Alzheimer's disease-like alterations in peripheral cells from presenilin-1 transgenic mice

Interactions of Mitochondria/Metabolism and Calcium Regulation in Alzheimer's Disease: A Calcinist Point of View

Decades of research suggest that alterations in calcium are central to the pathophysiology of Alzheimer's Disease (AD). Highly reproducible changes in calcium dynamics occur in cells from patients with both genetic and non-genetic forms of AD relative to controls. The most robust change is an exaggerated release of calcium from internal stores. Detailed analysis of these changes in animal and cell models of the AD-causing presenilin mutations reveal robust changes in ryanodine receptors, inositol tris-phosphate receptors, calcium leak channels and store activated calcium entry. Similar anomalies in calcium result when AD-like changes in mitochondrial enzymes or oxidative stress are induced experimentally. The calcium abnormalities can be directly linked to the altered tau phosphorylation, amyloid precursor protein processing and synaptic dysfunction that are defining features of AD. A better understanding of these changes is required before using calcium abnormalities as therapeutic targets.

Neurohormetic responses of quercetin and rutin in a cell line over-expressing the amyloid precursor protein (APPswe cells)

BACKGROUND

Plant secondary metabolites may induce adaptive cellular stress-responses in a variety of cells including neurons at the sub-toxic doses ingested by humans. Such 'neurohormesis' phenomenon, activated by flavonoids such as quercetin or rutin, may involve cell responses driven by modulation of signaling pathways which are responsible for its neuroprotective effects.

PURPOSE

We attempt to explore the molecular mechanisms involved in the neurohormetic responses to quercetin and rutin exposure, in a SH-SY5Y cell line which stably overexpresses the amyloid precursor protein (APP) Swedish mutation, based on a biphasic concentration-response relationship for cell viability.

METHODS

We examined the impact of both natural compounds, at concentrations in its hormetic range on the following cell parameters: chymotrypsin-like activity of the proteasome system; PARP-1 protein levels and expression and caspase activation; APP processing; and the main endogenous antioxidant enzymes.

RESULTS

Proteasome activities following quercetin or rutin treatment were significantly augmented in comparison with non-treated cells. Activity of caspase-3 was significantly attenuated by treatment with quercetin or rutin. Modest increased levels of PARP-1 protein and mRNA transcripts were observed in relation to the mild increase of proteasome activity. Significant reductions of the full-length APP and sAPP protein and APP mRNA levels were related to significant enhancements of α-secretase ADAM-10 protein and mRNA transcripts and significant increases of BACE processing in cells exposed to rutin. Furthermore, quercetin or rutin treatment displayed an overall increase of the four antioxidant enzymes.

CONCLUSIONS

The upregulation of the proteasome activity observed upon quercetin or rutin treatment could be afforded by a mild increased of PARP-1. Consequently, targeting the proteasome by quercetin or rutin to enhance its activity in a mild manner could avoid caspase activation. Moreover, it is likely that APP processing of cells upon rutin treatment is mostly driven by the non-amyloidogenic pathway leading to a putative reduction of βA production. Overall induction of endogenous antioxidant enzymes under quercetin or rutin treatments of APPswe cells might modulate its proteasome activity. We might conclude that quercetin and rutin might exert a neurohormetic cell response affecting various signaling pathways and molecular networks associated with modulation of proteasome function.

Mitochondrial oxygen consumption deficits in skeletal muscle isolated from an Alzheimer's disease-relevant murine model

Background

Age is considered a primary risk factor for neurodegenerative diseases including Alzheimer’s disease (AD). It is also now well understood that mitochondrial function declines with age. Mitochondrial deficits have been previously assessed in brain from both human autopsy tissue and disease-relevant transgenic mice. Recently it has been recognized that abnormalities of muscle may be an intrinsic aspect of AD and might contribute to the pathophysiology. However, deficits in mitochondrial function have yet to be clearly assessed in tissues outside the central nervous system (CNS). In the present study, we utilized a well-characterized AD-relevant transgenic mouse strain to assess mitochondrial respiratory deficits in both brain and muscle. In addition to mitochondrial function, we assessed levels of transgene-derived amyloid precursor protein (APP) in homogenates isolated from brain and muscle of these AD-relevant animals.

Results

We now demonstrate that skeletal muscles isolated from these animals have differential levels of mutant full-length APP depending on muscle type. Additionally, isolated muscle fibers from young transgenic mice (3 months) have significantly decreased maximal mitochondrial oxygen consumption capacity compared to non-transgenic, age-matched mice, with similar deficits to those previously described in brain.

Conclusions

This is the first study to directly examine mitochondrial function in skeletal muscle from an AD-relevant transgenic murine model. As with brain, these deficits in muscle are an early event, occurring prior to appearance of amyloid plaques.

Peripheral mitochondrial dysfunction in Alzheimer's disease: focus on lymphocytes

Alzheimer's disease (AD) is the most common progressive neurodegenerative disease. Today, AD affects millions of people worldwide and the number of AD cases will increase with increased life expectancy. The AD brain is marked by severe neurodegeneration like the loss of synapses and neurons, atrophy and depletion of neurotransmitter systems in the hippocampus and cerebral cortex. Recent findings suggest that these pathological changes are causally induced by mitochondrial dysfunction and increased oxidative stress. These changes are not only observed in the brain of AD patients but also in the periphery. In this review, we discuss the potential role of elevated apoptosis, increased oxidative stress and especially mitochondrial dysfunction as peripheral markers for the detection of AD in blood cells especially in lymphocytes. We discuss recent not otherwise published findings on the level of complex activities of the respiratory chain comprising mitochondrial respiration and the mitochondrial membrane potential (MMP). We obtained decreased basal MMP levels in lymphocytes from AD patients as well as enhanced sensitivity to different complex inhibitors of the respiratory chain. These changes are in line with mitochondrial defects obtained in AD cell and animal models, and in post-mortem AD tissue. Importantly, these mitochondrial alterations where not only found in AD patients but also in patients with mild cognitive impairment (MCI). These new findings point to a relevance of mitochondrial function as an early peripheral marker for the detection of AD and MCI.

Altered cell cycle-related gene expression in brain and lymphocytes from a transgenic mouse model of Alzheimer's disease [amyloid precursor protein/presenilin 1 (PS1)]

Cumulative evidence indicates that aberrant re-expression of many cell cycle-related proteins and inappropriate neuronal cell cycle control are critical events in Alzheimer's disease (AD) pathogenesis. Evidence of cell cycle activation in post-mitotic neurons has also been observed in murine models of AD, despite the fact that most of these mice do not show massive loss of neuronal bodies. Dysfunction of the cell cycle appears to affect cells other than neurons, as peripheral cells, such as lymphocytes and fibroblasts from patients with AD, show an altered response to mitogenic stimulation. We sought to determine whether cell cycle disturbances are present simultaneously in both brain and peripheral cells from the amyloid precursor protein (APP)/presenilin 1 (PS1) mouse model of AD, in order to validate the use of peripheral cells from patients not only to study cell cycle abnormalities as a pathogenic feature of AD, but also as a means to test novel therapeutic approaches. By using cell cycle pathway-specific RT(2)Profiler™ PCR Arrays, we detected changes in a number of cell cycle-related genes in brain as well as in lymphocytes from APP/PS1 mice. Moreover, we found enhanced 5'-bromo-2'-deoxyuridine incorporation into DNA in lymphocytes from APP/PS1 mice, and increased expression of the cell proliferation marker proliferating cell nuclear antigen (PCNA), and the cyclin-dependent kinase (CDK) inhibitor Cdkn2a, as detected by immunohistochemistry in cortical neurons of the APP/PS1 mice. Taken together, the cell cycle-related changes in brain and blood cells reported here support the mitosis failure hypothesis in AD and validate the use of peripheral cells as surrogate tissue to study the molecular basis of AD pathogenesis.

Neuregulin-1 protects against neurotoxicities induced by Swedish amyloid precursor protein via the ErbB4 receptor

Neuregulin-1 (NRG1) plays an important role in the development and plasticity of the brain and exhibits potent neuroprotective properties. However, little information on its role in Alzheimer's disease (AD) is known. The neuroprotective effect and mechanisms of NRG1 in SH-SY5Y cells overexpressing the Swedish mutant form of amyloid precursor protein (Swe-APP) and primary cortical neuronal cells treated with amyloid beta peptide(1-42) (Aβ(1-42)) were investigated in this study. NRG1 attenuated Swe-APP- or Aβ(1-42)-induced lactate dehydrogenase (LDH) release in a concentration-dependent manner. The mitigating effects of NRG1 on neuronal cell death were blocked by ErbB4 inhibition, a key NRG1 receptor, which suggests a role of ErbB4 in the neuroprotective function of NRG1. Moreover, NRG1 reduced the number of Swe-APP- and Aβ(1-42)-induced TUNEL-positive SH-SY5Y cells and primary cortical neurons, respectively. NRG1 reduced the accumulation of reactive oxygen species and attenuated Swe-APP-induced mitochondrial membrane potential loss. NRG1 also induced the upregulation of the expression of the anti-apoptotic protein, Bcl-2, and decreased caspase-3 activation. Collectively, our results demonstrate that NRG1 exerts neuroprotective effects via the ErbB4 receptor, which suggests the neuroprotective potential of NRG1 in AD.

Constitutive cAMP response element binding protein (CREB) activation by Alzheimer's disease presenilin-driven inositol trisphosphate receptor (InsP3R) Ca2+ signaling

Mutations in presenilins (PS) account for most early-onset familial Alzheimer's disease (FAD). Accumulating evidence suggests that disrupted Ca(2+) signaling may play a proximal role in FAD specifically, and Alzheimer's disease (AD) more generally, but its links to the pathogenesis of AD are obscure. Here we demonstrate that expression of FAD mutant PS constitutively activates the transcription factor cAMP response element binding protein (CREB) and CREB target gene expression in cultured neuronal cells and AD mouse models. Constitutive CREB activation was associated with and dependent on constitutive activation of Ca(2+)/CaM kinase kinase β and CaM kinase IV (CaMKIV). Depletion of endoplasmic reticulum Ca(2+) stores or plasma membrane phosphatidylinositol-bisphosphate and pharmacologic inhibition or knockdown of the expression of the inositol trisphosphate receptor (InsP(3)R) Ca(2+) release channel each abolished FAD PS-associated constitutive CaMKIV and CREB phosphorylation. CREB and CaMKIV phosphorylation and CREB target gene expression, including nitric oxide synthase and c-fos, were enhanced in brains of M146V-KI and 3xTg-AD mice expressing FAD mutant PS1 knocked into the mouse locus. FAD mutant PS-expressing cells demonstrated enhanced cell death and sensitivity to Aβ toxicity, which were normalized by interfering with the InsP(3)R-CAMKIV-CREB pathway. Thus, constitutive CREB phosphorylation by exaggerated InsP(3)R Ca(2+) signaling in FAD PS-expressing cells may represent a signaling pathway involved in the pathogenesis of AD.

Enhanced ROS generation mediated by Alzheimer's disease presenilin regulation of InsP3R Ca2+ signaling

Familial Alzheimer's disease (FAD) is caused by mutations in amyloid precursor protein and presenilins (PS1, PS2). Many FAD-linked PS mutations affect intracellular calcium (Ca(2+)) homeostasis by proximal mechanisms independent of amyloid production by dramatically enhancing gating of the inositol trisphosphate receptor (InsP(3)R) intracellular Ca(2+) release channel by a gain-of-function effect that mirrors genetics of FAD and is independent of secretase activity. Electrophysiological recordings of InsP(3)R in FAD patient B cells, cortical neurons of asymptomatic PS1-AD mice, and other cells revealed they have higher occupancy in a high open probability burst mode, resulting in enhanced Ca(2+) signaling. Exaggerated Ca(2+) signaling through this mechanism results in enhanced generation of reactive oxygen species, believed to be an important component in AD pathogenesis. Exaggerated Ca(2+) signaling through InsP(3)R-PS interaction is a disease specific and robust proximal mechanism in AD that may contribute to the pathology of AD by enhanced generation of reactive oxygen species.

Presenilin/gamma-Secretase and Inflammation

Presenilins (PS) are the catalytic components of γ-secretase, an aspartyl protease that regulates through proteolytic processing the function of multiple signaling proteins. Specially relevant is the γ-secretase-dependent cleavage of the β-amyloid precursor protein (APP) since generates the β-amyloid (Aβ) peptides that aggregate and accumulate in the brain of Alzheimer's disease (AD) patients. Abnormal processing and/or accumulation of Aβ disrupt synaptic and metabolic processes leading to neuron dysfunction and neurodegeneration. Studies in presenilin conditional knockout mice have revealed that presenilin-1 is essential for age-dependent Aβ accumulation and inflammation. By contrast, mutations in the presenilin genes responsible for early onset familial AD cause rapid disease progression and accentuate clinical and pathological features including inflammation. In addition, a number of loss of function mutations in presenilin-1 have been recently associated to non-Alzheimer's dementias including frontotemporal dementia and dementia with Lewy bodies. In agreement, total loss of presenilin function in the brain results in striking neurodegeneration and inflammation, which includes activation of glial cells and induction of proinflammatory genes, besides altered inflammatory responses in the periphery. Interestingly, some non-steroidal anti-inflammatory drugs that slow cognitive decline and reduce the risk of AD, decrease amyloidogenic Aβ42 levels by modulating allosterically PS/γ-secretase. In this review, I present current evidence supporting a role of presenilin/γ-secretase signaling on gliogenesis and gliosis in normal and pathological conditions. Understanding the cellular mechanisms regulated by presenilin/γ-secretase during chronic inflammatory processes may provide new approaches for the development of effective therapeutic strategies for AD.

Presenilin transgenic mice as models of Alzheimer's disease

Mutations in presenilin-1 (PS1) and presenilin-2 (PS2) cause familial Alzheimer's disease (FAD). Presenilins influence multiple molecular pathways and are best known for their role in the gamma-secretase cleavage of type I transmembrane proteins including the amyloid precursor protein (APP). PS1 and PS2 FAD mutant transgenic mice have been generated using a variety of promoters. PS1-associated FAD mutations have also been knocked into the endogenous mouse gene. PS FAD mutant mice consistently show elevations of Abeta42 with little if any effect on Abeta40. When crossed with plaque forming APP FAD mutant lines, the PS1 FAD mutants cause earlier and more extensive plaque deposition. Although single transgenic PS1 or PS2 mice do not form plaques, they exhibit a number of pathological features including age-related neuronal and synaptic loss as well as vascular pathology. They also exhibit increased susceptibility to excitotoxic injury most likely on the basis of exaggerated calcium release from the endoplasmic reticulum. Electrophysiologically long-term potentiation in the hippocampus is increased in young PS1 FAD mutant mice but this effect appears to be lost with aging. In most studies neurogenesis in the adult hippocampus is also impaired by PS1 FAD mutants. Mice in which PS1 has been conditionally knocked out in adult forebrain on a PS2 null background (PS1/2 cDKO) develop a striking neurodegeneration that mimics AD neuropathology in being associated with neuronal and synaptic loss, astrogliosis and hyperphosphorylation of tau, although it is not accompanied by plaque deposits. The relevance of PS transgenic mice as models of AD is discussed.

Can peripheral leukocytes be used as Alzheimer's disease biomarkers?

Alzheimer's disease (AD) is the leading cause of dementia in elderly populations throughout the world and its incidence is on the rise. Current clinical diagnosis of AD requires intensive examination that includes neuropsychological testing and costly brain imaging techniques, and a definitive diagnosis can only be made upon postmortem neuropathological examination. Additionally, antemortem clinical AD diagnosis is typically administered following onset of cognitive and behavioral symptoms. As these symptoms emerge relatively late in disease progression, therapeutic intervention occurs after significant neurodegeneration, thereby limiting efficacy. The identification of noninvasive diagnostic biomarkers of AD is becoming increasingly important to make diagnosis more widely available to clinics with limited access to neuropsychological testing or state-of-the-art brain imaging, reduce the cost of clinical diagnosis, provide a biological measure to track the course of therapeutic intervention, and most importantly, allow for earlier diagnosis--possibly even during the prodromal phase--with hopes of therapeutic intervention prior to appreciable neurodegeneration. Circulating leukocytes are attractive candidate AD biomarkers as they can be obtained in a minimally invasive manner and are easily analyzed by widely available flow cytometry techniques. In this review, we critically analyze the potential utility of peripheral leukocytes as biological markers for AD.

PKR, the double stranded RNA-dependent protein kinase as a critical target in Alzheimer's disease

Amyloid β-peptide (Aβ) deposits and neurofibrillary tangles are key hallmarks in Alzheimer's disease (AD). Aβ stimulates many signal transducers involved in the neuronal death. However, many mechanisms remain to be elucidated because no definitive therapy of AD exists. Some studies have focused on the control of translation which involves eIF2 and eIF4E, main eukaryotic factors of initiation. The availability of these factors depends on the activation of the double-stranded RNA-dependent protein kinase (PKR) and the mammalian target of rapamycin (mTOR), respectively. mTOR positively regulates the translation while PKR results in a protein synthesis shutdown. Many studies demonstrated that the PKR signalling pathway is up-regulated in cellular and animal models of AD and in the brain of AD patients. Interestingly, our results showed that phosphorylated PKR and eIF2α levels were significantly increased in lymphocytes of AD patients. These modifications were significantly correlated with cognitive and memory test scores performed in AD patients. On the contrary, the mTOR signalling pathway is down-regulated in cellular and animal models of AD. Recently, we showed that p53, regulated protein in development and DNA damage response 1 and tuberous sclerosis complex 2 could represent molecular links between PKR and mTOR signalling pathways. PKR could be an early biomarker of the neuronal death and a critical target for a therapeutic programme in AD.

PKR, a cognitive decline biomarker, can regulate translation via two consecutive molecular targets p53 and Redd1 in lymphocytes of AD patients

In Alzheimer's disease (AD), the control of translation is dysregulated, precisely, two opposite pathways: double-stranded RNA-dependent protein kinase (PKR) is up-regulated and mammalian target of rapamycin (mTOR) is down-regulated. These biochemical alterations were found at the periphery in lymphocytes of AD patients and were significantly correlated with cognitive and memory test scores. However, the molecular crosslink between these two opposite signalling pathways remains unknown. The tumour suppressor p53 and Redd1 (regulated in development and DNA damage response) could be two downstream targets of active PKR to explain the breakdown of translation in AD patients. In this study, the protein and gene levels of p53 and Redd1 were assayed in lymphocytes of AD patients and in age-matched controls by Western blotting and RT-PCR. Furthermore, correlations were analysed with both the level of active PKR and the Mini Mental State Examination score (MMSE). The results show that the gene and protein levels of p53 and Redd1 were significantly increased about 1.5-fold for both gene and Redd1 protein and 2.3-fold for active p53 in AD lymphocytes compared to age-matched controls. Furthermore, statistical correlations between proteins and genes suggest that active PKR could phosphorylate p53 which could induce the transcription of Redd1 gene. No correlations were found between MMSE scores and levels of p53 or Redd1, contrary to active PKR levels. PKR represents a cognitive decline biomarker able to dysregulate translation via two consecutive targets p53 and Redd1 in AD lymphocytes.

Defects of immune regulation in the presenilin-1 mutant knockin mouse

Mutations in the presenilin-1 (PS1) gene are causally linked to early-onset Alzheimer's disease (AD). Studies of neurons suggest that PS1 mutations result in a gain-of-function, which perturbs calcium regulation and increases cell vulnerability to apoptosis. Alterations in immune cell function have also been demonstrated in AD, and a role for PS1 in immune regulation has been suggested recently. We now report that splenocytes from PS1-mutant (M146V) knockin mice exhibit increased caspase activity, abnormal calcium regulation and aberrant mitochondrial function. Isolated splenic T cells from PS1-mutant mice respond poorly to proliferative signals and have downregulated cluster designation 3 and interleukin (IL)- 2-receptor expression necessary for a normal T-cell immune response. Thus, adverse effects of a mutation that causes AD on immune function that involves perturbed calcium regulation and cytokine signaling in lymphocytes, and associated sensitivity of lymphocytes to apoptosis are demonstrated. These findings suggest that abnormalities in immune function might play major roles in the pathogenesis of AD.

Enhanced apoptosis, oxidative stress and mitochondrial dysfunction in lymphocytes as potential biomarkers for Alzheimer's disease

Alzheimer's disease (AD) is the most common progressive neurodegenerative disease. Today, AD affects millions of people worldwide and the number of AD cases will increase with increased life expectancy. The AD brain is marked by severe neurodegeneration like the loss of synapses and neurons, atrophy and depletion of neurotransmitter systems in the hippocampus and cerebral cortex. Recent findings suggest that these pathological changes are causally induced by mitochondrial dysfunction, increased oxidative stress and elevated apoptosis. Until now, AD cannot be diagnosed by a valid clinical method or a biomarker before the disease has progressed so far that dementia is present. Furthermore, no valid method is available to determine which patient with mild cognitive impairment (MCI) will progress to AD. Therefore, a correct diagnosis in the early stage of AD is not only of importance considering that early drug treatment is more effective but also that the psychological burden of the patients and relatives could be decreased. In this review, we discuss the potential role of elevated apoptosis, increased oxidative stress and mitochondrial dysfunction as biomarker for AD in a peripheral cell model, the lymphocytes.

Increased T-cell reactivity and elevated levels of CD8+ memory T-cells in Alzheimer's disease-patients and T-cell hyporeactivity in an Alzheimer's disease-mouse model: implications for immunotherapy

Neuroinflammation is observed in neurodegenerative diseases like Alzheimer's disease (AD). However, a little is known about the mechanisms of neural-immune interactions. The involvement of peripheral T-cell function in AD is still far from clear, though it plays an important role in immunotherapy. The aim of this study was to determine peripheral T-cell reactivity in AD patients and in an AD mouse model. Mitogenic activation via ligation of the T-cell receptor (TCR) with PHA-L was measured in T lymphocytes from AD patients and Thy1(APP 751SL) x HMG(PS1 M146L)-transgenic mice (APP x PS1). In order to uncover failures in TCR signaling, the TCR was also bypassed by PMA and ionomycin treatment. All patients were sporadic late onset cases and the transgenic mice expressed no mutant APP in lymphocytes, so that direct interactions of mutant APP on T-cell function can be excluded. CD4+ and CD8+ T-cell showed increased reactivity (tyrosine phosphorylation, CD69 expression, and proliferation) in AD, while APP x PS1 transgenic mice displayed hyporeactive CD8+ T-cells after TCR ligation. Increased levels of CD8+ T memory cells and down regulation of CD8 receptor were found in AD and the animal model. Anergic TCR uncoupling was associated with loss of MAPK signaling (p38, ERK1 and ERK2) in APP x PS1. Our data implicate the generation of reactive memory T-cell in AD and of anergic memory T-cells in transgenic mice and should be taken into concern when designing immunotherapy.

Calcium dysregulation in Alzheimer's disease

Alzheimer disease (AD) is the most common form of adult dementia. Its pathological hallmarks are synaptic degeneration, deposition of amyloid plaques and neurofibrillary tangles, leading to neuronal loss. A few hypotheses have been proposed to explain AD pathogenesis. The beta-amyloid (Abeta) and hyperphosphorylated tau hypotheses suggest that these proteins are the main players in AD development. Another hypothesis proposes that the dysregulation of calcium homeostasis may be a key factor in accelerating other pathological changes. Although Abeta and tau have been extensively studied, recently published data provide a growing body of evidence supporting the critical role of calcium signalling in AD. For example, presenilins, which are mutated in familial cases of AD, were demonstrated to form low conductance calcium channels in the ER and elevated cytosolic calcium concentration increases amyloid generation. Moreover, memantine, an antagonist of the NMDA-calcium channel receptor, has been found to have a beneficial effect for AD patients offering novel possibilities for a calcium signalling targeted therapy of AD. This review underscores the growing importance of calcium ions in AD development and focuses on the relevant aspects of calcium homeostasis.

Alzheimer's disease: a lesson from mitochondrial dysfunction

Extensive literature exists supporting a role for mitochondrial dysfunction and oxidative damage in the pathogenesis of Alzheimer's disease. Mitochondria are a major source of intracellular reactive oxygen species and are particularly vulnerable to oxidative stress. This review discusses evidence supporting the notion that mitochondrial dysfunction is intimately associated with Alzheimer's disease pathogenesis. Furthermore, the potential connection between mitochondrial dysfunction/oxidative stress and autophagy in Alzheimer's disease is also discussed. As a result of insufficient digestion of oxidatively damaged macromolecules and organelles by autophagy, neurons progressively accumulate lipofuscin (biological garbage) that could exacerbate neuronal dysfunction. The knowledge that mitochondrial dysfunction has a preponderant role in several pathological conditions instigated the development of mitochondrial antioxidant therapies. Mitochondria-targeted antioxidant treatments are briefly discussed in this review.

Effects of Alzheimer's amyloid-beta and tau protein on mitochondrial function -- role of glucose metabolism and insulin signalling

Alzheimer's disease (AD) is the most frequent form of dementia among the elderly and is characterized by neuropathological hallmarks of extracellular amyloid-beta (Abeta) plaques and intracellular neurofibrillary tangles composed of abnormally hyperphosphorylated microtubular protein tau in the brains of AD patients. Of note, current data illustrate a complex interplay between the amyloid and tau pathology during the course of the disease. We hypothesize a direct impact of abnormally phosphorylated tau and Abeta on proteins/enzymes involved in metabolism, respiratory chain function and cellular detoxification. Probably at the level of mitochondria, both Alzheimer proteins exhibit synergistic effects finally leading to/accelerating neurodegenerative mechanisms. Moreover, accumulating evidence that mitochondria failure, reduced glucose utilization and deficient energy metabolism occur already very early in the course of the disease suggests a role of impaired insulin signalling in the pathogenesis of AD. Thus, this review addresses also the question if mitochondrial dysfunction may represent a link between diabetes and AD.

Calnuc binds to Alzheimer's beta-amyloid precursor protein and affects its biogenesis

Calnuc, a Golgi calcium binding protein, plays a key role in the constitution of calcium storage. Abnormal calcium homeostasis has been linked to Alzheimer's disease (AD). Excessive production and/or accumulation of beta-amyloid (Abeta) peptides that are proteolytically derived from the beta-amyloid precursor protein (APP) have been linked to the pathogenesis of AD. APP has also been indicated to play multiple physiological functions. In this study, we demonstrate that calnuc interacts with APP through direct binding to the carboxyl-terminal region of APP, possibly in a calcium-sensitive manner. Immunofluorescence study revealed that the two proteins co-localize in the Golgi in both cultured cells and mouse brains. Over-expression of calnuc in neuroblastoma cells significantly reduces the level of endogenous APP. Conversely, down-regulation of calnuc by siRNA increases cellular levels of APP. Additionally, we show that over-expression of calnuc down-regulates the APP mRNA level and inhibits APP biosynthesis, which in turn results in a parallel reduction of APP proteolytic metabolites, sAPP, CTFs and Abeta. Furthermore, we found that the level of calnuc was significantly decreased in the brain of AD patients as compared with that of age-matched non-AD controls. Our results suggest a novel function of calnuc in modulating the levels of APP and its proteolytic metabolites, which may further affect the patho/physiological functions of APP including AD pathogenesis.

Apolipoprotein E epsilon 4 is associated with an increased vulnerability to cell death in Alzheimer’s disease

The presumption to suffer from Alzheimer's disease (AD) accelerates with aging. One important risk factor seems to be the isoform epsilon 4 of the apolipoprotein E gene (Apo epsilon 4), which increases the risk to develop AD at an earlier age. Furthermore, convincing evidence is provided that apoptotic cell death mechanisms play an important role in neuronal cell death in AD. In the present study, we investigated whether abnormalities in apoptosis and caspase-3 activity can be found at the level of lymphocytes and a T cell subtype, CD4 T cells, from AD patients compared to aged sex- and ApoE genotype-matched non-demented controls. Under different experimental conditions (at baseline or after in vitro incubation in the presence of proapoptotic stimuli) increased levels of apoptosis and enhanced caspase-3 activity were detected in lymphocytes from AD patients. This difference was most pronounced in the CD4(+) T cell subtype. Notably, we found a significant increase of apoptotic cells and caspase-3 activity in lymphocytes from AD patients bearing one or two alleles of the ApoE4 compared to non-E4 carriers. Again, these effects were strongest in CD4(+) T cells. Circulating amyloid-beta (A beta) levels did not differ between AD patients bearing ApoE4 and non-ApoE4 and age-matched controls. Therefore, it is likely that circulating A beta is not responsible for the observed effects, which might rather reflect an ongoing systemic response in AD, e.g. an increase in CD95 expression.

Aging sensitizes toward ROS formation and lipid peroxidation in PS1M146L transgenic mice

Mutations in the presenilins (PS) account for the majority of familial Alzheimer disease (FAD) cases. To test the hypothesis that oxidative stress can underlie the deleterious effects of presenilin mutations, we analyzed lipid peroxidation products (4-hydroxynonenal (HNE) and malondialdehyde) and antioxidant defenses in brain tissue and levels of reactive oxygen species (ROS) in splenic lymphocytes from transgenic mice bearing human PS1 with the M146L mutation (PS1M146L) compared to those from mice transgenic for wild-type human PS1 (PS1wt) and nontransgenic littermate control mice. In brain tissue, HNE levels were increased only in aged (19-22 months) PS1M146L transgenic animals compared to PS1wt mice and not in young (3-4 months) or middle-aged mice (13-15 months). Similarly, in splenic lymphocytes expressing the transgenic PS1 proteins, mitochondrial and cytosolic ROS levels were elevated to 142.1 and 120.5% relative to controls only in cells from aged PS1M146L animals. Additionally, brain tissue HNE levels were positively correlated with mitochondrial ROS levels in splenic lymphocytes, indicating that oxidative stress can be detected in different tissues of PS1 transgenic mice. Antioxidant defenses (activities of antioxidant enzymes Cu/Zn-SOD, GPx, or GR) or susceptibility to in vitro oxidative stimulation was unaltered. In summary, these results demonstrate that the PS1M146L mutation increases mitochondrial ROS formation and oxidative damage in aged mice. Hence, oxidative stress caused by the combined effects of aging and PS1 mutations may be causative for triggering neurodegenerative events in FAD patients.

Mefenamic acid shows neuroprotective effects and improves cognitive impairment in in vitro and in vivo Alzheimer's disease models

Nonsteroidal anti-inflammatory drugs (NSAIDs) exert anti-inflammatory, analgesic, and antipyretic activities and suppress prostaglandin synthesis by inhibiting cyclooxygenase, an enzyme that catalyzes the formation of prostaglandin precursors from arachidonic acid. Epidemiological observations indicate that the long-term treatment of patients suffering from rheumatoid arthritis with NSAIDs results in reduced risk and delayed onset of Alzheimer's disease. In this study, we investigated the therapeutic potential for Alzheimer's disease of mefenamic acid, a commonly used NSAID that is a cyclooxygenase-1 and 2 inhibitor with only moderate anti-inflammatory properties. We found that mefenamic acid attenuates the neurotoxicities induced by amyloid beta peptide (Abeta)(1-42) treatment and the expression of a Swedish double mutation (KM595/596NL) of amyloid precursor protein (Swe-APP) or the C-terminal fragments of APP (APP-CTs) in neuronal cells. We also show that mefenamic acid decreases the production of the free radical nitric oxide and reduces cytochrome c release from mitochondria induced by Abeta(1-42), Swe-APP, or APP-CTs in neuronal cells. In addition, mefenamic acid up-regulates expression of the antiapoptotic protein Bcl-X(L). Moreover, our study demonstrates for the first time that mefenamic acid improves learning and memory impairment in an Abeta(1-42)-infused Alzheimer's disease rat model. Taking these in vitro and in vivo results together, our study suggests that mefenamic acid could be used as a therapeutic agent in Alzheimer's disease.

Pathophysiology of Alzheimer's Disease

Tremendous progress has been made in understanding the processes of the Alzheimer's disease (AD) cascade, laying the groundwork for improvements in diagnosis and treatment. Advancement has been made in understanding the genetic basis of AD, with identification of causative genes for early-onset familial AD, and the role of the polymorphism of the APOE gene in the late-onset form of the disease. Understanding cerebral degeneration and accumulation of beta-amyloid has generated hopes for discovery of disease-modifying treatments. Progress is needed in understanding the mechanisms that link beta-amyloid accumulation and neuronal death. The next 5 years will be crucial in this respect.

Altered transcriptional regulators in response to serum in immortalized lymphocytes from Alzheimer's disease patients

Cell cycle disturbances may precede neuronal death in Alzheimer's disease (AD). We described alterations, in lymphocytes from AD patients, on the activity of two transcription factors, E2F and NF-kappaB, involved in cell proliferation and survival regulation, demonstrating that cell cycle dysfunction also occurs in peripheral cells. The analysis of E2F-DNA binding activity revealed lower signal intensity of protein-DNA complexes in AD cells, which correlated with increased phosphorylation of retinoblastoma (pRb) related proteins and enhanced proliferation. The calmodulin (CaM) antagonist calmidazolium (CMZ) abrogated the increased activity of AD cells by partially dephosphorylating pRb and p130. The NF-kappaB-DNA binding activity increased as cell progress through the cell cycle. The reduced NF-kappaB activation observed in AD cells appears not to be related to the increased phosphorylation of the pRb family proteins nor with the enhanced proliferative activity of AD cells, but seems to protect them from death induced by the loss of trophic support. Ca2+/CaM antagonists rescue NF-kappaB-DNA binding activity and sensitize AD cells to serum withdrawal. These observations suggest that disruption of Ca2+/CaM signaling pathway could be linked mechanistically to its pro cell survival actions, promoting enhanced proliferation or decreased cell death depending on the presence of growth-stimulatory signals.

Mitochondrial function in fibroblasts with aging in culture and/or Alzheimer's disease

Mitochondrial membrane potentials (MMP) reflect the functional state of the mitochondria within cells. Our recently published method provides a quantitative estimate of the MMP of populations of mitochondrial-like particles (MLP) within living cells at 37 degrees C using the combination of conventional fluorescence microscopy, 3D-deconvolution and exhaustive photon reassignment (EPR). Although the method does not provide an absolute measure of MMP, these relative MMP allow direct comparison between various mitochondria in cells at various ages in culture and in different cell lines from multiple patients. Fibroblasts lines from four Alzheimer's disease (AD) patients bearing the presenilin-1 (PS-1) mutation and four appropriate controls were evaluated at different ages in culture. The results showed a large variation in the relative MMP, cell size and sum of relative MMP of all MLP within each cell or within each cell line. Nevertheless, combining the values of relative MMP for the cell lines in each group revealed changes in distribution with age in culture. The relative MMP decreased while the cell sizes and sum of relative MMP within each cell increased with age in fibroblasts. Values did not differ between controls and the AD patients bearing PS-1 mutation at any age in cultures. This new, sensitive and quantitative estimate of relative MMP indicates that under non-stressed conditions relative MMP change with aging in culture, but relative MMP do not differ between controls and AD subjects.

Biomarkers for apoptosis in Alzheimer's disease

Alzheimer's disease (AD) affects millions of people worldwide and the number of AD cases will increase with increased life expectancy. Today there is no cure for this devastating and always lethal disease and therefore it is of great interest for patients, relatives and societies to find new drugs that can hinder the disease process. During the progression of AD a substantial amount of neurons degenerate in the brain. The mechanisms of cell death involved in AD have not been fully elucidated. However, there are several reports showing that neurons die partly by apoptosis in the AD brain. Drugs blocking apoptosis could therefore be potentially useful for early prevention of neuronal cell death. Biomarkers for apoptosis should be important tools in the evaluation of drug effects and in the diagnostics of AD. Here we review the current knowledge in the field and discuss potential biomarkers for apoptosis in AD.

alpha-keto-beta-methyl-n-valeric acid diminishes reactive oxygen species and alters endoplasmic reticulum Ca(2+) stores

Mitochondrial dysfunction and oxidative stress occur in neurodegenerative diseases. Other results show that bombesin-releasable calcium stores (BRCS) from the endoplasmic reticulum (ER) are exaggerated in fibroblasts from patients with Alzheimer's disease (AD) compared with controls and in fibroblasts from a young control treated with H(2)O(2). We hypothesize that alterations in oxidative stress underlie the exaggeration in BRCS in AD, and that appropriate antioxidants may be useful in treating this abnormality. Two indicators of different oxidant species were used to determine the effects of select oxidants on cellular oxidation status: carboxydichlorofluorescein (c-DCF) to detect reactive oxygen species (ROS), and 4-amino-5-methylamino-2',7'-difluorofluorescein (DAF) to detect nitric oxide (NO(.-)). Various conditions that induce ROS, including H(2)O(2), oxygen/glucose deprivation, and 3-morpholinosyndnonimine (SIN-1), were used to test the ability of alpha-keto-ss-methyl-n-valeric acid (KMV) to scavenge ROS. KMV diminished c-DCF-detectable ROS that were induced by H(2)O(2), oxygen/glucose deprivation, or SIN-1 in PC12 cells, primary neuronal cultures, or fibroblasts. Furthermore, KMV reduced the H(2)O(2)-induced increase in BRCS and diminished the elevation in BRCS in cells from AD patients to control levels. On the other hand, DAF-detectable NO(.-) induced by SIN-1 was not scavenged by KMV and did not exaggerate BRCS. The results indicate that KMV is an effective antioxidant of c-DCF-detectable ROS. The effects of KMV are not cell type specific, but are ROS specific. The same H(2)O(2)-induced ROS that reacts with KMV may also underlie the changes in BRCS related to AD. Thus, KMV ameliorates the effects of ROS on calcium homeostasis related to oxidative stress and to AD.

Pathways towards and away from Alzheimer's disease

Slowly but surely, Alzheimer's disease (AD) patients lose their memory and their cognitive abilities, and even their personalities may change dramatically. These changes are due to the progressive dysfunction and death of nerve cells that are responsible for the storage and processing of information. Although drugs can temporarily improve memory, at present there are no treatments that can stop or reverse the inexorable neurodegenerative process. But rapid progress towards understanding the cellular and molecular alterations that are responsible for the neuron's demise may soon help in developing effective preventative and therapeutic strategies.

Aβ production as consequence of cellular death of a human neuroblastoma overexpressing APP

In human brain the Abeta peptide is produced mainly by neurons and the overexpression of amyloid precursor protein (APP) that involves an increase in Abeta secretion, has been observed in some areas of the Alzheimer's disease patients brain. We have generated two stably transfected human neuroblastoma lines which overexpress APP; both of them secreted Abeta and showed morphological changes and cell death with apoptotic program characteristics. Interestingly, coculture experiments with the untransfected human neuroblastoma cell line showed that the Abeta peptide was not responsible for the death in those cell lines; additionally, we indicate that upon cell death, Abeta peptide is secreted into cell medium.

Increased apoptotic cell death in sporadic and genetic Alzheimer's disease

Mounting evidence indicates increased susceptibility to cell death and increased oxidative damage as common features in neurons from sporadic Alzheimer's disease (AD) patients but also from familial AD (FAD) cases. Autosomal dominant forms of FAD are caused by mutations of the amyloid precursor protein (APP) gene and by mutations of the genes encoding for presenilin 1 or presenilin 2 (PS1/2). We investigated the effect of the Swedish APP double mutation (APPsw) on oxidative stress-induced cell death mechanisms in PC12 cells. This mutation results in from three- to sixfold increased beta-amyloid (Abeta) production compared with wild-type APP (APPwt). Because APPsw cells secrete low Abeta levels similar to the situation in FAD brains, our cell model represents a very suitable approach to elucidate the AD-specific cell death pathways under more likely physiological conditions. We found that APPsw-bearing cells show decreased mitochondrial membrane potential after exposure to hydrogen peroxide. In addition, activity of the executor caspase 3 after treatment with hydrogen peroxide was elevated in APPsw cells, which seems to be the result of an enhanced activation of both intrinsic and extrinsic apoptosis pathways. Our findings provide evidence that the massive neurodegeneration in early age of FAD patients could be a consequence of an increased vulnerability of neurons by mitochondrial abnormalities resulting in activation of different apoptotic pathways as a consequence to elevated oxidative stress levels. Finally, we propose a hypothetical sequence of the pathogenic steps linking sporadic AD, FAD, Abeta production, mitochondrial dysfunction with caspase pathway, and neuronal loss.

Mitochondrial dysfunction, apoptotic cell death, and Alzheimer’s disease

Being major sources of reactive oxygen species (ROS), mitochondrial structures are exposed to high concentrations of ROS and might therefore be particularly susceptible to oxidative injury. Mitochondrial damage may play a pivotal role in the cell death decision. Bolstered evidence indicates that mitochondrial abnormalities might be part of the spectrum of chronic oxidative stress occurring in Alzheimer's disease (AD) finally contributing to synaptic failure and neuronal degeneration. Accumulation and oligomerization of amyloid beta (Abeta) is also thought to play a central role in the pathogenesis of this disease by probably directly leading to mitochondrial dysfunction. Moreover, numerous lines of findings indicate increased susceptibility to apoptotic cell death and increased oxidative damage as common features in neurons from sporadic AD patients but also from familial AD (FAD) cases. Here we provide a summary of recent work demonstrating some key abnormalities that may initiate and promote pathological events in AD. Finally, we emphasize a hypothetical sequence of the pathogenic steps linking sporadic AD, FAD, and Abeta production with mitochondrial dysfunction, caspase pathway, and neuronal loss.

Neurotoxic mechanisms caused by the Alzheimer's disease-linked Swedish amyloid precursor protein mutation: oxidative stress, caspases, and the JNK pathway

Autosomal dominant forms of familial Alzheimer's disease (FAD) are caused by mutations of the amyloid precursor protein (APP) gene and by mutations of the genes encoding for presenilin 1 or presenilin 2. Simultaneously, evidence is provided that increased oxidative stress might play a crucial role in the rapid progression of the Swedish FAD. Here we investigated the effect of the Swedish double mutation (K670M/N671L) in the beta-amyloid precursor protein on oxidative stress-induced cell death mechanisms in PC12 cells. Western blot analysis and cleavage studies of caspase substrates revealed an elevated activity of the executor caspase 3 after treatment with hydrogen peroxide in cells containing the Swedish APP mutation. This elevated activity is the result of the enhanced activation of both intrinsic and extrinsic apoptosis pathways, including activation of caspase 2 and caspase 8. Furthermore, we observed an enhanced activation of JNK pathway and an attenuation of apoptosis by SP600125, a JNK inhibitor, through protection of mitochondrial dysfunction and reduction of caspase 9 activity. Our findings provide evidence that the massive neurodegeneration in early age of FAD patients could be a result of an increased vulnerability of neurons through activation of different apoptotic pathways as a consequence of elevated levels of oxidative stress.

Transgenic mice expressing the PS1-A246E mutation: effects on spatial learning, exploration, anxiety, and motor coordination

The functional consequence of the PS1-A246E mutation was assessed in transgenic mice on a background lacking the endogenous PS1 gene. These mice have elevated concentrations of A-beta protein (Abeta(42)) in the absence of plaque formation. By comparison to a mixed background strain (50% B6, 25% SJl, 25% 129Sv) controlled for age and gender, PS1-A246E transgenic mice displayed disinhibitory tendencies, as indicated by increased entries and duration in the open arms of the elevated plus-maze. Despite normal spontaneous alternation rates in a T-maze, latencies before responding were higher in PS1-A246E transgenic mice than controls. Moreover, the PS1-A246E transgenic mice fell more often from two stationary beams, but not from the coat-hanger and the rotorod. By contrast, ambulation in an automated photocell chamber and in an open-field was not affected. Nor was acquisition of place learning in the Morris water maze task. These results indicate that elevated Abeta(42) levels were insufficient for causing spatial defects but caused disinhibition, psychomotor slowing, and loss of motor skills in this model of familial Alzheimer's disease.

Selective impairment of p53-mediated cell death in fibroblasts from sporadic Alzheimer's disease patients

In this study, we evaluated the response of different human skin fibroblast cultures obtained from eight probable Alzheimer's disease patients and eight non-Alzheimer's disease subjects to an acute oxidative injury elicited by H(2)O(2). This treatment generates reactive oxygen species, which are responsible for DNA damage and apoptosis. To compare the sensitivity of fibroblasts from Alzheimer's disease or non-Alzheimer's disease patients to H(2)O(2) exposure, we evaluated different parameters, including cell viability, the extension of DNA damage and the ability of the cells to arrest proliferation and to activate an apoptotic program. We found that fibroblasts from Alzheimer's disease patients were more resistant that those from control subjects to H(2)O(2) treatment, although the extent of DNA damage induced by the oxidative injury was similar in both experimental groups. The protective mechanism of Alzheimer's disease fibroblasts was related to an impairment of H(2)O(2)-induced cell cycle arrest and characterized by an accelerated re-entry into the cell cycle and a diminished induction of apoptosis. Fibroblasts from Alzheimer's disease patients also have a profound impairment in the H(2)O(2)-activated, p53-dependent pathway, which results in a lack of activation of p53 or p53-target genes, including p21, GADD45 and bax. This study demonstrates a specific alteration of an intracellular pathway involved in sensing and repairing DNA damage in peripheral cells from Alzheimer's disease patients.

Intraneuronal advanced glycation endproducts in presenilin-1 Alzheimer's disease

The most frequently mutated gene resulting in dominantly inherited Alzheimer's disease is presenilin-1. We have used antibodies against advanced glycation endproducts (AGE) in brain tissue sections of four patients with three different presenilin I mutations. Accumulation of intracellular AGE was observed in 75-95% of pyramidal neurons in patients with presenilin-1 mutations, far exceeding the percentage of presenilin-1-, tau- or ubiquitin-positive neurons. This high level of AGE-modified proteins in vulnerable neurons is most likely explained by higher levels of their precursors (reactive (di)carbonyl products) or a slower turnover of the participating proteins. These conditions of carbonyl stress may contribute to increased neuronal dysfunction and vulnerability leading to the early disease onset.

Elevated vulnerability to oxidative stress-induced cell death and activation of caspase-3 by the Swedish amyloid precursor protein mutation

The Swedish double mutation (KM670/671NL) of amyloid precursor protein (APPsw) is associated with early-onset familial Alzheimer's disease (FAD) and results in from three- to sixfold increased beta-amyloid production. The goal of the present study was to elucidate the effects of APPsw on mechanisms of apoptotic cell death. Therefore, PC12 cells were stably transfected with human APPsw. Here we report that the vulnerability of APPsw-bearing PC12 cells to undergo apoptotic cell death was significantly enhanced after exposure to hydrogen peroxide compared to human wild-type APP-bearing cells, empty vector-transfected cells, and parent untransfected cells. In addition, we have analyzed the potential influence of several mechanisms that can interfere with the execution of the apoptotic cell death program: the inhibition of cell death by the use of caspase inhibitors and the reduction of oxidative stress by the use of (+/-)-alpha-tocopherol (vitamin E). Interestingly, oxidative stress-induced cell death was significantly attenuated in APPsw PC12 cells by pretreatment with caspase-3 inhibitors but not with caspase-1 inhibitors. In parallel, caspase-3 activity was markedly elevated in APPsw PC12 after stimulation with hydrogen peroxide for 6 hr, whereas caspase-1 activity was unaltered. In addition, oxidative stress-induced cell death could be reduced after pretreatment of APPsw cells with (+/-)-alpha-tocopherol. The protective potency of (+/-)-alpha-tocopherol was even greater than that of caspase-3 inhibitors. Our findings further emphasize the role of mutations in the amyloid precursor protein in apoptotic cell death and may provide the fundamental basis for further efforts to elucidate the underlying processes caused by FAD-related mutations.