G protein-mediated neuronal DNA fragmentation induced by familial Alzheimer's disease-associated mutants of APP

Gene expression profile in Alzheimer's brain screened by molecular indexing

Gene expression in the Alzheimer brain and normal brain was compared by molecular indexing, an advanced version of differential display. Using this technique, each gene was represented by a 3'-end cDNA fragment generated by class IIS restriction enzymes. The fragments were divided into 384 groups, and each group was separated by denaturing polyacrylamide gel electrophoresis. Comparison of gel patterns revealed 70 genes exhibiting marked differences in gene expression between AD and normal brain. A similarity search revealed 22 genes already reported, including those considered to be related to the pathogenesis such as G protein, G protein-related, and mitochondrial components. Detailed analysis of one from those only matched to EST sequences revealed a novel protein with leucine-zipper and SH3-binding motifs. Its expression was suppressed in a subpopulation of cortical pyramidal neurons in the AD brain, suggesting a possible relation to the pathogenesis. Thus, genome-scale analysis of gene expression of neurodegeneration is a potentially powerful approach to listing genes related to the pathogenesis.

Presenilin-1 P264L knock-in mutation: differential effects on abeta production, amyloid deposition, and neuronal vulnerability

The pathogenic mechanism linking presenilin-1 (PS-1) gene mutations to familial Alzheimer's disease (FAD) is uncertain, but has been proposed to include increased neuronal sensitivity to degeneration and enhanced amyloidogenic processing of the beta-amyloid precursor protein (APP). We investigated this issue by using gene targeting with the Cre-lox system to introduce an FAD-linked P264L mutation into the endogenous mouse PS-1 gene, an approach that maintains normal regulatory controls over expression. Primary cortical neurons derived from PS-1 homozygous mutant knock-in mice exhibit basal neurodegeneration similar to their PS-1 wild-type counterparts. Staurosporine and Abeta1-42 induce apoptosis, and neither the dose dependence nor maximal extent of cell death is altered by the PS-1 knock-in mutation. Similarly, glutamate-induced neuronal necrosis is unaffected by the PS-1P264L mutation. The lack of effect of the PS-1P264L mutation is confirmed by measures of basal- and toxin-induced caspase and calpain activation, biochemical indices of apoptotic and necrotic signaling, respectively. To analyze the influence of the PS-1P264L knock-in mutation on APP processing and the development of AD-type neuropathology, we created mouse lines carrying mutations in both PS-1 and APP. In contrast to the lack of effect on neuronal vulnerability, cortical neurons cultured from PS-1P264L homozygous mutant mice secrete Abeta42 at an increased rate, whereas secretion of Abeta40 is reduced. Moreover, the PS-1 knock-in mutation selectively increases Abeta42 levels in the mouse brain and accelerates the onset of amyloid deposition and its attendant reactive gliosis, even as a single mutant allele. We conclude that expression of an FAD-linked mutant PS-1 at normal levels does not generally increase cortical neuronal sensitivity to degeneration. Instead, enhanced amyloidogenic processing of APP likely is critical to the pathogenesis of PS-1-linked FAD.

Alzheimer-associated neuronal thread protein-induced apoptosis and impaired mitochondrial function in human central nervous system-derived neuronal cells

In Alzheimer Disease (AD), dementia is due to cell loss and impaired synaptic function. The cell loss is mediated by increased apoptosis, predisposition to apoptosis, and impaired mitochondrial function. Previous studies demonstrated that the AD7c-NTP neuronal thread protein gene is over-expressed in AD beginning early in the course of disease, and that in AD, AD7c-NTP protein accumulation in neurons co-localizes with phospho-tau-immunoreactivity. To determine the potential contribution of AD7c-NTP over-expression to cell loss in AD, we utilized an inducible mammalian expression system to regulate AD7c-NTP gene expression in human CNS-derived neuronal cells by stimulation with isopropyl-1-beta-D-thiogalactopyranoside (IPTG). IPTG induction of AD7c-NTP gene expression resulted in increased cell death mediated by apoptosis, impaired mitochondrial function, and increased cellular levels of the p53 and CD95 pro-apoptosis gene products as occur in AD. In addition, over-expression of AD7c-NTP was associated with increased levels of phospho-tau, but not amyloid-beta immunoreactivity. These results suggest that AD7c-NTP over-expression may have a direct role in mediating some of the important cell death cascades associated with AD neurodegeneration, and further establish a link between AD7c-NTP overexpression and the accumulation of phospho-tau in preapoptotic CNS neuronal cells.

Analysis of Galpha protein recognition profiles of angiotensin II receptors using chimeric Galpha proteins

Receptors with a heptahelical structure initiate signal transduction by interacting with specific Galpha proteins. The aim of this study was to analyze the ability of type 1 (AT1) and type 2 (AT2) angiotensin receptors to recognize the receptor coupling regions of Galpha proteins using our previously described technique (Ikezu, T., Okamoto, T., Komatsuzaki, K., Matsui, T., Martyn, J.A.J., Nishimoto, I., 1996. Negative transactivation of cAMP response element by familial Alzheimer's mutants of APP. EMBO J. 15, 2468-2475; Komatsuzaki, K., Murayama, Y., Giambarella, U., Ogata, E., Seino, S., Nishimoto, I., 1996. A novel system that reports the G-proteins linked to a given receptor: a study of the type 3 somatostatin receptor. FEBS Lett. 406, 165-170). Chimeric Galphas protein constructs, whose receptor binding regions contained sequences from the four major families of Galpha proteins (Galphaq, Galphai, Galpha12, Galphas), were cotransfected with AT1 or AT2 receptors in COS cells, then stimulated with angiotensin II (Ang II). Changes in cellular cAMP were assayed on cell lysates by enzyme immunoassay. In the case of the Galphaq family, cotransfection of AT1 with Galpha11/Galphas, Galpha14/Galphas, Galpha16/Galphas, elicited significant increases in cAMP after agonist stimulation. Confirmatory results were found using an independent [35S]GTPgammaS binding assay. Further examination using chimeric G proteins for Galpha12 proteins and Galphai family proteins provided evidence that the AT1 receptor can recognize sequences from Galpha12, Galphai1/i2, Galphaz, Galphao, while both receptors interacted with Galphai3. These results provide a Galpha protein recognition database for both AT1 and AT2 receptors, which may be important for understanding the full spectrum of cellular responses mediated by the hormone Ang II.

Alzheimer's disease: a dysfunction of the amyloid precursor protein(1)

In this review, we argue that at least one insult that causes Alzheimer's disease (AD) is disruption of the normal function of the amyloid precursor protein (APP). Familial Alzheimer's disease (FAD) mutations in APP cause a disease phenotype that is identical (with the exception that they cause an earlier onset of the disease) to that of 'sporadic' AD. This suggests that there are molecular pathways common to FAD and sporadic AD. In addition, all individuals with Down syndrome, who carry an extra copy of chromosome 21 and overexpress APP several-fold in the brain, develop the pathology of AD if they live past the age of 40. These data support the primacy of APP in the disease. Although APP is the source of the beta-amyloid (Abeta) that is deposited in amyloid plaques in AD brain, the primacy of APP in AD may not lie in the production of Abeta from this molecule. We suggest instead that APP normally functions in the brain as a cell surface signaling molecule, and that a disruption of this normal function of APP is at least one cause of the neurodegeneration and consequent dementia in AD. We hypothesize in addition that disruption of the normal signaling function of APP causes cell cycle abnormalities in the neuron, and that these abnormalities constitute one mechanism of neuronal death in AD. Data supporting these hypotheses have come from investigations of the molecular consequences of neuronal expression of FAD mutants of APP or overexpression of wild type APP, as well as from identification of binding proteins for the carboxyl-terminus (C-terminus) of APP.

Antibody-regulated neurotoxic function of cell-surface beta-amyloid precursor protein

APP is a transmembrane precursor of beta-amyloid, and its mutations cause early-onset familial Alzheimer's disease. We report a toxic function of normal wild-type APP (wtAPP). Treatment of neuronal F11 cells, immortalized embryonic day 13 neurons, overexpressing wtAPP with anti-APP antibodies caused death. Death was not induced by antibody in parental F11 cells. Death by antibody occurred through cell-surface APP, not through secreted APP, in a pertussis toxin-sensitive manner and was typical apoptosis, not observed in primary astrocytes or glioma cells overexpressing wtAPP, but observed in primary cortical neurons. Cell-surface APP thus performs a toxic function as an extracellularly controllable regulator of neuronal death. This study provides a novel insight into the normal and pathological functions of cell-surface wtAPP.

Neuronal cell apoptosis by a receptor-binding domain peptide of ApoE4, not through low-density lipoprotein receptor-related protein

Since an apolipoprotein E4 (ApoE4) peptide composed of the low-density lipoprotein (LDL) receptor-related protein (LRP)-binding domain [ApoE4(141-149)(2) or ApoE(141-155)(2)] exerts neurotoxicity in primary neurons and neuronal cell lines, it has been controversial whether these effects are mediated by LRP. Here, we examined whether ApoE4(141-149)(2)-induced toxicity is mediated by LRP in a neuronal cell system where ApoE4 toxicity is mediated by LRP: serum-deprived F11 neuronal cells. In these cells, where ApoE4 exerted toxicity by apoptosis in a manner sensitive to both caspase inhibitors and pertussis toxin (PTX), ApoE4(141-149)(2) also caused cell death by apoptosis but in a caspase-inhibitor-resistant, PTX-resistant manner. ApoE4(141-149)(2)-induced death was not inhibited by antisense oligonucleotides to LRP. Therefore, we conclude that ApoE4(141-149)(2) is able to exert neurotoxicity without involving LRP.

Inhibition of neuronal apoptosis by docosahexaenoic acid (22:6n-3). Role of phosphatidylserine in antiapoptotic effect

Enrichment of Neuro 2A cells with docosahexaenoic acid (22:6n-3) decreased apoptotic cell death induced by serum starvation as evidenced by the reduced DNA fragmentation and caspase-3 activity. The protective effect of 22:6n-3 became evident only after at least 24 h of enrichment before serum starvation and was potentiated as a function of the enrichment period. During enrichment 22:6n-3 incorporated into phosphatidylserine (PS) steadily, resulting in a significant increase in the total PS content. Similar treatment with oleic acid (18:1n-9) neither altered PS content nor resulted in protective effect. Hindering PS accumulation by enriching cells in a serine-free medium diminished the protective effect of 22:6n-3. Membrane translocation of Raf-1 was significantly enhanced by 22:6n-3 enrichment in Neuro 2A cells. Consistently, in vitro biomolecular interaction between PS/phosphatidylethanolamine /phosphatidylcholine liposomes, and Raf-1 increased in a PS concentration-dependent manner. Collectively, enrichment of neuronal cells with 22:6n-3 increases the PS content and Raf-1 translocation, down-regulates caspase-3 activity, and prevents apoptotic cell death. Both the antiapoptotic effect of 22:6n-3 and Raf-1 translocation are sensitive to 22:6n-3 enrichment-induced PS accumulation, strongly suggesting that the protective effect of 22:6n-3 may be mediated at least in part through the promoted accumulation of PS in neuronal membranes.

Multiple mechanisms underlie neurotoxicity by different types of Alzheimer's disease mutations of amyloid precursor protein

We examined a neuronal cell system in which single-cell expression of either familial Alzheimer's disease (FAD) gene V642I-APP or K595N/M596L-APP (NL-APP) in an inducible plasmid was controlled without affecting transfection efficiency. This system revealed that (i) low expression of both mutants exerted toxicity sensitive to both Ac-DEVD-CHO (DEVD) and glutathione ethyl ester (GEE), whereas wild-type APP (wtAPP) only at higher expression levels caused GEE/DEVD-resistant death to lesser degrees; (ii) toxicity by the V642I mutation was entirely GEE/DEVD sensitive; and (iii) toxicity by higher expression of NL-APP was GEE/DEVD resistant. The GEE/DEVD-sensitive death was sensitive to pertussis toxin and was due to G(o)-interacting His(657)-Lys(676) domain. The GEE/DEVD-resistant death was due to C-terminal Met(677)-Asn(695). APP mutants lacking either domain unraveled elaborate intracellular cross-talk between these domains. E618Q-APP, responsible for non-AD type of a human disease, only exerted GEE/DEVD-resistant death at higher expression. Therefore, (i) different FAD mutations in APP cause neuronal cell death through different cytoplasmic domains via different sets of mechanisms; (ii) expression levels of FAD genes are critical in activating specific death mechanisms; and (iii) toxicity by low expression of both mutants most likely reflects the pathogenetic mechanism of FAD.

Apoptosis in neural development and disease

Cell death via apoptosis is a prominent feature in mammalian neural development. Recent studies into the basic mechanism of apoptosis have revealed biochemical pathways that control and execute apoptosis in mammalian cells. Protein factors in these pathways play important roles during development in regulating the balance between neuronal life and death. Additionally, mounting evidence indicates such pathways may also be activated during several neurodegenerative diseases, resulting in improper loss of neurons.

V642I APP-inducible neuronal cells: a model system for investigating Alzheimer's disorders

APP is a precursor of beta amyloid deposited in Alzheimer's disease (AD). Although genetic studies established that mutations in APP cause familial AD (FAD), the mechanism for neuronal death by FAD mutants has not been well understood. We established neuronal cells (F11/EcR/V642I cells) in which V642I APP was inducibly expressed by ecdysone. Treatment with ecdysone, but not vehicle, killed most cells within a few days, with rounding, shrinkage, and detachment as well as nuclear fragmentation. Death was suppressed by Ac-DEVD-CHO and pertussis toxin. Electron microscopic analysis revealed that apoptosis occurred in ecdysone-treated cells. V642I-APP-induced death was suppressed by the anti-AD factors estrogen and apoE2. These data demonstrate not only that expression of this FAD gene causes neuronal apoptosis, but that F11/EcR/V642I cells, the first neuronal cells with inducible FAD gene expression, provide a useful model system in investigating AD disorders.

Apoptotic signaling through the beta -adrenergic receptor. A new Gs effector pathway

Stimulation of beta-adrenergic receptor normally results in signaling by the heterotrimeric G protein G(s), leading to the activation of adenylyl cyclase, production of cAMP, and activation of cAMP-dependent protein kinase (PKA). Here we report that cell death of thymocytes can be induced after stimulation of beta-adrenergic receptor, or by addition of exogenous cAMP. Apoptotic cell death in both cases was observed with the appearance of terminal deoxynucleotidyl transferase-mediated UTP end labeling reactivity and the activation of caspase-3 in S49 T cells. Using thymocytes deficient in either Galpha(s) or PKA, we find that engagement of beta-adrenergic receptors initiated a Galpha(s)-dependent, PKA-independent pathway leading to apoptosis. This alternative pathway involves Src family tyrosine kinase Lck. Furthermore, we show that Lck protein kinase activity can be directly stimulated by purified Galpha(s). Our data reveal a new signaling pathway for Galpha(s), distinct from the classical PKA pathway, that accounts for the apoptotic action of beta-adrenergic receptors.

Abortive oncogeny and cell cycle-mediated events in Alzheimer disease

Alzheimer disease, the leading cause of senile dementia, is characterised by the degeneration of select neuronal populations. While the mechanism(s) underlying such cell loss are largely unknown, recent findings indicate inappropriate re-entry into the cell cycle resembling an abortive oncogeny. In postmitotic neurons, such mitotic re-entrance is deleterious and one that involves virtually the entire spectrum of the described pathological events in Alzheimer disease including, ultimately, cell death.

Proteolytic processing and cell biological functions of the amyloid precursor protein

Recent research has identified some key players involved in the proteolytic processing of amyloid precursor protein (APP) to amyloid beta-peptide, the principal component of the amyloid plaques in Alzheimer patients. Interesting parallels exists with the proteolysis of other proteins involved in cell differentiation, cholesterol homeostasis and stress responses. Since the cytoplasmic domain of APP is anchored to a complex protein network that might function in axonal elongation, dendritic arborisation and neuronal cell migration, the proteolysis of APP might be critically involved in intracellular signalling events.

A monoclonal antibody to amyloid precursor protein induces neuronal apoptosis

Although there is considerable evidence suggesting that altered metabolism of beta-amyloid precursor protein (APP) and accumulation of its beta-amyloid fragment are key features of Alzheimer's disease (AD), the normal physiological function of APP remains elusive. We investigated the potential role of APP in neurons using the monoclonal antibody 22C11, which binds to the extracellular domain of the human, rat, or mouse APP. Exposure of cortical neurons to 22C11 induced morphological changes including neurite degeneration, nuclear condensation, and internucleosomal DNA cleavage that were consistent with neurons dying by apoptosis. Supporting a role for 22C11-mediated apoptosis occurring by binding to APP were data demonstrating that preincubation of 22C11 with either purified APP or a synthetic peptide (APP(66-81)) that contains the epitope for 22C11 significantly attenuated neuronal damage induced by 22C11. The specificity of 22C11 was further supported by data showing no apparent effects of either mouse IgG or the monoclonal antibody P2-1, which is specific for the aminoterminal end of human but not rat APP. In addition, biochemical features indicative of apoptosis were the formation of 120- and 150-kDa breakdown products of fodrin following treatment of cortical neurons with 22C11. Both the morphological and the biochemical changes induced by 22C11 were prevented following pretreatment of neurons with the general caspase inhibitor N-benzyloxycarbonyl-Val-Ala-Asp(O-methyl)-fluoromethyl ketone. Prior incubation of cortical neurons with GSH ethyl ester (GEE), a cell-permeable form of GSH, resulted in complete protection from the 22C11 insult, thus implicating an oxidative pathway in 22C11-mediated neuronal degeneration. This was further supported by the observation that prior treatment of neurons with buthionine sulfoximine, an inhibitor of gamma-glutamylcysteinyl synthetase, potentiated the toxic effects of 22C11. Finally, with use of compartmented cultures of hippocampal neurons, it was also demonstrated that selective application of 22C11 caused local neuritic degeneration that was prevented by the addition of GEE to the neuritic compartment. Thus, the binding of a monoclonal antibody to APP initially triggers neurite degeneration that is followed by caspase-dependent apoptosis in neuronal cultures and illustrates a novel property of this protein in neurons that may contribute to the profound neuronal cell death associated with AD.

Amyloid beta interacts with the amyloid precursor protein: a potential toxic mechanism in Alzheimer's disease

Amyloid beta protein (Abeta) deposition in the brain is a hallmark of Alzheimer's disease (AD). The fibrillar form of Abeta is neurotoxic, although the mechanism of its toxicity is unknown. We showed that conversion of Abeta to the fibrillar form markedly increased binding to specific neuronal membrane proteins, including amyloid precursor protein (APP). Nanomolar concentrations of fibrillar Abeta bound cell-surface holo-APP in cortical neurons. Reduced vulnerability of cultured APP-null neurons to Abeta neurotoxicity suggested that Abeta neurotoxicity involves APP. Thus Abeta toxicity may be mediated by the interaction of fibrillar Abeta with neuronal membrane proteins, notably APP. An Abeta-APP interaction reminiscent of the pathogenic mechanism of prions may thus contribute to neuronal degeneration in AD.

Neuronal cell death in Down's syndrome

Down's syndrome (DS), occurring in 0.8 out of 1,000 live births, is a genetic disorder in which an extra portion of chromosome 21 leads to several abnormalities. With respect to the nervous system, it causes mental retardation. It is conceived that abnormal neuronal cell death in development is involved, but there is no direct evidence yet. In addition to developmental brain abnormalities, almost all DS brains over 40 years old manifest a similar pathology to Alzheimer's disease (AD), including the presence of senile plaques (SP) and neurofibrillary tangles (NFT). Although there was a debate to segregate dementia from underlying mental retardation, at least some portion of DS patients exhibit deteriorated mental status with aging. The mechanism underlying these abnormalities at the molecular level remains to be elucidated. Recently there have been several reports suggesting abnormalities reflecting increased risk to apoptosis in DS brains. Increased expression of several apoptosis-related genes (p53, fas, ratio of bax to bcl-2, GAPDH) in DS brains has been reported. Cultured neurons from both patients and model animals are reportedly more vulnerable to apoptosis. Overproduction of reactive oxygen species and its causative roles for increased apoptosis in DS tissues are suggested. One possible hypothesis is an increased susceptibility to apoptosis due to p53 overactivation in DS brains. A beta 42, a critical peptide for AD pathology from amyloid precursor protein (APP), can be detected in DS brains. A beta 42 is deposited in SP from an early stage, suggesting common molecular mechanisms in DS and AD. Animal models for DS are important in the search of molecular mechanisms. Several types of models are now available. Future DS studies are expected to integrate information from animal models and human tissues.

Apoptosis and neurologic disease

Many neurological disorders involve cell death. During development of the nervous system, cell death is a normal feature. Elimination of substantial numbers of initially generated cells enables useful pruning of "mismatched" or excessive cells produced by exuberance during the proliferative and migratory phases of development. Such cell death, occurring by "programmed" pathways, is termed apoptosis. In mature organisms, cells die in two major fashions, either by necrosis or apoptosis. In the adult nervous system, because there is little cell production during adulthood, there is little normal cell death. However, neurological disease is often associated with significant neural cell death. Acute disorders, occurring over minutes to hours, such as brain trauma, infarction, hemorrhage, or infection, prominently involve cell death, much of which is by necrosis. Chronic disorders, with relatively slow central nervous system degeneration, may occur over years or decades, but may involve cell losses. Such disorders include motor neuron diseases such as amyotrophic lateral sclerosis (ALS), cerebral dementing disorders such as Alzheimer's disease and frontotemporal dementia, and a variety of degenerative movement disorders including Parkinson's disease, Huntington's disease, and the inherited ataxias. There is evidence that the mechanism of neuronal cell death in these disorders may involve apoptosis. Direct conclusive evidence of apoptosis is scarce in these chronic disorders, because of the swiftness of cell death in relation to the slowness of the disease. Thus, at any particular time point of assessment, very few cells would be expected to be undergoing death. However, it is clearly of importance to define the type of cell death in these disorders. Of significance is that while treating the underlying causes of these conditions is an admirable goal, it may also be possible to develop productive therapies based on alleviating the process of cell death. This is particularly likely if this cell loss is through apoptosis, a programmed process for which the molecular cascade is increasingly understood. This article reviews our understanding of apoptosis in the nervous system, concentrating on its possible roles in chronic neurodegenerative disorders.

Molecular genetics of Alzheimer's disease

Application of genetic paradigms to Alzheimer's disease (AD) has led to confirmation that genetic factors play a role in this disease. Additionally, researchers now understand that AD is genetically heterogeneous and that some genetic isoforms appear to have similar or related biochemical consequences. Genetic epidemiologic studies indicate that first-degree relatives of AD probands have an age-dependent risk for AD approximately equal to 38% by age 90 years (range 10% to 50%). This incidence strongly suggests that transmission may be more complicated than a simple autosomal dominant trait. Nevertheless, a small proportion of AD cases with unequivocal autosomal dominant transmission have been identified. Studies of these autosomal dominant familial AD (FAD) pedigrees have thus far identified four distinct FAD genes. The beta-amyloid precursor protein (beta APP) gene (on chromosome 21), the presenilin 1 (PS1) gene (on chromosome 14), and the presenilin 2 (PS2) gene (on chromosome 1) gene are all associated with early-onset AD. Missense mutations in these genes cause abnormal beta APP processing with resultant overproduction of A beta 42 peptides. In addition, the epsilon 4 allele of apolipoprotein E (APOE) is associated with a increased risk for late-onset AD. Although attempts to develop symptomatic treatments based on neurotransmitter replacement continue, some laboratories are attempting to design treatments that will modulate production or disposition of A beta peptides.

A unifying hypothesis of Alzheimer's disease. III. Risk factors

Normal ageing and Alzheimer's disease (AD) have many features in common and, in many respects, both conditions only differ by quantitative criteria. A variety of genetic, medical and environmental factors modulate the ageing-related processes leading the brain into the devastation of AD. In accordance with the concept that AD is a metabolic disease, these risk factors deteriorate the homeostasis of the Ca(2+)-energy-redox triangle and disrupt the cerebral reserve capacity under metabolic stress. The major genetic risk factors (APP and presenilin mutations, Down's syndrome, apolipoprotein E4) are associated with a compromise of the homeostatic triangle. The pathophysiological processes leading to this vulnerability remain elusive at present, while mitochondrial mutations can be plausibly integrated into the metabolic scenario. The metabolic leitmotif is particularly evident with medical risk factors which are associated with an impaired cerebral perfusion, such as cerebrovascular diseases including stroke, cardiovascular diseases, hypo- and hypertension. Traumatic brain injury represents another example due to the persistent metabolic stress following the acute event. Thyroid diseases have detrimental sequela for cerebral metabolism as well. Furthermore, major depression and presumably chronic stress endanger susceptible brain areas mediated by a host of hormonal imbalances, particularly the HPA-axis dysregulation. Sociocultural and lifestyle factors like education, physical activity, diet and smoking may also modulate the individual risk affecting both reserve capacity and vulnerability. The pathophysiological relevance of trace metals, including aluminum and iron, is highly controversial; at any rate, they may adversely affect cellular defences, antioxidant competence in particular. The relative contribution of these factors, however, is as individual as the pattern of the factors. In familial AD, the genetic factors clearly drive the sequence of events. A strong interaction of fat metabolism and apoE polymorphism is suggested by intercultural epidemiological findings. In cultures, less plagued by the 'blessings' of the 'cafeteria diet-sedentary' Western lifestyle, apoE4 appears to be not a risk factor for AD. This intriguing evidence suggests that, analogous to cardiovascular diseases, apoE4 requires a hyperlipidaemic lifestyle to manifest as AD risk factor. Overall, the etiology of AD is a key paradigm for a gene-environment interaction. Copyright 2000 John Wiley & Sons, Ltd.

Transient overexpression of murine dishevelled genes results in apoptotic cell death

The Dishevelled (Dvl) gene family encodes cytoplasmic proteins that are implicated in Wnt signal transduction. In mammals, the manner in which Wnt signals are transduced remains unclear. The biochemical and molecular mechanisms defining the Wnt-1 pathway are of great interest because of its important role in development and its activation in murine breast tumors. In order to elucidate Dvl's role in Wnt signaling, we attempted to overexpress Dvl in cells, but were unable to obtain stable cell lines. We show here that the overexpression of Dvl genes alters nuclear and cellular morphology of COS-1 and C57MG cells and causes cell death due to the induction of apoptosis. Deletion studies demonstrate that all three conserved domains of Dvl (DIX, PDZ, and DEP) are required for Dvl-mediated cell death. Coexpression of protein phosphatase 2Calpha, a Dvl-interacting protein identified in yeast two-hybrid studies, protects cells from the cell death observed in cells overexpressing Dvl alone. Furthermore, the adenomatous polyposis coli (APC) gene product appears to be required for Dvl-mediated cell death. The relevance of these findings to Wnt signal transduction, as well as to developmental processes and disease, are discussed.

Activation of caspase-3 in single neurons and autophagic granules of granulovacuolar degeneration in Alzheimer's disease. Evidence for apoptotic cell death

Neuronal loss is prominent in Alzheimer's disease (AD), and its mechanisms remain unresolved. Apoptotic cell death has been implicated on the basis of studies demonstrating DNA fragmentation and an up-regulation of proapoptotic proteins in the AD brain. However, DNA fragmentation in neurons is too frequent to account for the continuous neuronal loss in a degenerative disease extending over many years. Furthermore, the typical apoptotic morphology has not been convincingly documented in AD neurons with fragmented DNA. We report the detection of the activated form of caspase-3, the central effector enzyme of the apoptotic cascade, in AD and Down's syndrome (DS) brain using an affinity-purified antiserum. In AD and DS, single neurons with apoptotic morphology showed cytoplasmic immunoreactivity for activated caspase-3, whereas no neurons were labeled in age-matched controls. Apoptotic neurons were identified at an approximate frequency of 1 in 1100 to 5000 neurons in the cases examined. Furthermore, caspase-3 immunoreactivity was detected in granules of granulovacuolar degeneration. Our results provide direct evidence for apoptotic neuronal death in AD with a frequency compatible with the progression of neuronal degeneration in this chronic disease and identify autophagic vacuoles of granulovacuolar degeneration as possible means for the protective segregation of early apoptotic alterations in the neuronal cytoplasm.

Bcl-X(L) inhibits apoptosis and necrosis produced by Alzheimer's beta-amyloid1-40 peptide in PC12 cells

Recent studies have shown that neuronal apoptosis induced by the Alzheimer's disease (AD) beta-amyloid peptide (Abeta) is related to alteration of the Bax/Bcl-2 ratio. It has been demonstrated that Bcl-X(L) (Bcl-X(L) = protein, bcl-X(L) = gene), a Bcl-2-related protein, prevents apoptosis in mammalian cells. Additionally, TGF-beta1 is able to protect cultured neuronal cells from Abeta-induced apoptosis via upregulation of bcl-X(L) and bcl-2 gene expression. We show that Abeta treatment (500 nM, freshly solubilized) results in apoptosis and necrosis in differentiated PC12 cells maintained with a low dose of NGF-beta (1 ng/ml). To investigate whether transfection of PC12 cells with bcl-X(L) could block Abeta-induced apoptosis, we transfected these cells with a bcl-X(L) construct (pcDNA-bcl-X(L)). Data show that bcl-X(L) significantly inhibits both early-stage apoptosis and late-stage apoptosis/necrosis produced by Abeta treatment (1000 nM) in pcDNA3-bcl-X(L)-transfected PC12 cells as compared with pcDNA3 vector-transfected PC12 cells. These results suggest that Bcl-X(L) exhibits both anti-necrotic as well as anti-apoptotic roles in Abeta-challenged PC12 cells.

Activation of neuronal caspase-3 by intracellular accumulation of wild-type Alzheimer amyloid precursor protein

Forced overexpression of wild-type Alzheimer amyloid precursor protein (APP) causes postmitotic neurons to degenerate. Caspase-3 (CPP32) is a principal cell death protease involved in neuronal apoptosis during physiological development and under pathological conditions. Here, we investigated whether APP overexpression activates caspase-3 in human postmitotic neurons using adenovirus-mediated gene transfer. When a recombinant adenovirus vector expressing human wild-type APP695 was infected in vitro into neurally differentiated embryonal carcinoma NT2 cells, only postmitotic neurons underwent severe degeneration. Before neurodegeneration, full-length APP- and Abeta-immunoreactive peptides were accumulated in infected neurons, and caspase-3-like protease activity was markedly elevated. Western blot analysis revealed that activated caspase-3 subunits were generated in APP-accumulating neurons. Such neuronal caspase-3 activation was undetectable in NT2 neurons infected with beta-galactosidase-expressing adenovirus. Addition of the caspase-3 inhibitor acetyl-Asp-Glu-Val-Asp-aldehyde to the culture medium significantly reduced the severity of degeneration exhibited by APP-overexpressing neurons. Immunocytochemical analyses revealed that some APP-accumulating neurons contained activated caspase-3 subunits and exhibited the characteristics of apoptosis, such as chromatin condensation and DNA fragmentation. Activation of caspase-3 was also observed in vivo in rat hippocampal neurons infected with the APP-expressing adenovirus. These results suggest that wild-type APP is an intrinsic activator of caspase-3-mediated death machinery in postmitotic neurons.

Examination of the interactions of the amyloid precursor protein carboxyl terminus to intracellular protein: possible role in apoptosis

1. The carboxyl terminus of the amyloid precursor protein (APP) has several identified regions that may potentially contribute to the pathogenic effects of Alzheimer's disease (AD). To examine these effects, the authors iodinated a short synthetic peptide corresponding to amino acids 679-687 of APP695. They also produced a [35S]-Methionine labeled peptide corresponding to the entire carboxyl 100 amino acids of APP695 via a reticulocyte lysate coupled in vitro transcription/translation system. 2. Human neuroblastoma cells (SK-N-SH) and non-neuronal epithelial cells (RK-13) were cultured, harvested, and lysed. The S1 cell extract fractions were combined with either of the labeled peptides and incubated at different temperatures to allow for interaction and binding of cellular proteins with the peptides. These interactions were identified as gel mobility shift patterns on native PAGE gels. The presence of distinct bands on the gels indicate that the APP C-terminus interacts with several intracellular proteins, some of which may be detrimental to the cell. The authors have tested the possibility that the accumulation of C-terminal proteins may result in apoptosis. 3. Apoptosis in neural cells is one detrimental effect that has been attributed to APP. The authors examined hippocampal tissue sections from Alzheimer's disease (AD) and age-matched normal control patients for a difference in the number of apoptotic nuclei present using an in situ apoptosis detection kit that labels the numerous free DNA ends present in apoptotic nuclei. The number of apoptotic nuclei found in AD neuronal tissue was significantly higher than in normal tissue.

Endogenous bax translocation in SH-SY5Y human neuroblastoma cells and cerebellar granule neurons undergoing apoptosis

Changes at the mitochondria are an early, required step in apoptosis in various cell types. We used western blot analysis to demonstrate that the proapoptotic protein Bax translocated from the cytosolic to the mitochondrial fraction in SH-SY5Y human neuroblastoma cells undergoing staurosporine- or EGTA-mediated apoptosis. Levels of mitochondrial Bax increased 15 min after staurosporine treatment. In EGTA-treated cells, increased levels of mitochondrial Bax were seen at 4 h, consistent with a slower onset of apoptosis in EGTA versus staurosporine treatments. We also demonstrate the concomitant translocation of cytochrome c from the mitochondrial to the cytosolic fractions. We correlated these translocations with changes in caspase-3-like activity. An increase in caspase-3-like activity was evident 2 h after staurosporine treatment. Inhibition of the mitochondrial permeability transition had no effect on Bax translocation or caspase-3-like activity in staurosporine-treated SH-SY5Y cells. In primary cultures of cerebellar granule neurons undergoing low K(+)-mediated apoptosis, Bax translocation to the mitochondrial fraction was evident at 3 h. Cytochrome c release into the cytosol was not significant until 8 h after treatment. These data support a model of apoptosis in which Bax acts directly at the mitochondria to allow the release of cytochrome c.

The amyloid precursor protein interacts with Go heterotrimeric protein within a cell compartment specialized in signal transduction

The function of the beta-amyloid protein precursor (betaAPP), a transmembrane molecule involved in Alzheimer pathologies, is poorly understood. We recently reported the presence of a fraction of betaAPP in cholesterol and sphingoglycolipid-enriched microdomains (CSEM), a caveolae-like compartment specialized in signal transduction. To investigate whether betaAPP actually interferes with cell signaling, we reexamined the interaction between betaAPP and Go GTPase. In strong contrast with results obtained with reconstituted phospholipid vesicles (Okamoto et al., 1995), we find that incubating total neuronal membranes with 22C11, an antibody that recognizes an N-terminal betaAPP epitope, reduces high-affinity Go GTPase activity. This inhibition is specific of Galphao and is reproduced, in the absence of 22C11, by the addition of the betaAPP C-terminal domain but not by two distinct mutated betaAPP C-terminal domains that do not bind Galphao. This inhibition of Galphao GTPase activity by either 22C11 or wild-type betaAPP cytoplasmic domain suggests that intracellular interactions between betaAPP and Galphao could be regulated by extracellular signals. To verify whether this interaction is preserved in CSEM, we first used biochemical, immunocytochemical, and ultrastructural techniques to unambiguously confirm the colocalization of Galphao and betaAPP in CSEM. We show that inhibition of basal Galphao GTPase activity also occurs within CSEM and correlates with the coimmunoprecipitation of Galphao and betaAPP. The regulation of Galphao GTPase activity by betaAPP in a compartment specialized in signaling may have important consequences for our understanding of the physiopathological functions of betaAPP.

Interaction of heterotrimeric G protein Galphao with Purkinje cell protein-2. Evidence for a novel nucleotide exchange factor

The heterotrimeric G protein Galphao is ubiquitously expressed throughout the central nervous system, but many of its functions remain to be defined. To search for novel proteins that interact with Galphao, a mouse brain library was screened using the yeast two-hybrid interaction system. Pcp2 (Purkinje cell protein-2) was identified as a partner for Galphao in this system. Pcp2 is expressed in cerebellar Purkinje cells and retinal bipolar neurons, two locations where Galphao is also expressed. Pcp2 was first identified as a candidate gene to explain Purkinje cell degeneration in pcd mice (Nordquist, D. T., Kozak, C. A., and Orr, H. T. (1988) J. Neurosci. 8, 4780-4789), but its function remains unknown as Pcp2 knockout mice are normal (Mohn, A. R., Feddersen, R. M., Nguyen, M. S., and Koller, B. H. (1997) Mol. Cell. Neurosci. 9, 63-76). Galphao and Pcp2 binding was confirmed in vitro using glutathione S-transferase-Pcp2 fusion proteins and in vitro translated [35S]methionine-labeled Galphao. In addition, when Galphao and Pcp2 were cotransfected into COS cells, Galphao was detected in immunoprecipitates of Pcp2. To determine whether Pcp2 could modulate Galphao function, kinetic constants kcat and koff of bovine brain Galphao were determined in the presence and absence of Pcp2. Pcp2 stimulates GDP release from Galphao more than 5-fold without affecting kcat. These findings define a novel nucleotide exchange function for Pcp2 and suggest that the interaction between Pcp2 and Galphao is important to Purkinje cell function.

A betaPP peptide carboxyl-terminal to Abeta is neurotoxic

Extracellular Abeta-amyloid and intraneuronal paired helical filaments (PHFs) composed of tau protein are the neuropathological hallmark of Alzheimer's disease. Abeta is a 39- to 43-residue peptide derived by cleavage of a 695- to 770-amino-acid membrane-associate glycoprotein (termed beta-protein precursor, betaPP). Following the observation that an antiserum to an epitope located between residues 713 and 723 of betaPP770 (ie, the transmembrane region of the betaPP distal to Abeta) labels PHFs and that a synthetic peptide homologous to residues 713 to 730 of betaPP770 (betaPP713-730) is highly fibrillogenic and interacts with tau in vitro, it has been hypothesized that betaPP fragments other than Abeta may feature in the pathogenesis of Alzheimer's disease concurring with neuronal degeneration. To investigate this issue, we have analyzed the effects of the exposure of primary neuronal cultures to the synthetic peptide betaPP713-730. Cultures were prepared from rat hippocampus on embryonic day 17 and incubated with the peptide at 2.5 to 30 micromol/L concentration for 1 to 4 days. Cell viability was compared with that of control cultures exposed to a scrambled sequence of the peptide. A 4-day exposure to 20 micromol/L betaPP713-730 resulted in almost complete neuronal loss, whereas no changes were observed with the scrambled peptide. Degenerating neurons showed DNA fragmentation by agarose gel electrophoresis and apoptotic changes by light and electron microscopy. These findings support the view that betaPP sequences other than Abeta may play a role in nerve cell degeneration in Alzheimer's disease.

The role of cell cycle-mediated events in Alzheimer's disease

The mechanism(s) underlying selective neuronal death in Alzheimer's disease remain unresolved. However, recently, we and others showed that susceptible hippocampal neurones in Alzheimer's disease express markers common to cells in various phases of the cell cycle. Since neuronal maturation is associated with effective escape from the cell division cycle, emergence out of quiescence may be deleterious. Here, we review a number of current findings indicating that disregulated ectopic re-activation of cell cycle-mediated events, akin to neoplasia, represent an important early pathway associated with neuronal death and, more importantly, one that involves virtually the entire spectrum of the pathological events described in Alzheimer's disease.

Proteolytic processing of the Alzheimer's disease amyloid precursor protein within its cytoplasmic domain by caspase-like proteases

Alzheimer's disease is characterized by neurodegeneration and deposition of betaA4, a peptide that is proteolytically released from the amyloid precursor protein (APP). Missense mutations in the genes coding for APP and for the polytopic membrane proteins presenilin (PS) 1 and PS2 have been linked to familial forms of early-onset Alzheimer's disease. Overexpression of presenilins, especially that of PS2, induces increased susceptibility for apoptosis that is even more pronounced in cells expressing presenilin mutants. Additionally, presenilins themselves are targets for activated caspases in apoptotic cells. When we analyzed APP in COS-7 cells overexpressing PS2, we observed proteolytic processing close to the APP carboxyl terminus. Proteolytic conversion was increased in the presence of PS2-I, which encodes one of the known PS2 pathogenic mutations. The same proteolytic processing occurred in cells treated with chemical inducers of apoptosis, suggesting a participation of activated caspases in the carboxyl-terminal truncation of APP. This was confirmed by showing that specific caspase inhibitors blocked the apoptotic conversion of APP. Sequence analysis of the APP cytosolic domain revealed a consensus motif for group III caspases ((IVL)ExD). Mutation of the corresponding Asp664 residue abolished cleavage, thereby identifying APP as a target molecule for caspase-like proteases in the pathways of programmed cellular death.

A 127-kDa protein (UV-DDB) binds to the cytoplasmic domain of the Alzheimer's amyloid precursor protein

Alzheimer amyloid precursor protein (APP) is an integral membrane protein with a short cytoplasmic domain of 47 amino acids. It is hoped that identification of proteins that interact with the cytoplasmic domain will provide new insights into the physiological function of APP and, in turn, into the pathogenesis of Alzheimer's disease. To identify proteins that interact with the cytoplasmic domain of APP, we employed affinity chromatography using an immobilized synthetic peptide corresponding to residues 645-694 of APP695 and identified a protein of approximately 130 kDa in rat brain cytosol. Amino acid sequencing of the protein revealed the protein to be a rat homologue of monkey UV-DDB (UV-damaged DNA-binding protein, calculated molecular mass of 127 kDa). UV-DDB/p127 co-immunoprecipitated with APP using an anti-APP antibody from PC12 cell lysates. APP also co-immunoprecipitated with UV-DDB/p127 using an anti-UV-DDB/p127 antibody. These results indicate that UV-DDB/p127, which is present in the cytosolic fraction, forms a complex with APP through its cytoplasmic domain. In vitro binding experiments using a glutathione S-transferase-APP cytoplasmic domain fusion protein and several mutants indicated that the YENPTY motif within the APP cytoplasmic domain, which is important in the internalization of APP and amyloid beta protein secretion, may be involved in the interaction between UV-DDB/p127 and APP.

Recent advances in the genetics of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder that is the most common cause of dementia in the elderly. It is a clinical-pathologic entity characterized by progressive dementia associated with the neuropathologic hallmarks of Abeta amyloid plaques, neurofibrillary tangles (NFTs), neuronal loss, and amyloid angiopathy. Three "causative" AD genes (i.e., genes in which a mutation is sufficient to result in clinical AD) for early-onset familial Alzheimer's disease (FAD) and one "susceptibility" gene that affects risk and age of onset of AD in familial and sporadic late-onset AD have been identified. The three causative genes are the amyloid precursor protein (APP gene) on chromosome 21, the presenilin-1 gene on chromosome 14, and the presenilin-2 gene on chromosome 1. The susceptibility gene is the apolipoprotein E (APOE) gene on chromosome 19. Investigations of the normal and aberrant function of these genes will provide insights into the mechanisms underlying AD and will suggest new strategies for therapeutic intervention.

Kennedy's disease: caspase cleavage of the androgen receptor is a crucial event in cytotoxicity

X-linked spinal and bulbar muscular atrophy (SBMA), Kennedy's disease, is a degenerative disease of the motor neurons that is associated with an increase in the number of CAG repeats encoding a polyglutamine stretch within the androgen receptor (AR). Recent work has demonstrated that the gene products associated with open reading frame triplet repeat expansions may be substrates for the cysteine protease cell death executioners, the caspases. However, the role that caspase cleavage plays in the cytotoxicity associated with expression of the disease-associated alleles is unknown. Here, we report the first conclusive evidence that caspase cleavage is a critical step in cytotoxicity; the expression of the AR with an expanded polyglutamine stretch enhances its ability to induce apoptosis when compared with the normal AR. The AR is cleaved by a caspase-3 subfamily protease at Asp146, and this cleavage is increased during apoptosis. Cleavage of the AR at Asp146 is critical for the induction of apoptosis by AR, as mutation of the cleavage site blocks the ability of the AR to induce cell death. Further, mutation of the caspase cleavage site at Asp146 blocks the ability of the SBMA AR to form perinuclear aggregates. These studies define a fundamental role for caspase cleavage in the induction of neural cell death by proteins displaying expanded polyglutamine tracts, and therefore suggest a strategy that may be useful to treat neurodegenerative diseases associated with polyglutamine repeat expansions.

Overexpression in neurons of human presenilin-1 or a presenilin-1 familial Alzheimer disease mutant does not enhance apoptosis

Programmed cell death, or apoptosis, has been implicated in Alzheimer's disease (AD). DNA damage was assessed in primary cortical neurons infected with herpes simplex virus (HSV) vectors expressing the familial Alzheimer's disease (FAD) gene presenilin-1 (PS-1) or an FAD mutant of this gene, A246E. After infection, immunoreactivity for PS-1 was shown to be enhanced in infected cells. The infected cells exhibited no cytotoxicity, as evaluated by trypan blue exclusion and mitochondrial function assays. Quantitative analysis of cells that were immunohistochemically labeled using a Klenow DNA fragmentation assay or the TUNEL method revealed no enhancement of apoptosis in PS-1-infected cells. This result was confirmed using assays for chromatin condensation and for DNA fragmentation. Expression of PS-1 protected against induction of apoptosis in the cortical neurons by etoposide or staurosporine. The specificity of this phenotype was demonstrated by the fact that cortical cultures infected with recombinant HSV vectors expressing the amyloid precursor protein (APP-695) showed, in contrast, a significant increase in the number of apoptotic cells and an increase in DNA fragmentation for all parameters tested. Our results indicate that overexpression of wild-type or A246E mutant PS-1 does not enhance apoptosis in postmitotic cortical cells and suggest that the previously reported enhancement of apoptosis by presenilins may be dependent on cell type.

Characterization of human presenilin 1 transgenic rats: increased sensitivity to apoptosis in primary neuronal cultures

Mutations in the gene for presenilin 1 are causative for the majority of cases of early onset familial Alzheimer's disease. Yet, the physiological function of presenilin 1 and the pathological mechanisms of the mutations leading to Alzheimer's disease are still unknown. To analyse potential pathological effects of presenilin 1 over-expression, we have generated transgenic rats which express high levels of human presenilin 1 protein in the brain. The over-expression of presenilin 1 leads to saturation of its normal processing and to the appearance of full-length protein in the transgenic rat brain. The transgenic protein is expressed throughout the brain and is predominantly found in neuronal cells. Cultured primary cortical neurons derived from these transgenic rats are significantly more sensitive than non-transgenic controls to apoptosis induced by standard culture conditions and to apoptosis induced by trophic factor withdrawal. Furthermore, the observed apoptosis is directly correlated with the expression of the transgenic protein. The results further emphasize the role of presenilin 1 in apoptotic cell death in native neuronal cultures.

Regulation of apoptosis by alpha-subunits of G12 and G13 proteins via apoptosis signal-regulating kinase-1

Many growth factors and G protein-coupled receptors activate mitogen-activated protein (MAP) kinase pathways. The MAP kinase pathways are involved in the regulation of the ubiquitous process of apoptosis or programmed cell death. Two related MAP kinase kinase kinases, apoptosis-signal regulating kinase 1 (ASK1) and MAP kinase kinase kinase 1 (MEKK1), stimulate c-Jun kinase (JNK) activity and induce apoptosis. Transient transfection of dominant negative and constitutively active components of the JNK pathway in COS-7 cells showed that two G protein subunits, Galpha12 and Galpha13, stimulated the JNK pathway in a ASK1- and MEKK1-dependent manner. Moreover, the mutationally activated Galpha12 and Galpha13 stimulated the kinase activity of ASK1. Both Galpha12 and Galpha13 employ small GTPases, Cdc42 and Rac1, to transduce signal to MEKK1 and, subsequently, to JNK. However, activation of JNK by Cdc42 and Rac1 did not require ASK1. Additionally, ASK1 and MEKK1 are involved in the apoptosis induced by Galpha12 and Galpha13. We conclude that Galpha12 and Galpha13 can induce apoptosis using two separate MAP kinase pathways; one is initiated by ASK1, and the other is initiated by MEKK1. Furthermore, Bcl-2 can block apoptosis induced by Galpha12 and Galpha13. This death-sparing function was associated with increased Bcl-2 phosphorylation, suggesting that phosphorylation of Bcl-2 may be a critical mechanism protecting cells from Galpha12- and Galpha13-induced apoptosis.

Caspase-3-like activity is necessary for IL-2 release in activated Jurkat T-cells

The caspase family of proteases has previously been implicated in the biochemical cascade leading to apoptotic cell death. Recently caspase-3 was reported to be cleaved into its catalytically active subunits (17 and 13 kDa) following phytohemagglutinin (PHA) activation of peripheral blood mononuclear cells (C. Miossec et al., J. Biol. Chem. 272, 13459-13462). More recently, J. M. Zapata and colleagues (J. Biol. Chem. 273, 6916-6920, 1998), however, proposed that caspase-3 activity detected during T-cell activation was due to a methodological artifact related to the composition of the cell lysis buffer. Here we show that in PHA-activated Jurkat T-cells using the recommended lysis buffer detailed by Zapata et al., a caspase-3-like protease is activated and is accompanied by cleavage of PARP and alpha-spectrin into cleavage products suggestive of caspase-3 proteolytic activation. LDH release did not increase following PHA stimulation in this paradigm. Two caspase inhibitors, carbobenzoxy-Asp-CH2OC(O)-2,6-dichlorobenzene (Z-D-DCB) and acetyl-Asp-Glu-Val-Asp-CHO, blocked IL-2 release in a dose-dependent manner. Caspase-3-like protease-generated PARP and alpha-spectrin breakdown product formation was also reduced by Z-D-DCB. In addition, Jurkat T-cells costimulated with anti-CD3 plus anti-CD28 produced significant levels of IL-2 that were also blocked by these caspase inhibitors. Importantly, IL-2 was determined in cell culture supernatants, thus avoiding a cell lysis step that might have enabled activation of caspase-3 by granzyme B. Collectively, these data support the role of caspase-3-like protease activity in Jurkat T-cell activation and demonstrate that caspase-3 like activity is necessary for IL-2 release in PHA-activated and anti-CD3/anti-CD28 costimulated Jurkat T-cells.

Intracellular aggregate formation of dentatorubral-pallidoluysian atrophy (DRPLA) protein with the extended polyglutamine

Dentatorubral-pallidoluysian atrophy (DRPLA) is an autosomal dominant neurodegenerative disorder caused by the abnormal CAG triplet-repeat expansion resulting in an elongated polyglutamine (polyQ) stretch. We have recently showed that the DRPLA protein is cleaved during apoptosis by caspase-3, one of the cysteine protease family members known to be activated during apoptosis. We report here the subcellular localization of the DRPLA protein by fusing the green fluorescent protein as a tag. The full length DRPLA protein is localized predominantly but not exclusively in the nucleus regardless of the length of the polyQ stretch. In contrast, an N-terminal-deleted fragment containing polyQ produced by the proteolytic cleavage with caspase-3 is found both in the nucleus and the cytoplasm. Moreover, the same fragment with the elongated polyQ showed aggregation when overexpressed. Some cells with aggregate formation showed apoptotic phenotype. These findings raise the possibility that the DRPLA protein processed by caspase-3 may lead to aggregation of the protein resulting in the development of neurodegeneration.

Fragments of amyloid beta induce apoptosis in vascular endothelial cells

Injury to cells that was triggered by fragments of amyloid beta protein (A beta) was studied in human vascular endothelial cells. A fragment of A beta containing amino acids 25-35 promoted cell death, but fragments of A beta containing amino acids 31-35 and 35-25 did not have such an effect. The fragment of A beta containing amino acids 25-35 induced cell death that was characterized as programmed cell death (apoptosis) in view of the accompanying morphological changes, the fragmentation of DNA, and the requirement for protein synthesis.

Endothelin-induced apoptosis of A375 human melanoma cells

Endothelin-1 (ET-1) inhibited serum-dependent growth of asynchronized A375 human melanoma cells, and the growth inhibitory effect was markedly enhanced when ET-1 was applied to the cells synchronized at G1/S boundary by double thymidine blocks. Flow cytometric analysis revealed that ET-1 did not inhibit the cell cycle progression after the release of the block but caused a significant increase of the hypodiploid cell population that is characteristic of apoptotic cell death. ET-1-induced apoptosis was confirmed by the appearance of chromatin condensation on nuclear staining and DNA fragmentation on gel electrophoresis. The increase in the hypodiploid cell peak was manifest within 16 h of exposure to 5 nM ET-1. Within the same time range, ET-1 caused actin reorganization and drastic morphological changes of the surviving cells from epithelioid to an elongated bipolar shape. These phenotypical changes were preceded by ET-1-induced increase and nuclear accumulation of the tumor suppressor protein p53. All of these effects of ET-1 were mediated by ETB via a pertussis toxin-sensitive G protein. Flow cytometric analysis with fluorescent dye-labeled ET-1 revealed up-regulation of ETB expressed by the cells in G1/early S phases, and overexpression of the receptor protein by cDNA microinjection conferred the responsiveness (both apoptosis and morphological changes) to ET-1 irrespective of the position of the cell in the cell cycle. These results indicated the presence of ETB-mediated signaling pathways to apoptotic cell machinery and cytoskeletal organization. Furthermore, the densities of ETB expressed by individual A375 melanoma cells appeared to be regulated by a cell cycle-dependent mechanism, and the receptor density can be a limiting factor to control the apoptotic and cytoskeletal responses of the cells to ET-1. Although the molecular mechanisms remain to be elucidated, these findings added a new dimension to the diverse biological activities of ETs and also indicated a novel mechanism to control the responsiveness of the cell to the peptides.

Caveolae, plasma membrane microdomains for alpha-secretase-mediated processing of the amyloid precursor protein

Caveolae are plasma membrane invaginations where key signaling elements are concentrated. In this report, both biochemical and histochemical analyses demonstrate that the amyloid precursor protein (APP), a source of Abeta amyloid peptide, is enriched within caveolae. Caveolin-1, a principal component of caveolae, is physically associated with APP, and the cytoplasmic domain of APP directly participates in this binding. The characteristic C-terminal fragment that results from APP processing by alpha-secretase, an as yet unidentified enzyme that cleaves APP within the Abeta amyloid sequence, was also localized within these caveolae-enriched fractions. Further analysis by cell surface biotinylation revealed that this cleavage event occurs at the cell surface. Importantly, alpha-secretase processing was significantly promoted by recombinant overexpression of caveolin in intact cells, resulting in increased secretion of the soluble extracellular domain of APP. Conversely, caveolin depletion using antisense oligonucletotides prevented this cleavage event. Our current results indicate that caveolae and caveolins may play a pivotal role in the alpha-secretase-mediated proteolysis of APP in vivo.

GABAergic deafferentation hypothesis of brain aging and Alzheimer's disease revisited

Considering the mechanisms responsible for age- and Alzheimer's disease (AD)-related neuronal degeneration, little attention was paid to the opposing relationships between the energy-rich phosphates, mainly the availability of the adenosine triphosphate (ATP), and the activity of the glutamic acid decarboxylase (GAD), the rate-limiting enzyme synthesizing the gamma-amino butyric acid (GABA). Here, it is postulated that in all neuronal phenotypes the declining ATP-mediated negative control of GABA synthesis gradually declines and results in age- and AD-related increases of GABA synthesis. The Ca2+-independent carrier-mediated GABA release interferes with Ca2+-dependent exocytotic release of all transmitter-modulators, because the interstitial (ambient) GABA acts on axonal preterminal and terminal varicosities endowed with depolarizing GABA(A)-benzodiazepine receptors; this makes GABA the "executor" of virtually all age- and AD-related neurodegenerative processes. Such a role of GABA is diametrically opposite to that in the perinatal phase, when the carrier-mediated GABA release, acting on GABA(A)/chloride ionophore receptors, positively controls chemotactic migration of neuronal precursor cells, has trophic actions and initiates synaptogenesis, thereby enabling retrograde axonal transport of target produced factors that trigger differentiation of neuronal phenotypes. However, with advancing age, and prematurely in AD, the declining mitochondrial ATP synthesis unleashes GABA synthesis, and its carrier-mediated release blocks Ca2+-dependent exocytotic release of all transmitter-modulators, leading to dystrophy of chronically depolarized axon terminals and block of retrograde transport of target-produced trophins, causing "starvation" and death of neuronal somata. The above scenario is consistent with the following observations: 1) a 10-month daily administration to aging rats of the GABA-chloride ionophore antagonist, pentylenetetrazol, or of the BDZ antagonist, flumazenil (FL), each forestalls the age-related decline in cognitive functions and losses of hippocampal neurons; 2) the brains of aging rats, relative to young animals, and the postmortem brains of AD patients, relative to age-matched controls, show up to two-fold increases in GABA synthesis; 3) the aging humans and those showing symptoms of AD, as well as the aging nonhuman primates and rodents--all show in the forebrain dystrophic axonal varicosities, losses of transmitter vesicles, and swollen mitochondria. These markers, currently regarded as the earliest signs of aging and AD, can be reproduced in vitro cell cultures by 1 microM GABA; the development of these markers can be prevented by substituting Cl- with SO4(2-); 4) the extrasynaptic GABA suppresses the membrane Na+, K+-ATPase and ion pumping, while the resulting depolarization of soma-dendrites relieves the "protective" voltage-dependent Mg2+ control of the N-methyl-D-aspartate (NMDA) channels, thereby enabling Ca2+-dependent persistent toxic actions of the excitatory amino acids (EAA); and 5) in whole-cell patch-clamp recording from neurons of aging rats, relative to young rats, the application of 3 microM GABA, causes twofold increases in the whole-cell membrane Cl- conductances and a loss of the physiologically important neuronal ability to desensitize to repeated GABA applications. These age-related alterations in neuronal membrane functions are amplified by 150% in the presence of agonists of BDZ recognition sites located on GABA receptor. The GABA deafferentation hypothesis also accounts for the age- and AD-related degeneration in the forebrain ascending cholinergic, glutamatergic, and the ascending mesencephalic monoaminergic system, despite that the latter, to foster the distribution-utilization of locally produced trophins, evolved syncytium-like connectivities among neuronal somata, axon collaterals, and dendrites, to bidirectionally transport trophins. (ABSTRACT TRUNCATED)

Apoptosis, excitotoxicity, and neuropathology

While a high rate of cell loss is tolerated and even required to model the developing nervous system, an increased rate of cell death in the adult nervous system underlies neurodegenerative disease. Evolutionarily conserved mechanisms involving proteases, Bcl-2-related proteins, p53, and mitochondrial factors participate in the modulation and execution of cell death. In addition, specific death mechanisms, based on specific neuronal characteristics such as excitability and the presence of specific channels or enzymes, have been unraveled in the brain. Particularly important for various human diseases are excessive nitric oxide (NO) production and excitotoxicity. These two pathological mechanisms are closely linked, since excitotoxic stimulation of neurons may trigger enhanced NO production and exposure of neurons to NO may trigger the release of excitotoxins. Depending on the experimental situation and cell type, excitotoxic neuronal death may either be apoptotic or necrotic.

A neuronal C5a receptor and an associated apoptotic signal transduction pathway

1. We report the first experimental evidence of a neuronal C5a receptor (nC5aR) in human cells of neuronal origin. Expression of nC5aR mRNA was demonstrated by the reverse transcriptase-polymerase chain reaction (RT-PCR) in TGW human neuroblastoma cells. 2. Expression of a functional C5aR was supported by the finding that C5a evoked a transient increase in the intracellular calcium level as measured by flow cytometry (FACS). 3. To analyse the function of the nC5aR, an antisense peptide fragment of the C5aR was used. Previous data showed that a C5aR fragment (a peptide termed PR226) has C5aR agonist and antagonist effects in U-937 cells depending on the concentration of the peptide. We found that a multiple antigenic peptide (MAP) form of the same peptide (termed PR226-MAP) induced rapid elevation of nuclear c-fos immunoreactivity and resulted in DNA fragmentation, a characteristic sign of apoptosis, in TGW cells. 4. Early electrophysiological events characteristic of apoptosis were also detected: intermittent calcium current pulses were recorded within 1-2 min of peptide administration. C5a pretreatment delayed the onset of this calcium influx. 5. We also demonstrated that the apoptotic pathway is linked to nC5aR via pertussis toxin-sensitive G-proteins. 6. Although the function of C5a and its receptor on neurons is unknown, these results suggest that an abnormal activation of this signal transduction pathway can result in apoptosis and, subsequently, in neurodegeneration.

Increased amyloidogenic secretion in cerebellar granule cells undergoing apoptosis

Some clues suggest that neuronal damage induces a secondary change of amyloid beta protein (Abeta) metabolism. We investigated this possibility by analyzing the secretion of Abeta and processing of its precursor protein (amyloid precursor protein, APP) in an in vitro model of neuronal apoptosis. Primary cultures of rat cerebellar granule neurons were metabolically labeled with [35S]methionine. Apoptosis was induced by shifting extracellular KCl concentration from 25 mM to 5 mM for 6 h. Control and apoptotic neurons were then subjected to depolarization-stimulated secretion. Constitutive and stimulated secretion media and cell lysates were immunoprecipitated with antibodies recognizing regions of Abeta, full-length APP, alpha- and beta-APP secreted forms. Immunoprecipitated proteins were separated by SDS/PAGE and quantitated with a PhosphorImager densitometer. Although intracellular full-length APP was not significantly changed after apoptosis, the monomeric and oligomeric forms of 4-kDa Abeta were 3-fold higher in depolarization-stimulated secretion compared with control neurons. Such increments were paralleled by a corresponding increase of the beta-APPs/alpha-APPs ratio in apoptotic secretion. Immunofluorescence studies performed with an antibody recognizing an epitope located in the Abeta sequence showed that the Abeta signal observed in the cytoplasm and in the Golgi apparatus of control neurons is uniformly redistributed in the condensed cytoplasm of apoptotic cells. These studies indicate that neuronal apoptosis is associated with a significant increase of metabolic products derived from beta-secretase cleavage and suggest that an overproduction of Abeta may be the consequence of neuronal damage from various causes.