Exercise Therapy in Spinobulbar Muscular Atrophy and Other Neuromuscular Disorders

Insights into dentatorubral-pallidoluysian atrophy from a new Drosophila model of disease

Dentatorubral-pallidoluysian atrophy (DRPLA) is a neurodegenerative disorder that presents with ataxia, dementia and epilepsy. As a member of the polyglutamine family of diseases, DRPLA is caused by abnormal CAG triplet expansion beyond 48 repeats in the protein-coding region of ATROPHIN 1 (ATN1), a transcriptional co-repressor. To better understand DRPLA, we generated new Drosophila lines that can be induced to express full-length, human ATN1 with a normal (Q7) or pathogenic (Q88) repeat in a variety of cells, including neuronal, glial or any other type of tissue. Expression of ATN1 is toxic, with the polyglutamine-expanded version being consistently more problematic than wild-type ATN1. Fly motility, longevity and internal structures are negatively impacted by pathogenic ATN1. RNA-seq identified altered protein quality control and immune pathways in the presence of pathogenic ATN1. Based on these data, we conducted genetic experiments that confirmed the role of protein quality control components that ameliorate or exacerbate ATN1 toxicity. Hsc70-3, a chaperone, arose as a likely suppressor of toxicity. VCP (a proteasome-related AAA ATPase), Rpn11 (a proteasome-related deubiquitinase) and select DnaJ proteins (co-chaperones) were inconsistently protective, depending on the tissues where they were expressed. Lastly, informed by RNA-seq data that exercise-related genes may also be involved in this model of DRPLA, we conducted short-term exercise, which improved overall fly motility. This new model of DRPLA will prove important to understanding this understudied disease and will help to identify therapeutic targets for it.

Insights into Dentatorubral-Pallidoluysian Atrophy from a new Drosophila model of disease

Dentatorubral-pallidoluysian atrophy (DRPLA) is a neurodegenerative disorder that presents with ataxia, dementia and epilepsy. As a member of the polyglutamine family of diseases, DRPLA is caused by abnormal CAG triplet expansion beyond 48 repeats in the protein-coding region of ATROPHIN 1 (ATN1), a transcriptional co-repressor. To better understand DRPLA, we generated new Drosophila lines that express full-length, human ATN1 with a normal (Q7) or pathogenic (Q88) repeat. Expression of ATN1 is toxic, with the polyglutamine-expanded version being consistently more problematic than wild-type ATN1. Fly motility, longevity and internal structures are negatively impacted by pathogenic ATN1. RNA-seq identified altered protein quality control and immune pathways in the presence of pathogenic ATN1. Based on these data, we conducted genetic experiments that confirmed the role of protein quality control components that ameliorate or exacerbate ATN1 toxicity. Hsc70-3, a chaperone, arose as a likely suppressor of toxicity. VCP (a proteasome-related AAA ATPase), Rpn11 (a proteasome-related deubiquitinase) and select DnaJ proteins (co-chaperones) were inconsistently protective, depending on the tissues where they were expressed. Lastly, informed by RNA-seq data that exercise-related genes may also be involved in this model of DRPLA, we conducted short-term exercise, which improved overall fly motility. This new model of DRPLA will prove important to understanding this understudied disease and will help to identify therapeutic targets for it.

Exercise attenuates polyglutamine-mediated neuromuscular degeneration in a mouse model of spinal and bulbar muscular atrophy

BACKGROUND

Spinal and bulbar muscular atrophy (SBMA) is a hereditary neuromuscular disorder caused by the expansion of trinucleotide cytosine-adenine-guanine (CAG) repeats, which encodes a polyglutamine (polyQ) tract in the androgen receptor (AR) gene. Recent evidence suggests that, in addition to motor neuron degeneration, defective skeletal muscles are also the primary contributors to the pathogenesis in SBMA. While benefits of physical exercise have been suggested in SBMA, underlying mechanism remains elusive.

METHODS

We investigated the effect of running exercise in a transgenic mouse model of SBMA carrying human AR with 97 expanded CAGs (AR97Q). We assigned AR97Q mice to exercise and sedentary control groups, and mice in the exercise group received 1-h forced running wheel (5 m/min) 5 days a week for 4 weeks during the early stage of the disease. Motor function (grip strength and rotarod performance) and survival of each group were analysed, and histopathological and biological features in skeletal muscles and motor neurons were evaluated.

RESULTS

AR97Q mice in the exercise group showed improvement in motor function (~40% and ~50% increase in grip strength and rotarod performance, respectively, P < 0.05) and survival (median survival 23.6 vs. 16.7 weeks, P < 0.05) with amelioration of neuronal and muscular histopathology (~1.4-fold and ~2.8-fold increase in motor neuron and muscle fibre size, respectively, P < 0.001) compared to those in the sedentary group. Nuclear accumulation of polyQ-expanded AR in skeletal muscles and motor neurons was suppressed in the mice with exercise compared to the sedentary mice (~50% and ~30% reduction in 1C2-positive cells in skeletal muscles and motor neurons, respectively, P < 0.05). We found that the exercise activated 5'-adenosine monophosphate-activated protein kinase (AMPK) signalling and inhibited mammalian target of rapamycin pathway that regulates protein synthesis in skeletal muscles of SBMA mice. Pharmacological activation of AMPK inhibited protein synthesis and reduced polyQ-expanded AR proteins in C2C12 muscle cells.

CONCLUSIONS

Our findings suggest the therapeutic potential of exercise-induced effect via AMPK activation in SBMA.

Association of Body Mass Index With Disease Progression in Children With Charcot-Marie-Tooth Disease

BACKGROUND AND OBJECTIVES

The aim of this study was to evaluate the impact of body mass index (BMI) on disease progression over 2 years in children with Charcot-Marie-Tooth disease (CMT).

METHODS

BMI was classified in 242 participants aged 3-20 years with CMT enrolled in the Inherited Neuropathy Consortium, using the International Obesity Task Force (based on adult BMI values, kg/m2) criteria. Groups were categorized as severely underweight (BMI <17 kg/m2), underweight (BMI ≥17 to <18.5 kg/m2), healthy weight (BMI ≥18.5 to <25 kg/m2), overweight (BMI ≥25 to <30 kg/m2), and obese (BMI ≥30 kg/m2). Disease severity was assessed using the CMT Pediatric Scale (CMTPedS), a clinical outcome assessment of disability (0-44 points, mild to severe).

RESULTS

At baseline, compared with individuals being of a healthy weight (mean CMTPedS 15.48, SD 9.22), children who were severely underweight (mean CMTPedS difference 9.03, 95% CI 0.94-17.12; p = 0.02), underweight (mean CMTPedS difference 5.97, 95% CI 0.62-11.31; p = 0.02), or obese (mean CMTPedS difference 7.96, 95% CI 1.03-14.88; p = 0.015) exhibited greater disability. At 2 years, compared with individuals being of a healthy weight (mean CMTPedS 17.53, SD 9.41), children who were severely underweight exhibited greater disability (mean CMTPedS difference 9.27, 95% CI 0.90-17.64; p = 0.02). Over the 2-year periods, the mean CMTPedS for the whole sample deteriorated by 1.72 points (95% CI 1.09-2.38; p < 0.001), with severely underweight children progressing at the fastest rate (mean CMTPedS change of 2.3, 95% CI 1.53-6.13; p = 0.21). In children who did not have a change in BMI categories over 2 years (69% of sample), CMTPedS scores deteriorated faster in those who were severely underweight (mean CMTPedS change 6.40 points, 95% CI 2.42-10.38; p = 0.01) than those of healthy weight (mean CMTPedS change 1.79 points, 95% CI 0.93-2.69; p < 0.001). For children who changed BMI categories (31% of sample), CMTPedS scores deteriorated faster in children who became overweight/obese (mean CMTPedS change 2.76 points, 95% CI 0.11-5.41; p = 0.031).

DISCUSSION

Children with CMT who were severely underweight, underweight, or obese exhibited greater disability at baseline. Over the 2-year period in those whose BMI remained stable, severely underweight children deteriorated at the fastest rate. For children who changed BMI categories over the 2 years, CMTPedS scores deteriorated faster in children who became overweight/obese. Interventions that maintain or improve BMI toward healthy weight may reduce disability in children with CMT.

The protective role of exercise against age-related neurodegeneration

Endurance exercise is a widely accessible, low-cost intervention with a variety of benefits to multiple organ systems. Exercise improves multiple indices of physical performance and stimulates pronounced health benefits reducing a range of pathologies including metabolic, cardiovascular, and neurodegenerative disorders. Endurance exercise delays brain aging, preserves memory and cognition, and improves symptoms of neurodegenerative pathologies like Amyotrophic Lateral Sclerosis, Alzheimer's disease, Parkinson's disease, Huntington's disease, and various ataxias. Potential mechanisms underlying the beneficial effects of exercise include neuronal survival and plasticity, neurogenesis, epigenetic modifications, angiogenesis, autophagy, and the synthesis and release of neurotrophins and cytokines. In this review, we discuss shared benefits and molecular pathways driving the protective effects of endurance exercise on various neurodegenerative diseases in animal models and in humans.

Functional and surgical treatments in patients with spinal muscular atrophy (SMA)

Spinal muscular atrophies (SMA type 1, 2, 3) present with various severities according to the motor semeiology related to lesions of the peripheral nervous system (lesions of the anterior horn cells motoneuron or even brain stem). Early motor deficiency causes skeletal deformities responsible for the alteration or even absence of motor skills acquisition. The management of these patients involves several practitioners: pediatric neurologist, pediatric pneumologist, physical medicine and rehabilitation therapist, pediatric orthopedic surgeon, psychologist, physiotherapist, etc. Therefore, this multidisciplinary management must take place in a reference center. This has allowed for improvement of the natural history of SMA. Despite the severity of clinical presentation, especially in SMA type 1 or 2, the functional aspect is always to be taken into account in the first instance. Furthermore, the natural history of the disease is currently being modified by the emergence of innovative therapies that will change the evolution of the disease and its management. Indeed, current treatment objectives are the comfort of installation and the fight against neuro-orthopedic degradation. Although the rise in the number of innovative therapies has led to increased expectancies, such as motor function improvement, practitioners should be aware that these innovative treatments should be balanced against child development and the disease's natural history. Scoliosis surgery is almost systematic in SMA type 2 because of trunk muscular deficiency, especially intercostal muscle insufficiency, and spino-pelvic complex disorder. However, surgical techniques have evolved to become less invasive and more growth friendly in order to follow child development. The final goal of surgery in SMA patients is to obtain a 3-dimensional deformity correction along with a spino-pelvic realignment in order to allow for a comfortable seated position, which is the position of function in these patients, and to allow for better ventilation. Faced with this global approach and innovative therapies, global assessment is warranted not solely in an isolated manner, as is usually the case during hospital stays with traditional scales, but rather during daily activities. This is the case of daily monitoring, which allows for motor skill and activity assessments throughout the day. The principle is to characterize, according to SMA type and treatment, the activity type (standing, seated, walking), duration, intensity and frequency. The ultimate goal would be to identify the variety and occurrence of motor activities, and finally to clarify if the different treatments, including innovative therapies, lead to functional improvement in these patients. © 2020 French Society of Pediatrics. Published by Elsevier Masson SAS. All rights reserved.

Effect of Muscular Exercise on Patients With Muscular Dystrophy: A Systematic Review and Meta-Analysis of the Literature

Background: Muscular dystrophy causes weakness and muscle loss. The effect of muscular exercise in these patients remains controversial. Objective: To assess the effects of muscular exercise vs. no exercise in patients with muscular dystrophy. Methods: We performed a comprehensive systematic literature search in the Medline, Embase, Web of Science, Scopus, and Pedro electronic databases, as well as in the reference literature. We included randomized clinical trials (RCTs) that reported the effect of muscular exercise on muscle strength, endurance during walking, motor abilities, and fatigue. Data were extracted independently by two reviewers. Mean difference (MD) and 95% confidence intervals (CI) were used to quantify the effect associated with each outcome. We performed pairwise meta-analyses and trial sequential analyses (TSA) and used GRADE to rate the overall certainty of evidence. Results: We identified 13 RCTs involving 617 patients. The median duration of exercise interventions was 16 weeks [interquartile range [IQR] 12-24]. In the patients with facio-scapulo-humeral dystrophy and myotonic dystrophy, no significant difference in extensor muscle strength was noted between the exercise and the control groups [four studies, 115 patients, MD 4.34, 95% CI -4.20 to 12.88, I 2 = 69%; p = 0.32; minimal important difference [MID] 5.39 m]. Exercise was associated with improved endurance during walking [five studies, 380 patients, MD 17.36 m, 95% CI 10.91-23.81, I 2 = 0; p < 0.00001; MID 34 m]. TSA excluded random error as a cause of the findings for endurance during walking. Differences in fatigue and motor abilities were small. Not enough information was found for other types of dystrophy. Conclusions: Muscular exercise did not improve muscle strength and was associated with modest improvements in endurance during walking in patients with facio-scapulo-humeral and myotonic dystrophy. Future trials should explore which type of muscle exercise could lead to better improvements in muscle strength. PROSPERO: CRD42019127456.

Psychosocial impact of sport activity in neuromuscular disorders

Previous studies demonstrated the benefits of motor exercise and physical activity in neuromuscular disorders. However, very few papers assessed the effects of sport practise. The aim of this multicentre study was to assess the impact of sport activity on self-esteem and emotional regulation in a cohort of athletes with neuromuscular disorders. The 38 patients with Duchenne, Becker or other types of muscular dystrophy or spinal muscular atrophy practising sport (aged 13-49 years) and 39 age-, gender-, disability- and disease-matched patients not practising sport were enrolled. Testing procedures to assess self-esteem, anxiety and depression disorder, personality trait and quality of life (QoL) were used. Patients practising sport had a significantly higher self-esteem, lower level of depression, greater social own identity and adherence and QoL. Frequency of sport activity may represent a complementary therapy in neuromuscular disorders to improve mental and social well-being.

Molecular Mechanisms and Therapeutics for SBMA/Kennedy's Disease

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disease caused by a polyglutamine (polyQ) expansion in the androgen receptor (AR). Despite the fact that the monogenic cause of SBMA has been known for nearly 3 decades, there is no effective treatment for this disease, underscoring the complexity of the pathogenic mechanisms that lead to a loss of motor neurons and muscle in SBMA patients. In the current review, we provide an overview of the system-wide clinical features of SBMA, summarize the structure and function of the AR, discuss both gain-of-function and loss-of-function mechanisms of toxicity caused by polyQ-expanded AR, and describe the cell and animal models utilized in the study of SBMA. Additionally, we summarize previously conducted clinical trials which, despite being based on positive results from preclinical studies, proved to be largely ineffective in the treatment of SBMA; nonetheless, these studies provide important insights as researchers develop the next generation of therapies.

Physical Exercise for Muscle Atrophy

The most direct characteristic of muscle atrophy is reduction in muscle mass, which is due to increased protein degradation or reduced protein synthesis in skeletal muscle. The loss of muscle mass can directly affect the quality of daily life, prolong the recovery period, and become the main risk factor for chronic diseases. However, there is currently no effective way to prevent and treat this disease, and therefore it is imperative to explore effective therapeutic approaches for muscle atrophy. It is well known that physical exercise is important for maintaining good health and long-term adherence to exercise can reduce the risk of cardiovascular diseases, obesity, and diabetes. It is also well established that exercise training can promote the synthesis of muscle protein and activate signaling pathways that regulate the metabolism and function of muscle fibers. Therefore, exercise can be used as a method to treat muscle atrophy in many of these conditions. Mitochondria play an important role in skeletal muscle homeostasis and bioenergy metabolism. Mitochondria are sensitive to contractile signals, and hence exercise can improve mitochondrial function and promote biosynthesis, which ultimately maintains the healthy state of cells and the whole body. On the other hand, frequent unaccustomed exercise will change the structure and function of skeletal muscle fibers, which is called exercise-induced muscle damage. When the exercise-induced muscle damage happens, it can cause temporary muscle damage and soreness, giving a negative effect on the muscle function.

Rescue of Metabolic Alterations in AR113Q Skeletal Muscle by Peripheral Androgen Receptor Gene Silencing

Spinal and bulbar muscular atrophy (SBMA), a progressive degenerative disorder, is caused by a CAG/glutamine expansion in the androgen receptor (polyQ AR). Recent studies demonstrate that skeletal muscle is an important site of toxicity that contributes to the SBMA phenotype. Here, we sought to identify critical pathways altered in muscle that underlie disease manifestations in AR113Q mice. This led to the unanticipated identification of gene expression changes affecting regulators of carbohydrate metabolism, similar to those triggered by denervation. AR113Q muscle exhibits diminished glycolysis, altered mitochondria, and an impaired response to exercise. Strikingly, the expression of genes regulating muscle energy metabolism is rescued following peripheral polyQ AR gene silencing by antisense oligonucleotides (ASO), a therapeutic strategy that alleviates disease. Our data establish the occurrence of a metabolic imbalance in SBMA muscle triggered by peripheral expression of the polyQ AR and indicate that alterations in energy utilization contribute to non-neuronal disease manifestations.

Kennedy disease (X-linked recessive bulbospinal neuronopathy): A comprehensive review from pathophysiology to therapy

Kennedy's disease, also known as spinal and bulbar muscular atrophy (SBMA), is a rare, adult-onset, X-linked recessive neuromuscular disease caused by expansion of a CAG repeat sequence in exon 1 of the androgen receptor gene (AR) encoding a polyglutamine (polyQ) tract. The polyQ-expanded AR accumulates in nuclei, and initiates degeneration and loss of motor neurons and dorsal root ganglia. While the disease has long been considered a pure lower motor neuron disease, recently, the presence of major hyper-creatine-kinase (CK)-emia and myopathic alterations on muscle biopsy has suggested the presence of a primary myopathy underlying a wide range of clinical manifestations. The disease, which affects male adults, is characterized by muscle weakness and atrophy localized proximally in the limbs, and bulbar involvement. Sensory disturbances are associated with the motor phenotype, but may be subclinical. The most frequent systemic symptom is gynecomastia related to androgen insensitivity, but other abnormalities, such as heart rhythm and urinary disturbances, have also been reported. The course of the disease is slowly progressive with normal life expectancy. The diagnosis of SBMA is based on genetic testing, with 38 CAG repeats taken as pathogenic. Despite several therapeutic attempts made in mouse models, no effective disease-modifying therapy is yet available, although symptomatic therapy is beneficial for the management of the weakness, fatigue and bulbar symptoms.

Introduction to the Special Issue on Spinal and Bulbar Muscular Atrophy

This special issue is dedicated to spinal and bulbar muscular atrophy (SBMA) and is based on the conference sponsored by the European Neuromuscular Centre (ENMC) held in March 2015. SBMA, also known as Kennedy's disease, is a neurodegenerative disease caused by an expansion of a repeat of the trinucleotide CAG encoding glutamine in the gene encoding androgen receptor (AR). Expansion of polyglutamine in the AR results in selective lower motor neuron degeneration and skeletal muscle atrophy. SBMA belongs to the family of polyglutamine diseases, which also includes Huntington's disease, dentatorubral-pallidoluysian atrophy, and spinocerebellar ataxia (SCA) types 1, 2, 3, 6, 7, and 17. Within the family of polyglutamine diseases, SBMA is unique in its gender-specificity, with full disease manifestation restricted to males. Since the disease is ligand (androgen)-dependent, SBMA manifests primarily in males which have high levels of circulating androgens in the serum; females are usually asymptomatic. Indeed, the polyglutamine-expanded AR is converted to a neurotoxic species upon binding to androgens. The mechanisms through which androgen binding triggers the disease are under investigation. Although several therapeutic strategies have been proposed to date, there is currently no effective therapy to arrest or delay disease progression in patients.