Generation of the First Human In Vitro Model for McArdle Disease Based on iPSC Technology.

McArdle disease is a rare autosomal recessive disorder caused by mutations in the PYGM gene. This gene encodes for the skeletal muscle isoform of glycogen phosphorylase (myophosphorylase), the first enzyme in glycogenolysis. Patients with this disorder are unable to obtain energy from their glycogen stored in skeletal muscle, prompting an exercise intolerance. Currently, there is no treatment for this disease, and the lack of suitable in vitro human models has prevented the search for therapies against it. In this article, we have established the first human iPSC-based model for McArdle disease. For the generation of this model, induced pluripotent stem cells (iPSCs) from a patient with McArdle disease (harbouring the homozygous mutation c.148C>T; p.R50* in the PYGM gene) were differentiated into myogenic cells able to contract spontaneously in the presence of motor neurons and generate calcium transients, a proof of their maturity and functionality. Additionally, an isogenic skeletal muscle model of McArdle disease was created. As a proof-of-concept, we have tested in this model the rescue of PYGM expression by two different read-through compounds (PTC124 and RTC13). The developed model will be very useful as a platform for testing drugs or compounds with potential pharmacological activity.

Mitochondrial DNA from osteoarthritic patients drives functional impairment of mitochondrial activity: a study on transmitochondrial cybrids.

With the redefinition of osteoarthritis (OA) and the understanding that the joint behaves as an organ, OA is now considered a systemic illness with a low grade of chronic inflammation. Mitochondrial dysfunction is well documented in OA and has the capacity to alter chondrocyte and synoviocyte function. Transmitochondrial cybrids are suggested as a useful cellular model to study mitochondrial biology in vitro, as they carry different mitochondrial variants with the same nuclear background. The aim of this work was to study mitochondrial and metabolic function of cybrids with mitochondrial DNA from healthy (N) and OA donors. In this work, the authors demonstrate that cybrids from OA patients behave differently from cybrids from N donors in several mitochondrial parameters. Furthermore, OA cybrids behave similarly to OA chondrocytes. These results enhance our understanding of the role of mitochondria in the degeneration process of OA and present cybrids as a useful model to study OA pathogenesis.

Mitochondrial Dysfunction and Calcium Dysregulation in Leigh Syndrome Induced Pluripotent Stem Cell Derived Neurons.

Leigh syndrome (LS) is the most frequent infantile mitochondrial disorder (MD) and is characterized by neurodegeneration and astrogliosis in the basal ganglia or the brain stem. At present, there is no cure or treatment for this disease, partly due to scarcity of LS models. Current models generally fail to recapitulate important traits of the disease. Therefore, there is an urgent need to develop new human in vitro models. Establishment of induced pluripotent stem cells (iPSCs) followed by differentiation into neurons is a powerful tool to obtain an in vitro model for LS. Here, we describe the generation and characterization of iPSCs, neural stem cells (NSCs) and iPSC-derived neurons harboring the mtDNA mutation m.13513G>A in heteroplasmy. We have performed mitochondrial characterization, analysis of electrophysiological properties and calcium imaging of LS neurons. Here, we show a clearly compromised oxidative phosphorylation (OXPHOS) function in LS patient neurons. This is also the first report of electrophysiological studies performed on iPSC-derived neurons harboring an mtDNA mutation, which revealed that, in spite of having identical electrical properties, diseased neurons manifested mitochondrial dysfunction together with a diminished calcium buffering capacity. This could lead to an overload of cytoplasmic calcium concentration and the consequent cell death observed in patients. Importantly, our results highlight the importance of calcium homeostasis in LS pathology.

Correction: Enhanced tumorigenicity by mitochondrial DNA mild mutations.

[This corrects the article DOI: 10.18632/oncotarget.3698.].

The mutation m.13513G>A impairs cardiac function, favoring a neuroectoderm commitment, in a mutant-load dependent way.

Mitochondrial disorders (MDs) arise as a result of a respiratory chain dysfunction. While some MDs can affect a single organ, many involve several organs, the brain being the most affected, followed by heart and/or muscle. Many of these diseases are associated with heteroplasmic mutations in the mitochondrial DNA (mtDNA). The proportion of mutated mtDNA must exceed a critical threshold to produce disease. Therefore, understanding how embryonic development determines the heteroplasmy level in each tissue could explain the organ susceptibility and the clinical heterogeneity observed in these patients. In this report, the dynamics of heteroplasmy and the influence in cardiac commitment of the mutational load of the m.13513G>A mutation has been analyzed. This mutation has been reported as a frequent cause of Leigh syndrome (LS) and is commonly associated with cardiac problems. In this report, induced pluripotent stem cell (iPSc) technology has been used to delve into the molecular mechanisms underlying cardiac disease in LS. When mutation m.13513G>A is above a threshold, iPSc-derived cardiomyocytes (iPSc-CMs) could not be obtained due to an inefficient epithelial-mesenchymal transition. Surprisingly, these cells are redirected toward neuroectodermal lineages that would give rise to the brain. However, when mutation is below that threshold, dysfunctional CM are generated in a mutant-load dependent way. We suggest that distribution of the m.13513G>A mutation during cardiac differentiation is not at random. We propose a possible explanation of why neuropathology is a frequent feature of MD, but cardiac involvement is not always present.

Derivation of an aged mouse induced pluripotent stem cell line, IISHDOi005-A.

A mouse iPSC line, IISHDOi005-A, generated from fibroblasts obtained from a mouse C57BL/6J with an age of 1 year and a half, has been obtained. For this purpose, reprogramming factors Oct3/4, Sox2, Klf4, and c-Myc were delivered using Sendai virus.

Pathogenic variants in glutamyl-tRNAGln amidotransferase subunits cause a lethal mitochondrial cardiomyopathy disorder.

Mitochondrial protein synthesis requires charging mt-tRNAs with their cognate amino acids by mitochondrial aminoacyl-tRNA synthetases, with the exception of glutaminyl mt-tRNA (mt-tRNAGln). mt-tRNAGln is indirectly charged by a transamidation reaction involving the GatCAB aminoacyl-tRNA amidotransferase complex. Defects involving the mitochondrial protein synthesis machinery cause a broad spectrum of disorders, with often fatal outcome. Here, we describe nine patients from five families with genetic defects in a GatCAB complex subunit, including QRSL1, GATB, and GATC, each showing a lethal metabolic cardiomyopathy syndrome. Functional studies reveal combined respiratory chain enzyme deficiencies and mitochondrial dysfunction. Aminoacylation of mt-tRNAGln and mitochondrial protein translation are deficient in patients' fibroblasts cultured in the absence of glutamine but restore in high glutamine. Lentiviral rescue experiments and modeling in S. cerevisiae homologs confirm pathogenicity. Our study completes a decade of investigations on mitochondrial aminoacylation disorders, starting with DARS2 and ending with the GatCAB complex.

Establishment of a human iPSC line, IISHDOi004-A, from a patient with Usher syndrome associated with the mutation c.2276G>T; p.Cys759Phe in the USH2A gene.

A human iPSC line, IISHDOi004-A, from fibroblasts obtained from a patient with Usher syndrome, harboring a homozygous mutation in the USH2A gene (c.2276G>T; p.Cys759Phe) has been generated. Reprogramming factors Oct3/4, Sox2, Klf4, and c-Myc were delivered using Sendai virus.

Generation of a human iPSC line, IISHDOi002-A, with a 46, XY/47, XYY mosaicism and belonging to an African mitochondrial haplogroup.

We have generated a human iPSC line, IISHDOi002-A, from commercial primary normal human dermal fibroblasts belonging to an African mitochondrial haplogroup (L3), and with a 46, XY/47, XYY mosaicism. For this purpose, reprogramming factors Oct3/4, Sox2, Klf4 and cMyc were delivered using a non-integrative methodology that involves the use of Sendai virus.

Establishment of a human DOA 'plus' iPSC line, IISHDOi003-A, with the mutation in the OPA1 gene: c.1635C>A; p.Ser545Arg.

We have generated a human iPSC line IISHDOi003-A from fibroblasts of a patient with a dominant optic atrophy 'plus' phenotype, harbouring a heterozygous mutation, c.1635C>A; p.Ser545Arg, in the OPA1 gene. Reprogramming factors Oct3/4, Sox2, Klf4, and c-Myc were delivered using Sendai virus.

Establishment of a human iPSC line (IISHDOi001-A) from a patient with McArdle disease.

Human iPSC line IISHDOi001-A was generated from fibroblasts of a patient with McArdle disease harbouring the mutation, c.148C>T; p.Arg50Ter, in the PYGM gene. Reprogramming factors Oct3/4, Sox2, Klf4, and c-Myc were delivered using Sendai virus.

Mitochondrial DNA haplogroups influence the risk of incident knee osteoarthritis in OAI and CHECK cohorts. A meta-analysis and functional study.

OBJECTIVE: To evaluate the influence of the mitochondrial DNA (mtDNA) haplogroups in the risk of incident knee osteoarthritis (OA) and to explain the functional consequences of this association to identify potential diagnostic biomarkers and therapeutic targets. METHODS: Two prospective cohorts contributed participants. The osteoarthritis initiative (OAI) included 2579 subjects of the incidence subcohort, and the cohort hip and cohort knee (CHECK) included 635, both with 8-year follow-up. The analysis included the association of mtDNA haplogroups with the rate of incident knee OA in subjects from both cohorts followed by a subsequent meta-analysis. Transmitochondrial cybrids harbouring haplogroup J or H were constructed to detect differences between them in relation to physiological features including specific mitochondrial metabolic parameters, reactive oxygen species production, oxidative stress and apoptosis. RESULTS: Compared with H, the haplogroup J associates with decreased risk of incident knee OA in subjects from OAI (HR=0.680; 95% CI 0.470 to 0.968; p<0.05) and CHECK (HR=0.728; 95% CI 0.469 to 0.998; p<0.05). The subsequent meta-analysis including 3214 cases showed that the haplogroup J associates with a lower risk of incident knee OA (HR=0.702; 95% CI 0.541 to 0.912; p=0.008). J cybrids show a lower free radical production, higher cell survival under oxidative stress conditions, lower grade of apoptosis as well as lower expression of the mitochondrially related pro-apoptotic gene BCL2 binding component 3 (BBC3). In addition, J cybrids also show a lower mitochondrial respiration and glycolysis leading to decreased ATP production. CONCLUSIONS: The physiological effects of the haplogroup J are beneficial to have a lower rate of incident knee OA over time. Potential drugs to treat OA could focus on emulating the mitochondrial behaviour of this haplogroup.

Generating Rho-0 Cells Using Mesenchymal Stem Cell Lines.

INTRODUCTION: The generation of Rho-0 cells requires the use of an immortalization process, or tumor cell selection, followed by culture in the presence of ethidium bromide (EtBr), incurring the drawbacks its use entails. The purpose of this work was to generate Rho-0 cells using human mesenchymal stem cells (hMSCs) with reagents having the ability to remove mitochondrial DNA (mtDNA) more safely than by using EtBr. METHODOLOGY: Two immortalized hMSC lines (3a6 and KP) were used; 143B.TK-Rho-0 cells were used as reference control. For generation of Rho-0 hMSCs, cells were cultured in medium supplemented with each tested reagent. Total DNA was isolated and mtDNA content was measured by real-time polymerase chain reaction (PCR). Phenotypic characterization and gene expression assays were performed to determine whether 3a6 Rho-0 hMSCs maintain the same stem properties as untreated 3a6 hMSCs. To evaluate whether 3a6 Rho-0 hMSCs had a phenotype similar to that of 143B.TK-Rho-0 cells, in terms of reactive oxygen species (ROS) production, apoptotic levels and mitochondrial membrane potential (Δψm) were measured by flow cytometry and mitochondrial respiration was evaluated using a SeaHorse XFp Extracellular Flux Analyzer. The differentiation capacity of 3a6 and 3a6 Rho-0 hMSCs was evaluated using real-time PCR, comparing the relative expression of genes involved in osteogenesis, adipogenesis and chondrogenesis. RESULTS: The results showed the capacity of the 3a6 cell line to deplete its mtDNA and to survive in culture with uridine. Of all tested drugs, Stavudine (dt4) was the most effective in producing 3a6-Rho cells. The data indicate that hMSC Rho-0 cells continue to express the characteristic MSC cell surface receptor pattern. Phenotypic characterization showed that 3a6 Rho-0 cells resembled 143B.TK-Rho-0 cells, indicating that hMSC Rho-0 cells are Rho-0 cells. While the adipogenic capability was higher in 3a6 Rho-0 cells than in 3a6 cells, the osteogenic and chondrogenic capacities were lower. CONCLUSION: Among the drugs and conditions tested, the use of d4t was the best option for producing Rho-0 cells from hMSCs. Rho-0 cells are useful for studying the role of mitochondria in hMSC differentiation.

Human COA3 Is an Oligomeric Highly Flexible Protein in Solution.

The assembly of the protein complex of cytochrome c oxidase (COX), which participates in the mitochondrial respiratory chain, requires a large number of accessory proteins (the so-called assembly factors). Human COX assembly factor 3 (hCOA3), also known as MITRAC12 or coiled-coil domain-containing protein 56 (CCDC56), interacts with the first subunit protein of COX to form its catalytic core and promotes its assemblage with the other units. Therefore, hCOA3 is involved in COX biogenesis in humans and can be exploited as a drug target in patients with mitochondrial dysfunctions. However, to be considered a molecular target, its structure and conformational stability must first be elucidated. We have embarked on the description of such features by using spectroscopic and hydrodynamic techniques, in aqueous solution and in the presence of detergents, together with computational methods. Our results show that hCOA3 is an oligomeric protein, forming aggregates of different molecular masses in aqueous solution. Moreover, on the basis of fluorescence and circular dichroism results, the protein has (i) its unique tryptophan partially shielded from solvent and (ii) a relatively high percentage of secondary structure. However, this structure is highly flexible and does not involve hydrogen bonding. Experiments in the presence of detergents suggest a slightly higher content of nonrigid helical structure. Theoretical results, based on studies of the primary structure of the protein, further support the idea that hCOA3 is a disordered protein. We suggest that the flexibility of hCOA3 is crucial for its interaction with other proteins to favor mitochondrial protein translocation and assembly of proteins involved in the respiratory chain.

Generation of a human iPSC line from a patient with Leigh syndrome.

Human iPSC line LND554SV.3 was generated from heteroplasmic fibroblasts of a patient with Leigh syndrome carrying a mutation in the MT-ND5 gene (m.13513GNA; p.D393N). Reprogramming factors Oct3/4, Sox2, Klf4,and cMyc were delivered using a non-integrative methodology that involves the use of Sendai virus.

Generation of a human control iPSC line with a European mitochondrial haplogroup U background.

Human iPSC line N44SV.5 was generated from primary normal human dermal fibroblasts belonging to the European mitochondrial haplogroup U. For this purpose, reprogramming factors Oct3/4, Sox2, Klf4, and cMyc were delivered using a non-integrative methodology that involves the use of Sendai virus.

Generation of a human iPSC line from a patient with a defect of intergenomic communication.

Human iPSC line PG64SV.2 was generated from fibroblasts of a patient with a defect of intergenomic communication. This patient harbored a homozygous mutation (c.2243G>C; p.Trp748Ser) in the gene encoding the catalytic subunit of the mitochondrial DNA polymerase gamma gene (POLG). Reprogramming factors Oct3/4, Sox2, Klf4, and cMyc were delivered using a non integrative methodology that involves the use of Sendai virus.

Generation of a human iPSC line from a patient with a mitochondrial encephalopathy due to mutations in the GFM1 gene.

Human iPSC line GFM1SV.25 was generated from fibroblasts of a child with a severe mitochondrial encephalopathy associated with mutations in the GFM1 gene, encoding the mitochondrial translation elongation factor G1. Reprogramming factors OCT3/4, SOX2, CMYC and KLF4 were delivered using a non integrative methodology that involves the use of Sendai virus.

Generation of a human iPSC line from a patient with an optic atrophy 'plus' phenotype due to a mutation in the OPA1 gene.

Human iPSC line Oex2054SV.4 was generated from fibroblasts of a patient with an optic atrophy 'plus' phenotype associated with a heterozygous mutation in the OPA1 gene. Reprogramming factors OCT3/4, SOX2, CMYC and KLF4 were delivered using a non-integrative methodology that involves the use of Sendai virus.