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1.  PTBP1 and PTBP2 repress nonconserved cryptic exons 
Cell reports  2016;17(1):104-113.
The fidelity of RNA splicing is maintained by a network of factors, but the molecular mechanisms that govern this process have yet to be fully elucidated. We previously found that TDP-43, an RNA-binding protein implicated in neurodegenerative disease, utilizes UG microsatellites to repress nonconserved cryptic exons and prevent their incorporation into mRNA. Here, we report that two well characterized splicing factors, polypyrimidine tract-binding protein 1 (PTBP1) and polypyrimidine tract-binding protein 2 (PTBP2), are also nonconserved cryptic exon repressors. In contrast to TDP-43, PTBP1 and PTBP2 utilize CU microsatellites to repress both conserved tissue-specific exons as well as nonconserved cryptic exons. Analysis of these conserved splicing events suggests that PTBP1 and PTBP2 repression is titrated to generate the transcriptome diversity required for neuronal differentiation. Together, we establish that PTBP1 and PTBP2 are members of a family of cryptic exon repressors.
Graphical abstract
doi:10.1016/j.celrep.2016.08.071
PMCID: PMC5082185  PMID: 27681424
2.  The neuritic plaque facilitates pathological conversion of tau in an Alzheimer's disease mouse model 
Nature Communications  2016;7:12082.
A central question in Alzheimer's Disease (AD) is whether the neuritic plaque is necessary and sufficient for the development of tau pathology. Hyperphosphorylation of tau is found within dystrophic neurites surrounding β-amyloid deposits in AD mouse models but the pathological conversion of tau is absent. Likewise, expression of a human tau repeat domain in mice is insufficient to drive the pathological conversion of tau. Here we developed an Aβ-amyloidosis mouse model that expresses the human tau repeat domain and show that in these mice, the neuritic plaque facilitates the pathological conversion of wild-type tau. We show that this tau fragment seeds the neuritic plaque-dependent pathological conversion of wild-type tau that spreads from the cortex and hippocampus to the brain stem. These results establish that in addition to the neuritic plaque, a second determinant is required to drive the conversion of wild-type tau.
Alzheimer's disease (AD) is pathologically characterized by the accumulation of neuritic plaques and neurofibrillary tangles but it is not known whether the neuritic plaque is necessary to drive the conversion of wild-type tau. Here the authors developed a mouse model in which wild-type tau is converted into pathological tau in a neuritic plaque-dependent manner.
doi:10.1038/ncomms12082
PMCID: PMC4932197  PMID: 27373369
3.  Low dietary protein content alleviates motor symptoms in mice with mutant dynactin/dynein-mediated neurodegeneration 
Human Molecular Genetics  2014;24(8):2228-2240.
Mutations in components of the molecular motor dynein/dynactin lead to neurodegenerative diseases of the motor system or atypical parkinsonism. These mutations are associated with prominent accumulation of vesicles involved in autophagy and lysosomal pathways, and with protein inclusions. Whether alleviating these defects would affect motor symptoms remain unknown. Here, we show that a mouse model expressing low levels of disease linked-G59S mutant dynactin p150Glued develops motor dysfunction >8 months before loss of motor neurons or dopaminergic degeneration is observed. Abnormal accumulation of autophagosomes and protein inclusions were efficiently corrected by lowering dietary protein content, and this was associated with transcriptional upregulations of key players in autophagy. Most importantly this dietary modification partially rescued overall neurological symptoms in these mice after onset. Similar observations were made in another mouse strain carrying a point mutation in the dynein heavy chain gene. Collectively, our data suggest that stimulating the autophagy/lysosomal system through appropriate nutritional intervention has significant beneficial effects on motor symptoms of dynein/dynactin diseases even after symptom onset.
doi:10.1093/hmg/ddu741
PMCID: PMC4447824  PMID: 25552654
4.  TDP-43 repression of nonconserved cryptic exons is compromised in ALS-FTD 
Science (New York, N.Y.)  2015;349(6248):650-655.
Cytoplasmic aggregation of TDP-43, accompanied by its nuclear clearance, is a key common pathological hallmark of amyotrophic lateral sclerosis and frontotemporal dementia (ALS-FTD). However, a limited understanding of this RNA-binding protein (RBP) impedes the clarification of pathogenic mechanisms underlying TDP-43 proteinopathy. In contrast to RBPs that regulate splicing of conserved exons, we found that TDP-43 repressed the splicing of nonconserved cryptic exons, maintaining intron integrity. When TDP-43 was depleted from mouse embryonic stem cells, these cryptic exons were spliced into messenger RNAs, often disrupting their translation and promoting nonsense-mediated decay. Moreover, enforced repression of cryptic exons prevented cell death in TDP-43–deficient cells. Furthermore, repression of cryptic exons was impaired in ALS-FTD cases, suggesting that this splicing defect could potentially underlie TDP-43 proteinopathy.
doi:10.1126/science.aab0983
PMCID: PMC4825810  PMID: 26250685
5.  GGGGCC repeat expansion in C9ORF72 compromises nucleocytoplasmic transport 
Nature  2015;525(7567):129-133.
GGGGCC (G4C2) repeat expansion in a noncoding region of C9ORF72 is the most common cause of sporadic and familial forms of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD)1,2. The basis for pathogenesis is unknown. To capture the consequences of G4C2 repeat expansion in a tractable genetic system, we generated transgenic fly lines expressing 8, 28 or 58 G4C2 repeat-containing transcripts that do not have a translation start site (AUG) but contain an open-reading frame for green fluorescent protein (GFP) to detect repeat-associated non-AUG (RAN) translation. These transgenic animals show dosage-dependent, repeat length-dependent degeneration in neuronal tissues and RAN translation of dipeptide repeat (DPR) proteins as observed in patients. This model was used in a large-scale, unbiased genetic screen ultimately leading to the identification of 18 genetic modifiers that encode components of the nuclear pore complex (NPC) as well as the machinery that coordinates the export of nuclear RNA and the import of nuclear proteins. Consistent with these results we found morphological abnormalities in the architecture of the nuclear envelope in cells expressing expanded G4C2 repeats in vitro and in vivo. Moreover, we identified a substantial defect in RNA export resulting in retention of RNA in the nuclei of Drosophila cells expressing expanded G4C2 repeats and also in mammalian cells, including aged iPSC-derived neurons from C9ORF72 patients. These studies show that a primary consequence of G4C2 repeat expansion is the compromise of nucleocytoplasmic transport through the nuclear pore, revealing a novel mechanism of neurodegeneration.
doi:10.1038/nature14974
PMCID: PMC4631399  PMID: 26308899
ALS; C9ORF72; DPR; Drosophila; FTD; genetic screen; nuclear pore; RAN translation; repeat expansion
6.  Defective Age-Dependent Metaplasticity in a Mouse Model of Alzheimer's Disease 
The Journal of Neuroscience  2015;35(32):11346-11357.
Much of the molecular understanding of synaptic pathology in Alzheimer's disease (AD) comes from studies of various mouse models that express familial AD (FAD)-linked mutations, often in combinations. Most studies compare the absolute magnitudes of long-term potentiation (LTP) and long-term depression (LTD) to assess deficits in bidirectional synaptic plasticity accompanying FAD-linked mutations. However, LTP and LTD are not static, but their induction threshold is adjusted by overall neural activity via metaplasticity. Hence LTP/LTD changes in AD mouse models may reflect defects in metaplasticity processes. To determine this, we examined the LTP/LTD induction threshold in APPswe;PS1ΔE9 transgenic (Tg) mice across two different ages. We found that in young Tg mice (1 month), LTP is enhanced at the expense of LTD, but in adults (6 months), the phenotype is reversed to promote LTD and reduce LTP, compared to age-matched wild-type (WT) littermates. The apparent opposite phenotype across age was due to an initial offset in the induction threshold to favor LTP and the inability to undergo developmental metaplasticity in Tg mice. In WTs, the synaptic modification threshold decreased over development to favor LTP and diminish LTD in adults. However, in Tg mice, the magnitudes of LTP and LTD stayed constant across development. The initial offset in LTP/LTD threshold in young Tg mice did not accompany changes in the LTP/LTD induction mechanisms, but altered AMPA receptor phosphorylation and appearance of Ca2+-permeable AMPA receptors. We propose that the main synaptic defect in AD mouse models is due to their inability to undergo developmental metaplasticity.
SIGNIFICANCE STATEMENT This work offers a new insight that metaplasticity defects are central to synaptic dysfunctions seen in AD mouse models. In particular, we demonstrate that the apparent differences in LTP/LTD magnitude seen across ages in AD transgenic mouse models reflect the inability to undergo a normal developmental shift in metaplasticity.
doi:10.1523/JNEUROSCI.5289-14.2015
PMCID: PMC4532762  PMID: 26269641
AD; APPswe;PS1ΔE9; LTD; LTP; pull–push metaplasticity; sliding threshold
7.  Function, therapeutic potential and cell biology of BACE proteases: current status and future prospects 
Journal of neurochemistry  2014;130(1):4-28.
The β-site APP cleaving enzymes 1 and 2 (BACE1 and BACE2) were initially identified as transmembrane aspartyl proteases cleaving the amyloid precursor protein (APP). BACE1 is a major drug target for Alzheimer’s disease because BACE1-mediated cleavage of APP is the first step in the generation of the pathogenic amyloid-β peptides. BACE1, which is highly expressed in the nervous system, is also required for myelination by cleaving neuregulin 1. Several recent proteomic and in vivo studies usingBACE1-andBACE2-deficient mice demonstrate a much wider range of physiological substrates and functions for both proteases within and outside of the nervous system. For BACE1 this includes axon guidance, neurogenesis, muscle spindle formation, and neuronal network functions, whereas BACE2 was shown to be involved in pigmentation and pancreatic β-cell function. This review highlights the recent progress in understanding cell biology, substrates, and functions of BACE proteases and discusses the therapeutic options and potential mechanism-based liabilities, in particular for BACE inhibitors in Alzheimer’s disease.
doi:10.1111/jnc.12715
PMCID: PMC4086641  PMID: 24646365
Alzheimer’s disease; BACE1; BACE2; protease; regulated intramembrane proteolysis; secretase
8.  Postsynaptic Target Specific Synaptic Dysfunctions in the CA3 Area of BACE1 Knockout Mice 
PLoS ONE  2014;9(3):e92279.
Beta-amyloid precursor protein cleaving enzyme 1 (BACE1), a major neuronal β-secretase critical for the formation of β-amyloid (Aβ) peptide, is considered one of the key therapeutic targets that can prevent the progression of Alzheimer’s disease (AD). Although a complete ablation of BACE1 gene prevents Aβ formation, we previously reported that BACE1 knockouts (KOs) display presynaptic deficits, especially at the mossy fiber (MF) to CA3 synapses. Whether the defect is specific to certain inputs or postsynaptic targets in CA3 is unknown. To determine this, we performed whole-cell recording from pyramidal cells (PYR) and the stratum lucidum (SL) interneurons in the CA3, both of which receive excitatory MF terminals with high levels of BACE1 expression. BACE1 KOs displayed an enhancement of paired-pulse facilitation at the MF inputs to CA3 PYRs without changes at the MF inputs to SL interneurons, which suggests postsynaptic target specific regulation. The synaptic dysfunction in CA3 PYRs was not restricted to excitatory synapses, as seen by an increase in the paired-pulse ratio of evoked inhibitory postsynaptic currents from SL to CA3 PYRs. In addition to the changes in evoked synaptic transmission, BACE1 KOs displayed a reduction in the frequency of miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs) in CA3 PYRs without alteration in mEPSCs recorded from SL interneurons. This suggests that the impairment may be more global across diverse inputs to CA3 PYRs. Our results indicate that the synaptic dysfunctions seen in BACE1 KOs are specific to the postsynaptic target, the CA3 PYRs, independent of the input type.
doi:10.1371/journal.pone.0092279
PMCID: PMC3956924  PMID: 24637500
9.  BACE1, a Major Determinant of Selective Vulnerability of the Brain to Amyloid-β Amyloidogenesis, is Essential for Cognitive, Emotional, and Synaptic Functions 
A transmembrane aspartyl protease termed β-site APP cleavage enzyme 1 (BACE1) that cleaves the amyloid-β precursor protein (APP), which is abundant in neurons, is required for the generation of amyloid-β (Aβ) peptides implicated in the pathogenesis of Alzheimer’s disease (AD). We now demonstrate that BACE1, enriched in neurons of the CNS, is a major determinant that predisposes the brain to Aβ amyloidogenesis. The physiologically high levels of BACE1 activity coupled with low levels of BACE2 and α-secretase anti-amyloidogenic activities in neurons is a major contributor to the accumulation of Aβ in the CNS, whereas other organs are spared. Significantly, deletion of BACE1 in APPswe;PS1ΔE9 mice prevents both Aβ deposition and age-associated cognitive abnormalities that occur in this model of Aβ amyloidosis. Moreover, Aβ deposits are sensitive to BACE1 dosage and can be efficiently cleared from the CNS when BACE1 is silenced. However, BACE1 null mice manifest alterations in hippocampal synaptic plasticity as well as in performance on tests of cognition and emotion. Importantly, memory deficits but not emotional alterations in BACE1-/- mice are prevented by coexpressing APPswe;PS1ΔE9 transgenes, indicating that other potential substrates of BACE1 may affect neural circuits related to emotion. Our results establish BACE1 and APP processing pathways as critical for cognitive, emotional, and synaptic functions, and future studies should be alert to potential mechanism-based side effects that may occur with BACE1 inhibitors designed to ameliorate Aβ amyloidosis in AD.
doi:10.1523/JNEUROSCI.2766-05.2005
PMCID: PMC2564291  PMID: 16354928
BACE1 null mice; selective vulnerability; Aβ amyloidosis; Alzheimer’s; cognition; synaptic plasticity; RNAi
11.  Treatment with bexarotene, a compound that increases apolipoprotein-E, provides no cognitive benefit in mutant APP/PS1 mice 
Background
Though the precise cause(s) of Alzheimer’s disease (AD) remain unknown, there is strong evidence that decreased clearance of β-amyloid (Aβ) from the brain can contribute to the disease. Therapeutic strategies to promote natural Aβ clearance mechanisms, such as the protein apolipoprotein-E (APOE), hold promise for the treatment of AD. The amount of APOE in the brain is regulated by nuclear receptors including retinoid X receptors (RXRs). Drugs that activate RXRs, including bexarotene, can increase APOE and ABCA1 production, and have been shown to decrease the Aβ burden and improve cognition in mouse models of Aβ amyloidosis. Although recent bexarotene studies failed to replicate the rapid clearance of Aβ from brains, behavioral and cognitive effects of this compound remain controversial.
Findings
In efforts to clarify these behavioral findings, mutant APP/PS1 mice were acutely dosed with bexarotene. While ABCA1 was upregulated in mutant APP/PS1 mice treated with bexarotene, this drug failed to attenuate Aβ plaques or cognitive deficits in these mice.
Conclusions
We recommend rigorous preclinical study to evaluate the mechanism and utility of such a compound for AD therapy.
doi:10.1186/1750-1326-8-18
PMCID: PMC3693923  PMID: 23764200
Bexarotene; Alzheimer’s disease; Mouse model; RXR agonist; APOE; Cognition
12.  Rodent models of TDP-43: Recent advances 
Brain research  2012;1462:26-39.
Recently, missense mutations in the gene TARDBP encoding TDP-43 have been linked to familial ALS. The discovery of genes encoding these RNA binding proteins, such as TDP-43 and FUS/TLS, raised the notion that altered RNA metabolism is a major factor underlying the pathogenesis of ALS. To begin to unravel how mutations in TDP-43 cause dysfunction and death of motor neurons, investigators have employed both gain- and loss-of-function studies in rodent model systems. Here, we will summarize major findings from the initial sets of TDP-43 transgenic and knockout rodent models, identify their limitations, and point to future directions toward clarification of disease mechanism(s) and testing of therapeutic strategies that ultimately may lead to novel therapy for this devastating disease.
doi:10.1016/j.brainres.2012.04.031
PMCID: PMC3613131  PMID: 22608070
TDP-43; Transgenic; Conditional knockout
13.  Specific domains in anterior pharynx-defective 1 determine its intramembrane interactions with nicastrin and presenilin 
Neurobiology of aging  2010;33(2):277-285.
γ-Secretase, a multi-subunit transmembrane protease comprised of presenilin, nicastrin, presenilin enhancer 2, and anterior pharynx-defective 1, participates in the regulated intramembrane proteolysis of Type I membrane proteins including the amyloid precursor protein (APP). Although Aph-1 is thought to play a structural role in the assembly of γ-secretase complex and several transmembrane domains (TMDs) of Aph-1 have been shown to be critical for its function, the importance of the other domains of Aph-1 remains elusive. We screened a series of Aph-1 mutants and focused on 9 mutations distributed in 6 different TMDs of human APH-1aS, assessing their ability to complement mouse embryonic fibroblasts lacking Aph-1. We showed that mutations in TMD4 (G126) and TMD5 (H171) of Aph-1a prevented the formation of the Nct/Aph-1 subcomplex. Importantly, although mutations in TMD3 (Q83/E84/R85) and TMD6 (H197) of APH-1aS did not affect Nct/Aph-1 subcomplex formation, both mutations prevented further association/endoproteolysis of PS1. We propose a model that identifies critical TMDs of Aph-1 for associations with Nct and PS for the stepwise assembly of γ-secretase components.
doi:10.1016/j.neurobiolaging.2009.12.028
PMCID: PMC2904414  PMID: 20382452
γ-Secretase; Aph-1; Nct; PS; mutagenesis; transmembrane domain
14.  Arc/Arg3.1 Regulates an Endosomal Pathway Essential for Activity-Dependent β-Amyloid Generation 
Cell  2011;147(3):615-628.
Summary
Assemblies of β-amyloid (Aβ) peptides are pathological mediators of Alzheimer's Disease (AD) and are produced by the sequential cleavages of amyloid precursor protein (APP) by β-secretase (BACE1) and γ-secretase. The generation of Aβ is coupled to neuronal activity, however the molecular basis is unknown. Here, we report that the immediate early gene Arc is required for activity-dependent generation of Aβ. Arc is a postsynaptic protein that recruits endophilin2/3 and dynamin to early/recycling endosomes that traffic AMPA receptors to reduce synaptic strength in both Hebbian and non-Hebbian forms of plasticity. The Arc-endosome also traffics APP and BACE1, and Arc physically associates with presenilin1 (PS1) to regulate γ-secretase trafficking and confer activity-dependence. Genetic deletion of Arc reduces Aβ load in a transgenic mouse model of AD. In concert with the finding that patients with AD can express anomalously high levels of Arc, we hypothesize that Arc participates in the pathogenesis of AD.
doi:10.1016/j.cell.2011.09.036
PMCID: PMC3207263  PMID: 22036569
15.  Reduced BACE1 activity enhances clearance of myelin debris and regeneration of axons in the injured peripheral nervous system 
The Journal of Neuroscience  2011;31(15):5744-5754.
β- site amyloid precursor protein (APP) cleaving enzyme 1 (BACE1) is an aspartyl protease best known for its role in generating the amyloid β peptides that are present in plaques of Alzheimer's Disease. BACE1 has been an attractive target for drug development. In cultured embryonic neurons BACE1-cleaved N-terminal APP is further processed to generate a fragment that can trigger axonal degeneration, suggesting a vital role for BACE1 in axonal health. In addition, BACE1 cleaves neuregulin 1 type III, a protein critical for myelination of peripheral axons by Schwann cells during development. Here, we asked if axonal degeneration or axonal regeneration in adult nerves might be affected by inhibition or elimination of BACE1. We report that BACE1 knockout and wild-type nerves degenerated at a similar rate after axotomy and to a similar extent in the experimental neuropathies produced by administration of paclitaxel and acrylamide. These data indicate N-APP is not the sole culprit in axonal degeneration in adult nerves. Unexpectedly, however, we observed that BACE1 knockout mice had markedly enhanced clearance of axonal and myelin debris from degenerated fibers, accelerated axonal regeneration, and earlier reinnervation of neuromuscular junctions, compared to littermate controls. These observations were reproduced in part by pharmacological inhibition of BACE1. These data suggest BACE1 inhibition as a therapeutic approach to accelerate regeneration and recovery after peripheral nerve damage.
doi:10.1523/JNEUROSCI.6810-10.2011
PMCID: PMC3302726  PMID: 21490216
16.  Increased Expression of PS1 Is Sufficient to Elevate the Level and Activity of γ-Secretase In Vivo 
PLoS ONE  2011;6(11):e28179.
Increase in the generation and deposition of amyloid-β (Aβ) plays a central role in the development of Alzheimer's Disease (AD). Elevation of the activity of γ-secretase, a key enzyme required for the generation for Aβ, can thus be a potential risk factor in AD. However, it is not known whether γ-secretase can be upregulated in vivo. While in vitro studies showed that expression of all four components of γ-secretase (Nicastrin, Presenilin, Pen-2 and Aph-1) are required for upregulation of γ-secretase, it remains to be established as to whether this is true in vivo. To investigate whether overexpressing a single component of the γ-secretase complex is sufficient to elevate its level and activity in the brain, we analyzed transgenic mice expressing either wild type or familial AD (fAD) associated mutant PS1. In contrast to cell culture studies, overexpression of either wild type or mutant PS1 is sufficient to increase levels of Nicastrin and Pen-2, and elevate the level of active γ-secretase complex, enzymatic activity of γ-secretase and the deposition of Aβ in brains of mice. Importantly, γ-secretase comprised of mutant PS1 is less active than that of wild type PS1-containing γ-secretase; however, γ-secretase comprised of mutant PS1 cleaves at the Aβ42 site of APP-CTFs more efficiently than at the Aβ40 site, resulting in greater accumulation of Aβ deposits in the brain. Our data suggest that whereas fAD-linked PS1 mutants cause early onset disease, upregulation of PS1/γ-secretase activity may be a risk factor for late onset sporadic AD.
doi:10.1371/journal.pone.0028179
PMCID: PMC3226664  PMID: 22140537
17.  Amyloid Precursor Protein Processing and Alzheimer’s Disease 
Annual review of neuroscience  2011;34:185-204.
Alzheimer’s disease (AD), the leading cause of dementia worldwide, is characterized by the accumulation of the β-amyloid peptide (Aβ) within the brain along with hyperphosphorylated and cleaved forms of the microtubule-associated protein tau. Genetic, biochemical, and behavioral research suggest that physiologic generation of the neurotoxic Aβ peptide from sequential amyloid precursor protein (APP) proteolysis is the crucial step in the development of AD. APP is a single-pass transmembrane protein expressed at high levels in the brain and metabolized in a rapid and highly complex fashion by a series of sequential proteases, including the intramembranous γ-secretase complex, which also process other key regulatory molecules. Why Aβ accumulates in the brains of elderly individuals is unclear but could relate to changes in APP metabolism or Aβ elimination. Lessons learned from biochemical and genetic studies of APP processing will be crucial to the development of therapeutic targets to treat AD.
doi:10.1146/annurev-neuro-061010-113613
PMCID: PMC3174086  PMID: 21456963
Neurodegeneration; dementia; BACE1; α-secretase; γ-secretase; aging
18.  Selectivity to amyloid-β precursor protein cleavage provides hope against Alzheimer's 
Toward development of a safe and effective treatment for Alzheimer's disease, Elan Pharmaceuticals reported a novel γ-secretase inhibitor that specifically targets the cleavage of amyloid-β precursor protein, opening the way to design of substrate-specific γ-secretase inhibitors that would reduce the amyloid burden without significant adverse events.
doi:10.1186/alzrt66
PMCID: PMC3226269  PMID: 21418547
19.  Mossy fiber LTP deficits in BACE1 knockouts can be rescued by activation of α7 nicotinic acetylcholine receptors 
Beta-site amyloid precursor protein cleaving enzyme 1 (BACE1)–the neuronal β-secretase responsible for producing β-amyloid (Aβ) peptides–emerged as one of the key therapeutic targets of Alzheimer's disease (AD). Although complete ablation of the BACE1 gene prevents Aβ formation, we reported that BACE1 knockout mice display severe presynaptic deficits at mossy fiber (MF) to CA3 synapses in the hippocampus, a major locus of BACE1 expression. We also found that the deficits are likely due to abnormal presynaptic Ca2+ regulation. Cholinergic system has been implicated in AD, in some cases involving Ca2+-permeable α7-nicotinic acetylcholine receptors (nAChRs). Here we report that brief application of nicotine, via α7-nAChRs, can restore mossy fiber LTP (mfLTP) in BACE1 knockouts. Our data suggest that activating α7-nAChRs can recover the presynaptic deficits in BACE1 knockouts.
doi:10.1523/JNEUROSCI.1070-10.2010
PMCID: PMC3137882  PMID: 20943921
long-term potentiation; presynaptic; paired-pulse facilitation; beta-secretase; Alzheimer's disease; α7-nAchR
20.  An Overview of APP Processing Enzymes and Products 
Neuromolecular medicine  2010;12(1):1-12.
The generation of amyloid β-peptide (Aβ) by enzymatic cleavages of the β-amyloid precursor protein (APP) has been at the center of Alzheimer’s disease (AD) research. While the basic process of β- and γ-secretase-mediated generation of Aβ is text book knowledge, new aspects of Aβ and other cleavage products have emerged in recent years. Also our understanding of the enzymes involved in APP proteolysis has increased dramatically. All of these discoveries contribute to a more complete understanding of APP processing and the physiological and pathological roles of its secreted and intracellular protein products. Understanding APP processing is important for any therapeutic strategy aimed at reducing Aβ levels in AD. In this review we provide a concise description of the current state of understanding the enzymes involved in APP processing, the cleavage products generated by different processing patterns, and the potential functions of those cleavage products.
doi:10.1007/s12017-009-8104-z
PMCID: PMC2889200  PMID: 20232515
Amyloid beta; α-secretase; β-secretase; γ-secretase; APP; AICD
21.  The β-Secretase Enzyme BACE in Health and Alzheimer's Disease: Regulation, Cell Biology, Function, and Therapeutic Potential 
The β-amyloid (Aβ) peptide is the major constituent of amyloid plaques in Alzheimer's disease (AD) brain and is likely to play a central role in the pathogenesis of this devastating neurodegenerative disorder. The β-secretase, β-site amyloid precursor protein cleaving enzyme (BACE1; also called Asp2, memapsin 2), is the enzyme responsible for initiating Aβ generation. Thus, BACE is a prime drug target for the therapeutic inhibition of Aβ production in AD. Since its discovery 10 years ago, much has been learned about BACE. This review summarizes BACE properties, describes BACE translation dysregulation in AD, and discusses BACE physiological functions in sodium current, synaptic transmission, myelination, and schizophrenia. The therapeutic potential of BACE will also be considered. This is a summary of topics covered at a symposium held at the 39th annual meeting of the Society for Neuroscience and is not meant to be a comprehensive review of BACE.
doi:10.1523/JNEUROSCI.3657-09.2009
PMCID: PMC2879048  PMID: 19828790
22.  Modeling an Anti-Amyloid Combination Therapy for Alzheimer's Disease 
Science translational medicine  2010;2(13):13ra1.
As only symptomatic treatments are now available for Alzheimer's disease (AD), safe and effective mechanism-based therapies remain a great unmet need for patients with this neurodegenerative disease. Although γ-secretase and BACE1 [β-site β-amyloid (Aβ) precursor protein (APP) cleaving enzyme 1] are well-recognized therapeutic targets for AD, untoward side effects associated with strong inhibition or reductions in amounts of these aspartyl proteases have raised concerns regarding their therapeutic potential. Although moderate decreases of either γ-secretase or BACE1 are not associated with mechanism-based toxicities, they provide only modest benefits in reducing Aβ in the brains of APPswe/PS1ΔE9 mice. Because the processing of APP to generate Aβ requires both γ-secretase and BACE1, it is possible that moderate reductions of both enzymes would provide additive and significant protection against Aβ amyloidosis. Here, we test this hypothesis and assess the value of this novel anti-amyloid combination therapy in mutant mice. We demonstrate that genetic reductions of both BACE1 and γ-secretase additively attenuate the amyloid burden and ameliorate cognitive deficits occurring in aged APPswe/PS1ΔE9 animals. No evidence of mechanism-based toxicities was associated with such decreases in amounts of both enzymes. Thus, we propose that targeting both γ-secretase and BACE1 may be an effective and safe treatment strategy for AD.
doi:10.1126/scitranslmed.3000337
PMCID: PMC2852193  PMID: 20371462
23.  Beta-amyloid precursor protein cleavage enzyme 1 (BACE1) knockouts display deficits in activity-dependent potentiation of synaptic transmission at mossy fiber to CA3 synapses in the hippocampus 
Beta-amyloid precursor protein cleavage enzyme 1 (BACE1) has been identified as a major neuronal β-secretase critical for the formation of β-amyloid (Aβ) peptide, which is thought responsible for the pathology of Alzheimer’s disease (AD). Therefore, BACE1 is one of the key therapeutic targets that can prevent the progression of AD. Previous studies showed that knocking out the BACE1 gene prevents Aβ formation, but results in behavioral deficits and specific synaptic dysfunctions at Schaffer collateral to CA1 synapses. However, BACE1 protein is most highly expressed at the mossy fiber projections in CA3. Here we report that BACE1 knockout mice display reduced presynaptic function, as measured by an increase in paired-pulse facilitation ratio. More dramatically, mossy fiber LTP, which is normally expressed via an increase in presynaptic release, was eliminated in the knockouts. While LTD was slightly larger in the BACE1 knockouts, it could not be reversed. The specific deficit in mossy fiber LTP was upstream of cAMP signaling, and could be “rescued” by transiently elevating extracellular Ca2+ concentration. These results suggest that BACE1 may play a critical role in regulating presynaptic function, especially activity-dependent strengthening of presynaptic release, at mossy fiber synapses.
doi:10.1523/JNEUROSCI.2440-08.2008
PMCID: PMC2728626  PMID: 18753368
long-term potentiation; long-term depression; presynaptic; paired-pulse facilitation; beta-secretase; Alzheimer’s disease
24.  APH1 Polar Transmembrane Residues Regulate the Assembly and Activity of Presenilin Complexes* 
The Journal of Biological Chemistry  2009;284(24):16298-16307.
Complexes involved in the γ/ϵ-secretase-regulated intramembranous proteolysis of substrates such as the amyloid-β precursor protein are composed primarily of presenilin (PS1 or PS2), nicastrin, anterior pharynx defective-1 (APH1), and PEN2. The presenilin aspartyl residues form the catalytic site, and similar potentially functional polar transmembrane residues in APH1 have been identified. Substitution of charged (E84A, R87A) or polar (Q83A) residues in TM3 had no effect on complex assembly or activity. In contrast, changes to either of two highly conserved histidines (H171A, H197A) located in TM5 and TM6 negatively affected PS1 cleavage and altered binding to other secretase components, resulting in decreased amyloid generating activity. Charge replacement with His-to-Lys substitutions rescued nicastrin maturation and PS1 endoproteolysis leading to assembly of the formation of structurally normal but proteolytically inactive γ-secretase complexes. Substitution with a negatively charged side chain (His-to-Asp) or altering the structural location of the histidines also disrupted γ-secretase binding and abolished functionality of APH1. These results suggest that the conserved transmembrane histidine residues contribute to APH1 function and can affect presenilin catalytic activity.
doi:10.1074/jbc.M109.000067
PMCID: PMC2713549  PMID: 19369254
25.  Progressive Behavioral Deficits in DJ-1 Deficient Mice are Associated with Normal Nigrostriatal Function 
Neurobiology of disease  2007;29(3):505-514.
Loss-of-function mutations in the DJ-1 gene account for an autosomal recessive form of Parkinson’s disease (PD). To investigate the physiological functions of DJ-1 in vivo, we generated DJ-1 knockout (DJ-1-/-) mice. Younger (< 1year) DJ-1 -/- mice were hypoactive and had mild gait abnormalities. Older DJ-1-/-, however, showed decreased bodyweight and grip strength, and more severe gait irregularities compared to wild-type littermates. The basal level of extracellular dopamine, evoked dopamine release and dopamine receptor D2 sensitivity appeared normal in the striatum of DJ-1-/- mice, which was consistent with similar results between DJ-1-/- and controls in behavioral paradigms specific for the dopaminergic system. An examination of spinal cord, nerve and muscle tissues failed to identify any pathological changes that were consistent with the noted motor deficits. Taken together, our findings suggest that loss of DJ-1 leads to progressive behavioral changes without significant alterations in nigrostriatal dopaminergic and spinal motor systems.
doi:10.1016/j.nbd.2007.11.011
PMCID: PMC2271119  PMID: 18187333
DJ-1; knockout mouse; Parkinson’s disease; dopamine; striatum; spinal cord; muscle; motor behavior

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