Mitochondrial MDM2 Regulates Respiratory Complex I Activity Independently of p53.

Accumulating evidence indicates that the MDM2 oncoprotein promotes tumorigenesis beyond its canonical negative effects on the p53 tumor suppressor, but these p53-independent functions remain poorly understood. Here, we show that a fraction of endogenous MDM2 is actively imported in mitochondria to control respiration and mitochondrial dynamics independently of p53. Mitochondrial MDM2 represses the transcription of NADH-dehydrogenase 6 (MT-ND6) in vitro and in vivo, impinging on respiratory complex I activity and enhancing mitochondrial ROS production. Recruitment of MDM2 to mitochondria increases during oxidative stress and hypoxia. Accordingly, mice lacking MDM2 in skeletal muscles exhibit higher MT-ND6 levels, enhanced complex I activity, and increased muscular endurance in mild hypoxic conditions. Furthermore, increased mitochondrial MDM2 levels enhance the migratory and invasive properties of cancer cells. Collectively, these data uncover a previously unsuspected function of the MDM2 oncoprotein in mitochondria that play critical roles in skeletal muscle physiology and may contribute to tumor progression.

Evolutionary characteristics of the mitochondrial NADH dehydrogenase subunit 6 gene in some populations of four sympatric Mustela species (Mustelidae, Mammalia) from central Europe.

BACKGROUND: Selection on or reticulate evolution of mtDNA is documented in various mammalian taxa and could lead to misleading phylogenetic conclusions if not recognized. We sequenced the MT-ND6 gene of four sympatric Mustelid species of the genus Mustela from some central European populations. We hypothesised positive selection on MT-ND6, given its functional importance and the different body sizes and life histories of the species, even though climatic differences may be unimportant for adaptation in sympatry. METHODS AND RESULTS: MT-ND6 genes were sequenced in 187 sympatric specimens of weasels, Mustela nivalis, stoats, M. erminea, polecats, M. putorius, and steppe polecats, M. eversmannii, from eastern Austria and of fourteen allopatric polecats from eastern-central Germany. Median joining networks, neighbour joining and maximum likelihood analyses as well as Bayesian inference grouped all species according to earlier published phylogenetic models. However, polecats and steppe polecats, two very closely related species, shared the same two haplotypes. We found only negative selection within the Mustela sequences, including 131 downloaded ones covering thirteen species. Positive selection was observed on three MT-ND6 codons of other mustelid genera retrieved from GenBank. CONCLUSIONS: Negative selection for MT-ND6 within the genus Mustela suggests absence of both environmental and species-specific effects of cellular energy metabolism despite large species-specific differences in body size. The presently found shared polymorphism in European polecats and steppe polecats may result from ancestral polymorphism before speciation and historical or recent introgressive hybridization; it may indicate mtDNA capture of steppe polecats by M. putorius in Europe.

Salidroside protects dopaminergic neurons by regulating the mitochondrial MEF2D-ND6 pathway in the MPTP/MPP+ -induced model of Parkinson's disease.

Mitochondrial complex I damage and oxidative stress play critical roles in the degeneration of dopaminergic (DA) neurons during the progression of Parkinson's disease (PD). Our previous study showed that NADH dehydrogenase 6 (ND6), exclusively regulated by mitochondrial myocyte enhancer factor 2D (MEF2D), was critical for mitochondrial complex I assembly. Recently, we found that Salidroside (Sal), isolated from Rhodiola rosea L., protected DA neurons by regulating oxidative stress-related mitochondrial pathways. Here, we investigated whether the mitochondrial MEF2D-ND6 pathway was involved in the neuroprotective effects of Sal. Our results showed that in 1-methyl-4-phenylpyridinium (MPP+ )-injured SN4741 cells, Sal pretreatment improved cellular viability, inhibited apoptosis, and restored both the mitochondrial membrane potential and complex I activity. Similarly, the protective effects of Sal on mitochondrial complex I activity, DA neurons, and behavior were also confirmed in 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP)-lesioned mice. Besides, Sal pretreatment restored the expression of mitochondrial MEF2D and ND6 in MPP+ -injured SN4741 cells and MPTP-lesioned mice. Finally and interestingly, the protective effects of Sal were not observed in cells transfected with Mt2Ddn, a specific blocker of mitochondrial MEF2D function, suggesting that Sal protects DA neurons primarily by regulating the mitochondrial MEF2D-ND6 pathway. Our study sheds light upon the protective role of Sal through targeting the mitochondrial MEF2D-ND6 pathway in regulations of mitochondrial function and DA neuronal viability, providing novel mechanistic insights into the neuroprotective effects of Sal against PD.

Late-onset MELAS syndrome with mtDNA 14453G→A mutation masquerading as an acute encephalitis: a case report.

BACKGROUND: A unique patient with MELAS syndrome, who initially masqueraded as having acute encephalitis and was eventually diagnosed with MELAS syndrome harboring a mtDNA 14453G → A mutation, is described. CASE PRESENTATION: A 74-year-old Japanese man was admitted to another hospital due to acute onset of cognitive impairment and psychosis. After 7 days he was transferred to our hospital with seizures and deteriorating psychosis. The results of primary ancillary tests that included EEG, CSF findings, and brain MRI supported the diagnosis of an acute encephalitis. HSV-DNA and antibodies against neuronal surface antigens in the CSF were all negative. With the assistance of the lactate peak on the brain lesions in the magnetic resonance spectroscopy image and genetic analysis of the biopsied muscle, he was eventually diagnosed with MELAS syndrome harboring mtDNA 14453G → A mutation in the ND6 gene. CONCLUSIONS: This case provides a caveat that MELAS syndrome can manifest in the symptoms and ancillary tests masquerading as an acute encephalitis caused by infection or autoimmunity. This is the first adult patient seen to harbor the mtDNA14453G → A with a unique onset, which broadens the phenotypic spectrum of MELAS syndrome associated with ND6 gene mutation.

A novel mitochondrial m.14430A>G (MT-ND6, p.W82R) variant causes complex I deficiency and mitochondrial Leigh syndrome.

Objectives Leigh syndrome (LS) is one of the most common mitochondrial diseases and has variable clinical symptoms. However, the genetic variant spectrum of this disease is incomplete. Methods Next-generation sequencing (NGS) was used to identify the m.14430A > G (p.W82R) variant in a patient with LS. The pathogenesis of this novel complex I (CI) variant was verified by determining the mitochondrial respiration, assembly of CI, ATP, MMP and lactate production, and cell growth rate in cybrids with and without this variant. Results A novel m.14430A > G (p.W82R) variant in the NADH dehydrogenase 6 (ND6) gene was identified in the patient; the mutant loads of m.14430A > G (p.W82R) in the patient were much higher than those in his mother. Although the transmitochondrial cybrid-based study showed that mitochondrial CI assembly remains unaffected in cells with the m.14430G variant, control cells had significantly higher endogenous and CI-dependent mitochondrial respiration than mutant cells. Accordingly, mutant cells had a lower ATP, MMP and higher extracellular lactate production than control cells. Notably, mutant cells had impaired growth in a galactose-containing medium when compared to wild-type cells. Conclusions A novel m.14430A > G (p.W82R) variant in the ND6 gene was identified from a patient suspected to have LS, and this variant impaired mitochondrial respiration by decreasing the activity of mitochondrial CI.

Interplay between early-life malnutrition, epigenetic modulation of the immune function and liver diseases.

Early-life nutrition plays a critical role in fetal growth and development. Food intake absence and excess are the two main types of energy malnutrition that predispose to the appearance of diseases in adulthood, according to the hypothesis of 'developmental origins of health and disease'. Epidemiological data have shown an association between early-life malnutrition and the metabolic syndrome in later life. Evidence has also demonstrated that nutrition during this period of life can affect the development of the immune system through epigenetic mechanisms. Thus, epigenetics has an essential role in the complex interplay between environmental factors and genetics. Altogether, this leads to the inflammatory response that is commonly seen in non-alcoholic fatty liver disease (NAFLD), the hepatic manifestation of the metabolic syndrome. In conjunction, DNA methylation, covalent modification of histones and the expression of non-coding RNA are the epigenetic phenomena that affect inflammatory processes in the context of NAFLD. Here, we highlight current understanding of the mechanisms underlying developmental programming of NAFLD linked to epigenetic modulation of the immune system and environmental factors, such as malnutrition.

Next Generation Sequencing expression profiling of mitochondrial subunits in men with Klinefelter syndrome.

Objectives: Klinefelter syndrome (KS) is one of the most common sex-chromosome disorders as it affects up to 1 in every 600-1000 newborn males. Men with KS carry one extra X chromosome and they usually present a 47,XXY karyotype, but less frequent variants have also been reported in literature. KS typical symptoms include tall stature, gynecomastia, broad hips, hypogonadism and absent spermatogenesis. The syndrome is also related to a wide range of cognitive deficits, among which language-based learning disabilities and verbal cognition impairment are frequently diagnosed. The present study was carried out to investigate the role of mitochondrial subunits in KS, since the molecular mechanisms underlying KS pathogenesis are not fully understood. Methods: The study was performed by the next generation sequencing analysis and qRT-PCR assay. Results: We were able to identify a significant down-expression of mitochondrial encoded NADH: ubiquinone oxidoreductase core subunit 6 (MT-ND6) in men with KS. Conclusion: It is known that defects of the mtDNA encoding mitochondrial subunits are responsible for the malfunction of Complex I, which will eventually lead to the Complex I deficiency, the most common respiratory chain defect in human disorders. Since it has been shown that decreased Complex I protein levels could induce apoptosis, wehypothesizethat the above-mentioned MT-ND6 down-expression contributes to the wide range of phenotypes observed in men with KS.

PGD for the m.14487 T>C mitochondrial DNA mutation resulted in the birth of a healthy boy.

We report on the first PGD performed for the m.14487 T>C mitochondrial DNA (mtDNA) mutation in the MT-ND6 gene, associated with Leigh syndrome. The female carrier gave birth to a healthy baby boy at age 42. This case adds to the successes of PGD for mtDNA mutations.

Genetic diversity and population structure of Anastrepha striata (Diptera: Tephritidae) in three natural regions of southwestern Colombia using mitochondrial sequences.

Anastrepha striata is widely distributed across the Americas and is a pest of economically important crops, especially crops of the Myrtaceae family. Insect population structures can be influenced by the presence of physical barriers or characteristics associated with habitat differences. This study evaluated the effect of the Western Andes on the population structure of A. striata. Individuals were collected from Psidium guajava fruits from three natural regions of southwestern Colombia (Pacific Coast, mountainous region and the inter-Andean valley of the Cauca River). Based on a 1318 bp concatenated of the genes Cytochrome Oxidase subunit I (COI) and NADH dehydrogenase subunit 6 (ND6), 14 haplotypes with few changes among them (between 1 and 3) were found. There was only one dominant haplotype in all three regions. No genetic structure associated with the three eco-geographical regions of the study was found. Moreover, the Western Andes are not an effective barrier for the genetic isolation of the populations from the Pacific Coast compared with the inter-Andean valley populations. This genetic homogeneity could be partially due to anthropogenic intervention, which acts as a dispersal agent of infested fruits. Another hypothesis to explain the lack of structure would be the relatively recent arrival of A. striata to the region, as indicated by an analysis of the demographic history, which reveals a process of population expansion. This study represents the first attempt to understand the population genetics of A. striata in Colombia and could contribute to the integral management of this pest.

Hereditary Retinal Dystrophy.

As our understanding of the genetic basis for inherited retinal disease has expanded, gene therapy has advanced into clinical development. When the gene mutations associated with inherited retinal dystrophies were identified, it became possible to create animal models in which individual gene were altered to match the human mutations. The retina of these animals were then characterized to assess whether the mutated genes produced retinal phenotypes characteristic of disease-affected patients. Following the identification of a subpopulation of patients with the affected gene and the development of techniques for the viral gene transduction of retinal cells, it has become possible to deliver a copy of the normal gene into the retinal sites of the mutated genes. When this was performed in animal models of monogenic diseases, at an early stage of retinal degeneration when the affected cells remained viable, successful gene augmentation corrected the structural and functional lesions characteristic of the specific diseases in the areas of the retina that were successfully transduced. These studies provided the essential proof-of-concept needed to advance monogenic gene therapies into clinic development; these therapies include treatments for: Leber's congenital amaurosis type 2, caused by mutations to RPE65, retinoid isomerohydrolase; choroideremia, caused by mutations to REP1, Rab escort protein 1; autosomal recessive Stargardt disease, caused by mutations to ABCA4, the photoreceptor-specific ATP-binding transporter; Usher 1B disease caused by mutations to MYO7A, myosin heavy chain 7; X-linked juvenile retinoschisis caused by mutations to RS1, retinoschisin; autosomal recessive retinitis pigmentosa caused by mutations to MERTK, the proto-oncogene tyrosine-protein kinase MER; Leber's hereditary optic neuropathy caused by mutations to ND4, mitochondrial nicotinamide adenine dinucleotide ubiquinone oxidoreductase (complex I) subunit 4 and achromatopsia, caused by mutations to CNGA3, cyclic nucleotide-gated channel alpha 3 and CNGB3, cyclic nucleotide-gated channel beta 3. This review includes a tabulated summary of treatments for these monogenic retinal dystrophies that have entered into clinical development, as well as a brief summary of the preclinical data that supported their advancement into clinical development.

Redefining the roles of mitochondrial DNA-encoded subunits in respiratory Complex I assembly.

Respiratory Complex I deficiency is implicated in numerous degenerative and metabolic diseases. In particular, mutations in several mitochondrial DNA (mtDNA)-encoded Complex I subunits including ND4, ND5 and ND6 have been identified in several neurological diseases. We previously demonstrated that these subunits played essential roles in Complex I assembly which in turn affected mitochondrial function. Here, we carried out a comprehensive study of the Complex I assembly pathway. We identified a new Complex I intermediate containing both membrane and matrix arms at an early assembly stage. We find that lack of the ND6 subunit does not hinder membrane arm formation; instead it recruits ND1 and ND5 enters the intermediate. While ND4 is important for the formation of the newly identified intermediate, the addition of ND5 stabilizes the complex and is required for the critical transition from Complex I to supercomplex assembly. As a result, the Complex I assembly pathway has been redefined in this study.

Epigenetic modification of liver mitochondrial DNA is associated with histological severity of nonalcoholic fatty liver disease.

OBJECTIVE & DESIGN: Nonalcoholic fatty liver disease (NAFLD) is a clinical condition that refers to progressive histological changes ranging from simple steatosis (SS) to nonalcoholic steatohepatitis (NASH). We evaluated the status of cytosine methylation (5mC) of liver mitochondrial DNA (mtDNA) in selected regions of the mtDNA genome, such as D-loop control region, and mitochondrially encoded NADH dehydrogenase 6 (MT-ND6) and cytochrome C oxidase I (MT-CO1), to contrast the hypothesis that epigenetic modifications play a role in the phenotypic switching from SS to NASH. METHODS: We studied liver biopsies obtained from patients with NAFLD in a case-control design; 45 patients and 18 near-normal liver-histology subjects. RESULTS: MT-ND6 methylation was higher in the liver of NASH than SS patients (p < 0.04) and MT-ND6 methylated DNA/unmethylated DNA ratio was significantly associated with NAFLD activity score (p < 0.02). Liver MT-ND6 mRNA expression was significantly decreased in NASH patients (0.26 ± 0.30) versus SS (0.74 ± 0.48), p < 0.003, and the protein level was also diminished. The status of liver MT-ND6 methylation in NASH group was inversely correlated with the level of regular physical activity (R = -0.54, p < 0.02). Hepatic methylation levels of D-Loop and MT-CO1 were not associated with the disease severity. DNA (cytosine-5) methyltransferase 1 was significantly upregulated in NASH patients (p < 0.002). Ultrastructural evaluation showed that NASH is associated with mitochondrial defects and peroxisome proliferation. CONCLUSION: Hepatic methylation and transcriptional activity of the MT-ND6 are associated with the histological severity of NAFLD. Epigenetic changes of mtDNA are potentially reversible by interventional programs, as physical activity could modulate the methylation status of MT-ND6.

Mitochondrial DNA methylation in metabolic associated fatty liver disease.

Introduction: Hepatic lipid accumulation and mitochondrial dysfunction are hallmarks of metabolic associated fatty liver disease (MAFLD), yet molecular parameters underlying MAFLD progression are not well understood. Differential methylation within the mitochondrial DNA (mtDNA) has been suggested to be associated with dysfunctional mitochondria, also during progression to Metabolic Steatohepatitis (MeSH). This study further investigates whether mtDNA methylation is associated with hepatic lipid accumulation and MAFLD. Methods: HepG2 cells were constructed to stably express mitochondria-targeted viral and prokaryotic cytosine DNA methyltransferases (mtM.CviPI or mtM.SssI for GpC or CpG methylation, respectively). A catalytically inactive variant (mtM.CviPI-Mut) was constructed as a control. Mouse and human patients' samples were also investigated. mtDNA methylation was assessed by pyro- or nanopore sequencing. Results and discussion: Differentially induced mtDNA hypermethylation impaired mitochondrial gene expression and metabolic activity in HepG2-mtM.CviPI and HepG2-mtM.SssI cells and was associated with increased lipid accumulation, when compared to the controls. To test whether lipid accumulation causes mtDNA methylation, HepG2 cells were subjected to 1 or 2 weeks of fatty acid treatment, but no clear differences in mtDNA methylation were detected. In contrast, hepatic Nd6 mitochondrial gene body cytosine methylation and Nd6 gene expression were increased in mice fed a high-fat high cholesterol diet (HFC for 6 or 20 weeks), when compared to controls, while mtDNA content was unchanged. For patients with simple steatosis, a higher ND6 methylation was confirmed using Methylation Specific PCR, but no additional distinctive cytosines could be identified using pyrosequencing. This study warrants further investigation into a role for mtDNA methylation in promoting mitochondrial dysfunction and impaired lipid metabolism in MAFLD.

Mitochondrial Diabetes is Associated with tRNALeu(UUR) A3243G and ND6 T14502C Mutations.

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

Mesenchymal stem cells improve redox homeostasis and mitochondrial respiration in fibroblast cell lines with pathogenic MT-ND3 and MT-ND6 variants.

The most frequent biochemical defect of inherited mitochondrial disease is isolated complex I deficiency. There is no cure for this disorder, and treatment is mainly supportive. In this study, we investigated the effects of human mesenchymal stem cells (MSCs) on skin fibroblast derived from three individuals with complex I deficiency carrying different pathogenic variants in mitochondrial DNA-encoded subunits (MT-ND3, MT-ND6). Complex I-deficient fibroblasts were transiently co-cultured with bone marrow-derived MSCs. Mitochondrial transfer was analysed by fluorescence labelling and validated by Sanger sequencing. Levels of reactive oxygen species (ROS) were measured using MitoSOX Red. Moreover, mitochondrial respiration was analysed by Seahorse XFe96 Extracellular Flux Analyzer. Levels of antioxidant proteins were investigated via immunoblotting. Co-culturing of complex I-deficient fibroblast with MSCs lowered cellular ROS levels. The effect on ROS production was more sustained compared to treatment of patient fibroblasts with culture medium derived from MSC cultures. Investigation of cellular antioxidant defence systems revealed an upregulation of SOD2 (superoxide dismutase 2, mitochondrial) and HO-1 (heme oxygenase 1) in patient-derived cell lines. This adaptive response was normalised upon MSC treatment. Moreover, Seahorse experiments revealed a significant improvement of mitochondrial respiration, indicating a mitigation of the oxidative phosphorylation defect. Experiments with repetitive MSC co-culture at two consecutive time points enhanced this effect. Our study indicates that MSC-based treatment approaches might constitute an interesting option for patients with mitochondrial DNA-encoded mitochondrial diseases. We suggest that this strategy may prove more promising for defects caused by mitochondrial DNA variants compared to nuclear-encoded defects.

Expression signature of the Leigh syndrome French-Canadian type.

As a result of a founder effect, a Leigh syndrome variant called Leigh syndrome, French-Canadian type (LSFC, MIM / 220,111) is more frequent in Saguenay-Lac-Saint-Jean (SLSJ), a geographically isolated region on northeastern Quebec, Canada. LSFC is a rare autosomal recessive mitochondrial neurodegenerative disorder due to damage in mitochondrial energy production. LSFC is caused by pathogenic variants in the nuclear gene leucine-rich pentatricopeptide repeat-containing (LRPPRC). Despite progress understanding the molecular mode of action of LRPPRC gene, there is no treatment for this disease. The present study aims to identify the biological pathways altered in the LSFC disorder through microarray-based transcriptomic profile analysis of twelve LSFC cell lines compared to twelve healthy ones, followed by gene ontology (GO) and pathway analyses. A set of 84 significantly differentially expressed genes were obtained (p ≥ 0.05; Fold change (Flc) ≥ 1.5). 45 genes were more expressed (53.57%) in LSFC cell lines compared to controls and 39 (46.43%) had lower expression levels. Gene ontology analysis highlighted altered expression of genes involved in the mitochondrial respiratory chain and energy production, glucose and lipids metabolism, oncogenesis, inflammation and immune response, cell growth and apoptosis, transcription, and signal transduction. Considering the metabolic nature of LSFC disease, genes included in the mitochondrial respiratory chain and energy production cluster stood out as the most important ones to be involved in LSFC mitochondrial disorder. In addition, the protein-protein interaction network indicated a strong interaction between the genes included in this cluster. The mitochondrial gene NDUFA4L2 (NADH dehydrogenase [ubiquinone] 1 alpha subcomplex, 4-like 2), with higher expression in LSFC cells, represents a target for functional studies to explain the role of this gene in LSFC disease. This work provides, for the first time, the LSFC gene expression profile in fibroblasts isolated from affected individuals. This represents a valuable resource to understand the pathogenic basis and consequences of LRPPRC dysfunction.

Function and Molecular Ecology Significance of Two Catechol-Degrading Gene Clusters in Pseudomonas putida ND6.

Many bacteria metabolize aromatic compounds via catechol as a catabolic intermediate, and possess multiple genes or clusters encoding catechol-cleavage enzymes. The presence of multiple isozyme-encoding genes is a widespread phenomenon that seems to give the carrying strains a selective advantage in the natural environment over those with only a single copy. In the naphthalene-degrading strain Pseudomonas putida ND6, catechol can be converted into intermediates of the tricarboxylic acid cycle via either the ortho- or meta-cleavage pathways. In this study, we demonstrated that the catechol ortho-cleavage pathway genes (catBICIAI and catBIICIIAII) on the chromosome play an important role. The catI and catII operons are co-transcribed, whereas catAI and catAII are under independent transcriptional regulation. We examined the binding of regulatory proteins to promoters. In the presence of cis-cis-muconate, a well-studied inducer of the cat gene cluster, CatRI and CatRII occupy an additional downstream site, designated as the activation binding site. Notably, CatRI binds to both the catI and catII promoters with high affinity, while CatRII binds weakly. This is likely caused by a T to G mutation in the G/T-N11-A motif. Specifically, we found that CatRI and CatRII regulate catBICIAI and catBIICIIAII in a cooperative manner, which provides new insights into naphthalene degradation.

Mild Leber hereditary optic neuropathy (LHON) in a Western European family due to the rare Asian m.14502T>C variant in the MT-ND6 gene.

BACKGROUND: Leber hereditary optic neuropathy (LHON) is a mitochondrial neurodegenerative disease. The majority (>90%) is related to three primary mitochondrial DNA (mtDNA) variants: ND1 m.3460G>A, ND4 m.11778G>A and ND6 m.14484T>C. The remaining 10% is associated with >40 secondary variants with variable penetrance and incidence between different ethnic backgrounds. MATERIALS AND METHODS: Five sisters underwent an extensive ophthalmic workup including psychophysical, electrophysiological, multimodal brain imaging, biochemical testing and molecular screening. MT-ND6 protein modelling was performed. RESULTS: A 23-year-old woman presented with acute central visual loss to counting fingers in the right eye. She developed a central visual field scotoma, severe color vision deficiencies and impaired pattern visual evoked responses. Progressive optic atrophy ensued. The left eye was unremarkable, except for borderline thinning of the temporal retinal nerve fiber layer. Alcohol use and passive smoking were noted. MtDNA analysis revealed a rare variant, m.14502T>C in MT-ND6, exclusively known to cause optic neuropathy in an Asian population. Three sisters of the proband, two of whom reported tobacco and alcohol abuse, had bilateral temporal optic disc pallor without functional impact. A fourth non-smoker sister had a completely normal eye exam. CONCLUSIONS: The rare Asian m.14502T>C variant in the MT-ND6 gene was linked to a mild LHON phenotype in a Western European family. Penetrance in this family was likely triggered by alcohol and tobacco abuse. A full mtDNA sequencing is warranted in the case of high clinical suspicion of LHON when mutation analysis for the three common pathogenic variants is negative.

Hypermethylation of Hepatic Mitochondrial ND6 Provokes Systemic Insulin Resistance.

Mitochondrial epigenetics is rising as intriguing notion for its potential involvement in aging and diseases, while the details remain largely unexplored. Here it is shown that among the 13 mitochondrial DNA (mtDNA) encoded genes, NADH-dehydrogenase 6 (ND6) transcript is primarily decreased in obese and type 2 diabetes populations, which negatively correlates with its distinctive hypermethylation. Hepatic mtDNA sequencing in mice unveils that ND6 presents the highest methylation level, which dramatically increases under diabetic condition due to enhanced mitochondrial translocation of DNA methyltransferase 1 (DNMT1) promoted by free fatty acid through adenosine 5'-monophosphate (AMP)-activated protein kinase (AMPK) activation. Hepatic knockdown of ND6 or overexpression of Dnmt1 similarly impairs mitochondrial function and induces systemic insulin resistance both in vivo and in vitro. Genetic or chemical targeting hepatic DNMT1 shows significant benefits against insulin resistance associated metabolic disorders. These findings highlight the pivotal role of ND6 epigenetic network in regulating mitochondrial function and onset of insulin resistance, shedding light on potential preventive and therapeutic strategies of insulin resistance and related metabolic disorders from a perspective of mitochondrial epigenetics.

Circulating nicotinamide adenine dinucleotide-ubiquinone oxidoreductase chain 6 is associated with disease activity of anti-neutrophil cytoplasmic antibody-associated vasculitis.

BACKGROUND: Increased serum and urinary mitochondrial DNA have been demonstrated in antineutrophil cytoplasmic antibody-associated vasculitis (AAV). Here we investigated the significance of serum nicotinamide adenine dinucleotide-ubiquinone oxidoreductase chain 6 (ND6), which is encoded by mtDNA and can attract neutrophils, in AAV. METHODS: Thirty-seven AAV patients (32 patients with positive myeloperoxidase-ANCA and 5 patients with proteinase 3-ANCA) were enrolled. Relationship between serum ND6 and clinico-laboratory characteristics were analyzed. RESULTS: The ND6 level of patients was higher than normal people (46.56 ± 23.67 pg/mL vs. 4.95 ± 2.45 pg/mL, P < 0.001) The ND6 levels of patients who needed hemodialysis at disease onset and who had pulmonary hemorrhage (PH) were higher than that of the corresponding controls (P = 0.004 and 0.044 respectively). The ND6 level negatively correlated with the percentages of normal glomeruli in kidney biopsy. The AUC of ROC curve to diagnose hemodialysis and PH was 0.804 and 0.750 respectively. ND6 level positively correlated with Birmingham Vasculitis Activity Score in active disease, and returned to normal after remission. Patients with higher serum ND6 had higher mortality (P = 0.023). CONCLUSIONS: Serum ND6 increases in active AAV, and its level correlates with the severity of disease. High ND6 level is associated with severe organ injury and predicts poor prognosis of AAV.