Oxidative Phosphorylation Chain Research Articles

Evolution of translational control and the emergence of genes and open reading frames in human and non-human primate hearts.

Evolutionary innovations can be driven by changes in the rates of RNA translation and the emergence of new genes and small open reading frames (sORFs). In this study, we characterized the transcriptional and translational landscape of the hearts of four primate and two rodent species through integrative ribosome and transcriptomic profiling, including adult left ventricle tissues and induced pluripotent stem cell-derived cardiomyocyte cell cultures. We show here that the translational efficiencies of subunits of the mitochondrial oxidative phosphorylation chain complexes IV and V evolved rapidly across mammalian evolution. Moreover, we discovered hundreds of species-specific and lineage-specific genomic innovations that emerged during primate evolution in the heart, including 551 genes, 504 sORFs and 76 evolutionarily conserved genes displaying human-specific cardiac-enriched expression. Overall, our work describes the evolutionary processes and mechanisms that have shaped cardiac transcription and translation in recent primate evolution and sheds light on how these can contribute to cardiac development and disease.

Mitochondrial Protein SLIRP Affects Biosynthesis of Cytochrome c Oxidase Subunits in HEK293T Cells.

Mitochondria carry out various vital roles in eukaryotic cells, including ATP energy synthesis, the regulation of apoptosis, Fe-S cluster formation, and the metabolism of fatty acids, amino acids, and nucleotides. Throughout evolution, mitochondria lost most of their ancestor's genome but kept the replication, transcription, and translation machinery. Protein biosynthesis in mitochondria is specialized in the production of highly hydrophobic proteins encoded by mitochondria. These proteins are components of oxidative phosphorylation chain complexes. The coordination of protein synthesis must be precise to ensure the correct assembly of nuclear-encoded subunits for these complexes. However, the regulatory mechanisms of mitochondrial translation in human cells are not yet fully understood. In this study, we examined the contribution of the SLIRP protein in regulating protein biosynthesis in mitochondria. Using a click-chemistry approach, we discovered that deletion of the SLIRP gene disturbs mitochondrial translation, leading to the dysfunction of complexes I and IV, but it has no significant effect on complexes III and V. We have shown that this protein interacts only with the small subunit of the mitochondrial ribosome, which may indicate its involvement in the regulation of the mitochondrial translation initiation stage.

Exploring the role of brown algae and algal polyphenols in muscle hypertrophy and strength enhancement in physically inactive adult mice

The prevalent sedentary lifestyle of adults has led to decreased physical activity and increased health risks. We aimed to investigate the effects of Ishige okamurae extract (IO) and its active compound diphlorethohydroxycarmalol (DPHC) on muscle characteristics of physically inactive adult male mice. IO and DPHC supplementation did not lead to significant male hormonal imbalance in adult sedentary mice. However, they significantly increased muscle strength and hypertrophy in four major muscle groups. Furthermore, IO and DPHC treatment upregulated the expression of oxidative phosphorylation chain enzyme complexes in the muscle tissue, indicating enhanced mitochondrial activity. Thus, IO and DPHC exert positive effects on muscle health and function by improving mitochondrial function in physically inactive adult mice. Algal consumption can improve muscle-related indicators and prevent muscle deterioration in sedentary individuals. Understanding the mechanisms underlying these effects could provide valuable insights for developing interventions to enhance muscle health in individuals with limited physical activity.

Mitochondrial transport of catalytic RNAs and targeting of the organellar transcriptome in human cells.

Mutations in the small genome present in mitochondria often result in severe pathologies. Different genetic strategies have been explored, aiming to rescue such mutations. A number of these strategies were based on the capacity of human mitochondria to import RNAs from the cytosol and designed to repress the replication of the mutated genomes or to provide the organelles with wild-type versions of mutant transcripts. However, the mutant RNAs present in mitochondria turned out to be an obstacle to therapy and little attention has been devoted so far to their elimination. Here, we present the development of a strategy to knockdown mitochondrial RNAs in human cells using the transfer RNA-like structure of Brome mosaic virus or Tobacco mosaic virus as a shuttle to drive trans-cleaving ribozymes into the organelles in human cell lines. We obtained a specific knockdown of the targeted mitochondrial ATP6 mRNA, followed by a deep drop in ATP6 protein and a functional impairment of the oxidative phosphorylation chain. Our strategy provides a powerful approach to eliminate mutant organellar transcripts and to analyse the control and communication of the human organellar genetic system.

Tcf20 deficiency is associated with increased liver fibrogenesis and alterations in mitochondrial metabolism in mice and humans.

Transcription co-activator factor 20 (TCF20) is a regulator of transcription factors involved in extracellular matrix remodelling. In addition, TCF20 genomic variants in humans have been associated with impaired intellectual disability. Therefore, we hypothesized that TCF20 has several functions beyond those described in neurogenesis, including the regulation of fibrogenesis. Tcf20 knock-out (Tcf20-/- ) and Tcf20 heterozygous mice were generated by homologous recombination. TCF20 gene genotyping and expression was assessed in patients with pathogenic variants in the TCF20 gene. Neural development was investigated by immufluorescense. Mitochondrial metabolic activity was evaluated with the Seahorse analyser. The proteome analysis was carried out by gas chromatography mass-spectrometry. Characterization of Tcf20-/- newborn mice showed impaired neural development and death after birth. In contrast, heterozygous mice were viable but showed higher CCl4 -induced liver fibrosis and a differential expression of genes involved in extracellular matrix homeostasis compared to wild-type mice, along with abnormal behavioural patterns compatible with autism-like phenotypes. Tcf20-/- embryonic livers and mouse embryonic fibroblast (MEF) cells revealed differential expression of structural proteins involved in the mitochondrial oxidative phosphorylation chain, increased rates of mitochondrial metabolic activity and alterations in metabolites of the citric acid cycle. These results parallel to those found in patients with TCF20 pathogenic variants, including alterations of the fibrosis scores (ELF and APRI) and the elevation of succinate concentration in plasma. We demonstrated a new role of Tcf20 in fibrogenesis and mitochondria metabolism in mice and showed the association of TCF20 deficiency with fibrosis and metabolic biomarkers in humans.

BET Protein Inhibitor JQ1 Modulates Mitochondrial Dysfunction and Oxidative Stress Induced by Chronic Kidney Disease.

Among the mechanisms involved in the progression of kidney disease, mitochondrial dysfunction has special relevance. Epigenetic drugs such as inhibitors of extra-terminal domain proteins (iBET) have shown beneficial effects in experimental kidney disease, mainly by inhibiting proliferative and inflammatory responses. The impact of iBET on mitochondrial damage was explored in in vitro studies in renal cells stimulated with TGF-β1 and in vivo in murine unilateral ureteral obstruction (UUO) model of progressive kidney damage. In vitro, JQ1 pretreatment prevented the TGF-β1-induced downregulation of components of the oxidative phosphorylation chain (OXPHOS), such as cytochrome C and CV-ATP5a in human proximal tubular cells. In addition, JQ1 also prevented the altered mitochondrial dynamics by avoiding the increase in the DRP-1 fission factor. In UUO model, renal gene expression levels of cytochrome C and CV-ATP5a as well as protein levels of cytochrome C were reduced These changes were prevented by JQ1 administration. In addition, JQ1 decreased protein levels of the DRP1 fission protein and increased the OPA-1 fusion protein, restoring mitochondrial dynamics. Mitochondria also participate in the maintenance of redox balance. JQ1 restored the gene expression of antioxidant proteins, such as Catalase and Heme oxygenase 1 in TGF-β1-stimulated human proximal tubular cells and in murine obstructed kidneys. Indeed, in tubular cells, JQ1 decreased ROS production induced by stimulation with TGF-β1, as evaluated by MitoSOXTM. iBETs, such as JQ1, improve mitochondrial dynamics, functionality, and oxidative stress in kidney disease.

Diagnostic Testing in Suspected Primary Mitochondrial Myopathy

The diagnosis of primary mitochondrial myopathy is often delayed by years due to non-specific clinical symptoms as well as variable testing of mitochondrial disorders. The aim of this review is to summarize and discuss the collective findings and novel insights regarding the diagnosing, testing, and clinical presentation of primary mitochondrial myopathy (PMM). PMM results from a disruption of the oxidative phosphorylation (OXPHOS) chain in mitochondria due to mutations in mitochondrial DNA (mtDNA) or nuclear DNA (nDNA). Although there are many named syndromes caused by mitochondrial mutations, this review will focus on PMM, which are mitochondrial disorders mainly affecting, but not limited to, the skeletal muscle. Clinical presentation may include muscle weakness, exercise intolerance, myalgia, and rhabdomyolysis. Although skeletal muscle and respiratory function are most frequently affected due to their high energy demand, multisystem dysfunction may also occur, which may lead to the inclusion of mitochondrial myopathies on the differential. Currently, there are no effective disease-modifying treatments, and treatment programs typically only focus on managing the symptomatic manifestations of the disease. Although the field has a large unmet need regarding treatment options, diagnostic pathways are better understood and can help shorten the diagnostic journey to aid in disease management and clinical trial enrollment.

Impact of Roux-en-Y Gastric Bypass on Mitochondrial Biogenesis and Dynamics in Leukocytes of Obese Women.

The chronic low-grade inflammation widely associated with obesity can lead to a prooxidant status that triggers mitochondrial dysfunction. To date, Roux-en-Y gastric bypass (RYGB) is considered the most effective strategy for obese patients. However, little is known about its molecular mechanisms. This interventional study aimed to investigate whether RYGB modulates oxidative stress, inflammation and mitochondrial dynamics in the leukocytes of 47 obese women at one year follow-up. We evaluated biochemical parameters and serum inflammatory cytokines -TNFα, IL6 and IL1β- to assess systemic status. Total superoxide production -dHe-, mitochondrial membrane potential -TMRM-, leucocyte protein expression of inflammation mediators -MCP1 and NF-kB-, antioxidant defence -GPX1-, mitochondrial regulation—PGC1α, TFAM, OXPHOS and MIEAP- and dynamics -MFN2, MNF1, OPA1, FIS1 and p-DRP1- were also determined. After RYGB, a significant reduction in superoxide and mitochondrial membrane potential was evident, while GPX1 content was significantly increased. Likewise, a marked upregulation of the transcription factors PGC1α and TFAM, complexes of the oxidative phosphorylation chain (I–V) and MIEAP and MFN1 was observed. We conclude that women undergoing RYGB benefit from an amelioration of their prooxidant and inflammatory status and an improvement in mitochondrial dynamics of their leukocytes, which is likely to have a positive effect on clinical outcome.

Acute exposure to environmentally relevant levels of DDT alters muscle mitochondrial function in vivo in rats but not in vitro in L6 myotubes: A pilot study

Under insulin-stimulated conditions, skeletal muscle is the largest glucose consumer in the body. Mitochondrial dysfunction and damage to this tissue from oxidative stress are linked to the pathogenesis of type 2 diabetes. Environmental exposure to dichlorodiphenyltrichloroethane (DDT) and its metabolite, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE), has been associated with the incidence of type 2 diabetes as well as altered oxidative stress and mitochondrial dysfunction in non-muscle tissues. We hypothesized that energy metabolism and insulin sensitivity in skeletal muscle will be altered with exposure to DDT and DDE. In this pilot study, mitochondrial function was measured in permeabilized muscle fibers from Sprague-Dawley rats after one week of exposure to a single injection of DDT (40 μg/kg), a dose comparable to DDT levels in the diets of the Inuit of Northern Canada. The levels of oxidative phosphorylation chain complexes and ROS detoxification enzymes were measured in muscle tissue from these specimens. This acute in vivo exposure to DDT decreased muscle mitochondrial function by 45% without affecting the levels of mitochondrial oxidative phosphorylation chain complexes nor levels of ROS detoxification enzymes. To isolate the effects of DDT and DDE exposure on muscle, L6 myotubes were exposed to DDT or DDE (0, 10, 100, 1000, 10 000 nM) for 24 h. Only very high concentrations of DDT and DDE (1 000 – 10 000 nM) altered maximal respiration with only DDT altering basal glucose uptake in L6 myotubes. This did not alter levels of ROS detoxification enzymes or malondialdehyde (MDA) in L6 myotubes. Altogether, acute exposure to environmentally relevant doses of DDT resulted in muscle mitochondrial dysfunction in vivo in rats, but not when muscle cells were directly exposed to the pollutant or its metabolite.

Evolutionary rate covariation identifies SLC30A9 (ZnT9) as a mitochondrial zinc transporter.

Recent advances in genome sequencing have led to the identification of new ion and metabolite transporters, many of which have not been characterized. Due to the variety of subcellular localizations, cargo and transport mechanisms, such characterization is a daunting task, and predictive approaches focused on the functional context of transporters are very much needed. Here we present a case for identifying a transporter localization using evolutionary rate covariation (ERC), a computational approach based on pairwise correlations of amino acid sequence evolutionary rates across the mammalian phylogeny. As a case study, we find that poorly characterized transporter SLC30A9 (ZnT9) coevolves with several components of the mitochondrial oxidative phosphorylation chain, suggesting mitochondrial localization. We confirmed this computational finding experimentally using recombinant human SLC30A9. SLC30A9 loss caused zinc mishandling in the mitochondria, suggesting that under normal conditions it acts as a zinc exporter. We therefore propose that ERC can be used to predict the functional context of novel transporters and other poorly characterized proteins.

Mitochondrial dysfunction triggers the pathogenesis of Parkinson's disease in neuronal C/EBPβ transgenic mice.

Respiratory chain complex I deficiency elicits mitochondrial dysfunction and reactive oxidative species (ROS), which plays a crucial role in Parkinson's disease (PD) pathogenesis. However, it remains unclear whether the impairment in other complexes in the mitochondrial oxidative phosphorylation chain is also sufficient to trigger PD onset. Here we show that inhibition of Complex II or III in the electron transport chain (ETC) induces the motor disorder and PD pathologies in neuronal Thy1-C/EBPβ transgenic mice. Through a cell-based screening of mitochondrial respiratory chain inhibitors, we identified TTFA (complex II inhibitor) and Atovaquone (complex III inhibitor), which robustly block the oxidative phosphorylation functions, strongly escalate ROS, and activate C/EBPβ/AEP pathway that triggers dopaminergic neuronal cell death. Oral administration of these inhibitors to Thy1-C/EBPβ mice elicits constipation and motor defects, associated with Lewy body-like inclusions. Deletion of SDHD (Succinate dehydrogenase) gene from the complex II in the Substantia Nigra of Thy1-C/EBPβ mice triggers ROS and PD pathologies, resulting in motor disorders. Hence, our findings demonstrate that mitochondrial ETC inactivation triggers PD pathogenesis via activating C/EBPβ/AEP pathway.

Metformin in Locally Advanced Non–Small Cell Lung Cancer

Metformin is proposed to suppress tumor growth through metabolic stress caused by inhibition of the mitochondria oxidative phosphorylation chain. In

Metformin in Combination With Chemoradiotherapy in Locally Advanced Non–Small Cell Lung Cancer

Unresected locally advanced non-small cell lung cancer (LA-NSCLC) shows poor survival outcomes even after aggressive concurrent chemoradiotherapy. Whether metformin, a diabetes agent that inhibits the mitochondria oxidative phosphorylation chain, could improve radiotherapy and chemotherapy response in LA-NSCLC remains to be studied. To examine whether metformin, given concurrently with chemoradiotherapy and as consolidation treatment, could improve outcomes in patients with LA-NSCLC. The Ontario Clinical Oncology Group Advanced Lung Cancer Treatment With Metformin and Chemoradiotherapy (OCOG-ALMERA) study was a multicenter phase 2 randomized clinical trial. Patients were stratified for stage IIIA vs IIIB LA-NSCLC and use of consolidation chemotherapy. The trial was designed to enroll 96 patients with unresected LA-NSCLC who did not have diabetes. The trial was conducted from September 24, 2014, to March 8, 2019. Patients were randomized to platinum-based chemotherapy, concurrent with chest radiotherapy (60-63 Gy), with or without consolidation chemotherapy or the same treatment plus metformin, 2000 mg/d, during chemoradiotherapy and afterward for up to 12 months. The primary outcome was the proportion of patients who experienced a failure event (ie, locoregional disease progression, distant metastases, death, and discontinuation of trial treatment or planned evaluations for any reason within 12 months). Proportions were compared using a 2-sided Fisher exact test. Conventional progression-free and overall survival were estimated using the Kaplan-Meier method. Adverse events were graded with Common Terminology Criteria for Adverse Events, version 4.03. All randomized patients were included in an intention-to-treat analysis. The trial was stopped early due to slow accrual. Between 2014 and 2019, 54 patients were randomized (26 in experimental arm and 28 in control arm). Participants included 30 women (55.6%); mean (SD) age was 65.6 (7.6) years. Treatment failure was detected in 18 patients (69.2%) receiving metformin within 1 year vs 12 (42.9%) control patients (P = .05). The 1-year progression-free survival rate was 34.8% (95% CI, 16.6%-53.7%) in the metformin arm and 63.0% (95% CI, 42.1%-78.1%) in the control arm (hazard ratio, 2.42; 95% CI, 1.14-5.10) The overall survival rates were 47.4% (95% CI, 26.3%-65.9%) in the metformin arm and 85.2% (95% CI, 65.2%-94.2%) in the control arm (hazard ratio, 3.80; 95% CI, 1.49-9.73). More patients in the experimental arm vs control arm (53.8% vs 25.0%) reported at least 1 grade 3 or higher adverse event. In this randomized clinical trial, the addition of metformin to chemoradiotherapy was associated with worse treatment efficacy and increased toxic effects compared with combined modality therapy alone. Metformin is not recommended in patients with LA-NSCLC who are candidates for chemoradiotherapy. ClinicalTrials.gov Identifier: NCT02115464.

Exercise Testing, Physical Training and Fatigue in Patients with Mitochondrial Myopathy Related to mtDNA Mutations.

Mutations in mitochondrial DNA (mtDNA) cause disruption of the oxidative phosphorylation chain and impair energy production in cells throughout the human body. Primary mitochondrial disorders due to mtDNA mutations can present with symptoms from adult-onset mono-organ affection to death in infancy due to multi-organ involvement. The heterogeneous phenotypes that patients with a mutation of mtDNA can present with are thought, at least to some extent, to be a result of differences in mtDNA mutation load among patients and even among tissues in the individual. The most common symptom in patients with mitochondrial myopathy (MM) is exercise intolerance. Since mitochondrial function can be assessed directly in skeletal muscle, exercise studies can be used to elucidate the physiological consequences of defective mitochondria due to mtDNA mutations. Moreover, exercise tests have been developed for diagnostic purposes for mitochondrial myopathy. In this review, we present the rationale for exercise testing of patients with MM due to mutations in mtDNA, evaluate the diagnostic yield of exercise tests for MM and touch upon how exercise tests can be used as tools for follow-up to assess disease course or effects of treatment interventions.

MITOCHONDRIA: Succinate dehydrogenase subunit B-associated phaeochromocytoma and paraganglioma.

Phaeochromocytomas and paragangliomas are rare neuroendocrine tumours. So far, over 20 causative genes have been identified, of which the most frequent and strongest indicator for malignancies are mutations in succinate dehydrogenase subunit B. No curative therapy is available for patients with metastases resulting in poor prognosis. Therapy development has been hindered by lack of suitable model systems. The succinate dehydrogenase complex is located in the inner membrane of the mitochondria and plays a crucial role in the oxidative phosphorylation chain and the tricarboxylic acid-cycle. Succinate dehydrogenase deficiency results in accumulation of the oncometabolite succinate inducing hypoxia inducible factor stabilization, deoxyribonucleic acid and histone methylation inhibition, and impaired production of adenosine triphosphate. It remains unknown which combination of pathways and/or triggers are decisive for metastases development. In this review, the role of mitochondria in malignant succinate dehydrogenase subunit B-associated phaeochromocytomas and paragangliomas and implications for mitochondria as therapeutic target are discussed.

How does secondary hypogonadism affect the spermatozoa proteome? Lessons from a porcine animal model

Secondary hypogonadism is a consequence of congenital or acquired diseases that affect the hypothalamus and/or pituitary gland, impairing secretion of gonadotrophin-releasing hormone (GnRH). Androgen deficiency resulting from reduced GnRH secretion is likely to have disrupting effects in epididymal epithelial cells, impairing the sperm maturation process. The aim of this study was to describe changes in the proteome of epididymal spermatozoa in a porcine model of secondary hypogonadism. Cauda epididymal spermatozoa were obtained from 10 boars previously immunised against GnRH (Vivax; Pfizer) and from 10 healthy boars. Protein extracts were analysed by multidimensional protein identification technology. In all, 1322 unique proteins were identified in the protein extracts of cauda epididymal spermatozoa, with significant changes in the abundance of key proteins involved in sperm metabolism (enolase, pyruvate dehydrogenase), acrosome reaction and capacitation (oxoprolinase, acrosomal protein SP-10, dihydrolipoyl dehydrogenase) and sperm–oocyte interactions (zona pellucida-binding protein, zonadhesin, sperm adhesion molecule 1). In addition, the abundance of mitochondrial proteins was severely affected, with significant changes in proteins of Complex I and II, as well as ATPase of the oxidative phosphorylation chain. The proteins identified in this study are potential sperm biomarkers of testicular and epididymal dysfunction related to disruption of the hypothalamus–pituitary–testis axis.

294-LB: Transcriptome-Wide Signals Converge Upon Mitochondrial Function in Developmental Stages of Type 2 Diabetes in Human Skeletal Muscle

Skeletal muscle is a major contributor to overall glucose homeostasis in the body and together with the liver is chiefly responsible for the whole-body insulin sensitivity. However, few studies have investigated the transcriptional signature of insulin resistance in skeletal muscles, at different stages of T2D development. Thus, the aim of this study was to identify the transcriptional signature of dysregulated glucose metabolism in skeletal muscle in humans by profiling the transcriptome with next-generation sequencing (NGS). We selected 40 sedentary males, aged 40-65 years, with BMI 26-33 kg/m2, diagnosed into three groups: 18 normoglycemics, 14 prediabetics and 8 subjects with type 2 diabetes. mRNA was extracted from biopsied Vastus lateralis muscles and sequenced with Illumina HiSeq 4000.Comparing normoglycemic and diabetic subjects revealed 4404 significantly differentially expressed (DE) genes, which represents around 30% of all mapped genes in studied samples. For the comparison between type 2 diabetics and prediabetics, the number of DE genes was 4055 genes. Interestingly we found no significantly DE genes between normoglycemics and prediabetics. KEGG enrichment analysis revealed that DE pathways between diabetics vs. nondiabetics were enriched for pathways related to oxidative phosphorylation, thermogenesis, nonalcoholic fatty liver disease and neurological diseases, which share the same underlying mechanism: mitochondrial dysfunction.These results indicate that skeletal muscle contributes most to overt T2D, with a possible indication that the liver contributes most to early stages the disease development. Differences observed between type 2 diabetics and the two remaining groups, occurring primarily in oxidative phosphorylation and electron transport chain pathways suggests that mitochondrial dysfunction plays the predominant role in the pathogenesis of T2D. Disclosure L. Szczerbinski: None. M. Niemira: None. K. Szczerbinski: None. U. Puchta: None. E. Siewiec: None. A. Citko: None. J. Zapolska: None. M. Taylor: None. S. Larsen: None. M. Gorska: None. A. Kretowski: None.

Increased Degradation Rates in the Components of the Mitochondrial Oxidative Phosphorylation Chain in the Cerebellum of Old Mice.

Brain structures differ in the magnitude of age-related neuron loss with the cerebellum being more affected. An underlying cause could be an age-related decline in mitochondrial bioenergetics. Successful aging of mitochondria reflects a balanced turnover of proteins involved in mitochondrial biogenesis and mitophagy. Thus, an imbalance in mitochondrial turnover can contribute to the diminution of cellular function seen during aging. Mitochondrial biogenesis and mitophagy are mediated by a set of proteins including MFN1, MFN2, OPA1, DRP1, FIS1 as well as DMN1l and DNM1, all of which are required for mitochondrial fission. Using N15 labeling, we report that the turnover rates for DMN1l and FIS1 go in opposite directions in the cerebellum of 22-month-old C57BL6j mice as compared to 3-month-old mice. Previous studies have reported decreased turnover rates for the mitochondrial respiratory complexes of aged rodents. In contrast, we found increased turnover rates for mitochondrial proteins of the oxidative phosphorylation chain in the aged mice as compared to young mice. Furthermore, the turnover rate of the components that are most affected by aging –complex III components (ubiquinol cytochrome C oxidoreductase) and complex IV components (cytochrome C oxidase)– was significantly increased in the senescent cerebellum. However, the turnover rates of proteins involved in mitophagy (i.e., the proteasomal and lysosomal degradation of damaged mitochondria) were not significantly altered with age. Overall, our results suggest that an age-related imbalance in the turnover rates of proteins involved in mitochondrial biogenesis and mitophagy (DMN1l, FIS1) in conjunction with an age-related imbalance in the turnover rates of proteins of the complexes III and IV of the electron transfer chain, might impair cerebellar mitochondrial bioenergetics in old mice.

Oxidative stress and altered mitochondrial protein expression in the absence of amyloid-β and tau pathology in iPSC-derived neurons from sporadic Alzheimer's disease patients

Mitochondrial dysfunction is a prominent feature of Alzheimer's disease (AD) and increased production of reactive oxygen species (ROS) has been described in postmortem brain samples and animal models. However, these observations were made at a late stage of disease and the inability to examine an early, presymptomatic phase in human neurons impeded our understanding of cause or consequence of mitochondrial dysfunction in AD. We used human induced pluripotent stem cell-derived neuronal cells (iN cells) from sporadic AD (SAD) patients and healthy control subjects (HCS) to show aberrant mitochondrial function in patient-derived cells. We observed that neuronal cultures from some patients produced more ROS and displayed higher levels of DNA damage. Furthermore, patient-derived cells showed increased levels of oxidative phosphorylation chain complexes, whereas mitochondrial fission and fusion proteins were not affected. Surprisingly, these effects neither correlated with Aβ nor phosphorylated and total tau levels. Synaptic protein levels were also unaffected in SAD iN cells. The results of this study give new insights into constitutional metabolic changes in neurons from subjects prone to develop Alzheimer's pathology. They suggest that increased ROS production may have an integral role in the development of sporadic AD prior to the appearance of amyloid and tau pathology.

Mitochondrial genome architecture in non-alcoholic fatty liver disease.

Non-alcoholic fatty liver disease (NAFLD) is associated with mitochondrial dysfunction, a decreased liver mitochondrial DNA (mtDNA) content, and impaired energy metabolism. To understand the clinical implications of mtDNA diversity in the biology of NAFLD, we applied deep-coverage whole sequencing of the liver mitochondrial genomes. We used a multistage study design, including a discovery phase, a phenotype-oriented study to assess the mutational burden in patients with steatohepatitis at different stages of liver fibrosis, and a replication study to validate findings in loci of interest. We also assessed the potential protein-level impact of the observed mutations. To determine whether the observed changes are tissue-specific, we compared the liver and the corresponding peripheral blood entire mitochondrial genomes. The nuclear genes POLG and POLG2 (mitochondrial DNA polymerase-γ) were also sequenced. We observed that the liver mtDNA of patients with NAFLD harbours complex genomes with a significantly higher mutational (1.28-fold) rate and degree of heteroplasmy than in controls. The analysis of liver mitochondrial genomes of patients with different degrees of fibrosis revealed that the disease severity is associated with an overall 1.4-fold increase in mutation rate, including mutations in genes of the oxidative phosphorylation (OXPHOS) chain. Significant differences in gene and protein expression patterns were observed in association with the cumulative number of OXPHOS polymorphic sites. We observed a high degree of homology (∼98%) between the blood and liver mitochondrial genomes. A missense POLG p.Gln1236His variant was associated with liver mtDNA copy number. In conclusion, we have demonstrated that OXPHOS genes contain the highest number of hotspot positions associated with a more severe phenotype. The variability of the mitochondrial genomes probably originates from a common germline source; hence, it may explain a fraction of the 'missing heritability' of NAFLD. Copyright © 2016 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.