was fused with specific mtDNA bearing E and B4 haplogroups donated by healthy Taiwanese subjects. Chenodeoxycholic acid treatment resulted in significantly lower free radical production, higher mitochondrial membrane potential, more viable cells, and fewer apoptotic cybrid B4 cells than parental 143B and cybrid E cells. Bile acid treatment resulted in a significantly greater protective mitochondrial reaction with significantly higher mitochondrial DNA copy number and mitofusin 1 and 2 concentrations in cybrid B4 and parental cells than in cybrid E cells. The results of the study suggested that the specific mitochondrial DNA haplogroups B4 and E were not only associated with lower and higher prevalence of BA respectively, in the study population, but also with differential susceptibility to hydrophobic bile acid in the cybrid harboring different haplogroups.

Mitochondrial dysfunction has been implicated in the pathogenesis of biliary atresia (BA). We determined 40 mitochondrial single nucleotide polymorphisms in different mitochondrial haplogroups in BA patients and controls. The prevalence of haplogroup B4 and E was significantly lower and higher respectively, in the patients with BA than in the controls. The survival rate with native liver was significantly lower in haplogroup E than the other haplogroups. The in vitro study using cybrid cells revealed significantly lower free radical production, higher mitochondrial membrane potential, higher mitochondrial DNA copy number and fewer apoptotic in cybrid B4 cells than cybrid E cells. The study provides a novel insight into the etiopathogenesis and the predictive value of mitochondrial haplogroups in BA.

Haplogroup T is an obesity risk factor: mitochondrial DNA haplotyping in a morbid obese population from southern Italy

Mitochondrial DNA (mtDNA) haplogroups have been associated with the expression of mitochondrial-related diseases and with metabolic alterations, but their role has not yet been investigated in morbid obese Caucasian subjects. Therefore, we investigated the association between mitochondrial haplogroups and morbid obesity in patients from southern Italy. The mtDNA D-loop of morbid obese patients (n = 500; BMI > 40 kg/m²) and controls (n = 216; BMI < 25 kg/m²) was sequenced to determine the mtDNA haplogroups. The T and J haplogroup frequencies were higher and lower, respectively, in obese subjects than in controls. Women bearing haplogroup T or J had twice or half the risk of obesity. Binomial logistic regression analysis showed that haplogroup T and systolic blood pressure are risk factors for a high degree of morbid obesity, namely, BMI > 45 kg/m² and in fact together account for 8% of the BMI. In conclusion, our finding that haplogroup T increases the risk of obesity by about two-fold, suggests that, besides nuclear genome variations and environmental factors, the T haplogroup plays a role in morbid obesity in our study population from southern Italy.

Mitochondrial NADH:ubiquinone oxidoreductase alterations are associated with endometriosis

Genetic alterations and aberrant expression of 'mitochondrial membrane complex I' (MMC-I) underlie several complex human disorders, but no reports are documented to date in endometriosis. Sequencing of mitochondrially encoded MMC-I subunits revealed 72 mutations of which 2 missense (G10398A; A13603A/G) mutations and 1 synonymous (T10400C) mutation showed higher prevalence in patients. In silico functional analysis predicted A13603A/G, a novel heteroplasmy as a 'damaging variant'. Our results indicate higher endometriosis risk for haplotype '10398A/10400C/13603AG' and haplogroup 'N'. Immunohistochemical analysis revealed elevated MMC-I expression in eutopic endometria of patients compared to controls. In conclusion, MMC-I alterations may constitute an inheritable risk factor for endometriosis.

Complete mitochondrial genome sequencing reveals novel haplotypes in a Polynesian population

The high risk of metabolic disease traits in Polynesians may be partly explained by elevated prevalence of genetic variants involved in energy metabolism. The genetics of Polynesian populations has been shaped by island hoping migration events which have possibly favoured thrifty genes. The aim of this study was to sequence the mitochondrial genome in a group of Maoris in an effort to characterise genome variation in this Polynesian population for use in future disease association studies. We sequenced the complete mitochondrial genomes of 20 non-admixed Maori subjects using Affymetrix technology. DNA diversity analyses showed the Maori group exhibited reduced mitochondrial genome diversity compared to other worldwide populations, which is consistent with historical bottleneck and founder effects. Global phylogenetic analysis positioned these Maori subjects specifically within mitochondrial haplogroup - B4a1a1. Interestingly, we identified several novel variants that collectively form new and unique Maori motifs – B4a1a1c, B4a1a1a3 and B4a1a1a5. Compared to ancestral populations we observed an increased frequency of non-synonymous coding variants of several mitochondrial genes in the Maori group, which may be a result of positive selection and/or genetic drift effects. In conclusion, this study reports the first complete mitochondrial genome sequence data for a Maori population. Overall, these new data reveal novel mitochondrial genome signatures in this Polynesian population and enhance the phylogenetic picture of maternal ancestry in Oceania. The increased frequency of several mitochondrial coding variants makes them good candidates for future studies aimed at assessment of metabolic disease risk in Polynesian populations.

Mechanisms underlying skeletal muscle insulin resistance induced by fatty acids: importance of the mitochondrial function

Insulin resistance condition is associated to the development of several syndromes, such as obesity, type 2 diabetes mellitus and metabolic syndrome. Although the factors linking insulin resistance to these syndromes are not precisely defined yet, evidence suggests that the elevated plasma free fatty acid (FFA) level plays an important role in the development of skeletal muscle insulin resistance. Accordantly, in vivo and in vitro exposure of skeletal muscle and myocytes to physiological concentrations of saturated fatty acids is associated with insulin resistance condition. Several mechanisms have been postulated to account for fatty acids-induced muscle insulin resistance, including Randle cycle, oxidative stress, inflammation and mitochondrial dysfunction. Here we reviewed experimental evidence supporting the involvement of each of these propositions in the development of skeletal muscle insulin resistance induced by saturated fatty acids and propose an integrative model placing mitochondrial dysfunction as an important and common factor to the other mechanisms.

Is mitochondrial tRNA(phe) variant m.593T>C a synergistically pathogenic mutation in Chinese LHON families with m.11778G>A?

Mitochondrial transfer RNA (mt-tRNA) mutations have been reported to be associated with a variety of diseases. In a previous paper that studied the mtDNA background effect on clinical expression of Leber's hereditary optic neuropathy (LHON) in 182 Chinese families with m.11778G>A, we found a strikingly high frequency (7/182) of m.593T>C in the mitochondrially encoded tRNA phenylalanine (MT-TF) gene in unrelated LHON patients. To determine the potential role of m.593T>C in LHON, we compared the frequency of this variant in 479 LHON patients with m.11778G>A, 843 patients with clinical features of LHON but without the three known primary mutations, and 2374 Han Chinese from the general populations. The frequency of m.593T>C was higher in LHON patients (14/479) than in suspected LHON subjects (12/843) or in general controls (49/2374), but the difference was not statistically significant. The overall penetrance of LHON in families with both m.11778G>A and m.593T>C (44.6%) was also substantially higher than that of families with only m.11778G>A (32.9%) (P = 0.083). Secondary structure prediction of the MT-TF gene with the wild type or m.593T>C showed that this nucleotide change decreases the free energy. Electrophoretic mobility of the MT-TF genes with the wild type or m.593T>C transcribed in vitro further confirmed the change of secondary structure in the presence of this variant. Although our results could suggest a modest synergistic effect of variant m.593T>C on the LHON causing mutation m.11778G>A, the lack of statistical significance probably due to the relatively small sample size analyzed, makes necessary more studies to confirm this effect.

The tRNAMet 4435A>G mutation in the mitochondrial haplogroup G2a1 is responsible for maternally inherited hypertension in a Chinese pedigree

Mutations in mitochondrial DNA (mtDNA) have been associated with hypertension in several pedigrees with maternal inheritance. However, the pathophysiology of maternally inherited hypertension remains poorly understood. We reported here clinical, genetic evaluations and molecular analysis of mtDNA in a three-generation Han Chinese family with essential hypertension. Eight of 17 matrilineal relatives exhibited a wide range of severity in essential hypertension, whereas none of the offsprings of the affected father had hypertension. The age-at-onset of hypertension in the maternal kindred varied from 31 to 65 years, with an average of 52 years. Sequence analysis of mtDNA in this pedigree identified the known homoplasmic 4435A>G mutation, which is located at immediately 3' end to the anticodon, corresponding to the conventional position 37 of tRNA(Met), and 41 variants belonging to the Asian haplogroup G2a1. In contrast, the 4435A>G mutation occurred among mtDNA haplogroups B5a, D, M7a2 and J. The adenine (A37) at this position of tRNA(Met) is extraordinarily conserved from bacteria to human mitochondria. This modified A37 was shown to contribute to the high fidelity of codon recognition, structural formation and stabilization of functional tRNAs. However, 41 other mtDNA variants in this pedigree were the known polymorphisms. The occurrence of the 4435A>G mutation in two genetically unrelated families affected by hypertension indicates that this mutation is involved in hypertension. Our present investigations further supported our previous findings that the 4435A>G mutation acted as an inherited risk factor for the development of hypertension. Our findings will be helpful for counseling families of maternally inherited hypertension.

Surveyor nuclease detection of mutations and polymorphisms of mtDNA in children

Mitochondrial encephalomyopathies are complex disorders with wide range of clinical manifestations. Particularly time-consuming is the identification of mutations in mitochondrial DNA. A group of 20 children with clinical manifestations of mitochondrial encephalomyopathies was selected for molecular studies. The aims were (a) to identify mutations in mtDNA isolated from muscle and (b) to verify detected mutations in DNA isolated from blood, in order to assess the utility of a Surveyor nuclease assay kit for patient screening. The most common changes found were polymorphisms, including a few missense mutations altering the amino acid sequence of mitochondrial proteins. In two boys with MELAS (i.e., mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes), a mutation A→G3243 was detected in the tRNALeu gene of mtDNA isolated from muscle and blood. In one boy, the carrier status of his mother was confirmed, based on molecular analysis of DNA isolated from blood. A method using Surveyor nuclease allows systematic screening for small mutations in mtDNA, using as its source blood of the patients and asymptomatic carriers. The method still requires confirmation studying a larger group. In some patients, the use of this method should precede and might limit indications for traumatic muscle and skin biopsy.

Mitochondrial DNA haplogroups and risk of transient ischaemic attack and ischaemic stroke: a genetic association study

Background

Genetic factors have a role in the pathogenesis of ischaemic stroke, but the main genes involved have yet to be defined. Mitochondrial mechanisms have been implicated in the pathophysiology of acute stroke, but the role of mitochondrial DNA (mtDNA) has not been comprehensively studied. We investigated whether there is an association between mtDNA haplotypes and incidence of stroke.

Methods

The major European mtDNA haplogroups were identified in two independent subpopulations (n=950) from a study of occurrence of transient ischaemic attack (TIA) and ischaemic stroke and were compared with those of patients with acute coronary syndromes from the same populations (n=340) and with those of independent population controls (n=2939).

Findings

The presence of mtDNA sub-haplogroup K was significantly less frequent in patients with TIA or stroke than in controls in both subpopulations separately and in a pooled analysis (odds ratio 0·54, 95% CI 0·39–0·75, p<0·00001). This association remained highly significant after adjustment for multiple haplogroup comparisons. The association was significant for patients with TIA and stroke separately and was independent of known risk factors, but was not found for patients with acute coronary events. The mtDNA sub-haplogroup K was present in 8·7% of the total UK population controls and therefore confers a 4·0% (95% CI 2·2–5·7) reduction in population attributable risk of TIA and stroke.

Interpretation

Genetic variation of mtDNA sub-haplogroup K is an independent determinant of risk of cerebral, but not coronary, ischaemic vascular events. These findings implicate mitochondrial mechanisms in the aetiology of ischaemic stroke and provide a new means for the identification of individuals with a high susceptibility of developing ischaemic stroke.

Funding

Medical Research Council UK, National Institute of Health Research (NIHR), the Stroke Association, the Dunhill Medical Trust, the NIHR-funded Oxford Biomedical Research Centre, the NIHR-funded Newcastle Biomedical Research Centre in Ageing, and the Wellcome Trust.

Mitochondrial DNA haplogroup 'R' is associated with Noonan syndrome of south India

Mutations in PTPN11 gene was responsible for approximately 50% of the Noonan syndrome (NS), however, we did not find any mutation in PTPN11 in any of seven NS patients analysed. Whereas, the complete mtDNA sequencing revealed 146 mutations, of which five, including one heteroplasmic (A11144R; Thr-->Ala) non-synonymous mutation, were novel and exclusively observed in NS patients. Interestingly all the seven probands and their maternal relatives were clustered under a major haplogroup R and its novel sub-haplogroups (R7b1b, R30a1, R30c, T2b7, U9a1) exclusive in NS, therefore we strongly suggest that these haplogroups may influence NS in South Indian populations.

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 tRNA(Met), and 35 other variants belonging to the Asian haplogroup B5a. The adenine (A37) at this position of tRNA(Met) 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 tRNA(Met) 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 approximately 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.

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.

Novel mutations of mitochondrial DNA associated with type 2 diabetes in Chinese Han population

Mitochondrial single nucleotide polymorphisms (mtSNPs) have been reported to associate with type-2 diabetes mellitus (T2DM), but mtSNPs appear to be considerably different among different populations and regions. To determine mtSNPs in Chinese Han patients with T2DM, the entire sequences of the mitochondrial genomes from 72 T2DM Chinese (59 +/- 4 years) and 50 age-matched healthy subjects (controls) in Chongqing region of Western China were directly sequenced and mtSNPs were analyzed. We found that M8, M9, D, G, R and A haplogroups exist in Chinese Han population and the frequency of haplogroup M9 was significantly higher in patients with T2DM than in the controls (p = 0.0006, OR 0.06 [95% CI 0.008-0.476]). MtSNPs T3394C in NADH dehydrogenase subunit 1 (ND1), G4491A in ND2, T16189C and T16519C were found with significantly higher frequency in patients with T2DM than in the controls (T16189C, p = 0.0045; T16519C, p < 0.0001; T3394C, p = 0.0015; G4491A, p = 0.0015). In contrast, the frequency of C5178A in ND2 and A10398G in ND3 was higher in the controls than in patients with T2DM (C5178A, p = 0.014; A10398G, p = 0.0011). Our results indicate that mtSNPs T3394C, G4491A, T16189C and T16519C show susceptible tendency to T2DM and mtSNPs C5178A and A10398G seem to be genetic factors for against T2DM. These mtSNPs determined in our study is useful and could be used for early diagnosis and prevention of T2DM in Chinese Han population.

The genetics of gestational diabetes mellitus: evidence for relationship with type 2 diabetes mellitus

Gestational diabetes is a major public health problem because of its prevalence, its associated complications during pregnancy, and its increased risk for type 2 diabetes later in life. Insulin resistance is one of many physiological changes occurring during pregnancy, and when insulin resistance is accompanied by pancreatic beta-cell insufficiency, gestational diabetes may develop. Several lines of evidence suggest that gestational diabetes shares a common etiology with type 2 diabetes and support the hypothesis that gestational diabetes serves as a window to reveal a predisposition to type 2 diabetes. Pregnancy is an environmental stressor that may catalyze the progression to a diabetic state in genetically predisposed women; therefore, identification of these women during pregnancy could decrease the occurrence of type 2 diabetes through targeted prevention. This review presents an overview of the genetics of gestational diabetes, focusing on human association studies with candidate genes common to both type 2 diabetes and gestational diabetes.

Effect of a polymorphism in the ND1 mitochondrial gene on human skeletal muscle mitochondrial function

OBJECTIVE

A non-silent polymorphism in the mitochondrial coding region of the ND1 gene, a subunit of reduced nicotinamide adenine dinucleotide (NADH) dehydrogenase is associated with resting metabolic rate (RMR) in 245 non-diabetic Pima Indians. The purpose of this investigation was to determine the effect of the ND1 gene polymorphism on mitochondrial function in 14 male Pima Indians.

METHODS AND PROCEDURES

Seven subjects with an A at site 3547 of the ND1 gene (Ile at amino acid 81), and seven with a G at this site (Val) were studied. Mitochondria were isolated from 0.8 to 1.5 g of skeletal muscle obtained by needle biopsy of the lateral quadriceps muscle. In intact mitochondria, maximal (state-3) and resting (state-4) respiration rates were measured polarographically at 37 degrees C with a variety of single substrates or substrate combinations. Disrupted mitochondria were analyzed for maximal capacities through the entire electron transport chain (ETC) (NADH oxidase (NADHOX)), as well as through a segment of Complex I that is independent of the ND1 component (NADH-ferricyanide (NADH-FeCN) reductase).

RESULTS

Mitochondria were well coupled and exhibited higher respiratory control ratios (RCRs) than rodent muscle. There were no differences between the two groups for any of the measured parameters.

DISCUSSION

These results indicate that the cause of the observed association between RMR and the ND1 polymorphism is not related to in vitro mitochondrial function.