Treatment of dilated cardiomyopathy in a mouse model of Friedreich's ataxia using N-acetylcysteine and identification of alterations in microRNA expression that could be involved in its pathogenesis

An RNA-seq study in Friedreich ataxia patients identified hsa-miR-148a-3p as a putative prognostic biomarker of the disease

Friedreich ataxia (FRDA) is a life-threatening hereditary ataxia; its incidence is 1:50,000 individuals in the Caucasian population. A unique therapeutic drug for FRDA, the antioxidant Omaveloxolone, has been recently approved by the US Food and Drug Administration (FDA). FRDA is a multi-systemic neurodegenerative disease; in addition to a progressive neurodegeneration, FRDA is characterized by hypertrophic cardiomyopathy, diabetes mellitus and musculoskeletal deformities. Cardiomyopathy is the predominant cause of premature death. The onset of FRDA typically occurs between the ages of 5 and 15. Given the complexity and heterogeneity of clinical features and the variability of their onset, the identification of biomarkers capable of assessing disease progression and monitoring the efficacy of treatments is essential to facilitate decision making in clinical practice. We conducted an RNA-seq analysis in peripheral blood mononuclear cells from FRDA patients and healthy donors, identifying a signature of small non-coding RNAs (sncRNAs) capable of distinguishing healthy individuals from the majority of FRDA patients. Among the differentially expressed sncRNAs, microRNAs are a class of small non-coding endogenous RNAs that regulate posttranscriptional silencing of target genes. In FRDA plasma samples, hsa-miR-148a-3p resulted significantly upregulated. The analysis of the Receiver Operating Characteristic (ROC) curve, combining the circulating expression levels of hsa-miR-148a-3p and hsa-miR-223-3p (previously identified by our group), revealed an Area Under the Curve (AUC) of 0.86 (95%, Confidence Interval 0.77-0.95; p-value < 0.0001). An in silico prediction analysis indicated that the IL6ST gene, an interesting marker of neuroinflammation in FRDA, is a common target gene of both miRNAs. Our findings support the evaluation of combined expression levels of different circulating miRNAs as potent epi-biomarkers in FRDA. Moreover, we found hsa-miR-148a-3p significantly over-expressed in Intermediate and Late-Onset Friedreich Ataxia patients' group (IOG and LOG, respectively) compared to healthy individuals, indicating it as a putative prognostic biomarker in this pathology.

Butyrate prevents visceral adipose tissue inflammation and metabolic alterations in a Friedreich's ataxia mouse model

Friedreich's ataxia (FA) is a neurodegenerative disease resulting from a mutation in the FXN gene, leading to mitochondrial frataxin deficiency. FA patients exhibit increased visceral adiposity, inflammation, and heightened diabetes risk, negatively affecting prognosis. We investigated visceral white adipose tissue (vWAT) in a murine model (KIKO) to understand its role in FA-related metabolic complications. RNA-seq analysis revealed altered expression of inflammation, angiogenesis, and fibrosis genes. Diabetes-like traits, including larger adipocytes, immune cell infiltration, and increased lactate production, were observed in vWAT. FXN downregulation in cultured adipocytes mirrored vWAT diabetes-like features, showing metabolic shifts toward glycolysis and lactate production. Metagenomic analysis indicated a reduction in fecal butyrate-producing bacteria, known to exert antidiabetic effects. A butyrate-enriched diet restrained vWAT abnormalities and mitigated diabetes features in KIKO mice. Our work emphasizes the role of vWAT in FA-related metabolic issues and suggests butyrate as a safe and promising adjunct for FA management.

Omaveloxolone: an activator of Nrf2 for the treatment of Friedreich ataxia

INTRODUCTION

Friedreich ataxia (FRDA) is a rare autosomal recessive degenerative disorder characterized by ataxia, dysarthria, diabetes, cardiomyopathy, scoliosis, and occasionally vision loss in late-stage disease. The discovery of the abnormal gene in FRDA and its product frataxin has provided insight into the pathophysiology and mechanisms of treatment.

AREAS COVERED

Although the neurologic phenotype of FRDA is well defined, there are currently no established pharmacological treatments. Omaveloxolone, a nuclear factor erythroid 2-related factor 2 (Nrf2) activator, is currently under review by the Food and Drug Administration (FDA) and has the potential to be the first approved treatment for FRDA. In the present report, we have reviewed the basic and clinical literature on Nrf2 deficiency in FRDA, and evidence for the benefit of omaveloxolone.

EXPERT OPINION

The present perspective suggests that omaveloxolone is a rational and efficacious therapy that is possibly disease modifying in treatment of FRDA.

The Role of MicroRNAs in Dilated Cardiomyopathy: New Insights for an Old Entity

Dilated cardiomyopathy (DCM) is a clinical diagnosis characterized by left ventricular or biventricular dilation and systolic dysfunction. In most cases, DCM is progressive, leading to heart failure (HF) and death. This cardiomyopathy has been considered a common and final phenotype of several entities. DCM occurs when cellular pathways fail to maintain the pumping function. The etiology of this disease encompasses several factors, such as ischemia, infection, autoimmunity, drugs or genetic susceptibility. Although the prognosis has improved in the last few years due to red flag clinical follow-up, early familial diagnosis and ongoing optimization of treatment, due to its heterogeneity, there are no targeted therapies available for DCM based on each etiology. Therefore, a better understanding of the mechanisms underlying the pathophysiology of DCM will provide novel therapeutic strategies against this cardiac disease and their different triggers. MicroRNAs (miRNAs) are a group of small noncoding RNAs that play key roles in post-transcriptional gene silencing by targeting mRNAs for translational repression or, to a lesser extent, degradation. A growing number of studies have demonstrated critical functions of miRNAs in cardiovascular diseases (CVDs), including DCM, by regulating mechanisms that contribute to the progression of the disease. Herein, we summarize the role of miRNAs in inflammation, endoplasmic reticulum (ER) stress, oxidative stress, mitochondrial dysfunction, autophagy, cardiomyocyte apoptosis and fibrosis, exclusively in the context of DCM.

NAC alleviative ferroptosis in diabetic nephropathy via maintaining mitochondrial redox homeostasis through activating SIRT3-SOD2/Gpx4 pathway

Diabetic nephropathy (DN) is known as a major microvascular complication in type 1 diabetes. The effect of insulin treatment alone on controlling blood glucose is unsatisfactory. N-acetylcysteine (NAC), a chemical agent with thiol group, is found to confer a protective effect in renal injury. However, whether NAC combined with insulin treatment can further enhance the therapeutic effect in DN remains unclear. Here, we firstly used large mammal beagle as DN model to explore the effect of NAC combined with insulin treatment on DN during 120 d. Our results showed that NAC further alleviated mitochondrial oxidative damage and ferroptosis by enhancing activity of mitochondria GSH and maintaining mitochondrial redox homeostasis in DN. Additionally, the upregulated acetylation level of SOD2 was further abrogated by NAC treatment. In MDCK cells, NAC reduced high glucose (HG)-caused ferroptosis via activating Gpx4 expression. Of note, inhibition of Gpx4 by FIN56 abolished the protective effects of NAC on HG-induced ferroptosis. More importantly, 3-TYP reversed the effect of NAC on the mitochondria ROS under HG treatment, as well as eliminated its following beneficial effects for ferroptosis against HG-stimulated cells. These results reveal that NAC attenuated ferroptosis in DN via maintaining mitochondrial redox homeostasis through activating SIRT3-SOD2-Gpx4 signaling pathway.

Discovery of Therapeutics Targeting Oxidative Stress in Autosomal Recessive Cerebellar Ataxia: A Systematic Review

Autosomal recessive cerebellar ataxias (ARCAs) are a heterogeneous group of rare neurodegenerative inherited disorders. The resulting motor incoordination and progressive functional disabilities lead to reduced lifespan. There is currently no cure for ARCAs, likely attributed to the lack of understanding of the multifaceted roles of antioxidant defense and the underlying mechanisms. This systematic review aims to evaluate the extant literature on the current developments of therapeutic strategies that target oxidative stress for the management of ARCAs. We searched PubMed, Web of Science, and Science Direct Scopus for relevant peer-reviewed articles published from 1 January 2016 onwards. A total of 28 preclinical studies fulfilled the eligibility criteria for inclusion in this systematic review. We first evaluated the altered cellular processes, abnormal signaling cascades, and disrupted protein quality control underlying the pathogenesis of ARCA. We then examined the current potential therapeutic strategies for ARCAs, including aromatic, organic and pharmacological compounds, gene therapy, natural products, and nanotechnology, as well as their associated antioxidant pathways and modes of action. We then discussed their potential as antioxidant therapeutics for ARCAs, with the long-term view toward their possible translation to clinical practice. In conclusion, our current understanding is that these antioxidant therapies show promise in improving or halting the progression of ARCAs. Tailoring the therapies to specific disease stages could greatly facilitate the management of ARCAs.

Hsa-miR223-3p circulating level is upregulated in Friedreich's ataxia and inversely associated with HCLS1 associated protein X-1, HAX-1

Frataxin (FXN) deficiency is responsible for Friedreich's ataxia (FRDA) in which, besides the characteristic features of spinocerebellar ataxia, two thirds of patients develop hypertrophic cardiomyopathy that often progresses to heart failure and premature death. Different mechanisms might underlie FRDA pathogenesis. Among them, the role of miRNAs deserves investigations. We carried out a miRNA PCR-array analysis of plasma samples of early-, intermediate- and late-onset FRDA groups, defining a set of 30 differentially expressed miRNAs. Hsa-miR223-3p is the only miRNA shared between the three patient groups and appears upregulated in all of them. The upregulation of hsa-miR223-3p was further validated in all enrolled patients (n = 37, Fc = +2.3; p < 0.0001). Using a Receiver Operating Characteristic (ROC) curve analysis, we quantified the predictive value of circulating hsa-miR223-3p for FRDA, obtaining an AUC (Area Under the ROC Curve) value of 0.835 (p < 0.0001) for all patients. Interestingly, we found a significant positive correlation between hsa-miR223-3p expression and cardiac parameters in typical FRDA patients (onset < 25 years). Moreover, a significant negative correlation between hsa-miR223-3p expression and HAX-1 (HCLS1 associated protein X-1) at mRNA and protein level was observed in all FRDA patients. In silico analyses suggested HAX-1 as a target gene of hsa-miR223-3p. Accordingly, we report that HAX-1 is negatively regulated by hsa-miR223-3p in cardiomyocytes (AC16) and neurons (SH-SY5Y), which are critically affected cell types in FRDA. This study describes for the first time the association between hsa-miR223-3p and HAX-1 expression in FRDA, thus supporting a potential role of this microRNA as non-invasive epigenetic biomarker for FRDA.

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.

Amniotic fluid microRNA profiles in twin-twin transfusion syndrome with and without severe recipient cardiomyopathy

BACKGROUND

Twin-twin transfusion syndrome presents many challenges for clinicians, and the optimal means of identifying pregnancies that will benefit most from intervention is controversial. There is currently no clinically available biomarker to detect twin-twin transfusion syndrome or to stratify cases based on the risk factors. microRNAs are small RNAs that regulate gene expression and are biomarkers for various disease processes, including adult and pediatric heart failure. To date, no studies have investigated amniotic fluid microRNAs as biomarkers for disease severity, specifically for severe recipient cardiomyopathy in twin-twin transfusion syndrome cases.

OBJECTIVE

This study aimed to assess whether amniotic fluid microRNAs could be useful as biomarkers to identify pregnancies at greatest risk for severe recipient cardiomyopathy associated with twin-twin transfusion syndrome.

STUDY DESIGN

Amniotic fluid was collected at the time of amnioreduction or selective fetoscopic laser photocoagulation from monochorionic diamniotic twin pregnancies with twin-twin transfusion syndrome at any stage. Fetal echocardiography was performed on all twins before the procedure, and severe cardiomyopathy was defined as a right ventricular myocardial performance index of the recipient fetus of >4 Z-scores. microRNA was extracted from the amniotic fluid samples and analyzed using an array panel assessing 379 microRNAs (TaqMan Open Array, ThermoFisher). Student t tests were performed to determine significant differences in microRNA expression between pregnancies with severe recipient cardiomyopathy and those with preserved cardiac function. A stringent q value of <.0025 was used to determine differential microRNA expression. Random forest plots identified the top 3 microRNAs that separated the 2 groups, and hierarchical cluster analysis was used to determine if these microRNAs properly segregated the samples according to their clinical groups.

RESULTS

A total of 14 amniotic fluid samples from pregnancies with twin-twin transfusion syndrome with severe cardiomyopathy were compared with samples from 12 twin-twin transfusion syndrome control cases with preserved cardiac function. A total of 110 microRNAs were identified in the amniotic fluid samples. Twenty microRNAs were differentially expressed, and the top 3 differentiating microRNAs were hsa-miR-200c-3p, hsa-miR-17-5p, and hsa-miR-539-5p. Hierarchical cluster analysis based on these top 3 microRNAs showed a strong ability to differentiate severe cardiomyopathy cases from controls. The top 3 microRNAs were used to investigate the sensitivity and specificity of these microRNAs to differentiate between the 2 groups with a receiver operating characteristic curve demonstrating sensitivity and specificity of 80.8%. All 20 differentially expressed microRNAs were down-regulated in the group with severe cardiomyopathy.

CONCLUSION

Amniotic fluid microRNAs demonstrated differential expression between twin-twin transfusion syndrome recipient fetuses with severe cardiomyopathy and those without and have the potential to be important biomarkers of disease severity in this population.

Omaveloxolone: potential new agent for Friedreich ataxia

Friedreich ataxia is a slowly progressive neurodegenerative disorder leading to ataxia, dyscoordination, dysarthria and in many individuals vision and hearing loss. It is associated with cardiomyopathy, the leading cause of death in Friedreich ataxia (FRDA), diabetes and scoliosis. There are no approved therapies, but elucidation of the pathophysiology of FRDA suggest that agents that increase the activity of the transcription factor Nrf2 may provide a mechanism for ameliorating disease progression or severity. In this work, we review the evidence for use of omaveloxolone in FRDA from recent clinical trials. Though not at present approved for any indication, the present data suggest that this agent acting though increases in Nrf2 activity may provide a novel therapy for FRDA.

Thioredoxin and Glutaredoxin Systems as Potential Targets for the Development of New Treatments in Friedreich's Ataxia

The thioredoxin family consists of a small group of redox proteins present in all organisms and composed of thioredoxins (TRXs), glutaredoxins (GLRXs) and peroxiredoxins (PRDXs) which are found in the extracellular fluid, the cytoplasm, the mitochondria and in the nucleus with functions that include antioxidation, signaling and transcriptional control, among others. The importance of thioredoxin family proteins in neurodegenerative diseases is gaining relevance because some of these proteins have demonstrated an important role in the central nervous system by mediating neuroprotection against oxidative stress, contributing to mitochondrial function and regulating gene expression. Specifically, in the context of Friedreich’s ataxia (FRDA), thioredoxin family proteins may have a special role in the regulation of Nrf2 expression and function, in Fe-S cluster metabolism, controlling the expression of genes located at the iron-response element (IRE) and probably regulating ferroptosis. Therefore, comprehension of the mechanisms that closely link thioredoxin family proteins with cellular processes affected in FRDA will serve as a cornerstone to design improved therapeutic strategies.

Molecular Defects in Friedreich's Ataxia: Convergence of Oxidative Stress and Cytoskeletal Abnormalities

Friedreich’s ataxia (FRDA) is a multi-faceted disease characterized by progressive sensory–motor loss, neurodegeneration, brain iron accumulation, and eventual death by hypertrophic cardiomyopathy. FRDA follows loss of frataxin (FXN), a mitochondrial chaperone protein required for incorporation of iron into iron–sulfur cluster and heme precursors. After the discovery of the molecular basis of FRDA in 1996, over two decades of research have been dedicated to understanding the temporal manifestations of disease both at the whole body and molecular level. Early research indicated strong cellular iron dysregulation in both human and yeast models followed by onset of oxidative stress. Since then, the pathophysiology due to dysregulation of intracellular iron chaperoning has become central in FRDA relative to antioxidant defense and run-down in energy metabolism. At the same time, limited consideration has been given to changes in cytoskeletal organization, which was one of the first molecular defects noted. These alterations include both post-translational oxidative glutathionylation of actin monomers and differential DNA processing of a cytoskeletal regulator PIP5K1β. Currently unknown in respect to FRDA but well understood in the context of FXN-deficient cell physiology is the resulting impact on the cytoskeleton; this disassembly of actin filaments has a particularly profound effect on cell–cell junctions characteristic of barrier cells. With respect to a neurodegenerative disorder such as FRDA, this cytoskeletal and tight junction breakdown in the brain microvascular endothelial cells of the blood–brain barrier is likely a component of disease etiology. This review serves to outline a brief history of this research and hones in on pathway dysregulation downstream of iron-related pathology in FRDA related to actin dynamics. The review presented here was not written with the intent of being exhaustive, but to instead urge the reader to consider the essentiality of the cytoskeleton and appreciate the limited knowledge on FRDA-related cytoskeletal dysfunction as a result of oxidative stress. The review examines previous hypotheses of neurodegeneration with brain iron accumulation (NBIA) in FRDA with a specific biochemical focus.

Antioxidant defense mechanisms and its dysfunctional regulation in the mitochondrial disease, Friedreich's ataxia

Redox stress is associated with the pathogenesis of a wide variety of disease states. This can be amplified potentially through redox active iron deposits in oxidatively active organelles such as the mitochondrion. There are a number of disease states, including Friedreich's ataxia (FA) and sideroblastic anemia, where iron metabolism is dysregulated and leads to mitochondrial iron accumulation. Considering FA, which is due to the decreased expression of the mitochondrial protein, frataxin, this iron accumulation does not occur within protective storage proteins such as mitochondrial ferritin. Instead, it forms unbound biomineral aggregates composed of high spin iron(III), phosphorous and sulfur, which probably contributes to the observed redox stress. There is also a dysregulated response to the ensuing redox assault, as the master regulator of oxidative stress, nuclear factor erythroid 2-related factor-2 (Nrf2), demonstrates marked down-regulation. The dysfunctional response of Nrf2 in FA is due to multiple mechanisms including: (1) up-regulation of Keap1 that is involved in Nrf2 degradation; (2) activation of the nuclear Nrf2 export/degradation machinery via glycogen synthase kinase-3β (Gsk3β) signaling; and (3) inhibited nuclear translocation of Nrf2. More recently, increased microRNA (miRNA) 144 expression has been demonstrated to down-regulate Nrf2 in several disease states, including an animal model of FA. Other miRNAs have also demonstrated to be dysregulated upon frataxin depletion in vivo in humans and animal models of FA. Collectively, frataxin depletion results in multiple, complex responses that lead to detrimental redox effects that could contribute to the mechanisms involved in the pathogenesis of FA.

Parkin overexpression reduces inflammation-mediated cardiomyocyte apoptosis through activating Nrf2/ARE signaling pathway

Inflammation has been acknowledged as one of the pathological alterations in various cardiovascular disorders. Parkin has been found to be associated with mitochondrial protection. In the present study, we explored the influence of Parkin overexpression on cardiomyocyte induced by LPS-mediated inflammation response. Our results demonstrated that cardiomyocyte viability was reduced and apoptotic rate was increased upon LPS treatment, an effect that may be caused by cardiomyocyte oxidative stress. At the molecular levels, LPS treatment promoted ROS production, a result that was followed by a drop in the levels of anti-oxidants. Interestingly, Parkin overexpression significantly promoted cardiomyocyte survival and this cardioprotective was attributable to the anti-oxidative property. Parkin overexpression enhanced the expression of anti-oxidative factors such as GSH, SOD and GPX, resulting into depressed ROS production. Further, we found that Parkin modulated cellular anti-oxidative capacity through the Nrf2/ARE signaling pathway. This finding demonstrates that oxidative stress could be considered as the core of inflammation response. Further, therapeutic approaches targeting Parkin would improve cardiomyocyte anti-oxidative capacity through activating Nrf2/ARE signaling pathway.