Akira Tamaoka

Drug Screening for ALS Using Patient-Specific Induced Pluripotent Stem Cells

Anacardic acid attenuates mutant TDP-43–associated abnormalities in motor neurons derived from ALS patient–specific induced pluripotent stem cells. A Stepping Stone to ALS Drug Screening Amyotrophic lateral sclerosis (ALS) is an untreatable disorder in which the motor neurons degenerate, resulting in paralysis and death. Induced pluripotent stem cell (iPSC) technology makes it possible to analyze motor neurons from patients with ALS and to use them for screening new candidate drugs. In new work, Egawa et al. obtained motor neurons by inducing differentiation of iPSC lines derived from several patients with familial ALS. These patients carried disease-causing mutations in the gene encoding Tar DNA binding protein-43 (TDP-43). The ALS motor neurons in culture recapitulated cellular and molecular abnormalities associated with ALS. For example, the authors found that mutant TDP-43 in the ALS motor neurons perturbed RNA metabolism and that the motor neurons were more vulnerable to cellular stressors such as arsenite. The researchers then used the ALS motor neurons in a drug screening assay and identified a compound called anacardic acid, a histone acetyltransferase inhibitor, that could reverse some of the ALS phenotypes observed in the motor neurons. The new work provides an encouraging step toward using motor neurons generated from iPSCs derived from ALS patients to learn more about what triggers the death of motor neurons in this disease and to identify new candidate drugs that may be able to slow or reverse the devastating loss of motor neurons. Amyotrophic lateral sclerosis (ALS) is a late-onset, fatal disorder in which the motor neurons degenerate. The discovery of new drugs for treating ALS has been hampered by a lack of access to motor neurons from ALS patients and appropriate disease models. We generate motor neurons from induced pluripotent stem cells (iPSCs) from familial ALS patients, who carry mutations in Tar DNA binding protein-43 (TDP-43). ALS patient–specific iPSC–derived motor neurons formed cytosolic aggregates similar to those seen in postmortem tissue from ALS patients and exhibited shorter neurites as seen in a zebrafish model of ALS. The ALS motor neurons were characterized by increased mutant TDP-43 protein in a detergent-insoluble form bound to a spliceosomal factor SNRPB2. Expression array analyses detected small increases in the expression of genes involved in RNA metabolism and decreases in the expression of genes encoding cytoskeletal proteins. We examined four chemical compounds and found that a histone acetyltransferase inhibitor called anacardic acid rescued the abnormal ALS motor neuron phenotype. These findings suggest that motor neurons generated from ALS patient–derived iPSCs may provide a useful tool for elucidating ALS disease pathogenesis and for screening drug candidates.

Altered CpG methylation in sporadic Alzheimer's disease is associated with APP and MAPT dysregulation

The hallmark of Alzheimers disease (AD) pathology is an accumulation of amyloid β (Aβ) and phosphorylated tau, which are encoded by the amyloid precursor protein (APP) and microtubule-associated protein tau (MAPT) genes, respectively. Less than 5% of all AD cases are familial in nature, i.e. caused by mutations in APP, PSEN1 or PSEN2. Almost all mutations found in them are related to an overproduction of Aβ1-42, which is prone to aggregation. While these genes are mutation free, their function, or those of related genes, could be compromised in sporadic AD as well. In this study, pyrosequencing analysis of post-mortem brains revealed aberrant CpG methylation in APP, MAPT and GSK3B genes of the AD brain. These changes were further evaluated by a newly developed in vitro-specific DNA methylation system, which in turn highlighted an enhanced expression of APP and MAPT. Cell nucleus sorting of post-mortem brains revealed that the methylation changes of APP and MAPT occurred in both neuronal and non-neuronal cells, whereas GSK3B was abnormally methylated in non-neuronal cells. Further analysis revealed an association between abnormal APP CpG methylation and apolipoprotein E ε4 allele (APOE ε4)-negative cases. The presence of a small number of highly methylated neurons among normal neurons contribute to the methylation difference in APP and MAPT CpGs, thus abnormally methylated cells could compromise the neural circuit and/or serve as seed cells for abnormal protein propagation. Our results provide a link between familial AD genes and sporadic neuropathology, thus emphasizing an epigenetic pathomechanism for sporadic AD.

Molecular analysis and biochemical classification of TDP-43 proteinopathy

Amyotrophic lateral sclerosis and frontotemporal lobar degeneration with TAR DNA-binding protein of 43 kDa pathology are progressive neurodegenerative diseases that are characterized by intracytoplasmic aggregates of hyperphosphorylated TAR DNA-binding protein of 43 kDa. These TAR DNA-binding protein 43 proteinopathies can be classified into subtypes, which are closely correlated with clinicopathological phenotypes, although the differences in the molecular species of TAR DNA-binding protein 43 in these diseases and the biological significance thereof, remain to be clarified. Here, we have shown that although the banding patterns of abnormally phosphorylated C-terminal fragments of TAR DNA-binding protein 43 differ between the neuropathological subtypes, these are indistinguishable between multiple brain regions and spinal cord in individual patients. Immunoblot analysis of protease-resistant TAR DNA-binding protein 43 demonstrated that the fragment patterns represent different conformations of TAR DNA-binding protein 43 molecular species in the diseases. These results suggest a new clinicopathological classification of TAR DNA-binding protein 43 proteinopathies based on their molecular properties.

The Src/c-Abl pathway is a potential therapeutic target in amyotrophic lateral sclerosis

Analysis of ALS patient iPSC-derived motor neurons indicates that Src/c-Abl inhibitors may have potential for treating ALS. A stepping stone to ALS drug discovery ALS is a heterogeneous motor neuron disease for which there is no treatment and for which a common therapeutic target has yet to be identified. In a new study, Imamura et al. developed a drug screen using motor neurons generated from ALS patient induced pluripotent stem cells (iPSCs). They screened existing drugs and showed that inhibitors of Src/c-Abl kinases promoted autophagy and rescued ALS motor neurons from degeneration. One of the drugs was effective for promoting survival of motor neurons derived from ALS patients with different genetic mutations. The Src/c-Abl pathway may be a potential therapeutic target for developing new drugs to treat ALS. Amyotrophic lateral sclerosis (ALS), a fatal disease causing progressive loss of motor neurons, still has no effective treatment. We developed a phenotypic screen to repurpose existing drugs using ALS motor neuron survival as readout. Motor neurons were generated from induced pluripotent stem cells (iPSCs) derived from an ALS patient with a mutation in superoxide dismutase 1 (SOD1). Results of the screen showed that more than half of the hits targeted the Src/c-Abl signaling pathway. Src/c-Abl inhibitors increased survival of ALS iPSC-derived motor neurons in vitro. Knockdown of Src or c-Abl with small interfering RNAs (siRNAs) also rescued ALS motor neuron degeneration. One of the hits, bosutinib, boosted autophagy, reduced the amount of misfolded mutant SOD1 protein, and attenuated altered expression of mitochondrial genes. Bosutinib also increased survival in vitro of ALS iPSC-derived motor neurons from patients with sporadic ALS or other forms of familial ALS caused by mutations in TAR DNA binding protein (TDP-43) or repeat expansions in C9orf72. Furthermore, bosutinib treatment modestly extended survival of a mouse model of ALS with an SOD1 mutation, suggesting that Src/c-Abl may be a potentially useful target for developing new drugs to treat ALS.

Neuronal β-amyloid generation is independent of lipid raft association of β-secretase BACE1: analysis with a palmitoylation-deficient mutant

β‐Secretase, BACE1 is a neuron‐specific membrane‐associated protease that cleaves amyloid precursor protein (APP) to generate β‐amyloid protein (Aβ). BACE1 is partially localized in lipid rafts. We investigated whether lipid raft localization of BACE1 affects Aβ production in neurons using a palmitoylation‐deficient mutant and further analyzed the relationship between palmitoylation of BACE1 and its shedding and dimerization. We initially confirmed that BACE1 is mainly palmitoylated at four C‐terminal cysteine residues in stably transfected neuroblastoma cells. We found that raft localization of mutant BACE1 lacking the palmitoylation modification was markedly reduced in comparison to wild‐type BACE1 in neuroblastoma cells as well as rat primary cortical neurons expressing BACE1 via recombinant adenoviruses. In primary neurons, expression of wild‐type and mutant BACE1 enhanced production of Aβ from endogenous or overexpressed APP to similar extents with the β‐C‐terminal fragment (β‐CTF) of APP mainly distributed in nonraft fractions. Similarly, β‐CTF was recovered mainly in nonraft fractions of neurons expressing Swedish mutant APP only. These results show that raft association of BACE1 does not influence β‐cleavage of APP and Aβ production in neurons, and support the view that BACE1 cleaves APP mainly in nonraft domains. Thus, we propose a model of neuronal Aβ generation involving mobilization of β‐CTF from nonraft to raft domains. Additionally, we obtained data indicating that palmitoylation plays a role in BACE1 shedding but not dimerization.

The immunoreceptor adapter protein DAP12 suppresses B lymphocyte–driven adaptive immune responses

Human and mouse B cells lacking functional DAP12 are hyperresponsive, and DAP12 works with MAIR-II (CD300d) to negatively regulate B cell activity.

Statins Reduce Amyloid β-Peptide Production by Modulating Amyloid Precursor Protein Maturation and Phosphorylation Through a Cholesterol-Independent Mechanism in Cultured Neurons

Statins, 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors, have been reported to attenuate amyloid-β peptide (Aβ) production in various cellular models. However, the mechanisms by which statins affect neuronal Aβ production have not yet been clarified. Here, we investigated this issue in rat primary cortical neurons using two statins, pitavastatin (PV) and atorvastatin (AV). Treatment of neurons with 0.2–2.5xa0μM PV or AV for 4xa0days induced a concentration- and time-dependent reduction in the secretion of both Aβ40 and Aβ42. Moreover, Western blot analyses of cell lysates showed that treatment with PV or AV significantly reduced expression levels of the mature form of amyloid precursor protein (APP) and Thr668-phosphorylated APP (P-APP), but not immature form of APP; the decreases in P-APP levels were more notable than those of mature APP levels. The statin treatment did not alter expression of BACE1 (β-site APP-cleaving enzyme 1) or γ-secretase complex proteins (presenilin 1, nicastrin, APH-1, and PEN-2). In neurons overexpressing APP via recombinant adenoviruses, PV or AV similarly reduced Aβ secretion and the levels of mature APP and P-APP. Statins also markedly reduced cellular cholesterol content in neurons in a concentration-dependent manner. Co-treatment with mevalonate reversed the statin-induced decreases in Aβ secretion and mature APP and P-APP levels, whereas co-treatment with cholesterol did not, despite recovery of cellular cholesterol levels. Finally, cell-surface biotinylation experiments revealed that both statins significantly reduced the levels of cell-surface P-APP without changing those of cell surface mature APP. These results suggest that statins reduce Aβ production by selectively modulating APP maturation and phosphorylation through a mechanism independent of cholesterol reduction in cultured neurons.

LC3, an autophagosome marker, is expressed on oligodendrocytes in Nasu-Hakola disease brains.

BackgroundNasu-Hakola disease (NHD) is a rare autosomal recessive disorder characterized by sclerosing leukoencephalopathy and multifocal bone cysts, caused by a loss-of-function mutation of either DAP12 or TREM2. TREM2 and DAP12 constitute a receptor/adaptor signaling complex expressed exclusively on osteoclasts, dendritic cells, macrophages, and microglia. Neuropathologically, NHD exhibits profound loss of myelin and accumulation of axonal spheroids, accompanied by intense gliosis accentuated in the white matter of the frontal and temporal lobes. At present, the molecular mechanism responsible for development of leukoencephalopathy in NHD brains remains totally unknown.MethodsBy immunohistochemistry, we studied the expression of microtubule-associated protein 1 light chain 3 (LC3), an autophagosome marker, in 5 NHD and 12 control brains.ResultsIn all NHD brains, Nogo-A-positive, CNPase-positive oligodendrocytes surviving in the non-demyelinated white matter intensely expressed LC3. They also expressed ubiquitin, ubiquilin-1, and histone deacetylase 6 (HDAC6) but did not express Beclin 1 or sequestosome 1 (p62). Substantial numbers of axonal spheroids were also labeled with LC3 in NHD brains. In contrast, none of oligodendrocytes expressed LC3 in control brains. Furthermore, surviving oligodendrocytes located at the demyelinated lesion edge of multiple sclerosis (MS) did not express LC3, whereas infiltrating Iba1-positive macrophages and microglia intensely expressed LC3 in MS lesions.ConclusionsThese results propose a novel hypothesis that aberrant regulation of autophagy might induce oligodendrogliopathy causative of leukoencephalopathy in NHD brains.

Sequential imaging analysis using MIBG scintigraphy revealed progressive degeneration of cardiac sympathetic nerve in Parkinson’s disease

Background:u2002 Metaiodobenzylguanidine (MIBG) cardiac scintigraphy was used to differentiate Parkinson’s disease (PD) with Lewy body pathology from other degenerative parkinsonisms. MIBG cardiac scintigraphy demonstrates the extent of degeneration of myocardial post‐ganglionic sympathetic nerves in patients with PD. Because of its specificity for Lewy body (LB) pathology, MIBG scan might also be useful biomarker for the neurodegeneration attributed to PD. To estimate the utility of the imaging technique as a biomarker, we conducted sequential imaging analysis and power analysis.

Neuron-specific methylome analysis reveals epigenetic regulation and tau-related dysfunction of BRCA1 in Alzheimer’s disease

Significance To extract critical information from Alzheimer’s disease (AD) postmortem brains that may otherwise be lost, we chose to screen epigenetic signatures. Epigenome analysis is a robust methodology in terms of its cell type and gene specificity, suitability for high-throughput analysis, and resistance to postmortem degradation. Analysis of the neuron-specific methylome revealed a variety of differentially methylated genes, including BRCA1. We demonstrate the pathogenic relevance of compromised genomic integrity by analyzing the neuroprotective function of BRCA1 against amyloid β (Aβ)-induced DNA double-strand breaks. Furthermore, insolubility of BRCA1 under the presence of aggregated tau suggested the reason for its dysfunction despite enhanced expression. We provide insight into the pathomechanism of AD and demonstrate the potential of screening neuron-specific methylome to reveal new pathogenic contributors. Alzheimer’s disease (AD) is a chronic neurodegenerative disease characterized by pathology of accumulated amyloid β (Aβ) and phosphorylated tau proteins in the brain. Postmortem degradation and cellular complexity within the brain have limited approaches to molecularly define the causal relationship between pathological features and neuronal dysfunction in AD. To overcome these limitations, we analyzed the neuron-specific DNA methylome of postmortem brain samples from AD patients, which allowed differentially hypomethylated region of the BRCA1 promoter to be identified. Expression of BRCA1 was significantly up-regulated in AD brains, consistent with its hypomethylation. BRCA1 protein levels were also elevated in response to DNA damage induced by Aβ. BRCA1 became mislocalized to the cytoplasm and highly insoluble in a tau-dependent manner, resulting in DNA fragmentation in both in vitro cellular and in vivo mouse models. BRCA1 dysfunction under Aβ burden is consistent with concomitant deterioration of genomic integrity and synaptic plasticity. The Brca1 promoter region of AD model mice brain was similarly hypomethylated, indicating an epigenetic mechanism underlying BRCA1 regulation in AD. Our results suggest deterioration of DNA integrity as a central contributing factor in AD pathogenesis. Moreover, these data demonstrate the technical feasibility of using neuron-specific DNA methylome analysis to facilitate discovery of etiological candidates in sporadic neurodegenerative diseases.