Ryuji Yajima

Hyperphosphorylation of Tau Induced by Naturally Secreted Amyloid-β at Nanomolar Concentrations Is Modulated by Insulin-dependent Akt-GSK3β Signaling Pathway

Background: Little is known about the underlying mechanisms by which extracellular amyloid-β (Aβ) induces Tau phosphorylation in Alzheimer disease (AD). Results: Naturally secreted Aβ induced hyperphosphorylation of Tau and impaired insulin signal transduction. Conclusion: A disturbed insulin signaling cascade may be implicated in the pathway of Aβ-induced Tau hyperphosphorylation. Significance: These findings may explain the molecular link between Alzheimer disease and insulin signaling. Alzheimer disease (AD) is neuropathologically characterized by the formation of senile plaques from amyloid-β (Aβ) and neurofibrillary tangles composed of phosphorylated Tau. Although there is growing evidence for the pathogenic role of soluble Aβ species in AD, the major question of how Aβ induces hyperphosphorylation of Tau remains unanswered. To address this question, we here developed a novel cell coculture system to assess the effect of extracellular Aβ at physiologically relevant levels naturally secreted from donor cells on the phosphorylation of Tau in recipient cells. Using this assay, we demonstrated that physiologically relevant levels of secreted Aβ are sufficient to cause hyperphosphorylation of Tau in recipient N2a cells expressing human Tau and in primary culture neurons. This hyperphosphorylation of Tau is inhibited by blocking Aβ production in donor cells. The expression of familial AD-linked PSEN1 mutants and APP ΔE693 mutant that induce the production of oligomeric Aβ in donor cells results in a similar hyperphosphorylation of Tau in recipient cells. The mechanism underlying the Aβ-induced Tau hyperphosphorylation is mediated by the impaired insulin signal transduction because we demonstrated that the phosphorylation of Akt and GSK3β upon insulin stimulation is less activated under this condition. Treating cells with the insulin-sensitizing drug rosiglitazone, a peroxisome proliferator-activated receptor γ agonist, attenuates the Aβ-dependent hyperphosphorylation of Tau. These findings suggest that the disturbed insulin signaling cascade may be implicated in the pathways through which soluble Aβ induces Tau phosphorylation and further support the notion that correcting insulin signal dysregulation in AD may offer a potential therapeutic approach.

Evidence for a Common Founder and Clinical Characteristics of Japanese Families with the MAPT R406W Mutation.

Background/Aim: Mutations in MAPT cause frontotemporal dementia with parkinsonism linked to chromosome 17 (FTDP-17). Patients with the MAPT R406W mutation were reported to show phenotypic heterogeneity in different ethnic backgrounds. We here report the clinical and genetic characteristics of Japanese families with the R406W mutation. Methods: We examined the clinical and neuroimaging features of 6 patients from three families with the R406W mutation. We determined the genotypes of intragenic MAPT single-nucleotide polymorphisms (SNPs) and the flanking microsatellite markers to search for a common founder. Results: The initial symptom was memory loss with the average age at onset being 54 years. Anterograde amnesia with episodic memory impairment was the predominant phenotype. Behavioral and personality changes or parkinsonism is not a prominent feature. A brain MRI study revealed marked atrophy of the medial temporal lobe. Genetic analysis of SNPs and microsatellite markers revealed that the affected members of the three families share common genotypes. Conclusion: The findings of the affected members in this study, which corroborate previously reported findings of European families, suggest that the R406W mutation may represent a phenotype of predominant anterograde amnesia in FTLD-17. Our genetic data suggest that a founder effect may account for some families with the R406W mutation.

ApoE-isoform-dependent cellular uptake of amyloid-β is mediated by lipoprotein receptor LR11/SorLA

The formation of senile plaques composed of β-amyloid (Aβ) in the brain is likely the initial event in Alzheimers disease (AD). Possession of the APOE ε4 allele, the strong genetic factor for AD, facilitates the Aβ deposition from the presymptomatic stage of AD in a gene-dosage-dependent manner. However, the precise mechanism by which apoE isoforms differentially induce the AD pathology is largely unknown. LR11/SorLA is a type I membrane protein that functions as the neuronal lipoprotein endocytic receptor of apoE and the sorting receptor of the amyloid precursor protein (APP) to regulate amyloidogenesis. Recently, LR11/SorLA has been reported to be involved in the lysosomal targeting of extracellular amyloid-β (Aβ) through the binding of Aβ to the vacuolar protein sorting 10 (VPS10) protein domain of LR11/SorLA. Here, we attempted to examine the human-apoE-isoform-dependent effect on the cellular uptake of Aβ through the formation of a complex between an apoE isoform and LR11/SorLA. Cell culture experiments using Neuro2a cells revealed that the cellular uptake of secreted apoE3 and apoE4 was enhanced by the overexpression of LR11/SorLA. In contrast, the cellular uptake of apoE2 was not affected by the expression of LR11/SorLA. Co-immunoprecipitation assay revealed that apoE-isoform-dependent differences were observed in the formation of an apoE-LR11 complex (apoE4>apoE3>apoE2). ApoE-isoform-dependent differences in cellular uptake of FAM-labeled Aβ were further investigated by coculture assay in which donor cells secrete one of the apoE isoforms and recipient cells express FL-LR11. The cellular uptake of extracellular Aβ into the recipient cells was most prominently accentuated when cocultured with the donor cells secreting apoE4 in the medium, followed by apoE3 and apoE2. Taken together, our results provide evidence for the mechanism whereby human-apoE-isoform-dependent differences modulate the cellular uptake of Aβ mediated by LR11/SorLA.

Varicella-zoster virus encephalitis localized to the bilateral medial temporal lobes

### Case report. An immunocompetent 66-year-old man was admitted to a local hospital with fever and severe amnesia without a rash. T2-weighted MRI revealed symmetric hyperintense lesions in the bilateral medial temporal lobes. Magnetic resonance angiography showed no abnormalities. CSF analysis

A Patient with Fragile X-Associated Tremor/Ataxia Syndrome Presenting with Executive Cognitive Deficits and Cerebral White Matter Lesions

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder that primarily affects males who are carriers of a premutation of a CGG expansion in the FMR1 gene. In Asian populations, FXTAS has rarely been reported. Here, we report the case of a Japanese FXTAS patient who showed predominant executive cognitive deficits as the main feature of his disease. In contrast, the patient exhibited only very mild symptoms of intention tremor and ataxia, which did not interfere with daily activities. A gene analysis revealed that the patient carried a premutation of a CGG expansion (111 CGG repeats) in the FMR1 gene. The mRNA expression level of FMR1 in the patient was 1.5-fold higher than in controls. On brain MRI scans, fluid-attenuated inversion recovery images showed high-intensity lesions in the middle cerebellar peduncles and the cerebral white matter, with a frontal predominance. The present case extends previous notions regarding the cognitive impairment in FXTAS patients. Recognizing FXTAS patients with predominant cognitive impairment from various ethnic backgrounds would contribute to our understanding of the phenotypic variation of this disease.

Japanese case of Emery–Dreifuss muscular dystrophy with a novel LMNA missense mutation

Lamin A/C gene (LMNA) mutations are associated with various clinical phenotypes, which include the autosomal dominant and recessive Emery–Dreifuss muscular dystrophy (EDMD2 and EDMD3), limb-girdle muscular dystrophy type 1B, dilated cardiomyopathy with conduction defects, congenital muscular dystrophy, Charcot–Marie– Tooth disease type 2B1, heart–hand syndrome, familial partial lipodystrophy of the Dunnigan-type, HutchinsonGilford progeria syndrome, the atypical form of Werner syndrome, restrictive dermopathy and mandibuloacral dysplasia. EDMD is characterized by the clinical triad of early contractures of elbows, slowly progressive wasting and weakness in scapulohumeroperoneal muscles, and cardiac involvement with conduction defects and arrhythmias. Interestingly, EDMD2 shows a marked intrafamilial variability characterized by a wide range of age-at-onset and clinical manifestations, which range from patients expressing the full clinical picture of EDMD to partial clinical manifestation of the disease in Japan and abroad. Furthermore, there is no clear correlation between the phenotype and type or localization of the mutations. The present report describes a novel LMNA candidate missense mutation (c.107A > T: p.Gln36Leu) associated with EDMD2.

A Fulminant Case of Granulomatosis with Polyangiitis with Meningeal and Parenchymal Involvement

Central nervous system (CNS) involvement, such as pachymeningitis and/or cerebrovascular events, is rare in patients with granulomatosis with polyangiitis (GPA). Furthermore, the details of pathological examinations of cases have rarely been described. We describe a case of GPA that manifested as an isolated paranasal sinus disease that invaded the subarachnoid space and caused a hemorrhagic venous infarction. We also describe the pathological characteristics of the biopsied brain material from the successful decompressive craniectomy. In particular, granulomatous inflammation with geographic necrosis and multinucleated giant cells were observed in the perivascular area of the thickened dura mater and leptomeninges. Small vessels in the meninges were involved in the granulomatous lesions, and the lumens of the veins were often occluded. In the cerebral cortices and white matter in these areas, hemorrhagic infarction was widely observed. We suggest that our findings represent a novel mechanism of CNS involvement in GPA. Moreover, we believe that the emergency decompressive craniectomy and partial lobectomy for the cerebral infarction in this patient with GPA likely contributed to his survival.

A case of slowly progressive anti-Yo-associated paraneoplastic cerebellar degeneration successfully treated with antitumor and immunotherapy.

We report a case of slowly progressive anti-Yo-associated paraneoplastic cerebellar degeneration (PCD) with breast cancer in a 54-year-old woman. The symptoms of limb and truncal ataxia, and dysarthria gradually progressed during the course of 1 year, and the modified Rankin scale (mRS) score was 2. A mastectomy with sentinel lymph node resection was performed for the breast cancer. No malignant cells were found on histopathological examination of the lymph node. Combination chemotherapy with adriamycin and cyclophosphamide (AC) prevented neurologic deterioration. However, subsequent treatment with trastuzumab and paclitaxel did not prevent progression of the symptoms (mRS score 3). Brain magnetic resonance imaging showed atrophy of the cerebellar hemispheres without brain stem atrophy. Anti-Yo antibody was detected in the serum, which led to a diagnosis of anti-Yo-associated PCD. We resected an enlarged axillary lymph node, which was found on computed tomography. The histopathological analysis of the lymph node revealed foreign body granuloma, which suggested an association with necrotic malignant tissue. Following additional tegafur-uracil therapy and two courses of intravenous immunoglobulin (IVIg), the cerebellar signs and symptoms gradually improved (mRS score 2). The clinical course shows that PCD can present as a slowly progressive cerebellar symptom. We propose an active treatment for anti-Yo-associated PCD consisting of tumor resection, combined chemotherapy, and IVIg.

Impaired insulin signal transduction in neurons may be involved in β-amyloid-induced hyperphosphorylation of tau

Background: Alzheimer’s disease (AD) is pathologically characterized by the presence of senile plaque and neurofibrillary tangle, which consist of ß-amyloid (Aß) and hyperphosphorylated tau, respectively. The mechanism(s) by which Aß deposition leads to hyperphosphorylation of tau remain unknown. Recent epidemiological results have suggested a close rink between AD and type 2 diabetes mellitus (T2DM). T2DM is characterized by insulin resistance and hyperinsulinemia associated with insulin signal dysfunction. Insulin signal transduction is mediated by glycogen synthase kinase 3ß (GSK3ß), which is known as a tau phospharylation kinase. With this background, we hypothesized that insulin signaling dysfunction may be involved in the pathophisiology of Aß-induced hyperphosphorylation of tau. Methods:We established a co-culture system in which Neuro2a stably expressing human tau (4R1N)(N2a MAPT) or rat primary cultured neurons (recipient cells) are co-incubated with HEK293 cells (host cells) expressing the Swedish mutant of APP. By this assay, we examined the effect of Aß overproduction on tau phosphorylation in the recipient cells. We next examined the effects of Aß42 overproduction and Aß oligomer on tau phosphorylation by expressing the familial AD-linked PSEN1 mutants (deltaT440 and L166P) and APP deltaE693 mutant. To assess the role of insulin signal transduction in the Aß-induced tau phosphorylation, we investigated the activation of downstream molecules of insulin signaling including phosphorylated Akt and GSK3ß upon insulin stimulation. Results: When N2a MAPT and rat primary cultured cortical neurons were co-incubated with the host cells producing a large amount of Aß, the levels of phosphorylated tau determined by immunoblot with the AT8 antibody were substantially increased. Similar enhancement of tau phosphorylation occurs in the recipient cells when co-incubated with the host cells expressing the PSEN1 mutants and APP deltaE693. We next examined insulin signal transduction upon insulin stimulation in the recipient N2a cells and primary culture neurons. The levels of phospho-Akt and phosho-GSK3ß were not efficiently activated upon insulin stimulation when co-incubated with the host cells producing a large amount of Aß. Conclusions: These results suggest that Aß accumulation might cause abnormal tau phosphorylation through impaired insulin signal transduction and that improvement of insulin signal transduction could be a new therapeutic target of AD treatment.