Preferential occurrence of chromosome 21 malsegregation in peripheral blood lymphocytes of Alzheimer disease patients

Aneuploidy is Linked to Neurological Phenotypes Through Oxidative Stress

Aneuploidy, having an aberrant genome, is gaining increasing attention in neurodegenerative diseases. It gives rise to proteotoxic stress as well as a stereotypical oxidative shift which makes these cells sensitive to internal and environmental stresses. A growing body of research from numerous laboratories suggests that many neurodegenerative disorders, especially Alzheimer's disease and frontotemporal dementia, are characterised by neuronal aneuploidy and the ensuing apoptosis, which may contribute to neuronal loss. Using Drosophila as a model, we investigated the effect of induced aneuploidy in GABAergic neurons. We found an increased proportion of aneuploidy due to Mad2 depletion in the third-instar larval brain and increased cell death. Depletion of Mad2 in GABAergic neurons also gave a defective climbing and seizure phenotype. Feeding animals an antioxidant rescued the climbing and seizure phenotype. These findings suggest that increased aneuploidy leads to higher oxidative stress in GABAergic neurons which causes cell death, climbing defects, and seizure phenotype. Antioxidant feeding represents a potential therapy to reduce the aneuploidy-driven neurological phenotype.

Trisomy 21-associated increases in chromosomal instability are unmasked by comparing isogenic trisomic/disomic leukocytes from people with mosaic Down syndrome

Down syndrome, which results from a trisomic imbalance for chromosome 21, has been associated with 80+ phenotypic traits. However, the cellular changes that arise in somatic cells due to this aneuploid condition are not fully understood. The primary aim of this study was to determine if germline trisomy 21 is associated with an increase in spontaneous somatic cell chromosomal instability frequencies (SCINF). To achieve this aim, we quantified SCINF in people with mosaic Down syndrome using a cytokinesis-blocked micronucleus assay. By comparing values in their isogenic trisomic/disomic cells, we obtained a measure of differences in SCINF that are directly attributable to a trisomy 21 imbalance, since differential effects attributable to "background" genetic factors and environmental exposures could be eliminated. A cross-sectional assessment of 69 people with mosaic Down syndrome (ages 1 to 44; mean age of 12.84 years) showed a significantly higher frequency of micronuclei in their trisomic (0.37 ± 0.35 [mean ± standard deviation]) compared to disomic cells (0.18 ± 0.11)(P <0.0001). The daughter binucleates also showed significantly higher levels of abnormal patterns in the trisomic (1.68 ± 1.21) compared to disomic (0.35 ± 0.45) cells (P <0.0001). Moreover, a significant Age x Cell Type interaction was noted (P = 0.0113), indicating the relationship between age and SCINF differed between the trisomic and disomic cells. Similarly, a longitudinal assessment (mean time interval of 3.9 years; range of 2 to 6 years) of 18 participants showed a mean 1.63-fold increase in SCINF within individuals over time for their trisomic cells (P = 0.0186), compared to a 1.13-fold change in their disomic cells (P = 0.0464). In summary, these results showed a trisomy 21-associated, age-related increase in SCINF. They also underscore the strength of the isogenic mosaic Down syndrome model system for "unmasking" cellular changes arising from a trisomy 21 imbalance.

Micronucleus frequency in buccal mucosa cells of patients with neurodegenerative diseases

Neurodegenerative diseases show an increase in prevalence and incidence, with the most prominent example being Alzheimer’s disease. DNA damage has been suggested to play a role in the pathogenesis, but the exact mechanisms remain elusive. We enrolled 425 participants with and without neurodegenerative diseases and analyzed DNA damage in the form of micronuclei in buccal mucosa samples. In addition, other parameters such as binucleated cells, karyolytic cells, and karyorrhectic cells were quantified. No relevant differences in DNA damage and cytotoxicity markers were observed in patients compared to healthy participants. Furthermore, other parameters such as lifestyle factors and diseases were also investigated. Overall, this study could not identify a direct link between changes in buccal cells and neurogenerative diseases, but highlights the influence of lifestyle factors and diseases on the human buccal cytome.

Micronuclei as biomarkers of DNA damage, aneuploidy, inducers of chromosomal hypermutation and as sources of pro-inflammatory DNA in humans

Micronuclei (MNi) are among the most widely studied biomarkers of DNA damage and chromosomal instability in humans. They originate from chromosome fragments or intact chromosomes that are not included in daughter nuclei during mitosis. The main reasons for their formation are a lack of functional centromere in the chromosome fragments or whole chromosomes or defects in one or more of the proteins of the mitotic system that, consequently, fails to segregate chromosomes properly. Assays have been developed to measure MNi in peripheral blood lymphocytes, red blood cells as well as various types of epithelial cells such as buccal, nasal, urothelial and cervical cells. Some of the assays have been further developed into micronucleus (MN) cytome assays to include additional nuclear anomalies, cell death and nuclear division biomarkers. In addition, the use of molecular probes has been adopted widely for the purpose of understanding the mechanistic origin of MNi. MN assays in humans are used for the purpose of investigating the genotoxic effects of adverse environmental, life-style and occupational factors, genetic susceptibility to DNA damage, and for determining risk of accelerated aging and diseases affected by genomic instability such as developmental defects and cancer. The emerging new knowledge showing that chromosomes trapped in MNi can undergo a high rate of fragmentation and become massively re-arranged have highlighted the possibility that MN formation is not only a biomarker of induced DNA damage but also a mechanism that drives hypermutation. Furthermore, another line of recent research showed that DNA and chromatin leaking from disrupted MNi triggers the innate immune cGAS-STING mechanism that promotes inflammation which can cause a wide-range of age-related diseases if left unresolved. For these reasons, MN assays in humans have become an increasingly important biomarker of disease initiation and progression across all life-stages.

Determination of Lymphocyte Cytokinesis-Block Micronucleus Values in Apparently Healthy Children by means of Age and Sex

The cytokinesis-block micronucleus (MN) assay on blood lymphocytes is one of the most important tests implemented in cytogenetics for the measurement of genotoxicity. For the purpose of biological dosing, it is crucial to know the spontaneous frequency of MN and its normal values in general population, especially in children, which are used for the population databases. In this study, MN levels were investigated in cytokinesis-blocked lymphocytes of 150 apparently healthy children aged 1 to 15. Our aim was to assess the variability of MN values according to age and sex. The mean MN frequency among boys was 3.69 ± 1.747‰ and 4.12 ± 1.867‰ in girls where there was no significant difference in relation to age and sex. However, when we separated age groups as 0–2 years, 3–5 years, 6–10 years, and 11–15 years, one-way ANOVA test showed significant association. Significance was obvious in the 0–2 years age group with the 3–5 years age group and 6–10 years age group. When we grouped our study population as 0–2 years and 3–15 years, the mean MN frequency among the 0–2 years age group was 2.85 ± 1.599‰ and 4.07 ± 1.867‰ in the 3–15 years age group which was also statistically significant. This difference may be attributed to age-related increase of close contact with environmental hazardous agents. In conclusion, normal values of MN obtained in this study will add valuable information in regard to update the current childhood population data and will act as a reference for further genotoxicity studies.

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.

Micronuclei and Their Association with Infertility, Pregnancy Complications, Developmental Defects, Anaemias, Inflammation, Diabetes, Chronic Kidney Disease, Obesity, Cardiovascular Disease, Neurodegenerative Diseases and Cancer

Micronuclei (MN) are a strong cytogenetic indicator of a catastrophic change in the genetic structure and stability of a cell because they originate from either chromosome breaks or whole chromosomes that have been lost from the main nucleus during cell division. The resulting genetic abnormalities can to lead to cellular malfunction, altered gene expression and impaired regenerative capacity. Furthermore, MN are increased as a consequence of genetic defects in DNA repair, deficiency in micronutrients required for DNA replication and repair and exposure to genotoxic chemicals and ultraviolet or ionising radiation. For all of these reasons, the measurement of MN has become one of the best-established methods to measure DNA damage in humans at the cytogenetic level. This chapter is a narrative review of the current evidence for the association of increased MN frequency with developmental and degenerative diseases. In addition, important knowledge gaps are identified, and recommendations for future studies required to consolidate the evidence are provided. The great majority of published studies show a significant association of increased MN in lymphocytes and/or buccal cells with infertility, pregnancy complications, developmental defects, anaemias, inflammation, diabetes, cardiovascular disease, kidney disease, neurodegenerative diseases and cancer. However, the strongest evidence is from prospective studies showing that MN frequency in lymphocytes predicts cancer risk and cardiovascular disease mortality.

Somatic mosaicism of sex chromosomes in the blood and brain

In the blood, mosaic somatic aneuploidy (mSA) of all chromosomes has been found to be associated with adverse health outcomes, including hematological cancer. Sex chromosome mSA in the blood has been found to occur at a higher rate than autosomal mSA. Mosaic loss of the Y chromosome is the most common copy number alteration in males, and has been found to be associated with Alzheimer's disease (AD) in blood lymphocytes. mSA of the sex chromosomes has also been identified in the brain; however, little is known about its frequency across individuals. Using WGS data from 362 males and 719 females from the ROSMAP cohort, we quantified the relative rate of sex chromosome mSA in the dorsolateral prefrontal cortex (DLPFC), cerebellum and whole blood. To ascertain the functionality of observed sex chromosome mosaicism in the DLPFC, we examined its correlation with chromosome X and Y gene expression as well as neuropathological and clinical characteristics of AD and cognitive ageing. In males, we found that mSA of the Y chromosome occurs more frequently in blood than in the DLPFC or cerebellum. In the DLPFC, the presence of at least one APOE4 allele was associated with a reduction in read depth of the Y chromosome (p = 1.9e-02). In the female DLPFC, a reduction in chromosome X read depth was associated with reduced cognition at the last clinical visit and faster rate of cognitive decline (p = 7.8e-03; p = 1.9e-02). mSA of all sex chromosomes in the DLPFC were associated with aggregate measures of gene expression, implying functional impact. Our results provide insight into the relative rate of mSA between tissues and suggest that Y and female X chromosome read depth in the DLPFC is modestly associated with late AD risk factors and cognitive pathologies.

γH2AX is increased in peripheral blood lymphocytes of Alzheimer's disease patients in the South Australian Neurodegeneration, Nutrition and DNA Damage (SAND) study of aging

An early cellular response to DNA double-strand breaks is the phosphorylation of histone H2AX to form γH2AX. Although increased levels of γH2AX have been reported in neuronal nuclei of Alzheimer's disease (AD) patients, γH2AX responses in the lymphocytes of individuals with mild cognitive impairment (MCI) and AD remain unexplored. In this study, the endogenous γH2AX level was measured, using laser scanning cytometry (LSC) and visual scoring, in lymphocyte nuclei from MCI (n = 18), or AD (n = 20) patients and healthy controls (n = 40). Levels were significantly elevated in nuclei of the AD group compared to the MCI and control groups, and there was a concomitant increase, with a significant trend, from the control group through MCI to the AD group. A significant negative correlation was seen between γH2AX and the mini mental state examination (MMSE) score, when the analysis included all subjects. Receiver Operation Characteristic curves were carried out for different γH2AX parameters; visually scored percent cells containing overlapping γH2AX foci displayed the best area under the curve value of 0.9081 with 85% sensitivity and 92% specificity for the identification of AD patients versus control. Plasma homocysteine, creatinine, and chitinase-3-like protein 1 (CHI3L1) were positively correlated with lymphocyte γH2AX signals, while glomerular filtration rate (GFR) was negatively correlated. Finally, there was a diminished γH2AX response to X-rays in lymphocytes of the MCI and AD groups compared to the control group. Our results indicate that lymphocyte γH2AX levels are a potential marker for identifying individuals at increased risk of developing AD. Prospective studies with normal healthy individuals are needed to test whether there is indeed a link between γH2AX levels and AD risk.

Region- and Cell-specific Aneuploidy in Brain Aging and Neurodegeneration

Variations in genomic DNA content, or aneuploidy, are a well-recognized feature of normal human brain development. Whether changes in the levels of aneuploidy are a factor in Alzheimer's disease (AD) is less clear, as the data reported to date vary substantially in the levels of aneuploidy detected (0.7-11.5%), possibly due to methodological limitations, but also influenced by individual, regional and cellular heterogeneity as well as variations in cell subtypes. These issues have not been adequately addressed to date. While it is known that the DNA damage response increases with age, the limited human studies investigating aneuploidy in normal aging also show variable results, potentially due to susceptibility to age-related neurodegenerative processes. Neuronal aneuploidy has recently been reported in multiple brain regions in Lewy body disease, but similar genomic changes are not a feature of all synucleinopathies and aneuploidy does not appear to be related to alpha-synuclein aggregation. Rather, aneuploidy was associated with Alzheimer's pathology in the hippocampus and anterior cingulate cortex and neuronal degeneration in the substantia nigra. The association between Alzheimer's pathology and aneuploidy in regions with limited neurodegeneration is supported by a growing body of in vitro and in vivo data on aneuploidy and beta-amyloid and tau abnormalities. Large-scale studies using high-resolution techniques alongside other sensitive and specific methodologies are now required to assess the true extent of cell- and region-specific aneuploidy in aging and neurodegeneration, and to determine any associations with pathologies.

Genome instability in Alzheimer disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common form of dementia. Autosomal dominant, familial AD (fAD) is very rare and caused by mutations in amyloid precursor protein (APP), presenilin-1 (PSEN-1), and presenilin-2 (PSEN-2) genes. The pathogenesis of sporadic AD (sAD) is more complex and variants of several genes are associated with an increased lifetime risk of AD. Nuclear and mitochondrial DNA integrity is pivotal during neuronal development, maintenance and function. DNA damage and alterations in cellular DNA repair capacity have been implicated in the aging process and in age-associated neurodegenerative diseases, including AD. These findings are supported by research using animal models of AD and in DNA repair deficient animal models. In recent years, novel mechanisms linking DNA damage to neuronal dysfunction have been identified and have led to the development of noninvasive treatment strategies. Further investigations into the molecular mechanisms connecting DNA damage to AD pathology may help to develop novel treatment strategies for this debilitating disease. Here we provide an overview of the role of genome instability and DNA repair deficiency in AD pathology and discuss research strategies that include genome instability as a component.

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.

Beyond Trisomy 21: Phenotypic Variability in People with Down Syndrome Explained by Further Chromosome Mis-segregation and Mosaic Aneuploidy

Phenotypic variability is a fundamental feature of the human population and is particularly evident among people with Down syndrome and/or Alzheimer’s disease. Herein, we review current theories of the potential origins of this phenotypic variability and propose a novel mechanism based on our finding that the Alzheimer’s disease-associated Aβ peptide, encoded on chromosome 21, disrupts the mitotic spindle, induces abnormal chromosome segregation, and produces mosaic populations of aneuploid cells in all tissues of people with Alzheimer’s disease and in mouse and cell models thereof. Thus, individuals exposed to increased levels of the Aβ peptide should accumulate mosaic populations of aneuploid cells, with different chromosomes affected in different tissues and in different individuals. Specifically, people with Down syndrome, who express elevated levels of Aβ peptide throughout their lifetimes, would be predicted to accumulate additional types of aneuploidy, beyond trisomy 21 and including changes in their trisomy 21 status, in mosaic cell populations. Such mosaic aneuploidy would introduce a novel form of genetic variability that could potentially underlie much of the observed phenotypic variability among people with Down syndrome, and possibly also among people with Alzheimer’s disease. This mosaic aneuploidy theory of phenotypic variability in Down syndrome is supported by several observations, makes several testable predictions, and identifies a potential approach to reducing the frequency of some of the most debilitating features of Down syndrome, including Alzheimer’s disease.

DNA damage in neurodegenerative diseases

Following the observation of increased oxidative DNA damage in nuclear and mitochondrial DNA extracted from post-mortem brain regions of patients affected by neurodegenerative diseases, the last years of the previous century and the first decade of the present one have been largely dedicated to the search of markers of DNA damage in neuronal samples and peripheral tissues of patients in early, intermediate or late stages of neurodegeneration. Those studies allowed to demonstrate that oxidative DNA damage is one of the earliest detectable events in neurodegeneration, but also revealed cytogenetic damage in neurodegenerative conditions, such as for example a tendency towards chromosome 21 malsegregation in Alzheimer's disease. As it happens for many neurodegenerative risk factors the question of whether DNA damage is cause or consequence of the neurodegenerative process is still open, and probably both is true. The research interest in markers of oxidative stress was shifted, in recent years, towards the search of epigenetic biomarkers of neurodegenerative disorders, following the accumulating evidence of a substantial contribution of epigenetic mechanisms to learning, memory processes, behavioural disorders and neurodegeneration. Increasing evidence is however linking DNA damage and repair with epigenetic phenomena, thereby opening the way to a very attractive and timely research topic in neurodegenerative diseases. We will address those issues in the context of Alzheimer's disease, Parkinson's disease, and Amyotrophic Lateral Sclerosis, which represent three of the most common neurodegenerative pathologies in humans.

Biomarkers of Alzheimer's disease risk in peripheral tissues; focus on buccal cells

Alzheimer's disease (AD) is a progressive degenerative disorder of the brain and is the most common form of dementia. To-date no simple, inexpensive and minimally invasive procedure is available to confirm with certainty the early diagnosis of AD prior to the manifestations of symptoms characteristic of the disease. Therefore, if population screening of individuals is to be performed, more suitable, easily accessible tissues would need to be used for a diagnostic test that would identify those who exhibit cellular pathology indicative of mild cognitive impairment (MCI) and AD risk so that they can be prioritized for primary prevention. This need for minimally invasive tests could be achieved by targeting surrogate tissues, since it is now well recognized that AD is not only a disorder restricted to pathology and biomarkers within the brain. Human buccal cells for instance are accessible in a minimally invasive manner, and exhibit cytological and nuclear morphologies that may be indicative of accelerated ageing or neurodegenerative disorders such as AD. However, to our knowledge there is no review available in the literature covering the biology of buccal cells and their applications in AD biomarker research. Therefore, the aim of this review is to summarize some of the main findings of biomarkers reported for AD in peripheral tissues, with a further focus on the rationale for the use of the buccal mucosa (BM) for biomarkers of AD and the evidence to date of changes exhibited in buccal cells with AD.

Genome instability biomarkers and blood micronutrient risk profiles associated with mild cognitive impairment and Alzheimer's disease

Successful maintenance of metabolic systems relating to accurate DNA replication and repair is critical for optimal lifelong human health. Should this homeostatic balance become impaired, genomic instability events can arise, compromising the integrity of the genome, which may result in gene expression and human disease. Both genome instability and micronutrient imbalance have been identified and implicated in diseases associated with accelerated ageing which potentially leads to an increased risk for the future development of clinically defined neurodegenerative disorders. Cognitive decline leading to the clinical diagnosis of mild cognitive impairment (MCI) has been shown to predict an increased risk in later life of developing Alzheimer's disease (AD). Knowledge on the impact of dietary factors in relation to MCI and AD risk is improving but incomplete; in particular the role of nutrient combinations (i.e. nutriomes) has not been thoroughly investigated. Currently, there is a need for preventative strategies as well as the identification of robust and reproducible diagnostic biomarkers that will allow identification of those individuals with increased risk for neurodegenerative diseases. Growing evidence suggests cells originating from different somatic tissues derived from individuals that have been clinically diagnosed with neurodegenerative disorders exhibit elevated frequencies of DNA damage compared to tissues of cognitively normal individuals which could be due to malnutrition. The objective of this review is to discuss current evidence and identify knowledge gaps relating to genome instability biomarkers and blood micronutrient profiles from human studies of MCI and AD that may be specific to and contribute to the increased risk of these diseases. This is a vital step in order to create research strategies for the future development of diagnostics that are indicative of dementia risk and to inform preventative therapies.

Chromosomal DNA damage measured using the cytokinesis-block micronucleus cytome assay is significantly associated with cognitive impairment in South Australians

Loss of genome integrity may be associated with increased risk for neurodegenerative disease. The aim of this study was to investigate whether mild cognitive impairment (MCI) or Alzheimer's disease (AD) individuals have increased DNA damage relative to age- and gender- matched controls using the cytokinesis-block micronucleus cytome (CBMN-Cyt) assay. DNA damage was measured as micronuclei (MN), nucleoplasmic bridges (NPB), and nuclear buds (NBUD) in binucleated cells. The assay was performed on blood samples from 80 participants consisting of (i) MCI cases (N = 20) and age- and gender- matched controls (N = 20), and (ii) AD cases (N = 20) and age- and gender- matched controls (N = 20). There was a significant increase in MCI NBUD frequency (P = 0.006) relative to controls, which was also observed in male (P = 0.03) and female (P = 0.04) subgroups. For AD cases, there were no significant differences in assay biomarkers relative to controls. There was a significant negative correlation between Mini Mental State Examination (MMSE) and (i) MN in all controls, (R = -0.3, P = 0.04), and AD cases (R = -0.4, P = 0.03), (ii) NPB in all controls, (R = -0.4, P = 0.006) and AD cases (R = -0.5, P = 0.01), and (iii) NBUD in MCI cases (R = -0.5, P = 0.007) and AD cases (R = -0.7, P = 0.0002). The results suggest that an increase in lymphocyte CBMN-Cyt DNA damage biomarkers may be associated with cognitive decline.

DNA damage in non-communicable diseases: A clinical and epidemiological perspective

Non-communicable diseases (NCDs) are a leading cause of death and disability, representing 63% of the total death number worldwide. A characteristic phenotype of these diseases is the accelerated aging, which is the result of phenomena such as accumulated DNA damage, telomere capping loss and subcellular irreversible/nonrepaired oxidative damage. DNA damage, mostly oxidative, plays a key role in the development of most common NCDs. The present review will gather some of the most relevant knowledge concerning the presence of DNA damage in NCDs focusing on cardiovascular diseases, diabetes, chronic obstructive pulmonary disease, and neurodegenerative disorders, and discussing a selection of papers from the most informative literature. The challenge of comorbidity and the potential offered by new systems approaches for introducing these biomarkers into the clinical decision process will be discussed. Systems Medicine platforms represent the most suitable approach to personalized medicine, enabling to identify new patterns in the pathogenesis, diagnosis and prognosis of chronic diseases.

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.

Extracellular amyloid beta 42 causes necrosis, inhibition of nuclear division, and mitotic disruption under both folate deficient and folate replete conditions as measured by the cytokinesis-block micronucleus cytome assay

Alzheimer's disease is associated with accumulation of extracellular beta amyloid peptide 42 (Aβ42) which may induce DNA damage and reduce cellular regenerative potential. These effects may be exacerbated under conditions of folate deficiency. The aim of this study was to investigate whether extracellular Aβ42 induces DNA damage and cell death in human peripheral lymphocytes and whether there is an interactive effect between extracellular Aβ42 and folic acid status. Peripheral blood lymphocytes were cultured in medium under conditions of both low and high folate (20 and 200 nM, respectively) and challenged with either Aβ42 or the physiologically normal form Aβ40 (both at 5, 10, 15 µM). Genome stability and cytotoxicity events were investigated using the cytokinesis-block micronucleus cytome (CBMN-cyt) assay. Outcome measures scored included the nuclear division index (NDI), necrosis, apoptosis, binucleated cells with micronuclei (MN), nucleoplasmic bridges (NPB), and nuclear buds (NBUD) and abnormally shaped nuclei (circular, (CIR) and horse-shoe, (HS) that may be indicative of mitotic disruption. Folic acid deficiency significantly reduced NDI (P < 0.001) and increased all the DNA damage biomarkers (MN, NPB, NBUD, HS, CIR), (P < 0.001). In contrast, exposure to Aβ40 had no impact on CBMN cytome biomarkers but Aβ42 significantly reduced NDI (P < 0.01), increased necrosis (P < 0.05) and frequency of cells with circular nuclei (P < 0.01). There was no evidence of an interaction between Aβ42 and folic acid with respect to CBMN cytome biomarkers. Extracellular Aβ42 appears to have cytotoxic and cytostatic effects but its effect on chromosomal instability appears to be small relative to folate deficiency.

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.

A combination of micronucleus assay and fluorescence in situ hybridization analysis to evaluate the genotoxicity of formaldehyde

A genotoxic effect of formaldehyde (FA), particularly micronucleus (MN) induction, has been shown in several previous studies. The aim of the present study was to assess the frequency of micronuclei and to identify the type of chromosomal damage in Tunisian staff members working in the Pathologic Anatomy Laboratory of Farhat Hached hospital (Sousse, Tunisia) who were exposed to FA. Assessment of chromosomal damage was performed in peripheral lymphocytes of 31 FA-exposed employees compared with 31 control employees working in the administrative department of the same hospital. The clastogenic/aneugenic effect of FA was evaluated using the standard MN assay in combination with fluorescence in situ hybridization (FISH) using pan-centromeric probes. The mean level of exposure to FA was 3.4 ppm. The results showed a significant increase of MN frequency in lymphocytes of exposed workers compared with the control group (25.35 ± 6.28 ‰ vs. 7.08  ± 4.62 ‰, p < 0.05). As assessed by FISH, the frequency of centromeric micronuclei (C+MN) was greater in exposed subjects than in controls (18.38 ± 5.94 ‰ vs. 5.03 ± 3.64 ‰). Among the C+MN, the frequency of MN containing one centromere (C1+MN) was significantly greater in pathologists and anatomists than in controls (15.35 ± 6.0 ‰ vs. 3.33 ± 2.74 ‰, p < 0.05). The results showed an effect of sex and time of FA exposure with significantly increased frequencies of all end points measuring aneuploidy (C+MN, C1+MN, and Cx+MN [more then one MN]). The increased frequency of C1+MN observed in the exposed group may suggest a slight aneugenic effect of FA exposure.

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.

One-carbon metabolism and Alzheimer's disease: focus on epigenetics

Alzheimer’s disease (AD) represents the most common form of dementia in the elderly, characterized by progressive loss of memory and cognitive capacity severe enough to interfere with daily functioning and the quality of life. Rare, fully penetrant mutations in three genes (APP, PSEN1 and PSEN2) are responsible for familial forms of the disease. However, more than 90% of AD is sporadic, likely resulting from complex interactions between genetic and environmental factors. Increasing evidence supports a role for epigenetic modifications in AD pathogenesis. Folate metabolism, also known as one-carbon metabolism, is required for the production of S-adenosylmethionine (SAM), which is the major DNA methylating agent. AD individuals are characterized by decreased plasma folate values, as well as increased plasma homocysteine (Hcy) levels, and there is indication of impaired SAM levels in AD brains. Polymorphisms of genes participating in one-carbon metabolism have been associated with AD risk and/or with increased Hcy levels in AD individuals. Studies in rodents suggest that early life exposure to neurotoxicants or dietary restriction of folate and other B vitamins result in epigenetic modifications of AD related genes in the animal brains. Similarly, studies performed on human neuronal cell cultures revealed that folate and other B vitamins deprivation from the media resulted in epigenetic modification of the PSEN1 gene. There is also evidence of epigenetic modifications in the DNA extracted from blood and brains of AD subjects. Here I review one-carbon metabolism in AD, with emphasis on possible epigenetic consequences.

Germinal and Somatic Trisomy 21 Mosaicism: How Common is it, What are the Implications for Individual Carriers and How Does it Come About?

It is well known that varying degrees of mosaicism for Trisomy 21, primarily a combination of normal and Trisomy 21 cells within individual tissues, may exist in the human population. This involves both Trisomy 21 mosaicism occurring in the germ line and Trisomy 21 mosaicism documented in different somatic tissues, or indeed a combination of both in the same subjects. Information on the incidence of Trisomy 21 mosaicism in different tissue samples from people with clinical features of Down syndrome as well as in the general population is, however, still limited. One of the main reasons for this lack of detailed knowledge is the technological problem of its identification, where in particular low grade/cryptic Trisomy 21 mosaicism, i.e. occurring in less than 3-5% of the respective tissues, can only be ascertained by fluorescence in situ hybridization (FISH) methods on large cell populations from the different tissue samples.In this review we summarize current knowledge in this field with special reference to the question on the likely incidence of germinal and somatic Trisomy 21 mosaicism in the general population and its mechanisms of origin. We also highlight the reproductive and clinical implications of this type of aneuploidy mosaicism for individual carriers. We conclude that the risk of begetting a child with Trisomy 21 Down syndrome most likely is related to the incidence of Trisomy 21 cells in the germ line of any carrier parent. The clinical implications for individual carriers may likewise be dependent on the incidence of Trisomy 21 in the relevant somatic tissues. Remarkably, for example, there are indications that Trisomy 21 mosaicism will predispose carriers to conditions such as childhood leukemia and Alzheimer's Disease but there is on the other hand a possibility that the risk of solid cancers may be substantially reduced.

Detection of environmental clastogens and aneugens in human fibroblasts by cytokinesis-blocked micronucleus assay associated with immunofluorescent staining of CENP-A in micronuclei

The cytokinesis-blocked micronucleus (CBMN) assay, in combination with fluorescent in situ hybridization (FISH) of human pan-centromeric DNA probes, or with CREST antibodies that specifically stain kinetochore proteins, is widely used on several cell types. It distinguishes micronuclei containing one or several whole chromosomes, which are positively labeled (centromere positive micronucleus, C+MN, due to aneugenic effect), or acentric chromosome fragments, which are unlabeled due to the absence of centromere (centromere negative micronucleus, C-MN, due to clastogenic effect). However, the very slight level of the centromeric signals obtained with the FISH technique on primary human fibroblasts, a cell type commonly used in environmental genetic toxicology, leads to great difficulties in distinguishing C+MN and C-MN. Furthermore, the CREST technique may lead to inappropriate results particularly with regards to variations in antibody composition between patient sera. Our results show that the in vitro CBMN, in combination with immunofluorescence staining of CENP-A (centromere protein A), efficiently screens genotoxicants for their ability to induce clastogenic and/or aneugenic effects. We propose the in vitro CBMN assay in combination with immunofluorescence staining of CENP-A as a suitable tool in environmental genotoxicity testing of primary human fibroblasts.

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.

Association of micronucleus frequency with neurodegenerative diseases

Micronuclei (MNi) can originate either from chromosome breakage or chromosome malsegregation events and are therefore ideal biomarkers to investigate genomic instability. Studies in peripheral lymphocytes of patients with neurodegenerative diseases, mainly Alzheimer's disease (AD) and Parkinson's disease (PD), revealed an increased micronucleus (MN) frequency in both disorders but originating mainly from chromosome malsegregation events in AD and from chromosome breakage events in PD. Studies in other neurodegenerative diseases are largely missing, and some data in premature ageing disorders characterised by neurodegeneration and/or neurological complications, such as Ataxia telangiectasia, Werner's syndrome, Down's syndrome (DS) and Cockayne's syndrome, indicate that MNi increase with ageing in cultured cells. An increased frequency of aneuploidy characterises several tissues of AD patients, as well as of individuals at increased risk to develop AD, such as mothers of DS individuals and DS subjects themselves. The use of the buccal MN cytome assay in AD and DS subjects allowed finding significant changes in the MN frequency as well as other cellular modifications reflecting reduced regenerative capacity compared to age- and gender-matched controls. These changes in buccal cytome ratios may prove useful as potential future diagnostics to identify individuals of increased risk for these disorders.

Premature centromere division of metaphase chromosomes in peripheral blood lymphocytes of Alzheimer's disease patients: relation to gender and age

Chromosomal alterations are a feature of both aging and Alzheimer's disease (AD). This study examined if premature centromere division (PCD), a chromosomal instability indicator increased in AD, is correlated with aging or, instead, represents a de novo chromosomal alteration due to accelerating aging in AD. PCD in peripheral blood lymphocytes was determined in sporadic AD patients and gender and age-matched unaffected controls. Metaphase nuclei were analyzed for chromosomes showing PCD, X chromosomes with PCD (PCD,X), and acrocentric chromosomes showing PCD. AD patients, regardless of age, demonstrated increased PCD on any chromosome and PCD on acrocentric chromosomes in both genders, whereas an increase in frequency of PCD,X was expressed only in women. This cytogenetic analysis suggests that PCD is a feature of AD, rather than an epiphenomenon of chronological aging, and may be useful as a physiological biomarker that can be used for disease diagnosis.

Increased lymphocyte micronucleus frequency in early pregnancy is associated prospectively with pre-eclampsia and/or intrauterine growth restriction

Genome stability is essential for normal foetal growth and development. To date, genome stability in human lymphocytes has not been studied in relation to late pregnancy diseases, such as pre-eclampsia (PE) and intrauterine growth restriction (IUGR), which can be life-threatening to mother and baby and together affect >10% of pregnancies. We performed a prospective cohort study investigating the association of maternal chromosomal damage in mid-pregnancy (20 weeks gestation) with pregnancy outcomes. Chromosome damage was measured using the cytokinesis-block micronucleus cytome (CBMNcyt) assay in peripheral blood lymphocytes. The odds ratio for PE and/or IUGR in a mixed cohort of low- and high-risk pregnancies (N = 136) and a cohort of only high-risk pregnancies (N = 91) was 15.97 (P = 0.001) and 17.85 (P = 0.007), respectively, if the frequency of lymphocytes with micronuclei (MN) at 20 weeks gestation was greater than the mean + 2 SDs of the cohort. These results suggest that the presence of lymphocyte MN is significantly increased in women who develop PE and/or IUGR before the clinical signs or symptoms appear relative to women with normal pregnancy outcomes. The CBMNcyt assay may provide a new approach for the early detection of women at risk of developing these late pregnancy diseases and for biomonitoring the efficacy of interventions to reduce DNA damage, which may in turn ameliorate pregnancy outcome.

Dietary reference values of individual micronutrients and nutriomes for genome damage prevention: current status and a road map to the future

Damage to the genome is recognized as a fundamental cause of developmental and degenerative diseases. Several micronutrients play an important role in protecting against DNA damage events generated through endogenous and exogenous factors by acting as cofactors or substrates for enzymes that detoxify genotoxins as well as enzymes involved in DNA repair, methylation, and synthesis. In addition, it is evident that either micronutrient deficiency or micronutrient excess can modify genome stability and that these effects may also depend on nutrient-nutrient and nutrient-gene interaction, which is affected by genotype. These observations have led to the emerging science of genome health nutrigenomics, which is based on the principle that DNA damage is a fundamental cause of disease that can be diagnosed and nutritionally prevented on an individual, genetic subgroup, or population basis. In this article, the following topics are discussed: 1) biomarkers used to study genome damage in humans and their validation, 2) evidence for the association of genome damage with developmental and degenerative disease, 3) current knowledge of micronutrients required for the maintenance of genome stability in humans, 4) the effect of nutrient-nutrient and nutrient-genotype interaction on DNA damage, and 5) strategies to determine dietary reference values of single micronutrients and micronutrient combinations (nutriomes) on the basis of DNA damage prevention. This article also identifies important knowledge gaps and future research directions required to shed light on these issues. The ultimate goal is to match the nutriome to the genome to optimize genome maintenance and to prevent pathologic amounts of DNA damage.

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.

The X-chromosome instability phenotype in Alzheimer's disease: a clinical sign of accelerating aging?

Premature centromere division, or premature centromere separation (PCS), occurs when chromatid separation is dysfunctional, occurring earlier than usual during the interphase stage of mitosis. This phenomenon, seen in Robert's syndrome and various cancers, has also been documented in peripheral as well as neuronal cells of Alzheimer's disease (AD). In the latter instances, fluorescent in situ hybridization (FISH), applied to the centromere region of the X-chromosome in interphase nuclei of lymphocytes from peripheral blood in AD patients, demonstrated premature chromosomal separation before mitotic metaphase directly after completion of DNA replication in G(2) phase of the cell cycle. Furthermore, and perhaps unexpectedly given the presumptive post-mitotic status of terminally differentiated neurons, neurons in AD patients also showed significantly increased levels of PCS of the X-chromosome. Taken together with other phenomena such as cell cycle re-activation and ectopic re-expression of cyclins and cyclin dependent proteins, we propose that AD is an oncogenic phenotype leading to accelerated aging of the affected brain.

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.

FISH glossary: an overview of the fluorescence in situ hybridization technique

The introduction of FISH (fluorescence in situ hybridization) marked the beginning of a new era for the study of chromosome structure and function. As a combined molecular and cytological approach, the major advantage of this visually appealing technique resides in its unique ability to provide an intermediate degree of resolution between DNA analysis and chromosomal investigations while retaining information at the single-cell level. Used to support large-scale mapping and sequencing efforts related to the human genome project, FISH accuracy and versatility were subsequently capitalized on in biological and medical research, providing a wealth of diverse applications and FISH-based diagnostic assays. The diversification of the original FISH protocol into the impressive number of procedures available these days has been promoted throughout the years by a number of interconnected factors: the improvement in sensitivity, specificity and resolution, together with the advances in the fields of fluorescence microscopy and digital imaging, and the growing availability of genomic and bioinformatic resources. By assembling in a glossary format many of the "acronymed" FISH applications published so far, this review intends to celebrate the ability of FISH to re-invent itself and thus remain at the forefront of biomedical research.

Premature centromere division of the X chromosome in neurons in Alzheimer's disease

Premature centromere division (PCD) represents a loss of control over the sequential separation and segregation of chromosome centromeres. Although first described in aging women, PCD on the X chromosome (PCD,X) is markedly elevated in peripheral blood lymphocytes of individuals suffering from Alzheimer disease (AD). The present study evaluated PCD,X, using a fluorescent in situ hybridization method, in interphase nuclei of frontal cerebral cortex neurons from sporadic AD patients and age-matched controls. The average frequency of PCD,X in AD patients (8.60 +/- 1.20%) was almost three times higher (p < 0.01) than in the control group (2.96 +/- 1.20). However, consistent with previous studies, no mitotic cells were found in neurons in either AD or control brain, suggesting an intrinsic inability of post-mitotic neurons to divide. In view of the fact that it has been well-documented that neurons in AD can re-enter into the cell division cycle, the findings presented here of increased PCD advance the hypothesis that deregulation of the cell cycle may contribute to neuronal degeneration and subsequent cognitive deficits in AD.

Genome-health nutrigenomics and nutrigenetics: nutritional requirements or ‘nutriomes’ for chromosomal stability and telomere maintenance at the individual level

It is becoming increasingly evident that (a) risk for developmental and degenerative disease increases with more DNA damage, which in turn is dependent on nutritional status, and (b) the optimal concentration of micronutrients for prevention of genome damage is also dependent on genetic polymorphisms that alter the function of genes involved directly or indirectly in the uptake and metabolism of micronutrients required for DNA repair and DNA replication. The development of dietary patterns, functional foods and supplements that are designed to improve genome-health maintenance in individuals with specific genetic backgrounds may provide an important contribution to an optimum health strategy based on the diagnosis and individualised nutritional prevention of genome damage, i.e. genome health clinics. The present review summarises some of the recent knowledge relating to micronutrients that are associated with chromosomal stability and provides some initial insights into the likely nutritional factors that may be expected to have an impact on the maintenance of telomeres. It is evident that developing effective strategies for defining nutrient doses and combinations or ‘nutriomes’ for genome-health maintenance at the individual level is essential for further progress in this research field.

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.

Is the time dimension of the cell cycle re-entry in AD regulated by centromere cohesion dynamics?

Chromosomal involvement is a legitimate, yet not well understood, feature of Alzheimer disease (AD). Firstly, AD affects more women than men. Secondly, the amyloid-β protein precursor genetic mutations, responsible for a cohort of familial AD cases, reside on chromosome 21, the same chromosome responsible for the developmental disorder Down's syndrome. Thirdly, lymphocytes from AD patients display a novel chromosomal phenotype, namely premature centromere separation (PCS). Other documented morphological phenomena associated with AD include the occurrence of micronuclei, aneuploidy, binucleation, telomere instability, and cell cycle re-entry protein expression. Based on these events, here we present a novel hypothesis that the time dimension of cell cycle re-entry in AD is highly regulated by centromere cohesion dynamics. In view of the fact that neurons can re-enter the cell division cycle, our hypothesis predicts that alterations in the signaling pathway leading to premature cell death in neurons is a consequence of altered regulation of the separation of centromeres as a function of time. It is well known that centromeres in the metaphase-anaphase transition separate in a non-random, sequential order. This sequence has been shown to be deregulated in aging cells, various tumors, syndromes of chromosome instability, following certain chemical inductions, as well as in AD. Over time, premature chromosome separation is both a result of, and a driving force behind, further cohesion impairment, activation of cyclin dependent kinases, and mitotic catastrophe, a vicious circle resulting in cellular degeneration and death.