中枢神経系疾患の治療は正常細胞（ニューロン）の機能維持を目的とするが，脳血管障害のように機能障害の原因が細胞の死滅に基づくことは多い．一方，脳腫瘍の治療においては薬物療法や放射線療法といった腫瘍細胞の死滅を目標とするものが大きな位置を占める．いずれの場合にも，細胞死の機序を理解することは各種病態や治療法の理解のうえで重要である．現在のところ最も研究の進んでいる細胞死の型はアポトーシスである．そのなかで重要な位置を占めるミトコンドリアにおける反応および抗アポトーシス因子について概要を紹介する．

Neuroscience 細胞死：最近の知見

https://www.cell.com/cell/pdf/S0092-8674(19)31007-4.pdf

Alzheimer Disease: An Update on Pathobiology and Treatment Strategies.

BACE is an enzyme necessary for the generation of neurotoxic amyloid-β in Alzheimer's disease. Claes Wahlestedt and his colleagues identify a noncoding RNA that is upregulated in the brains of individuals with Alzheimer's disase. This noncoding RNA increases expression of BACE, driving amyloid-β generation and possibly disease progression.

/pdf/expression-of-a-noncoding-rna-is-elevated-in-alzheimer-s-59kgugwn46.pdf

Expression of a noncoding RNA is elevated in Alzheimer's disease and drives rapid feed-forward regulation of β-secretase

Cellular states are determined by differential expression of the cell’s proteins. The relationship between protein and mRNA expression levels informs about the combined outcomes of translation and protein degradation which are, in addition to transcription and mRNA stability, essential contributors to gene expression regulation. This review summarizes the state of knowledge about large-scale measurements of absolute protein and mRNA expression levels, and the degree of correlation between the two parameters. We summarize the information that can be derived from comparison of protein and mRNA expression levels and discuss how corresponding sequence characteristics suggest modes of regulation.

/pdf/global-signatures-of-protein-and-mrna-expression-levels-1qve1qwtri.pdf

Global signatures of protein and mRNA expression levels

Although the role of APP and PSEN genes in genetic Alzheimer's disease (AD) cases is well established, fairly little is known about the molecular mechanisms affecting A generation in sporadic AD. Deficiency in A clearance is certainly a possibility, but increased expression of proteins like APP or BACE1/-secretase may also be associated with the disease. We therefore investigated changes in microRNA (miRNA) expression profiles of sporadic AD patients and found that several miRNAs potentially involved in the regulation of APP and BACE1 expression appeared to be decreased in diseased brain. We show here that miR-29a, -29b-1, and -9 can regulate BACE1 expression in vitro. The miR-29a/b-1 cluster was signifi- cantly (and AD-dementia-specific) decreased in AD patients dis- playing abnormally high BACE1 protein. Similar correlations be- tween expression of this cluster and BACE1 were found during brain development and in primary neuronal cultures. Finally, we provide evidence for a potential causal relationship between miR-29a/b-1 expression and A generation in a cell culture model. We propose that loss of specific miRNAs can contribute to in- creased BACE1 and A levels in sporadic AD. neurodegeneration amyloid noncoding RNA

https://www.pnas.org/content/pnas/105/17/6415.full.pdf

Loss of microRNA cluster miR-29a/b-1 in sporadic Alzheimer's disease correlates with increased BACE1/beta-secretase expression.

Phosphorylation of the Translation Initiation Factor eIF2α Increases BACE1 Levels and Promotes Amyloidogenesis

Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) (beta-secretase) initiates generation of beta-amyloid (Abeta), which plays an early role in Alzheimer's disease (AD). BACE1 levels are increased in postmortem AD brain, suggesting BACE1 elevation promotes Abeta production and AD. Alternatively, the BACE1 increase may be an epiphenomenon of late-stage AD. To distinguish between these possibilities, we analyzed BACE1 elevation using a highly specific BACE1 antibody, BACE-Cat1, made in BACE1-/- mice, which mount a robust anti-BACE1 immune response. Previous BACE1 immunohistochemical studies lack consistent results because typical BACE1 antibodies produce nonspecific background, but BACE-Cat1 immunolabels BACE1 only. BACE1 elevation was recapitulated in two amyloid precursor protein (APP) transgenic mouse lines. 5XFAD mice form amyloid plaques at young ages and exhibit neuron loss. In contrast, Tg2576 form plaques at a more advanced age and do not show cell death. These two mouse lines allow differentiation between early Abeta-induced events and late phenomena related to neuron death. BACE1 levels became elevated in parallel with amyloid burden in each APP transgenic, starting early in 5XFAD and late in Tg2576. The increase in BACE1 protein occurred without any change in BACE1 mRNA level, indicating a posttranscriptional mechanism. In APP transgenic and AD brains, high BACE1 levels were observed in an annulus around Abeta42-positive plaque cores and colocalized with neuronal proteins. These results demonstrate that amyloid plaques induce BACE1 in surrounding neurons at early stages of pathology before neuron death occurs. We conclude that BACE1 elevation is most likely triggered by the amyloid pathway and may drive a positive-feedback loop in AD.

https://www.jneurosci.org/content/jneuro/27/14/3639.full.pdf

β-Site Amyloid Precursor Protein Cleaving Enzyme 1 Levels Become Elevated in Neurons around Amyloid Plaques: Implications for Alzheimer's Disease Pathogenesis

β-Site Amyloid Precursor Protein (APP)-cleaving Enzyme 1 (BACE1)-deficient Mice Exhibit a Close Homolog of L1 (CHL1) Loss-of-function Phenotype Involving Axon Guidance Defects *♦

BACE1 is a key enzyme in the generation of the Aβ peptide that plays a central role in the pathogenesis of Alzheimer's disease. While BACE1 is an attractive therapeutic target, its normal physiological function remains largely unknown. Examination of BACE1-/- mice can provide insight into this function and also help anticipate consequences of BACE1 inhibition. Here we report a seizure-susceptibility phenotype that we have identified and characterized in BACE1-/- mice. We find that electroencephalographic recordings reveal epileptiform abnormalities in some BACE1-/- mice, occasionally including generalized tonic-clonic and absence seizures. In addition, we find that kainic acid injection induces seizures of greater severity in BACE1-/- mice relative to BACE1+/+ littermates, and causes excitotoxic cell death in a subset of BACE1-/- mice. This hyperexcitability phenotype is variable and appears to be manifest in approximately 30% of BACE1-/- mice. Finally, examination of the expression and localization of the voltage-gated sodium channel α-subunit Nav1.2 reveals no correlation with BACE1 genotype or any measure of seizure susceptibility. Our data indicate that BACE1 deficiency predisposes mice to spontaneous and pharmacologically-induced seizure activity. This finding has implications for the development of safe therapeutic strategies for reducing Aβ levels in Alzheimer's disease. Further, we demonstrate that altered sodium channel expression and axonal localization are insufficient to account for the observed effect, warranting investigation of alternative mechanisms.

/pdf/bace1-mice-exhibit-seizure-activity-that-does-not-correlate-4359eo7hwq.pdf

BACE1-/- mice exhibit seizure activity that does not correlate with sodium channel level or axonal localization

Neurodegenerative tauopathies such as Alzheimer’s disease (AD) are caused by brain accumulation of tau assemblies. Evidence suggests tau functions as a prion, and cells and animals efficiently propagate unique tau assemblies. This suggests a dedicated cellular replication machinery, with normal physiologic function for tau seeds. Consequently, we hypothesized that healthy control brains would have seeding activity. We recently developed a novel monoclonal antibody (MD3.1) specific for tau seeds. We used this antibody to immunopurify tau from the parietal and cerebellar cortices of 19 healthy subjects ranging 19-65 years. We detected seeding in the parietal cortex, but not in the cerebellum, or in wild-type or human tau knockin mice, suggesting that cellular/genetic context dictates development of seed-competent tau. Seeding did not correlate with subject age or brain tau levels. Dot blot analyses revealed no AT8 immunoreactivity above background levels in parietal and cerebellar extracts and <1/100 of that present in AD. Based on binding to a panel of antibodies, the conformational characteristics of control seeds differed from AD, suggesting a unique underlying assembly, or structural ensemble. Tau’s ability to adopt self-replicating conformations under non-pathogenic conditions may reflect normal function that goes awry in disease states.

/pdf/tau-seeding-without-tauopathy-5t3noj3o.pdf

Brian Hitt

Papers

Phosphorylation of the Translation Initiation Factor eIF2α Increases BACE1 Levels and Promotes Amyloidogenesis

β-Site Amyloid Precursor Protein Cleaving Enzyme 1 Levels Become Elevated in Neurons around Amyloid Plaques: Implications for Alzheimer's Disease Pathogenesis

β-Site Amyloid Precursor Protein (APP)-cleaving Enzyme 1 (BACE1)-deficient Mice Exhibit a Close Homolog of L1 (CHL1) Loss-of-function Phenotype Involving Axon Guidance Defects *♦

BACE1-/- mice exhibit seizure activity that does not correlate with sodium channel level or axonal localization

Tau seeding without tauopathy