Emiko Miura

The AAA-ATPase VPS4 Regulates Extracellular Secretion and Lysosomal Targeting of α-Synuclein

Many neurodegenerative diseases share a common pathological feature: the deposition of amyloid-like fibrils composed of misfolded proteins. Emerging evidence suggests that these proteins may spread from cell-to-cell and encourage the propagation of neurodegeneration in a prion-like manner. Here, we demonstrated that α-synuclein (αSYN), a principal culprit for Lewy pathology in Parkinsons disease (PD), was present in endosomal compartments and detectably secreted into the extracellular milieu. Unlike prion protein, extracellular αSYN was mainly recovered in the supernatant fraction rather than in exosome-containing pellets from the neuronal culture medium and cerebrospinal fluid. Surprisingly, impaired biogenesis of multivesicular body (MVB), an organelle from which exosomes are derived, by dominant-negative mutant vacuolar protein sorting 4 (VPS4) not only interfered with lysosomal targeting of αSYN but facilitated αSYN secretion. The hypersecretion of αSYN in VPS4-defective cells was efficiently restored by the functional disruption of recycling endosome regulator Rab11a. Furthermore, both brainstem and cortical Lewy bodies in PD were found to be immunoreactive for VPS4. Thus, VPS4, a master regulator of MVB sorting, may serve as a determinant of lysosomal targeting or extracellular secretion of αSYN and thereby contribute to the intercellular propagation of Lewy pathology in PD.

VPS35 dysfunction impairs lysosomal degradation of α-synuclein and exacerbates neurotoxicity in a Drosophila model of Parkinson's disease

Mutations in vacuolar protein sorting 35 (VPS35) have been linked to familial Parkinsons disease (PD). VPS35, a component of the retromer, mediates the retrograde transport of cargo from the endosome to the trans-Golgi network. Here we showed that retromer depletion increases the lysosomal turnover of the mannose 6-phosphate receptor, thereby affecting the trafficking of cathepsin D (CTSD), a lysosome protease involved in α-synuclein (αSYN) degradation. VPS35 knockdown perturbed the maturation step of CTSD in parallel with the accumulation of αSYN in the lysosomes. Furthermore, we found that the knockdown of Drosophila VPS35 not only induced the accumulation of the detergent-insoluble αSYN species in the brain but also exacerbated both locomotor impairments and mild compound eye disorganization and interommatidial bristle loss in flies expressing human αSYN. These findings indicate that the retromer may play a crucial role in αSYN degradation by modulating the maturation of CTSD and might thereby contribute to the pathogenesis of the disease.

Suppression of dynamin GTPase decreases α-synuclein uptake by neuronal and oligodendroglial cells: a potent therapeutic target for synucleinopathy

BackgroundThe intracellular deposition of misfolded proteins is a common neuropathological hallmark of most neurodegenerative disorders. Increasing evidence suggests that these pathogenic proteins may spread to neighboring cells and induce the propagation of neurodegeneration.ResultsIn this study, we have demonstrated that α-synuclein (αSYN), a major constituent of intracellular inclusions in synucleinopathies, was taken up by neuronal and oligodendroglial cells in both a time- and concentration-dependent manner. Once incorporated, the extracellular αSYN was immediately assembled into high-molecular-weight oligomers and subsequently formed cytoplasmic inclusion bodies. Furthermore, αSYN uptake by neurons and cells of the oligodendroglial lineage was markedly decreased by the genetic suppression and pharmacological inhibition of the dynamin GTPases, suggesting the involvement of the endocytic pathway in this process.ConclusionsOur findings shed light on the mode of αSYN uptake by neuronal and oligodendroglial cells and identify therapeutic strategies aimed at reducing the propagation of protein misfolding.

Lys-63-linked ubiquitination by E3 ubiquitin ligase Nedd4-1 facilitates endosomal sequestration of internalized α-synuclein.

Background: Nedd4-1 catalyzes the Lys-63-linked ubiquitination of aS. Results: The Lys-63-linked ubiquitination of aS by Nedd4-1 facilitates endosomal targeting of extracellular aS. Conclusion: Compared with C-terminal deficient mutants, wild type-aS is preferentially internalized and translocates to endosomes. The overexpression of Nedd4-1 leads to the accumulation of aS in endosomes. Significance: Nedd4-1-mediated Lys-63 ubiquitination specifies the fate of internalized aS. α-Synuclein (aS) is a major constituent of Lewy bodies, which are not only a pathological marker for Parkinson disease but also a trigger for neurodegeneration. Cumulative evidence suggests that aS spreads from cell to cell and thereby propagates neurodegeneration to neighboring cells. Recently, Nedd4-1 (neural precursor cell expressed developmentally down-regulated protein 4-1), an E3 ubiquitin ligase, was shown to catalyze the Lys-63-linked polyubiquitination of intracellular aS and thereby facilitate aS degradation by the endolysosomal pathway. Because Nedd4-1 exerts its activity in close proximity to the inner leaflet of the plasma membrane, we speculate that after the internalization of aS the membrane resident aS is preferentially ubiquitinated by Nedd4-1. To clarify the role of Nedd4-1 in aS internalization and endolysosomal sequestration, we generated aS mutants, including ΔPR1(1–119 and 129–140), ΔC(1–119), and ΔPR2(1–119 and 134–140), that lack the proline-rich sequence, a putative Nedd4-1 recognition site. We show that wild type aS, but not ΔPR1, ΔPR2, or ΔC aS, is modified by Nedd4-1 in vitro, acquiring a Lys-63-linked ubiquitin chain. Compared with the mutants lacking the proline-rich sequence, wild type-aS is preferentially internalized and translocated to endosomes. The overexpression of Nedd4-1 increased aS in endosomes, whereas RNAi-mediated silencing of Nedd4-1 decreased endosomal aS. Although aS freely passes through plasma membranes within minutes, a pulse-chase experiment revealed that the overexpression of Nedd4-1 markedly decreased the re-secretion of internalized aS. Together, these findings demonstrate that Nedd4-1-linked Lys-63 ubiquitination specifies the fate of extrinsic and de novo synthesized aS by facilitating their targeting to endosomes.

Olfactory Dysfunction and Dementia in Parkinson's Disease

Dementia is one of the most debilitating symptoms of Parkinsons disease (PD), but the development of dementia is still difficult to predict at early stages of the disease. We recently found that hyposmia, one of the most typical non-motor features of PD, was a predictive feature of Parkinsons disease with dementia (PDD). In that work, multivariate logistic analysis identified severe hyposmia and visuoperceptual impairment as independent risk factors for subsequent dementia within 3 years. The patients with severe hyposmia had an 18.7-fold increase in their risk of dementia for each 1 SD (2.8) decrease in scores on the odor stick identification test for Japanese (OSIT-J). We also found an association between severe hyposmia and a specific pattern of cerebral metabolic decline, which was identical to findings observed in PDD. Furthermore, volumetric magnetic resonance imaging analyses demonstrated close relationships between olfactory dysfunction and atrophy of focal brain structures, including the amygdala and other limbic structures. Our findings suggest that brain regions related to olfactory function are closely associated with cognitive decline and that severe hyposmia is a prominent clinical feature that predicts the subsequent development of PDD. We have now started a randomized, double-blind study using donepezil for the PD group with severe hyposmia. We hope that this clinical trial will allow us to establish a therapeutic intervention that can improve the prognosis of advanced PD.

Hypometabolism in the supplementary and anterior cingulate cortices is related to dysphagia in Parkinson's disease: a cross-sectional and 3-year longitudinal cohort study

Objective Dysphagia is one of the cardinal symptoms of Parkinson’s disease (PD). It is closely related to the quality of life and longevity of PD patients. The aim of the study is to clarify the pathophysiological mechanisms responsible for dysphagia in PD. Design A cross-sectional and longitudinal comparative study. Setting Tohoku University Hospital. Participants Eight patients with dysphagia, 15 patients without dysphagia and 10 normal control subjects. Main outcome measures The time needed for swallowing initiation and changes in brain glucose metabolism at baseline and after a 3-year follow-up period. Results The time needed for swallowing initiation was significantly longer in the patients with dysphagia compared with the patients without dysphagia at baseline and after the 3-year follow-up period (p<0.05). The patients with dysphagia exhibited hypometabolism in the supplementary motor area (SMA) and the anterior cingulate cortex (ACC) compared with the 10 normal control subjects at baseline (uncorrected p<0.001). After the 3-year follow-up period, the number of brain areas showing hypometabolism increased, involving not only the SMA and the ACC but also the bilateral medial frontal lobes, middle cingulate cortex, thalamus and right superior, middle, inferior and orbital frontal gyri (uncorrected p<0.001). In contrast, the patients without dysphagia showed virtually no regional hypometabolism at baseline (uncorrected p<0.001) and only a small degree of hypometabolism in the SMA and ACC after the 3-year follow-up period (uncorrected p<0.001). Conclusions These results suggest that dysphagia in PD patients is mainly related to a difficulty in swallowing initiation that is based on a combination of poor movement planning due to SMA dysfunction and impaired cognitive processing due to ACC dysfunction.

Improvement of freezing of gait in patients with Parkinson's disease by imagining bicycling.

Freezing of gait (FOG) is one of the factors that reduce the quality of life in patients with Parkinsons disease (PD). Imagining bicycling before gait start provided improvement in FOG in 2 PD patients. Imagining and mimicking bicycling after the initiation of gait allowed the rhythmic gait to continue without interruption. We suggest that imagining and mimicking bicycling, which are nonexternal cues, could serve as a helpful therapeutic approach for the intractable freezing and interruption of gait of PD patients.

Recurrent hypogeusia in a patient with chronic inflammatory demyelinating polyradiculoneuropathy (CIDP)

Hypogeusia, a condition with diminished sense of taste, is caused by several conditions, including zinc deficiency and as a side-effect of drugs, but is not common in neurological disorders. A 55-year-old Japanese man with a 30-year history of chronic inflammatory demyelinating polyradiculoneuropathy (CIDP) presented with hypogeusia during hospitalization for a recurrence of CIDP. The hypogeusia improved after treatment with high-dose intravenous methylprednisolone (HIMP). Two years later, hypogeusia developed again. A complete taste deficit was revealed by a filter paper test. Brain MRI showed enhancement of the bilateral facial nerve ganglia. Hypogeusia was partially ameliorated after extensive immunosuppressive therapy with repeated HIMP and plasma exchange. Improvement was more prominent in the area innervated by the chorda tympani nerve than that innervated by the glossopharyngeal nerve. To our knowledge, this is the first report of recurrent hypogeusia, which might be caused by cranial nerve injury associated with CIDP.

Brain Metabolic Changes of Cervical Dystonia with Spinocerebellar Ataxia Type 1 after Botulinum Toxin Therapy.

We occasionally observe long-term remission of cervical dystonia after several botulinum toxin treatments. However, botulinum toxin transiently acts on neuromuscular junctions. We herein report that a cervical dystonia patient with spinocerebellar ataxia type 1 could have long-term remission as a result of the depression of hypermetabolism in the bilateral putamen and primary sensorimotor cortex after botulinum toxin therapy. We suggest that botulinum toxin impacts the central nervous system, causing prolonged improvement through the normalization of basal ganglia circuits in addition to its effects at neuromuscular junctions.

Non-paraneoplastic Lambert–Eaton myasthenic syndrome presenting dropped head and respiratory failure with normoreflexia

A 57‐year‐old woman developed insidious dropped head, respiratory failure and autonomic dysfunction with inconspicuous limb weakness, but without diminished deep tendon reflexes. Progressive myopathy affecting truncal muscles was initially suspected, but non‐paraneoplastic Lambert–Eaton myasthenic syndrome was finally diagnosed based on the results of electrophysiological studies and positivity for anti‐P/Q‐type voltage‐gated calcium channel antibody without any evidence of malignancy. In general, most patients with Lambert–Eaton myasthenic syndrome have more than one of the core manifestations of Lambert–Eaton myasthenic syndrome including proximal‐dominant limb weakness, diminished or absent deep tendon reflexes and autonomic dysfunction. However, this patient presented atypical manifestations, and lacked two core manifestations except for autonomic dysfunction. It is important to take Lambert–Eaton myasthenic syndrome into consideration in the differential diagnosis of patients showing atypical presentation, such as dropped head or respiratory failure, when they have only one core manifestation of Lambert–Eaton myasthenic syndrome.