Mitochondrial Deletions Research Articles

A narrative review of mitochondrial dysfunction and male infertility.

Recent investigations have highlighted mitochondrial dysfunction as a major component in reduced sperm function and male infertility. The creation of energy, control of reactive oxygen species (ROS), apoptosis, and sperm motility are all critically dependent on mitochondria. The health of the male reproductive system may be significantly impacted by any alteration of mitochondrial structure, function, or integrity. This review intends to open the door to better diagnostic methods, novel therapy strategies, and improved reproductive outcomes for infertile couples by clarifying the crucial function of mitochondria. We searched PubMed, Google Scholar, and others for articles related to male infertility and mitochondrial dysfunction from 2014 to 2023. The articles related to the theme were preliminarily screened by abstract, and then the selected literature was read and summarized. In this essay, we examine the research on male infertility and mitochondrial malfunction. We investigate the intricate connection between sperm quality, deoxyribonucleic acid damage, oxidative stress (OS), and mitochondrial bioenergetics. We discuss about how spermatogenesis and sperm function are affected by mitochondrial mutations, deletions, and single nucleotide polymorphisms. We also explore the impact of age-related changes, lifestyle choices, and environmental factors on mitochondrial function and male fertility. This review also clarifies the mechanisms by which mitochondrial dysfunction impacts the viability, morphology, and capacitation of sperm, among other aspects of male reproductive health. Furthermore, we go over the recently developed field of mitochondrial treatments and possible therapeutic approaches that target mitochondrial malfunction to enhance male fertility. Mitochondria are important for sperm: The control of sperm motility, capacitation, and general quality is largely dependent on mitochondria. Deterioration of sperm motility and male infertility may result from disruption of the structure, function, or integrity of the mitochondria. Future studies should focus on figuring out the processes underlying mitochondrial dysfunction as fertility and reproductive health are significantly impacted by it. We discuss the evaluation of infertile men mitochondrial function defects and difficulties, and make recommendations for further study in this area. This article provides a thorough resource for clinicians, researchers, and reproductive biologists to understand the underlying mechanisms of male infertility and explore potential therapeutic interventions.

Multi-Allelic Mitochondrial DNA Deletions in an Adult Dog with Chronic Weakness, Exercise Intolerance and Lactic Acidemia.

(1) Background: An adult dog was presented to a board-certified veterinary neurologist for evaluation of chronic weakness, exercise intolerance and lactic acidemia. (2) Methods: A mitochondrial myopathy was diagnosed based on the histological and histochemical phenotype of numerous COX-negative muscle fibers. Whole-genome sequencing established the presence of multiple extended deletions in the mitochondrial DNA (mtDNA), with the highest prevalence between the 1-11 kb positions of the approximately 16 kb mitochondrial chromosome. Such findings are typically suggestive of an underlying nuclear genome variant affecting mitochondrial replication, repair, or metabolism. (3) Results: Numerous variants in the nuclear genome unique to the case were identified in the whole-genome sequence data, and one, the insertion of a DYNLT1 retrogene, whose parent gene is a regulator of the mitochondrial voltage-dependent anion channel (VDAC), was considered a plausible causal variant. (4) Conclusions: Here, we add mitochondrial deletion disorders to the spectrum of myopathies affecting adult dogs.

The long term effects of uncoupling interventions as a therapy for dementia in humans

In this paper we use simulation methods to study a hypothetical uncoupling agent as a therapy for dementia. We simulate the proliferation of mitochondrial deletion mutants amongst a population of wild-type in human neurons. Mitochondria play a key role in ATP generation. Clonal expansion can lead to the wild-type being overwhelmed by deletions such that a diminished population can no longer fulfil a cell’s energy requirement, eventually leading to its demise. The intention of uncoupling is to reduce the formation of deletion mutants by reducing mutation rate. However, a consequence of uncoupling is that the energy production efficacy is also reduced which in turn increases wild-type copy number in order to compensate for the energy deficit. The results of this paper showed that uncoupling reduced the severity of dementia, however, there was some increase in cognitive dysfunction pre-onset of dementia. The effectiveness of uncoupling was dependent upon the timing of intervention relative to the onset of dementia and would necessitate predicting its onset many years in advance.

Unravelling the complexities of depression with medical intelligence: exploring the interplay of genetics, hormones, and brain function

Depression is a multifactorial disease with unknown etiology affecting globally. It’s the second most significant reason for infirmity in 2020, affecting about 50 million people worldwide, with 80% living in developing nations. Recently, a surge in depression research has been witnessed, resulting in a multitude of emerging techniques developed for prediction, evaluation, detection, classification, localization, and treatment. The main purpose of this study is to determine the volume of depression research conducted on different aspects such as genetics, proteins, hormones, oxidative stress, inflammation, mitochondrial dysfunction, and associations with other mental disorders like anxiety and stress using traditional and medical intelligence (medical with AI). In addition, it also designs a comprehensive survey on detection, treatment planning, and genetic predisposition, along with future recommendations. This work is designed through different methods, including a systematic mapping process, literature review, and network visualization. In addition, we also used VOSviewer software and some authentic databases such as Google Scholar, Scopus, PubMed, and Web of Science for data collection, analysis, and designing comprehensive picture of the study. We analyzed 60 articles related to medical intelligence, including 47 from machine learning with 513,767 subjects (mean ± SD = 10,931.212 ± 35,624.372) and 13 from deep learning with 37,917 subjects (mean ± SD = 3159.75 ± 6285.57). Additionally, we also found that stressors impact the brain's cognitive and autonomic functioning, resulting in increased production of catecholamine, decreased cholinergic and glucocorticoid activity, with increased cortisol. These factors lead to chronic inflammation and hinder the brain's normal functioning, leading to depression, anxiety, and cardiovascular disorders. In the brain, reactive oxygen species (ROS) production is increased by IL-6 stimulation and mitochondrial cytochrome c oxidase is inhibited by nitric oxide, a potent inhibitor. Proteins, lipids, oxidative phosphorylation enzymes, and mtDNA are further disposed to oxidative impairment in the mitochondria. Consequently, mitochondrial dysfunction exacerbates oxidative stress, impairs mitochondrial DNA (mtDNA) or deletions of mtDNA, increases intracellular Ca2+ levels, changes in fission/fusion and mitochondrial morphology, and lastly leads to neuronal death. This study highlights the multidisciplinary approaches to depression with different aspects using traditional and medical intelligence. It will open a new way for depression research through new emerging technologies.

Common mitochondrial deletions in RNA-Seq: evaluation of bulk, single-cell, and spatial transcriptomic datasets

Common mitochondrial DNA (mtDNA) deletions are large structural variants in the mitochondrial genome that accumulate in metabolically active tissues with age and have been investigated in various diseases. We applied the Splice-Break2 pipeline (designed for high-throughput quantification of mtDNA deletions) to human RNA-Seq datasets and describe the methodological considerations for evaluating common deletions in bulk, single-cell, and spatial transcriptomics datasets. A robust evaluation of 1570 samples from 14 RNA-Seq studies showed: (i) the abundance of some common deletions detected in PCR-amplified mtDNA correlates with levels observed in RNA-Seq data; (ii) RNA-Seq library preparation method has a strong effect on deletion detection; (iii) deletions had a significant, positive correlation with age in brain and muscle; (iv) deletions were enriched in cortical grey matter, specifically in layers 3 and 5; and (v) brain regions with dopaminergic neurons (i.e., substantia nigra, ventral tegmental area, and caudate nucleus) had remarkable enrichment of common mtDNA deletions.

MtDNA deletions and aging.

Aging is the major risk factor in most of the leading causes of mortality worldwide, yet its fundamental causes mostly remain unclear. One of the clear hallmarks of aging is mitochondrial dysfunction. Mitochondria are best known for their roles in cellular energy generation, but they are also critical biosynthetic and signaling organelles. They also undergo multiple changes with organismal age, including increased genetic errors in their independent, circular genome. A key group of studies looking at mice with increased mtDNA mutations showed that premature aging phenotypes correlated with increased deletions but not point mutations. This generated an interest in mitochondrial deletions as a potential fundamental cause of aging. However, subsequent studies in different models have yielded diverse results. This review summarizes the research on mitochondrial deletions in various organisms to understand their possible roles in causing aging while identifying the key complications in quantifying deletions across all models.

Friend turned foe: selfish behavior of a spontaneously arising mitochondrial deletion in an experimentally evolved Caenorhabditis elegans population.

Selfish mitochondrial DNA (mtDNA) mutations are variants that can proliferate within cells and enjoy a replication or transmission bias without fitness benefits for the host. mtDNA deletions in Caenorhabditis elegans can reach high heteroplasmic frequencies despite significantly reducing fitness, illustrating how new mtDNA variants can give rise to genetic conflict between different levels of selection and between the nuclear and mitochondrial genomes. During a mutation accumulation experiment in C. elegans, a 1,034-bp deletion originated spontaneously and reached an 81.7% frequency within an experimental evolution line. This heteroplasmic mtDNA deletion, designated as meuDf1, eliminated portions of 2 protein-coding genes (coxIII and nd4) and tRNA-thr in entirety. mtDNA copy number in meuDf1 heteroplasmic individuals was 35% higher than in individuals with wild-type mitochondria. After backcrossing into a common genetic background, the meuDf1 mitotype was associated with reduction in several fitness traits and independent competition experiments found a 40% reduction in composite fitness. Experiments that relaxed individual selection by single individual bottlenecks demonstrated that the deletion-bearing mtDNA possessed a strong transmission bias, thereby qualifying it as a novel selfish mitotype.

The mitochondrial DNA common deletion as a potential biomarker of cancer-associated fibroblasts from skin basal and squamous cell carcinomas

Cancer-associated fibroblasts (CAFs) are components of the tumor microenvironment and represent appealing therapeutic targets for translational studies. Conventional protein-based biomarkers for CAFs have been reported to be limited in their specificity, rendering difficult the identification of CAFs from normal fibroblasts (NFs) in clinical samples and dampening the development of CAF-targeted therapies to treat cancer. In this study, we propose the mitochondrial RNA and the mitochondrial DNA (mtDNA) common deletion (CD) as novel indicators of CAF identity. We found that cancer-activation correlated with decreased levels of the mtDNA CD, a condition not due to altered mitochondria count or cellular redox state, but potentially linked to the generalized overexpression of mtDNA maintenance genes in CAFs. Decreased mtDNA CD content in CAFs was associated with moderate to strong overexpression of mtDNA-encoded genes and to slightly improved mitochondrial function. We identified similar patterns of upregulation of mtDNA-encoded genes in independent single-cell RNA seq data obtained from squamous cell carcinoma (SCC) patients. By using the identified nucleic acids-based indicators, identification of CAFs from NFs could be improved, leading to potential therapeutic benefits in advancing translational and clinical studies.

The clinical, myopathological, and genetic analysis of 155 Chinese mitochondrial ophthalmoplegia patients with mitochondrial DNA single large deletions.

Progressive external ophthalmoplegia (PEO) is a common subtype of mitochondrial encephalomyopathy. The study aimed to investigate the relationship between mitochondrial DNA (mtDNA) abnormalities, muscle pathology, and clinical manifestations in Chinese patients with single large-scale mtDNA deletion presenting with PEO. This is a retrospective single-center study. Patients with PEO who had a single large deletion in mitochondrial DNA were included in this study. The associations were analyzed between mtDNA deletion patterns, myopathological changes, and clinical characteristics. In total, 155 patients with mitochondrial PEO carrying single large-scale mtDNA mutations were enrolled, including 137 chronic progressive external ophthalmoplegia (CPEO) and 18 Kearns-Sayre syndrome (KSS) patients. The onset ages were 9.61 ± 4.12 in KSS and 20.15 ± 9.06 in CPEO. The mtDNA deletions ranged from 2225 bp to 9131 bp, with m.8470_13446del being the most common. The KSS group showed longer deletions than the CPEO group (p = 0.004). Additionally, a higher number of deleted genes encoding respiratory chain complex subunits (p = 0.001) and tRNA genes (p = 0.009) were also observed in the KSS group. A weak negative correlation between the mtDNA deletion size and ages of onset (p < 0.001, r = -0.369) was observed. The proportion of ragged red fibers, ragged blue fibers, and cytochrome c negative fibers did not correlate significantly with onset ages (p > 0.05). However, a higher percentage of abnormal muscle fibers corresponds to an increased prevalence of exercise intolerance, limb muscle weakness, dysphagia, and cerebellar ataxia. We reported a large Chinese cohort consisting of mitochondrial PEO patients with single large-scale mtDNA deletions. Our results demonstrated that the length and locations of mtDNA deletions may influence onset ages and clinical phenotypes. The severity of muscle pathology could not only indicate diagnosis but also may be associated with clinical manifestations beyond the extraocular muscles.

Mitochondrial Common Deletion Level in Adipose Tissue Is Not Associated with Obesity but Is Associated with a Structural Change in Triglycerides as Revealed by FTIR Spectroscopy

Objective: Several studies have shown that mitochondrial metabolism may be disrupted if the rate of the specific 4,977 bp deletion of mitochondrial DNA (mtDNA) reaches a threshold. This study aimed to investigate the possible associations between the mtDNA4977 deletion load and obesity-related metabolic abnormalities in the adipose tissue. Methods: The study included thirty obese individuals, who underwent bariatric surgery, and twelve control subjects. mtDNA4977 deletion, adenine nucleotides, and lactate levels, which show the bioenergetic status were evaluated in visceral adipose tissues. Fourier transform infrared (FTIR) spectroscopy was used to investigate the structural variations and composition of adipose tissues in the context of deletion load. Results: There were no differences between the two groups in terms of mtDNA4977 deletion, adenine nucleotides, and lactate levels. The FTIR spectra indicated a few obesity-related alterations in adipose tissues that were not related to the mtDNA deletion load. Also, statistical analysis showed a correlation between the deletion load and a band shift of 1,744 cm−1, which assigns C = O stretching of the carbonyl group of the ester group in triglycerides and other esterified fatty acids, although it is not associated with obesity. Conclusions: Our data suggest that the mtDNA4977 deletion in visceral adipose tissues of obese individuals do not have a significant impact on the bioenergetic status. However, the increased accumulation of deletion may be associated with a specific change in the ester bond, indicating structural differences in the lipids. These findings shed light on our understanding of the tissue-specific distribution of mtDNA deletions and obesity-related adipose tissue pathogeneses.

Targeted knockout of a conserved plant mitochondrial gene by genome editing

Fusion proteins derived from transcription activator-like effectors (TALEs) have emerged as genome editing tools for mitochondria. TALE nucleases (TALENs) have been applied to delete chimaeric reading frames and duplicated (redundant) genes but produced complex genomic rearrangements due to the absence of non-homologous end-joining. Here we report the targeted deletion of a conserved mitochondrial gene, nad9, encoding a subunit of respiratory complex I. By generating a large number of TALEN-mediated mitochondrial deletion lines, we isolated, in addition to mutants with rearranged genomes, homochondriomic mutants harbouring clean nad9 deletions. Characterization of the knockout plants revealed impaired complex I biogenesis, male sterility and defects in leaf and flower development. We show that these defects can be restored by expressing a functional Nad9 protein from the nuclear genome, thus creating a synthetic cytoplasmic male sterility system. Our data (1) demonstrate the feasibility of using genome editing to study mitochondrial gene functions by reverse genetics, (2) highlight the role of complex I in plant development and (3) provide proof-of-concept for the construction of synthetic cytoplasmic male sterility systems for hybrid breeding by genome editing.

SAT674 Lipodystrophy: A Hidden Culprit In Uncontrolled Diabetes

Abstract Disclosure: F. El Sayed: None. A. Banka: None. Introduction: Lipodystrophies are rare disorders with selective absence/accumulation of fat tissue. The “common” genetic forms include Congenital Generalized Lipodystrophy or Familial Partial Lipodystrophy (FPLD). Non-genetic factors like autoimmune disorders, chronic infections, or malnutrition can also contribute to a lipodystrophy phenotype. Clinical case: A 49-year-old female with diabetes mellitus, hypertriglyceridemia, gait disturbances, hypertension, hereditary hemorrhagic telangiectasias, asthma, presents with suspected lipodystrophy. She notes truncal obesity as a child, with progression as an adult and subsequent loss of volume from her arms and legs around age 30. Family history is significant for multiple family members with diabetes mellitus. On physical exam, the patient has a BMI of 22.86 kg/m2. She walks with a cane and has abdominal fat deposition, a dorsocervical fat pad, and reduced fat and muscle mass in her lower extremities. Her diabetes is poorly controlled with multiple complications including retinopathy, microalbuminuria, neuropathy, CVA, and CAD. Her medications include metformin, pioglitazone, detemir, aspart, and an insulin sliding scale for diabetes management, and rosuvastatin, fenofibrate, and omega-3-acid ethyl esters for hyperlipidemia. Her last A1C was 12.7%, and urine analysis was positive for glucosuria and ketonuria. Her lipid panel revealed high triglycerides (800s) and low HDL levels. Other pertinent labs include elevated GDF15 at 761 pg/mL. and lactate elevation at 3.4 mml/L. Given suspicion for hypercortisolism, she underwent a dexamethasone suppression test which was negative for Cushing’s disease. She subsequently underwent exome sequencing with mitochondrial deletion testing, which led to the diagnosis of FPLD. Discussion: FPLD results in loss of fat from the extremities starting around puberty, often leading to metabolic complications. Although both sexes are affected, women usually present with more severe disease. Currently, multiple genes are associated with FPLD, most commonly LMNA and PPARG which both follow autosomal dominant inheritance. Conclusion: Presently, there is no cure for lipodystrophy syndromes. However, in patients with diabetes and resistant metabolic syndrome features, a diagnosis of lipodystrophy should be considered. Further evaluation with genetic testing is warranted and has implications for family planning and medical management. Presentation: Saturday, June 17, 2023

Targeting MCL-1 triggers DNA damage and an anti-proliferative response independent from apoptosis induction

MCL-1 is a high-priority target due to its dominant role in the pathogenesis and chemoresistance of cancer, yet clinical trials of MCL-1 inhibitors are revealing toxic side effects. MCL-1 biology is complex, extending beyond apoptotic regulation and confounded by its multiple isoforms, its domains of unresolved structure and function, and challenges in distinguishing noncanonical activities from the apoptotic response. We find that, in the presence or absence of an intact mitochondrial apoptotic pathway, genetic deletion or pharmacologic targeting of MCL-1 induces DNA damage and retards cell proliferation. Indeed, the cancer cell susceptibility profile of MCL-1 inhibitors better matches that of anti-proliferative than pro-apoptotic drugs, expanding their potential therapeutic applications, including synergistic combinations, but heightening therapeutic window concerns. Proteomic profiling provides a resource for mechanistic dissection and reveals the minichromosome maintenance DNA helicase as an interacting nuclear protein complex that links MCL-1 to the regulation of DNA integrity and cell-cycle progression.

Understanding the impact of pediatric single large-scale mtDNA deletion syndromes on caregivers: Burdens and challenges.

Single large-scale mitochondrial deletion syndromes (SLSMDS) are ultra-rare, progressive multi-system diseases that make children largely dependent on their caregivers for both medical and non-medical needs. Yet, few studies have examined the burden felt among caregivers. As part of a larger research study, 42 caregivers of children with SLSMDS completed two surveys to assess caregiver burden. The Mitochondrial Care Network Patient Needs Survey (MCN-PNS) is a novel assessment that examines the logistical, time, and financial costs experienced by caregivers of children with SLSMDS. The Zarit Burden Interview (ZBI-22) is a validated assessment that examines caregivers' psychological health. Results demonstrate the unique burden experienced by caregivers of children with SLSMDS. One notable finding was the high psychological burden. Nearly 90% of caregivers experience psychological burden, with 20% of caregivers at risk for anxiety and depression. Caregivers were primarily concerned about what the future held for their child. Additional burdens included the time required to coordinate the child's healthcare visits and financial strains. Caregivers reported minimal delays in establishing care with a mitochondrial care specialist and felt confident in their understanding of their child's disease and treatment(s). Overall, there is a need for expanded logistical, financial, and psychological support from mitochondrial disease centers and advocacy groups for caregivers of children with SLSMDS.

Nanopore long-read next-generation sequencing for detection of mitochondrial DNA large-scale deletions.

Primary mitochondrial diseases are progressive genetic disorders affecting multiple organs and characterized by mitochondrial dysfunction. These disorders can be caused by mutations in nuclear genes coding proteins with mitochondrial localization or by genetic defects in the mitochondrial genome (mtDNA). The latter include point pathogenic variants and large-scale deletions/rearrangements. MtDNA molecules with the wild type or a variant sequence can exist together in a single cell, a condition known as mtDNA heteroplasmy. MtDNA single point mutations are typically detected by means of Next-Generation Sequencing (NGS) based on short reads which, however, are limited for the identification of structural mtDNA alterations. Recently, new NGS technologies based on long reads have been released, allowing to obtain sequences of several kilobases in length; this approach is suitable for detection of structural alterations affecting the mitochondrial genome. In the present work we illustrate the optimization of two sequencing protocols based on long-read Oxford Nanopore Technology to detect mtDNA structural alterations. This approach presents strong advantages in the analysis of mtDNA compared to both short-read NGS and traditional techniques, potentially becoming the method of choice for genetic studies on mtDNA.

Oxygen consumption rate to evaluate mitochondrial dysfunction and toxicity in cardiomyocytes.

The increase in the types and complexity of diseases has led to significant advances in diagnostic techniques and the availability of effective therapies. Recent studies have focused on the role of mitochondrial dysfunction in the pathogenesis of cardiovascular diseases (CVDs). Mitochondria are important organelles in cells that generate energy. Besides the production of adenosine triphosphate (ATP), the energy currency of cells, mitochondria are also involved in thermogenesis, control of intracellular calcium ions (Ca2+), apoptosis, regulation of reactive oxygen species (ROS), and inflammation. Mitochondrial dysfunction has been implicated in several diseases including cancer, diabetes, some genetic diseases, and neurogenerative and metabolic diseases. Furthermore, the cardiomyocytes of the heart are rich in mitochondria due to the large energy requirement for optimal cardiac function. One of the main causes of cardiac tissue injuries is believed to be mitochondrial dysfunction, which occurs via complicated pathways which have not yet been completely elucidated. There are various types of mitochondrial dysfunction including mitochondrial morphological change, unbalanced levels of substances to maintain mitochondria, mitochondrial damage by drugs, and mitochondrial deletion and synthesis errors. Most of mitochondrial dysfunctions are linked with symptoms and diseases, thus we focus on parts of mitochondrial dysfunction about fission and fusion in cardiomyocytes, and ways to understand the mechanism of cardiomyocyte damage by detecting oxygen consumption levels in the mitochondria.

Secondary structure of the human mitochondrial genome affects formation of deletions

BackgroundAging in postmitotic tissues is associated with clonal expansion of somatic mitochondrial deletions, the origin of which is not well understood. Such deletions are often flanked by direct nucleotide repeats, but this alone does not fully explain their distribution. Here, we hypothesized that the close proximity of direct repeats on single-stranded mitochondrial DNA (mtDNA) might play a role in the formation of deletions.ResultsBy analyzing human mtDNA deletions in the major arc of mtDNA, which is single-stranded during replication and is characterized by a high number of deletions, we found a non-uniform distribution with a “hot spot” where one deletion breakpoint occurred within the region of 6–9 kb and another within 13–16 kb of the mtDNA. This distribution was not explained by the presence of direct repeats, suggesting that other factors, such as the spatial proximity of these two regions, can be the cause. In silico analyses revealed that the single-stranded major arc may be organized as a large-scale hairpin-like loop with a center close to 11 kb and contacting regions between 6–9 kb and 13–16 kb, which would explain the high deletion activity in this contact zone. The direct repeats located within the contact zone, such as the well-known common repeat with a first arm at 8470–8482 bp (base pair) and a second arm at 13,447–13,459 bp, are three times more likely to cause deletions compared to direct repeats located outside of the contact zone. A comparison of age- and disease-associated deletions demonstrated that the contact zone plays a crucial role in explaining the age-associated deletions, emphasizing its importance in the rate of healthy aging.ConclusionsOverall, we provide topological insights into the mechanism of age-associated deletion formation in human mtDNA, which could be used to predict somatic deletion burden and maximum lifespan in different human haplogroups and mammalian species.

Primary mitochondrial disease as a rare cause of unclear breathlessness and distinctive performance degradation – a case report

BackgroundPrimary muscular disorders (metabolic myopathies, including mitochondrial disorders) are a rare cause of dyspnea. We report a case of dyspnea caused by a mitochondrial disorder with a pattern of clinical findings that can be classified in the known pathologies of mitochondrial deletion syndrome.Case presentationThe patient presented to us at 29 years of age, having had tachycardia, dyspnea, and functional impairment since childhood. She had been diagnosed with bronchial asthma and mild left ventricular hypertrophy and treated accordingly, but her symptoms had worsened. After more than 20 years of progressive physical and social limitations was a mitochondrial disease suspected in the exercise testing. We performed cardiopulmonary exercise testing (CPET) with right heart catheterization showed typical signs of mitochondrial myopathy. Genetic testing confirmed the presence of a ~ 13 kb deletion in mitochondrial DNA from the muscle. The patient was treated with dietary supplements for 1 year. In the course of time, the patient gave birth to a healthy child, which is developing normally.ConclusionCPET and lung function data over 5 years demonstrated stable disease. We conclude that CPET and lung function analysis should be used consistently to evaluate the cause of dyspnea and for long-term observation.

Structure of the T. brucei kinetoplastid RNA editing substrate-binding complex core component, RESC5.

Kinetoplastid protists such as Trypanosoma brucei undergo an unusual process of mitochondrial uridine (U) insertion and deletion editing termed kinetoplastid RNA editing (kRNA editing). This extensive form of editing, which is mediated by guide RNAs (gRNAs), can involve the insertion of hundreds of Us and deletion of tens of Us to form a functional mitochondrial mRNA transcript. kRNA editing is catalyzed by the 20 S editosome/RECC. However, gRNA directed, processive editing requires the RNA editing substrate binding complex (RESC), which is comprised of 6 core proteins, RESC1-RESC6. To date there are no structures of RESC proteins or complexes and because RESC proteins show no homology to proteins of known structure, their molecular architecture remains unknown. RESC5 is a key core component in forming the foundation of the RESC complex. To gain insight into the RESC5 protein we performed biochemical and structural studies. We show that RESC5 is monomeric and we report the T. brucei RESC5 crystal structure to 1.95 Å. RESC5 harbors a dimethylarginine dimethylaminohydrolase-like (DDAH) fold. DDAH enzymes hydrolyze methylated arginine residues produced during protein degradation. However, RESC5 is missing two key catalytic DDAH residues and does bind DDAH substrate or product. Implications of the fold for RESC5 function are discussed. This structure provides the first structural view of an RESC protein.

Adrenal Dysfunction in Mitochondrial Diseases.

Cortisol is central to several homeostatic mechanisms including the stress and immune response. Adrenal insufficiency and impaired cortisol production leads to severe, potentially fatal disorders. Several fundamental stages of steroidogenesis occur within the mitochondria. These dynamic organelles not only contribute ATP for steroidogenesis, but also detoxify harmful by-products generated during cortisol synthesis (reactive oxygen species). Mutations in nuclear or mitochondrial DNA that impair mitochondrial function lead to debilitating multi-system diseases. Recently, genetic variants that impair mitochondrial function have been identified in people with isolated cortisol insufficiency. This review aimed to clarify the association between mitochondrial diseases and adrenal insufficiency to produce cortisol. Mitochondrial diseases are rare and mitochondrial diseases that feature adrenal insufficiency are even rarer. We identified only 14 cases of adrenal insufficiency in people with confirmed mitochondrial diseases globally. In line with previous reviews, adrenal dysfunction was most prevalent in mitochondrial deletion syndromes (particularly Pearson syndrome and Kearns-Sayre syndrome) and with point mutations that compromised oxidative phosphorylation. Although adrenal insufficiency has been reported with mitochondrial diseases, the incidence reflects that expected in the general population. Thus, it is unlikely that mitochondrial mutations alone are responsible for an insufficiency to produce cortisol. More research is needed into the pathogenesis of adrenal disease in these individuals.