Efficient attenuation of Friedreich's ataxia (FRDA) cardiomyopathy by modulation of iron homeostasis-human induced pluripotent stem cell (hiPSC) as a drug screening platform for FRDA

Human frataxin, the Friedreich ataxia deficient protein, interacts with mitochondrial respiratory chain

Friedreich ataxia (FRDA) is a rare, inherited neurodegenerative disease caused by an expanded GAA repeat in the first intron of the FXN gene, leading to transcriptional silencing and reduced expression of frataxin. Frataxin participates in the mitochondrial assembly of FeS clusters, redox cofactors of the respiratory complexes I, II and III. To date it is still unclear how frataxin deficiency culminates in the decrease of bioenergetics efficiency in FRDA patients' cells. We previously demonstrated that in healthy cells frataxin is closely attached to the mitochondrial cristae, which contain both the FeS cluster assembly machinery and the respiratory chain complexes, whereas in FRDA patients' cells with impaired respiration the residual frataxin is largely displaced in the matrix. To gain novel insights into the function of frataxin in the mitochondrial pathophysiology, and in the upstream metabolic defects leading to FRDA disease onset and progression, here we explored the potential interaction of frataxin with the FeS cluster-containing respiratory complexes I, II and III. Using healthy cells and different FRDA cellular models we found that frataxin interacts with these three respiratory complexes. Furthermore, by EPR spectroscopy, we observed that in mitochondria from FRDA patients' cells the decreased level of frataxin specifically affects the FeS cluster content of complex I. Remarkably, we also found that the frataxin-like protein Nqo15 from T. thermophilus complex I ameliorates the mitochondrial respiratory phenotype when expressed in FRDA patient's cells. Our data point to a structural and functional interaction of frataxin with complex I and open a perspective to explore therapeutic rationales for FRDA targeted to this respiratory complex.

Patient-derived iPSC models of Friedreich ataxia: a new frontier for understanding disease mechanisms and therapeutic application

Friedreich ataxia (FRDA) is a rare genetic multisystem disorder caused by a pathological GAA trinucleotide repeat expansion in the FXN gene. The numerous drawbacks of historical cellular and rodent models of FRDA have caused difficulty in performing effective mechanistic and translational studies to investigate the disease. The recent discovery and subsequent development of induced pluripotent stem cell (iPSC) technology provides an exciting platform to enable enhanced disease modelling for studies of rare genetic diseases. Utilising iPSCs, researchers have created phenotypically relevant and previously inaccessible cellular models of FRDA. These models enable studies of the molecular mechanisms underlying GAA-induced pathology, as well as providing an exciting tool for the screening and testing of novel disease-modifying therapies. This review explores how the use of iPSCs to study FRDA has developed over the past decade, as well as discussing the enormous therapeutic potentials of iPSC-derived models, their current limitations and their future direction within the field of FRDA research.

Frataxin deficiency alters gene expression in Friedreich ataxia derived IPSC-neurons and cardiomyocytes

BACKGROUND

Friedreich's ataxia (FRDA) is an autosomal recessive disease, whereby homozygous inheritance of an expanded GAA trinucleotide repeat expansion in the first intron of the FXN gene leads to transcriptional repression of the encoded protein frataxin. FRDA is a progressive neurodegenerative disorder, but the primary cause of death is heart disease which occurs in 60% of the patients. Several functions of frataxin have been proposed, but none of them fully explain why its deficiency causes the FRDA phenotypes nor why the most affected cell types are neurons and cardiomyocytes.

METHODS

To investigate, we generated iPSC-derived neurons (iNs) and cardiomyocytes (iCMs) from an FRDA patient and upregulated FXN expression via lentivirus without altering genomic GAA repeats at the FXN locus.

RESULTS

RNA-seq and differential gene expression enrichment analyses demonstrated that frataxin deficiency affected the expression of glycolytic pathway genes in neurons and extracellular matrix pathway genes in cardiomyocytes. Genes in these pathways were differentially expressed when compared to a control and restored to control levels when FRDA cells were supplemented with frataxin.

CONCLUSIONS

These results offer novel insight into specific roles of frataxin deficiency pathogenesis in neurons and cardiomyocytes.

Recent Advances in Modeling Mitochondrial Cardiomyopathy Using Human Induced Pluripotent Stem Cells

Around one third of patients with mitochondrial disorders develop a kind of cardiomyopathy. In these cases, severity is quite variable ranging from asymptomatic status to severe manifestations including heart failure, arrhythmias, and sudden cardiac death. ATP is primarily generated in the mitochondrial respiratory chain via oxidative phosphorylation by utilizing fatty acids and carbohydrates. Genes in both the nuclear and the mitochondrial DNA encode components of this metabolic route and, although mutations in these genes are extremely rare, the risk to develop cardiac symptoms is significantly higher in this patient cohort. Additionally, infants with cardiovascular compromise in mitochondrial deficiency display a worse late survival compared to patients without cardiac symptoms. At this point, the mechanisms behind cardiac disease progression related to mitochondrial gene mutations are poorly understood and current therapies are unable to substantially restore the cardiac performance and to reduce the disease burden. Therefore, new strategies are needed to uncover the pathophysiological mechanisms and to identify new therapeutic options for mitochondrial cardiomyopathies. Here, human induced pluripotent stem cell (iPSC) technology has emerged to provide a suitable patient-specific model system by recapitulating major characteristics of the disease in vitro, as well as to offer a powerful platform for pre-clinical drug development and for the testing of novel therapeutic options. In the present review, we summarize recent advances in iPSC-based disease modeling of mitochondrial cardiomyopathies and explore the patho-mechanistic insights as well as new therapeutic approaches that were uncovered with this experimental platform. Further, we discuss the challenges and limitations of this technology and provide an overview of the latest techniques to promote metabolic and functional maturation of iPSC-derived cardiomyocytes that might be necessary for modeling of mitochondrial disorders.

Cellular pathophysiology of Friedreich's ataxia cardiomyopathy

Friedreich's ataxia (FRDA) is a hereditary neuromuscular disorder. Cardiomyopathy is the leading cause of premature death in FRDA. FRDA cardiomyopathy is a complex and progressive disease with no cure or treatment to slow its progression. At the cellular level, cardiomyocyte hypertrophy, apoptosis and fibrosis contribute to the cardiac pathology. However, the heart is composed of multiple cell types and several clinical studies have reported the involvement of cardiac non-myocytes such as vascular cells, autonomic neurons, and inflammatory cells in the pathogenesis of FRDA cardiomyopathy. In fact, several of the cardiac pathologies associated with FRDA including cardiomyocyte necrosis, fibrosis, and arrhythmia, could be contributed to by a diseased vasculature and autonomic dysfunction. Here, we review available evidence regarding the current understanding of cellular mechanisms for, and the involvement of, cardiac non-myocytes in the pathogenesis of FRDA cardiomyopathy.

Molecular approaches for the treatment and prevention of Friedreich's ataxia

Friedreich's ataxia (FRDA) is caused by an intronic guanine-adenine-adenine (GAA) trinucleotide expansion in the gene encoding the frataxin protein (FXN). This triggers the transcriptional silencing of the fratxin gene (FXN) and subsequent FXN deficiency in affected cells, which accounts for the multisystemic symptoms of this condition. Current management strategies aim for symptomatic relief and no treatments can prevent disease onset or progression. Thus, research efforts have focused on targeting the molecular pathways that silence FXN and downstream pathological processes. However, progression of potential therapies into clinical use has been hindered by inconclusive clinical trials because of the small patient sample size associated with the low prevalence of this condition. Here, we discuss various molecular approaches and explore their therapeutic potential to alter the course of this progressive condition.

Modeling Secondary Iron Overload Cardiomyopathy with Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes

Excessive iron accumulation in the heart causes iron overload cardiomyopathy (IOC), which initially presents as diastolic dysfunction and arrhythmia but progresses to systolic dysfunction and end-stage heart failure when left untreated. However, the mechanisms of iron-related cardiac injury and how iron accumulates in human cardiomyocytes are not well understood. Herein, using human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs), we model IOC and screen for drugs to rescue the iron overload phenotypes. Human iPSC-CMs under excess iron exposure recapitulate early-stage IOC, including oxidative stress, arrhythmia, and contractile dysfunction. We find that iron-induced changes in calcium kinetics play a critical role in dysregulation of CM functions. We identify that ebselen, a selective divalent metal transporter 1 (DMT1) inhibitor and antioxidant, could prevent the observed iron overload phenotypes, supporting the role of DMT1 in iron uptake into the human myocardium. These results suggest that ebselen may be a potential preventive and therapeutic agent for treating patients with secondary iron overload.

Oxidative stress-dependent frataxin inhibition mediated alcoholic hepatocytotoxicity through ferroptosis

Alcoholic liver disease (ALD) is one of the severe liver diseases, resulting in high morbidity and mortality. However, frataxin, a mitochondrial protein mainly participating in iron homeostasis and oxidative stress, remains uncertain in the pathogenesis of ALD. In the present study, the role of frataxin in ALD was investigated. Ethanol (100 mM) decreased frataxin expression at 48 and 72 h in HepG2. Dramatically, in HepG2 overexpressing cytochrome P450 2E1 (HepG2CYP2E1+/+), frataxin level was down-regulated with ethanol stimulation at 12 h. Moreover, chronically feeding ethanol to mice via Lieber-DeCarli liquid diet (30 % of total calories) for 15 weeks significantly inhibited frataxin expression. Ferroptosis signature proteins were dysregulated, accompanied by mitochondrial damage of morphology, enhanced malondialdehyde and decreased glutathione in the liver, as well as accumulation of reactive oxygen species and mitochondrial labile iron pool in primary hepatocytes. Notably, proteomics screening of frataxin deficient-HepG2 further suggested frataxin was associated with ferroptosis. Furthermore, the ferroptosis inhibitor ferrostatin-1 blocked the increase of lactate dehydrogenase release by ethanol in HepG2CYP2E1+/+. Most importantly, frataxin deficiency enhanced ferroptosis driven by ethanol via evaluating the levels of lactate dehydrogenase, cell morphological changes, mitochondrial labile iron pool, and lipid peroxidation. Conversely, restoring frataxin alleviated the sensitivity to ferroptosis. In addition, frataxin overexpression mitigated the sensitivity of ethanol-induced ferroptosis in HepG2CYP2E1+/+. Collectively, our study revealed that frataxin-mediated ferroptosis contributed to ALD, highlighting a potential therapeutic strategy for ALD.

Human pluripotent stem cell-derived cardiomyocytes for studying energy metabolism

Cardiomyocyte energy metabolism is altered in heart failure, and primary defects of metabolic pathways can cause heart failure. Studying cardiac energetics in rodent models has principal shortcomings, raising the question to which extent human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CM) can provide an alternative. As metabolic maturation of CM occurs mostly after birth during developmental hypertrophy, the immaturity of hiPSC-CM is an important limitation. Here we shortly review the physiological drivers of metabolic maturation and concentrate on methods to mature hiPSC-CM with the goal to benchmark the metabolic state of hiPSC-CM against in vivo data and to see how far known abnormalities in inherited metabolic disorders can be modeled in hiPSC-CM. The current data indicate that hiPSC-CM, despite their immature, approximately mid-fetal state of energy metabolism, faithfully recapitulate some basic metabolic disease mechanisms. Efforts to improve their metabolic maturity are underway and shall improve the validity of this model.

Modelling inherited cardiac disease using human induced pluripotent stem cell-derived cardiomyocytes: progress, pitfalls, and potential

In the past few years, the use of specific cell types derived from induced pluripotent stem cells (iPSCs) has developed into a powerful approach to investigate the cellular pathophysiology of numerous diseases. Despite advances in therapy, heart disease continues to be one of the leading causes of death in the developed world. A major difficulty in unravelling the underlying cellular processes of heart disease is the extremely limited availability of viable human cardiac cells reflecting the pathological phenotype of the disease at various stages. Thus, the development of methods for directed differentiation of iPSCs to cardiomyocytes (iPSC-CMs) has provided an intriguing option for the generation of patient-specific cardiac cells. In this review, a comprehensive overview of the currently published iPSC-CM models for hereditary heart disease is compiled and analysed. Besides the major findings of individual studies, detailed methodological information on iPSC generation, iPSC-CM differentiation, characterization, and maturation is included. Both, current advances in the field and challenges yet to overcome emphasize the potential of using patient-derived cell models to mimic genetic cardiac diseases.

Excision of the expanded GAA repeats corrects cardiomyopathy phenotypes of iPSC-derived Friedreich's ataxia cardiomyocytes

Friedreich's ataxia is caused by large homozygous, intronic expansions of GAA repeats in the frataxin (FXN) gene, resulting in severe downregulation of its expression. Pathogenic repeats are located in intron one, hence patients express unaffected FXN protein, albeit in low quantities. Although FRDA symptoms typically afflict the nervous system, hypertrophic cardiomyopathy is the predominant cause of death. Our studies were conducted using cardiomyocytes differentiated from induced pluripotent stem cells derived from control individuals, FRDA patients, and isogenic cells corrected by zinc finger nucleases-mediated excision of pathogenic expanded GAA repeats. This correction of the FXN gene removed the primary trigger of the transcription defect, upregulated frataxin expression, reduced pathological lipid accumulation observed in patient cardiomyocytes, and reversed gene expression signatures of FRDA cardiomyocytes. Transcriptome analyses revealed hypertrophy-specific expression signatures unique to FRDA cardiomyocytes, and emphasized similarities between unaffected and ZFN-corrected FRDA cardiomyocytes. Thus, the iPSC-derived FRDA cardiomyocytes exhibit various molecular defects characteristic for cellular models of cardiomyopathy that can be corrected by genome editing of the expanded GAA repeats. These results underscore the utility of genome editing in generating isogenic cellular models of FRDA and the potential of this approach as a future therapy for this disease.

Correlation between frataxin expression and contractility revealed by in vitro Friedreich's ataxia cardiac tissue models engineered from human pluripotent stem cells

BACKGROUND

Friedreich's ataxia (FRDA) is an autosomal recessive disease caused by a non-coding mutation in the first intron of the frataxin (FXN) gene that suppresses its expression. Compensatory hypertrophic cardiomyopathy, dilated cardiomyopathy, and conduction system abnormalities in FRDA lead to cardiomyocyte (CM) death and fibrosis, consequently resulting in heart failure and arrhythmias. Murine models have been developed to study disease pathology in the past two decades; however, differences between human and mouse physiology and metabolism have limited the relevance of animal studies in cardiac disease conditions. To bridge this gap, we aimed to generate species-specific, functional in vitro experimental models of FRDA using 2-dimensional (2D) and 3-dimensional (3D) engineered cardiac tissues from FXN-deficient human pluripotent stem cell-derived ventricular cardiomyocytes (hPSC-hvCMs) and to compare their contractile and electrophysiological properties with healthy tissue constructs.

METHODS

Healthy control and FRDA patient-specific hPSC-hvCMs were derived by directed differentiation using a small molecule-based protocol reported previously. We engineered the hvCMs into our established human ventricular cardiac tissue strip (hvCTS) and human ventricular cardiac anisotropic sheet (hvCAS) models, and functional assays were performed on days 7-17 post-tissue fabrication to assess the electrophysiology and contractility of FRDA patient-derived and FXN-knockdown engineered tissues, in comparison with healthy controls. To further validate the disease model, forced expression of FXN was induced in FXN-deficient tissues to test if disease phenotypes could be rescued.

RESULTS

Here, we report for the first time the generation of human engineered tissue models of FRDA cardiomyopathy from hPSCs: FXN-deficient hvCTS displayed attenuated developed forces (by 70-80%) compared to healthy controls. High-resolution optical mapping of hvCAS with reduced FXN expression also revealed electrophysiological defects consistent with clinical observations, including action potential duration prolongation and maximum capture frequency reduction. Interestingly, a clear positive correlation between FXN expression and contractility was observed (ρ > 0.9), and restoration of FXN protein levels by lentiviral transduction rescued contractility defects in FXN-deficient hvCTS.

CONCLUSIONS

We conclude that human-based in vitro cardiac tissue models of FRDA provide a translational, disease-relevant biomimetic platform for the evaluation of novel therapeutics and to provide insight into FRDA disease progression.

The Role of Iron in Friedreich's Ataxia: Insights From Studies in Human Tissues and Cellular and Animal Models

Friedreich’s ataxia (FRDA) is a rare early-onset degenerative disease that affects both the central and peripheral nervous systems, and other extraneural tissues, mainly the heart and endocrine pancreas. This disorder progresses as a mixed sensory and cerebellar ataxia, primarily disturbing the proprioceptive pathways in the spinal cord, peripheral nerves and nuclei of the cerebellum. FRDA is an inherited disease with an autosomal recessive pattern caused by an insufficient amount of the nuclear-encoded mitochondrial protein frataxin, which is an essential and highly evolutionary conserved protein whose deficit results in iron metabolism dysregulation and mitochondrial dysfunction. The first experimental evidence connecting frataxin with iron homeostasis came from Saccharomyces cerevisiae; iron accumulates in the mitochondria of yeast with deletion of the frataxin ortholog gene. This finding was soon linked to previous observations of iron deposits in the hearts of FRDA patients and was later reported in animal models of the disease. Despite advances made in the understanding of FRDA pathophysiology, the role of iron in this disease has not yet been completely clarified. Some of the questions still unresolved include the molecular mechanisms responsible for the iron accumulation and iron-mediated toxicity. Here, we review the contribution of the cellular and animal models of FRDA and relevance of the studies using FRDA patient samples to gain knowledge about these issues. Mechanisms of mitochondrial iron overload are discussed considering the potential roles of frataxin in the major mitochondrial metabolic pathways that use iron. We also analyzed the effect of iron toxicity on neuronal degeneration in FRDA by reactive oxygen species (ROS)-dependent and ROS-independent mechanisms. Finally, therapeutic strategies based on the control of iron toxicity are considered.

Progress in understanding Friedreich's ataxia using human induced pluripotent stem cells

Introduction

Friedreich's ataxia (FRDA) is an autosomal recessive multisystem disease mainly affecting the peripheral and central nervous systems, and heart. FRDA is caused by a GAA repeat expansion in the first intron of the frataxin (FXN) gene, that leads to reduced expression of FXN mRNA and frataxin protein. Neuronal and cardiac cells are primary targets of frataxin deficiency and generating models via differentiation of induced pluripotent stem cells (iPSCs) into these cell types is essential for progress towards developing therapies for FRDA.

Areas covered

This review is focused on modeling FRDA using human iPSCs and various iPSC-differentiated cell types. We emphasized the importance of patient and corrected isogenic cell line pairs to minimize effects caused by biological variability between individuals.

Expert opinion

The versatility of iPSC-derived cellular models of FRDA is advantageous for developing new therapeutic strategies, and rigorous testing in such models will be critical for approval of the first treatment for FRDA. Creating a well-characterized and diverse set of iPSC lines, including appropriate isogenic controls, will facilitate achieving this goal. Also, improvement of differentiation protocols, especially towards proprioceptive sensory neurons and organoid generation, is necessary to utilize the full potential of iPSC technology in the drug discovery process.

Cardiomyopathy phenotypes in human-induced pluripotent stem cell-derived cardiomyocytes-a systematic review

Human-induced pluripotent stem cells (hiPSC) can be differentiated to cardiomyocytes at high efficiency and are increasingly used to study cardiac disease in a human context. This review evaluated 38 studies on hypertrophic (HCM) and dilated cardiomyopathy (DCM) of different genetic causes asking to which extent published data allow the definition of an in vitro HCM/DCM hiPSC-CM phenotype. The data are put in context with the prevailing hypotheses on HCM/DCM dysfunction and pathophysiology. Relatively consistent findings in HCM not reported in DCM were larger cell size (156 ± 85%, n = 15), more nuclear localization of nuclear factor of activated T cells (NFAT; 175 ± 65%, n = 3), and higher β-myosin heavy chain gene expression levels (500 ± 547%, n = 8) than respective controls. Conversely, DCM lines showed consistently less force development than controls (47 ± 23%, n = 9), while HCM forces scattered without clear trend. Both HCM and DCM lines often showed sarcomere disorganization, higher NPPA/NPPB expression levels, and arrhythmic beating behaviour. The data have to be taken with the caveat that reporting frequencies of the various parameters (e.g. cell size, NFAT expression) differ widely between HCM and DCM lines, in which data scatter is large and that only 9/38 studies used isogenic controls. Taken together, the current data provide interesting suggestions for disease-specific phenotypes in HCM/DCM hiPSC-CM but indicate that the field is still in its early days. Systematic, quantitative comparisons and robust, high content assays are warranted to advance the field.

Coenzyme Q10 supplementation reduces oxidative stress and decreases antioxidant enzyme activity in children with autism spectrum disorders

Antioxidants and oxidative stress can participate in pathobiochemical mechanisms of autism spectrum disorders (ASDs). The aim was to identify the effects of early CoQ₁₀ supplementation on oxidative stress in children with ASDs. Ninety children with ASDs were included in this study, based on DSM-IV criteria and using Childhood Autism Rating Scale (CARS) scores. Concentrations of CoQ₁₀, MDA, total antioxidant status (TAS) assay, and antioxidant enzymes (superoxide dismutase or SOD and glutathione peroxidase or GPx) activity were determined in serum before and after 100 days of supportive therapy with CoQ₁₀ at daily doses of 30 and 60 mg. Data on children's behavior were collected from parents and babysitters. CoQ₁₀ supportive therapy was determined after three months with daily dose 2 ͯ 30 mg improved oxidative stress in the children with ASDs. A relation was seen between serum MDA (r² = 0.668) and TAS (r² = 0.007), and antioxidant enzymes (SOD [r² = 0.01] and GPx [r² = 0.001]) activity and CARS score. Based on the results, high doses of CoQ₁₀ can improve gastrointestinal problems (P = 0.004) and sleep disorders (P = 0.005) in children with ASDs with an increase in the CoQ₁₀ of the serum. We concluded that the serum concentration of CoQ₁₀ and oxidative stress could be used as relevant biomarkers in helping the improvement of ASDs.

The transcriptional regulator CCCTC-binding factor limits oxidative stress in endothelial cells

The CCCTC-binding factor (CTCF) is a versatile transcriptional regulator required for embryogenesis, but its function in vascular development or in diseases with a vascular component is poorly understood. Here, we found that endothelial Ctcf is essential for mouse vascular development and limits accumulation of reactive oxygen species (ROS). Conditional knockout of Ctcf in endothelial progenitors and their descendants affected embryonic growth, and caused lethality at embryonic day 10.5 because of defective yolk sac and placental vascular development. Analysis of global gene expression revealed Frataxin (Fxn), the gene mutated in Friedreich's ataxia (FRDA), as the most strongly down-regulated gene in Ctcf-deficient placental endothelial cells. Moreover, in vitro reporter assays showed that Ctcf activates the Fxn promoter in endothelial cells. ROS are known to accumulate in the endothelium of FRDA patients. Importantly, Ctcf deficiency induced ROS-mediated DNA damage in endothelial cells in vitro, and in placental endothelium in vivo Taken together, our findings indicate that Ctcf promotes vascular development and limits oxidative stress in endothelial cells. These results reveal a function for Ctcf in vascular development, and suggest a potential mechanism for endothelial dysfunction in FRDA.

Human pluripotent stem cell models of cardiac disease: from mechanisms to therapies

It is now a decade since human induced pluripotent stem cells (hiPSCs) were first described. The reprogramming of adult somatic cells to a pluripotent state has become a robust technology that has revolutionised our ability to study human diseases. Crucially, these cells capture all the genetic aspects of the patient from which they were derived. Combined with advances in generating the different cell types present in the human heart, this has opened up new avenues to study cardiac disease in humans and investigate novel therapeutic approaches to treat these pathologies. Here, we provide an overview of the current state of the field regarding the generation of cardiomyocytes from human pluripotent stem cells and methods to assess them functionally, an essential requirement when investigating disease and therapeutic outcomes. We critically evaluate whether treatments suggested by these in vitro models could be translated to clinical practice. Finally, we consider current shortcomings of these models and propose methods by which they could be further improved.

Modeling Treatment Response for Lamin A/C Related Dilated Cardiomyopathy in Human Induced Pluripotent Stem Cells

BACKGROUND

Precision medicine is an emerging approach to disease treatment and prevention that takes into account individual variability in the environment, lifestyle, and genetic makeup of patients. Patient-specific human induced pluripotent stem cells hold promise to transform precision medicine into real-life clinical practice. Lamin A/C (LMNA)-related cardiomyopathy is the most common inherited cardiomyopathy in which a substantial proportion of mutations in the LMNA gene are of nonsense mutation. PTC124 induces translational read-through over the premature stop codon and restores production of the full-length proteins from the affected genes. In this study we generated human induced pluripotent stem cells-derived cardiomyocytes from patients who harbored different LMNA mutations (nonsense and frameshift) to evaluate the potential therapeutic effects of PTC124 in LMNA-related cardiomyopathy.

METHODS AND RESULTS

We generated human induced pluripotent stem cells lines from 3 patients who carried distinctive mutations (R225X, Q354X, and T518fs) in the LMNA gene. The cardiomyocytes derived from these human induced pluripotent stem cells lines reproduced the pathophysiological hallmarks of LMNA-related cardiomyopathy. Interestingly, PTC124 treatment increased the production of full-length LMNA proteins in only the R225X mutant, not in other mutations. Functional evaluation experiments on the R225X mutant further demonstrated that PTC124 treatment not only reduced nuclear blebbing and electrical stress-induced apoptosis but also improved the excitation-contraction coupling of the affected cardiomyocytes.

CONCLUSIONS

Using cardiomyocytes derived from human induced pluripotent stem cells carrying different LMNA mutations, we demonstrated that the effect of PTC124 is codon selective. A premature stop codon UGA appeared to be most responsive to PTC124 treatment.

Mitochondrial biogenesis and neural differentiation of human iPSC is modulated by idebenone in a developmental stage-dependent manner

Idebenone, the synthetic analog of coenzyme Q10 can improve electron transport in mitochondria. Therefore, it is used in the treatment of Alzheimer’s disease and other cognitive impairments. However, the mechanism of its action on neurodevelopment is still to be elucidated. Here we demonstrate that the cellular response of human induced pluripotent stem cells (hiPSC) to idebenone depends on the stage of neural differentiation. When: neural stem cells (NSC), early neural progenitors (eNP) and advanced neural progenitors (NP) have been studied a significant stimulation of mitochondrial biogenesis was observed only at the eNP stage of development. This coexists with the enhancement of cell viability and increase in total cell number. In addition, we report novel idebenone properties in a possible regulation of neural stem cells fate decision: only eNP stage responded with up-regulation of both neuronal (MAP2), astrocytic (GFAP) markers, while at NSC and NP stages significant down-regulation of MAP2 expression was observed, promoting astrocyte differentiation. Thus, idebenone targets specific stages of hiPSC differentiation and may influence the neural stem cell fate decision.

Friedreich's ataxia induced pluripotent stem cell-derived cardiomyocytes display electrophysiological abnormalities and calcium handling deficiency

We sought to identify the impacts of Friedreich's ataxia (FRDA) on cardiomyocytes. FRDA is an autosomal recessive degenerative condition with neuronal and non-neuronal manifestations, the latter including progressive cardiomyopathy of the left ventricle, the leading cause of death in FRDA. Little is known about the cellular pathogenesis of FRDA in cardiomyocytes. Induced pluripotent stem cells (iPSCs) were derived from three FRDA individuals with characterized GAA repeats. The cells were differentiated into cardiomyocytes to assess phenotypes. FRDA iPSC- cardiomyocytes retained low levels of FRATAXIN (FXN) mRNA and protein. Electrophysiology revealed an increased variation of FRDA- cardiomyocyte beating rates which was prevented by addition of nifedipine, suggestive of a calcium handling deficiency. Finally, calcium imaging was performed and we identified small amplitude, diastolic and systolic calcium transients confirming a deficiency in calcium handling. We defined a robust FRDA cardiac-specific electrophysiological profile in patient-derived iPSCs which could be used for high throughput compound screening. This cell-specific signature will contribute to the identification and screening of novel treatments for this life-threatening disease.

Human Induced Pluripotent Stem Cells as a Platform for Personalized and Precision Cardiovascular Medicine

Human induced pluripotent stem cells (hiPSCs) have revolutionized the field of human disease modeling, with an enormous potential to serve as paradigm shifting platforms for preclinical trials, personalized clinical diagnosis, and drug treatment. In this review, we describe how hiPSCs could transition cardiac healthcare away from simple disease diagnosis to prediction and prevention, bridging the gap between basic and clinical research to bring the best science to every patient.

Using human pluripotent stem cells to study Friedreich ataxia cardiomyopathy

Friedreich ataxia (FRDA) is the most common of the inherited ataxias. It is an autosomal recessive disease characterised by degeneration of peripheral sensory neurons, regions of the central nervous system and cardiomyopathy. FRDA is usually due to homozygosity for trinucleotide GAA repeat expansions found within first intron of the FRATAXIN (FXN) gene, which results in reduced levels of the mitochondrial protein FXN. Reduced FXN protein results in mitochondrial dysfunction and iron accumulation leading to increased oxidative stress and cell death in the nervous system and heart. Yet the precise functions of FXN and the underlying mechanisms leading to disease pathology remain elusive. This is particularly true of the cardiac aspect of FRDA, which remains largely uncharacterized at the cellular level. Here, we summarise current knowledge on experimental models in which to study FRDA cardiomyopathy, with a particular focus on the use of human pluripotent stem cells as a disease model.

Stem cells and exosomes in cardiac repair

Cardiac diseases currently lead in the number of deaths per year, giving rise an interest in transplanting embryonic and adult stem cells as a means to improve damaged tissue from conditions such as myocardial infarction and coronary artery disease. After testing these cells as a treatment option in both animal and human models, it is believed that these cells improve the damaged tissue primarily through the release of autocrine and paracrine factors. Major concerns such as teratoma formation, immune response, difficulty harvesting cells, and limited cell proliferation and differentiation, hinder the routine use of these cells as a treatment option in the clinic. The advent of stem cell-derived exosomes circumvent those concerns, while still providing the growth factors, miRNA, and additional cell protective factors that aid in repairing and regenerating the damaged tissue. These exosomes have been found to be anti-apoptotic, anti-fibrotic, pro-angiogenic, as well as enhance cardiac differentiation, all of which are key to repairing damaged tissue. As such, stem cell derived exosomes are considered to be a potential new and novel approach in the treatment of various cardiac diseases.