Jun Sone

Disulfide bond mediates aggregation, toxicity, and ubiquitylation of familial amyotrophic lateral sclerosis-linked mutant SOD1

Mutations in the Cu/Zn-superoxide dismutase (SOD1) gene cause familial amyotrophic lateral sclerosis (ALS) through the gain of a toxic function; however, the nature of this toxic function remains largely unknown. Ubiquitylated aggregates of mutant SOD1 proteins in affected brain lesions are pathological hallmarks of the disease and are suggested to be involved in several proposed mechanisms of motor neuron death. Recent studies suggest that mutant SOD1 readily forms an incorrect disulfide bond upon mild oxidative stress in vitro, and the insoluble SOD1 aggregates in spinal cord of ALS model mice contain multimers cross-linked via intermolecular disulfide bonds. Here we show that a non-physiological intermolecular disulfide bond between cysteines at positions 6 and 111 of mutant SOD1 is important for high molecular weight aggregate formation, ubiquitylation, and neurotoxicity, all of which were dramatically reduced when the pertinent cysteines were replaced in mutant SOD1 expressed in Neuro-2a cells. Dorfin is a ubiquityl ligase that specifically binds familial ALS-linked mutant SOD1 and ubiquitylates it, thereby promoting its degradation. We found that Dorfin ubiquitylated mutant SOD1 by recognizing the Cys6- and Cys111-disulfide cross-linked form and targeted it for proteasomal degradation.

TDP-43 Depletion Induces Neuronal Cell Damage through Dysregulation of Rho Family GTPases

The 43-kDa TAR DNA-binding protein (TDP-43) is known to be a major component of the ubiquitinated inclusions characteristic of amyotrophic lateral sclerosis and frontotemporal lobar degeneration with ubiquitin-positive inclusions. Although TDP-43 is a nuclear protein, it disappears from the nucleus of affected neurons and glial cells, implicating TDP-43 loss of function in the pathogenesis of neurodegeneration. Here we show that the knockdown of TDP-43 in differentiated Neuro-2a cells inhibited neurite outgrowth and induced cell death. In knockdown cells, the Rho family members RhoA, Rac1, and Cdc42 GTPases were inactivated, and membrane localization of these molecules was reduced. In addition, TDP-43 depletion significantly suppressed protein geranylgeranylation, a key regulating factor of Rho family activity and intracellular localization. In contrast, overexpression of TDP-43 mitigated the cellular damage caused by pharmacological inhibition of geranylgeranylation. Furthermore administration of geranylgeranyl pyrophosphate partially restored cell viability and neurite outgrowth in TDP-43 knockdown cells. In summary, our data suggest that TDP-43 plays a key role in the maintenance of neuronal cell morphology and survival possibly through protein geranylgeranylation of Rho family GTPases.

Skin biopsy is useful for the antemortem diagnosis of neuronal intranuclear inclusion disease

Background: Neuronal intranuclear inclusion disease (NIID) is a progressive neurodegenerative disease characterized by eosinophilic hyaline intranuclear inclusions in neuronal and somatic cells. Because of the variety of clinical manifestations, antemortem diagnosis of NIID is difficult. Methods: Seven skin biopsy samples from patients with familial NIID were evaluated histochemically, and the results were compared with those of skin samples from normal control subjects and from patients with other neurologic diseases. We also examined skin biopsy samples from patients with NIID by electron microscopy. Results: In NIID skin biopsy samples, intranuclear inclusions were observed in adipocytes, fibroblasts, and sweat gland cells. These inclusions were stained with both anti-ubiquitin and anti-SUMO1 antibodies. Electron microscopy revealed that the features of the intranuclear inclusions in adipocytes, fibroblasts, and sweat gland cells were identical to those of neuronal cells. Approximately 10% of adipocytes showed intranuclear inclusions. No intranuclear inclusions were identified in the skin samples from normal control subjects and patients with other neurologic diseases. Conclusions: Skin biopsy is an effective and less invasive antemortem diagnostic tool for NIID.

Neuronal intranuclear hyaline inclusion disease showing motor-sensory and autonomic neuropathy

Background: Neuronal intranuclear hyaline inclusion disease (NIHID), a rare neurodegenerative disease in which eosinophilic intranuclear inclusions develop mainly in neurons, has not yet been described to present as hereditary motor-sensory and autonomic neuropathy. Methods: Patients in two NIHID families showing peripheral neuropathy were evaluated clinically, electrophysiologically, and histopathologically. Results: In both families, patients had severe muscle atrophy and weakness in limbs, limb girdle, and face; sensory impairment in the distal limbs; dysphagia, episodic intestinal pseudoobstruction with vomiting attacks; and urinary and fecal incontinence. No patients developed symptoms suggesting CNS involvement. Electrophysiologic study showed the reduced motor and sensory nerve conduction velocities and amplitudes, and also extensive denervation potentials. In sural nerve specimens, numbers of myelinated and unmyelinated fibers were decreased. In two autopsy cases, eosinophilic intranuclear inclusions were widespread, particularly in sympathetic and myenteric ganglion neurons, dorsal root ganglion neurons, and spinal motor neurons. These neurons also were decreased in number. Conclusion: Patients with neuronal intranuclear hyaline inclusion disease (NIHID) can manifest symptoms limited to those of peripheral neuropathy. NIHID therefore is part of the differential diagnosis of hereditary motor-sensory neuropathy associated with autonomic symptoms. Intranuclear hyaline inclusions in Schwann cells and in the myenteric plexus may permit antemortem diagnosis of NIHID.

Neuronal intranuclear inclusion disease cases with leukoencephalopathy diagnosed via skin biopsy

Neuronal intranuclear inclusion disease (NIID) is a progressive neurodegenerative disease characterised by eosinophilic hyaline intranuclear inclusions which are widely observed in neuronal and somatic cells.1 ,2 NIID has been considered to be a heterogeneous disease with highly variable clinical manifestations such as neuropathy, cerebellar ataxia and dementia, which may occur concomitantly in certain cases.1–5 Sporadic and familial cases have been reported, and the onset of disease varies from the infantile stages to late middle age. These factors made the antemortem diagnosis of NIID difficult. However, in 2011, we reported that skin biopsy is a useful antemortem diagnostic tool for familial neuronal intranuclear inclusion disease because it detects intranuclear inclusions in the dermal cells.3 Recently, some autopsies of NIID patients with leukoencephalopathy have been reported.4 In this study, we identified intranuclear inclusions in skin biopsy samples from three sporadic NIID patients who presented with cognitive dysfunction along with notable brain MRIs findings of leukoencephalopathy. A patient aged in the late sixties with neither significant past medical history nor family history of neurological disease was referred to our hospital with gait disturbance and dementia with symptoms including frequent disorientation over 3 years. A neurological examination revealed no ataxia, sensory disturbances or urinary incontinence. The patients Mini-Mental State Examination (MMSE) Score was 29. A brain MRI showed moderate cerebral and cerebellar atrophy and high-intensity areas in the cerebral white matter in the T2-weighted and fluid-attenuated inversion recovery (FLAIR) images (figure 1A). The MRI diffusion-weighted imaging (DWI) revealed a high-intensity signal in the corticomedullary junction, and these areas showed isointensity and low intensity on the ADC map (figure 1A). A cerebrospinal fluid (CSF) examination showed no pleocytosis or protein elevation and a normal glucose level. The nerve conduction studies …

c-Abl Inhibition Delays Motor Neuron Degeneration in the G93A Mouse, an Animal Model of Amyotrophic Lateral Sclerosis

Background Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive death of motor neurons. Although the pathogenesis of ALS remains unclear, several cellular processes are known to be involved, including apoptosis. A previous study revealed the apoptosis-related gene c-Abl to be upregulated in sporadic ALS motor neurons. Methodology/Findings We investigated the possibility that c-Abl activation is involved in the progression of ALS and that c-Abl inhibition is potentially a therapeutic strategy for ALS. Using a mouse motor neuron cell line, we found that mutation of Cu/Zn-superoxide dismutase-1 (SOD1), which is one of the causative genes of familial ALS, induced the upregulation of c-Abl and decreased cell viability, and that the c-Abl inhibitor dasatinib inhibited cytotoxicity. Activation of c-Abl with a concomitant increase in activated caspase-3 was observed in the lumbar spine of G93A-SOD1 transgenic mice (G93A mice), a widely used model of ALS. The survival of G93A mice was improved by oral administration of dasatinib, which also decreased c-Abl phosphorylation, inactivated caspase-3, and improved the innervation status of neuromuscular junctions. In addition, c-Abl expression in postmortem spinal cord tissues from sporadic ALS patients was increased by 3-fold compared with non-ALS patients. Conclusions/Significance The present results suggest that c-Abl is a potential therapeutic target for ALS and that the c-Abl inhibitor dasatinib has neuroprotective properties in vitro and in vivo.

Dorfin ameliorates phenotypes in a transgenic mouse model of amyotrophic lateral sclerosis.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that is characterized by progressive motor neuron degeneration and leads to death within a few years of diagnosis. One of the pathogenic mechanisms of ALS is proposed to be a dysfunction in the protein quality‐control machinery. Dorfin has been identified as a ubiquitin ligase (E3) that recognizes and ubiquitinates mutant SOD1 proteins, thereby accelerating their degradation and reducing their cellular toxicity. We examined the effects of human Dorfin overexpression in G93A mutant SOD1 transgenic mice, a mouse model of familial ALS. In addition to causing a decrease in the amount of mutant SOD1 protein in the spinal cord, Dorfin overexpression ameliorated neurological phenotypes and motor neuron degeneration. Our results indicate that Dorfin overexpression or the activation or induction of E3 may be a therapeutic avenue for mutant SOD1‐associated ALS.

Clinicopathological features of adult-onset neuronal intranuclear inclusion disease

Neuronal intranuclear inclusion disease (NIID) has highly variable clinical manifestations. Sone et al. describe the clinical and pathological features of 57 adult-onset cases diagnosed by postmortem dissection/antemortem skin biopsy. They report ‘dementia dominant’ and ‘limb weakness’ subtypes, and recommend consideration of NIID in the differential diagnosis of leukoencephalopathy and neuropathy.

Archaeal Proteasomes Effectively Degrade Aggregation-prone Proteins and Reduce Cellular Toxicities in Mammalian Cells

The 20 S proteasome is a ubiquitous, barrel-shaped protease complex responsible for most of cellular proteolysis, and its reduced activity is thought to be associated with accumulations of aberrant or misfolded proteins, resulting in a number of neurodegenerative diseases, including amyotrophic lateral sclerosis, spinal and bulbar muscular atrophy, Parkinson disease, and Alzheimer disease. The 20 S proteasomes of archaebacteria (archaea) are structurally simple and proteolytically powerful and thought to be an evolutionary precursor to eukaryotic proteasomes. We successfully reproduced the archaeal proteasome in a functional state in mammalian cells, and here we show that the archaeal proteasome effectively accelerated species-specific degradation of mutant superoxide dismutase-1 and the mutant polyglutamine tract-extended androgen receptor, causative proteins of familial amyotrophic lateral sclerosis and spinal and bulbar muscular atrophy, respectively, and reduced the cellular toxicities of these mutant proteins. Further, we demonstrate that archaeal proteasome can also degrade other neurodegenerative disease-associated proteins such as α-synuclein and tau. Our study showed that archaeal proteasomes can degrade aggregation-prone proteins whose toxic gain of function causes neurodegradation and reduce protein cellular toxicity.

Neuronal Intranuclear Inclusion Disease Presenting with Resting Tremor

Neuronal intranuclear inclusion disease (NIID) is a rare neurodegenerative disease with various neurological symptoms. A 73-year-old woman presented with slowly progressive tremor in both hands. The resting tremor was enhanced by cognitive activity and walking. However, there were no other signs of parkinsonism. Levodopa and trihexyphenidyl were ineffective against the tremor. A diagnosis of NIID was made based on skin biopsy findings. The tremor in this case was very similar to that seen in Parkinsons disease (PD). Previous reports and the present case indicate that NIID patients can develop tremor that is similar in character to that seen in PD. NIID should be considered in the differential diagnosis of resting tremor similar to PD.