Alzheimer presenilins in the nuclear membrane, interphase kinetochores, and centrosomes suggest a role in chromosome segregation

Centrosomes and cilia in neurodegeneration: main actors or mere spectators?

Centrosomes are intracellular organelles traditionally recognized as the primary microtubule (MT) organizing centres (MTOCs) in the cell, playing a crucial role in organizing the cytoskeleton and forming the MT-based spindle during cell division. However, it is now well established that centrosomes also function as central hubs for a wide range of signalling pathways. In non-dividing cells, they give rise to the primary cilium, a surface antenna that serves as a key structure for signalling. Neurons are highly specialized cells with a distinctive morphology, and most neurons have cilia. During brain development, cilia regulate the self-renewal of neural progenitors, as well as the differentiation, migration and synapse formation of newly generated neurons. As a consequence, defects in cilia result in various neurodevelopmental disorders. The role of centrosomes and cilia in neurodegeneration, or the progressive loss of neurons, is less understood. Centrosomes take part in several cellular processes that are often disrupted in neurodegenerative diseases (NDDs), and many proteins associated with these conditions have been found at centrosomes or cilia suggesting a link between these organelles and the underlying mechanisms that contribute to neuronal decline. Unravelling if and how centrosome dysfunction contributes to neurodegeneration could significantly deepen our understanding of the underlying biology of these disorders. Such insights may pave the way for new therapeutic approaches to address these debilitating conditions.

Genomic stress and impaired DNA repair in Alzheimer disease

Alzheimer disease (AD) is the most prominent form of dementia and has received considerable attention due to its growing burden on economic, healthcare and basic societal infrastructures. The two major neuropathological hallmarks of AD, i.e., extracellular amyloid beta (Aβ) peptide plaques and intracellular hyperphosphorylated Tau neurofibrillary tangles, have been the focus of much research, with an eye on understanding underlying disease mechanisms and identifying novel therapeutic avenues. One often overlooked aspect of AD is how Aβ and Tau may, through indirect and direct mechanisms, affect genome integrity. Herein, we review evidence that Aβ and Tau abnormalities induce excessive genomic stress and impair genome maintenance mechanisms, events that can promote DNA damage-induced neuronal cell loss and associated brain atrophy.

Presenilin-1, mutated in familial Alzheimer's disease, maintains genome stability via a γ-secretase dependent way

Mutations in Presenilin-1 (PS1) account for over 80 % mutations linked to familial Alzheimer's disease (AD). However, the mechanisms of action of PS1 mutations in causing familial AD are not fully understood, limiting opportunities to develop targeted disease-modifying therapies for individuals carrying PS1 mutation. To gain more comprehensive insights into the impact of PS1 mutations on genome stability, we knocked down PS1 in SH-SY5Y, HMC3 and A549 cells. This revealed that PS1 knockdown (KD) dramatically induces genome instability (GIN) in all cell types, as indicated by the increased incidence of micronuclei, nucleoplasmic bridges and/or nuclear buds. Although amyloid β (Aβ) was able to induce GIN, PS1-KD was associated with decreased expression of Aβ in SH-SY5Y cells, suggesting Aβ is not the primary cause of GIN in PS1-KD cells. In contrast, inhibiting the PS1 γ-secretase activity by DAPT recapitulated GIN phenotype as seen in PS1-KD cells, indicating that the induction of GIN following PS1 KD can be attributed to the loss of γ-secretase activity. PS1 KD or γ-secretase inhibition markedly sensitizes SH-SY5Y to the genotoxicity of mitomycin C. Interestingly, overexpression of the wildtype PS1 dramatically increased GIN in SH-SY5Y. Collectively, our study demonstrates the potential of PS1 and its γ-secretase activity in maintaining genome stability, highlighting a novel potential link between PS1 loss-of-function or gain-of-function mutations and familial AD through GIN. Several mechanisms by which GIN induced by PS1 dys-expression may contribute to AD are discussed.

PSEN2 and ABCA7 variants causing early-onset preclinical pathological changes in Alzheimer's disease: a case report and literature review

BACKGROUND

Alzheimer's disease (AD) is a debilitating and highly heritable neurodegenerative disease. Early-onset AD (EOAD) was defined as AD occurring before age 65. Although it has a high genetic risk, EOAD due to PSEN2 variation is very rare. ABCA7 is an important risk gene for AD. Previously reported cases mainly carried variations in a single pathogenic or risk gene. METHODS AND RESULTS: In this study, we report a 35-year-old female carrying variants in both the PSEN2 gene (c.640G > T p.V214L) and ABCA7 gene (c.2848G > A p.V950M). Four previously reported cases carried PSEN2 V214L, and no reported cases carried ABCA7 V950M. She had a history of migraine, patent foramen ovale, spontaneous subarachnoid hemorrhage without aneurysm, and multiple cerebral microhemorrhages. Her MMSE score was 24/30, and her MoCA score was 22/30. The concentration of Aβ42 and the ratio of Aβ42 to Aβ40 in cerebral spinal fluid were obviously decreased. Published variants of PSEN2 and ABCA7 in PubMed were reviewed, and the patients' characteristics were summarized and compared to provide information for the clinical diagnosis of AD.

CONCLUSIONS

It is necessary to conduct genetic screening in cases with atypical manifestations.

The Cilioprotist Cytoskeleton , a Model for Understanding How Cell Architecture and Pattern Are Specified: Recent Discoveries from Ciliates and Comparable Model Systems

The cytoskeletons of eukaryotic, cilioprotist microorganisms are complex, highly patterned, and diverse, reflecting the varied and elaborate swimming, feeding, reproductive, and sensory behaviors of the multitude of cilioprotist species that inhabit the aquatic environment. In the past 10-20 years, many new discoveries and technologies have helped to advance our understanding of how cytoskeletal organelles are assembled in many different eukaryotic model systems, in relation to the construction and modification of overall cellular architecture and function. Microtubule organizing centers, particularly basal bodies and centrioles, have continued to reveal their central roles in architectural engineering of the eukaryotic cell, including in the cilioprotists. This review calls attention to (1) published resources that illuminate what is known of the cilioprotist cytoskeleton; (2) recent studies on cilioprotists and other model organisms that raise specific questions regarding whether basal body- and centriole-associated nucleic acids, both DNA and RNA, should continue to be considered when seeking to employ cilioprotists as model systems for cytoskeletal research; and (3) new, mainly imaging, technologies that have already proven useful for, but also promise to enhance, future cytoskeletal research on cilioprotists.

A transcriptomic analysis of Nsmce1 overexpression in mouse hippocampal neuronal cell by RNA sequencing

Mouse Nsmce1 gene is the homolog of non-structural maintenance of chromosomes element 1 (NSE1) that is mainly involved in maintenance of genome integrity, DNA damage response, and DNA repair. Defective DNA repair may cause neurological disorders such as Alzheimer's disease (AD). So far, there is no direct evidence for the correlation between Nsmce1 and AD. In order to explore the function of Nsmce1 in the regulation of nervous system, we have overexpressed or knocked down Nsmce1 in the mouse hippocampal neuronal cells (MHNCs) HT-22 and detected its regulation of AD marker genes as well as cell proliferation. The results showed that the expression of App, Bace2, and Mapt could be inhibited by Nsmce1 overexpression and activated by the knockdown of Nsmce1. Moreover, the HT-22 cell proliferation ability could be promoted by Nsmce1 overexpression and inhibited by knockdown of Nsmce1. Furthermore, we performed a transcriptomics study by RNA sequencing (RNA-seq) to evaluate and quantify the gene expression profiles in response to the overexpression of Nsmce1 in HT-22 cells. As a result, 224 significantly dysregulated genes including 83 upregulated and 141 downregulated genes were identified by the comparison of Nsmce1 /+ to WT cells, which were significantly enriched in several Gene Ontology (GO) terms and pathways. In addition, the complexity of the alternative splicing (AS) landscape was increased by Nsmce1 overexpression in HT-22 cells. Thousands of AS events were identified to be mainly involved in the pathway of ubiquitin-mediated proteolysis (UMP) as well as 3 neurodegenerative diseases including AD. The protein-protein interaction network was reconstructed to show top 10 essential genes regulated by Nsmce1. Our sequencing data is available in the Gene Expression Omnibus (GEO) database with accession number as GSE113436. These results may provide some evidence of molecular and cellular functions of Nsmce1 in MHNCs.

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.

Overactive BRCA1 Affects Presenilin 1 in Induced Pluripotent Stem Cell-Derived Neurons in Alzheimer's Disease

The BRCA1 protein, one of the major players responsible for DNA damage response has recently been linked to Alzheimer's disease (AD). Using primary fibroblasts and neurons reprogrammed from induced pluripotent stem cells (iPSC) derived from familial AD (FAD) patients, we studied the role of the BRCA1 protein underlying molecular neurodegeneration. By whole-transcriptome approach, we have found wide range of disturbances in cell cycle and DNA damage response in FAD fibroblasts. This was manifested by significantly increased content of BRCA1 phosphorylated on Ser1524 and abnormal ubiquitination and subcellular distribution of presenilin 1 (PS1). Accordingly, the iPSC-derived FAD neurons showed increased content of BRCA1(Ser1524) colocalized with degraded PS1, accompanied by an enhanced immunostaining pattern of amyloid-β. Finally, overactivation of BRCA1 was followed by an increased content of Cdc25C phosphorylated on Ser216, likely triggering cell cycle re-entry in FAD neurons. This study suggests that overactivated BRCA1 could both influence PS1 turnover leading to amyloid-β pathology and promote cell cycle re-entry-driven cell death of postmitotic neurons in AD.

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.

Combined association of Presenilin-1 and Apolipoprotein E polymorphisms with maternal meiosis II error in Down syndrome births

Alzheimer's disease and Down syndrome often exhibit close association and predictively share common genetic risk-factors. Presenilin-1 (PSEN-1) and Apolipoprotein E (APOE) genes are associated with early and late onset of Alzheimer's disease, respectively. Presenilin -1 is involved in faithful chromosomal segregation. A higher frequency of the APOE ε4 allele has been reported among young mothers giving birth to Down syndrome children. In this study, 170 Down syndrome patients, grouped according to maternal meiotic stage of nondisjunction and maternal age at conception, and their parents were genotyped for PSEN-1 intron-8 and APOE polymorphisms. The control group consisted of 186 mothers of karyotypically normal children. The frequencies of the PSEN-1 T allele and TT genotype, in the presence of the APOE ε4 allele, were significantly higher among young mothers (< 35 years) with meiosis II nondisjunction than in young control mothers (96.43% vs. 65.91% P = 0.0002 and 92.86% vs. 45.45% P < 0.0001 respectively) but not among mothers with meiosis I nondisjunction. We infer that the co-occurrence of the PSEN-1 T allele and the APOE ε4 allele associatively increases the risk of meiotic segregation error II among young women.

Mitochondrion to endoplasmic reticulum apposition length in zebrafish embryo spinal progenitors is unchanged in response to perturbations associated with Alzheimer's disease

Mutations in the human genes PRESENILIN1 (PSEN1), PRESENILIN2 (PSEN2) and AMYLOID BETA A4 PRECURSOR PROTEIN (APP) have been identified in familial Alzheimer’s disease (AD). The length of mitochondrion-endoplasmic reticulum (M-ER) appositions is increased in Psen1^-/-/Psen2^-/- double knockout murine embryonic fibroblasts and in fibroblasts from AD-affected individuals. Development of an easily accessible, genetically manipulable, in vivo system for studying M-ER appositions would be valuable so we attempted to manipulate M-ER apposition length in zebrafish (Danio rerio) embryos. We injected fertilized zebrafish eggs with antisense morpholino oligonucleotides (MOs) that inhibit expression of zebrafish familial AD gene orthologues psen1 and psen2. Furthermore, we treated zebrafish embryos with DAPT (a highly specific γ-secretase inhibitor) or with sodium azide (to mimic partially hypoxic conditions). We then analyzed M-ER apposition in an identified, presumably proliferative neural cell type using electron microscopy. Our analysis showed no significant differences in M-ER apposition lengths at 48 hours post fertilization (hpf) between psen1 & psen2 MO co-injected embryos, embryos treated with DAPT, or sodium azide, and control embryos. Instead, the distribution of M-ER apposition lengths into different length classes was close to identical. However, this indicates that it is feasible to reproducibly measure M-ER size distributions in zebrafish embryos. While our observations differ from those of murine and human studies, this may be due to differences in cellular differentiation and metabolic state, cell age, or species-specific responses. In particular, by focusing on a presumably proliferative embryonic cell type, we may have selected a cell heavily already reliant on anaerobic glycolysis and less responsive to factors affecting M-ER apposition. Future examination of more differentiated, more secretory cell types may reveal measurable responses of M-ER apposition to environmental and genetic manipulation.

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.

Gene regulation and genetics in neurochemistry, past to future

Ask any neuroscientist to name the most profound discoveries in the field in the past 60 years, and at or near the top of the list will be a phenomenon or technique related to genes and their expression. Indeed, our understanding of genetics and gene regulation has ushered in whole new systems of knowledge and new empirical approaches, many of which could not have even been imagined prior to the molecular biology boon of recent decades. Neurochemistry, in the classic sense, intersects with these concepts in the manifestation of neuropeptides, obviously dependent upon the central dogma (the established rules by which DNA sequence is eventually converted into protein primary structure) not only for their conformation but also for their levels and locales of expression. But, expanding these considerations to non-peptide neurotransmitters illustrates how gene regulatory events impact neurochemistry in a much broader sense, extending beyond the neurochemicals that translate electrical signals into chemical ones in the synapse, to also include every aspect of neural development, structure, function, and pathology. From the beginning, the mutability - yet relative stability - of genes and their expression patterns were recognized as potential substrates for some of the most intriguing phenomena in neurobiology - those instances of plasticity required for learning and memory. Near-heretical speculation was offered in the idea that perhaps the very sequence of the genome was altered to encode memories. A fascinating component of the intervening progress includes evidence that the central dogma is not nearly as rigid and consistent as we once thought. And this mutability extends to the potential to manipulate that code for both experimental and clinical purposes. Astonishing progress has been made in the molecular biology of neurochemistry during the 60 years since this journal debuted. Many of the gains in conceptual understanding have been driven by methodological progress, from automated high-throughput sequencing instruments to recombinant-DNA vectors that can convey color-coded genetic modifications in the chromosomes of live adult animals. This review covers the highlights of these advances, both theoretical and technological, along with a brief window into the promising science ahead. This article is part of the 60th Anniversary special issue.

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.

Mutations in presenilin 2 and its implications in Alzheimer's disease and other dementia-associated disorders

Alzheimer's disease (AD) is the most common form of dementia. Mutations in the genes encoding presenilin 1 (PSEN1), presenilin 2 (PSEN2), and amyloid precursor protein have been identified as the main genetic causes of familial AD. To date, more than 200 mutations have been described worldwide in PSEN1, which is highly homologous with PSEN2, while mutations in PSEN2 have been rarely reported. We performed a systematic review of studies describing the mutations identified in PSEN2. Most PSEN2 mutations were detected in European and in African populations. Only two were found in Korean populations. Interestingly, PSEN2 mutations appeared not only in AD patients but also in patients with other disorders, including frontotemporal dementia, dementia with Lewy bodies, breast cancer, dilated cardiomyopathy, and Parkinson's disease with dementia. Here, we have summarized the PSEN2 mutations and the potential implications of these mutations in dementia-associated disorders.

Alzheimer's disease-related peptide PS2V plays ancient, conserved roles in suppression of the unfolded protein response under hypoxia and stimulation of γ-secretase activity

The PRESENILIN1 and PRESENILIN2 genes encode structurally related proteases essential for γ-secretase activity. Of nearly 200 PRESENILIN mutations causing early onset, familial Alzheimer's disease (FAD) only the K115Efx10 mutation of PSEN2 causes truncation of the open reading frame. If translated, the truncated product would resemble a naturally occurring isoform of PSEN2 named PS2V that is induced by hypoxia and found at elevated levels in late onset Alzheimer's disease (AD) brains. The function of PS2V is largely unexplored. We show that zebrafish possess a PS2V-like isoform, PS1IV, produced from the fish's PSEN1 rather than PSEN2 orthologous gene. The molecular mechanism controlling formation of PS2V/PS1IV was probably present in the ancient common ancestor of the PSEN1 and PSEN2 genes. Human PS2V and zebrafish PS1IV have highly divergent structures but conserved abilities to stimulate γ-secretase activity and to suppress the unfolded protein response (UPR) under hypoxia. The putative protein truncation caused by K115Efx10 resembles PS2V in its ability to increase γ-secretase activity and suppress the UPR. This supports increased Aβ levels as a common link between K115Efx10 early onset AD and sporadic, late onset AD. The ability of mutant variants of PS2V to stimulate γ-secretase activity partially correlates with their ability to suppress the UPR. The cytosolic, transmembrane and luminal domains of PS2V are all critical to its γ-secretase and UPR-suppression activities. Our data support a model in which chronic hypoxia in aged brains promotes excessive Notch signalling and accumulation of Aβ that contribute to AD pathogenesis.

The centrosome: a prospective entrant in cancer therapy

INTRODUCTION

The centrosome plays an essential role in the cell cycle. The centrosome and its associated proteins assist in nucleating and organizing microtubules. A structural or a functional aberration in the centrosome is known to cause abnormal cell proliferation leading to tumors. Therefore, the centrosome is considered as a promising anti-cancer target.

AREAS COVERED

This review begins with a brief introduction to the centrosome and its role in the cell cycle. We elaborate on the centrosome-associated proteins that regulate microtubule dynamics. In addition, we discuss the centrosomal protein kinase targets such as cyclin-dependent, polo-like and aurora kinases. Inhibitors targeting these kinases are undergoing clinical trials for cancer chemotherapy. Further, we shed light on new approaches to target the centrosomal proteins for cancer therapy.

EXPERT OPINION

Insights into the functioning of the centrosomal proteins will be extremely beneficial in validating the centrosome as a target in cancer therapy. New strategies either as a single entity or in combination with current chemotherapeutic agents should be researched or exploited to reveal the promises that the centrosome holds for future cancer therapy.

An ancestral non-proteolytic role for presenilin proteins in multicellular development of the social amoeba Dictyostelium discoideum

Mutations in either of two presenilin genes can cause familial Alzheimer's disease. Presenilins have both proteolysis-dependent functions, as components of the γ-secretase complex, and proteolysis-independent functions in signalling. In this study, we investigate a conserved function of human presenilins in the development of the simple model organism Dictyostelium discoideum. We show that the block in Dictyostelium development caused by the ablation of both Dictyostelium presenilins is rescued by the expression of human presenilin 1, restoring the terminal differentiation of multiple cell types. This developmental role is independent of proteolytic activity, because the mutation of both catalytic aspartates does not affect presenilin ability to rescue development, and the ablation of nicastrin, a γ-secretase component that is crucial for proteolytic activity, does not block development. The role of presenilins during Dictyostelium development is therefore independent of their proteolytic activity. However, presenilin loss in Dictyostelium results in elevated cyclic AMP (cAMP) levels and enhanced stimulation-induced calcium release, suggesting that presenilins regulate these intracellular signalling pathways. Our data suggest that presenilin proteins perform an ancient non-proteolytic role in regulating intracellular signalling and development, and that Dictyostelium is a useful model for analysing human presenilin function.

Alzheimer amyloid beta inhibition of Eg5/kinesin 5 reduces neurotrophin and/or transmitter receptor function

The mechanism by which amyloid beta (Aβ) causes neuronal dysfunction and/or death in Alzheimer's disease (AD) is unclear. Previously, we showed that Aβ inhibits several microtubule-dependent kinesin motors essential for mitosis and also present in mature neurons. Here, we show that inhibition of kinesin 5 (Eg5) by Aβ blocks neuronal function by reducing transport of neurotrophin and neurotransmitter receptors to the cell surface. Specifically, cell-surface NGF/NTR(p75) and NMDA receptors decline in cells treated with Aβ or the kinesin 5 inhibitor monastrol, or expressing APP. Aβ and monastrol also inhibit NGF-dependent neurite outgrowth from PC12 cells and glutamate-dependent Ca++ entry into primary neurons. Like Aβ, monastrol inhibits long-term potentiation, a cellular model of NMDA-dependent learning and memory, and kinesin 5 activity is absent from APP/PS transgenic mice brain or neurons treated with Aβ. These data imply that cognitive deficits in AD may derive in part from inhibition of neuronal Eg5 by Aβ, resulting in impaired neuronal function and/or survival through receptor mislocalization. Preventing inhibition of Eg5 or other motors by Aβ may represent a novel approach to AD therapy.

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.

Mitotic spindle defects and chromosome mis-segregation induced by LDL/cholesterol-implications for Niemann-Pick C1, Alzheimer's disease, and atherosclerosis

Elevated low-density lipoprotein (LDL)-cholesterol is a risk factor for both Alzheimer's disease (AD) and Atherosclerosis (CVD), suggesting a common lipid-sensitive step in their pathogenesis. Previous results show that AD and CVD also share a cell cycle defect: chromosome instability and up to 30% aneuploidy-in neurons and other cells in AD and in smooth muscle cells in atherosclerotic plaques in CVD. Indeed, specific degeneration of aneuploid neurons accounts for 90% of neuronal loss in AD brain, indicating that aneuploidy underlies AD neurodegeneration. Cell/mouse models of AD develop similar aneuploidy through amyloid-beta (Aß) inhibition of specific microtubule motors and consequent disruption of mitotic spindles. Here we tested the hypothesis that, like upregulated Aß, elevated LDL/cholesterol and altered intracellular cholesterol homeostasis also causes chromosomal instability. Specifically we found that: 1) high dietary cholesterol induces aneuploidy in mice, satisfying the hypothesis' first prediction, 2) Niemann-Pick C1 patients accumulate aneuploid fibroblasts, neurons, and glia, demonstrating a similar aneugenic effect of intracellular cholesterol accumulation in humans 3) oxidized LDL, LDL, and cholesterol, but not high-density lipoprotein (HDL), induce chromosome mis-segregation and aneuploidy in cultured cells, including neuronal precursors, indicating that LDL/cholesterol directly affects the cell cycle, 4) LDL-induced aneuploidy requires the LDL receptor, but not Aß, showing that LDL works differently than Aß, with the same end result, 5) cholesterol treatment disrupts the structure of the mitotic spindle, providing a cell biological mechanism for its aneugenic activity, and 6) ethanol or calcium chelation attenuates lipoprotein-induced chromosome mis-segregation, providing molecular insights into cholesterol's aneugenic mechanism, specifically through its rigidifying effect on the cell membrane, and potentially explaining why ethanol consumption reduces the risk of developing atherosclerosis or AD. These results suggest a novel, cell cycle mechanism by which aberrant cholesterol homeostasis promotes neurodegeneration and atherosclerosis by disrupting chromosome segregation and potentially other aspects of microtubule physiology.

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.

Phlorotannin-rich Ecklonia cava reduces the production of beta-amyloid by modulating alpha- and gamma-secretase expression and activity

Beta-amyloid (Aβ) is a major pathogenic peptide in Alzheimer's disease (AD) and is generated by the processing of amyloid precursor protein (APP). We have previously reported that the brown algae Ecklonia cava, which has anti-oxidant and anti-inflammatory functions, decreased Aβ production and further aggregation in HEK293 cells expressing the APP Swedish mutation. Here, we show the reduction mechanism of Aβ production using the butanol extract of Ecklonia cava through the examination of expression and activity of alpha-, beta-, and gamma-secretase. Treatment with the extract resulted in the activation of alpha-secretase with a contrasting decrease in its mRNA and protein expression. This activation was consistent with the translocation of the extract into the plasma membrane of the secretase. Gamma-secretase activity was lowered by E. cava, and this effect may be due to the decreased expression of PSEN1 mRNA and protein. In addition, the basal nuclear location of PSEN1, which may affect chromosome missegregation in neurodegenerative disease, was reduced by the extract, despite the significance of this finding remains unclear. Taken together, these results led us to conclude that E. cava regulated the expression and activity of gamma-secretase and alpha-secretase, leading to a reduction in Aβ production by the stable cells. Our data indicate that E. cava is a novel natural-product candidate for AD treatment, although further in vivo studies are needed.

Presenilin-1 regulates the constitutive turnover of the fibronectin matrix in endothelial cells

BACKGROUND

Presenilin-1 (PS1) is a transmembrane protein first discovered because of its association with familial Alzheimer's disease. Mice with null mutations in PS1 die shortly after birth exhibiting multiple CNS and non-CNS abnormalities. One of the most prominent features in the brains of PS1-/- embryos is a vascular dysgenesis that leads to multiple intracerebral hemorrhages. The molecular and cellular basis for the vascular dysgenesis in PS1-/- mice remains incompletely understood. Because the extracellular matrix plays key roles in vascular development we hypothesized that an abnormal extracellular matrix might be present in endothelial cells lacking PS1 and examined whether the lack of PS1 affects expression of fibronectin a component of the extracellular matrix known to be essential for vascular development.

RESULTS

We report that primary as well as continuously passaged PS1-/- endothelial cells contain more fibronectin than wild type cells and that the excess fibronectin in PS1-/- endothelial cells is incorporated into a fibrillar network. Supporting the in vivo relevance of this observation fibronectin expression was increased in microvascular preparations isolated from E14.5 to E18.5 PS1-/- embryonic brain. Reintroduction of PS1 into PS1-/- endothelial cells led to a progressive decrease in fibronectin levels showing that the increased fibronectin in PS1-/- endothelial cells was due to loss of PS1. Increases in fibronectin protein in PS1-/- endothelial cells could not be explained by increased levels of fibronectin RNA nor based on metabolic labeling studies by increased protein synthesis. Rather we show based on the rate of turnover of exogenously added biotinylated fibronectin that increased fibronectin in PS1-/- endothelial cells results from a slower degradation of the fibronectin fibrillar matrix on the cell surface.

CONCLUSIONS

These studies show that PS1 regulates the constitutive turnover of the fibronectin matrix in endothelial cells. These studies provide molecular clues that may help to explain the origin of the vascular dysgenesis that develops in PS1-/- embryonic mice.

RNAi-mediated inhibition of presenilin 2 inhibits glioma cell growth and invasion and is involved in the regulation of Nrg1/ErbB signaling

Gliomas are the leading cause of death among adults with primary brain malignancies. Treatment for malignant gliomas remains limited, and targeted therapies have been incompletely explored. In this study, we found that the protein expression of presenilin 2 (PS2) was significantly increased in glioma tissues, at least partially because of promoter demethylation. We further evaluated the biological functions of PS2 in U251 glioma cell proliferation, migration, invasion, and tumor growth in vivo by specific inhibition of PS2 using short hairpin RNA (shRNA). We found that PS2 depletion inhibited glioma cell growth as the result of inhibited proliferation and induced apoptosis. PS2 depletion also decreased the invasive capability of glioma cells and anchorage-independent colony formation in soft agar. Moreover, suppression of PS2 expression significantly impaired the growth of glioma xenografts in nude mice. Finally, the decrease in glioma cell growth caused by PS2 depletion seems to involve Nrg1/ErbB signaling. In summary, our data highlight the use of RNA interference (RNAi) as a tool to better understand the molecular basis of PS2 in glioma progression and to uncover new targets for the treatment of glioma.

Cell cycle activation and aneuploid neurons in Alzheimer's disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder, characterized by synaptic degeneration associated with fibrillar aggregates of the amyloid-ß peptide and the microtubule-associated protein tau. The progression of neurofibrillary degeneration throughout the brain during AD follows a predictive pattern which provides the basis for the neuropathological staging of the disease. This pattern of selective neuronal vulnerability against neurofibrillary degeneration matches the regional degree of neuronal plasticity and inversely recapitulates ontogenetic and phylogenetic brain development which links neurodegenerative cell death to neuroplasticity and brain development. Here, we summarize recent evidence for a loss of neuronal differentiation control as a critical pathogenetic event in AD, associated with a reactivation of the cell cycle and a partial or full replication of DNA giving rise to neurons with a content of DNA above the diploid level. Neurons with an aneuploid set of chromosomes are also present at a low frequency in the normal brain where they appear to be well tolerated. In AD, however, where the number of aneuploid neurons is highly increased, a rather selective cell death of neurons with this chromosomal aberrancy occurs. This finding add aneuploidy to the list of critical molecular events that are shared between neurodegeneration and oncogenesis. It defines a molecular signature for neuronal vulnerability and directs our attention to a failure of neuronal differentiation control as a critical pathogenetic event and potential therapeutic target in AD.

Neurodegeneration in Alzheimer disease: role of amyloid precursor protein and presenilin 1 intracellular signaling

Alzheimer disease (AD) is a heterogeneous neurodegenerative disorder characterized by (1) progressive loss of synapses and neurons, (2) intracellular neurofibrillary tangles, composed of hyperphosphorylated Tau protein, and (3) amyloid plaques. Genetically, AD is linked to mutations in few proteins amyloid precursor protein (APP) and presenilin 1 and 2 (PS1 and PS2). The molecular mechanisms underlying neurodegeneration in AD as well as the physiological function of APP are not yet known. A recent theory has proposed that APP and PS1 modulate intracellular signals to induce cell-cycle abnormalities responsible for neuronal death and possibly amyloid deposition. This hypothesis is supported by the presence of a complex network of proteins, clearly involved in the regulation of signal transduction mechanisms that interact with both APP and PS1. In this review we discuss the significance of novel finding related to cell-signaling events modulated by APP and PS1 in the development of neurodegeneration.

The DNA replication stress hypothesis of Alzheimer's disease

A well-recognized theory of Alzheimer's disease (AD) pathogenesis suggests ectopic cell cycle events to mediate neurodegeneration. Vulnerable neurons of the AD brain exhibit biomarkers of cell cycle progression and DNA replication suggesting a reentry into the cell cycle. Chromosome reduplication without proper cell cycle completion and mitotic division probably causes neuronal cell dysfunction and death. However, this theory seems to require some inputs in accordance with the generally recognized amyloid cascade theory as well as to explain causes and consequences of genomic instability (aneuploidy) in the AD brain. We propose that unscheduled and incomplete DNA replication (replication stress) destabilizes (epi)genomic landscape in the brain and leads to DNA replication "catastrophe" causing cell death during the S phase (replicative cell death). DNA replication stress can be a key element of the pathogenetic cascade explaining the interplay between ectopic cell cycle events and genetic instabilities in the AD brain. Abnormal cell cycle reentry and somatic genome variations can be used for updating the cell cycle theory introducing replication stress as a missing link between cell genetics and neurobiology of AD.

Addressing the complex etiology of Alzheimer’s disease: the role of p25/Cdk5

Alzheimer’s disease (AD) is an age-related neurodegenerative disorder characterized by the progressive loss of forebrain neurons and the deterioration of learning and memory. Therapies for AD have primarily focused upon either the inhibition of amyloid synthesis or its deposition in the brain, but clinical testing to date has not yet found an effective amelioration of cognitive symptoms. Synaptic loss closely correlates with the degree of dementia in AD patients. However, mouse AD models that target the amyloid-β pathway generally do not exhibit a profound loss of synapses, despite extensive synaptic dysfunction. The increased generation of p25, an activator of the cyclin-dependent kinase 5 (Cdk5) has been found in both human patients and mouse models of neurodegeneration. The current work reviews our knowledge, to date, on the role of p25/Cdk5 in Alzheimer’s disease, with a focus upon the interaction of amyloid-β and p25/Cdk5 in synaptic dysfunction and neuronal loss.

Fish-on-a-chip: a sensitive detection microfluidic system for Alzheimer's disease

Microfluidics has become an important tool in diagnosing many diseases, including neurological and genetic disorders. Alzheimer's disease (AD) is a neurodegenerative disease that irreversibly and progressively destroys memory, language ability, and thinking skills. Commonly, detection of AD is expensive and complex. Fluorescence in situ hybridization (FISH)-based microfluidic chip platform is capable of diagnosing AD at an early stage and they are effective tools for the diagnosis with low cost, high speed, and high sensitivity. In this review, we tried to provide basic information on the diagnosis of AD via FISH-based microfluidics. Different sample preparations using a microfluidic chip for diagnosis of AD are highlighted. Moreover, rapid innovations in nanotechnology for diagnosis are explained. This review will provide information on dynamic quantification methods for the diagnosis and treatment of AD. The knowledge provided in this review will help develop new integration diagnostic techniques based on FISH and microfluidics.

Alzheimer Aβ disrupts the mitotic spindle and directly inhibits mitotic microtubule motors

Chromosome mis-segregation and aneuploidy are greatly induced in Alzheimer's disease and models thereof by mutant forms of the APP and PS proteins and by their product, the Ab peptide. Here we employ human somatic cells and Xenopus egg extracts to show that Aβ impairs the assembly and maintenance of the mitotic spindle. Mechanistically, these defects result from Aβ's inhibition of mitotic motor kinesins, including Eg5, KIF4A and MCAK. In vitro studies show that oligomeric Aβ directly inhibits recombinant MCAK by a noncompetitive mechanism. In contrast, inhibition of Eg5 and KIF4A is competitive with respect to both ATP and microtubules, indicating that Aβ interferes with their interactions with the microtubules of the mitotic spindle. Consistently, increased levels of polymerized microtubules or of the microtubule stabilizing protein Tau significantly decrease the inhibitory effect of Aβ on Eg5 and KIF4A. Together, these results indicate that by disrupting the interaction between specific kinesins and microtubules and by exerting a direct inhibitory effect on the motor activity, excess Ab deregulates the mechanical forces that govern the spindle and thereby leads to the generation of defective mitotic structures. The resulting defect in neurogenesis can account for the over 30% aneuploid/hyperploid, degeneration-prone neurons observed in Alzheimer disease brain. The finding of mitotic motors including Eg5 in mature post-mitotic neurons implies that their inhibition by Ab may also disrupt neuronal function and plasticity.

Presenilin-1 processing of ErbB4 in fetal type II cells is necessary for control of fetal lung maturation

Maturation of pulmonary fetal type II cells to initiate adequate surfactant production is crucial for postnatal respiratory function. Little is known about specific mechanisms of signal transduction controlling type II cell maturation. The ErbB4 receptor and its ligand neuregulin (NRG) are critical for lung development. ErbB4 is cleaved at the cell membrane by the γ-secretase enzyme complex whose active component is either presenilin-1 (PSEN-1) or presenilin-2. ErbB4 cleavage releases the 80kDa intracellular domain (4ICD), which associates with chaperone proteins such as YAP (Yes-associated protein) and translocates to the nucleus to regulate gene expression. We hypothesized that PSEN-1 and YAP have a development-specific expression in fetal type II cells and are important for ErbB4 signaling in surfactant production. In primary fetal mouse E16, E17, and E18 type II cells, PSEN-1 and YAP expression increased at E17 and E18 over E16. Subcellular fractionation showed a strong cytosolic and a weaker membrane location of both PSEN-1 and YAP. This was enhanced by NRG stimulation. Co-immunoprecipitations showed ErbB4 associated separately with PSEN-1 and with YAP. Their association, phosphorylation, and co-localization were induced by NRG. Confocal immunofluorescence and nuclear fractionation confirmed these associations in a time-dependent manner after NRG stimulation. Primary ErbB4-deleted E17 type II cells were transfected with a mutant ErbB4 lacking the γ-secretase binding site. When compared to transfection with wild-type ErbB4, the stimulatory effect of NRG on surfactant protein mRNA expression was lost. We conclude that PSEN-1 and YAP have crucial roles in ErbB4 signal transduction during type II cell maturation.

Zebrafish as a tool in Alzheimer's disease research

Alzheimer's disease is the most prevalent form of neurodegenerative disease. Despite many years of intensive research our understanding of the molecular events leading to this pathology is far from complete. No effective treatments have been defined and questions surround the validity and utility of existing animal models. The zebrafish (and, in particular, its embryos) is a malleable and accessible model possessing a vertebrate neural structure and genome. Zebrafish genes orthologous to those mutated in human familial Alzheimer's disease have been defined. Work in zebrafish has permitted discovery of unique characteristics of these genes that would have been difficult to observe with other models. In this brief review we give an overview of Alzheimer's disease and transgenic animal models before examining the current contribution of zebrafish to this research area. This article is part of a Special Issue entitled Zebrafish Models of Neurological Diseases.

Pathological implications of cell cycle re-entry in Alzheimer disease

The complex neurodegeneration underlying Alzheimer disease (AD), although incompletely understood, is characterised by an aberrant re-entry into the cell cycle in neurons. Pathological evidence, in the form of cell cycle markers and regulatory proteins, suggests that cell cycle re-entry is an early event in AD, which precedes the formation of amyloid-beta plaques and neurofibrillary tangles (NFTs). Although the exact mechanisms that induce and mediate these cell cycle events in AD are not clear, significant advances have been made in further understanding the pathological role of cell cycle re-entry in AD. Importantly, recent studies indicate that cell cycle re-entry is not a consequence, but rather a cause, of neurodegeneration, suggesting that targeting of cell cycle re-entry may provide an opportunity for therapeutic intervention. Moreover, multiple inducers of cell cycle re-entry and their interactions in AD have been proposed. Here, we review the most recent advances in understanding the pathological implications of cell cycle re-entry in AD.

LDLR expression and localization are altered in mouse and human cell culture models of Alzheimer's disease

Background

Alzheimer's disease (AD) is a chronic neurodegenerative disorder and the most common form of dementia. The major molecular risk factor for late-onset AD is expression of the ε-4 allele of apolipoprotein E (apoE), the major cholesterol transporter in the brain. The low-density lipoprotein receptor (LDLR) has the highest affinity for apoE and plays an important role in brain cholesterol metabolism.

Methodology/Principal Findings

Using RT-PCR and western blotting techniques we found that over-expression of APP caused increases in both LDLR mRNA and protein levels in APP transfected H4 neuroglioma cells compared to H4 controls. Furthermore, immunohistochemical experiments showed aberrant localization of LDLR in H4-APP neuroglioma cells, Aβ-treated primary neurons, and in the PSAPP transgenic mouse model of AD. Finally, immunofluorescent staining of LDLR and of γ- and α-tubulin showed a change in LDLR localization preferentially away from the plasma membrane that was paralleled by and likely the result of a disruption of the microtubule-organizing center and associated microtubule network.

Conclusions/Significance

These data suggest that increased APP expression and Aβ exposure alters microtubule function, leading to reduced transport of LDLR to the plasma membrane. Consequent deleterious effects on apoE uptake and function will have implications for AD pathogenesis and/or progression.

Alzheimer Abeta peptide induces chromosome mis-segregation and aneuploidy, including trisomy 21: requirement for tau and APP

Chromosome aneuploidy, especially trisomy 21, arises in both familial and sporadic Alzheimer's disease. Expression of FAD genes or exposure to Aβ peptide induces aneuploidy in tg-mice and cultured cells. The requirement for GSK-3β, calpain, and Tau in Aβ-induced chromosome mis-segregation points to MT dysfunction as contributing to AD pathogenesis.

Both sporadic and familial Alzheimer's disease (AD) patients exhibit increased chromosome aneuploidy, particularly trisomy 21, in neurons and other cells. Significantly, trisomy 21/Down syndrome patients develop early onset AD pathology. We investigated the mechanism underlying mosaic chromosome aneuploidy in AD and report that FAD mutations in the Alzheimer Amyloid Precursor Protein gene, APP, induce chromosome mis-segregation and aneuploidy in transgenic mice and in transfected cells. Furthermore, adding synthetic Aβ peptide, the pathogenic product of APP, to cultured cells causes rapid and robust chromosome mis-segregation leading to aneuploid, including trisomy 21, daughters, which is prevented by LiCl addition or Ca²⁺ chelation and is replicated in tau KO cells, implicating GSK-3β, calpain, and Tau-dependent microtubule transport in the aneugenic activity of Aβ. Furthermore, APP KO cells are resistant to the aneugenic activity of Aβ, as they have been shown previously to be resistant to Aβ-induced tau phosphorylation and cell toxicity. These results indicate that Aβ-induced microtubule dysfunction leads to aneuploid neurons and may thereby contribute to the pathogenesis of AD.

Presenilins are enriched in endoplasmic reticulum membranes associated with mitochondria

Presenilin-1 (PS1) and -2 (PS2), which when mutated cause familial Alzheimer disease, have been localized to numerous compartments of the cell, including the endoplasmic reticulum, Golgi, nuclear envelope, endosomes, lysosomes, the plasma membrane, and mitochondria. Using three complementary approaches, subcellular fractionation, gamma-secretase activity assays, and immunocytochemistry, we show that presenilins are highly enriched in a subcompartment of the endoplasmic reticulum that is associated with mitochondria and that forms a physical bridge between the two organelles, called endoplasmic reticulum-mitochondria-associated membranes. A localization of PS1 and PS2 in mitochondria-associated membranes may help reconcile the disparate hypotheses regarding the pathogenesis of Alzheimer disease and may explain many seemingly unrelated features of this devastating neurodegenerative disorder.

Independent and cooperative action of Psen2 with Psen1 in zebrafish embryos

Presenilin1 (PSEN1) and presenilin2 (PSEN2) are involved in the processing of type-1 transmembrane proteins including the amyloid precursor protein (APP), Notch and several others. PSEN1 has been shown to be crucial for proteolytic cleavage of Notch in developing animal embryos. Mouse embryos lacking Psen1 function show disturbed neurogenesis and somite formation, resembling Notch pathway mutants. However, loss of Psen2 activity reveals only a minor phenotype. Zebrafish embryos are a valuable tool for analysis of the molecular genetic control of cell differentiation since endogenous gene expression can be modulated in subtle and complex ways to give a phenotypic readout. Using injection of morpholino antisense oligonucleotides to inhibit protein translation in zebrafish embryos, we show that reduced Psen2 activity decreases the number of melanocytes in the trunk but not in the cranial area at 2 days post fertilisation (dpf). Reduced Psen2 activity apparently reduces Notch signalling resulting in perturbed spinal neurogenin1 (neurog1) expression, neurogenesis and trunk and tail neural crest development. Similar effects are seen for reduced Psen1 activity. These results suggest that Psen2 plays a more prominent role in Notch signalling and embryo development in zebrafish than in mammals. Intriguingly, decreased Psen2 activity increases the number of Dorsal Longitudinal Ascending (DoLA) interneurons in the spinal cord while decreased Psen1 activity has no effect. However, the effect on DoLAs of reduced Psen2 can be ameliorated by Psen1 loss. The effects of changes in Psen2 activity on DoLA interneurons and other cells in zebrafish embryos provide bioassays for more detailed dissection of Psen2 function.

Cell cycle re-entry mediated neurodegeneration and its treatment role in the pathogenesis of Alzheimer's disease

As one of the earliest pathologic changes, the aberrant re-expression of many cell cycle-related proteins and inappropriate cell cycle control in specific vulnerable neuronal populations in Alzheimer's disease (AD) is emerging as an important component in the pathogenesis leading to AD and other neurodegenerative diseases. These events are clearly representative of a true cell cycle, rather than epiphenomena of other processes since, in AD and other neurodegenerative diseases, there is a true mitotic alteration that leads to DNA replication. While the exact role of cell cycle re-entry is unclear, recent studies using cell culture and animal models strongly support the notion that the dysregulation of cell cycle in neurons leads to the development of AD-related pathology such as hyperphosphorylation of tau and amyloid-beta deposition and ultimately causes neuronal cell death. Importantly, cell cycle re-entry is also evident in mutant amyloid-beta precursor protein and tau transgenic mice and, as in human disease, occurs prior to the development of the pathological hallmarks, neurofibrillary tangles and amyloid-beta plaques. Therefore, the study of aberrant cell cycle regulation in model systems, both cellular and animal, may provide extremely important insights into the pathogenesis of AD and also serve as a means to test novel therapeutic approaches.

Aneuploidy in the normal, Alzheimer's disease and ataxia-telangiectasia brain: differential expression and pathological meaning

Recently it has been suggested that the human brain contains aneuploid cells; however the nature and magnitude of neural aneuploidy in health and disease remain obscure. Here, we have monitored aneuploidy in the cerebral cortex of the normal, Alzheimer's disease (AD) and ataxia telangiectasia (AT) brain by molecular cytogenetic approaches scoring more than 480,000 neural cells. Using arbitrarily selected set of DNA probes for chromosomes 1, 7, 11, 13, 14, 17, 18, 21, X and Y we have determined the mean rate of stochastic aneuploidy per chromosome as 0.5% in the normal human brain (95%CI 0.2-0.7%; SD 0.2%). The overall proportion of aneuploid cells in the normal brain has been estimated at approximately 10%. In the AT brain, we observed a 2-to-5 fold increase of stochastic aneuploidy randomly affecting different chromosomes (mean 2.1%; 95%CI - 1.5-2.6%; SD 0.8%). The overall proportion of aneuploid cells in the brain of AT individuals was estimated at approximately 20-50%. Compared with sex- and age-matched controls, the level of stochastic aneuploidy in the AD brain was not significantly increased. However, a dramatic 10-fold increase of chromosome 21-specific aneuploidy (both hypoploidy and hyperploidy) was detected in the AD cerebral cortex (6-15% versus 0.8-1.8% in control). We conclude that somatic mosaic aneuploidy differentially contributes to intercellular genomic variation in the normal, AD and AT brain. Neural aneuploidy leading to altered cellular physiology may significantly contribute to the pathogenesis of neurodegenerative diseases. These data indicate neural aneuploidy to be a newly identified feature of neurodegenerative diseases, similar to other devastative disorders hallmarked by aneuploidy such as chromosome syndromes and cancer.

Alzheimer's disease and HIV associated dementia related genes: I. location and function

Alzheimer's disease (AD), the most common cause of dementia, has few clinical similarities to HIV-1-associated dementia (HAD). However, genes were identified related among these dementias. Discovering correlations between gene function, expression, and structure in the human genome continues to aid in understanding the similarities between pathogenesis of these two dementing disorders. The current work attempts to identify relationships between these dementias in spite of their clinical differences, based on genomic structure, function, and expression. In this comparative study, the NCBI Entrez Genome Database is used to detect these relationships. This approach serves as a model for future diagnosis and treatment in the clinical arena as well as suggesting parallel pathways of disease mechanisms. Identifying a correlation among expression, structure, and function of genes involved in pathogenesis of these dementing disorders, may assist to understand better their interaction with each other and the human genome.

Centrosomal RNA correlates with intron-poor nuclear genes in Spisula oocytes

The evolutionary origin of centriole/kinetosomes, centrosomes, and other microtubule organizing centers (MTOCs), whether by direct filiation or symbiogenesis, has been controversial for >50 years. Centrioles, like mitochondria and chloroplasts, duplicate independently of the nucleus and constitute a heritable system independent of chromosomal DNA. Nucleic acids endogenous to the MTOC would support evolutionary origin by symbiogenesis. To date, most reports of centrosome-associated nucleic acids have used generalized reagents such as RNases and nucleic acid dyes. Here, from a library of RNAs extracted from isolated surf clam (Spisula solidissima) centrosomes, we describe a group of centrosome-associated transcripts representing a structurally unique intron-poor collection of nuclear genes skewed toward nucleic acid metabolism. Thus, we resolve the debate over the existence of centrosome-associated RNA (cnRNA). A subset of cnRNAs contain functional domains that are highly conserved across distant taxa, such as nucleotide polymerase motifs. In situ localization of cnRNA65, a molecule with an RNA polymerase domain, showed it is present in the intact oocyte nucleus (germinal vesicle). Its expression, therefore, precedes the appearance of gamma-tubulin-containing centrosomes. At this stage, the in situ signal resembles the nucleolinus, a poorly understood organelle proposed to play a role in spindle formation. After oocyte activation and germinal vesicle breakdown, cnRNA65 persists as a cytoplasmic patch within which gamma-tubulin-stained centrosomes can be seen. These observations provoke the question of whether cnRNAs and the nucleolinus serve as cytological progenitors of the centrosome and may support a symbiogenetic model for its evolution.

Alzheimer's presenilin 1 causes chromosome missegregation and aneuploidy

Mutations in the presenilin 1 gene cause most early onset familial Alzheimer's disease (FAD). Here, we report that a defect in the cell cycle - improper chromosome segregation - can be caused by abnormal presenilin function and therefore may contribute to AD pathogenesis. Specifically we find that either over-expression or FAD mutation in presenilin 1 (M146L and M146V) leads to chromosome missegregation and aneuploidy in vivo and in vitro: (1) Up to 20% of lymphocytes and neurons of FAD-PS-1 transgenic and knocking mice are aneuploid by metaphase chromosome analysis and in situ hybridization. (2) Transiently transfected human cells over-expressing normal or mutant PS-1 develop similar aneuploidy within 48 h, including trisomy 21. (3) Mitotic spindles in the PS-1 transfected cells contain abnormal microtubule arrays and lagging chromosomes. Several mechanisms by which chromosome missegregation induced by presenilin may contribute to Alzheimer's disease are discussed.

The mitochondrial serine protease HtrA2/Omi: an overview

The HtrA family refers to a group of related oligomeric serine proteases that combine a trypsin-like protease domain with at least one PDZ interaction domain. Mammals encode four HtrA proteases, named HtrA1-4. The protease activity of the HtrA member HtrA2/Omi is required for mitochondrial homeostasis in mice and humans and inactivating mutations associated with neurodegenerative disorders such as Parkinson's disease. Moreover, HtrA2/Omi is released in the cytosol, where it contributes to apoptosis through both caspase-dependent and -independent pathways. Here, we review the current knowledge of HtrA2/Omi biology and discuss the signaling pathways that underlie its mitochondrial and apoptotic functions from an evolutionary perspective.

Glucose and endoplasmic reticulum calcium channels regulate HIF-1beta via presenilin in pancreatic beta-cells

Pancreatic beta-cell death is a critical event in type 1 diabetes, type 2 diabetes, and clinical islet transplantation. We have previously shown that prolonged block of ryanodine receptor (RyR)-gated release from intracellular Ca(2+) stores activates calpain-10-dependent apoptosis in beta-cells. In the present study, we further characterized intracellular Ca(2+) channel expression and function in human islets and the MIN6 beta-cell line. All three RyR isoforms were identified in human islets and MIN6 cells, and these endoplasmic reticulum channels were observed in close proximity to mitochondria. Blocking RyR channels, but not sarco/endoplasmic reticulum ATPase (SERCA) pumps, reduced the ATP/ADP ratio. Blocking Ca(2+) flux through RyR or inositol trisphosphate receptor channels, but not SERCA pumps, increased the expression of hypoxia-inducible factor (HIF-1beta). Moreover, inhibition of RyR or inositol trisphosphate receptor channels, but not SERCA pumps, increased the expression of presenilin-1. Both HIF-1beta and presenilin-1 expression were also induced by low glucose. Overexpression of presenilin-1 increased HIF-1beta, suggesting that HIF is downstream of presenilin. Our results provide the first evidence of a presenilin-HIF signaling network in beta-cells. We demonstrate that this pathway is controlled by Ca(2+) flux through intracellular channels, likely via changes in mitochondrial metabolism and ATP. These findings provide a mechanistic understanding of the signaling pathways activated when intracellular Ca(2+) homeostasis and metabolic activity are suppressed in diabetes and islet transplantation.

Down’s syndrome and Alzheimer’s disease: two sides of the same coin

All Down’s syndrome individuals develop Alzheimer’s disease (AD) neuropathology by the age of 40 years. To unite the two diseases under one hypothesis, we have suggested that classical AD, both of the genetic and late-onset sporadic forms, might be promoted by small numbers of trisomy 21 cells developing during the life of the affected individual. Recent evidence from several laboratories will be presented, which strongly supports the trisomy 21 hypothesis that defects in mitosis, and particularly in chromosome segregation, may be a part of the AD process. Specifically, genetic mutations that cause familial AD disrupt the cell cycle and lead to chromosome aneuploidy, including trisomy 21, in transgenic mice and transfected cells; cells from both familial and sporadic AD patients exhibit chromosome aneuploidy, including trisomy 21. The possibility that many cases of AD are mosaic for trisomy 21 suggests novel approaches to diagnosis and therapy.

Amyloid precursor protein and presenilin involvement in cell signaling

To date the most relevant role for the amyloid precursor protein (APP) and for the presenilins (PSs) on Alzheimer's disease (AD) genesis is linked to the 'amyloid hypothesis', which considers an aberrant formation of amyloid-beta peptides the cause of neurodegeneration. In this view, APP is merely a substrate, cleaved by the gamma-secretase complex to form toxic amyloid peptides, PSs are key players in gamma-secretase complex, and corollary or secondary events are Tau-linked pathology and gliosis. A second theory, complementary to the amyloid hypothesis, proposes that APP and PSs may modulate a yet unclear cell signal, the disruption of which may induce cell-cycle abnormalities, neuronal death, eventually amyloid formation and finally dementia. This hypothesis is supported by the presence of a complex network of proteins, with a clear relevance for signal transduction mechanisms, which interact with APP or PSs. In this scenario, the C-terminal domain of APP has a pivotal role due to the presence of the 682YENPTY687 motif that represents the docking site for multiple interacting proteins involved in cell signaling. In this review we discuss the significance of novel findings related to cell signaling events modulated by APP and PSs for AD development.