Cyclin' toward dementia: cell cycle abnormalities and abortive oncogenesis in Alzheimer disease

Pathological Nuclear Hallmarks in Dentate Granule Cells of Alzheimer’s Patients: A Biphasic Regulation of Neurogenesis

The dentate gyrus (DG) of the human hippocampus is a complex and dynamic structure harboring mature and immature granular neurons in diverse proliferative states. While most mammals show persistent neurogenesis through adulthood, human neurogenesis is still under debate. We found nuclear alterations in granular cells in autopsied human brains, detected by immunohistochemistry. These alterations differ from those reported in pyramidal neurons of the hippocampal circuit. Aging and early AD chromatin were clearly differentiated by the increased epigenetic markers H3K9me3 (heterochromatin suppressive mark) and H3K4me3 (transcriptional euchromatin mark). At early AD stages, lamin B2 was redistributed to the nucleoplasm, indicating cell-cycle reactivation, probably induced by hippocampal nuclear pathology. At intermediate and late AD stages, higher lamin B2 immunopositivity in the perinucleus suggests fewer immature neurons, less neurogenesis, and fewer adaptation resources to environmental factors. In addition, senile samples showed increased nuclear Tau interacting with aged chromatin, likely favoring DNA repair and maintaining genomic stability. However, at late AD stages, the progressive disappearance of phosphorylated Tau forms in the nucleus, increased chromatin disorganization, and increased nuclear autophagy support a model of biphasic neurogenesis in AD. Therefore, designing therapies to alleviate the neuronal nuclear pathology might be the only pathway to a true rejuvenation of brain circuits.

REPS1 as a Potential Biomarker in Alzheimer’s Disease and Vascular Dementia

Vascular dementia (VD) and Alzheimer’s disease (AD) are common types of dementia for which no curative therapies are known. In this study, we identified hub genes associated with AD and VD in order to explore new potential therapeutic targets. Genes differentially expressed in VD and AD in all three datasets (GSE122063, GSE132903, and GSE5281) were identified and used to construct a protein–protein interaction network. We identified 10 modules containing 427 module genes in AD and VD. Module genes showing an area under the diagnostic curve > 0.60 for AD or VD were used to construct a least absolute shrinkage and selection operator model and were entered into a support vector machine-recursive feature elimination algorithm, which identified REPS1 as a hub gene in AD and VD. Furthermore, REPS1 was associated with activation of pyruvate metabolism and inhibition of Ras signaling pathway. Module genes, together with differentially expressed microRNAs from the dataset GSE46579, were used to construct a regulatory network. REPS1 was predicted to bind to the microRNA hsa_miR_5701. Single-sample gene set enrichment analysis was used to explore immune cell infiltration, which suggested a negative correlation between REPS1 expression and infiltration by plasmacytoid dendritic cells in AD and VD. In conclusion, our results suggest core pathways involved in both AD and VD, and they identify REPS1 as a potential biomarker of both diseases. This protein may aid in early diagnosis, monitoring of treatment response, and even efforts to prevent these debilitating disorders.

Schisandrin A and B affect the proliferation and differentiation of neural stem cells

Schisandrin A and B (Sch A and B) are the important components of Asian dietary supplement and phytomedicine Schisandra chinensis (S. chinensis). They can enhance adult neurogenesis in vivo; however, these effects still need to be verified. Here NE-4 C neural stem cells (NSCs) were employed as the in vitro model and treated with Sch A and B at 0.1 μg/mL. EdU (5-Ethynyl-2'-deoxyuridine) labeling showed that both Sch A and B treatments enhanced NSC proliferation. Real-time PCR analysis showed the mRNA abundances of telomerase gene Tert and cell cycle gene Cyclin D1 were significantly up-regulated after the treatments. During the neurosphere induction, Sch B enhanced the neurosphere formation and neuronal differentiation, and increased the neurosphere semidiameters. Detection of the neuron differentiation marker Mapt indicates that both Sch A and B, especially Sch B, benefits the induced neuronal differentiation. Sch B treatment also enhanced mRNA expressions of the neurosphere-specific adhesion molecule Cdh2 and Wnt pathway-related genes including Mmp9, Cyclin D1 and β-catenin. Together, Sch A especially Sch B, promotes the proliferation, affects the survival, differentiation and neurogenesis of NSCs, which is consistent with their in vivo effects. This study provides further clue on the potential neuropharmacological effects of S. chinensis.

Insights into the neuropathology of cerebral ischemia and its mechanisms

Cerebral ischemia is a result of insufficient blood flow to the brain. It leads to limited supply of oxygen and other nutrients to meet metabolic demands. These phenomena lead to brain damage. There are two types of cerebral ischemia: focal and global ischemia. This condition has significant impact on patient’s health and health care system requirements. Animal models such as transient occlusion of the middle cerebral artery and permanent occlusion of extracranial vessels have been established to mimic the conditions of the respective type of cerebral ischemia and to further understand pathophysiological mechanisms of these ischemic conditions. It is important to understand the pathophysiology of cerebral ischemia in order to identify therapeutic strategies for prevention and treatment. Here, we review the neuropathologies that are caused by cerebral ischemia and discuss the mechanisms that occur in cerebral ischemia such as reduction of cerebral blood flow, hippocampal damage, white matter lesions, neuronal cell death, cholinergic dysfunction, excitotoxicity, calcium overload, cytotoxic oedema, a decline in adenosine triphosphate (ATP), malfunctioning of Na+/K+-ATPase, and the blood-brain barrier breakdown. Altogether, the information provided can be used to guide therapeutic strategies for cerebral ischemia.

Emerging Roles of Inhibitor of Differentiation-1 in Alzheimer's Disease: Cell Cycle Reentry and Beyond

Inhibitor of DNA-binding/differentiation (Id) proteins, a family of helix-loop-helix (HLH) proteins that includes four members of Id1 to Id4 in mammalian cells, are critical for regulating cell growth, differentiation, senescence, cell cycle progression, and increasing angiogenesis and vasculogenesis, as well as accelerating the ability of cell migration. Alzheimer’s disease (AD), the most common neurodegenerative disease in the adult population, manifests the signs of cognitive decline, behavioral changes, and functional impairment. The underlying mechanisms for AD are not well-clarified yet, but the aggregation of amyloid-beta peptides (Aβs), the major components in the senile plaques observed in AD brains, contributes significantly to the disease progression. Emerging evidence reveals that aberrant cell cycle reentry may play a central role in Aβ-induced neuronal demise. Recently, we have shown that several signaling mediators, including Id1, hypoxia-inducible factor-1 (HIF-1), cyclin-dependent kinases-5 (CDK5), and sonic hedgehog (Shh), may contribute to Aβ-induced cell cycle reentry in postmitotic neurons; furthermore, Id1 and CDK5/p25 mutually antagonize the expression/activity of each other. Therefore, Id proteins may potentially have clinical applications in AD. In this review article, we introduce the underlying mechanisms for cell cycle dysregulation in AD and present some examples, including our own studies, to show different aspects of Id1 in terms of cell cycle reentry and other signaling that may be crucial to alter the neuronal fates in this devastating neurodegenerative disease. A thorough understanding of the underlying mechanisms may provide a rationale to make an earlier intervention before the occurrence of cell cycle reentry and subsequent apoptosis in the fully differentiated neurons during the progression of AD or other neurodegenerative diseases.

Phosphodiesterase Inhibitors for Alzheimer's Disease: A Systematic Review of Clinical Trials and Epidemiology with a Mechanistic Rationale

BACKGROUND

Preclinical studies, clinical trials, and reviews suggest increasing 3',5'-cyclic adenosine monophosphate (cAMP) and 3',5'-cyclic guanosine monophosphate (cGMP) with phosphodiesterase inhibitors is disease-modifying in Alzheimer's disease (AD). cAMP/protein kinase A (PKA) and cGMP/protein kinase G (PKG) signaling are disrupted in AD. cAMP/PKA and cGMP/PKG activate cAMP response element binding protein (CREB). CREB binds mitochondrial and nuclear DNA, inducing synaptogenesis, memory, and neuronal survival gene (e.g., brain-derived neurotrophic factor) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α). cAMP/PKA and cGMP/PKG activate Sirtuin-1, which activates PGC1α. PGC1α induces mitochondrial biogenesis and antioxidant genes (e.g.,Nrf2) and represses BACE1. cAMP and cGMP inhibit BACE1-inducing NFκB and tau-phosphorylating GSK3β.

OBJECTIVE AND METHODS

We review efficacy-testing clinical trials, epidemiology, and meta-analyses to critically investigate whether phosphodiesteraseinhibitors prevent or treat AD.

RESULTS

Caffeine and cilostazol may lower AD risk. Denbufylline and sildenafil clinical trials are promising but preliminary and inconclusive. PF-04447943 and BI 409,306 are ineffective. Vinpocetine, cilostazol, and nicergoline trials are mixed. Deprenyl/selegiline trials show only short-term benefits. Broad-spectrum phosphodiesterase inhibitor propentofylline has been shown in five phase III trials to improve cognition, dementia severity, activities of daily living, and global assessment in mild-to-moderate AD patients on multiple scales, including the ADAS-Cogand the CIBIC-Plus in an 18-month phase III clinical trial. However, two books claimed based on a MedScape article an 18-month phase III trial failed, so propentofylline was discontinued. Now, propentofylline is used to treat canine cognitive dysfunction, which, like AD, involves age-associated wild-type Aβ deposition.

CONCLUSION

Phosphodiesterase inhibitors may prevent and treat AD.

Perinuclear Lamin A and Nucleoplasmic Lamin B2 Characterize Two Types of Hippocampal Neurons through Alzheimer's Disease Progression

BACKGROUND

Recent reports point to a nuclear origin of Alzheimer's disease (AD). Aged postmitotic neurons try to repair their damaged DNA by entering the cell cycle. This aberrant cell cycle re-entry involves chromatin modifications where nuclear Tau and the nuclear lamin are involved. The purpose of this work was to elucidate their participation in the nuclear pathological transformation of neurons at early AD.

METHODOLOGY

The study was performed in hippocampal paraffin embedded sections of adult, senile, and AD brains at I-VI Braak stages. We analyzed phospho-Tau, lamins A, B1, B2, and C, nucleophosmin (B23) and the epigenetic marker H4K20me3 by immunohistochemistry.

RESULTS

Two neuronal populations were found across AD stages, one is characterized by a significant increase of Lamin A expression, reinforced perinuclear Lamin B2, elevated expression of H4K20me3 and nuclear Tau loss, while neurons with nucleoplasmic Lamin B2 constitute a second population.

CONCLUSIONS

The abnormal cell cycle reentry in early AD implies a fundamental neuronal transformation. This implies the reorganization of the nucleo-cytoskeleton through the expression of the highly regulated Lamin A, heterochromatin repression and building of toxic neuronal tangles. This work demonstrates that nuclear Tau and lamin modifications in hippocampal neurons are crucial events in age-related neurodegeneration.

Activation of cyclin D1 affects mitochondrial mass following traumatic brain injury

Cell cycle activation has been associated with varying types of neurological disorders including brain injury. Cyclin D1 is a critical modulator of cell cycle activation and upregulation of Cyclin D1 in neurons contributes to the pathology associated with traumatic brain injury (TBI). Mitochondrial mass is a critical factor to maintain the mitochondrial function, and it can be regulated by different signaling cascades and transcription factors including NRF1. However, the underlying mechanism of how TBI leads to impairment of mitochondrial mass following TBI remains obscure. Our results indicate that augmentation of CyclinD1 attenuates mitochondrial mass formation following TBI. To elucidate the molecular mechanism, we found that Cyclin D1 interacts with a transcription factor NRF1 in the nucleus and prevents NRF1's interaction with p300 in the pericontusional cortex following TBI. As a result, the acetylation level of NRF1 was decreased, and its transcriptional activity was attenuated. This event leads to a loss of mitochondrial mass in the pericontusional cortex following TBI. Intranasal delivery of Cyclin D1 RNAi immediately after TBI rescues transcriptional activation of NRF1 and recovers mitochondrial mass after TBI.

Ethnopharmacological Approaches for Dementia Therapy and Significance of Natural Products and Herbal Drugs

Dementia is a clinical syndrome wherein gradual decline of mental and cognitive capabilities of an afflicted person takes place. Dementia is associated with various risk factors and conditions such as insufficient cerebral blood supply, toxin exposure, mitochondrial dysfunction, oxidative damage, and often coexisting with some neurodegenerative disorders such as Alzheimer's disease (AD), Huntington's disease (HD), and Parkinson's disease (PD). Although there are well-established (semi-)synthetic drugs currently used for the management of AD and AD-associated dementia, most of them have several adverse effects. Thus, traditional medicine provides various plant-derived lead molecules that may be useful for further medical research. Herein we review the worldwide use of ethnomedicinal plants in dementia treatment. We have explored a number of recognized databases by using keywords and phrases such as “dementia”, “Alzheimer's,” “traditional medicine,” “ethnopharmacology,” “ethnobotany,” “herbs,” “medicinal plants” or other relevant terms, and summarized 90 medicinal plants that are traditionally used to treat dementia. Moreover, we highlight five medicinal plants or plant genera of prime importance and discuss the physiological effects, as well as the mechanism of action of their major bioactive compounds. Furthermore, the link between mitochondrial dysfunction and dementia is also discussed. We conclude that several drugs of plant origin may serve as promising therapeutics for the treatment of dementia, however, pivotal evidence for their therapeutic efficacy in advanced clinical studies is still lacking.

Neuroanatomical Distribution of DEK Protein in Corticolimbic Circuits Associated with Learning and Memory in Adult Male and Female Mice

DEK, a chromatin-remodeling gene expressed in most human tissues, is known for its role in cancer biology and autoimmune diseases. DEK depletion in vitro reduces cellular proliferation, induces DNA damage subsequently leading to apoptosis, and down-regulates canonical Wnt/β-catenin signaling, a molecular pathway essential for learning and memory. Despite a recognized role in cancer (non-neuronal) cells, DEK expression and function is not well characterized in the central nervous system. We conducted a gene ontology analysis (ToppGene), using a cancer database to identify genes associated with DEK deficiency, which pinpointed several genes associated with cognitive-related diseases (i.e., Alzheimer's disease, presenile dementia). Based on this information, we examined DEK expression in corticolimbic structures associated with learning and memory in adult male and female mice using immunohistochemistry. DEK was expressed throughout the brain in both sexes, including the medial prefrontal cortex (prelimbic, infralimbic and dorsal peduncular). DEK was also abundant in all amygdalar subdivisions (basolateral, central and medial) and in the hippocampus including the CA1, CA2, CA3, dentate gyrus (DG), ventral subiculum and entorhinal cortex. Of note, compared to males, females had significantly higher DEK immunoreactivity in the CA1, indicating a sex difference in this region. DEK was co-expressed with neuronal and microglial markers in the CA1 and DG, whereas only a small percentage of DEK cells were in apposition to astrocytes in these areas. Given the reported inverse cellular and molecular profiles (e.g., cell survival, Wnt pathway) between cancer and Alzheimer's disease, these findings suggest a potentially important role of DEK in cognition.

A Unified Hypothesis of Early- and Late-Onset Alzheimer's Disease Pathogenesis

Early-onset familial Alzheimer's disease (EOFAD) and late-onset sporadic AD (LOSAD) both follow a similar pathological and biochemical course that includes: neuron and synapse loss and dysfunction, microvascular damage, microgliosis, extracellular amyloid-β deposition, tau phosphorylation, formation of intracellular neurofibrillary tangles, endoreduplication and related cell cycle events in affected brain regions. Any mechanistic explanation of AD must accommodate these biochemical and neuropathological features for both forms of the disease. In this insight paper we provide a unifying hypothesis for EOFAD and LOSAD that proposes that the aberrant re-entry of terminally differentiated, post-mitotic neurons into the cell division cycle is a common pathway that explains both early and late-onset forms of AD. Cell cycle abnormalities appear very early in the disease process, prior to the appearance of plaques and tangles, and explain the biochemical (e.g. tau phosphorylation), neuropathological (e.g. neuron hypertrophy; polypoidy) and cognitive changes observed in EOFAD and LOSAD. Genetic mutations in AβPP, PSEN1, and PSEN2 that alter amyloid-β precursor protein and Notch processing drive reactivation of the cell cycle in EOFAD, while age-related reproductive endocrine dyscrasia that upregulates mitogenic TNF signaling and AβPP processing toward the amyloidogenic pathway drives reactivation of the cell cycle in LOSAD. In essence, AβPP and presenilin mutations initiate early, what endocrine dyscrasia initiates later: aberrant cell cycle re-entry of post-mitotic neurons leading to neurodegeneration and cognitive decline in AD. Inhibition of cell cycle re-entry in post-mitotic neurons may be a useful therapeutic strategy to prevent, slow or halt disease progression.

Overexpression of Cell Cycle Proteins of Peripheral Lymphocytes in Patients with Alzheimer's Disease

OBJECTIVE

Biological markers for Alzheimer's disease (AD) will help clinicians make objective diagnoses early during the course of dementia. Previous studies have suggested that cell cycle dysregulation begins earlier than the onset of clinical manifestations in AD.

METHODS

We examined the lymphocyte expression of cell cycle proteins in AD patients, dementia controls (DC), and normal controls (NC). One-hundred seventeen subjects (36 AD, 31 DC, and 50 NC) were recruited. The cell cycle proteins CDK2, CDK4, CDK6, cyclin B, and cyclin D were measured in peripheral lymphocytes. Cell cycle protein expression in the three groups was compared after adjusting for age and sex.

RESULTS

The levels of cell cycle proteins CDK2, CDK4, CDK6, cyclin B, and cyclin D were significantly higher in AD patients than in the NC subjects. The DC group manifested intermediate levels of cell cycle proteins compared with the AD patients and the NC subjects. The present study indicates that cell cycle proteins are upregulated in the peripheral lymphocytes of AD patients.

CONCLUSION

Cell cycle dysregulation in peripheral lymphocytes may present a promising starting point for identifying peripheral biomarkers of AD.

The endocrine dyscrasia that accompanies menopause and andropause induces aberrant cell cycle signaling that triggers re-entry of post-mitotic neurons into the cell cycle, neurodysfunction, neurodegeneration and cognitive disease

This article is part of a Special Issue "SBN 2014". Sex hormones are physiological factors that promote neurogenesis during embryonic and fetal development. During childhood and adulthood these hormones support the maintenance of brain structure and function via neurogenesis and the formation of dendritic spines, axons and synapses required for the capture, processing and retrieval of information (memories). Not surprisingly, changes in these reproductive hormones that occur with menopause and during andropause are strongly correlated with neurodegeneration and cognitive decline. In this connection, much evidence now indicates that Alzheimer's disease (AD) involves aberrant re-entry of post-mitotic neurons into the cell cycle. Cell cycle abnormalities appear very early in the disease, prior to the appearance of plaques and tangles, and explain the biochemical, neuropathological and cognitive changes observed with disease progression. Intriguingly, a recent animal study has demonstrated that induction of adult neurogenesis results in the loss of previously encoded memories while decreasing neurogenesis after memory formation during infancy mitigated forgetting. Here we review the biochemical, epidemiological and clinical evidence that alterations in sex hormone signaling associated with menopause and andropause drive the aberrant re-entry of post-mitotic neurons into an abortive cell cycle that leads to neurite retraction, neuron dysfunction and neuron death. When the reproductive axis is in balance, gonadotropins such as luteinizing hormone (LH), and its fetal homolog, human chorionic gonadotropin (hCG), promote pluripotent human and totipotent murine embryonic stem cell and neuron proliferation. However, strong evidence supports menopausal/andropausal elevations in the LH:sex steroid ratio as driving aberrant mitotic events. These include the upregulation of tumor necrosis factor; amyloid-β precursor protein processing towards the production of mitogenic Aβ; and the activation of Cdk5, a key regulator of cell cycle progression and tau phosphorylation (a cardinal feature of both neurogenesis and neurodegeneration). Cognitive and biochemical studies confirm the negative consequences of a high LH:sex steroid ratio on dendritic spine density and human cognitive performance. Prospective epidemiological and clinical evidence in humans supports the premise that rebalancing the ratio of circulating gonadotropins:sex steroids reduces the incidence of AD. Together, these data support endocrine dyscrasia and the subsequent loss of cell cycle control as an important etiological event in the development of neurodegenerative diseases including AD, stroke and Parkinson's disease.

Neuronal response in Alzheimer's and Parkinson's disease: the effect of toxic proteins on intracellular pathways

Accumulation of protein aggregates is the leading cause of cellular dysfunction in neurodegenerative disorders. Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease, Prion disease and motor disorders such as amyotrophic lateral sclerosis, present with a similar pattern of progressive neuronal death, nervous system deterioration and cognitive impairment. The common characteristic is an unusual misfolding of proteins which is believed to cause protein deposition and trigger degenerative signals in the neurons. A similar clinical presentation seen in many neurodegenerative disorders suggests the possibility of shared neuronal responses in different disorders. Despite the difference in core elements of deposits in each neurodegenerative disorder, the cascade of neuronal reactions such as activation of glycogen synthase kinase-3 beta, mitogen-activated protein kinases, cell cycle re-entry and oxidative stress leading to a progressive neurodegeneration are surprisingly similar. This review focuses on protein toxicity in two neurodegenerative diseases, AD and PD. We reviewed the activated mechanisms of neurotoxicity in response to misfolded beta-amyloid and α-synuclein, two major toxic proteins in AD and PD, leading to neuronal apoptosis. The interaction between the proteins in producing an overlapping pathological pattern will be also discussed.

Synopsis on the linkage of Alzheimer's and Parkinson's disease with chronic diseases

Neurodegeneration is the progressive loss of neuronal structure and function, which ultimately leads to neurological disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), multiple sclerosis, and Huntington's disease. Even after the recent significant advances in neurobiology, the above-mentioned disorders continue to haunt the global population. Several studies have suggested the role of specific environmental and genetic risk factors associated with these disorders. However, the exact mechanism associated with the progression of these disorders still needs to be elucidated. In the recent years, sophisticated research has revealed interesting association of prominent neurodegenerative disorders such as AD and PD with chronic diseases such as cancer, diabetes, and cardiovascular diseases. Several common molecular mechanisms such as generation of free radicals, oxidative DNA damage, aberrations in mitochondrial DNA, and dysregulation of apoptosis have been highlighted as possible points of connection. The present review summarizes the possible mechanism of coexistence of AD and PD with other chronic diseases.

Inverse association between cancer and neurodegenerative disease: review of the epidemiologic and biological evidence

Growing evidence suggests an unusual epidemiologic association between cancer and certain neurological conditions, particularly age-related neurodegenerative diseases. Cancer survivors have a 20-50% lower risk of developing Parkinson's and Alzheimer's disease, and patients with these neurodegenerative conditions have a substantially lower incidence of cancer. We review the epidemiologic evidence for this inverse co-morbidity and show that it is not simply an artifact of survival bias or under-diagnosis. We then review the potential biological explanations for this association, which is intimately linked to the very different nature of dividing cells and neurons. The known genetic and metabolic connections between cancer and neurodegeneration generally fall within two categories. The first includes shared genes and pathways such as Pin1 and the ubiquitin proteasome system that are dysregulated in different directions to cause one disease or the other. The second includes common pathophysiological mechanisms such as mitochondrial dysfunction, oxidative stress and DNA damage that drive both conditions, but with different cellular fates. We discuss examples of these biological links and their implications for developing new approaches to prevention and treatment of both diseases.

Neuropathology and treatment of Alzheimer disease: did we lose the forest for the trees?

Although amyloid-beta-containing senile plaques and phospho-tau containing neurofibrillary tangles are hallmark lesions of Alzheimer disease (AD), neither is specific for AD, nor even a marker of AD. Rather, they are empirical lesions that require close correlation with age and clinical signs for optimal interpretation. In essence, these lesions represent the effect rather than the cause of disease. In this review, we discuss diagnostic criteria for AD, the relationship between pathology, pathogenesis and multiple treatment approaches that have so far been disappointing, including those that presume to address pathological lesions. An acceptance that lesion-based therapies do not address etiology or rate-limiting pathogenic factors is probably necessary for the best chance of significant advances that have thus far been elusive.

Reciprocal induction between α-synuclein and β-amyloid in adult rat neurons

In spite of definite roles for β-amyloid (Aβ) in familial Alzheimer's disease (AD), the cause of sporadic AD remains unknown. Amyloid senile plaques and Lewy body pathology frequently coexist in neocortical and hippocampal regions of AD and Parkinson's diseases. However, the relationship between Aβ and α-synuclein (α-Syn), the principle components in the pathological structures, in neuronal toxicity and the mechanisms of their interaction are not well studied. As Aβ and α-Syn accumulate in aging patients, the biological functions and toxicity of these polypeptides in the aging brain may be different from those in young brain. We examined the neurotoxicity influences of Aβ1-42 or α-Syn on mature neurons and the effects of Aβ1-42 or α-Syn on the production of endogenous α-Syn or Aβ1-40 reciprocally using a model of culture enriched with primary neurons from the hippocampus of adult rats. Treatment of neurons with high concentrations of Aβ1-42 or α-Syn caused significant apoptosis of neurons. Following Aβ1-42 treatment at sub apoptotic concentrations, both intra- and extra-cellular α-Syn levels were significantly increased. Reciprocally, the non-toxic levels of α-Syn treatment also increased intra- and extra-cellular Aβ1-40 levels. The phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002, suppressed α-Syn-induced Aβ1-40 elevation, as well as Aβ1-42-induced α-Syn elevation. Thus, high concentrations of Aβ1-42 and α-Syn exert toxic effects on mature neurons; however, non-toxic concentration treatment of these polypeptides induced the production of each other reciprocally with possible involvement of PI3K pathway.

Is TNF a link between aging-related reproductive endocrine dyscrasia and Alzheimer's disease?

This commentary addresses a novel mechanism by which aging-related changes in reproductive hormones could mediate their action in the brain. It presents the evidence that dyotic endocrine signals modulate the expression of tumor necrosis factor (TNF) and related cytokines, and that these cytokines are a functionally important downstream link mediating neurodegeneration and dysfunction. This convergence of dyotic signaling on TNF-mediated degeneration and dysfunction has important implications for understanding the pathophysiology of AD, stroke, and traumatic brain disease, and also for the treatment of these diseases.

Inverse association between cancer and Alzheimer's disease: results from the Framingham Heart Study

OBJECTIVES

To relate cancer since entry into the Framingham Heart Study with the risk of incident Alzheimer's disease and to estimate the risk of incident cancer among participants with and without Alzheimer's disease.

DESIGN

Community based prospective cohort study; nested age and sex matched case-control study.

SETTING

Framingham Heart Study, USA.

PARTICIPANTS

1278 participants with and without a history of cancer who were aged 65 or more and free of dementia at baseline (1986-90).

MAIN OUTCOME MEASURES

Hazard ratios and 95% confidence intervals for the risks of Alzheimer's disease and cancer.

RESULTS

Over a mean follow-up of 10 years, 221 cases of probable Alzheimer's disease were diagnosed. Cancer survivors had a lower risk of probable Alzheimer's disease (hazard ratio 0.67, 95% confidence interval 0.47 to 0.97), adjusted for age, sex, and smoking. The risk was lower among survivors of smoking related cancers (0.26, 0.08 to 0.82) than among survivors of non-smoking related cancers (0.82, 0.57 to 1.19). In contrast with their decreased risk of Alzheimer's disease, survivors of smoking related cancer had a substantially increased risk of stroke (2.18, 1.29 to 3.68). In the nested case-control analysis, participants with probable Alzheimer's disease had a lower risk of subsequent cancer (0.39, 0.26 to 0.58) than reference participants, as did participants with any Alzheimer's disease (0.38) and any dementia (0.44).

CONCLUSIONS

Cancer survivors had a lower risk of Alzheimer's disease than those without cancer, and patients with Alzheimer's disease had a lower risk of incident cancer. The risk of Alzheimer's disease was lowest in survivors of smoking related cancers, and was not primarily explained by survival bias. This pattern for cancer is similar to that seen in Parkinson's disease and suggests an inverse association between cancer and neurodegeneration.

Cyclin D1 gene ablation confers neuroprotection in traumatic brain injury

Cell cycle activation (CCA) is one of the principal secondary injury mechanisms following brain trauma, and it leads to neuronal cell death, microglial activation, and neurological dysfunction. Cyclin D1 (CD1) is a key modulator of CCA and is upregulated in neurons and microglia following traumatic brain injury (TBI). In this study we subjected CD1-wild-type (CD1(+/+)) and knockout (CD1(-/-)) mice to controlled cortical impact (CCI) injury to evaluate the role of CD1 in post-traumatic neurodegeneration and neuroinflammation. As early as 24 h post-injury, CD1(+/+) mice showed markers of CCA in the injured hemisphere, including increased CD1, E2F1, and proliferating cell nuclear antigen (PCNA), as well as increased Fluoro-Jade B staining, indicating neuronal degeneration. Progressive neuronal loss in the hippocampus was observed through 21 days post-injury in these mice, which correlated with a decline in cognitive function. Microglial activation in the injured hemisphere peaked at 7 days post-injury, with sustained increases at 21 days. In contrast, CD1(-/-) mice showed reduced CCA and neurodegeneration at 24 h, as well as improved cognitive function, attenuated hippocampal neuronal cell loss, decreased lesion volume, and cortical microglial activation at 21 days post-injury. These findings indicate that CD1-dependent CCA plays a significant role in the neuroinflammation, progressive neurodegeneration, and related neurological dysfunction resulting from TBI. Our results further substantiate the proposed role of CCA in post-traumatic secondary injury, and suggest that inhibition of CD1 may be a key therapeutic target for TBI.

Cell cycle reactivation in mature neurons: a link with brain plasticity, neuronal injury and neurodegenerative diseases?

Although the cell cycle machinery is essentially linked to cellular proliferation, recent findings suggest that neuronal cell death is frequently concurrent with the aberrant expression of cell cycle proteins in post-mitotic neurons. The present work reviews the evidence of cell cycle reentry and expression of cell cycle-associated proteins as a complex response of neurons to insults in the adult brain but also as a mechanism underlying brain plasticity. The basic aspects of cell cycle mechanisms, as well as the evidence showing cell cycle protein expression in the injured brain, are reviewed. The discussion includes recent experimental work attempting to establish a correlation between altered brain plasticity and neuronal death, and an analysis of recent evidence on how neural cell cycle dysregulation is related to neurodegenerative diseases especially the Alzheimer's disease. Understanding the mechanisms that control reexpression of proteins required for cell cycle progression which is involved in brain remodeling, may shed new light into the mechanisms involved in neuronal demise under diverse pathological circumstances. This would provide valuable clues about the possible therapeutic targets, leading to potential treatment of presently challenging neurodegenerative diseases.

Neurodegenerative processes in Alzheimer’s disease: an overview of pathogenesis with strategic biomarker potential

Since Alzheimer’s disease (AD) is the leading cause of senile dementia in the USA, affecting 15% of people over the age of 65 years and almost 50% of those aged over 85 years, the need for an adequate and early diagnosis as well as preventative measure against disease onset and progression is increasing. Epidemiological and molecular studies suggest that AD has multiple etiologies, including genetic mutations, genetic variations affecting susceptibility and environmental factors. All these aspects can promote the formation and the accumulation of insoluble amyloid-β and hyperphosphorylated tau. Since the disease is multifactorial and clinical diagnosis is highly exclusive, the need for a sensitive, specific and reliable biomarker for the disease is crucial. While amyloid and amyloid-related compounds may be useful biomarkers in the early diagnosis of AD, the multitude of other characteristic features of AD presented in this article may be similarly appropriate. For example, genetic mutations play a role in a subset of AD patients (often with early disease onset and more severe disease progression), and genetic analysis could thus play a role in disease diagnosis. Similarly, oxidative damage to various proteins, nucleic acids and other cellular compounds, probably arising from mitochondrial abnormalities, is found early in the disease and may provide certain biochemical signatures of disease. Ultimately, specific assays for genetic, protein and oxidative profiles and mitochondrial abnormalities, as well as those for amyloid-β and its immunological response, may serve as a relevant group of biomarkers that could be informative to individuals regarding risk of disease, as well as for indicators of the progression of disease. Correspondingly, new developments in treatment options will probably be available.

Cell cycle deregulation in the neurons of Alzheimer's disease

The cell cycle consists of four main phases: G(1), S, G(2), and M. Most cells undergo these cycles up to 40-60 times in their life. However, neurons remain in a nondividing, nonreplicating phase, G(0). Neurons initiate but do not complete cell division, eventually entering apoptosis. Research has suggested that like cancer, Alzheimer's disease (AD) involves dysfunction in neuronal cell cycle reentry, leading to the development of the two-hit hypothesis of AD. The first hit is abnormal cell cycle reentry, which typically results in neuronal apoptosis and prevention of AD. However, with the second hit of chronic oxidative damage preventing apoptosis, neurons gain "immortality" analogous to tumor cells. Once both of these hits are activated, AD can develop and produce senile plaques and neurofibrillary tangles throughout brain tissue. In this review, we propose a mechanism for neuronal cell cycle reentry and the development of AD.

Activation of ataxia telangiectasia muted under experimental models and human Parkinson's disease

In the present study we demonstrated that neurotoxin MPP(+)-induced DNA damage is followed by ataxia telangiectasia muted (ATM) activation either in cerebellar granule cells (CGC) or in B65 cell line. In CGC, the selective ATM inhibitor KU-55933 showed neuroprotective effects against MPP(+)-induced neuronal cell loss and apoptosis, lending support to the key role of ATM in experimental models of Parkinson's disease. Likewise, we showed that knockdown of ATM levels in neuroblastoma B65 cells using an ATM-specific siRNA attenuates the phosphorylation of retinoblastoma protein without affecting other cell-cycle proteins involved in the G(0)/G(1) cell-cycle phase. Moreover, we demonstrated DNA damage, in human brain samples of PD patients. These findings support a model in which MPP(+) leads to ATM activation with a subsequent DNA damage response and activation of pRb. Therefore, this study demonstrates a new link between DNA damage by MPP(+) and cell-cycle re-entry through retinoblastoma protein phosphorylation.

S phase entry causes homocysteine-induced death while ataxia telangiectasia and Rad3 related protein functions anti-apoptotically to protect neurons

A major phenotype seen in neurodegenerative disorders is the selective loss of neurons due to apoptotic death and evidence suggests that inappropriate re-activation of cell cycle proteins in post-mitotic neurons may be responsible. To investigate whether reactivation of the G1 cell cycle proteins and S phase entry was linked with apoptosis, we examined homocysteine-induced neuronal cell death in a rat cortical neuron tissue culture system. Hyperhomocysteinaemia is a physiological risk factor for a variety of neurodegenerative diseases, including Alzheimer's disease. We found that in response to homocysteine treatment, cyclin D1, and cyclin-dependent kinases 4 and 2 translocated to the nucleus, and p27 levels decreased. Both cyclin-dependent kinases 4 and 2 regained catalytic activity, the G1 gatekeeper retinoblastoma protein was phosphorylated and DNA synthesis was detected, suggesting transit into S phase. Double-labelling immunofluorescence showed a 95% co-localization of anti-bromodeoxyuridine labelling with apoptotic markers, demonstrating that those cells that entered S phase eventually died. Neurons could be protected from homocysteine-induced death by methods that inhibited G1 phase progression, including down-regulation of cyclin D1 expression, inhibition of cyclin-dependent kinases 4 or 2 activity by small molecule inhibitors, or use of the c-Abl kinase inhibitor, Gleevec, which blocked cyclin D and cyclin-dependent kinase 4 nuclear translocation. However, blocking cell cycle progression post G1, using DNA replication inhibitors, did not prevent apoptosis, suggesting that death was not preventable post the G1-S phase checkpoint. While homocysteine treatment caused DNA damage and activated the DNA damage response, its mechanism of action was distinct from that of more traditional DNA damaging agents, such as camptothecin, as it was p53-independent. Likewise, inhibition of the DNA damage sensors, ataxia-telangiectasia mutant and ataxia telangiectasia and Rad3 related proteins, did not rescue apoptosis and in fact exacerbated death, suggesting that the DNA damage response might normally function neuroprotectively to block S phase-dependent apoptosis induction. As cell cycle events appear to be maintained in vivo in affected neurons for weeks to years before apoptosis is observed, activation of the DNA damage response might be able to hold cell cycle-induced death in check.

Targeting gonadotropins: an alternative option for Alzheimer disease treatment

Recent evidence indicates that, alongside oxidative stress, dysregulation of the cell cycle in neurons susceptible to degeneration in Alzheimer disease may play a crucial role in the initiation of the disease. As such, the role of reproductive hormones, which are closely associated with the cell cycle both during development and after birth, may be of key import. While estrogen has been the primary focus, the protective effects of hormone replacement therapy on cognition and dementia only during a “crucial period” led us to expand the study of hormonal influences to other members of the hypothalamic pituitary axis. Specifically, in this review, we focus on luteinizing hormone, which is not only increased in the sera of patients with Alzheimer disease but, like estrogen, is modulated by hormone replacement therapy and also influences cognitive behavior and pathogenic processing in animal models of the disease. Targeting gonadotropins may be a useful treatment strategy for disease targeting multiple pleiotropic downstream consequences.

Biomarkers in Alzheimer's disease: past, present and future

Epidemiological and molecular studies suggest that Alzheimer's disease (AD) has multiple etiologies including genetic mutations, genetic variations affecting susceptibility and environmental factors. These aspects can promote the formation and accumulation of insoluble amyloid-beta and hyperphosphorylated tau. Since the disease is multifactorial and clinical diagnosis is highly exclusive, the need for a sensitive, specific and reliable biomarker is crucial. The concept of a biomarker implies sensitivity and specificity relative to the condition being considered. For clinical practice, AD diagnosis has been based on adherence to clinical criteria such as the NINCDS/ADRDA and DSM-IV. A more recent set of diagnostic criteria proposed incorporates imaging findings into the diagnosis of AD. In this article, we consider the most studied candidates or group of candidates for AD biomarkers, including pathological processes and proteins (amyloid-beta, tau, oxidative stress, mitochondrial/metabolic changes and cell-cycle processes), or autoantibodies thereto, as well as genetic factors.

Redox control of the cell cycle in health and disease

The cellular oxidation and reduction (redox) environment is influenced by the production and removal of reactive oxygen species (ROS). In recent years, several reports support the hypothesis that cellular ROS levels could function as ''second messengers'' regulating numerous cellular processes, including proliferation. Periodic oscillations in the cellular redox environment, a redox cycle, regulate cell-cycle progression from quiescence (G(0)) to proliferation (G(1), S, G(2), and M) and back to quiescence. A loss in the redox control of the cell cycle could lead to aberrant proliferation, a hallmark of various human pathologies. This review discusses the literature that supports the concept of a redox cycle controlling the mammalian cell cycle, with an emphasis on how this control relates to proliferative disorders including cancer, wound healing, fibrosis, cardiovascular diseases, diabetes, and neurodegenerative diseases. We hypothesize that reestablishing the redox control of the cell cycle by manipulating the cellular redox environment could improve many aspects of the proliferative disorders.

Linking cell cycle reentry and DNA damage in neurodegeneration

Aberrant cell cycle activity and DNA damage have been observed in neurons in association with various neurodegenerative conditions. While there is strong evidence for a causative role for these events in neurotoxicity, it is unclear how they are triggered and why they are toxic. Here, we introduce a brief background of the current view on cell cycle activity and DNA damage in neurons and speculate on their relevance to neuronal survival. Furthermore, we suggest that the two events may be triggered in common by deregulation of fundamental processes, such as chromatin modulation, which are required for maintaining both DNA integrity and proper regulation of cell cycle gene expression.

Differential processing of amyloid-beta precursor protein directs human embryonic stem cell proliferation and differentiation into neuronal precursor cells

The amyloid-beta precursor protein (AbetaPP) is a ubiquitously expressed transmembrane protein whose cleavage product, the amyloid-beta (Abeta) protein, is deposited in amyloid plaques in neurodegenerative conditions such as Alzheimer disease, Down syndrome, and head injury. We recently reported that this protein, normally associated with neurodegenerative conditions, is expressed by human embryonic stem cells (hESCs). We now report that the differential processing of AbetaPP via secretase enzymes regulates the proliferation and differentiation of hESCs. hESCs endogenously produce amyloid-beta, which when added exogenously in soluble and fibrillar forms but not oligomeric forms markedly increased hESC proliferation. The inhibition of AbetaPP cleavage by beta-secretase inhibitors significantly suppressed hESC proliferation and promoted nestin expression, an early marker of neural precursor cell (NPC) formation. The induction of NPC differentiation via the non-amyloidogenic pathway was confirmed by the addition of secreted AbetaPPalpha, which suppressed hESC proliferation and promoted the formation of NPCs. Together these data suggest that differential processing of AbetaPP is normally required for embryonic neurogenesis.

Manganese neurotoxicity: lessons learned from longitudinal studies in nonhuman primates

BACKGROUND

Exposure to excess levels of the essential trace element manganese produces cognitive, psychiatric, and motor abnormalities. The understanding of Mn neurotoxicology is heavily governed by pathologic and neurochemical observations derived from rodent studies that often employ acute Mn exposures. The comparatively sparse studies incorporating in vivo neuroimaging in nonhuman primates provide invaluable insights on the effects of Mn on brain chemistry.

OBJECTIVES

The purpose of this review is to discuss important aspects of Mn neurotoxicology and to synthesize recent findings from one of the largest cohorts of nonhuman primates used to study the neurologic effects of chronic Mn exposure.

DISCUSSION

We reviewed our recent in vivo and ex vivo studies that have significantly advanced the understanding of Mn-induced neurotoxicity. In those studies, we administered weekly doses of 3.3-5.0 (n=4), 5.0-6.7 (n=5), or 8.3-10.0 mg Mn/kg (n=3) for 7-59 weeks to cynomolgus macaque monkeys. Animals expressed subtle deficits in cognition and motor function and decreases in the N-acetylaspartate-to-creatine ratio in the parietal cortex measured by magnetic resonance spectroscopy reflective of neuronal dysfunction. Impaired striatal dopamine release measured by positron emission tomography was observed in the absence of changes in markers of dopamine neuron degeneration. Neuropathology indicated decreased glutamine synthetase expression in the globus pallidus with otherwise normal markers of glutamatergic and GABAergic neurotransmission. Increased amyloid beta (A4) precursor-like protein 1 gene expression with multiple markers of neurodegeneration and glial cell activation was observed in the frontal cortex.

CONCLUSIONS

These findings provide new information on mechanisms by which Mn affects behavior, neurotransmitter function, and neuropathology in nonhuman primates.

Reduced amyloidogenic processing of the amyloid beta-protein precursor by the small-molecule Differentiation Inducing Factor-1

The detection of cell cycle proteins in Alzheimer's disease (AD) brains may represent an early event leading to neurodegeneration. To identify cell cycle modifiers with anti-Abeta properties, we assessed the effect of Differentiation-Inducing Factor-1 (DIF-1), a unique, small-molecule from Dictyostelium discoideum, on the proteolysis of the amyloid beta-protein precursor (APP) in a variety of different cell types. We show that DIF-1 slows cell cycle progression through G0/G1 that correlates with a reduction in cyclin D1 protein levels. Western blot analysis of DIF-treated cells and conditioned medium revealed decreases in the levels of secreted APP, mature APP, and C-terminal fragments. Assessment of conditioned media by sandwich ELISA showed reduced levels of Abeta40 and Abeta42, also demonstrating that treatment with DIF-1 effectively decreases the ratio of Abeta42 to Abeta40. In addition, DIF-1 significantly diminished APP phosphorylation at residue T668. Interestingly, site-directed mutagenesis of APP residue Thr668 to alanine or glutamic acid abolished the effect of DIF-1 on APP proteolysis and restored secreted levels of Abeta. Finally, DIF-1 prevented the accumulation of APP C-terminal fragments induced by the proteasome inhibitor lactacystin, and calpain inhibitor N-acetyl-leucyl-leucyl-norleucinal (ALLN). Our findings suggest that DIF-1 affects G0/G1-associated amyloidogenic processing of APP by a gamma-secretase-, proteasome- and calpain-insensitive pathway, and that this effect requires the presence of residue Thr668.

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.

An integral approach to the etiopathogenesis of human neurodegenerative diseases (HNDDs) and cancer. Possible therapeutic consequences within the frame of the trophic factor withdrawal syndrome (TFWS)

A novel and integral approach to the understanding of human neurodegenerative diseases (HNDDs) and cancer based upon the disruption of the intracellular dynamics of the hydrogen ion (H(+)) and its physiopathology, is advanced. From an etiopathological perspective, the activity and/or deficiency of different growth factors (GFs) in these pathologies are studied, and their relationships to intracellular acid-base homeostasis reviewed. Growth and trophic factor withdrawal in HNDDs indicate the need to further investigate the potential utilization of certain GFs in the treatment of Alzheimer disease and other neurodegenerative diseases. Platelet abnormalities and the therapeutic potential of platelet-derived growth factors in these pathologies, either through platelet transfusions or other clinical methods, are considered. Finally, the etiopathogenic mechanisms of apoptosis and antiapoptosis in HNDDs and cancer are viewed as opposite biochemical and biological disorders of cellular acid-base balance and their secondary effects on intracellular signaling pathways and aberrant cell metabolism are considered in the light of the both the seminal and most recent data available. The "trophic factor withdrawal syndrome" is described for the first time in English-speaking medical literature, as well as a Darwinian-like interpretation of cellular behavior related to specific and nonspecific aspects of cell biology.

Cell cycle proteins preceded neuronal death after chronic cerebral hypoperfusion in rats

OBJECTIVES

To explore the re-expression of cell cycle related proteins and delayed neuronal death after chronic cerebral hypoperfusion in rats and to investigate the relationship between aberrant expression of cell cycle proteins and apoptotic cell death.

METHODS

Rat model of chronic cerebral hypoperfusion was established by permanent bilateral common carotid arteries occlusion (2VO) in the retired rats. The apoptotic cells were assessed by TUNEL method. The expression of cell cycle related proteins, i.e. CDK4 and cyclin B1, were detected by immunohistochemical staining and Western blotting. A cyclin-dependent kinases (CDKs) inhibitor, roscovitine, was intracerebroventricularly administered 1 day before 2VO insult. Spatial learning behavior was assessed by the Morris water maze 7, 14 and 21 days after the surgery.

RESULTS

Aberrant expression of CDK4 and cyclin B1 became present 7 days after 2VO insult surgery and last for a long period. On the other hand, TUNEL positive cells appeared as early as 14 days after the surgery and peaked at day 21. Furthermore, roscovitine significantly improve behavioral deficit in the Morris water maze test 7 and 14 days after the surgery.

CONCLUSION

These findings indicated that aberrant expression of CDK4 and cyclin B1 takes place in the brain after chronic cerebral hypoperfusion in retired rat, and aberrant expression of cell cycle proteins preceded neuronal death in this model. Our data also suggest that the CDK inhibitor, roscovitine, has therapeutic potential for the treatment of dementia caused by chronic cerebral hypoperfusion.

Menopause, estrogen, and gonadotropins in Alzheimer's disease

For decades, Alzheimer's disease (AD) has been linked to aging, gender, and menopause. Not surprisingly, this led most investigators to focus on the role of estrogen. While undoubtedly important, estrogen is unlikely the key determinant of disease pathogenesis. Rather, it appears that estrogen may work in conjunction with a novel determinant of disease pathogenesis, namely gonadotropins. The fact that gonadotropins, specifically luteinizing hormone, play a pivotal role in disease is apparent from significant etiological, epidemiological, and pathological evidences. Moreover, targeting gonadotropins appears to have beneficial actions as a therapeutic regimen.

Increased APLP1 expression and neurodegeneration in the frontal cortex of manganese-exposed non-human primates

Chronic manganese (Mn) exposure produces a neurological syndrome with psychiatric, cognitive, and parkinsonian features. Gene expression profiling in the frontal cortex of Cynomologous macaques receiving 3.3-5.0 mg Mn/kg weekly for 10 months showed that 61 genes were increased and four genes were decreased relative to controls from a total of 6766 genes. Gene changes were associated with cell cycle regulation, DNA repair, apoptosis, ubiquitin-proteasome system, protein folding, cholesterol homeostasis, axonal/vesicular transport, and inflammation. Amyloid-beta (Abeta) precursor-like protein 1, a member of the amyloid precursor protein family, was the most highly up-regulated gene. Immunohistochemistry confirmed increased amyloid precursor-like protein 1 protein expression and revealed the presence of diffuse Abeta plaques in Mn-exposed frontal cortex. Cortical neurons and white matter fibers from Mn-exposed animals accumulated silver grains indicative of on-going degeneration. Cortical neurons also exhibited nuclear hypertrophy, intracytoplasmic vacuoles, and apoptosis stigmata. p53 immunolabeling was increased in the cytoplasm of neurons and in the nucleus and processes of glial cells in Mn-exposed tissue. In summary, chronic Mn exposure produces a cellular stress response leading to neurodegenerative changes and diffuse Abeta plaques in the frontal cortex. These changes may explain the subtle cognitive deficits previously demonstrated in these same animals.

Genetic signatures for a rodent model of Parkinson's disease using combinatorial optimization methods

This chapter illustrates the use of the combinatorial optimization models presented in Chapter 19 for the Feature Set selection and Gene Ordering problems to find genetic signatures for diseases using micro-array data. We demonstrate the quality of this approach by using a microarray dataset from a mouse model of Parkinson's disease. The results are accompanied by a description of the currently known molecular functions and biological processes of the genes in the signatures.

Neuronal binucleation in Alzheimer disease hippocampus

AIMS

The literature and teachings instruct that neurones in the adult brain are fully differentiated, quiescent cells that never divide. Somewhat surprisingly, and counter to such dogma, susceptible neurones in Alzheimer disease display an activated cell cycle phenotype. However, whether this leads to a coordinated procession through the cell cycle is unclear, particularly whether neurones enter anaphase and beyond. To begin to address this issue, in this study we sought to determine whether nuclear division occurs in these neurones.

METHODS

We examined a series of 101 archived, routinely stained hippocampal sections collected at post mortem for neuropathological evaluation for evidence of neuronal binucleation.

RESULTS

We report for the first time, binucleated neurones within the hippocampus in cases of Alzheimer disease but not in control cases (P < 0.05).

CONCLUSIONS

While a relatively rare event, occurring once every 20,000 neurones, this morphological evidence that neuronal cells within the cortical regions of the adult human brain in Alzheimer disease contain two nuclei supports the hypothesis that neuronal cells can re-enter into a coordinated cell cycle that culminates in nuclear division.

Enhanced proteasome-dependent degradation of the CDK inhibitor p27(kip1) in immortalized lymphocytes from Alzheimer's dementia patients

Cyclin-dependent kinase inhibitor p27(kip1) (p27), a critical determinant for cell cycle progression, is an important regulation target of mitogenic signals. We have recently reported the existence of a molecular link between decreased p27 levels and enhanced phosphorylation of pRb protein and proliferation of immortalized lymphocytes from Alzheimer's disease (AD) patients. These cell cycle disturbances might be considered systemic manifestations, which mirror changes thought to occur in the brain, where post-mitotic neurons have been shown to display various cell cycle markers prior to degeneration. This work was undertaken to delineate the molecular mechanisms underlying the p27 down-regulation associated with AD. To this end, we evaluated the p27 protein stability in control and AD lymphoblasts. Half-life of p27 protein was markedly reduced in lymphoblasts from AD patients compared with that in control cells. The increased phosphorylation of p27 at Thr187, rather than changes in the 26S proteasome activity, is likely responsible for the enhanced degradation of p27 in AD cells. The serum-induced enhanced proliferation of AD lymphoblasts and decreased levels of p27 were abrogated by calmodulin (CaM) antagonists. The findings presented here suggest that Ca(2+)/CaM-dependent overactivation of PI3K/Akt signaling cascade in AD cells, plays an important role in regulating p27 abundance by increasing its degradation in the ubiquitin-proteasome pathway.

The cell cycle hypothesis of Alzheimer's disease: Suggestions for drug development

The cell cycle of hypothesis of neural dysfunction in chronic neurodegenerative conditions such as Alzheimer's disease (AD) offers a unified approach to understanding both existing and novel strategies for drug development. At the present time, a ligand based approach is a pragmatic solution for identifying new chemical leads on which to base future discovery and optimisation. We have pursued a ligand based approach on the basis of public domain data to identify existing compounds capable of abrogating the cell cycle at the G0-G1 interface. Selected on this basis, irrespective of the tissue under study, we identified several classes of compounds as potential chemical leads. Of these compounds, at least ten have already been shown to be neuroprotective in animal models of acute neurodegeneration. Such compounds could form the basis of a screening exercise after development of suitable screening tools. Progressing of chemical leads through such an approach will be more efficient if future leads display relevant "drug-like" properties. Further, drug development in this arena should take account of the special concerns raised by targeting an elderly population. This will involve accounting for frequent polypharmacy in the aging population, and age-related alterations in physiology.

Pin1 in Alzheimer's disease: multiple substrates, one regulatory mechanism?

Presence of neuritic plaques and neurofibrillary tangles in the brain are two neuropathological hallmarks of Alzheimer's disease (AD), although the molecular basis of their coexistence remains elusive. The neurofibrillary tangles are composed of microtubule binding protein Tau, whereas neuritic plaques consist of amyloid-beta peptides derived from amyloid precursor protein (APP). Recently, the peptidyl-prolyl cis/trans isomerase Pin1 has been identified to regulate the function of certain proteins after phosphorylation and to play an important role in cell cycle regulation and cancer development. New data indicate that Pin1 also regulates the function and processing of Tau and APP, respectively, and is important for protecting against age-dependent neurodegeneration. Furthermore, Pin1 is the only gene known so far that, when deleted in mice, can cause both Tau and Abeta-related pathologies in an age-dependent manner, resembling many aspects of human Alzheimer's disease. Moreover, in the human AD brain Pin1 is downregulated or inhibited by oxidative modifications and/or genetic changes. These results suggest that Pin1 deregulation may provide a link between formation of tangles and plaques in AD.

Neuronal cell cycle re-entry mediates Alzheimer disease-type changes

Evidence showing the ectopic re-expression of cell cycle-related proteins in specific vulnerable neuronal populations in Alzheimer disease led us to formulate the hypothesis that neurodegeneration, like cancer, is a disease of inappropriate cell cycle control. To test this notion, we used adenoviral-mediated expression of c-myc and ras oncogenes to drive postmitotic primary cortical neurons into the cell cycle. Cell cycle re-entry in neurons was associated with increased DNA content, as determined using BrdU and DAPI, and the re-expression of cyclin B1, a marker for the G2/M phase of the cell cycle. Importantly, we also found that cell cycle re-entry in primary neurons leads to tau phosphorylation and conformational changes similar to that seen in Alzheimer disease. This study establishes that the cell cycle can be instigated in normally quiescent neuronal cells and results in a phenotype that shares features of degenerative neurons in Alzheimer disease. As such, our neuronal cell model may be extremely valuable for the development of novel therapeutic strategies.