Toru Baba

Severe olfactory dysfunction is a prodromal symptom of dementia associated with Parkinson's disease: a 3 year longitudinal study

Dementia is one of the most debilitating symptoms of Parkinsons disease. A recent longitudinal study suggests that up to 80% of patients with Parkinsons disease will eventually develop dementia. Despite its clinical importance, the development of dementia is still difficult to predict at early stages. We previously identified olfactory dysfunction as one of the most important indicators of cortical hypometabolism in Parkinsons disease. In this study, we investigated the possible associations between olfactory dysfunction and the risk of developing dementia within a 3-year observation period. Forty-four patients with Parkinsons disease without dementia underwent the odour stick identification test for Japanese, memory and visuoperceptual assessments, (18)F-fluorodeoxyglucose positron emission tomography scans and magnetic resonance imaging scans at baseline and 3 years later. A subgroup of patients with Parkinsons disease who exhibited severe hyposmia at baseline showed more pronounced cognitive decline at the follow-up survey. By the end of the study, 10 of 44 patients with Parkinsons disease had developed dementia, all of whom had severe hyposmia at baseline. The 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 the score of odour stick identification test for Japanese. We also found an association between severe hyposmia and a characteristic distribution of cerebral metabolic decline, which was identical to that of dementia associated with Parkinsons disease. Furthermore, volumetric magnetic resonance imaging analyses demonstrated close relationships between olfactory dysfunction and the atrophy of focal brain structures, including the amygdala and other limbic structures. Together, 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 Parkinsons disease dementia.

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.

In vivo visualization of α-synuclein deposition by carbon-11-labelled 2-[2-(2-dimethylaminothiazol-5-yl)ethenyl]-6-[2-(fluoro)ethoxy]benzoxazole positron emission tomography in multiple system atrophy

The histopathological hallmark of multiple system atrophy is the appearance of intracellular inclusion bodies, named glial cytoplasmic inclusions, which are mainly composed of alpha-synuclein fibrils. In vivo visualization of alpha-synuclein deposition should be used for the diagnosis and assessment of therapy and severity of pathological progression in multiple system atrophy. Because 2-[2-(2-dimethylaminothiazol-5-yl)ethenyl]-6-[2-(fluoro)ethoxy] benzoxazole could stain alpha-synuclein-containing glial cytoplasmic inclusions in post-mortem brains, we compared the carbon-11-labelled 2-[2-(2-dimethylaminothiazol-5-yl)ethenyl]-6-[2-(fluoro)ethoxy] benzoxazole positron emission tomography findings of eight multiple system atrophy cases to those of age-matched normal controls. The positron emission tomography data demonstrated high distribution volumes in the subcortical white matter (uncorrected P < 0.001), putamen and posterior cingulate cortex (uncorrected P < 0.005), globus pallidus, primary motor cortex and anterior cingulate cortex (uncorrected P < 0.01), and substantia nigra (uncorrected P < 0.05) in multiple system atrophy cases compared to the normal controls. They were coincident with glial cytoplasmic inclusion-rich brain areas in multiple system atrophy and thus, carbon-11-labelled 2-[2-(2-dimethylaminothiazol-5-yl)ethenyl]-6-[2-(fluoro)ethoxy] benzoxazole positron emission tomography is a promising surrogate marker for monitoring intracellular alpha-synuclein deposition in living brains.

Narcolepsy as an initial manifestation of neuromyelitis optica with antiaquaporin-4 antibody

JO N 3139 brospinal fluid (CSF) hypocretin level is useful for a diagnosis of narcolepsy [3]. The symptoms of narcolepsy are also known to occur secondary to hypothalamic lesions of various neurological conditions, such as brain tumors [6] and multiple sclerosis (MS) [2, 9]. Neuromyelitis optica (NMO) is a demyelinating disease typically manifesting transverse myelitis and bilateral optic neuritis. Anti-aquaporin-4 (AQP4) antibody was discovered as a disease-specific autoantibody in NMO patients [5]. Recently, brain lesions of NMO have been identified by many investigators and it has been reported that the lesions are generally observed in the hypothalamic region [7, 10]. In this paper, we report a case of NMO with anti-AQP4 antibody, whose initial manifestation was narcolepsy and marked decrease of CSF hypocretin level. A 35-year-old woman was referred for evaluation of excessive daytime sleepiness. On examination, apart from excessive daytime sleepiness, no neurological deficit was detected. She had no episode of cataplexy. A MRI scan showed a nonenhancing T2 lesion in the hypothalamus (Fig. 1 A). CSF study showed a slight degree of pleocytosis (12/mm3) and a normal protein level (23 mg/dl). The CSF hypocretin-1 level was markedly decreased (91 pg/ml; normal 200–350 pg/ml). She had narcolepsy-associated HLA haplotypes such as DR2 [3], but the DNA haplotypes were not typical for this disease (DRB1*1502, DQB1*0301, and DQB1*0601). Her sleep pattern was evaluated by nocturnal polysomnography (PSG) and multiple sleep latency test (MSLT). Her sleep latency was less than 10 min with SOREMP and total sleep time was 9.5 hours in PSG. The mean sleep latency by MSLT (4 naps) was 6 min with 4 SOREMPs. She was diagnosed as having narcolepsy due to Toru Baba Ichiro Nakashima Takashi Kanbayashi Masatoshi Konno Toshiyuki Takahashi Kazuo Fujihara Tatsuro Misu Atsushi Takeda Yusei Shiga Hiromasa Ogawa Yasuto Itoyama

Association of olfactory dysfunction and brain. Metabolism in Parkinson's disease

Hyposmia is one of the cardinal early symptoms of Parkinson disease (PD). Accumulating clinical and pathological evidence suggests that dysfunction of the olfactory‐related cortices may be responsible for the impaired olfactory processing observed in PD; however, there are no clear data showing a direct association between altered brain metabolism and hyposmia in PD. In this study, we evaluated brain glucose metabolism and smell‐identification ability in 69 Japanese patients with nondemented PD. Olfactory function was assessed using the Odor Stick Identification Test for Japanese. The regional cerebral metabolic rate of glucose consumption at rest was measured using 18F‐fluorodeoxyglucose positron emission tomography and was analyzed using SPM‐based group comparisons and the brain–behavior partial least‐squares method. We found that olfactory dysfunction was closely related to cognitive dysfunction, including memory impairment. Moreover, brain–behavior partial least‐squares analysis revealed that odor‐identification performance was closely associated with broad cortical dysfunction, including dysfunction of the piriform cortex and amygdala. Our results suggest that the cognitive deficit in olfactory perception is an important aspect of hyposmia in PD and that this deficit is caused by altered brain metabolism in the amygdala and piriform cortex.

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.

Role of TPPP/p25 on α-synuclein-mediated oligodendroglial degeneration and the protective effect of SIRT2 inhibition in a cellular model of multiple system atrophy ☆

Multiple system atrophy (MSA) is a progressive neurodegenerative disorder presenting variable combinations of parkinsonism, cerebellar ataxia, corticospinal and autonomic dysfunction. Alpha-synuclein (α-SYN)-immunopositive glial cytoplasmic inclusions (GCIs) represent the neuropathological hallmark of MSA, and tubulin polymerization promoting protein (TPPP)/p25 in oligodendroglia has been known as a potent stimulator of α-SYN aggregation. To gain insight into the molecular pathomechanisms of GCI formation and subsequent oligodendroglial degeneration, we ectopically expressed α-SYN and TPPP in HEK293T and oligodendroglial KG1C cell lines. Here we showed that TPPP specifically accelerated α-SYN oligomer formation and co-immunoprecipitation analysis revealed the specific interaction of TPPP and α-SYN. Moreover, phosphorylation of α-SYN at Ser-129 facilitated the TPPP-mediated α-SYN oligomerization. TPPP facilitated α-SYN-positive cytoplasmic perinuclear inclusions mimicking GCI in both cell lines; however, apoptotic cell death was only observed in KG1C cells. This apoptotic cell death was partly rescued by sirtuin 2 (SIRT2) inhibition. Together, our results provide further insight into the molecular pathogenesis of MSA and potential therapeutic approaches.

In vivo visualization of tau deposits in corticobasal syndrome by 18F-THK5351 PET

Objective: To determine whether 18F-THK5351 PET can be used to visualize tau deposits in brain lesions in live patients with corticobasal syndrome (CBS). Methods: We evaluated the in vitro binding of 3H-THK5351 in postmortem brain tissues from a patient with corticobasal degeneration (CBD). In clinical PET studies, 18F-THK5351 retention in 5 patients with CBS was compared to that in 8 age-matched normal controls and 8 patients with Alzheimer disease (AD). Results: 3H-THK5351 was able to bind to tau deposits in the postmortem brain with CBD. In clinical PET studies, the 5 patients with CBS showed significantly higher 18F-THK5351 retention in the frontal, parietal, and globus pallidus than the 8 age-matched normal controls and patients with AD. Higher 18F-THK5351 retention was observed contralaterally to the side associated with greater cortical dysfunction and parkinsonism. Conclusions: 18F-THK5351 PET demonstrated high tracer signal in sites susceptible to tau deposition in patients with CBS. 18F-THK5351 should be considered as a promising candidate radiotracer for the in vivo imaging of tau deposits in CBS.

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.