Mitosis-specific phosphorylation of amyloid precursor protein at threonine 668 leads to its altered processing and association with centrosomes

Dual-specificity tyrosine phosphorylation-regulated kinase 1A promotes the inclusion of amyloid precursor protein exon 7

Extracellular amyloid plaques made of Amyloid-β (Aβ) derived from amyloid precursor protein (APP) is one of the major neuropathological hallmarks of Alzheimer's disease (AD). There are three major isoforms of APP, APP770, APP751, and APP695 generated by alternative splicing of exons 7 and 8. Exon 7 encodes the Kunitz protease inhibitor (KPI) domain. Its inclusion generates APP isoforms containing KPI, APPKPI+, which is elevated in AD and Down syndrome (DS) brains and associated with increased Aβ deposition. Dual-specificity tyrosine phosphorylation-regulated kinase 1A (Dyrk1A) phosphorylates many splicing factors and regulates the alternative splicing of pre-mRNA. It is upregulated in DS and AD brain. However, it is not yet clear whether Dyrk1A could regulate APP alternative splicing. In the present study, we overexpressed or knocked down Dyrk1A in cultured cells and observed that Dyrk1A promoted the inclusion of both APP exons 7 and 8. Moreover, a significant increase in APP exon7 inclusion was also detected in the forebrain and hippocampus of human Dyrk1A transgenic mice - Tg/Dyrk1A. Screening for splicing factors regulated by Dyrk1A revealed that serine/arginine-rich protein 9G8 inhibited APP exon7 inclusion and interacted with APP pre-mRNA. In vitro, expression of exon 7 facilitated APP cleavage. In human Dyrk1A transgenic mice, we also found an increase in Aβ production. These findings suggest that Dyrk1A inhibits the splicing factor 9G8 and promotes APP exon 7 inclusion, leading to more APPKPI+ expression and APP cleavage and potentially contributing to Aβ production in vivo.

A common molecular and cellular pathway in developing Alzheimer and cancer

Globally cancer and Alzheimer's disease (AD) are two major diseases and still, there is no clearly defined molecular mechanism. There is an opposite relation between cancer and AD which are the proportion of emerging cancer was importantly slower in AD patients, whereas slow emerging AD in patients with cancer. In cancer, regulation of cell mechanisms is interrupted by an increase in cell survival and proliferation, while on the contrary, AD is related to augmented neuronal death, that may be either produced by or associated with amyloid-β (Aβ) and tau deposition. Stated that the probability that disruption of mechanisms takes part in the regulation of cell survival/death and might be implicated in both diseases. The mechanism of actions such as DNA-methylation, genetic polymorphisms, or another mechanism of actions that induce alteration in the action of drugs with significant roles in resolving the finding to repair and live or die might take part in the pathogenesis of these two ailments. The functions of miRNA, p53, Pin1, the Wnt signaling pathway, PI3 KINASE/Akt/mTOR signaling pathway GRK2 signaling pathway, and the pathophysiological role of oxidative stress are presented in this review as potential candidates which hypothetically describe inverse relations between cancer and AD. Innovative materials almost mutual mechanisms in the aetiology of cancer and AD advocates novel treatment approaches. Among these treatment strategies, the most promising use treatment such as tyrosine kinase inhibitor, nilotinib, protein kinase C, and bexarotene.

E2F1 Mediates Traumatic Brain Injury and Regulates BDNF-AS to Promote the Progression of Alzheimer's Disease

Traumatic brain injury (TBI) is one of the important risk factors for the development of Alzheimer's disease (AD). However, the molecular mechanism by which TBI promotes the progression of AD is not elucidated. In this study, we showed that the abnormal production of E2F1 is a major factor in promoting the neuropathological and cognitive deterioration of AD post-TBI. We found that repeated mild TBI can aggravate the neuropathology of AD in APP/PS1 mice. At the same time, the co-expression of E2F1 and beta-site APP cleaving enzyme 1 (BACE1) was upregulated when the mouse hippocampus was dissected. BACE1 is recognized as a rate-limiting enzyme for the production of Aβ. Here, we speculate that E2F1 may play a role in promoting BACE1 expression in AD. Therefore, we collected peripheral blood from patients with AD. Interestingly, there is a positive correlation between E2F1 and brain-derived neurotrophic factor-antisense (BDNF-AS), whereas BDNF-AS in AD can promote the expression of BACE1 and exhibit a neurotoxic effect. We established a cell model and found a regulatory relationship between E2F1 and BDNF-AS. Therefore, based on our results, we concluded that E2F1 regulates BDNF-AS, promotes the expression of BACE1, and affects the progression of AD. Furthermore, E2F1 mediates the TBI-induced neurotoxicity of AD.

Tu-Xian Decoction ameliorates diabetic cognitive impairment by inhibiting DAPK-1

Tu-Xian decoction (TXD), a traditional Chinese medicine (TCM) formula, has been frequently administered to manage diabetic cognitive impairment (DCI). Despite its widespread use, the mechanisms underlying TXD's protective effects on DCI have yet to be fully elucidated. As a significant regulator in neurodegenerative conditions, death-associated protein kinase-1 (DAPK-1) serves as a focus for understanding the action of TXD. This study was designed to whether TXD mediates its beneficial outcomes by inhibiting DAPK-1. To this end, a diabetic model was established using Sprague-Dawley (SD) rats through a high-fat, high-sugar (HFHS) diet regimen, followed by streptozotocin (STZ) injection. The experimental cohort was stratified into six groups: Control, Diabetic, TC-DAPK6, high-dose TXD, medium-dose TXD, and low-dose TXD groups. Following a 12-week treatment period, various assessments-including blood glucose levels, body weight measurements, Morris water maze (MWM) testing for cognitive function, brain magnetic resonance imaging (MRI), and histological analyses using hematoxylin-eosin (H&E), and Nissl staining-were conducted. Protein expression in the hippocampus was quantified through Western blotting analysis. The results revealed that TXD significantly improved spatial learning and memory abilities, and preserved hippocampal structure in diabetic rats. Importantly, TXD administration led to a down-regulation of proteins indicative of neurological damage and suppressed DAPK-1 activity within the hippocampal region. These results underscore TXD's potential in mitigating DCIvia DAPK-1 inhibition, positioning it as a viable therapeutic candidate for addressing this condition. Further investigation into TXD's molecular mechanisms may elucidate new pathways for the treatment of DCI.

Neurodevelopmental disorders and microcephaly: how apoptosis, the cell cycle, tau and amyloid-β precursor protein APPly

Recent studies promote new interest in the intersectionality between autism spectrum disorder (ASD) and Alzheimer's Disease. We have reported high levels of Amyloid-β Precursor Protein (APP) and secreted APP-alpha (sAPPa ) and low levels of amyloid-beta (Aβ) peptides 1-40 and 1-42 (Aβ40, Aβ42) in plasma and brain tissue from children with ASD. A higher incidence of microcephaly (head circumference less than the 3rd percentile) associates with ASD compared to head size in individuals with typical development. The role of Aβ peptides as contributors to acquired microcephaly in ASD is proposed. Aβ may lead to microcephaly via disruption of neurogenesis, elongation of the G1/S cell cycle, and arrested cell cycle promoting apoptosis. As the APP gene exists on Chromosome 21, excess Aβ peptides occur in Trisomy 21-T21 (Down's Syndrome). Microcephaly and some forms of ASD associate with T21, and therefore potential mechanisms underlying these associations will be examined in this review. Aβ peptides' role in other neurodevelopmental disorders that feature ASD and acquired microcephaly are reviewed, including dup 15q11.2-q13, Angelman and Rett syndrome.

Unraveling the links between neurodegeneration and Epstein-Barr virus-mediated cell cycle dysregulation

The Epstein-Barr virus is a well-known cell cycle modulator. To establish successful infection in the host, EBV alters the cell cycle at multiple steps via antigens such as EBNAs, LMPs, and certain other EBV-encoded transcripts. Interestingly, several recent studies have indicated the possibility of EBV's neurotrophic potential. However, the effects and outcomes of EBV infection in the CNS are under-explored. Additionally, more and more epidemiological evidence implicates the cell-cycle dysregulation in neurodegeneration. Numerous hypotheses which describe the triggers that force post-mitotic neurons to re-enter the cell cycle are prevalent. Apart from the known genetic and epigenetic factors responsible, several reports have shown the association of microbial infections with neurodegenerative pathology. Although, studies implicating the herpesvirus family members in neurodegeneration exist, the involvement of Epstein-Barr virus (EBV), in particular, is under-evaluated. Interestingly, a few clinical studies have reported patients of AD or PD to be seropositive for EBV. Based on the findings mentioned above, in this review, we propose that EBV infection in neurons could drive it towards neurodegeneration through dysregulation of cell-cycle events and induction of apoptosis.

Reactive astrocytes acquire neuroprotective as well as deleterious signatures in response to Tau and Aß pathology

Alzheimer's disease (AD) alters astrocytes, but the effect of Aß and Tau pathology is poorly understood. TRAP-seq translatome analysis of astrocytes in APP/PS1 ß-amyloidopathy and MAPT^P301S tauopathy mice revealed that only Aß influenced expression of AD risk genes, but both pathologies precociously induced age-dependent changes, and had distinct but overlapping signatures found in human post-mortem AD astrocytes. Both Aß and Tau pathology induced an astrocyte signature involving repression of bioenergetic and translation machinery, and induction of inflammation pathways plus protein degradation/proteostasis genes, the latter enriched in targets of inflammatory mediator Spi1 and stress-activated cytoprotective Nrf2. Astrocyte-specific Nrf2 expression induced a reactive phenotype which recapitulated elements of this proteostasis signature, reduced Aß deposition and phospho-tau accumulation in their respective models, and rescued brain-wide transcriptional deregulation, cellular pathology, neurodegeneration and behavioural/cognitive deficits. Thus, Aß and Tau induce overlapping astrocyte profiles associated with both deleterious and adaptive-protective signals, the latter of which can slow patho-progression.

PROTACs technology for treatment of Alzheimer's disease: Advances and perspectives

Neurodegenerative diseases (NDs) are characteristic with progression of neuron degeneration, resulting in dysfunction of cognition and mobility. Many neurodegenerative diseases are because of proteinopathies that results from unusual protein accumulations and aggregations. The aggregation of misfolded proteins like β-amyloid, α-synuclein, tau, and polyglutamates are hallmarked in Alzheimer's disease (AD), which are undruggable targets, and usually do not respond to conventional small-molecule agents. Therefore, developing novel technology and strategy for reducing the levels of protein aggregates would be critical for treatment of AD. Recently, the emerging proteolysis targeting chimeras (PRPTACs) technology has been significantly considered for artificial and selective degradation of aberrant target proteins. These engineered bifunctional molecules engage target proteins to be degraded by either the cellular degradation machinery in the ubiquitin-proteasome system (UPS) or via the autophagy-lysosome degradation pathway. Although the application of PROTACs technology is preferable than oligonucleotide and antibodies for treatment of NDs, many limitations such as their pharmacokinetic properties, tissue distribution and cell permeabilities, still need to be corrected. Herein, we review the recent advances in PROTACs technology with their limitation for pharmaceutical targeting of aberrant proteins involved in Alzheimer's diseases. We also review therapeutic potential of dysregulated signaling such as PI3K/AKT/mTOR axis for the management of AD.

Putative Factors Interfering Cell Cycle Re-Entry in Alzheimer's Disease: An Omics Study with Differential Expression Meta-Analytics and Co-Expression Profiling

BACKGROUND

Neuronal cell cycle re-entry (CCR) is a mechanism, along with amyloid-β (Aβ) oligomers and hyperphosphorylated tau proteins, contributing to toxicity in Alzheimer's disease (AD).

OBJECTIVE

This study aimed to examine the putative factors in CCR based on evidence corroboration by combining meta-analysis and co-expression analysis of omic data.

METHODS

The differentially expressed genes (DEGs) and CCR-related modules were obtained through the differential analysis and co-expression of transcriptomic data, respectively. Differentially expressed microRNAs (DEmiRNAs) were extracted from the differential miRNA expression studies. The dysregulations of DEGs and DEmiRNAs as binary outcomes were independently analyzed by meta-analysis based on a random-effects model. The CCR-related modules were mapped to human protein-protein interaction databases to construct a network. The importance score of each node within the network was determined by the PageRank algorithm, and nodes that fit the pre-defined criteria were treated as putative CCR-related factors.

RESULTS

The meta-analysis identified 18,261 DEGs and 36 DEmiRNAs, including genes in the ubiquitination proteasome system, mitochondrial homeostasis, and CCR, and miRNAs associated with AD pathologies. The co-expression analysis identified 156 CCR-related modules to construct a protein-protein interaction network. Five genes, UBC, ESR1, EGFR, CUL3, and KRAS, were selected as putative CCR-related factors. Their functions suggested that the combined effects of cellular dyshomeostasis and receptors mediating Aβ toxicity from impaired ubiquitination proteasome system are involved in CCR.

CONCLUSION

This study identified five genes as putative factors and revealed the significance of cellular dyshomeostasis in the CCR of AD.

"Amyloid-beta accumulation cycle" as a prevention and/or therapy target for Alzheimer's disease

The cell cycle and its regulators are validated targets for cancer drugs. Reagents that target cells in a specific cell cycle phase (e.g., antimitotics or DNA synthesis inhibitors/replication stress inducers) have demonstrated success as broad-spectrum anticancer drugs. Cyclin-dependent kinases (CDKs) are drivers of cell cycle transitions. A CDK inhibitor, flavopiridol/alvocidib, is an FDA-approved drug for acute myeloid leukemia. Alzheimer's disease (AD) is another serious issue in contemporary medicine. The cause of AD remains elusive, although a critical role of latent amyloid-beta accumulation has emerged. Existing AD drug research and development targets include amyloid, amyloid metabolism/catabolism, tau, inflammation, cholesterol, the cholinergic system, and other neurotransmitters. However, none have been validated as therapeutically effective targets. Recent reports from AD-omics and preclinical animal models provided data supporting the long-standing notion that cell cycle progression and/or mitosis may be a valid target for AD prevention and/or therapy. This review will summarize the recent developments in AD research: (a) Mitotic re-entry, leading to the "amyloid-beta accumulation cycle," may be a prerequisite for amyloid-beta accumulation and AD pathology development; (b) AD-associated pathogens can cause cell cycle errors; (c) thirteen among 37 human AD genetic risk genes may be functionally involved in the cell cycle and/or mitosis; and (d) preclinical AD mouse models treated with CDK inhibitor showed improvements in cognitive/behavioral symptoms. If the "amyloid-beta accumulation cycle is an AD drug target" concept is proven, repurposing of cancer drugs may emerge as a new, fast-track approach for AD management in the clinic setting.

Chromosome Instability and Mosaic Aneuploidy in Neurodegenerative and Neurodevelopmental Disorders

Evidence from multiple laboratories has accumulated to show that mosaic neuronal aneuploidy and consequent apoptosis characterizes and may underlie neuronal loss in many neurodegenerative diseases, particularly Alzheimer’s disease and frontotemporal dementia. Furthermore, several neurodevelopmental disorders, including Seckel syndrome, ataxia telangiectasia, Nijmegen breakage syndrome, Niemann–Pick type C, and Down syndrome, have been shown to also exhibit mosaic aneuploidy in neurons in the brain and in other cells throughout the body. Together, these results indicate that both neurodegenerative and neurodevelopmental disorders with apparently different pathogenic causes share a cell cycle defect that leads to mosaic aneuploidy in many cell types. When such mosaic aneuploidy arises in neurons in the brain, it promotes apoptosis and may at least partly underlie the cognitive deficits that characterize the neurological symptoms of these disorders. These findings have implications for both diagnosis and treatment/prevention.

Alzheimer's Disease and Cancer: When Two Monsters Cannot Be Together

Alzheimer's disease (AD) and cancer are among the leading causes of human death around the world. While neurodegeneration is the main feature of AD, the most important characteristic of malignant tumors is cell proliferation, placing these two diseases in opposite sides of cell division spectrum. Interestingly, AD and cancer's pathologies consist of a remarkable common feature and that is the presence of active cell cycle in both conditions. In an in vitro model of primary adult neuronal culture, we previously showed that treating cell with beta amyloid forced neurons to start a cell cycle. Instead of cell division, however, neuronal cell cycle was aborted and a massive neurodegeneration was left behind as the consequence. A high level of cell cycle entry, which is a requirement for cancer pathogenesis, was reported in clinically diagnosed cases of AD, leading to neurodegeneration. The diverse clinical manifestation of a similar etiology, have puzzled researchers for many years. In fact, the evidence showed an inverse association between AD and cancer prevalence, suggesting that switching pathogenesis toward AD protects patients against cancer and vice versa. In this mini review, we discussed the possibility of involvement of cell proliferation and survival dysregulation as the underlying mechanism of neurodegeneration in AD, and the leading event to develop both disorders' pathology. As examples, the role of phosphoinositide 3 kinase/Akt/ mammalian target of rapamycin (PI3K/Akt/mTOR) signaling pathway in cell cycle re-entry and blocking autophagy are discussed as potential common intracellular components between AD and cancer pathogenesis, with diverse clinical diagnosis.

Critical role of mitosis in spontaneous late-onset Alzheimer's disease; from a Shugoshin 1 cohesinopathy mouse model

From early-onset Alzheimer's disease (EOAD) studies, the amyloid-beta hypothesis emerged as the foremost theory of the pathological causes of AD. However, how amyloid-beta accumulation is triggered and progresses toward senile plaques in spontaneous late-onset Alzheimer's disease (LOAD) in humans remains unanswered. Various LOAD facilitators have been proposed, and LOAD is currently considered a complex disease with multiple causes. Mice do not normally develop LOAD. Possibly due to the multiple causes, proposed LOAD facilitators have not been able to replicate spontaneous LOAD in mice, representing a disease modeling issue. Recently, we reported spontaneous late-onset development of amyloid-beta accumulation in brains of Shugoshin 1 (Sgo1) haploinsufficient mice, a cohesinopathy-mediated chromosome instability model. The result for the first time expands disease relevance of mitosis studies to a major disease other than cancers. Reverse-engineering of the model would shed light on the process of late-onset amyloid-beta accumulation in the brain and spontaneous LOAD development, and contribute to development of interventions for LOAD. This review will discuss the Sgo1 model, our current "three-hit hypothesis" regarding LOAD development with an emphasis on critical role of prolonged mitosis in amyloid-beta accumulation, and implications for human LOAD intervention and treatment. Abbreviations: Alzheimer's disease (AD); Late-onset Alzheimer's disease (LOAD); Early-onset Alzheimer's disease (EOAD); Shugoshin-1 (Sgo1); Chromosome Instability (CIN); apolipoprotein (Apoe); Central nervous system (CNS); Amyloid precursor protein (APP); N-methyl-d-aspartate (NMDA); Hazard ratio (HR); Cyclin-dependent kinase (CDK); Chronic Atrial Intestinal Dysrhythmia (CAID); beta-secretase 1 (BACE); phosphor-Histone H3 (p-H3); Research and development (R&D); Non-steroidal anti-inflammatory drugs (NSAIDs); Brain blood barrier (BBB).

Spontaneous development of Alzheimer's disease-associated brain pathology in a Shugoshin-1 mouse cohesinopathy model

Spontaneous late-onset Alzheimer's disease (LOAD) accounts for more than 95% of all human AD. As mice do not normally develop AD and as understanding on molecular processes leading to spontaneous LOAD has been insufficient to successfully model LOAD in mouse, no mouse model for LOAD has been available. Existing mouse AD models are all early-onset AD (EOAD) models that rely on forcible expression of AD-associated protein(s), which may not recapitulate prerequisites for spontaneous LOAD. This limitation in AD modeling may contribute to the high failure rate of AD drugs in clinical trials. In this study, we hypothesized that genomic instability facilitates development of LOAD and tested two genomic instability mice models in the brain pathology at the old age. Shugoshin-1 (Sgo1) haploinsufficient (∓) mice, a model of chromosome instability (CIN) with chromosomal and centrosomal cohesinopathy, spontaneously exhibited a major feature of AD pathology; amyloid beta accumulation that colocalized with phosphorylated Tau, beta-secretase 1 (BACE), and mitotic marker phospho-Histone H3 (p-H3) in the brain. Another CIN model, spindle checkpoint-defective BubR1-/+ haploinsufficient mice, did not exhibit the pathology at the same age, suggesting the prolonged mitosis-origin of the AD pathology. RNA-seq identified ten differentially expressed genes, among which seven genes have indicated association with AD pathology or neuronal functions (e.g., ARC, EBF3). Thus, the model represents a novel model that recapitulates spontaneous LOAD pathology in mouse. The Sgo1-/+ mouse may serve as a novel tool for investigating mechanisms of spontaneous progression of LOAD pathology, for early diagnosis markers, and for drug development.

Mitotic defects lead to neuronal aneuploidy and apoptosis in frontotemporal lobar degeneration caused by MAPT mutations

Mutant Tau (MAPT) can lead to frontotemporal lobar degeneration (FTLD). Previous studies associated MAPT mutations and altered function with aneuploidy and chromosome instability in human lymphocytes and in Drosophila development. Here we examine whether FTLD-causing mutations in human MAPT induce aneuploidy and apoptosis in the mammalian brain. First, aneuploidy was found in brain cells from MAPT mutant transgenic mice expressing FTLD mutant human MAPT. Then brain neurons from mice homozygous or heterozygous for the Tau (Mapt) null allele were found to exhibit increasing levels of aneuploidy with decreasing Tau gene dosage. To determine whether aneuploidy leads to neurodegeneration in FTLD, we measured aneuploidy and apoptosis in brain cells from patients with MAPT mutations and identified both increased aneuploidy and apoptosis in the same brain neurons and glia. To determine whether there is a direct relationship between MAPT-induced aneuploidy and apoptosis, we expressed FTLD-causing mutant forms of MAPT in karyotypically normal human cells and found that they cause aneuploidy and mitotic spindle defects that then result in apoptosis. Collectively, our findings reveal a neurodegenerative pathway in FTLD-MAPT in which neurons and glia exhibit mitotic spindle abnormalities, chromosome mis-segregation, and aneuploidy, which then lead to apoptosis.

Normalizing the gene dosage of Dyrk1A in a mouse model of Down syndrome rescues several Alzheimer's disease phenotypes

The intellectual disability that characterizes Down syndrome (DS) is primarily caused by prenatal changes in central nervous system growth and differentiation. However, in later life stages, the cognitive abilities of DS individuals progressively decline due to accelerated aging and the development of Alzheimer's disease (AD) neuropathology. The AD neuropathology in DS has been related to the overexpression of several genes encoded by Hsa21 including DYRK1A (dual-specificity tyrosine-(Y)-phosphorylation regulated kinase 1A), which encodes a protein kinase that performs crucial functions in the regulation of multiple signaling pathways that contribute to normal brain development and adult brain physiology. Studies performed in vitro and in vivo in animal models overexpressing this gene have demonstrated that the DYRK1A gene also plays a crucial role in several neurodegenerative processes found in DS. The Ts65Dn (TS) mouse bears a partial triplication of several Hsa21 orthologous genes, including Dyrk1A, and replicates many DS-like abnormalities, including age-dependent cognitive decline, cholinergic neuron degeneration, increased levels of APP and Aβ, and tau hyperphosphorylation. To use a more direct approach to evaluate the role of the gene dosage of Dyrk1A on the neurodegenerative profile of this model, TS mice were crossed with Dyrk1A KO mice to obtain mice with a triplication of a segment of Mmu16 that includes this gene, mice that are trisomic for the same genes but only carry two copies of Dyrk1A, euploid mice with a normal Dyrk1A dosage, and CO animals with a single copy of Dyrk1A. Normalizing the gene dosage of Dyrk1A in the TS mouse rescued the density of senescent cells in the cingulate cortex, hippocampus and septum, prevented cholinergic neuron degeneration, and reduced App expression in the hippocampus, Aβ load in the cortex and hippocampus, the expression of phosphorylated tau at the Ser202 residue in the hippocampus and cerebellum and the levels of total tau in the cortex, hippocampus and cerebellum. Thus, the present study provides further support for the role of the Dyrk1A gene in several AD-like phenotypes found in TS mice and indicates that this gene could be a therapeutic target to treat AD in DS.

Modifications and Trafficking of APP in the Pathogenesis of Alzheimer's Disease

Alzheimer's disease (AD), the most common neurodegenerative disorder, is the leading cause of dementia. Neuritic plaque, one of the major characteristics of AD neuropathology, mainly consists of amyloid β (Aβ) protein. Aβ is derived from amyloid precursor protein (APP) by sequential cleavages of β- and γ-secretase. Although APP upregulation can promote AD pathogenesis by facilitating Aβ production, growing evidence indicates that aberrant post-translational modifications and trafficking of APP play a pivotal role in AD pathogenesis by dysregulating APP processing and Aβ generation. In this report, we reviewed the current knowledge of APP modifications and trafficking as well as their role in APP processing. More importantly, we discussed the effect of aberrant APP modifications and trafficking on Aβ generation and the underlying mechanisms, which may provide novel strategies for drug development in AD.

Activation of Ras-ERK Signaling and GSK-3 by Amyloid Precursor Protein and Amyloid Beta Facilitates Neurodegeneration in Alzheimer's Disease

It is widely accepted that amyloid β (Aβ) generated from amyloid precursor protein (APP) oligomerizes and fibrillizes to form neuritic plaques in Alzheimer’s disease (AD), yet little is known about the contribution of APP to intracellular signaling events preceding AD pathogenesis. The data presented here demonstrate that APP expression and neuronal exposure to oligomeric Aβ42 enhance Ras/ERK signaling cascade and glycogen synthase kinase 3 (GSK-3) activation. We find that RNA interference (RNAi)-directed knockdown of APP in B103 rat neuroblastoma cells expressing APP inhibits Ras-ERK signaling and GSK-3 activation, indicating that APP acts upstream of these signal transduction events. Both ERK and GSK-3 are known to induce hyperphosphorylation of tau and APP at Thr668, and our findings suggest that aberrant signaling by APP facilitates these events. Supporting this notion, analysis of human AD brain samples showed increased expression of Ras, activation of GSK-3, and phosphorylation of APP and tau, which correlated with Aβ levels in the AD brains. Furthermore, treatment of primary rat neurons with Aβ recapitulated these events and showed enhanced Ras-ERK signaling, GSK-3 activation, upregulation of cyclin D1, and phosphorylation of APP and tau. The finding that Aβ induces Thr668 phosphorylation on APP, which enhances APP proteolysis and Aβ generation, denotes a vicious feedforward mechanism by which APP and Aβ promote tau hyperphosphorylation and neurodegeneration in AD. Based on these results, we hypothesize that aberrant proliferative signaling by APP plays a fundamental role in AD neurodegeneration and that inhibition of this would impede cell cycle deregulation and neurodegeneration observed in AD.

Developmental Expression of 4-Repeat-Tau Induces Neuronal Aneuploidy in Drosophila Tauopathy Models

Tau-mediated neurodegeneration in Alzheimer’s disease and tauopathies is generally assumed to start in a normally developed brain. However, several lines of evidence suggest that impaired Tau isoform expression during development could affect mitosis and ploidy in post-mitotic differentiated tissue. Interestingly, the relative expression levels of Tau isoforms containing either 3 (3R-Tau) or 4 repeats (4R-Tau) play an important role both during brain development and neurodegeneration. Here, we used genetic and cellular tools to study the link between 3R and 4R-Tau isoform expression, mitotic progression in neuronal progenitors and post-mitotic neuronal survival. Our results illustrated that the severity of Tau-induced adult phenotypes depends on 4R-Tau isoform expression during development. As recently described, we observed a mitotic delay in 4R-Tau expressing cells of larval eye discs and brains. Live imaging revealed that the spindle undergoes a cycle of collapse and recovery before proceeding to anaphase. Furthermore, we found a high level of aneuploidy in post-mitotic differentiated tissue. Finally, we showed that overexpression of wild type and mutant 4R-Tau isoform in neuroblastoma SH-SY5Y cell lines is sufficient to induce monopolar spindles. Taken together, our results suggested that neurodegeneration could be in part linked to neuronal aneuploidy caused by 4R-Tau expression during brain development.

Potential role of PCTAIRE-2, PCTAIRE-3 and P-Histone H4 in amyloid precursor protein-dependent Alzheimer pathology

Amyloid Precursor Protein (APP) is regulated in a mitosis-specific manner and plays a role in proliferative signaling in cells. Though APP-derived Aβ generation has a well-established role in neurodegeneration, the mechanistic role of APP in this process is not fully understood. Here, we performed an unbiased, comprehensive analysis of the phosphoproteome signature in APP-null neuroblastoma cells (B103) compared to those expressing APP-695 isoform (B103-695) to determine if APP expression affects protein phosphorylation. Stable isotope labeling by amino acids in cell culture (SILAC) followed by mass spectrometry-based phosphoproteomic analysis with PolyMAC identified a total of 2,478 phosphopeptides in the B103 and B103-695 cell culture model system. We observed that phosphorylation of PCTAIRE-2 (CDK17), PCTAIRE-3 (CDK18), and Histone H4 are significantly elevated in B103-695 cells; western blot analysis confirmed overexpression of PCTAIREs and increased phosphorylation of Histone H4. More importantly, analysis of primary neurons treated with Aβ, as well as brain samples from MCI (mild cognitive impaired) and AD patients recapitulated these results, showing increased levels of PCTAIREs and P-Histone H4. These novel findings identify a hitherto uncharacterized mechanism by which APP and/or Aβ may promote AD neurodegeneration, and raises the possibility that their inhibition may protect against pathology development in AD.

Fendiline inhibits proliferation and invasion of pancreatic cancer cells by interfering with ADAM10 activation and β-catenin signaling

ADAM10 (A Disintegrin and Metalloprotease Domain 10) affects the pathophysiology of various cancers, and we had shown that inhibition of ADAM10 sensitizes pancreatic cancer cells to gemcitabine. ADAM10 is activated in response to calcium influx, and here we examined if calcium channel blockers (CCB) would impede ADAM10 activation and affect biology of pancreatic cancer cells. We find that the CCB, fendiline, significantly reduces proliferation, migration, invasion, and anchorage independent growth of pancreatic cancer cells. This was associated with ADAM10 inhibition and its localization at the actin-rich membrane protrusions. Further, fendiline-treated cells formed cadherin-catenin positive tight adherens junctions and elicited defective protein trafficking and recycling. Furthermore, the expression of β-catenin target genes, cyclinD1, c-Myc and CD44, were significantly decreased, suggesting that fendiline might prevent cell proliferation and migration by inhibiting ADAM10 function, cadherin proteolysis and stabilization of cadherin-catenin interaction at the plasma membrane. This will subsequently diminish β-catenin intracellular signaling and repress TCF/LEF target gene expression. Supporting this notion, RNAi-directed downregulation of ADAM10 in cancer cells decreased the expression of cyclinD1, c-Myc and CD44. Furthermore, analysis of human pancreatic tumor tissue microarrays and lysates showed elevated levels of ADAM10, suggesting that aberrant activation of ADAM10 plays a fundamental role in growth and metastasis of PDACs and inhibiting this pathway might be a viable strategy to combat PDACs.

Extensive nuclear sphere generation in the human Alzheimer's brain

Nuclear spheres are protein aggregates consisting of FE65, TIP60, BLM, and other yet unknown proteins. Generation of these structures in the cellular nucleus is putatively modulated by the amyloid precursor protein (APP), either by its cleavage or its phosphorylation. Nuclear spheres were preferentially studied in cell culture models and their existence in the human brain had not been known. Existence of nuclear spheres in the human brain was studied using immunohistochemistry. Cell culture experiments were used to study regulative mechanisms of nuclear sphere generation. The comparison of human frontal cortex brain samples from Alzheimer's disease (AD) patients to age-matched controls revealed a dramatically and highly significant enrichment of nuclear spheres in the AD brain. Costaining demonstrated that neurons are distinctly affected by nuclear spheres, but astrocytes never are. Nuclear spheres were predominantly found in neurons that were negative for threonine 668 residue in APP phosphorylation. Cell culture experiments revealed that JNK3-mediated APP phosphorylation reduces the amount of sphere-positive cells. The study suggests that nuclear spheres are a new APP-derived central hallmark of AD, which might be of crucial relevance for the molecular mechanisms in neurodegeneration.

Role of Trisomy 21 Mosaicism in Sporadic and Familial Alzheimer's Disease

Trisomy 21 and the consequent extra copy of the amyloid precursor protein (APP) gene and increased beta-amyloid (Aβ) peptide production underlie the universal development of Alzheimer's disease (AD) pathology and high risk of AD dementia in people with Down syndrome (DS). Trisomy 21 and other forms of aneuploidy also arise among neurons and peripheral cells in both sporadic and familial AD and in mouse and cell models thereof, reinforcing the conclusion that AD and DS are two sides of the same coin. The demonstration that 90% of the neurodegeneration in AD can be attributed to the selective loss of aneuploid neurons generated over the course of the disease indicates that aneuploidy is an essential feature of the pathogenic pathway leading to the depletion of neuronal cell populations. Trisomy 21 mosaicism also occurs in neurons and other cells from patients with Niemann-Pick C1 disease and from patients with familial or sporadic frontotemporal lobar degeneration (FTLD), as well as in their corresponding mouse and cell models. Biochemical studies have shown that Aβ induces mitotic spindle defects, chromosome mis-segregation, and aneuploidy in cultured cells by inhibiting specific microtubule motors required for mitosis. These data indicate that neuronal trisomy 21 and other types of aneuploidy characterize and likely contribute to multiple neurodegenerative diseases and are a valid target for therapeutic intervention. For example, reducing extracellular calcium or treating cells with lithium chloride (LiCl) blocks the induction of trisomy 21 by Aβ. The latter finding is relevant in light of recent reports of a lowered risk of dementia in bipolar patients treated with LiCl and in the stabilization of cognition in AD patients treated with LiCl.

GSI promotes vincristine-induced apoptosis by enhancing multi-polar spindle formation

Gamma secretase inhibitors (GSI), cell-permeable small-molecule inhibitors of gamma secretase activity, had been originally developed for the treatment of Alzheimer disease. In recent years, it has been exploited in cancer research to inhibit Notch signaling that is aberrantly activated in various cancers. We previously found that GSI could synergize with anti-microtubule agent, vincristine (VCR) in a Notch-independent manner. Here, we delineate the underlying cell cycle-related mechanism using HeLa cells, which have strong mitotic checkpoints. GSI enhanced VCR-induced cell death, although GSI alone did not affect cell viability at all. GSI augmented VCR-induced mitotic arrest in a dose-dependent manner, which was preceded by apoptotic cell death, as shown by an increase in Annexin V-positive and caspase-positive cell population. Furthermore, GSI amplified multi-polar spindle formation triggered by VCR. Altogether, we show the evidence that GSI enhances VCR-induced apoptosis in HeLa cells via multi-polar mitotic spindle formation, independent of Notch signaling. These data suggest that one or more GS substrates, yet to be identified, in a post-GS processed form, may play a role in maintaining functional centrosomes/mitotic spindles. More significantly, the synergistic effect of GSI in combination with VCR could be exploited in clinical setting to improve the efficacy of VCR.

SILAC-based proteomic analysis to investigate the impact of amyloid precursor protein expression in neuronal-like B103 cells

Alzheimer's disease (AD) is the most prevalent form of dementia in the elderly. Amyloid plaque formation through aggregation of the amyloid beta peptide derived from amyloid precursor protein (APP) is considered one of the hallmark processes leading to AD pathology; however, the precise role of APP in plaque formation and AD pathogenesis is yet to be determined. Using stable isotope labeling by amino acids in cell culture (SILAC) and MS, protein expression profiles of APP null, rat neuronal-like B103 cells were compared to B103-695 cells that express the APP isoform, APP-695. A total of 2979 unique protein groups were identified among three biological replicates and significant protein expression changes were identified in a total of 102 nonredundant proteins. Some of the top biological functions associated with the differentially expressed proteins identified include cellular assembly, organization and morphology, cell cycle, lipid metabolism, protein folding, and PTMs. We report several novel biological pathways influenced by APP-695 expression in neuronal-like cells and provide additional framework for investigating altered molecular mechanisms associated with APP expression and processing and contribution to AD pathology.

The genomically mosaic brain: aneuploidy and more in neural diversity and disease

Genomically identical cells have long been assumed to comprise the human brain, with post-genomic mechanisms giving rise to its enormous diversity, complexity, and disease susceptibility. However, the identification of neural cells containing somatically generated mosaic aneuploidy - loss and/or gain of chromosomes from a euploid complement - and other genomic variations including LINE1 retrotransposons and regional patterns of DNA content variation (DCV), demonstrate that the brain is genomically heterogeneous. The precise phenotypes and functions produced by genomic mosaicism are not well understood, although the effects of constitutive aberrations, as observed in Down syndrome, implicate roles for defined mosaic genomes relevant to cellular survival, differentiation potential, stem cell biology, and brain organization. Here we discuss genomic mosaicism as a feature of the normal brain as well as a possible factor in the weak or complex genetic linkages observed for many of the most common forms of neurological and psychiatric diseases.

Altered processing of amyloid precursor protein in cells undergoing apoptosis

Altered proteolysis of amyloid precursor protein is an important determinant of pathology development in Alzheimer's disease. Here, we describe the detection of two novel fragments of amyloid precursor protein in H4 neuroglioma cells undergoing apoptosis. Immunoreactivity of these 25-35 kDa fragments to two different amyloid precursor protein antibodies suggests that they contain the amyloid-β region and an epitope near the C-terminus of amyloid precursor protein. Generation of these fragments is associated with cleavage of caspase-3 and caspase-7, suggesting activation of these caspases. Studies in neurons undergoing DNA damage-induced apoptosis also showed similar results. Inclusion of caspase inhibitors prevented the generation of these novel fragments, suggesting that they are generated by a caspase-dependent mechanism. Molecular weight prediction and immunoreactivity of the fragments generated suggested that such fragments could not be generated by cleavage at any previously identified caspase, secretase, or calpain site on amyloid precursor protein. Bioinformatic analysis of the amino acid sequence of amyloid precursor protein revealed that fragments fitting the observed size and immunoreactivity could be generated by either cleavage at a novel, hitherto unidentified, caspase site or at a previously identified matrix metalloproteinase site in the extracellular domain. Proteolytic cleavage at any of these sites leads to a decrease in the generation of α-secretase cleaved secreted APP, which has both anti-apoptotic and neuroprotective properties, and thus may contribute to neurodegeneration in Alzheimer's disease.

Role of tau protein in neuronal damage in Alzheimer's disease and Down syndrome

Neurodegenerative disorders constitute a growing concern worldwide. Their incidence has increased steadily, in particular among the elderly, a high-risk population that is becoming an important segment of society. Neurodegenerative mechanisms underlie many ailments such as Parkinson's disease, Huntington's disease, Alzheimer's disease (AD) and Down syndrome (DS, trisomy 21). Interestingly, there is increasing evidence suggesting that many such diseases share pathogenic mechanisms at the cellular and subcellular levels. These include altered protein misfolding, impaired autophagy, mitochondrial dysfunction, membrane damage, and altered axonal transport. Regarding AD and DS, the first common link comes from observations that DS patients undergo AD-like pathology early in adulthood. Also, the gene encoding for the amyloid precursor protein is present in human autosome 21 and in murine chromosome 16, an animal model of DS. Important functions related to preservation of normal neuronal architecture are impaired in both conditions. In particular, the stable assembly of microtubules, which is critical for the cytoskeleton, is impaired in AD and DS. In this process, tau protein plays a pivotal role in controlling microtubule stability. Abnormal tau expression and hyperphosphorylation are common features in both conditions, yet the mechanisms leading to these phenomena remain obscure. In the present report we review possible common mechanisms that may alter tau expression and function, in particular in relation to the effect of certain overexpressed DS-related genes, using cellular models of human DS. The latter contributes to the identification of possible therapeutic targets that could aid in the treatment of both AD and DS.

Berberine ameliorates β-amyloid pathology, gliosis, and cognitive impairment in an Alzheimer's disease transgenic mouse model

The accumulation of β-amyloid (Aβ) peptide derived from abnormal processing of amyloid precursor protein (APP) is a common pathological hallmark of Alzheimer's disease (AD) brains. In this study, we evaluated the therapeutic effect of berberine (BBR) extracted from Coptis chinensis Franch, a Chinese medicinal herb, on the neuropathology and cognitive impairment in TgCRND8 mice, a well established transgenic mouse model of AD. Two-month-old TgCRND8 mice received a low (25 mg/kg per day) or a high dose of BBR (100 mg/kg per day) by oral gavage until 6 months old. BBR treatment significantly ameliorated learning deficits, long-term spatial memory retention, as well as plaque load compared with vehicle control treatment. In addition, enzyme-linked immunosorbent assay (ELISA) measurement showed that there was a profound reduction in levels of detergent-soluble and -insoluble β-amyloid in brain homogenates of BBR-treated mice. Glycogen synthase kinase (GSK)3, a major kinase involved in APP and tau phosphorylation, was significantly inhibited by BBR treatment. We also found that BBR significantly decreased the levels of C-terminal fragments of APP and the hyperphosphorylation of APP and tau via the Akt/glycogen synthase kinase 3 signaling pathway in N2a mouse neuroblastoma cells stably expressing human Swedish mutant APP695 (N2a-SwedAPP). Our results suggest that BBR provides neuroprotective effects in TgCRND8 mice through regulating APP processing and that further investigation of the BBR for therapeutic use in treating AD is warranted.