Decreased antioxidant enzyme activity and increased mitochondrial DNA damage in cellular models of Machado-Joseph disease

The Role of NRF2 in Trinucleotide Repeat Expansion Disorders

Trinucleotide repeat expansion disorders, a diverse group of neurodegenerative diseases, are caused by abnormal expansions within specific genes. These expansions trigger a cascade of cellular damage, including protein aggregation and abnormal RNA binding. A key contributor to this damage is oxidative stress, an imbalance of reactive oxygen species that harms cellular components. This review explores the interplay between oxidative stress and the NRF2 pathway in these disorders. NRF2 acts as the master regulator of the cellular antioxidant response, orchestrating the expression of enzymes that combat oxidative stress. Trinucleotide repeat expansion disorders often exhibit impaired NRF2 signaling, resulting in inadequate responses to excessive ROS production. NRF2 activation has been shown to upregulate antioxidative gene expression, effectively alleviating oxidative stress damage. NRF2 activators, such as omaveloxolone, vatiquinone, curcumin, sulforaphane, dimethyl fumarate, and resveratrol, demonstrate neuroprotective effects by reducing oxidative stress in experimental cell and animal models of these diseases. However, translating these findings into successful clinical applications requires further research. In this article, we review the literature supporting the role of NRF2 in the pathogenesis of these diseases and the potential therapeutics of NRF2 activators.

Polyglutamine disorders: Pathogenesis and potential drug interventions

Polyglutamine/poly(Q) diseases are a group nine hereditary neurodegenerative disorders caused due to abnormally expanded stretches of CAG trinucleotide in functionally distinct genes. All human poly(Q) diseases are characterized by the formation of microscopically discernable poly(Q) positive aggregates, the inclusion bodies. These toxic inclusion bodies are responsible for the impairment of several cellular pathways such as autophagy, transcription, cell death, etc., that culminate in disease manifestation. Although, these diseases remain largely without treatment, extensive research has generated mounting evidences that various events of poly(Q) pathogenesis can be developed as potential drug targets. The present review article briefly discusses the key events of disease pathogenesis, model system-based investigations that support the development of effective therapeutic interventions against pathogenesis of human poly(Q) disorders, and a comprehensive list of pharmacological and bioactive compounds that have been experimentally shown to alleviate poly(Q)-mediated neurotoxicity. Interestingly, due to the common cause of pathogenesis, all poly(Q) diseases share etiology, thus, findings from one disease can be potentially extrapolated to other poly(Q) diseases as well.

Metabolic Syndrome: A Narrative Review from the Oxidative Stress to the Management of Related Diseases

Metabolic syndrome (MS) is a growing disorder affecting thousands of people worldwide, especially in industrialised countries, increasing mortality. Oxidative stress, hyperglycaemia, insulin resistance, inflammation, dysbiosis, abdominal obesity, atherogenic dyslipidaemia and hypertension are important factors linked to MS clusters of different pathologies, such as diabesity, cardiovascular diseases and neurological disorders. All biochemical changes observed in MS, such as dysregulation in the glucose and lipid metabolism, immune response, endothelial cell function and intestinal microbiota, promote pathological bridges between metabolic syndrome, diabesity and cardiovascular and neurodegenerative disorders. This review aims to summarise metabolic syndrome's involvement in diabesity and highlight the link between MS and cardiovascular and neurological diseases. A better understanding of MS could promote a novel strategic approach to reduce MS comorbidities.

From reactive species to disease development: Effect of oxidants and antioxidants on the cellular biomarkers

The influence of modern lifestyle, diet, exposure to chemicals such as phytosanitary substances, together with sedentary lifestyles and lack of exercise play an important role in inducing reactive stress (RS) and disease. The imbalance in the production and scavenging of free radicals and the induction of RS (oxidative, nitrosative, and halogenative) plays an essential role in the etiology of various chronic pathologies, such as cardiovascular diseases, diabetes, neurodegenerative diseases, and cancer. The implication of free radicals and reactive species injury in metabolic disturbances and the onset of many diseases have been accumulating for several decades, and are now accepted as a major cause of many chronic diseases. Exposure to elevated levels of free radicals can cause molecular structural impact on proteins, lipids, and DNA, as well as functional alteration of enzyme homeostasis, leading to aberrations in gene expression. Endogenous depletion of antioxidant enzymes can be mitigated using exogenous antioxidants. The current interest in the use of exogenous antioxidants as adjunctive agents for the treatment of human diseases allows a better understanding of these diseases, facilitating the development of new therapeutic agents with antioxidant activity to improve the treatment of various diseases. Here we examine the role that RS play in the initiation of disease and in the reactivity of free radicals and RS in organic and inorganic cellular components.

The Key Role of Astrocytes in Amyotrophic Lateral Sclerosis and Their Commitment to Glutamate Excitotoxicity

In the last two decades, there has been increasing evidence supporting non-neuronal cells as active contributors to neurodegenerative disorders. Among glial cells, astrocytes play a pivotal role in driving amyotrophic lateral sclerosis (ALS) progression, leading the scientific community to focus on the "astrocytic signature" in ALS. Here, we summarized the main pathological mechanisms characterizing astrocyte contribution to MN damage and ALS progression, such as neuroinflammation, mitochondrial dysfunction, oxidative stress, energy metabolism impairment, miRNAs and extracellular vesicles contribution, autophagy dysfunction, protein misfolding, and altered neurotrophic factor release. Since glutamate excitotoxicity is one of the most relevant ALS features, we focused on the specific contribution of ALS astrocytes in this aspect, highlighting the known or potential molecular mechanisms by which astrocytes participate in increasing the extracellular glutamate level in ALS and, conversely, undergo the toxic effect of the excessive glutamate. In this scenario, astrocytes can behave as "producers" and "targets" of the high extracellular glutamate levels, going through changes that can affect themselves and, in turn, the neuronal and non-neuronal surrounding cells, thus actively impacting the ALS course. Moreover, this review aims to point out knowledge gaps that deserve further investigation.

Mitochondrial Dysfunction and Decreased Cytochrome c in Cell and Animal Models of Machado-Joseph Disease

Mitochondrial dysfunction has been described in many neurodegenerative disorders; however, there is less information regarding mitochondrial deficits in Machado-Joseph disease (MJD), a polyglutamine (polyQ) disorder caused by CAG repeat expansion in the ATXN3 gene. In the present study, we characterized the changes in mitochondrial function and biogenesis markers in two MJD models, CMVMJD135 (MJD135) transgenic mice at a fully established phenotype stage and tetracycline-regulated PC6-3 Q108 cell line expressing mutant ataxin-3 (mATXN3). We detected mATXN3 in the mitochondrial fractions of PC6-3 Q108 cells, suggesting the interaction of expanded ATXN3 with the organelle. Interestingly, in both the cerebella of the MJD135 mouse model and in PC6-3 Q108 cells, we found decreased mitochondrial respiration, ATP production and mitochondrial membrane potential, strongly suggesting mitochondrial dysfunction in MJD. Also, in PC6-3 Q108 cells, an additional enhanced glycolytic flux was observed. Supporting the functional deficits observed in MJD mitochondria, MJD135 mouse cerebellum and PC6-3 Q108 cells showed reduced cytochrome c mRNA and protein levels. Overall, our findings show compromised mitochondrial function associated with decreased cytochrome c levels in both cell and animal models of MJD.

Telomerase reverse transcriptase and neurodegenerative diseases

Neurodegenerative diseases (NDs) are chronic conditions that result in progressive damage to the nervous system, including Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), and Amyotrophic lateral sclerosis (ALS). Age is a major risk factor for NDs. Telomere shortening is a biological marker of cellular aging, and telomerase reverse transcriptase (TERT) has been shown to slow down this process by maintaining telomere length. The blood-brain barrier (BBB) makes the brain a unique immune organ, and while the number of T cells present in the central nervous system is limited, they play an important role in NDs. Research suggests that NDs can be influenced by modulating peripheral T cell immune responses, and that TERT may play a significant role in T cell senescence and NDs. This review focuses on the current state of research on TERT in NDs and explores the potential connections between TERT, T cells, and NDs. Further studies on aging and telomeres may provide valuable insights for developing therapeutic strategies for age-related diseases.

Coenzyme Q10: Role in Less Common Age-Related Disorders

In this article we have reviewed the potential role of coenzyme Q10 (CoQ10) in the pathogenesis and treatment of a number of less common age-related disorders, for many of which effective therapies are not currently available. For most of these disorders, mitochondrial dysfunction, oxidative stress and inflammation have been implicated in the disease process, providing a rationale for the potential therapeutic use of CoQ10, because of its key roles in mitochondrial function, as an antioxidant, and as an anti-inflammatory agent. Disorders reviewed in the article include multi system atrophy, progressive supranuclear palsy, sporadic adult onset ataxia, and pulmonary fibrosis, together with late onset versions of Huntington’s disease, Alexander disease, lupus, anti-phospholipid syndrome, lysosomal storage disorders, fibromyalgia, Machado-Joseph disease, acyl-CoA dehydrogenase deficiency, and Leber’s optic neuropathy.

Coenzyme Q10 Supplementation Increases Removal of the ATXN3 Polyglutamine Repeat, Reducing Cerebellar Degeneration and Improving Motor Dysfunction in Murine Spinocerebellar Ataxia Type 3

Coenzyme Q10 (CoQ10), a well-known antioxidant, has been explored as a treatment in several neurodegenerative diseases, but its utility in spinocerebellar ataxia type 3 (SCA3) has not been explored. Herein, the protective effect of CoQ10 was examined using a transgenic mouse model of SCA3 onset. These results demonstrated that a diet supplemented with CoQ10 significantly improved murine locomotion, revealed by rotarod and open-field tests, compared with untreated controls. Additionally, a histological analysis showed the stratification of cerebellar layers indistinguishable from that of wild-type littermates. The increased survival of Purkinje cells was reflected by the reduced abundance of TUNEL-positive nuclei and apoptosis markers of activated p53, as well as lower levels of cleaved caspase 3 and cleaved poly-ADP-ribose polymerase. CoQ10 effects were related to the facilitation of the autophagy-mediated clearance of mutant ataxin-3 protein, as evidenced by the increased expression of heat shock protein 27 and autophagic markers p62, Beclin-1 and LC3II. The expression of antioxidant enzymes heme oxygenase 1 (HO-1), glutathione peroxidase 1 (GPx1) and superoxide dismutase 1 (SOD1) and 2 (SOD2), but not of glutathione peroxidase 2 (GPx2), were restored in 84Q SCA3 mice treated with CoQ10 to levels even higher than those measured in wild-type control mice. Furthermore, CoQ10 treatment also prevented skeletal muscle weight loss and muscle atrophy in diseased mice, revealed by significantly increased muscle fiber area and upregulated muscle protein synthesis pathways. In summary, our results demonstrated biochemical and pharmacological bases for the possible use of CoQ10 in SCA3 therapy.

Relationship between Brain Metabolic Disorders and Cognitive Impairment: LDL Receptor Defect

The low-density-lipoprotein receptor (LDLr) removes low-density lipoprotein (LDL), an endovascular transporter that carries cholesterol from the bloodstream to peripheral tissues. The maintenance of cholesterol content in the brain, which is important to protect brain function, is affected by LDLr. LDLr co-localizes with the insulin receptor and complements the internalization of LDL. In LDLr deficiency, LDL blood levels and insulin resistance increase, leading to abnormal cholesterol control and cognitive deficits in atherosclerosis. Defects in brain cholesterol metabolism lead to neuroinflammation and blood–brain-barrier (BBB) degradation. Moreover, interactions between endoplasmic reticulum stress (ER stress) and mitochondria are induced by ox-LDL accumulation, apolipoprotein E (ApoE) regulates the levels of amyloid beta (Aβ) in the brain, and hypoxia is induced by apoptosis induced by the LDLr defect. This review summarizes the association between neurodegenerative brain disease and typical cognitive deficits.

In Vitro Efficacy and Molecular Mechanism of Curcumin Analog in Pathological Regulation of Spinocerebellar Ataxia Type 3

Unlike other nuclear factor erythroid-2-related factor 2 (Nrf2) activators, the mechanism of action of curcumin analog, ASC-JM17 (JM17), in regulating oxidative homeostasis remains unknown. Spinocerebellar ataxia type 3 (SCA3) is an inherited polyglutamine neurodegenerative disease caused mainly by polyglutamine neurotoxicity and oxidative stress. Presently, we compared actions of JM17 with those of known Nrf2 activators, omaveloxolone (RTA-408) and dimethyl fumarate (DMF), using human neuroblastoma SK-N-SH cells with stable transfection of full-length ataxin-3 protein with 78 CAG repeats (MJD78) to clarify the resulting pathological mechanism by assaying mitochondrial function, mutant ataxin-3 protein toxicity, and oxidative stress. JM17, 1 μM, comprehensively restored mitochondrial function, decreased mutant protein aggregates, and attenuated intracellular/mitochondrial reactive oxygen species (ROS) levels. Although JM17 induced dose-dependent Nrf2 activation, a low dose of JM17 (less than 5 μM) still had a better antioxidant ability compared to the other Nrf2 activators and specifically increased mitochondrial superoxide dismutase 2 in an Nrf2-dependent manner as shown by knockdown experiments with siRNA. It showed that activation of Nrf2 in response to ROS generated in mitochondria could play an import role in the benefit of JM17. This study presents the diversified regulation of JM17 in a pathological process and helped develop more effective therapeutic strategies for SCA3.

Mitochondrial Dysfunction in Spinocerebellar Ataxia Type 3 Is Linked to VDAC1 Deubiquitination

Dysfunctional mitochondria are linked to several neurodegenerative diseases. Metabolic defects, a symptom which can result from dysfunctional mitochondria, are also present in spinocerebellar ataxia type 3 (SCA3), also known as Machado–Joseph disease, the most frequent, dominantly inherited neurodegenerative ataxia worldwide. Mitochondrial dysfunction has been reported for several neurodegenerative disorders and ataxin-3 is known to deubiquitinylate parkin, a key protein required for canonical mitophagy. In this study, we analyzed mitochondrial function and mitophagy in a patient-derived SCA3 cell model. Human fibroblast lines isolated from SCA3 patients were immortalized and characterized. SCA3 patient fibroblasts revealed circular, ring-shaped mitochondria and featured reduced OXPHOS complexes, ATP production and cell viability. We show that wildtype ataxin-3 deubiquitinates VDAC1 (voltage-dependent anion channel 1), a member of the mitochondrial permeability transition pore and a parkin substrate. In SCA3 patients, VDAC1 deubiquitination and parkin recruitment to the depolarized mitochondria is inhibited. Increased p62-linked mitophagy, autophagosome formation and autophagy is observed under disease conditions, which is in line with mitochondrial fission. SCA3 fibroblast lines demonstrated a mitochondrial phenotype and dysregulation of parkin-VDAC1-mediated mitophagy, thereby promoting mitochondrial quality control via alternative pathways.

CRISPR/Cas9 mediated gene correction ameliorates abnormal phenotypes in spinocerebellar ataxia type 3 patient-derived induced pluripotent stem cells

Spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD) is a progressive autosomal dominant neurodegenerative disease caused by abnormal CAG repeats in the exon 10 of ATXN3. The accumulation of the mutant ataxin-3 proteins carrying expanded polyglutamine (polyQ) leads to selective degeneration of neurons. Since the pathogenesis of SCA3 has not been fully elucidated, and no effective therapies have been identified, it is crucial to investigate the pathogenesis and seek new therapeutic strategies of SCA3. Induced pluripotent stem cells (iPSCs) can be used as the ideal cell model for the molecular pathogenesis of polyQ diseases. Abnormal CAG expansions mediated by CRISPR/Cas9 genome engineering technologies have shown promising potential for the treatment of polyQ diseases, including SCA3. In this study, SCA3-iPSCs can be corrected by the replacement of the abnormal CAG expansions (74 CAG) with normal repeats (17 CAG) using CRISPR/Cas9-mediated homologous recombination (HR) strategy. Besides, corrected SCA3-iPSCs retained pluripotent and normal karyotype, which can be differentiated into a neural stem cell (NSCs) and neuronal cells, and maintained electrophysiological characteristics. The expression of differentiation markers and electrophysiological characteristics were similar among the neuronal differentiation from normal control iPSCs (Ctrl-iPSCs), SCA3-iPSCs, and isogenic control SCA3-iPSCs. Furthermore, this study proved that the phenotypic abnormalities in SCA3 neurons, including aggregated IC2-polyQ protein, decreased mitochondrial membrane potential (MMP) and glutathione expressions, increased reactive oxygen species (ROS), intracellular Ca²⁺ concentrations, and lipid peroxidase malondialdehyde (MDA) levels, all were rescued in the corrected SCA3-NCs. For the first time, this study demonstrated the feasibility of CRISPR/Cas9-mediated HR strategy to precisely repair SCA3-iPSCs, and reverse the corresponding abnormal disease phenotypes. In addition, the importance of genetic control using CRISPR/Cas9-mediated iPSCs for disease modeling. Our work may contribute to providing a potential ideal model for molecular mechanism research and autologous stem cell therapy of SCA3 or other polyQ diseases, and offer a good gene therapy strategy for future treatment.

Oxidative Stress and Neurodegeneration: Interconnected Processes in PolyQ Diseases

Neurodegenerative polyglutamine (polyQ) disorders are caused by trinucleotide repeat expansions within the coding region of disease-causing genes. PolyQ-expanded proteins undergo conformational changes leading to the formation of protein inclusions which are associated with selective neuronal degeneration. Several lines of evidence indicate that these mutant proteins are associated with oxidative stress, proteasome impairment and microglia activation. These events may correlate with the induction of inflammation in the nervous system and disease progression. Here, we review the effect of polyQ-induced oxidative stress in cellular and animal models of polyQ diseases. Furthermore, we discuss the interplay between oxidative stress, neurodegeneration and neuroinflammation using as an example the well-known neuroinflammatory disease, Multiple Sclerosis. Finally, we review some of the pharmaceutical interventions which may delay the onset and progression of polyQ disorders by targeting disease-associated mechanisms.

Role of Vitamin E and the Orexin System in Neuroprotection

Microglia are the first line of defense at the level of the central nervous system (CNS). Phenotypic change in microglia can be regulated by various factors, including the orexin system. Neuroinflammation is an inflammatory process mediated by cytokines, by the lack of interaction between neurotransmitters and their specific receptors, caused by systemic tissue damage or, more often, associated with direct damage to the CNS. Chronic activation of microglia could lead to long-term neurodegenerative diseases. This review aims to explore how tocopherol (vitamin E) and the orexin system may play a role in the prevention and treatment of microglia inflammation and, consequently, in neurodegenerative diseases thanks to its antioxidant properties. The results of animal and in vitro studies provide evidence to support the use of tocopherol for a reduction in microglia inflammation as well as a greater activation of the orexinergic system. Although there is much in vivo and in vitro evidence of vitamin E antioxidant and protective abilities, there are still conflicting results for its use as a treatment for neurodegenerative diseases that speculate that vitamin E, under certain conditions or genetic predispositions, can be pro-oxidant and harmful.

Spirulina supplementation and oxidative stress and pro-inflammatory biomarkers: A systematic review and meta-analysis of controlled clinical trials

Studies investigating the effects of spirulina on inflammation and oxidative stress status are controversial. Therefore, the current systematic review and meta-analysis aimed to evaluate the impacts of spirulina supplementation on oxidative stress indicators and inflammatory markers. PubMed-Medline, SCOPUS, Web of Science, Embase databases and Google Scholar were searched up to 1 October 2020. Random-effect analysis was applied to perform meta-analysis. Subgroup analyses and multivariate meta-regression were performed to find heterogeneity sources. Quality assessment was conducted using Cochrane Collaboration's tool. A total of 11 studies that enrolled 465 subjects were included in our meta-analysis. Pooled results demonstrated a significant increase in interleukin-2 (IL-2) concentrations [Standardized mean difference (SMD = 2.69 pg/mL; 95% CI: 0.26, 5.11; P = .03)]; however this result changed to insignificant (SMD = 0.54 pg/mL; 95% CI: -1.29, 2.27; P > .05) when sensitivity analysis performed. A marginal decreasing effect were also found on interleukin-6 (IL-6) (SMD = -0.72 mg/dL; 95% CI: -1.50, 0.07; P = .073) and thiobarbituric acid reactive substances (TBARS) levels (SMD = -0.65; 95% CI: -1.37, 0.08; P = .08). In addition, results of subgroup analysis revealed a significant reduction in IL-6 and TBARS concentrations when the baseline body mass index (BMI) of participants was lower than 25 kg/m2 . Moreover, spirulina had no significant effect on tumour necrosis factor-α (TNF-α) (SMD = -0.07 mg/dL; 95% CI: -0.33, 0.18; P = .56) and malondialdehyde (MDA) concentrations (SMD = -0.42; 95% CI: -0.98, 0.14; P = .14). Spirulina consumption contributed to a significant increase in IL-2 concentrations changing to insignificant after sensitivity analysis and marginal decreasing effects on IL-6 and TBARS levels. No considerable impacts were observed on TNF-α and MDA concentrations.

Rating scales and biomarkers for CAG-repeat spinocerebellar ataxias: Implications for therapy development

Spinocerebellar ataxias (SCAs) are a group of dominantly-inherited cerebellar ataxias, among which CAG expansion-related SCAs are most common. These diseases have very high penetrance with defined disease progression, and emerging therapies are being developed to provide either symptomatic or disease-modifying benefits. In clinical trial design, it is crucial to incorporate biomarkers to test target engagement or track disease progression in response to therapies, especially in rare diseases such as SCAs. In this article, we review the available rating scales and recent advances of biomarkers in CAG-repeat SCAs. We divided biomarkers into neuroimaging, body fluid, and physiological studies. Understanding the utility of each biomarker will facilitate the design of robust clinical trials to advance therapies for SCAs.

Pathological ATX3 Expression Induces Cell Perturbations in E. coli as Revealed by Biochemical and Biophysical Investigations

Amyloid aggregation of human ataxin-3 (ATX3) is responsible for spinocerebellar ataxia type 3, which belongs to the class of polyglutamine neurodegenerative disorders. It is widely accepted that the formation of toxic oligomeric species is primarily involved in the onset of the disease. For this reason, to understand the mechanisms underlying toxicity, we expressed both a physiological (ATX3-Q24) and a pathological ATX3 variant (ATX3-Q55) in a simplified cellular model, Escherichia coli. It has been observed that ATX3-Q55 expression induces a higher reduction of the cell growth compared to ATX3-Q24, due to the bacteriostatic effect of the toxic oligomeric species. Furthermore, the Fourier transform infrared microspectroscopy investigation, supported by multivariate analysis, made it possible to monitor protein aggregation and the induced cell perturbations in intact cells. In particular, it has been found that the toxic oligomeric species associated with the expression of ATX3-Q55 are responsible for the main spectral changes, ascribable mainly to the cell envelope modifications. A structural alteration of the membrane detected through electron microscopy analysis in the strain expressing the pathological form supports the spectroscopic results.

Pathomechanism characterization and potential therapeutics identification for SCA3 targeting neuroinflammation

Polyglutamine (polyQ)-mediated spinocerebellar ataxias (SCA) are caused by mutant genes with expanded CAG repeats encoding polyQ tracts. The misfolding and aggregation of polyQ proteins result in increased reactive oxygen species (ROS) and cellular toxicity. Inflammation is a common manifestation of oxidative stress and inflammatory process further reduces cellular antioxidant capacity. Increase of activated microglia in the pons of SCA type 3 (SCA3) patients suggests the involvement of neuroinflammation in the disease pathogenesis. In this study, we evaluated the anti-inflammatory potentials of indole compound NC009-1, 4-aminophenol-arachidonic acid derivative AM404, quinoline compound VB-037 and chalcone-coumarin derivative LM-031 using human HMC3 microglia and SCA3 ATXN3/Q₇₅-GFP SH-SY5Y cells. The four tested compounds displayed anti-inflammatory activity by suppressing NO, IL-1β, TNF-α and IL-6 production and CD68 expression of IFN-γ-activated HMC3 microglia. In retinoic acid-differentiated ATXN3/Q₇₅-GFP SH-SY5Y cells inflamed with IFN-γ-primed HMC3 conditioned medium, treatment with the tested compounds mitigated the increased caspase 1 activity and lactate dehydrogenase release, reduced polyQ aggregation and ROS and/or promoted neurite outgrowth. Examination of IL-1β- and TNF-α-mediated signaling pathways revealed that the tested compounds decreased IκBα/P65, JNK/JUN and/or P38/STAT1 signaling. The study results suggest the potential of NC009-1, AM404, VB-037 and LM-031 in treating SCA3 and probable other polyQ diseases.

Polyglutamine spinocerebellar ataxias: emerging therapeutic targets

INTRODUCTION

Six of the most frequent dominantly inherited spinocerebellar ataxias (SCAs) worldwide - SCA1, SCA2, SCA3, SCA6, SCA7, and SCA17 - are caused by an expansion of a polyglutamine (polyQ) tract in the corresponding proteins. While the identification of the causative mutation has advanced knowledge on the pathogenesis of polyQ SCAs, effective therapeutics able to mitigate the severe clinical manifestation of these highly incapacitating disorders are not yet available.

AREAS COVERED

This review provides a comprehensive and critical perspective on well-established and emerging therapeutic targets for polyQ SCAs; it aims to inspire prospective drug discovery efforts.

EXPERT OPINION

The landscape of polyQ SCAs therapeutic targets and strategies includes (1) the mutant genes and proteins themselves, (2) enhancement of endogenous protein quality control responses, (3) abnormal protein-protein interactions of the mutant proteins, (4) disturbed neuronal function, (5) mitochondrial function, energy availability and oxidative stress, and (6) glial dysfunction, growth factor or hormone imbalances. Challenges include gaining a clearer definition of therapeutic targets for the drugs in clinical development, the discovery of novel drug-like molecules for challenging key targets, and the attainment of a stronger translation of preclinical findings to the clinic.

Promising Molecular Targets for Pharmacological Therapy of Neurodegenerative Pathologies

Drug development for the treatment of neurodegenerative diseases has to confront numerous problems occurring, in particular, because of attempts to address only one of the causes of the pathogenesis of neurological disorders. Recent advances in multitarget therapy research are gaining momentum by utilizing pharmacophores that simultaneously affect different pathological pathways in the neurodegeneration process. The application of such a therapeutic strategy not only involves the treatment of symptoms, but also mainly addresses prevention of the fundamental pathological processes of neurodegenerative diseases and the reduction of cognitive abilities. Neuroinflammation and oxidative stress, mitochondrial dysfunction, dysregulation of the expression of histone deacetylases, and aggregation of pathogenic forms of proteins are among the most common and significant pathological features of neurodegenerative diseases. In this review, we focus on the molecular mechanisms and highlight the main aspects, including reactive oxygen species, the cell endogenous antioxidant system, neuroinflammation triggers, metalloproteinases, α-synuclein, tau proteins, neuromelanin, histone deacetylases, presenilins, etc. The processes and molecular targets discussed in this review could serve as a starting point for screening leader compounds that could help prevent or slow down the development of neurodegenerative diseases.

Oxidative Stress in DNA Repeat Expansion Disorders: A Focus on NRF2 Signaling Involvement

DNA repeat expansion disorders are a group of neuromuscular and neurodegenerative diseases that arise from the inheritance of long tracts of nucleotide repetitions, located in the regulatory region, introns, or inside the coding sequence of a gene. Although loss of protein expression and/or the gain of function of its transcribed mRNA or translated product represent the major pathogenic effect of these pathologies, mitochondrial dysfunction and imbalance in redox homeostasis are reported as common features in these disorders, deeply affecting their severity and progression. In this review, we examine the role that the redox imbalance plays in the pathological mechanisms of DNA expansion disorders and the recent advances on antioxidant treatments, particularly focusing on the expression and the activity of the transcription factor NRF2, the main cellular regulator of the antioxidant response.

New Synthetic 3-Benzoyl-5-Hydroxy-2H-Chromen-2-One (LM-031) Inhibits Polyglutamine Aggregation and Promotes Neurite Outgrowth through Enhancement of CREB, NRF2, and Reduction of AMPKα in SCA17 Cell Models

Spinocerebellar ataxia type 17 (SCA17) is caused by a CAG/CAA expansion mutation encoding an expanded polyglutamine (polyQ) tract in TATA-box binding protein (TBP), a general transcription initiation factor. Suppression of cAMP-responsive element binding protein- (CREB-) dependent transcription, impaired nuclear factor erythroid 2-related factor 2 (NRF2) signaling, and interaction of AMP-activated protein kinase (AMPK) with increased oxidative stress have been implicated to be involved in pathogenic mechanisms of polyQ-mediated diseases. In this study, we demonstrated decreased pCREB and NRF2 and activated AMPK contributing to neurotoxicity in SCA17 SH-SY5Y cells. We also showed that licochalcone A and the related in-house derivative compound 3-benzoyl-5-hydroxy-2H-chromen-2-one (LM-031) exhibited antiaggregation, antioxidative, antiapoptosis, and neuroprotective effects in TBP/Q₇₉-GFP-expressing cell models. LM-031 and licochalcone A exerted neuroprotective effects by upregulating pCREB and its downstream genes, BCL2 and GADD45B, and enhancing NRF2. Furthermore, LM-031, but not licochalcone A, reduced activated AMPKα. Knockdown of CREB and NRF2 and treatment of AICAR (5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside), an AMPK activator, attenuated the aggregation-inhibiting and neurite outgrowth promoting effects of LM-031 on TBP/Q₇₉ SH-SY5Y cells. The study results suggest the LM-031 as potential therapeutics for SCA17 and probable other polyQ diseases.

Profiling of mitochondrial genomes in SCA3/MJD patients from mainland China

Spinocerebellar ataxia type 3, also known as Machado-Joseph disease (SCA3/MJD), is the most common type of autosomal dominant cerebellar ataxias. Few studies focused on the changes of the whole mitochondrial genomes of SCA3/MJD patients and its relationship with the pathogenesis of SCA3/MJD. We adapted one-step long-range PCR to amplify the entire mitochondrial DNA (mtDNA) followed by next-generation sequencing technology to investigate the information of whole mitochondrial genomes in 38 SCA3/MJD patients and 31 healthy controls from mainland China. Compared to the healthy control group, the mitochondrial variations in SCA3/MJD patients were more concentrated in the tRNA-transcribed genes which were further found to be potentially associated with the pathogenesis of SCA3/MJD by SKAT-O analysis. However, owning variations in tRNA-transcribed genes could not affect the age of onset (AO) of SCA3/MJD patients. We also noticed that the variant loads greater than 90% took up more in SCA3/MJD patients than in controls. Moreover, from our preliminary study, compared to the patients whose ages of onset were elder than 20, the mitochondrial genomes showed no difference in those AO less than 20. This is the first study to demonstrate the feasibility of using the next-generation sequencing technology for mtDNA variant analysis of SCA3/MJD patients from mainland China. And this research enriches the genetic information of SCA3/MJD and provides a direction for further investigations about the mitochondrial genomes in SCA3/MJD.

From Pathogenesis to Novel Therapeutics for Spinocerebellar Ataxia Type 3: Evading Potholes on the Way to Translation

Spinocerebellar ataxia type 3 (SCA3), also known as Machado-Joseph disease (MJD), is a neurodegenerative disorder caused by a polyglutamine expansion in the ATXN3 gene. In spite of the identification of a clear monogenic cause 25 years ago, the pathological process still puzzles researchers, impairing prospects for an effective therapy. Here, we propose the disruption of protein homeostasis as the hub of SCA3 pathogenesis, being the molecular mechanisms and cellular pathways that are deregulated in SCA3 downstream consequences of the misfolding and aggregation of ATXN3. Moreover, we attempt to provide a realistic perspective on how the translational/clinical research in SCA3 should evolve. This was based on molecular findings, clinical and epidemiological characteristics, studies of proposed treatments in other conditions, and how that information is essential for their (re-)application in SCA3. This review thus aims i) to critically evaluate the current state of research on SCA3, from fundamental to translational and clinical perspectives; ii) to bring up the current key questions that remain unanswered in this disorder; and iii) to provide a frame on how those answers should be pursued.

Altered Levels of Proteins and Phosphoproteins, in the Absence of Early Causative Transcriptional Changes, Shape the Molecular Pathogenesis in the Brain of Young Presymptomatic Ki91 SCA3/MJD Mouse

Spinocerebellar ataxia type 3 (SCA3/MJD) is a polyQ neurodegenerative disease where the presymptomatic phase of pathogenesis is unknown. Therefore, we investigated the molecular network of transcriptomic and proteomic triggers in young presymptomatic SCA3/MJD brain from Ki91 knock-in mouse. We found that transcriptional dysregulations resulting from mutant ataxin-3 are not occurring in young Ki91 mice, while old Ki91 mice and also postmitotic patient SCA3 neurons demonstrate the late transcriptomic changes. Unlike the lack of early mRNA changes, we have identified numerous early changes of total proteins and phosphoproteins in 2-month-old Ki91 mouse cortex and cerebellum. We discovered the network of processes in presymptomatic SCA3 with three main groups of disturbed processes comprising altered proteins: (I) modulation of protein levels and DNA damage (Pabpc1, Ddb1, Nedd8), (II) formation of neuronal cellular structures (Tubb3, Nefh, p-Tau), and (III) neuronal function affected by processes following perturbed cytoskeletal formation (Mt-Co3, Stx1b, p-Syn1). Phosphoproteins downregulate in the young Ki91 mouse brain and their phosphosites are associated with kinases that interact with ATXN3 such as casein kinase, Camk2, and kinases controlled by another Atxn3 interactor p21 such as Gsk3, Pka, and Cdk kinases. We conclude that the onset of SCA3 pathology occurs without altered transcript level and is characterized by changed levels of proteins responsible for termination of translation, DNA damage, spliceosome, and protein phosphorylation. This disturbs global cellular processes such as cytoskeleton and transport of vesicles and mitochondria along axons causing energy deficit and neurodegeneration also manifesting in an altered level of transcripts at later ages.

Protective roles of carbonic anhydrase 8 in Machado-Joseph Disease

Machado-Joseph disease (MJD)/Spinocerebellar ataxia type 3 (SCA3) is an inherited neurodegenerative disease that can lead to a regression of motor coordination and muscle control in the extremities. It is known that expansion of CAG repeats encodes abnormally long polyQ in mutant ataxin-3, the disease protein. It is also noted that mutant ataxin-3 interacts with 1,4,5-trisphosphate receptor type 1 (IP3R1) and induces abnormal Ca²⁺ release. Previously, we have shown a significant increase in the expression of carbonic anhydrase VIII (CA8) in SK-N-SH-MJD78 cells, which are human neuroblastoma cells overexpressing mutant ataxin-3 with 78 glutamine repeats. In the current study, we showed the presence of significantly increased CA8 expression in MJD mouse cerebellum in either early or late disease stage, with a gradual decrease in CA8 expression as the MJD mice naturally aged. By immunofluorescence and immunoprecipitation analysis, we also found that CA8 co-localized and interacted with mutant ataxin-3 in SK-N-SH-MJD78 cells harboring overexpressed CA8 (SK-MJD78-CA8). In addition, we found that SK-MJD78-CA8 cells, as well as cerebellar granule neurons (CGNs) of MJD transgenic (Tg) mouse with overexpressed CA8, were more resistant to reactive oxygen species (ROS) stress than the control cells. Importantly, overexpression of CA8 in SK-MJD78-CA8 cells and in MJD CGNs rescued abnormal Ca²⁺ release and caused an increase in cell survival. In summary, we demonstrate the protective function of CA8 in MJD disease models and speculate that the declining expression of CA8 following an initial increased expression may be related to the late onset phenomenon of MJD.

An insight into the mechanism of antifungal activity of biogenic nanoparticles than their chemical counterparts

Herein, we describe the enhanced antifungal activity of silver nanoparticles biosynthesized by cell free filtrate of Trichoderma viride (MTCC 5661) in comparison to chemically synthesized silver nanoparticles (CSNP) of similar shape and size. Biosynthesized silver nanoparticles (BSNP) enhanced the reduction in dry weight by 20 and 48.8% of fungal pathogens Fusarium oxysporum and Alternaria brassicicola respectively in comparison to their chemical counterparts (CSNP). Nitroblue tetrazolium and Propidium iodide staining demonstrated the higher generation of superoxide radicals lead to higher death in BSNP treated fungus in comparison to CSNP. Scanning electron microscopy of A. brassicicola revealed the osmotic imbalance and membrane disintegrity to be major cause for fungal cell death after treatment with BSNP. To gain an insight into the mechanistic aspect of enhanced fungal cell death after treatment of BSNP in comparison to CSNP, stress responses and real time PCR analysis was carried out with A. brassicicola. It revealed that generation of ROS, downregulation of antioxidant machinery and oxidative enzymes, disruption of osmotic balance and cellular integrity, and loss of virulence are the mechanisms employed by BSNP which establishes them as superior antifungal agent than their chemical counterparts. With increasing drug resistance and ubiquitous presence of fungal pathogens in plant kingdom, BSNP bears the candidature for new generation of antifungal agent.

Oxidative Stress: A Key Modulator in Neurodegenerative Diseases

Oxidative stress is proposed as a regulatory element in ageing and various neurological disorders. The excess of oxidants causes a reduction of antioxidants, which in turn produce an oxidation-reduction imbalance in organisms. Paucity of the antioxidant system generates oxidative-stress, characterized by elevated levels of reactive species (oxygen, hydroxyl free radical, and so on). Mitochondria play a key role in ATP supply to cells via oxidative phosphorylation, as well as synthesis of essential biological molecules. Various redox reactions catalyzed by enzymes take place in the oxidative phosphorylation process. An inefficient oxidative phosphorylation may generate reactive oxygen species (ROS), leading to mitochondrial dysfunction. Mitochondrial redox metabolism, phospholipid metabolism, and proteolytic pathways are found to be the major and potential source of free radicals. A lower concentration of ROS is essential for normal cellular signaling, whereas the higher concentration and long-time exposure of ROS cause damage to cellular macromolecules such as DNA, lipids and proteins, ultimately resulting in necrosis and apoptotic cell death. Normal and proper functioning of the central nervous system (CNS) is entirely dependent on the chemical integrity of brain. It is well established that the brain consumes a large amount of oxygen and is highly rich in lipid content, becoming prone to oxidative stress. A high consumption of oxygen leads to excessive production of ROS. Apart from this, the neuronal membranes are found to be rich in polyunsaturated fatty acids, which are highly susceptible to ROS. Various neurodegenerative diseases such as Parkinson's disease (PD), Alzheimer's disease (AD), Huntington's disease (HD), and amyotrophic lateral sclerosis (ALS), among others, can be the result of biochemical alteration (due to oxidative stress) in bimolecular components. There is a need to understand the processes and role of oxidative stress in neurodegenerative diseases. This review is an effort towards improving our understanding of the pivotal role played by OS in neurodegenerative disorders.

Differential biological effects in two pedigrees of clam Ruditapes philippinarum exposed to cadmium using iTRAQ-based proteomics

Due to the industrial discharges, cadmium (Cd) has been one of typical heavy metal pollutants in the Bohai Sea. Manila clam Ruditapes philippinarum is frequently used for pollution biomonitoring and consists of several pedigrees, of which White and Zebra clams are the dominant pedigrees along the Bohai Sea coast. However, limited attention has been paid on the differential biological effects in different pedigrees of clam to heavy metals. In this work, the proteome profiling analysis was performed to reveal the differential proteomic responses in White and Zebra clams to Cd exposure (200 μg/L) for 48 h, followed by bioinformatical analysis. The proteomic investigations showed that Cd treatment induced more differentially expressed proteins (DEPs) in White clam samples than in Zebra clam samples. Based on the DEPs, we found that some key biological processes consisting of immune response and metabolism were commonly induced in both two pedigrees of clam. Uniquely, some processes related to cellular signaling, proteolysis and energy production were enhanced in Cd-treated White clam samples. Comparatively, the depletion in some unique processes on proteolysis and energy production was elicited in Cd-treated Zebra clam samples, as well as disorder in gene expression. Moreover, Cd exposure caused increases in CAT and POD activities in White clam samples and decreases in SOD and CAT activities in Zebra clams samples, which were consistent with the proteomic responses. Overall, these findings confirmed the differential biological effects of White and Zebra clams to Cd treatment, suggesting that the pedigree of animal should be taken into consideration in ecotoxicology studies.

Mitochondrial DNA haplogroups and age at onset of Machado-Joseph disease/spinocerebellar ataxia type 3: a study in patients from multiple populations

BACKGROUND AND PURPOSE

Mitochondrial dysfunction has been implicated in the pathogenesis of several neurodegenerative disorders, including Machado-Joseph disease (MJD), an autosomal dominant late-onset polyglutamine ataxia that results from an unstable expansion of a CAG tract in the ATXN3 gene. The size of the CAG tract only partially explains age at onset (AO), highlighting the existence of disease modifiers. Mitochondrial DNA (mtDNA) haplogroups have been associated with clinical presentation in other polyglutamine disorders, constituting potential modifiers of MJD phenotype.

METHODS

A cross-sectional study, using 235 unrelated patients from Portugal, Brazil, India and Japan, was performed to investigate if mtDNA haplogroups contribute to AO of MJD. mtDNA haplogroups were obtained after sequencing the mtDNA hypervariable region I. Patients were classified in 15 phylogenetically related haplogroup clusters.

RESULTS

The AO was significantly different among populations, implying the existence of other non-CAG factors, which seem to be population specific. In the Portuguese population, patients classified as belonging to haplogroup JT presented the earliest onset (estimated onset 34.6 years of age). Haplogroups W and X seem to have a protective effect, causing a delay in onset (estimated onset 47 years of age). No significant association between haplogroup clusters and AO was detected in the other populations or when all patients were pooled. Although haplogroup JT has already been implicated in other neurodegenerative disorders, no previous reports of an association between haplogroups W and X and disease were found.

CONCLUSIONS

These findings suggest that haplogroups JT, W and X modify AO in MJD. Replication studies should be performed in European populations, where the frequency of the candidate modifiers is similar.

Protective Effects of Myxobacterial Extracts on Hydrogen Peroxide-induced Toxicity on Human Primary Astrocytes

Astrocytes, the main non-neuronal cells in the brain, have significant roles in the maintenance and survival of neurons. Oxidative stress has been implicated in various neurodegenerative disorders such as Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and Parkinson's disease (PD). Myxobacteria produce a wide range of bioactive metabolites with notable structures and modes of action, which introduce them as potent natural product producers. In the present study, we evaluated the effects of myxobacterial extracts on hydrogen peroxide (H₂O₂)-mediated toxicity on primary human astrocytes. We showed that myxobacterial extracts could decrease the formation of reactive oxygen species (ROS), nitric oxide (NO) production, and cell death assessed by the release of lactate dehydrogenase (LDH). Myxobacterial extracts were also able to reduce the nitric oxide synthase (NOS) activity. The extracts reduced the oxidative effect of H₂O₂ on over-activation of poly (ADP-ribose) polymerase (PARP1), therefore preventing the cell death by restoring the NAD⁺ levels. In addition, myxobacterial extracts ameliorated the oxidative stress by increasing the glutathione level in cells. The overall results showed myxobacterial extracts, especially from the strains Archangium sp. UTMC 4070 and Cystobacter sp. UTMC 4073, were able to protect human primary astrocytes from oxidative stress.

Mitochondrial Morphology, Function and Homeostasis Are Impaired by Expression of an N-terminal Calpain Cleavage Fragment of Ataxin-3

Alterations in mitochondrial morphology and function have been linked to neurodegenerative diseases, including Parkinson disease, Alzheimer disease and Huntington disease. Metabolic defects, resulting from dysfunctional mitochondria, have been reported in patients and respective animal models of all those diseases. Spinocerebellar Ataxia Type 3 (SCA3), another neurodegenerative disorder, also presents with metabolic defects and loss of body weight in early disease stages although the possible role of mitochondrial dysfunction in SCA3 pathology is still to be determined. Interestingly, the SCA3 disease protein ataxin-3, which is predominantly localized in cytoplasm and nucleus, has also been associated with mitochondria in both its mutant and wildtype form. This observation provides an interesting link to a potential mitochondrial involvement of mutant ataxin-3 in SCA3 pathogenesis. Furthermore, proteolytic cleavage of ataxin-3 has been shown to produce toxic fragments and even overexpression of artificially truncated forms of ataxin-3 resulted in mitochondria deficits. Therefore, we analyzed the repercussions of expressing a naturally occurring N-terminal cleavage fragment of ataxin-3 and the influence of an endogenous expression of the S256 cleavage fragment in vitro and in vivo. In our study, expression of a fragment derived from calpain cleavage induced mitochondrial fragmentation and cristae alterations leading to a significantly decreased capacity of mitochondrial respiration and contributing to an increased susceptibility to apoptosis. Furthermore, analyzing mitophagy revealed activation of autophagy in the early pathogenesis with reduced lysosomal activity. In conclusion, our findings indicate that cleavage of ataxin-3 by calpains results in fragments which interfere with mitochondrial function and mitochondrial degradation processes.

Machado-Joseph disease/spinocerebellar ataxia type 3: lessons from disease pathogenesis and clues into therapy

Machado-Joseph disease (MJD), also known as spinocerebellar ataxia type 3 (SCA3), is an incurable disorder, widely regarded as the most common form of spinocerebellar ataxia in the world. MJD/SCA3 arises from mutation of the ATXN3 gene, but this simple monogenic cause contrasts with the complexity of the pathogenic mechanisms that are currently admitted to underlie neuronal dysfunction and death. The aberrantly expanded protein product - ataxin-3 - is known to aggregate and generate toxic species that disrupt several cell systems, including autophagy, proteostasis, transcription, mitochondrial function and signalling. Over the years, research into putative therapeutic approaches has often been devoted to the development of strategies that counteract disease at different stages of cellular pathogenesis. Silencing the pathogenic protein, blocking aggregation, inhibiting toxic proteolytic processing and counteracting dysfunctions of the cellular systems affected have yielded promising ameliorating results in studies with cellular and animal models. The current review analyses the available studies dedicated to the investigation of MJD/SCA3 pathogenesis and the exploration of possible therapeutic strategies, focusing primarily on gene therapy and pharmacological approaches rooted on the molecular and cellular mechanisms of disease.

Transcriptional profiling and biomarker identification reveal tissue specific effects of expanded ataxin-3 in a spinocerebellar ataxia type 3 mouse model

Background

Spinocerebellar ataxia type 3 (SCA3) is a progressive neurodegenerative disorder caused by expansion of the polyglutamine repeat in the ataxin-3 protein. Expression of mutant ataxin-3 is known to result in transcriptional dysregulation, which can contribute to the cellular toxicity and neurodegeneration. Since the exact causative mechanisms underlying this process have not been fully elucidated, gene expression analyses in brains of transgenic SCA3 mouse models may provide useful insights.

Methods

Here we characterised the MJD84.2 SCA3 mouse model expressing the mutant human ataxin-3 gene using a multi-omics approach on brain and blood. Gene expression changes in brainstem, cerebellum, striatum and cortex were used to study pathological changes in brain, while blood gene expression and metabolites/lipids levels were examined as potential biomarkers for disease.

Results

Despite normal motor performance at 17.5 months of age, transcriptional changes in brain tissue of the SCA3 mice were observed. Most transcriptional changes occurred in brainstem and striatum, whilst cerebellum and cortex were only modestly affected. The most significantly altered genes in SCA3 mouse brain were Tmc3, Zfp488, Car2, and Chdh. Based on the transcriptional changes, α-adrenergic and CREB pathways were most consistently altered for combined analysis of the four brain regions. When examining individual brain regions, axon guidance and synaptic transmission pathways were most strongly altered in striatum, whilst brainstem presented with strongest alterations in the pi-3 k cascade and cholesterol biosynthesis pathways. Similar to other neurodegenerative diseases, reduced levels of tryptophan and increased levels of ceramides, di- and triglycerides were observed in SCA3 mouse blood.

Conclusions

The observed transcriptional changes in SCA3 mouse brain reveal parallels with previous reported neuropathology in patients, but also shows brain region specific effects as well as involvement of adrenergic signalling and CREB pathway changes in SCA3. Importantly, the transcriptional changes occur prior to onset of motor- and coordination deficits.

Electronic supplementary material

The online version of this article (10.1186/s13024-018-0261-9) contains supplementary material, which is available to authorized users.

CRISPR/Cas9-Targeted Deletion of Polyglutamine in Spinocerebellar Ataxia Type 3-Derived Induced Pluripotent Stem Cells

Spinocerebellar ataxia type 3 (SCA3) is caused by an abnormal expansion of the cytosine-adenine-guanine (CAG) triplet in ATXN3, which translates into a polyglutamine (polyQ) tract within ataxin-3 (ATXN3) protein. Although the pathogenic mechanisms remain unclear, it is well established that expression of mutant forms of ATXN3 carrying an expanded polyQ domain are involved in SCA3 pathogenesis, and several strategies to suppress mutant ATXN3 have shown promising potential for SCA3 treatment. In this study, we described successful clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9-mediated deletion of the expanded polyQ-encoding region of ATXN3 in induced pluripotent stem cells (iPSCs) derived from a SCA3 patient, and these patient-specific iPSCs retained pluripotency and neural differentiation following expanded polyQ deletion. Furthermore, the ubiquitin-binding capacity of ATXN3 was retained in the neural cells differentiated from the corrected iPSCs. For the first time, this work provides preliminary data for gene editing by CRISPR/Cas9 in SCA3, and demonstrates the feasibility of using a single-guide RNA pair to delete the expanded polyQ-encoding region of ATXN3, suggesting the potential efficacy of this method for future therapeutic application.

Accumulation of Mitochondrial DNA Common Deletion Since The Preataxic Stage of Machado-Joseph Disease

Molecular alterations reflecting pathophysiologic changes thought to occur many years before the clinical onset of Machado-Joseph disease (MJD)/spinocerebellar ataxia type 3 (SCA3), a late-onset polyglutamine disorder, remain unidentified. The absence of molecular biomarkers hampers clinical trials, which lack sensitive measures of disease progression, preventing the identification of events occurring prior to clinical onset. Our aim was to analyse the mtDNA content and the amount of the common deletion (m.8482_13460del4977) in a cohort of 16 preataxic MJD mutation carriers, 85 MJD patients and 101 apparently healthy age-matched controls. Relative expression levels of RPPH1, MT-ND1 and MT-ND4 genes were assessed by quantitative real-time PCR. The mtDNA content was calculated as the difference between the expression levels of a mitochondrial gene (MT-ND1) and a nuclear gene (RPPH1); the amount of mtDNA common deletion was calculated as the difference between expression levels of a deleted (MT-ND4) and an undeleted (MT-ND1) mitochondrial genes. mtDNA content in MJD carriers was similar to that of healthy age-matched controls, whereas the percentage of the common deletion was significantly increased in MJD subjects, and more pronounced in the preclinical stage (p < 0.05). The BCL2/BAX ratio was decreased in preataxic carriers compared to controls, suggesting that the mitochondrial-mediated apoptotic pathway is altered in MJD. Our findings demonstrate for the first time that accumulation of common deletion starts in the preclinical stage. Such early alterations provide support to the current understanding that any therapeutic intervention in MJD should start before the overt clinical phenotype.

Caffeic acid and resveratrol ameliorate cellular damage in cell and Drosophila models of spinocerebellar ataxia type 3 through upregulation of Nrf2 pathway

Polyglutamine (polyQ)-expanded mutant ataxin-3 protein, which is prone to misfolding and aggregation, leads to cerebellar neurotoxicity in spinocerebellar ataxia type 3 (SCA3), an inherited PolyQ neurodegenerative disease. Although the exact mechanism is unknown, the pathogenic effects of mutant ataxin-3 are associated with dysregulation of transcription, protein degradation, mitochondrial function, apoptosis, and antioxidant potency. In the present study we explored the protective role and possible mechanism of caffeic acid (CA) and resveratrol (Res) in cells and Drosophila expressing mutant ataxin-3. Treatment with CA and Res increased the levels of antioxidant and autophagy protein expression with consequently corrected levels of reactive oxygen species, mitochondrial membrane potential, mutant ataxin-3, and the aggregation of mutant ataxin-3 in SK-N-SH-MJD78 cells. Moreover, in SK-N-SH-MJD78 cells, CA and Res enhanced the transcriptional activity of nuclear factor erythroid-derived-2-like 2 (Nrf2), a master transcription factor that upregulates the expression of antioxidant defense genes and the autophagy gene p62. CA and Res improved survival and motor performance in SCA3 Drosophila. Additionally, the above-mentioned protective effects of CA were also observed in CA-supplemented SCA3 Drosophila. Notably, blockade of the Nrf2 pathway by use of small interfering RNA annulled the health effects of CA and Res on SCA3, which affirmed the importance of the increase in Nrf2 activation by CA and Res. Additional studies are need to dissect the protective role of CA and Res in modulating neurodegenerative progression in SCA3 and other polyQ diseases.

Towards the Identification of Molecular Biomarkers of Spinocerebellar Ataxia Type 3 (SCA3)/Machado-Joseph Disease (MJD)

Whereas spinocerebellar ataxia type 3 (SCA3)/Machado-Joseph disease (MJD) remains an untreatable disorder, disease-modifying compounds have begun being tested in the context of clinical trials; their success is dependent on the sensitivity of the methods used to measure subtle therapeutic benefits. Thus, efforts are being made to propose a battery of potential outcome measures, including molecular biomarkers (MBs), which remain to be identified; MBs are particularly pertinent if SCA3 trials are expected to enroll preataxic subjects. Recently, promising candidate MBs of SCA3 have emerged from gene expression studies. In this chapter we provide a synthesis of the cross-sectional and pilot longitudinal studies of blood-based transcriptional biomarkers conducted so far. Other alterations with potential to track the progression of SCA3, such as those involving mitochondrial DNA (mtDNA) are also referred. It is expected that a set of molecular biomarkers can be identified; these will be used in complementarity with clinical and imaging markers to fully track SCA3, from its preataxic phase to the disease stage.

Molecular Mechanisms and Cellular Pathways Implicated in Machado-Joseph Disease Pathogenesis

Machado-Joseph disease (MJD) is a dominantly inherited disorder originally described in people of Portuguese descent, and associated with the expansion of a CAG tract in the coding region of the causative gene MJD1/ATX3. The CAG repeats range from 10 to 51 in the normal population and from 55 to 87 in SCA3/MJD patients. MJD1 encodes ataxin-3, a protein whose physiological function has been linked to ubiquitin-mediated proteolysis. Despite the identification of the causative mutation, the pathogenic process leading to the neurodegeneration observed in the disease is not yet completely understood. In the past years, several studies identified different molecular mechanisms and cellular pathways as being impaired or deregulated in MJD. Autophagy, proteolysis or post-translational modifications, among other processes, were implicated in MJD pathogenesis. From these studies it was possible to identify new targets for therapeutic intervention, which in some cases proved successful in models of disease.

The CAG-polyglutamine repeat diseases: a clinical, molecular, genetic, and pathophysiologic nosology

Throughout the genome, unstable tandem nucleotide repeats can expand to cause a variety of neurologic disorders. Expansion of a CAG triplet repeat within a coding exon gives rise to an elongated polyglutamine (polyQ) tract in the resultant protein product, and accounts for a unique category of neurodegenerative disorders, known as the CAG-polyglutamine repeat diseases. The nine members of the CAG-polyglutamine disease family include spinal and bulbar muscular atrophy (SBMA), Huntington disease, dentatorubral pallidoluysian atrophy, and six spinocerebellar ataxias (SCA 1, 2, 3, 6, 7, and 17). All CAG-polyglutamine diseases are dominantly inherited, with the exception of SBMA, which is X-linked, and many CAG-polyglutamine diseases display anticipation, which is defined as increasing disease severity in successive generations of an affected kindred. Despite widespread expression of the different polyQ-expanded disease proteins throughout the body, each CAG-polyglutamine disease strikes a particular subset of neurons, although the mechanism for this cell-type selectivity remains poorly understood. While the different genes implicated in these disorders display amino acid homology only in the repeat tract domain, certain pathologic molecular processes have been implicated in almost all of the CAG-polyglutamine repeat diseases, including protein aggregation, proteolytic cleavage, transcription dysregulation, autophagy impairment, and mitochondrial dysfunction. Here we highlight the clinical and molecular genetic features of each distinct disorder, and then discuss common themes in CAG-polyglutamine disease pathogenesis, closing with emerging advances in therapy development.

Peripheral Oxidative Stress Biomarkers in Spinocerebellar Ataxia Type 3/Machado-Joseph Disease

OBJECTIVES

Spinocerebellar ataxia type 3/Machado-Joseph disease (SCA3/MJD) is a polyglutamine disorder with no current disease-modifying treatment. Conformational changes in mutant ataxin-3 trigger different pathogenic cascades, including reactive oxygen species (ROS) generation; however, the clinical relevance of oxidative stress elements as peripheral biomarkers of SCA3/MJD remains unknown. We aimed to evaluate ROS production and antioxidant defense capacity in symptomatic and presymptomatic SCA3/MJD individuals and correlate these markers with clinical and molecular data with the goal of assessing their properties as disease biomarkers.

METHODS

Molecularly confirmed SCA3/MJD carriers and controls were included in an exploratory case-control study. Serum ROS, measured by 2',7'-dichlorofluorescein diacetate (DCFH-DA) as well as superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) antioxidant enzyme activities, levels were assessed.

RESULTS

Fifty-eight early/moderate stage symptomatic SCA3/MJD, 12 presymptomatic SCA3/MJD, and 47 control individuals were assessed. The DCFH-DA levels in the symptomatic group were 152.82 nmol/mg of protein [95% confidence interval (CI), 82.57-223.08, p < 0.001] higher than in the control and 243.80 nmol/mg of protein (95% CI, 130.64-356.96, p < 0.001) higher than in the presymptomatic group. The SOD activity in the symptomatic group was 3 U/mg of protein (95% CI, 0.015-6.00, p = 0.048) lower than in the presymptomatic group. The GSH-Px activity in the symptomatic group was 13.96 U/mg of protein (95% CI, 5.90-22.03, p < 0.001) lower than in the control group and 20.52 U/mg of protein (95% CI, 6.79-34.24, p < 0.001) lower than in the presymptomatic group and was inversely correlated with the neurological examination score for spinocerebellar ataxias (R = -0.309, p = 0.049).

CONCLUSION

Early/moderate stage SCA3/MJD patients presented a decreased antioxidant capacity and increased ROS generation. GSH-Px activity was the most promising oxidative stress disease biomarker in SCA3/MJD. Further longitudinal studies are necessary to identify both the roles of redox parameters in SCA3/MJD pathophysiology and as surrogate outcomes for clinical trials.

Treatment with Caffeic Acid and Resveratrol Alleviates Oxidative Stress Induced Neurotoxicity in Cell and Drosophila Models of Spinocerebellar Ataxia Type3

Spinocerebellar ataxia type 3 (SCA3) is caused by the expansion of a polyglutamine (polyQ) repeat in the protein ataxin-3 which is involved in susceptibility to mild oxidative stress induced neuronal death. Here we show that caffeic acid (CA) and resveratrol (Res) decreased reactive oxygen species (ROS), mutant ataxin-3 and apoptosis and increased autophagy in the pro-oxidant tert-butyl hydroperoxide (tBH)-treated SK-N-SH-MJD78 cells containing mutant ataxin-3. Furthermore, CA and Res improved survival and locomotor activity and decreased mutant ataxin-3 and ROS levels in tBH-treated SCA3 Drosophila. CA and Res also altered p53 and nuclear factor-κB (NF-κB) activation and expression in tBH-treated cell and fly models of SCA3, respectively. Blockade of NF-κB activation annulled the protective effects of CA and Res on apoptosis, ROS, and p53 activation in tBH-treated SK-N-SH-MJD78 cells, which suggests the importance of restoring NF-κB activity by CA and Res. Our findings suggest that CA and Res may be useful in the management of oxidative stress induced neuronal apoptosis in SCA3.

The Truncated C-terminal Fragment of Mutant ATXN3 Disrupts Mitochondria Dynamics in Spinocerebellar Ataxia Type 3 Models

Spinocerebellar ataxia type 3 (SCA3), known as Machado-Joseph disease, is an autosomal dominant disease caused by an abnormal expansion of polyglutamine in ATXN3 gene, leading to neurodegeneration in SCA3 patients. Similar to other neurodegenerative diseases, the dysfunction of mitochondria is observed to cause neuronal death in SCA3 patients. Based on previous studies, proteolytic cleavage of mutant ATXN3 is found to produce truncated C-terminal fragments in SCA3 models. However, whether these truncated mutant fragments disturb mitochondrial functions and result in pathological death is still unclear. Here, we used neuroblastoma cell and transgenic mouse models to examine the effects of truncated mutant ATXN3 on mitochondria functions. In different models, we observed truncated mutant ATXN3 accelerated the formation of aggregates, which translocated into the nucleus to form intranuclear aggregates. In addition, truncated mutant ATXN3 caused more mitochondrial fission, and decreased the expression of mitochondrial fusion markers, including Mfn-1 and Mfn-2. Furthermore, truncated mutant ATXN3 decreased the mitochondrial membrane potential, increased reactive oxygen species and finally increased cell death rate. In transgenic mouse models, truncated mutant ATXN3 also led to more mitochondrial dysfunction, neurodegeneration and cell death in the cerebellums. This study supports the toxic fragment hypothesis in SCA3, and also provides evidence that truncated mutant ATXN3 is severer than full-length mutant one in vitro and in vivo.

Spinocerebellar Ataxia Type 2 Is Associated with the Extracellular Loss of Superoxide Dismutase but Not Catalase Activity

BACKGROUND

Spinocerebellar ataxia type 2 (SCA2) is an inherited and still incurable neurodegenerative disorder. Evidence suggests that pro-oxidant agents as well as factors involved in antioxidant cellular defenses are part of SCA2 physiopathology.

AIM

To assess the influence of superoxide dismutase (SOD3) and catalase (CAT) enzymatic activities on the SCA2 syndrome.

METHOD

Clinical, molecular, and electrophysiological variables, as well as SOD3 and CAT enzymatic activities were evaluated in 97 SCA2 patients and in 64 age- and sex-matched control individuals.

RESULTS

Spinocerebellar ataxia type 2 patients had significantly lower SOD3 enzymatic activity than the control group. However, there were no differences between patients and controls for CAT enzymatic activity. The effect size for the loss of patients' SOD3 enzymatic activity was 0.342, corresponding to a moderate effect. SOD3 and CAT enzymatic activities were not associated with the CAG repeat number at the ATXN2 gene. SOD3 and CAT enzymatic activities did not show significant associations with the age at onset, severity score, or the studied electrophysiological markers.

CONCLUSION

There is a reduced SOD3 enzymatic activity in SCA2 patients with no repercussion on the clinical phenotype.