mtDNA Deletions Research Articles

The Large-scale Deletions and Copy Numbers of Mitochondrial DNA in Gout Patients Treated with Allopurinol

Allopurinol is now the first-line treatment for managing gout and its increasing usage has brought more gout patients at risk of developing allopurinol-induced hypersensitive reactions. Up to now, our attempts to identify the biomarkers for hypersensitivity to allopurinol are still finite. Besides, the association between drug-induced hypersensitive reactions and some mitochondrial DNA (mtDNA) alterations has been proved but remains unclear in gout patients. In this study, 41 blood samples of gout patients prescribed with allopurinol including 22 hypersensitive and 29 tolerant ones were used to analyze their mtDNA large-scale deletions through PCR and determine the mtDNA deletion level and the copy number by quantitative PCR. The results indicated that the mtDNA large-scale deletions and mtDNA copy number of the hypersensitive group were lower than that of the tolerant one (p < 0.05). However, no association was found between the mtDNA deletion level and the appearance of hypersensitive reactions in gout patients. In addition, the study showed that the mtDNA deletion level and copy number were negatively correlated with the copy numbers of mitochondrial DNA in gout patients (R = -0.3495; p = 0.0119) and allopurinol hypersensitive group (R = -0.6744; p = 0.0005). Thus, a decrease in mtDNA copy number might serve as a potential biomarker for further investigation to assess the risk of hypersensitive reactions to allopurinol in gout patients.

Mitochondrial DNA involvement in patients with autism spectrum disorders and intellectual disability

BackgroundAutism spectrum disorders (ASD) are neurodevelopmental disorders, with heterogeneous etiology, characterized by deficiencies in social interaction, communication, and by repetitive and stereotyped behaviors.Mitochondrial encephalomyopathies are inherited disorders of oxidative metabolism, with a wide clinical, biochemical and genetic heterogeneity, requiring a complex diagnostic flow-chart. Infantile forms often occur with defects in development, intellectual disabilities and dysmorphisms.ASD has been associated with mitochondrial respiratory chain deficiency and/or mitochondrial DNA (mtDNA) mutations. However, few studies carried out detailed clinical, instrumental, morphological, biochemical investigations, and mtDNA sequencing in ASD patients. MethodThe purpose of this study was the identification of mitochondrial dysfunction due to mtDNA variants in 19 selected subjects presenting ASD and clinical features of mitochondrial disease. For these patients we adopted a multidisciplinary approach combining clinical and laboratory investigations on muscle biopsy, with biochemical, histological and genetic techniques. ResultsThe histological examination showed myogenic or neurogenic changes in 79 % of patients; furthermore, 58 % of the patients had lipid accumulation, mitochondrial proliferation and COX deficient fibers. The biochemical investigations reported in three patients impairments involving one or more of the respiratory chain complexes. In addition, genetic studies revealed in one patient with normal histology and biochemistry multiple mtDNA deletions, and in four patients different mtDNA point mutations. ConclusionsThe present study confirms the hypothesis of an association between ASD and mitochondrial dysfunction. However, further studies in a larger group of subjects are needed.

Retinal involvement in mitochondrial disease

AbstractRetinal involvement in mitochondrial disease is a variable feature of mitochondrial dysfunction. The retinal pigment epithelium and photoreceptor layers can both be affected. It manifests with signs ranging from asymptomatic peripheral salt‐and‐pepper retinopathy to classic bone‐spicule pigmentary changes. The consequences can be progressive mild or severe visual field constriction and central visual acuity loss. The pathophysiological mechanisms involved in retinal dysfunction in mitochondrial disease are still being elucidated and may include a range of metabolic and bioenergetic defects.Mitochondrial conditions affecting the eye that display prominent outer retinal involvement include.(a) mitochondrial encephalomyopathy, lactic acidosis and stroke‐like episodes (MELAS) secondary to the m.3243A > G mtDNA mutation in MT‐TL1,(b) neuropathy, ataxia and retinitis pigmentosa (NARP) secondary to the m.8993 T > G mtDNA mutation in MT‐ATP6,(c) chronic progressive external ophthalmoplegia (CPEO), in particular the Kearns‐Sayre syndrome (KSS) secondary to single large‐scale mtDNA deletions, and.(d) some newer entities, such as optic neuropathy and pigmentary retinopathy seen in patients with mutations in the gene SSBP1.The features and diagnostic pathway for these conditions will be illustrated and discussed.

When to suspect mitochondrial disease and how to investigate it

AbstractMitochondrial diseases are caused by both nuclear DNA (nDNA) and mitochondrial DNA (mtDNA) mutations and are characterized by heterogeneous clinical presentations due to the potential affection of each organ of the body, in particular those with high energy requirements.The most common clinical presentations of mitochondrial defects are mitochondrial myopathy, central nervous system manifestations including cerebral, cerebellar, brainstem and spinal cord atrophy, white matter disease, stroke‐like episodes and epilepsy, peripheral neuropathy, optic atrophy, pigmentary retinopathy, sensorineural deafness, cardiomyopathy, diabetes and kidney disorders.Thus, clinical diagnostic work‐out for mitochondrial disorders should include muscle biopsy, brain MRI with magnetic resonance spectroscopy, electromyography, electroencephalography, ophthalmological evaluation, audiometry, cardiac evaluation including echocardiogram, endocrinological and nephrological evaluation. Laboratory exams may include traditional markers as creatine kinase and lactic acid as well as more recent biomarkers such as GDF‐15 and FGF‐21.Genetic testing includes both nuclear and mtDNA sequencing based on family history that can point towards a matrilinear or mendelian transmission of the genetic defect. Sporadic cases are also possible and this particularly apply to single mtDNA deletions and nuclear de‐novo mutations. Biochemical analysis of muscle biopsy is also important to evaluate the presence of single/multiple respiratory chain complexes defect.The most common mitochondrial disorder due to mtDNA mutations is Leber's Hereditary Optic Neuropathy, followed by Mitochondrial Encephalopathy, Lactic Acidosis and Stroke‐like Episodes (MELAS), whereas among the nuclear genes OPA1 gene mutations are the most common cause of Dominant Optic Atrophy.ReferenceLa Morgia C, Maresca A, Caporali L, Valentino ML, Carelli V. Mitochondrial diseases in adults. J Intern Med. 2020 Jun;287(6):592–608. doi: 10.1111/joim.13064. PMID: 32463135.

Unleashing a novel function of Endonuclease G in mitochondrial genome instability.

Having its genome makes the mitochondrion a unique and semiautonomous organelle within cells. Mammalian mitochondrial DNA (mtDNA) is a double-stranded closed circular molecule of about 16 kb coding for 37 genes. Mutations, including deletions in the mitochondrial genome, can culminate in different human diseases. Mapping the deletion junctions suggests that the breakpoints are generally seen at hotspots. '9 bp deletion' (8271-8281), seen in the intergenic region of cytochrome c oxidase II/tRNALys, is the most common mitochondrial deletion. While it is associated with several diseases like myopathy, dystonia, and hepatocellular carcinoma, it has also been used as an evolutionary marker. However, the mechanism responsible for its fragility is unclear. In the current study, we show that Endonuclease G, a mitochondrial nuclease responsible for nonspecific cleavage of nuclear DNA during apoptosis, can induce breaks at sequences associated with '9 bp deletion' when it is present on a plasmid or in the mitochondrial genome. Through a series of in vitro and intracellular studies, we show that Endonuclease G binds to G-quadruplex structures formed at the hotspot and induces DNA breaks. Therefore, we uncover a new role for Endonuclease G in generating mtDNA deletions, which depends on the formation of G4 DNA within the mitochondrial genome. In summary, we identify a novel property of Endonuclease G, besides its role in apoptosis and the recently described 'elimination of paternal mitochondria during fertilisation.

Mitochondrial membrane proteins and VPS35 orchestrate selective removal of mtDNA

Understanding the mechanisms governing selective turnover of mutation-bearing mtDNA is fundamental to design therapeutic strategies against mtDNA diseases. Here, we show that specific mtDNA damage leads to an exacerbated mtDNA turnover, independent of canonical macroautophagy, but relying on lysosomal function and ATG5. Using proximity labeling and Twinkle as a nucleoid marker, we demonstrate that mtDNA damage induces membrane remodeling and endosomal recruitment in close proximity to mitochondrial nucleoid sub-compartments. Targeting of mitochondrial nucleoids is controlled by the ATAD3-SAMM50 axis, which is disrupted upon mtDNA damage. SAMM50 acts as a gatekeeper, influencing BAK clustering, controlling nucleoid release and facilitating transfer to endosomes. Here, VPS35 mediates maturation of early endosomes to late autophagy vesicles where degradation occurs. In addition, using a mouse model where mtDNA alterations cause impairment of muscle regeneration, we show that stimulation of lysosomal activity by rapamycin, selectively removes mtDNA deletions without affecting mtDNA copy number, ameliorating mitochondrial dysfunction. Taken together, our data demonstrates that upon mtDNA damage, mitochondrial nucleoids are eliminated outside the mitochondrial network through an endosomal-mitophagy pathway. With these results, we unveil the molecular players of a complex mechanism with multiple potential benefits to understand mtDNA related diseases, inherited, acquired or due to normal ageing.

Hybridization drives mitochondrial DNA degeneration and metabolic shift in a species with biparental mitochondrial inheritance.

Mitochondrial DNA (mtDNA) is a cytoplasmic genome that is essential for respiratory metabolism. Although uniparental mtDNA inheritance is most common in animals and plants, distinct mtDNA haplotypes can coexist in a state of heteroplasmy, either because of paternal leakage or de novo mutations. mtDNA integrity and the resolution of heteroplasmy have important implications, notably for mitochondrial genetic disorders, speciation, and genome evolution in hybrids. However, the impact of genetic variation on the transition to homoplasmy from initially heteroplasmic backgrounds remains largely unknown. Here, we use Saccharomyces yeasts, fungi with constitutive biparental mtDNA inheritance, to investigate the resolution of mtDNA heteroplasmy in a variety of hybrid genotypes. We previously designed 11 crosses along a gradient of parental evolutionary divergence using undomesticated isolates of Saccharomyces paradoxus and Saccharomyces cerevisiae Each cross was independently replicated 48 to 96 times, and the resulting 864 hybrids were evolved under relaxed selection for mitochondrial function. Genome sequencing of 446 MA lines revealed extensive mtDNA recombination, but the recombination rate was not predicted by parental divergence level. We found a strong positive relationship between parental divergence and the rate of large-scale mtDNA deletions, which led to the loss of respiratory metabolism. We also uncovered associations between mtDNA recombination, mtDNA deletion, and genome instability that were genotype specific. Our results show that hybridization in yeast induces mtDNA degeneration through large-scale deletion and loss of function, with deep consequences for mtDNA evolution, metabolism, and the emergence of reproductive isolation.

Pathogenic mtDNA variants, in particular single large-scale mtDNA deletions, are strongly associated with post-lingual onset sensorineural hearing loss in primary mitochondrial disease.

In this retrospective cohort study of 193 consecutive subjects with primary mitochondrial disease (PMD) seen at the Children's Hospital of Philadelphia Mitochondrial Medicine Frontier Program, we assessed prevalence, severity, and time of onset of sensorineural hearing loss (SNHL) for PMD cases with different genetic etiologies. Subjects were grouped by genetic diagnosis: mitochondrial DNA (mtDNA) pathogenic variants, single large-scale mtDNA deletions (SLSMD), or nuclear DNA (nDNA) pathogenic variants. SNHL was audiometrically confirmed in 27% of PMD subjects (20% in mtDNA pathogenic variants, 58% in SLSMD and 25% in nDNA pathogenic variants). SLSMD had the highest odds ratio for SNHL. SNHL onset was post-lingual in 79% of PMD cases, interestingly including all cases with mtDNA pathogenic variants and SLSMD, which was significantly different from PMD cases caused by nDNA pathogenic variants. SNHL onset during school age was predominant in this patient population. Regular audiologic assessment is important for PMD patients, and PMD of mtDNA etiology should be considered as a differential diagnosis in pediatric patients and young adults with post-lingual SNHL onset, particularly in the setting of multi-system clinical involvement. Pathogenic mtDNA variants and SLSMD are less likely etiologies in subjects with congenital, pre-lingual onset SNHL.

Highly asymmetrical distribution of muscle wasting correlates to the heteroplasmy in a patient carrying a large-scale mitochondrial DNA deletion: a novel pathophysiological mechanism for explaining asymmetry in mitochondrial myopathies

Mitochondrial diseases are a heterogeneous group of pathologies, caused by missense mutations, sporadic large-scale deletions of mitochondrial DNA (mtDNA) or mutations of nuclear maintenance genes. We report the case of a patient in whom extended muscle pathology, biochemical and genetic mtDNA analyses have proven to be essential to elucidate a unique asymmetrical myopathic presentation. From the age of 34 years on, the patient has presented with oculomotor disorders, right facial peripheral palsy and predominantly left upper limb muscle weakness and atrophy. By contrast, he displayed no motor weakness on the right hemi-body, and no sensory symptoms, cerebellar syndrome, hypoacusis, or parkinsonism. Cardiac function was normal. CK levels were elevated (671 UI/L). Electroneuromyography (ENMG) and muscle MRI showed diffuse myogenic alterations, more pronounced on the left side muscles. Biopsy of the left deltoid muscle showed multiple mitochondrial defects, whereas in the right deltoid, mitochondrial defects were much less marked. Extended mitochondrial biochemical and molecular workup revealed a unique mtDNA deletion, with a 63.4% heteroplasmy load in the left deltoid, versus 8.1% in the right one. This case demonstrates that, in mitochondrial myopathies, heteroplasmy levels may drastically vary for the same type of muscle, rising the hypothesis of a new pathophysiological mechanism explaining asymmetry in hereditary myopathies.

Remdesivir does not affect mitochondrial DNA copy number or deletion mutation frequency in aged male rats: A short report.

Remdesivir is a leading therapy in patients with moderate to severe coronavirus 2 (SARS-CoV-2) infection; the majority of whom are older individuals. Remdesivir is a nucleoside analog that incorporates into nascent viral RNA, inhibiting RNA-directed RNA polymerases, including that of SARS-CoV-2. Less is known about remdesivir’s effects on mitochondria, particularly in older adults where mitochondria are known to be dysfunctional. Furthermore, its effect on age-induced mitochondrial mutations and copy number has not been previously studied. We hypothesized that remdesivir adversely affects mtDNA copy number and deletion mutation frequency in aged rodents. To test this hypothesis, 30-month-old male F333BNF1 rats were treated with remdesivir for three months. To determine if remdesivir adversely affects mtDNA, we measured copy number and mtDNA deletion frequency in rat hearts, kidneys, and skeletal muscles using digital PCR. We found no effects from three months of remdesivir treatment on mtDNA copy number or deletion mutation frequency in 33-month-old rats. These data support the notion that remdesivir does not compromise mtDNA quality or quantity at old age in mammals. Future work should focus on examining additional tissues such as brain and liver, and extend testing to human clinical samples.

Long-Term Persistence of Mitochondrial DNA Instability among HCV-Cured People Who Inject Drugs.

People who inject drugs (PWID) are a population exposed to many genotoxicants and with a high prevalence of HCV infection. Direct-acting antiviral (DAA) regimens are now widely used to treat chronic HCV infection. Although side effects to treatment are currently rare, the long-term effects such as suspicions of de novo hepatocellular carcinoma (HCC) occurrence or HCC recurrence and cardiac defects are still up for debate. Given the structure of DAAs, the molecules have a potential mitochondrial DNA (mtDNA) genotoxicity. We have previously reported acute mtDNA toxicity of three DAA regimens among PWID with a strong impact on the rate of mtDNA deletion, less on the quantity of mtDNA copy per cell at sustained viral response at 12 weeks (SVR12). Herein, we report the mtDNA parameters nine months after drug discontinuation. We observed that the percentage of the deleted mtDNA genome increased over time. No exposure to any other genotoxicants during this period was associated with a high deletion percentage, suggesting that the replicative advantage of the deleted molecules outweighed their elimination processes. Such observation calls for longer-term follow-up and may contribute to the molecular basis of subclinical side effects of DAA treatments.

Mitochondrial Dysfunction in Polycystic Ovary Syndrome.

Polycystic ovary syndrome (PCOS) is a multi-causal condition. Among the genetic causes, variations in the mitochondrial DNA (mtDNA) are increasingly recognised as causative. PCOS not only occurs in known syndromic mitochondrial disorders due to pathogenic variants in the mtDNA but also in non-syndromic mitochondrial disorders. Additionally, mtDNA variants not causing a multi-system mitochondrial disorder but exclusively PCOS have been reported. Among the syndromic mitochondrial disorders, PCOS has been described in myoclonic epilepsy with ragged-red fibre (MERRF) syndrome. Among the non-syndromic mitochondrial disorders, PCOS has been described in association with insulin resistance. Several other studies suggest that mtDNA point mutations or mtDNA deletions can be associated with PCOS without manifesting in organs other than the ovaries. Evidence from animal studies suggests that function, morphology, and biogenesis of mitochondria in ovarian tissue are generally impaired in PCOS patients. In conclusion, there is increasing evidence that mtDNA variants play a pathophysiological role in the development of PCOS. Further studies are needed to establish the causal link between mtDNA variants and PCOS.

Non-B DNA conformations analysis through molecular dynamics simulations

BackgroundNon-B DNA conformations are molecular structures that do not follow the canonical DNA double helix. Mutagenetic instability in nuclear and mitochondrial DNA (mtDNA) genomes has been associated with simple non-B DNA conformations, as hairpins or more complex structures, as G-quadruplexes. One of these structures is Structure A, a cloverleaf-like non-B conformation predicted for a 93-nt (nucleotide) stretch of the mtDNA control region 5′-peripheral domain. Structure A is embedded in a hot spot for the 3′ end of human mtDNA deletions revealing its importance in influencing the mutational instability of the mtDNA genome. MethodsTo better characterize Structure A, we predicted its 3D conformation using state-of-art methods and algorithms. The methodologic workflow consisted in the prediction of non-B conformations using molecular dynamics simulations. The conservation scores of alignments of the Structure A region in humans, primates, and mammals, was also calculated. ResultsOur results show that these computational methods are able to measure the stability of non-B conformations by using the level of base pairing during molecular dynamics. Structure A showed high stability and low flexibility correlated with high conservation scores in mammalian, more specifically in primate lineages. ConclusionsWe showed that 3D non-B conformations can be predicted and characterized by our methodology. This allowed the in-depth analysis of the structure A, and the main results showed the structure remains stable during the simulations. General significanceThe fine-scale atomic molecular determination of this type of non-B conformation opens the way to perform computational molecular studies that can show their involvement in mtDNA cellular mechanisms.

Spectrum of sperm mtDNA deletions in men exposed to industrial air pollution.

Sperm mtDNA status can serve as a molecular marker of oxidative stress and environmental exposure. High levels of air pollution may be associated with increased mitochondrial DNA (mtDNA) deletion rates in sperm. We compared the length spectra of sperm mtDNA deletions in semen samples collected from city policemen exposed to traffic and industrial air pollution in two seasons with different levels of air pollution. We used long-range PCR to amplify a fragment of mtDNA (8066bp) frequently affected by deletions, visualized the PCR products by gel electrophoresis, and analysed aberrant bands corresponding to deleted mtDNA, using gel documentation software. The predominance of undeleted sperm mtDNA was accompanied by a variety of shorter PCR product lengths in the vast majority of sperm samples, in both seasons. Sperm mtDNA molecules and bands corresponding to long deletions were more frequently detected than shorter deletions, in both seasons. We did not detect any difference in the total number of electrophoretic bands corresponding to deleted sperm mtDNA and in the number of deleted sperm mtDNA molecules between the two seasons. In our study, air pollution during sperm maturation did not induce formation of large mtDNA deletions detectable by long PCR and gel electrophoresis (>1kb) in maturing sperm mtDNA.

FP.16 The effects of resistance exercise training on mitochondrial myopathy patients

Patients with single, large-scale mitochondrial DNA (mtDNA) deletions often present with mitochondrial myopathy (MM) for which no treatment is available. Exercise intervention induces beneficial effects in mitochondrial myopathy. However, the mechanisms for this are not yet understood. The aim of this study is to investigate genetic, biochemical and molecular changes triggered by 16-week resistance exercise training for the development of exercise mimetic drugs for the cure of MM patients. Quadriceps biopsies were taken from a cohort of single, large-scale mtDNA deletion patients before and after 16-week resistance exercise training. Biopsies were assessed for changes after exercise in oxidative phosphorylation (OXPHOS) staining for Laminin, VDAC1, Ndufb8 and COX1; fibre type distribution, size and contraction force staining for Myh7, Myh2 and Myh1; heteroplasmy using real-time PCR for MT-ND4, MT-CO1, MT-CO3 and MT-CYB genes; differentially expressed (DE) genes and related protein level using RNA-sequencing and imaging mass cytometry, respectively. Myopathy score is a strong predictor of resistance exercise training responsiveness. Compared to healthy controls, all patients present with a significantly lower contraction force of SKM fibres (p=0.003) and differential fibre type distribution with increased type 2a (p<0.04) and decreased fibre I (p<0.0001). After exercise, all cases show an increase in the proportion of fibres with higher level of COX1 (p<0.0012) and increase of Myh7⁺ fibre type size (all patients except P2, p < 0.0001). The majority of patients show a significant increase of mitochondrial mass that positively correlates with the increase of aerobic capability (R=0.81). Furthermore, 13,132 DE genes were identified between pre- and post-exercise cases, of which 40 DE genes were selected with p<0.05 and logarithmic fold change <1.5 or >1.5. Among these, 13 novel exercise-modulated targets were established with an increased protein level localising within the SKM fibres (e.g. Dock11, Edil3, Ikbkg, Gem). Further analysis will assess the protein level of targets with nuclear, perinuclear and extracellular localisation in SKM of MM patients. Resistance exercise training is effective in reducing the OXPHOS defects and induces SKM remodelling in MM patients. The identification of novel exercise-modulated targets may provide insight for the development of exercise mimetic drugs for the cure of mitochondrial myopathy patients.

Targeting Mitochondrial Function with Chemoptogenetics.

Mitochondria are ATP-generating organelles in eukaryotic cells that produce reactive oxygen species (ROS) during oxidative phosphorylation (OXPHOS). Mitochondrial DNA (mtDNA) is packaged within nucleoids and, due to its close proximity to ROS production, endures oxidative base damage. This damage can be repaired by base excision repair (BER) within the mitochondria, or it can be degraded via exonucleases or mitophagy. Persistent mtDNA damage may drive the production of dysfunctional OXPHOS components that generate increased ROS, or OXPHOS components may be directly damaged by ROS, which then can cause more mtDNA damage and create a vicious cycle of ROS production and mitochondrial dysfunction. If mtDNA damage is left unrepaired, mtDNA mutations including deletions can result. The accumulation of mtDNA mutations has been associated with conditions ranging from the aging process to cancer and neurodegenerative conditions, but the sequence of events leading to mtDNA mutations and deletions is yet unknown. Researchers have utilized many systems and agents for generating ROS in mitochondria to observe the downstream effects on mtDNA, ROS, and mitochondrial function; yet, there are various drawbacks to these methodologies that limit their precision. Here, we describe a novel chemoptogenetic approach to target oxidative damage to mitochondria and mtDNA with a high spatial and temporal resolution so that the downstream effects of ROS-induced damage can be measured with a high precision in order to better understand the mechanism of mitochondrial dysfunction in aging, cancer, and neurodegenerative diseases.

Cardiac Outcomes in Adults With Mitochondrial Diseases

BackgroundPatients with mitochondrial diseases are at risk of heart failure (HF) and arrhythmic major adverse cardiac events (MACE). ObjectivesWe developed prediction models to estimate the risk of HF and arrhythmic MACE in this population. MethodsWe determined the incidence and searched for predictors of HF and arrhythmic MACE using Cox regression in 600 adult patients from a multicenter registry with genetically confirmed mitochondrial diseases. ResultsOver a median follow-up time of 6.67 years, 29 patients (4.9%) reached the HF endpoint, including 19 hospitalizations for nonterminal HF, 2 cardiac transplantations, and 8 deaths from HF. Thirty others (5.1%) reached the arrhythmic MACE, including 21 with third-degree or type II second-degree atrioventricular blocks, 4 with sinus node dysfunction, and 5 sudden cardiac deaths. Predictors of HF were the m.3243A>G variant (HR: 4.3; 95% CI: 1.8-10.1), conduction defects (HR: 3.0; 95% CI: 1.3-6.9), left ventricular (LV) hypertrophy (HR: 2.6; 95% CI: 1.1-5.8), LV ejection fraction <50% (HR: 10.2; 95% CI: 4.6-22.3), and premature ventricular beats (HR: 4.1; 95% CI: 1.7-9.9). Independent predictors for arrhythmia were single, large-scale mtDNA deletions (HR: 4.3; 95% CI: 1.7-10.4), conduction defects (HR: 6.8; 95% CI: 3.0-15.4), and LV ejection fraction <50% (HR: 2.7; 95% CI: 1.1-7.1). C-indexes of the Cox regression models were 0.91 (95% CI: 0.88-0.95) and 0.80 (95% CI: 0.70-0.90) for the HF and arrhythmic MACE, respectively. ConclusionsWe developed the first prediction models for HF and arrhythmic MACE in patients with mitochondrial diseases using genetic variant type and simple cardiac assessments.

Age- and time-dependent mitochondrial genotoxic and myopathic effects of beta-guanidinopropionic acid, a creatine analog, on rodent skeletal muscles.

Beta-guanidinopropionic acid (GPA) is a creatine analog suggested as a treatment for hypertension, diabetes, and obesity, which manifest primarily in older adults. A notable side effect of GPA is the induction of mitochondrial DNA deletion mutations. We hypothesized that mtDNA deletions contribute to muscle aging and used the mutation promoting effect of GPA to examine the impact of mtDNA deletions on muscles with differential vulnerability to aging. Rats were treated with GPA for up to 4months starting at 14 or 30months of age. We examined quadriceps and adductor longus muscles as the quadriceps exhibits profound age-induced deterioration, while adductor longus is maintained. GPA decreased body and muscle mass and mtDNA copy number while increasing mtDNA deletion frequency. The interactions between age and GPA treatment observed in the quadriceps were not observed in the adductor longus. GPA had negative mitochondrial effects in as little as 4weeks. GPA treatment exacerbated mtDNA deletions and muscle aging phenotypes in the quadriceps, an age-sensitive muscle, while the adductor longus was spared. GPA has been proposed for use in age-associated diseases, yet the pharmacodynamics of GPA differ with age and include the detrimental induction of mtDNA deletions, a mitochondrial genotoxic stress that is pronounced in muscles that are most vulnerable to aging. Further research is needed to determine if the proposed benefits of GPA on hypertension, diabetes, and obesity outweigh the detrimental mitochondrial and myopathic side effects.

Mitochondrial stress in advanced fibrosis and cirrhosis associated with chronic hepatitis B, chronic hepatitis C, or nonalcoholic steatohepatitis.

Hepatitis B virus (HBV) infection causes oxidative stress (OS) and alters mitochondria in experimental models. Our goal was to investigate whether HBV might alter liver mitochondria also in humans, and the resulting mitochondrial stress might account for the progression of fibrosis in chronic hepatitis B (CHB). The study included 146 treatment-naïve CHB mono-infected patients. Patients with CHB and advanced fibrosis (AF) or cirrhosis (F3-F4) were compared to patients with no/mild-moderate fibrosis (F0-F2). Patients with CHB were further compared to patients with chronic hepatitis C (CHC; n = 33), nonalcoholic steatohepatatis (NASH; n = 12), and healthy controls ( n = 24). We detected oxidative damage to mitochondrial DNA (mtDNA), including mtDNA strand beaks, and identified multiple mtDNA deletions in patients with F3-F4 as compared to patients with F0-F2. Alterations in mitochondrial function, mitochondrial unfolded protein response, biogenesis, mitophagy, and liver inflammation were observed in patients with AF or cirrhosis associated with CHB, CHC, and NASH. In vitro , significant increases of the mitochondrial formation of superoxide and peroxynitrite as well as mtDNA damage, nitration of the mitochondrial respiratory chain complexes, and impairment of complex I occurred in HepG2 cells replicating HBV or transiently expressing hepatitits B virus X protein. mtDNA damage and complex I impairment were prevented with the superoxide-scavenging Mito-Tempo or with inducible nitric oxide synthase (iNOS)-specific inhibitor 1400 W. Our results emphasized the importance of mitochondrial OS, mtDNA damage, and associated alterations in mitochondrial function and dynamics in AF or cirrhosis in CHB and NASH. Mitochondria might be a target in drug development to stop fibrosis progression.

Mitochondrial DNA maintenance defects: potential therapeutic strategies.

Mitochondrial DNA (mtDNA) replication depends on the mitochondrial import of hundreds of nuclear encoded proteins that control the mitochondrial genome maintenance and integrity. Defects in these processes result in an expanding group of disorders called mtDNA maintenance defects that are characterized by mtDNA depletion and/or multiple mtDNA deletions with variable phenotypic manifestations. As it applies for mitochondrial disorders in general, current treatment options for mtDNA maintenance defects are limited. Lately, with the development of model organisms, improved understanding of the pathophysiology of these disorders, and a better knowledge of their natural history, the number of preclinical studies and existing and planned clinical trials has been increasing. In this review, we discuss recent preclinical studies and current and future clinical trials concerning potential therapeutic options for the different mtDNA maintenance defects.