Coenzyme Q deficiency in muscle

Retinopathy and optic atrophy in a case of COQ2-related primary coenzyme Q10 deficiency

PURPOSE

To describe a case of primary coenzyme Q10 deficiency in a child manifesting as early-onset renal failure, retinal dystrophy, and optic atrophy leading to progressive vision loss.

METHODS

Clinical presentation and workup including visual fields, electroretinogram, and optical coherence tomography are presented. Genetic testing was performed.

RESULTS

An eight-year-old female with nephropathy requiring renal transplantation subsequently developed progressive cone-rod dystrophy and optic atrophy. The patient had negative results on a targeted next-generation sequencing retinal dystrophy panel but whole-exome sequencing revealed two variants in COQ2 (likely biallelic), consistent with a diagnosis of primary coenzyme Q10 deficiency.

CONCLUSIONS

Primary coenzyme Q10 deficiency is a rare disorder with variable systemic and ocular findings; there is also genetic heterogeneity. Genetic testing aids in the diagnosis of this condition, and variants in the COQ2 and PDSS1 genes appear to have the strongest association with ocular manifestations. Oral supplementation of coenzyme Q10 may slow progression of disease. This case highlights the utility of whole-exome sequencing in the diagnosis of a rare syndromic form of ocular disease and reports a novel phenotypic association for this condition.

Mitochondrial Properties in Skeletal Muscle Fiber

Mitochondria are the primary source of energy production and are implicated in a wide range of biological processes in most eukaryotic cells. Skeletal muscle heavily relies on mitochondria for energy supplements. In addition to being a powerhouse, mitochondria evoke many functions in skeletal muscle, including regulating calcium and reactive oxygen species levels. A healthy mitochondria population is necessary for the preservation of skeletal muscle homeostasis, while mitochondria dysregulation is linked to numerous myopathies. In this review, we summarize the recent studies on mitochondria function and quality control in skeletal muscle, focusing mainly on in vivo studies of rodents and human subjects. With an emphasis on the interplay between mitochondrial functions concerning the muscle fiber type-specific phenotypes, we also discuss the effect of aging and exercise on the remodeling of skeletal muscle and mitochondria properties.

Biosynthesis, Deficiency, and Supplementation of Coenzyme Q

Originally identified as a key component of the mitochondrial respiratory chain, Coenzyme Q (CoQ or CoQ₁₀ for human tissues) has recently been revealed to be essential for many different redox processes, not only in the mitochondria, but elsewhere within other cellular membrane types. Cells rely on endogenous CoQ biosynthesis, and defects in this still-not-completely understood pathway result in primary CoQ deficiencies, a group of conditions biochemically characterised by decreased tissue CoQ levels, which in turn are linked to functional defects. Secondary CoQ deficiencies may result from a wide variety of cellular dysfunctions not directly linked to primary synthesis. In this article, we review the current knowledge on CoQ biosynthesis, the defects leading to diminished CoQ₁₀ levels in human tissues and their associated clinical manifestations.

Novel Homozygous Variant inCOQ7in Siblings With Hereditary Motor Neuropathy

Background and Objectives

Coenzyme Q10(CoQ10) is an important electron carrier and antioxidant. The COQ7 enzyme catalyzes the hydroxylation of 5-demethoxyubiquinone-10 (DMQ10), the second-to-last step in the CoQ10biosynthesis pathway. We report a consanguineous family presenting with a hereditary motor neuropathy associated with a homozygous c.1A > G p.? variant ofCOQ7with abnormal CoQ10biosynthesis.

Methods

Affected family members underwent clinical assessments that included nerve conduction testing, histologic analysis, and MRI. Pathogenicity of theCOQ7variant was assessed in cultured fibroblasts and skeletal muscle using a combination of immunoblots, respirometry, and quinone analysis.

Results

Three affected siblings, ranging from 12 to 24 years of age, presented with a severe length-dependent motor neuropathy with marked symmetric distal weakness and atrophy with normal sensation. Muscle biopsy of the quadriceps revealed chronic denervation pattern. An MRI examination identified moderate to severe fat infiltration in distal muscles. Exome sequencing demonstrated the homozygousCOQ7c.1A > G p.? variant that is expected to bypass the first 38 amino acid residues at the n-terminus, initiating instead with methionine at position 39. This is predicted to cause the loss of the cleavable mitochondrial targeting sequence and 2 additional amino acids, thereby preventing the incorporation and subsequent folding of COQ7 into the inner mitochondrial membrane. Pathogenicity of theCOQ7variant was demonstrated by diminished COQ7 and CoQ10levels in muscle and fibroblast samples of affected siblings but not in the father, unaffected sibling, or unrelated controls. In addition, fibroblasts from affected siblings had substantial accumulation of DMQ10, and maximal mitochondrial respiration was impaired in both fibroblasts and muscle.

Discussion

This report describes a new neurologic phenotype ofCOQ7-related primary CoQ10deficiency. Novel aspects of the phenotype presented by this family include pure distal motor neuropathy involvement, as well as the lack of upper motor neuron features, cognitive delay, or sensory involvement in comparison with cases ofCOQ7-related CoQ10deficiency previously reported in the literature.

Combined Supplementation of Coenzyme Q10 and Other Nutrients in Specific Medical Conditions

Coenzyme Q₁₀ (CoQ₁₀) is a compound with a crucial role in mitochondrial bioenergetics and membrane antioxidant protection. Despite the ubiquitous endogenous biosynthesis, specific medical conditions are associated with low circulating CoQ₁₀ levels. However, previous studies of oral CoQ₁₀ supplementation yielded inconsistent outcomes. In this article, we reviewed previous CoQ₁₀ trials, either single or in combination with other nutrients, and stratified the study participants according to their metabolic statuses and medical conditions. The CoQ₁₀ supplementation trials in elders reported many favorable outcomes. However, the single intervention was less promising when the host metabolic statuses were worsening with the likelihood of multiple nutrient insufficiencies, as in patients with an established diagnosis of metabolic or immune-related disorders. On the contrary, the mixed CoQ₁₀ supplementation with other interacting nutrients created more promising impacts in hosts with compromised nutrient reserves. Furthermore, the results of either single or combined intervention will be less promising in far-advanced conditions with established damage, such as neurodegenerative disorders or cancers. With the limited high-level evidence studies on each host metabolic category, we could only conclude that the considerations of whether to take supplementation varied by the individuals' metabolic status and their nutrient reserves. Further studies are warranted.

The efficacy of coenzyme Q10 treatment in alleviating the symptoms of primary coenzyme Q10 deficiency: A systematic review

Coenzyme Q₁₀ (CoQ₁₀) is necessary for mitochondrial electron transport. Mutations in CoQ₁₀ biosynthetic genes cause primary CoQ₁₀ deficiency (PCoQD) and manifest as mitochondrial disorders. It is often stated that PCoQD patients can be treated by oral CoQ₁₀ supplementation. To test this, we compiled all studies describing PCoQD patients up to May 2022. We excluded studies with no data on CoQ₁₀ treatment, or with insufficient description of effectiveness. Out of 303 PCoQD patients identified, we retained 89 cases, of which 24 reported improvements after CoQ₁₀ treatment (27.0%). In five cases, the patient's condition was reported to deteriorate after halting of CoQ₁₀ treatment. 12 cases reported improvement in the severity of ataxia and 5 cases in the severity of proteinuria. Only a subjective description of improvement was reported for 4 patients described as responding. All reported responses were partial improvements of only some symptoms. For PCoQD patients, CoQ₁₀ supplementation is replacement therapy. Yet, there is only very weak evidence for the efficacy of the treatment. Our findings, thus, suggest a need for caution when seeking to justify the widespread use of CoQ₁₀ for the treatment of any disease or as dietary supplement.

Technical Aspects of Coenzyme Q10 Analysis: Validation of a New HPLC-ED Method

The biochemical measurement of the CoQ status in different tissues can be performed using HPLC with electrochemical detection (ED). Because the production of the electrochemical cells used with the Coulochem series detectors was discontinued, we aimed to standardize a new HPLC-ED method with new equipment. We report all technical aspects, troubleshooting and its performance in different biological samples, including plasma, skeletal muscle homogenates, urine and cultured skin fibroblasts. Analytical variables (intra- and inter-assay precision, linearity, analytical measurement range, limit of quantification, limit of detection and accuracy) were validated in calibrators and plasma samples and displayed adequate results. The comparison of the results of a new ERNDIM external quality control (EQC) scheme for the plasma CoQ determination between HPLC-ED (Lab 1) and LC-MS/MS (Lab 2) methods shows that the results of the latter were slightly higher in most cases, although a good consistency was generally observed. In conclusion, the new method reported here showed a good analytical performance. The global quality of the EQC scheme results among different participants can be improved with the contribution of more laboratories.

Levels of Plasma Coenzyme Q10 Are Associated with Physical Capacity and Cardiovascular Risk in the Elderly

Coenzyme Q₁₀ (CoQ₁₀) is an essential factor for mitochondrial activity and antioxidant protection of cells, tissues and plasma lipoproteins. Its deficiency has been associated with aging progression in animals and humans. To determine if CoQ₁₀ levels in plasma can be associated with frailty in elderly people (aged > 65), we studied the relationship of CoQ₁₀ levels in blood with other parameters in plasma and with the physical activity and capacity in aged people. Our results indicate that high CoQ₁₀ levels are directly associated with lower cardiovascular risk measured by the quotient total cholesterol/HDL cholesterol. Furthermore, high CoQ₁₀ levels were found in people showing higher physical activity, stronger muscle capacity. CoQ₁₀ also showed a strong inverse relationship with sedentarism and the up and go test, which is considered to be a frailty index. Interestingly, we found gender differences, indicating stronger correlations in women than in men. The importance of the maintenance of CoQ₁₀ levels in elderly people to avoid sarcopenia and frailty in elderly people is discussed.

Coenzyme Q10 deficiency in patients with hereditary hemochromatosis

AIM

Hereditary hemochromatosis (HH) is a group of inherited disorders that causes a slow and progressive iron deposition in diverse organs, particularly in the liver. Iron overload induces oxidative stress and tissue damage. Coenzyme Q10 (CoQ10) is a cofactor in the electron-transport chain of the mitochondria, but it is also a potent endogenous antioxidant. CoQ10 interest has recently grown since various studies show that CoQ10 supplementation may provide protective and safe benefits in mitochondrial diseases and oxidative stress disorders. In the present study we sought to determine CoQ10 plasma level in patients recently diagnosed with HH and to correlate it with biochemical, genetic, and histological features of the disease.

METHODS

Plasma levels of CoQ10, iron, ferritin, transferrin and vitamins (A, C and E), liver tests (transaminases, alkaline phosphatase and bilirubin), and histology, as well as three HFE gene mutations (H63D, S654C and C282Y), were assessed in thirty-eight patients (32 males, 6 females) newly diagnosed with HH without treatment and in twenty-five age-matched normolipidemic healthy subjects with no HFE gene mutations (22 males, 3 females) and without clinical or biochemical signs of iron overload or liver diseases.

RESULTS

Patients with HH showed a significant decrease in CoQ10 levels respect to control subjects (0.31 ± 0.03 µM vs 0.70 ± 0.06 µM, p < 0.001, respectively) independently of the genetic mutation, cirrhosis, transferrin saturation, ferritin level or markers of hepatic dysfunction. Although a decreasing trend in CoQ10 levels was observed in patients with elevated iron levels, no correlation was found between both parameters in patients with HH. Vitamins C and A levels showed no changes in HH patients. Vitamin E was significantly decreased in HH patients (21.1 ± 1.3 µM vs 29.9 ± 2.5 µM, p < 0.001, respectively), but no correlation was observed with CoQ10 levels.

CONCLUSION

The decrease in CoQ10 levels found in HH patients suggests that CoQ10 supplementation could be a safe intervention strategy complementary to the traditional therapy to ameliorate oxidative stress and further tissue damage induced by iron overload.

Biomarkers and Mechanisms of Oxidative Stress-Last 20 Years of Research with an Emphasis on Kidney Damage and Renal Transplantation

Oxidative stress is an imbalance between pro- and antioxidants that adversely influences the organism in various mechanisms and on many levels. Oxidative damage occurring concomitantly in many cellular structures may cause a deterioration of function, including apoptosis and necrosis. The damage leaves a molecular “footprint”, which can be detected by specific methodology, using certain oxidative stress biomarkers. There is an intimate relationship between oxidative stress, inflammation, and functional impairment, resulting in various diseases affecting the entire human body. In the current narrative review, we strengthen the connection between oxidative stress mechanisms and their active compounds, emphasizing kidney damage and renal transplantation. An analysis of reactive oxygen species (ROS), antioxidants, products of peroxidation, and finally signaling pathways gives a lot of promising data that potentially will modify cell responses on many levels, including gene expression. Oxidative damage, stress, and ROS are still intensively exploited research subjects. We discuss compounds mentioned earlier as biomarkers of oxidative stress and present their role documented during the last 20 years of research. The following keywords and MeSH terms were used in the search: oxidative stress, kidney, transplantation, ischemia-reperfusion injury, IRI, biomarkers, peroxidation, and treatment.

Primary Mitochondrial Disorders of the Pediatric Central Nervous System: Neuroimaging Findings

Primary mitochondrial disorders (PMDs) constitute the most common cause of inborn errors of metabolism in children, and they frequently affect the central nervous system. Neuroimaging findings of PMDs are variable, ranging from unremarkable and nonspecific to florid and highly suggestive. An overview of PMDs, including a synopsis of the basic genetic concepts, main clinical symptoms, and neuropathologic features, is presented. In addition, eight of the most common PMDs that have a characteristic imaging phenotype in children are reviewed in detail. Online supplemental material is available for this article. ^©RSNA, 2020.

Secondary CoQ10 deficiency, bioenergetics unbalance in disease and aging

Coenzyme Q₁₀ (CoQ₁₀ ) deficiency is a rare disease characterized by a decreased accumulation of CoQ₁₀ in cell membranes. Considering that CoQ₁₀ synthesis and most of its functions are carried out in mitochondria, CoQ₁₀ deficiency cases are usually considered a mitochondrial disease. A relevant feature of CoQ₁₀ deficiency is that it is the only mitochondrial disease with a successful therapy available, the CoQ₁₀ supplementation. Defects in components of the synthesis machinery caused by mutations in COQ genes generate the primary deficiency of CoQ₁₀ . Mutations in genes that are not directly related to the synthesis machinery cause secondary deficiency. Cases of CoQ₁₀ deficiency without genetic origin are also considered a secondary deficiency. Both types of deficiency can lead to similar clinical manifestations, but the knowledge about primary deficiency is deeper than secondary. However, secondary deficiency cases may be underestimated since many of their clinical manifestations are shared with other pathologies. This review shows the current state of secondary CoQ₁₀ deficiency, which could be even more relevant than primary deficiency for clinical activity. The analysis covers the fundamental features of CoQ₁₀ deficiency, which are necessary to understand the biological and clinical differences between primary and secondary CoQ₁₀ deficiencies. Further, a more in-depth analysis of CoQ₁₀ secondary deficiency was undertaken to consider its origins, introduce a new way of classification, and include aging as a form of secondary deficiency.

Coenzyme Q10 supplementation - In ageing and disease

Coenzyme Q₁₀ (CoQ₁₀) is an essential component of the mitochondrial electron transport chain. It is also an antioxidant in cellular membranes and lipoproteins. All cells produce CoQ₁₀ by a specialized cytoplasmatic-mitochondrial pathway. CoQ₁₀ deficiency can result from genetic failure or ageing. Some drugs including statins, widely used by inter alia elderly, may inhibit endogenous CoQ₁₀ synthesis. There are also chronic diseases with lower levels of CoQ₁₀ in tissues and organs. High doses of CoQ₁₀ may increase both circulating and intracellular levels, but there are conflicting results regarding bioavailability. Here, we review the current knowledge of CoQ₁₀ biosynthesis and primary and acquired CoQ₁₀ deficiency, and results from clinical trials based on CoQ₁₀ supplementation. There are indications that supplementation positively affects mitochondrial deficiency syndrome and some of the symptoms of ageing. Cardiovascular disease and inflammation appear to be alleviated by the antioxidant effect of CoQ₁₀. There is a need for further studies and well-designed clinical trials, with CoQ₁₀ in a formulation of proven bioavailability, involving a greater number of participants undergoing longer treatments in order to assess the benefits of CoQ₁₀ treatment in neurodegenerative disorders, as well as in metabolic syndrome and its complications.

Primary Coenzyme Q deficiencies: A literature review and online platform of clinical features to uncover genotype-phenotype correlations

Primary Coenzyme Q (CoQ) deficiencies are clinically heterogeneous conditions and lack clear genotype-phenotype correlations, complicating diagnosis and prognostic assessment. Here we present a compilation of all the symptoms and patients with primary CoQ deficiency described in the literature so far and analyse the most common clinical manifestations associated with pathogenic variants identified in the different COQ genes. In addition, we identified new associations between the age of onset of symptoms and different pathogenic variants, which could help to a better diagnosis and guided treatment. To make these results useable for clinicians, we created an online platform (https://coenzymeQbiology.github.io/clinic-CoQ-deficiency) about clinical manifestations of primary CoQ deficiency that will be periodically updated to incorporate new information published in the literature. Since CoQ primary deficiency is a rare disease, the available data are still limited, but as new patients are added over time, this tool could become a key resource for a more efficient diagnosis of this pathology.

The multiple roles of coenzyme Q in cellular homeostasis and their relevance for the pathogenesis of coenzyme Q deficiency

Coenzyme Q (CoQ) is a redox active lipid that plays a central role in cellular homeostasis. It was discovered more than 60 years ago because of its role as electron transporter in the mitochondrial respiratory chain. Since then it has become evident that CoQ has many other functions, not directly related to bioenergetics. It is a cofactor of several mitochondrial dehydrogenases involved in the metabolism of lipids, amino acids, and nucleotides, and in sulfide detoxification. It is a powerful antioxidant and it is involved in the control of programmed cell death by modulating both apoptosis and ferroptosis. CoQ deficiency is a clinically and genetically heterogeneous group of disorders characterized by the impairment of CoQ biosynthesis. CoQ deficient patients display defects in cellular bioenergetics, but also in the other pathways in which CoQ is involved. In this review we will focus on the functions of CoQ not directly related to the respiratory chain, and on how their impairment is relevant for the pathophysiology of CoQ deficiency. A better understanding of the complex set of events triggered by CoQ deficiency will allow to design novel approaches for the treatment of this condition.

Muscle biopsy essential diagnostic advice for pathologists

Background

Muscle biopsies are important diagnostic procedures in neuromuscular practice. Recent advances in genetic analysis have profoundly modified Myopathology diagnosis.

Main body

The main goals of this review are: (1) to describe muscle biopsy techniques for non specialists; (2) to provide practical information for the team involved in the diagnosis of muscle diseases; (3) to report fundamental rules for muscle biopsy site choice and adequacy; (4) to highlight the importance of liquid nitrogen in diagnostic workup. Routine techniques include: (1) histochemical stains and reactions; (2) immunohistochemistry and immunofluorescence; (3) electron microscopy; (4) mitochondrial respiratory chain enzymatic studies; and (5) molecular studies. The diagnosis of muscle disease is a challenge, as it should integrate data from different techniques.

Conclusion

Formalin-fixed paraffin embedded muscle samples alone almost always lead to inconclusive or unspecific results. Liquid nitrogen frozen muscle sections are imperative for neuromuscular diagnosis. Muscle biopsy interpretation is possible in the context of detailed clinical, neurophysiological, and serum muscle enzymes data. Muscle imaging studies are strongly recommended in the diagnostic workup. Muscle biopsy is useful for the differential diagnosis of immune mediated myopathies, muscular dystrophies, congenital myopathies, and mitochondrial myopathies. Muscle biopsy may confirm the pathogenicity of new gene variants, guide cost-effective molecular studies, and provide phenotypic diagnosis in doubtful cases. For some patients with mitochondrial myopathies, a definite molecular diagnosis may be achieved only if performed in DNA extracted from muscle tissue due to organ specific mutation load.

High coenzyme Q10 plasma levels improve stress and damage markers in professional soccer players during competition

Ubiquinol, the reduced form of Coenzyme Q₁₀ (CoQ₁₀), is a key factor in bioenergetics and antioxidant protection. During competition, professional soccer players suffer from considerable physical stress causing high risk of muscle damage. For athletes, supplementation with several antioxidants, including CoQ₁₀, is widely recommended to avoid oxidative stress and muscle damage. We performed an observational study of plasma parameters associated with CoQ₁₀ levels in professional soccer players of the Spanish First League team Athletic Club de Bilbao over two consecutive seasons (n = 24-25) in order determine their relationship with damage, stress and performance during competition. We analyzed three different moments of the competition: preterm, initial phase and mid phase. Metabolites and factors related with stress (testosterone/cortisol) and muscle damage (creatine kinase) were determined. Physical activity during matches was analyzed over the 2015/16 season in those players participating in complete matches. In the mid phase of competition, CoQ₁₀ levels were higher in 2015/16 (906.8 ± 307.9 vs. 584.3 ± 196.3 pmol/mL, p = 0.0006) High levels of CoQ₁₀ in the hardest phase of competition were associated with a reduction in the levels of the muscle-damage marker creatine kinase (Pearsons' correlation coefficient (r) = - 0.460, p = 0.00168) and a trend for the stress marker cortisol (r = -0.252, p = 0.150). Plasma ubiquinol was also associated with better kidney function (r = -0.287, p = 0.0443 for uric acid). Furthermore, high CoQ₁₀ levels were associated with higher muscle performance during matches. Our results suggest that high levels of plasma CoQ₁₀ can prevent muscle damage, improve kidney function and are associated with higher performance in professional soccer players during competition.

Primary Coenzyme Q deficiency Due to Novel ADCK3 Variants, Studies in Fibroblasts and Review of Literature

Primary deficiency of coenzyme Q10 (CoQ10 ubiquinone), is classified as a mitochondrial respiratory chain disorder with phenotypic variability. The clinical manifestation may involve one or multiple tissue with variable severity and presentation may range from infancy to late onset. ADCK3 gene mutations are responsible for the most frequent form of hereditary CoQ10 deficiency (Q10 deficiency-4 OMIM #612016) which is mainly associated with autosomal recessive spinocerebellar ataxia (ARCA2, SCAR9). Here we provide the clinical, biochemical and genetic investigation for unrelated three nuclear families presenting an autosomal form of Spino-Cerebellar Ataxia due to novel mutations in the ADCK3 gene. Using next generation sequence technology we identified a homozygous Gln343Ter mutation in one family with severe, early onset of the disease and compound heterozygous mutations of Gln343Ter and Ser608Phe in two other families with variable manifestations. Biochemical investigation in fibroblasts showed decreased activity of the CoQ dependent mitochondrial respiratory chain enzyme succinate cytochrome c reductase (complex II + III). Exogenous CoQ slightly improved enzymatic activity, ATP production and decreased oxygen free radicals in some of the patient's cells. Our results are presented in comparison to previously reported mutations and expanding the clinical, molecular and biochemical spectrum of ADCK3 related CoQ10 deficiencies.

Sarcopenia: Aging-Related Loss of Muscle Mass and Function

Sarcopenia is a loss of muscle mass and function in the elderly that reduces mobility, diminishes quality of life, and can lead to fall-related injuries, which require costly hospitalization and extended rehabilitation. This review focuses on the aging-related structural changes and mechanisms at cellular and subcellular levels underlying changes in the individual motor unit: specifically, the perikaryon of the α-motoneuron, its neuromuscular junction(s), and the muscle fibers that it innervates. Loss of muscle mass with aging, which is largely due to the progressive loss of motoneurons, is associated with reduced muscle fiber number and size. Muscle function progressively declines because motoneuron loss is not adequately compensated by reinnervation of muscle fibers by the remaining motoneurons. At the intracellular level, key factors are qualitative changes in posttranslational modifications of muscle proteins and the loss of coordinated control between contractile, mitochondrial, and sarcoplasmic reticulum protein expression. Quantitative and qualitative changes in skeletal muscle during the process of aging also have been implicated in the pathogenesis of acquired and hereditary neuromuscular disorders. In experimental models, specific intervention strategies have shown encouraging results on limiting deterioration of motor unit structure and function under conditions of impaired innervation. Translated to the clinic, if these or similar interventions, by saving muscle and improving mobility, could help alleviate sarcopenia in the elderly, there would be both great humanitarian benefits and large cost savings for health care systems.

The dilemma of diagnosing coenzyme Q10 deficiency in muscle

BACKGROUND

Coenzyme Q₁₀ (CoQ₁₀) is an important component of the mitochondrial respiratory chain (RC) and is critical for energy production. Although the prevalence of CoQ₁₀ deficiency is still unknown, the general consensus is that the condition is under-diagnosed. The aim of this study was to retrospectively investigate CoQ₁₀ deficiency in frozen muscle specimens in a cohort of ethnically diverse patients who received muscle biopsies for the investigation of a possible RC deficiency (RCD).

METHODS

Muscle samples were homogenized whereby 600 ×g supernatants were used to analyze RC enzyme activities, followed by quantification of CoQ₁₀ by stable isotope dilution liquid chromatography tandem mass spectrometry. The experimental group consisted of 156 patients of which 76 had enzymatically confirmed RCDs. To further assist in the diagnosis of CoQ₁₀ deficiency in this cohort, we included sequencing of 18 selected nuclear genes involved with CoQ₁₀ biogenesis in 26 patients with low CoQ₁₀ concentration in muscle samples.

RESULTS

Central 95% reference intervals (RI) were established for CoQ₁₀ normalized to citrate synthase (CS) or protein. Nine patients were considered CoQ₁₀ deficient when expressed against CS, while 12 were considered deficient when expressed against protein. In two of these patients the molecular genetic cause could be confirmed, of which one would not have been identified as CoQ₁₀ deficient if expressed only against protein content.

CONCLUSION

In this retrospective study, we report a central 95% reference interval for 600 ×g muscle supernatants prepared from frozen samples. The study reiterates the importance of including CoQ₁₀ quantification as part of a diagnostic approach to study mitochondrial disease as it may complement respiratory chain enzyme assays with the possible identification of patients that may benefit from CoQ₁₀ supplementation. However, the anomaly that only a few patients were identified as CoQ₁₀ deficient against both markers (CS and protein), while the majority of patients where only CoQ₁₀ deficient against one of the markers (and not the other), remains problematic. We therefore conclude from our data that, to prevent possibly not diagnosing a potential CoQ₁₀ deficiency, the expression of CoQ₁₀ levels in muscle on both CS as well as protein content should be considered.

A family segregating lethal neonatal coenzyme Q10 deficiency caused by mutations in COQ9

Primary CoQ₁₀ deficiency is a clinically and genetically heterogeneous, autosomal recessive disorder resulting from mutations in genes involved in the synthesis of coenzyme Q₁₀ (CoQ₁₀). To date, mutations in nine proteins required for the biosynthesis of CoQ₁₀ cause CoQ₁₀ deficiency with varying clinical presentations. In 2009 the first patient with mutations in COQ9 was reported in an infant with a neonatal-onset, primary CoQ₁₀ deficiency with multi-system disease. Here we describe four siblings with a previously undiagnosed lethal disorder characterized by oligohydramnios and intrauterine growth restriction, variable cardiomyopathy, anemia, and renal anomalies. The first and third pregnancy resulted in live born babies with abnormal tone who developed severe, treatment unresponsive lactic acidosis after birth and died hours later. Autopsy on one of the siblings demonstrated brain changes suggestive of the subacute necrotizing encephalopathy of Leigh disease. Whole-exome sequencing (WES) revealed the siblings shared compound heterozygous mutations in the COQ9 gene with both variants predicted to affect splicing. RT-PCR on RNA from patient fibroblasts revealed that the c.521 + 2 T > C variant resulted in splicing out of exons 4-5 and the c.711 + 3G > C variant spliced out exon 6, resulting in undetectable levels of COQ9 protein in patient fibroblasts. The biochemical profile of patient fibroblasts demonstrated a drastic reduction in CoQ₁₀ levels. An additional peak on the chromatogram may represent accumulation of demethoxy coenzyme Q (DMQ), which was shown previously to accumulate as a result of a defect in COQ9. This family expands our understanding of this rare metabolic disease and highlights the prenatal onset, clinical variability, severity, and biochemical profile associated with COQ9-related CoQ₁₀ deficiencies.

Diffuse mesangial sclerosis in a PDSS2 mutation-induced coenzyme Q10 deficiency

BACKGROUND

A 7-month-old male infant was admitted because he was suffering from nephrotic syndrome, along with encephalomyopathy, hypertrophic cardiomyopathy, clinically suspected deafness and retinitis pigmentosa, and an elevated serum lactate level.

METHODS

Coenzyme Q₁₀ supplementation was started because of the clinical suspicion of primary CoQ₁₀ deficiency. Despite intensive efforts, he passed away 4 weeks after admission.

RESULTS

The results of genetic tests, available postmortem, explored two hitherto undescribed mutations in the PDSS2 gene. Both were located within the polyprenyl synthetase domain. Clinical exome sequencing revealed a heterozygous missense mutation in exon 3, and our in-house joint-analysis algorithm detected a heterozygous large 2923-bp deletion that affected the 5 prime end of exon 8. Other causative defects in the CoQ₁₀ and infantile nephrosis-related genes examined were not found. A postmortem histological, immunohistochemical, and electron microscopic evaluation of the glomeruli revealed collapsing-sclerosing lesions consistent with diffuse mesangial sclerosis. The extrarenal alterations included hypertrophic cardiomyopathy and diffuse alveolar damage. A histological evaluation of the central nervous system and skeletal muscles did not demonstrate any obvious abnormality.

CONCLUSIONS

Until now, the clinical features and the mutational status of 6 patients with a PDSS2 gene defect have been reported in the English literature. Here, we describe for the first time detailed kidney morphology features in a patient with nephrotic syndrome carrying mutations in the PDSS2 gene.

Coenzyme Q10 Supplementation in Aging and Disease

Coenzyme Q (CoQ) is an essential component of the mitochondrial electron transport chain and an antioxidant in plasma membranes and lipoproteins. It is endogenously produced in all cells by a highly regulated pathway that involves a mitochondrial multiprotein complex. Defects in either the structural and/or regulatory components of CoQ complex or in non-CoQ biosynthetic mitochondrial proteins can result in a decrease in CoQ concentration and/or an increase in oxidative stress. Besides CoQ₁₀ deficiency syndrome and aging, there are chronic diseases in which lower levels of CoQ₁₀ are detected in tissues and organs providing the hypothesis that CoQ₁₀ supplementation could alleviate aging symptoms and/or retard the onset of these diseases. Here, we review the current knowledge of CoQ₁₀ biosynthesis and primary CoQ₁₀ deficiency syndrome, and have collected published results from clinical trials based on CoQ₁₀ supplementation. There is evidence that supplementation positively affects mitochondrial deficiency syndrome and the symptoms of aging based mainly on improvements in bioenergetics. Cardiovascular disease and inflammation are alleviated by the antioxidant effect of CoQ₁₀. There is a need for further studies and clinical trials involving a greater number of participants undergoing longer treatments in order to assess the benefits of CoQ₁₀ treatment in metabolic syndrome and diabetes, neurodegenerative disorders, kidney diseases, and human fertility.

A novel inborn error of the coenzyme Q10 biosynthesis pathway: cerebellar ataxia and static encephalomyopathy due to COQ5 C-methyltransferase deficiency

Primary coenzyme Q10 (CoQ10 ; MIM# 607426) deficiencies are an emerging group of inherited mitochondrial disorders with heterogonous clinical phenotypes. Over a dozen genes are involved in the biosynthesis of CoQ10 , and mutations in several of these are associated with human disease. However, mutations in COQ5 (MIM# 616359), catalyzing the only C-methylation in the CoQ10 synthetic pathway, have not been implicated in human disease. Here, we report three female siblings of Iraqi-Jewish descent, who had varying degrees of cerebellar ataxia, encephalopathy, generalized tonic-clonic seizures, and cognitive disability. Whole-exome and subsequent whole-genome sequencing identified biallelic duplications in the COQ5 gene, leading to reduced levels of CoQ10 in peripheral white blood cells of all affected individuals and reduced CoQ10 levels in the only muscle tissue available from one affected proband. CoQ10 supplementation led to clinical improvement and increased the concentrations of CoQ10 in blood. This is the first report of primary CoQ10 deficiency caused by loss of function of COQ5, with delineation of the clinical, laboratory, histological, and molecular features, and insights regarding targeted treatment with CoQ10 supplementation.

Skeletal muscle mitochondrial bioenergetics and associations with myostatin genotypes in the Thoroughbred horse

Variation in the myostatin (MSTN) gene has been reported to be associated with race distance, body composition and skeletal muscle fibre composition in the horse. The aim of the present study was to test the hypothesis that MSTN variation influences mitochondrial phenotypes in equine skeletal muscle. Mitochondrial abundance and skeletal muscle fibre types were measured in whole muscle biopsies from the gluteus medius of n = 82 untrained (21 ± 3 months) Thoroughbred horses. Skeletal muscle fibre type proportions were significantly (p < 0.01) different among the three MSTN genotypes and mitochondrial content was significantly (p < 0.01) lower in the combined presence of the C-allele of SNP g.66493737C>T (C) and the SINE insertion 227 bp polymorphism (I). Evaluation of mitochondrial complex activities indicated higher combined mitochondrial complex I+III and II+III activities in the presence of the C-allele / I allele (p ≤ 0.05). The restoration of complex I+III and complex II+III activities following addition of exogenous coenzyme Q1 (ubiquinone1) (CoQ1) in vitro in the TT/NN (homozygous T allele/homozygous no insertion) cohort indicated decreased coenzyme Q in these animals. In addition, decreased gene expression in two coenzyme Q (CoQ) biosynthesis pathway genes (COQ4, p ≤ 0.05; ADCK3, p ≤ 0.01) in the TT/NN horses was observed. This study has identified several mitochondrial phenotypes associated with MSTN genotype in untrained Thoroughbred horses and in addition, our findings suggest that nutritional supplementation with CoQ may aid to restore coenzyme Q activity in TT/NN horses.

Steroid-resistant nephrotic syndrome caused by co-inheritance of mutations at NPHS1 and ADCK4 genes in two Chinese siblings

Hereditary nephrotic syndrome often presents with steroid-resistance and onset within the first year of life. Mutations in genes highly expressed in podocytes have been found in two thirds of these patients, especially NPHS1 and NPHS2 among at least 29 genetic causes that have been discovered. We reported two siblings with steroid-resistant nephrotic syndrome caused by co-inheritance of mutations at NPHS1 (c.1339G>A, p.E447K) and ACDK4 (c.748G>C, p.D250H) genes. The siblings presented with steroid-resistant nephrotic syndrome and pathological lesions of focal segmental glomerulosclerosis (FSGS), while the elder sister also developed hypertension, renal failure and cardiac dysfunction.

[Regulation of the expression of coenzyme Q-synthesis complex during ageing]

INTRODUCTION

Coenzyme Q is an essential component in the activity of the mitochondrial electron transport chain. Its synthesis involves, at least, a complex of ten different proteins. In this study, an attempt is made to determine the evolution of the expression of the genes involved in coenzyme Q synthesis during mouse ageing.

MATERIAL AND METHODS

The messenger RNA (mRNA) of different organs, such as brain, liver, kidney and skeletal muscle from young (8 months), mature (18 months), and old (24 months) mice was extracted by using Trizol and was then analysed by real time PCR (qPCR) using specific primers for all the known components of the coenzyme Q-synthesis complex (COQ genes).

RESULTS

Liver showed the highest age-dependent changes in mRNA levels of the different components of Q-synthesis complex, affecting the extent of the variation as well as the significance of the change. In most of the cases, mRNA levels of the different components were higher in mature animals compared to young and old animals. When mRNAs of young and old animals were compared, only minor reductions of mRNA levels were found. Kidney showed a pattern similar to that found in liver as regards the changes in expression, although with lower increases in mature animals than those observed in the liver. Brain and skeletal muscle showed low variations, with muscle being the tissue with less changes, although a pattern similar to that found in liver and kidney was found, with slight increases in mature animals.

DISCUSSION

The results of this study indicate that ageing is an important factor affecting COQ gene expression, but its effect depends on the organ, and that mature animals show higher levels of mRNA than young and old animals. Taken into consideration the importance of coenzyme Q in cell metabolism and ageing, a more detailed study is needed to understand the gene regulation of the coenzyme Q-synthesis mechanisms during ageing.

Genetics of Mitochondrial Disease

Mitochondria are intracellular organelles responsible for adenosine triphosphate production. The strict control of intracellular energy needs require proper mitochondrial functioning. The mitochondria are under dual controls of mitochondrial DNA (mtDNA) and nuclear DNA (nDNA). Mitochondrial dysfunction can arise from changes in either mtDNA or nDNA genes regulating function. There are an estimated ∼1500 proteins in the mitoproteome, whereas the mtDNA genome has 37 proteins. There are, to date, ∼275 genes shown to give rise to disease. The unique physiology of mitochondrial functioning contributes to diverse gene expression. The onset and range of phenotypic expression of disease is diverse, with onset from neonatal to seventh decade of life. The range of dysfunction is heterogeneous, ranging from single organ to multisystem involvement. The complexity of disease expression has severely limited gene discovery. Combining phenotypes with improvements in gene sequencing strategies are improving the diagnosis process. This chapter focuses on the interplay of the unique physiology and gene discovery in the current knowledge of genetically derived mitochondrial disease.

Genetic Rescue of Mitochondrial and Skeletal Muscle Impairment in an Induced Pluripotent Stem Cells Model of Coenzyme Q10 Deficiency

Coenzyme Q₁₀ (CoQ₁₀ ) plays a crucial role in mitochondria as an electron carrier within the mitochondrial respiratory chain (MRC) and is an essential antioxidant. Mutations in genes responsible for CoQ₁₀ biosynthesis (COQ genes) cause primary CoQ₁₀ deficiency, a rare and heterogeneous mitochondrial disorder with no clear genotype-phenotype association, mainly affecting tissues with high-energy demand including brain and skeletal muscle (SkM). Here, we report a four-year-old girl diagnosed with minor mental retardation and lethal rhabdomyolysis harboring a heterozygous mutation (c.483G > C (E161D)) in COQ4. The patient's fibroblasts showed a decrease in [CoQ₁₀ ], CoQ₁₀ biosynthesis, MRC activity affecting complexes I/II + III, and respiration defects. Bona fide induced pluripotent stem cell (iPSCs) lines carrying the COQ4 mutation (CQ4-iPSCs) were generated, characterized and genetically edited using the CRISPR-Cas9 system (CQ4^ed -iPSCs). Extensive differentiation and metabolic assays of control-iPSCs, CQ4-iPSCs and CQ4^ed -iPSCs demonstrated a genotype association, reproducing the disease phenotype. The COQ4 mutation in iPSC was associated with CoQ₁₀ deficiency, metabolic dysfunction, and respiration defects. iPSC differentiation into SkM was compromised, and the resulting SkM also displayed respiration defects. Remarkably, iPSC differentiation in dopaminergic or motor neurons was unaffected. This study offers an unprecedented iPSC model recapitulating CoQ₁₀ deficiency-associated functional and metabolic phenotypes caused by COQ4 mutation. Stem Cells 2017;35:1687-1703.

Pathogenicity of two COQ7 mutations and responses to 2,4-dihydroxybenzoate bypass treatment

Primary ubiquinone (co‐enzyme Q) deficiency results in a wide range of clinical features due to mitochondrial dysfunction. Here, we analyse and characterize two mutations in the ubiquinone biosynthetic gene COQ7. One mutation from the only previously identified patient (V141E), and one (L111P) from a 6‐year‐old girl who presents with spasticity and bilateral sensorineural hearing loss. We used patient fibroblast cell lines and a heterologous expression system to show that both mutations lead to loss of protein stability and decreased levels of ubiquinone that correlate with the severity of mitochondrial dysfunction. The severity of L111P is enhanced by the particular COQ7 polymorphism (T103M) that the patient carries, but not by a mitochondrial DNA mutation (A1555G) that is also present in the patient and that has been linked to aminoglycoside‐dependent hearing loss. We analysed treatment with the unnatural biosynthesis precursor 2,4‐dihydroxybenzoate (DHB), which can restore ubiquinone synthesis in cells completely lacking the enzymatic activity of COQ7. We find that the treatment is not beneficial for every COQ7 mutation and its outcome depends on the extent of enzyme activity loss.

The Value of Coenzyme Q10 Determination in Mitochondrial Patients

Coenzyme Q₁₀ (CoQ) is a lipid that is ubiquitously synthesized in tissues and has a key role in mitochondrial oxidative phosphorylation. Its biochemical determination provides insight into the CoQ status of tissues and may detect CoQ deficiency that can result from either an inherited primary deficiency of CoQ metabolism or may be secondary to different genetic and environmental conditions. Rapid identification of CoQ deficiency can also allow potentially beneficial treatment to be initiated as early as possible. CoQ may be measured in different specimens, including plasma, blood mononuclear cells, platelets, urine, muscle, and cultured skin fibroblasts. Blood and urinary CoQ also have good utility for CoQ treatment monitoring.

Biochemical Assessment of Coenzyme Q10 Deficiency

Coenzyme Q₁₀ (CoQ₁₀) deficiency syndrome includes clinically heterogeneous mitochondrial diseases that show a variety of severe and debilitating symptoms. A multiprotein complex encoded by nuclear genes carries out CoQ₁₀ biosynthesis. Mutations in any of these genes are responsible for the primary CoQ₁₀ deficiency, but there are also different conditions that induce secondary CoQ₁₀ deficiency including mitochondrial DNA (mtDNA) depletion and mutations in genes involved in the fatty acid β-oxidation pathway. The diagnosis of CoQ₁₀ deficiencies is determined by the decrease of its content in skeletal muscle and/or dermal skin fibroblasts. Dietary CoQ₁₀ supplementation is the only available treatment for these deficiencies that require a rapid and distinct diagnosis. Here we review methods for determining CoQ₁₀ content by HPLC separation and identification using alternative approaches including electrochemical detection and mass spectrometry. Also, we review procedures to determine the CoQ₁₀ biosynthesis rate using labeled precursors.

Cellular factories for coenzyme Q10 production

Coenzyme Q₁₀ (CoQ₁₀), a benzoquinone present in most organisms, plays an important role in the electron-transport chain, and its deficiency is associated with various neuropathies and muscular disorders. CoQ₁₀ is the only lipid-soluble antioxidant found in humans, and for this, it is gaining popularity in the cosmetic and healthcare industries. To meet the growing demand for CoQ₁₀, there has been considerable interest in ways to enhance its production, the most effective of which remains microbial fermentation. Previous attempts to increase CoQ₁₀ production to an industrial scale have thus far conformed to the strategies used in typical metabolic engineering endeavors. However, the emergence of new tools in the expanding field of synthetic biology has provided a suite of possibilities that extend beyond the traditional modes of metabolic engineering. In this review, we cover the various strategies currently undertaken to upscale CoQ₁₀ production, and discuss some of the potential novel areas for future research.

Generation, genome edition and characterization of iPSC lines from a patient with coenzyme Q10 deficiency harboring a heterozygous mutation in COQ4 gene

We report the generation, CRISPR/Cas9-edition and characterization of induced pluripotent stem cell (iPSC) lines from a patient with coenzyme Q₁₀ deficiency harboring the heterozygous mutation c.483G>C in the COQ4 gene. iPSCs were generated using non-integrative Sendai Viruses containing the reprogramming factors OCT4, SOX2, KLF4 and C-MYC. The iPSC lines carried the c.483G>C COQ4 mutation, silenced the OKSM expression and were mycoplasma-free. They were bona fide pluripotent cells as characterized by morphology, immunophenotype/gene expression for pluripotent-associated markers/genes, NANOG and OCT4 promoter demethylation, karyotype and teratoma formation. The COQ4 mutation was CRISPR/Cas9 edited resulting in isogenic, diploid and off-target free COQ4-corrected iPSCs.

Mitochondrial dysfunction in inherited renal disease and acute kidney injury

Mitochondria are increasingly recognized as key players in genetic and acquired renal diseases. Most mitochondrial cytopathies that cause renal symptoms are characterized by tubular defects, but glomerular, tubulointerstitial and cystic diseases have also been described. For example, defects in coenzyme Q10 (CoQ10) biosynthesis and the mitochondrial DNA 3243 A>G mutation are important causes of focal segmental glomerulosclerosis in children and in adults, respectively. Although they sometimes present with isolated renal findings, mitochondrial diseases are frequently associated with symptoms related to central nervous system and neuromuscular involvement. They can result from mutations in nuclear genes that are inherited according to classic Mendelian rules or from mutations in mitochondrial DNA, which are transmitted according to more complex rules of mitochondrial genetics. Diagnosis of mitochondrial disorders involves clinical characterization of patients in combination with biochemical and genetic analyses. In particular, prompt diagnosis of CoQ10 biosynthesis defects is imperative because of their potentially reversible nature. In acute kidney injury (AKI), mitochondrial dysfunction contributes to the physiopathology of tissue injury, whereas mitochondrial biogenesis has an important role in the recovery of renal function. Potential therapies that target mitochondrial dysfunction or promote mitochondrial regeneration are being developed to limit renal damage during AKI and promote repair of injured tissue.

Coenzyme Q biosynthesis in health and disease

Coenzyme Q (CoQ, or ubiquinone) is a remarkable lipid that plays an essential role in mitochondria as an electron shuttle between complexes I and II of the respiratory chain, and complex III. It is also a cofactor of other dehydrogenases, a modulator of the permeability transition pore and an essential antioxidant. CoQ is synthesized in mitochondria by a set of at least 12 proteins that form a multiprotein complex. The exact composition of this complex is still unclear. Most of the genes involved in CoQ biosynthesis (COQ genes) have been studied in yeast and have mammalian orthologues. Some of them encode enzymes involved in the modification of the quinone ring of CoQ, but for others the precise function is unknown. Two genes appear to have a regulatory role: COQ8 (and its human counterparts ADCK3 and ADCK4) encodes a putative kinase, while PTC7 encodes a phosphatase required for the activation of Coq7. Mutations in human COQ genes cause primary CoQ(10) deficiency, a clinically heterogeneous mitochondrial disorder with onset from birth to the seventh decade, and with clinical manifestation ranging from fatal multisystem disorders, to isolated encephalopathy or nephropathy. The pathogenesis of CoQ(10) deficiency involves deficient ATP production and excessive ROS formation, but possibly other aspects of CoQ(10) function are implicated. CoQ(10) deficiency is unique among mitochondrial disorders since an effective treatment is available. Many patients respond to oral CoQ(10) supplementation. Nevertheless, treatment is still problematic because of the low bioavailability of the compound, and novel pharmacological approaches are currently being investigated. This article is part of a Special Issue entitled 'EBEC 2016: 19th European Bioenergetics Conference, Riva del Garda, Italy, July 2-6, 2016', edited by Prof. Paolo Bernardi.

Hormetic and regulatory effects of lipid peroxidation mediators in pancreatic beta cells

Nutrient sensing mechanisms of carbohydrates, amino acids and lipids operate distinct pathways that are essential for the adaptation to varying metabolic conditions. The role of nutrient-induced biosynthesis of hormones is paramount for attaining metabolic homeostasis in the organism. Nutrient overload attenuate key metabolic cellular functions and interfere with hormonal-regulated inter- and intra-organ communication, which may ultimately lead to metabolic derangements. Hyperglycemia and high levels of saturated free fatty acids induce excessive production of oxygen free radicals in tissues and cells. This phenomenon, which is accentuated in both type-1 and type-2 diabetic patients, has been associated with the development of impaired glucose tolerance and the etiology of peripheral complications. However, low levels of the same free radicals also induce hormetic responses that protect cells against deleterious effects of the same radicals. Of interest is the role of hydroxyl radicals in initiating peroxidation of polyunsaturated fatty acids (PUFA) and generation of α,β-unsaturated reactive 4-hydroxyalkenals that avidly form covalent adducts with nucleophilic moieties in proteins, phospholipids and nucleic acids. Numerous studies have linked the lipid peroxidation product 4-hydroxy-2E-nonenal (4-HNE) to different pathological and cytotoxic processes. Similarly, two other members of the family, 4-hydroxyl-2E-hexenal (4-HHE) and 4-hydroxy-2E,6Z-dodecadienal (4-HDDE), have also been identified as potential cytotoxic agents. It has been suggested that 4-HNE-induced modifications in macromolecules in cells may alter their cellular functions and modify signaling properties. Yet, it has also been acknowledged that these bioactive aldehydes also function as signaling molecules that directly modify cell functions in a hormetic fashion to enable cells adapt to various stressful stimuli. Recent studies have shown that 4-HNE and 4-HDDE, which activate peroxisome proliferator-activated receptor δ (PPARδ) in vascular endothelial cells and insulin secreting beta cells, promote such adaptive responses to ameliorate detrimental effects of high glucose and diabetes-like conditions. In addition, due to the electrophilic nature of these reactive aldehydes they form covalent adducts with electronegative moieties in proteins, phosphatidylethanolamine and nucleotides. Normally these non-enzymatic modifications are maintained below the cytotoxic range due to efficient cellular neutralization processes of 4-hydroxyalkenals. The major neutralizing enzymes include fatty aldehyde dehydrogenase (FALDH), aldose reductase (AR) and alcohol dehydrogenase (ADH), which transform the aldehyde to the corresponding carboxylic acid or alcohols, respectively, or by biding to the thiol group in glutathione (GSH) by the action of glutathione-S-transferase (GST). This review describes the hormetic and cytotoxic roles of oxygen free radicals and 4-hydroxyalkenals in beta cells exposed to nutritional challenges and the cellular mechanisms they employ to maintain their level at functional range below the cytotoxic threshold.

Coenzyme Q biosynthesis and its role in the respiratory chain structure

Coenzyme Q (CoQ) is a unique electron carrier in the mitochondrial respiratory chain, which is synthesized on-site by a nuclear encoded multiprotein complex. CoQ receives electrons from different redox pathways, mainly NADH and FADH2 from tricarboxylic acid pathway, dihydroorotate dehydrogenase, electron transfer flavoprotein dehydrogenase and glycerol-3-phosphate dehydrogenase that support key aspects of the metabolism. Here we explore some lines of evidence supporting the idea of the interaction of CoQ with the respiratory chain complexes, contributing to their superassembly, including respirasome, and its role in reactive oxygen species production in the mitochondrial inner membrane. We also review the current knowledge about the involvement of mitochondrial genome defects and electron transfer flavoprotein dehydrogenase mutations in the induction of secondary CoQ deficiency. This mechanism would imply specific interactions coupling CoQ itself or the CoQ-biosynthetic apparatus with the respiratory chain components. These interactions would regulate mitochondrial CoQ steady-state levels and function. This article is part of a Special Issue entitled 'EBEC 2016: 19th European Bioenergetics Conference, Riva del Garda, Italy, July 2-6, 2016', edited by Prof. Paolo Bernardi.

Coenzyme Q10 defects may be associated with a deficiency of Q10-independent mitochondrial respiratory chain complexes

BACKGROUND

Coenzyme Q10 (CoQ10 or ubiquinone) deficiency can be due either to mutations in genes involved in CoQ10 biosynthesis pathway, or to mutations in genes unrelated to CoQ10 biosynthesis. CoQ10 defect is the only oxidative phosphorylation disorder that can be clinically improved after oral CoQ10 supplementation. Thus, early diagnosis, first evoked by mitochondrial respiratory chain (MRC) spectrophotometric analysis, then confirmed by direct measurement of CoQ10 levels, is of critical importance to prevent irreversible damage in organs such as the kidney and the central nervous system. It is widely reported that CoQ10 deficient patients present decreased quinone-dependent activities (segments I + III or G3P + III and II + III) while MRC activities of complexes I, II, III, IV and V are normal. We previously suggested that CoQ10 defect may be associated with a deficiency of CoQ10-independent MRC complexes. The aim of this study was to verify this hypothesis in order to improve the diagnosis of this disease.

RESULTS

To determine whether CoQ10 defect could be associated with MRC deficiency, we quantified CoQ10 by LC-MSMS in a cohort of 18 patients presenting CoQ10-dependent deficiency associated with MRC defect. We found decreased levels of CoQ10 in eight patients out of 18 (45 %), thus confirming CoQ10 disease.

CONCLUSIONS

Our study shows that CoQ10 defect can be associated with MRC deficiency. This could be of major importance in clinical practice for the diagnosis of a disease that can be improved by CoQ10 supplementation.

RNA-binding proteins regulate cell respiration and coenzyme Q biosynthesis by post-transcriptional regulation of COQ7

Coenzyme Q (CoQ) is a key component of the mitochondrial respiratory chain carrying electrons from complexes I and II to complex III and it is an intrinsic component of the respirasome. CoQ concentration is highly regulated in cells in order to adapt the metabolism of the cell to challenges of nutrient availability and stress stimuli. At least 10 proteins have been shown to be required for CoQ biosynthesis in a multi-peptide complex and COQ7 is a central regulatory factor of this pathway. We found that the first 765 bp of the 3′-untranslated region (UTR) of COQ7 mRNA contains cis-acting elements of interaction with RNA-binding proteins (RBPs) HuR and hnRNP C1/C2. Binding of hnRNP C1/C2 to COQ7 mRNA was found to require the presence of HuR, and hnRNP C1/C2 silencing appeared to stabilize COQ7 mRNA modestly. By contrast, lowering HuR levels by silencing or depriving cells of serum destabilized and reduced the half-life of COQ7 mRNA, thereby reducing COQ7 protein and CoQ biosynthesis rate. Accordingly, HuR knockdown decreased oxygen consumption rate and mitochondrial production of ATP, and increased lactate levels. Taken together, our results indicate that a reduction in COQ7 mRNA levels by HuR depletion causes mitochondrial dysfunction and a switch toward an enhanced aerobic glycolysis, the characteristic phenotype exhibited by primary deficiency of CoQ₁₀. Thus HuR contributes to efficient oxidative phosphorylation by regulating of CoQ₁₀ biosynthesis.

Determination of urinary coenzyme Q10 by HPLC with electrochemical detection: Reference values for a paediatric population

Kidney dysfunction is being increasingly associated with mitochondrial diseases and coenzyme Q10 (CoQ) deficiency. The assessment of CoQ status requires the biochemical determination of CoQ in biological fluids and different cell types, but no methods have been developed as yet for the analysis of CoQ in excretory systems. The aim of this study was to standardize a new procedure for urinary CoQ determination and to establish reference values for a paediatric population. Urinary CoQ was analyzed by HPLC with electrochemical detection. Reference values (n = 43) were stratified into two age groups (2-10 years: range 24-109 nmol CoQ/gram of pellet protein; 11-17 years: range 43-139 nmol CoQ/gram of pellet protein). In conclusion, urinary CoQ analysis is a noninvasive, reliable, and reproducible method to determine urinary tract CoQ status.

Mitochondrial responsibility in ageing process: innocent, suspect or guilty

Ageing is accompanied by the accumulation of damaged molecules in cells due to the injury produced by external and internal stressors. Among them, reactive oxygen species produced by cell metabolism, inflammation or other enzymatic processes are considered key factors. However, later research has demonstrated that a general mitochondrial dysfunction affecting electron transport chain activity, mitochondrial biogenesis and turnover, apoptosis, etc., seems to be in a central position to explain ageing. This key role is based on several effects from mitochondrial-derived ROS production to the essential maintenance of balanced metabolic activities in old organisms. Several studies have demonstrated caloric restriction, exercise or bioactive compounds mainly found in plants, are able to affect the activity and turnover of mitochondria by increasing biogenesis and mitophagy, especially in postmitotic tissues. Then, it seems that mitochondria are in the centre of metabolic procedures to be modified to lengthen life- or health-span. In this review we show the importance of mitochondria to explain the ageing process in different models or organisms (e.g. yeast, worm, fruitfly and mice). We discuss if the cause of aging is dependent on mitochondrial dysfunction of if the mitochondrial changes observed with age are a consequence of events taking place outside the mitochondrial compartment.

Primary coenzyme Q10 deficiency presenting as fatal neonatal multiorgan failure

Coenzyme Q10 deficiency is a clinically and genetically heterogeneous disorder, with manifestations that may range from fatal neonatal multisystem failure, to adult-onset encephalopathy. We report a patient who presented at birth with severe lactic acidosis, proteinuria, dicarboxylic aciduria, and hepatic insufficiency. She also had dilation of left ventricle on echocardiography. Her neurological condition rapidly worsened and despite aggressive care she died at 23 h of life. Muscle histology displayed lipid accumulation. Electron microscopy showed markedly swollen mitochondria with fragmented cristae. Respiratory-chain enzymatic assays showed a reduction of combined activities of complex I+III and II+III with normal activities of isolated complexes. The defect was confirmed in fibroblasts, where it could be rescued by supplementing the culture medium with 10 μM coenzyme Q10. Coenzyme Q10 levels were reduced (28% of controls) in these cells. We performed exome sequencing and focused the analysis on genes involved in coenzyme Q10 biosynthesis. The patient harbored a homozygous c.545T>G, p.(Met182Arg) alteration in COQ2, which was validated by functional complementation in yeast. In this case the biochemical and morphological features were essential to direct the genetic diagnosis. The parents had another pregnancy after the biochemical diagnosis was established, but before the identification of the genetic defect. Because of the potentially high recurrence risk, and given the importance of early CoQ10 supplementation, we decided to treat with CoQ10 the newborn child pending the results of the biochemical assays. Clinicians should consider a similar management in siblings of patients with CoQ10 deficiency without a genetic diagnosis.

Genetic bases and clinical manifestations of coenzyme Q10 (CoQ 10) deficiency

Coenzyme Q(10) is a remarkable lipid involved in many cellular processes such as energy production through the mitochondrial respiratory chain (RC), beta-oxidation of fatty acids, and pyrimidine biosynthesis, but it is also one of the main cellular antioxidants. Its biosynthesis is still incompletely characterized and requires at least 15 genes. Mutations in eight of them (PDSS1, PDSS2, COQ2, COQ4, COQ6, ADCK3, ADCK4, and COQ9) cause primary CoQ(10) deficiency, a heterogeneous group of disorders with variable age of onset (from birth to the seventh decade) and associated clinical phenotypes, ranging from a fatal multisystem disease to isolated steroid resistant nephrotic syndrome (SRNS) or isolated central nervous system disease. The pathogenesis is complex and related to the different functions of CoQ(10). It involves defective ATP production and oxidative stress, but also an impairment of pyrimidine biosynthesis and increased apoptosis. CoQ(10) deficiency can also be observed in patients with defects unrelated to CoQ(10) biosynthesis, such as RC defects, multiple acyl-CoA dehydrogenase deficiency, and ataxia and oculomotor apraxia.Patients with both primary and secondary deficiencies benefit from high-dose oral supplementation with CoQ(10). In primary forms treatment can stop the progression of both SRNS and encephalopathy, hence the critical importance of a prompt diagnosis. Treatment may be beneficial also for secondary forms, although with less striking results.In this review we will focus on CoQ(10) biosynthesis in humans, on the genetic defects and the specific clinical phenotypes associated with CoQ(10) deficiency, and on the diagnostic strategies for these conditions.

Strategies for oral delivery and mitochondrial targeting of CoQ10

Coenzyme Q10 (CoQ10), also known as ubiquinone or ubidecarenone, is a powerful, endogenously produced, intracellularly existing lipophilic antioxidant. It combats reactive oxygen species (ROS) known to be responsible for a variety of human pathological conditions. Its target site is the inner mitochondrial membrane (IMM) of each cell. In case of deficiency and/or aging, CoQ10 oral supplementation is warranted. However, CoQ10 has low oral bioavailability due to its lipophilic nature, large molecular weight, regional differences in its gastrointestinal permeability and involvement of multitransporters. Intracellular delivery and mitochondrial target ability issues pose additional hurdles. To maximize CoQ10 delivery to its biopharmaceutical target, numerous approaches have been undertaken. The review summaries the current research on CoQ10 bioavailability and highlights the headways to obtain a satisfactory intracellular and targeted mitochondrial delivery. Unresolved questions and research gaps were identified to bring this promising natural product to the forefront of therapeutic agents for treatment of different pathologies.

Mitochondrial damage and cholesterol storage in human hepatocellular carcinoma cells with silencing of UBIAD1 gene expression

Heterozygous mutations in the UBIAD1 gene cause Schnyder corneal dystrophy characterized by abnormal cholesterol and phospholipid deposits in the cornea. Ubiad1 protein was recently identified as Golgi prenyltransferase responsible for biosynthesis of vitamin K2 and CoQ10, a key protein in the mitochondrial electron transport chain. Our study shows that silencing UBIAD1 in cultured human hepatocellular carcinoma cells causes dramatic morphological changes and cholesterol storage in the mitochondria, emphasizing an important role of UBIAD1 in mitochondrial function.