Sensory involvement in X-linked spino-bulbar muscular atrophy (Kennedy's syndrome): an electrophysiological study

Clenbuterol-sensitive delayed outward potassium currents in a cell model of spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (SBMA) is a neuromuscular disease caused by polyglutamine (polyQ) expansions in the androgen receptor (AR) gene. SBMA is characterized by selective dysfunction and degeneration of motor neurons in the brainstem and spinal cord through still unclear mechanisms in which ion channel modulation might play a central role as for other neurodegenerative diseases. The beta2-adrenergic agonist clenbuterol was observed to ameliorate the SBMA phenotype in mice and patient-derived myotubes. However, the underlying molecular mechanism has yet to be clarified. Here, we unveil that ionic current alterations induced by the expression of polyQ-expanded AR in motor neuron-derived MN-1 cells are attenuated by the administration of clenbuterol. Our combined electrophysiological and pharmacological approach allowed us to reveal that clenbuterol modifies delayed outward potassium currents. Overall, we demonstrated that the protection provided by clenbuterol restores the normal function through the modulation of K_V2-type outward potassium currents, possibly contributing to the protective effect on motor neuron toxicity in SBMA.

Kennedy's disease: an under-recognized motor neuron disorder

Kennedy's disease or spinal bulbar muscular atrophy is a rare, inherited and slowly progressive multisystem disease mostly manifesting with a motor neuron disease phenotype leading to disability. The slow progression, partial androgen insensitivity, electrophysiological evidence of sensory neuronopathy, and relatively spared central nervous system pathways help differentiate it from amyotrophic lateral sclerosis. To date, there is no treatment or cure with clinical care mainly focused on accurate diagnosis, symptom management, patient education, and genetic counselling.

A Crucial Role for the Protein Quality Control System in Motor Neuron Diseases

Motor neuron diseases (MNDs) are fatal diseases characterized by loss of motor neurons in the brain cortex, in the bulbar region, and/or in the anterior horns of the spinal cord. While generally sporadic, inherited forms linked to mutant genes encoding altered RNA/protein products have also been described. Several different mechanisms have been found altered or dysfunctional in MNDs, like the protein quality control (PQC) system. In this review, we will discuss how the PQC system is affected in two MNDs—spinal and bulbar muscular atrophy (SBMA) and amyotrophic lateral sclerosis (ALS)—and how this affects the clearance of aberrantly folded proteins, which accumulate in motor neurons, inducing dysfunctions and their death. In addition, we will discuss how the PQC system can be targeted to restore proper cell function, enhancing the survival of affected cells in MNDs.

MEF2 impairment underlies skeletal muscle atrophy in polyglutamine disease

Polyglutamine (polyQ) tract expansion leads to proteotoxic misfolding and drives a family of nine diseases. We study spinal and bulbar muscular atrophy (SBMA), a progressive degenerative disorder of the neuromuscular system caused by the polyQ androgen receptor (AR). Using a knock-in mouse model of SBMA, AR113Q mice, we show that E3 ubiquitin ligases which are a hallmark of the canonical muscle atrophy machinery are not induced in AR113Q muscle. Similarly, we find no evidence to suggest dysfunction of signaling pathways that trigger muscle hypertrophy or impairment of the muscle stem cell niche. Instead, we find that skeletal muscle atrophy is characterized by diminished function of the transcriptional regulator Myocyte Enhancer Factor 2 (MEF2), a regulator of myofiber homeostasis. Decreased expression of MEF2 target genes is age- and glutamine tract length-dependent, occurs due to polyQ AR proteotoxicity, and is associated with sequestration of MEF2 into intranuclear inclusions in muscle. Skeletal muscle from R6/2 mice, a model of Huntington disease which develops progressive atrophy, also sequesters MEF2 into inclusions and displays age-dependent loss of MEF2 target genes. Similarly, SBMA patient muscle shows loss of MEF2 target gene expression, and restoring MEF2 activity in AR113Q muscle rescues fiber size and MEF2-regulated gene expression. This work establishes MEF2 impairment as a novel mechanism of skeletal muscle atrophy downstream of toxic polyglutamine proteins and as a therapeutic target for muscle atrophy in these disorders.

The Role of Sex and Sex Hormones in Neurodegenerative Diseases

Neurodegenerative diseases (NDs) are a wide class of disorders of the central nervous system (CNS) with unknown etiology. Several factors were hypothesized to be involved in the pathogenesis of these diseases, including genetic and environmental factors. Many of these diseases show a sex prevalence and sex steroids were shown to have a role in the progression of specific forms of neurodegeneration. Estrogens were reported to be neuroprotective through their action on cognate nuclear and membrane receptors, while adverse effects of male hormones have been described on neuronal cells, although some data also suggest neuroprotective activities. The response of the CNS to sex steroids is a complex and integrated process that depends on (i) the type and amount of the cognate steroid receptor and (ii) the target cell type-either neurons, glia, or microglia. Moreover, the levels of sex steroids in the CNS fluctuate due to gonadal activities and to local metabolism and synthesis. Importantly, biochemical processes involved in the pathogenesis of NDs are increasingly being recognized as different between the two sexes and as influenced by sex steroids. The aim of this review is to present current state-of-the-art understanding on the potential role of sex steroids and their receptors on the onset and progression of major neurodegenerative disorders, namely, Alzheimer's disease, Parkinson's diseases, amyotrophic lateral sclerosis, and the peculiar motoneuron disease spinal and bulbar muscular atrophy, in which hormonal therapy is potentially useful as disease modifier.

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.

Disentangling balance impairments in spinal and bulbar muscular atrophy

Spinal and bulbar muscular atrophy (Kennedy's disease) has been associated with balance dysfunction and falls. However, postural control has not been studied quantitatively. Here, we quantified upright stance and aimed to disentangle the role of vestibular, proprioceptive and oculomotor deficits. Static balance was assessed in Kennedy patients (n = 7) during quiet stance on a force platform under different visual and proprioceptive feedback conditions. Vestibular function was assessed with the video head impulse test. Sural nerve neurography was employed to evaluate the severity of peripheral neuropathy. Also, horizontal saccades were recorded and quantified by the main sequence relationship. Posturographic analyses revealed significantly increased body sway, more pronounced in conditions with closed eyes, which was also reflected in the calculated Romberg indices. Horizontal vestibulo-ocular reflex gains were normal, i.e. > 0.75. In contrast, compound sensory nerve action potentials were markedly decreased in all patients (mean = 2.4 μV). Two patients showed slow saccades with increased exponential main sequence constants. We conclude that Kennedy patients exhibit severe deficits in quiet stance. Postural instability is greatest in conditions of absent vision with reduced proprioception being the main determinant of unsteadiness. Some patients show slowed saccadic eye movements suggesting a nuclear abducens neuronopathy.

Autophagic and Proteasomal Mediated Removal of Mutant Androgen Receptor in Muscle Models of Spinal and Bulbar Muscular Atrophy

Spinal and bulbar muscular atrophy (SBMA) is an X-linked motoneuron disease (MND) caused by a mutant androgen receptor (AR) containing an elongated polyglutamine (polyQ) tract. ARpolyQ toxicity is triggered by androgenic AR ligands, which induce aberrant conformations (misfolding) of the ARpolyQ protein that aggregates. Misfolded proteins perturb the protein quality control (PQC) system leading to cell dysfunction and death. Spinal cord motoneurons, dorsal root ganglia neurons and skeletal muscle cells are affected by ARpolyQ toxicity. Here, we found that, in stabilized skeletal myoblasts (s-myoblasts), ARpolyQ formed testosterone-inducible aggregates resistant to NP-40 solubilization; these aggregates did not affect s-myoblasts survival or viability. Both wild type AR and ARpolyQ were processed via proteasome, but ARpolyQ triggered (and it was also cleared via) autophagy. ARpolyQ reduced two pro-autophagic proteins expression (BAG3 and VCP), leading to decreased autophagic response in ARpolyQ s-myoblasts. Overexpression of two components of the chaperone assisted selective autophagy (CASA) complex (BAG3 and HSPB8), enhanced ARpolyQ clearance, while the treatment with the mTOR independent autophagy activator trehalose induced complete ARpolyQ degradation. Thus, trehalose has beneficial effects in SBMA skeletal muscle models even when autophagy is impaired, possibly by stimulating CASA to assist the removal of ARpolyQ misfolded species/aggregates.

Non-neural phenotype of spinal and bulbar muscular atrophy: results from a large cohort of Italian patients

OBJECTIVE

To carry out a deep characterisation of the main androgen-responsive tissues involved in spinal and bulbar muscular atrophy (SBMA).

METHODS

73 consecutive Italian patients underwent a full clinical protocol including biochemical and hormonal analyses, genitourinary examination, bone metabolism and densitometry, cardiological evaluation and muscle pathology.

RESULTS

Creatine kinase levels were slightly to markedly elevated in almost all cases (68 of the 73; 94%). 30 (41%) patients had fasting glucose above the reference limit, and many patients had total cholesterol (40; 54.7%), low-density lipoproteins cholesterol (29; 39.7%) and triglyceride (35; 48%) levels above the recommended values. Although testosterone, luteinising hormone and follicle-stimulating hormone values were generally normal, in one-third of cases we calculated an increased Androgen Sensitivity Index reflecting the presence of androgen resistance in these patients. According to the International Prostate Symptom Score (IPSS), 7/70 (10%) patients reported severe lower urinal tract symptoms (IPSS score >19), and 21/73 (30%) patients were moderately symptomatic (IPSS score from 8 to 19). In addition, 3 patients were carriers of an indwelling bladder catheter. Videourodynamic evaluation indicated that 4 of the 7 patients reporting severe urinary symptoms had an overt prostate-unrelated bladder outlet obstruction. Dual-energy X-ray absorptiometry scan data were consistent with low bone mass in 25/61 (41%) patients. Low bone mass was more frequent at the femoral than at the lumbar level. Skeletal muscle biopsy was carried out in 20 patients and myogenic changes in addition to the neurogenic atrophy were mostly observed.

CONCLUSIONS

Our study provides evidence of a wide non-neural clinical phenotype in SBMA, suggesting the need for comprehensive multidisciplinary protocols for these patients.

The Role of the Protein Quality Control System in SBMA

Spinal and bulbar muscular atrophy (SBMA) or Kennedy's disease is an X-linked disease associated with the expansion of the CAG triplet repeat present in exon 1 of the androgen receptor (AR) gene. This results in the production of a mutant AR containing an elongated polyglutamine tract (polyQ) in its N-terminus. Interestingly, the ARpolyQ becomes toxic only after its activation by the natural androgenic ligands, possibly because of aberrant androgen-induced conformational changes of the ARpolyQ, which generate misfolded species. These misfolded ARpolyQ species must be cleared from motoneurons and muscle cells, and this process is mediated by the protein quality control (PQC) system. Experimental evidence suggested that failure of the PQC pathways occurs in disease, leading to ARpolyQ accumulation and toxicity in the target cells. In this review, we summarized the overall impact of mutant and misfolded ARpolyQ on the PQC system and described how molecular chaperones and the degradative pathways (ubiquitin-proteasome system (UPS), the autophagy-lysosome pathway (ALP), and the unfolded protein response (UPR), which activates the endoplasmic reticulum-associated degradation (ERAD)) are differentially affected in SBMA. We also extensively and critically reviewed several molecular and pharmacological approaches proposed to restore a global intracellular activity of the PQC system. Collectively, these data suggest that the fine and delicate equilibrium existing among the different players of the PQC system could be restored in a therapeutic perspective by the synergic/additive activities of compounds designed to tackle sequential or alternative steps of the intracellular defense mechanisms triggered against proteotoxic misfolded species.

Aberrant Autophagic Response in The Muscle of A Knock-in Mouse Model of Spinal and Bulbar Muscular Atrophy

Spinal and bulbar muscular atrophy (SBMA) is characterized by loss of motoneurons and sensory neurons, accompanied by atrophy of muscle cells. SBMA is due to an androgen receptor containing a polyglutamine tract (ARpolyQ) that misfolds and aggregates, thereby perturbing the protein quality control (PQC) system. Using SBMA AR113Q mice we analyzed proteotoxic stress-induced alterations of HSPB8-mediated PQC machinery promoting clearance of misfolded proteins by autophagy. In muscle of symptomatic AR113Q male mice, we found expression upregulation of Pax-7, myogenin, E2-ubiquitin ligase UBE2Q1 and acetylcholine receptor (AchR), but not of MyoD, and of two E3-ligases (MuRF-1 and Cullin3). TGFβ1 and PGC-1α were also robustly upregulated. We also found a dramatic perturbation of the autophagic response, with upregulation of most autophagic markers (Beclin-1, ATG10, p62/SQSTM1, LC3) and of the HSPB8-mediated PQC response. Both HSPB8 and its co-chaperone BAG3 were robustly upregulated together with other specific HSPB8 interactors (HSPB2 and HSPB3). Notably, the BAG3:BAG1 ratio increased in muscle suggesting preferential misfolded proteins routing to autophagy rather than to proteasome. Thus, mutant ARpolyQ induces a potent autophagic response in muscle cells. Alteration in HSPB8-based PQC machinery may represent muscle-specific biomarkers useful to assess SBMA progression in mice and patients in response to pharmacological treatments.

Multimodal Evoked Potentials of Kennedy's Disease

Background:

Kennedy's disease (KD) is an X-linked recessive polyglutamine disease. Traditionally, it is a lower motor neuron syndrome with additional features such as gynecomastia and tremor. Sensory symptoms are minimal if ever present. We used multimodal evoked potential (EPs) tests to study the distribution of the involvement of the disease.

Methods:

Visual, brainstem auditory, somatosensory and motor EPs were studied in six KD patients. All of them had typical presentations and had been proved genetically.

Results:

Abnormal findings were noted as follows: prolonged peak latencies of visual EPs, increased hearing threshold level, inconsistent brainstem auditory EPs, decreased amplitudes of cortical potentials of somatosensory EPs, and increased motor threshold to transcranial magnetic stimulation.

Conclusions:

Our multimodal EP studies showed that KD involved multiple levels of the nervous system. It implies the widespread effects of the mutant androgen receptors.

Discrimination of spinal and bulbar muscular atrophy from amyotrophic lateral sclerosis using sensory nerve action potentials

INTRODUCTION

Spinal and bulbar muscular atrophy (SBMA) and amyotrophic lateral sclerosis (ALS) are motor neuron diseases. Sensory impairment is sometimes observed, and electrophysiological involvement has been described in the sensory nerves of SBMA patients. We hypothesized that a sensory nerve conduction study (NCS) could be used to discriminate SBMA from ALS.

METHODS

We compared the results from NCSs in a total of 120 SBMA cases confirmed by genetic analysis, 188 ALS cases, and 50 normal subjects.

RESULTS

Sensory nerve action potential (SNAP) amplitudes of the SBMA group were significantly lower than in the ALS and control groups. In addition, receiver-operating characteristic curve analysis for SNAP amplitude showed that a cut-off value of 13.8 μV for median, 10.7 μV for ulnar, and 9.9 μV for sural nerve best discriminated SBMA from ALS.

CONCLUSIONS

The specific decrease of SNAP amplitude in SBMA provides another useful tool for the differential diagnosis of motor neuron diseases.

Are cognitive and behavioural deficits a part of the clinical picture in Kennedy's disease? A case study

Two years prior to diagnosis of Kennedy's disease (KD), a 53-year-old man began experiencing neurological symptoms, including nasal speech, postural tremor, tremor in the upper extremities, and muscle weakness. Genetic analysis revealed 46 CAG repeats in the androgen receptor gene. The patient's altered social conduct and complaints of forgetfulness led to a neuropsychological assessment. A mild impairment in visuospatial and visuoconstructive abilities, visual short-term memory, and a personality disorder were detected. Although cognition and behaviour in KD are typically normal, our findings suggest that the disease may cause mild cognitive and behavioural changes as part of the disease's clinical manifestation.

Decreased cortical somatosensory finger representation in X-linked recessive bulbospinal neuronopathy (Kennedy disease): a magnetoencephalographic study

BACKGROUND

Kennedy disease (KD) clinically presents as progressive lower motor neuron disease with minimal or no sensory impairment. However, electrophysiological studies found abnormal somatosensory-evoked potentials even in absence of clinical deficits. Little is known about possible influences of this sensory neuropathy on the central somatosensory processing.

METHODS

In this study, the cortical topography of index finger representation was studied in 7 patients with genetically proven KD compared to healthy control subjects by means of magnetoencephalography using an established stimulation paradigm. Data analysis was carried out with synthetic aperture magnetometry (SAM). Additionally, the latency and source amplitude of the earliest cortical somatosensory-evoked field (SEF) component were determined based on traditional single dipole source analysis.

RESULTS

In KD patients the latency of the SEF was prolonged (48.6 vs. 37.4 ms, P < .005). There was no significant difference in dipole source amplitude, but stimulus-related SAM activation of the contralateral sensorimotor cortex (pseudo-t-values -.107 vs. -.199, P < .05), including maximum activity (53.5%), was reduced.

CONCLUSIONS

These results implicate that even subclinical sensory neuropathy leads to possible functional reorganization of the sensorimotor cortex in KD patients and reinforces the view that in KD the somatosensory system is extensively involved.

Spinal and bulbar muscular atrophy: skeletal muscle pathology in male patients and heterozygous females

Spinal and bulbar muscular atrophy (SBMA) is an adult form of X-linked motor neuron disease caused by an expansion of a CAG repeat sequence in the first exon of the androgen receptor (AR) gene. Nuclear accumulation of mutant AR with expanded polyglutamines in motor neurons is a major pathogenic mechanism. To characterize muscle involvement in SBMA the skeletal muscle biopsies of 8 SBMA patients and 3 female carriers were studied. Six of 8 SBMA patients showed myogenic changes together with the neurogenic atrophy in their muscle biopsy. Myopathic abnormalities did not correlate with disease duration and were more prominent in the muscle of patients with an higher degree of disability. In all patients plasma CK levels were more elevated than what usually occurs in denervative diseases. Both neurogenic and myopathic changes were also observed in female carriers. Here we suggest that myopathic changes in SBMA muscle are not only related to denervation and that muscle satellite cells may have a role in the pathogenesis of muscle damage.

Kennedy's disease: pathogenesis and clinical approaches

Kennedy's disease, also known as spinal and bulbar muscular atrophy, is a progressive degenerative condition affecting lower motor neurons. It is one of nine neurodegenerative disorders caused by a polyglutamine repeat expansion. Affecting only men, Kennedy's disease is the only one of these conditions that follows an X-linked mode of inheritance. The causative protein in Kennedy's disease, with a polyglutamine expansion residing in the first N-terminal domain, is the androgen receptor. Research in this field has made significant advances in recent years, and with the increased understanding of pathogenic mechanisms, feasible approaches to treatments are being investigated. In Kennedy's disease research, the most significant issue to emerge recently is the role of androgens in exacerbating the disease process. On the basis of animal experiments, a viable hypothesis is that higher circulating levels of androgens in men could trigger the degeneration of motor neurons causing this disease, and that lower levels in heterozygous and homozygous women are protective. This is a major issue, as treatment of individuals affected by Kennedy's disease with testosterone has been considered a reasonable therapy by some neurologists. The rationale behind this approach relates to the fact that Kennedy's disease is accompanied by mild androgen insensitivity. It was therefore believed that treatment with high doses of testosterone might compensate for this loss of androgen action, with the added benefit of preventing muscle wasting. The current review provides an overview of recent advances in the field of Kennedy's disease research, including approaches to treatment.

Anatomically based guidelines for systematic investigation of the central somatosensory system and their application to a spinocerebellar ataxia type 2 (SCA2) patient

Dysfunctions of the somatosensory system are among the clinical signs that characterize a variety of polyglutamine or CAG-repeat diseases. Deficits within this system may hinder the perception of potential threats, be detrimental to somatomotor functions, and result in uncoordinated movements, ataxia, and falls. Despite the considerable clinical relevance of such deficits, however, no systematic pathoanatomical studies of the central somatosensory system in polyglutamine diseases are currently available. The present paper has two goals: (1) recommendation of an economical tissue sampling method and optimized histological processing of this tissue to allow rapid and reliable evaluation of the structural integrity of all known relay stations and interconnecting fibre tracts within this complex system, and (2) the proposal of guidelines for a rapid and detailed pathoanatomical investigative procedure of the human central somatosensory system. In so doing, we draw on the current state of neuroanatomic research and apply the methods and guidelines proposed here to a 25-year-old female patient with spinocerebellar ataxia type 2 (SCA2). The use of 100 microm serial sections through the SCA2 patient's central somatosensory components showed that obvious neuronal loss occurred in nearly all of the relay stations of this system (Clarke's column; cuneate, external cuneate and gracile nuclei; spinal, principal and mesencephalic trigeminal nuclei; ventral posterior lateral and ventral posterior medial nuclei of the thalamus), whereas the majority of interconnecting fibre tracts (dorsal spinocerebellar tract; cuneate and gracile fascicles; medial lemniscus; spinal trigeminal tract, trigeminal nerve and mesencephalic trigeminal tract) displayed signs of atrophy accompanied by demyelinization. These pathological findings suffice to explain the patient's impaired senses of vibration, position and temperature. Moreover, together with the lesions seen in the motor cerebellothalamocortical feedback loop (pontine nuclei, deep cerebellar nuclei and cerebellar cortex, ventral lateral nucleus of the thalamus), they also account for the somatomotor deficits that were observed in the young woman (gait, stance, and limb ataxia, falls, and impaired writing). In proposing these new guidelines, we hope to enable others to study the hitherto unknown morphological counterparts of somatosensory dysfunctions in additional CAG-repeat disease patients.

Epidemiological survey of X-linked bulbar and spinal muscular atrophy, or Kennedy disease, in the province of Reggio Emilia, Italy

Commencing with the work carried out during the epidemiological survey of amyotrophic lateral sclerosis in the period 1980-1992 and the pathology follow-up, we carried out a perspective incidence, prevalence and mortality survey of X-linked bulbar and spinal muscular atrophy (X-BSMA) in the province of Reggio Emilia in Northern Italy. Based on 11 patients (eight familial and three sporadic cases), the mean incidence per year for the period 1980 through 1997, as evaluated at the onset of symptoms, was 0.09 cases/100,000 for the total population and 0.19 cases/100,000 for the male population. On December 31, 1997, the prevalence rate was 1.6/100,000 for the total population and 3.3/100,000 for the male population. In the 18-year period of 1980-1997, the average yearly mortality rate was: 0.03 cases/100,000 per year for the total population and 0.06 cases/ 100,000 for the male population. The average age at onset was 44.8 +/- 10.1, and the average survival period was 27.3 +/- 2.3 years. The average age of the prevalence day was 58.9 +/- 14.9, and the average age at death was 71.3 +/- 4.7 years. Whereas the incidence rate of X-BSMA in the province of Reggio Emilia is 16 times lower that of amyotrophic lateral sclerosis (ALS), the incidence rate of progressive bulbar palsy in the male population is only slightly higher than X-BSMA; and the prevalence rate of ALS for males is two times the prevalence rate for X-BSMA, with overlapping of confidence intervals. X-BSMA is a rare disease, which is probably under-diagnosed, but due to the long survival period of this disease its frequency is not negligible. Because of the presence of sporadic cases or non-evident familial cases, it is appropriate to consider this diagnostic possibility in making a diagnosis of ALS in patients in whom lower motor neuron dysfunction or bulbar onset predominates.