Presenilin-1 mutation increases neuronal vulnerability to focal ischemia in vivo and to hypoxia and glucose deprivation in cell culture: involvement of perturbed calcium homeostasis

Regulated intramembrane proteolysis of the low-density lipoprotein receptor-related protein mediates ischemic cell death

The low-density lipoprotein receptor-related protein (LRP), a member of the low-density lipoprotein receptor gene family, mediates cellular signal transduction pathways. In this study we investigated the role of LRP in cell death. We found that incubation of mouse embryonic fibroblasts in serum-free media induces caspase-3 activation, an effect that is attenuated in LRP-deficient (LRP(-/-)) mouse embryonic fibroblasts. Since we previously demonstrated that middle cerebral artery occlusion (MCAO) in mice induces shedding of the LRP ectodomain, we investigated here whether cerebral ischemia induces regulated intramembrane proteolysis of LRP and whether this process is related to cell death. We found that MCAO induces an increase in gamma-secretase activity in the ischemic hemisphere and that treatment with the gamma-secretase inhibitor L-685,458 improves the neurological outcome and results in a 50% decrease in the volume of the ischemic lesion. Furthermore, MCAO caused nuclear translocation of the intracellular domain of LRP in neurons within the area of ischemic penumbra, and this effect was attenuated in mice treated with L-685,458. Finally, inhibition of either LRP or gamma-secretase attenuated cerebral ischemia-induced caspase-3 cleavage and apoptotic cell death. In summary, our results indicate that gamma-secretase-mediated regulated intramembrane proteolysis of LRP results in cell death under ischemic conditions.

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

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

Raloxifene acutely reduces glutamate-induced intracellular calcium increase in cultured rat cortical neurons via inhibition of high-voltage-activated calcium current

There is increasing evidence indicating that estrogen replacement therapy produces neuroprotective actions but has undesirable side effects on the reproductive system. Raloxifene is a selective estrogen receptor modulator that exerts estrogen agonist action in the brain while acting as an estrogen antagonist in the reproductive system. In the present study, we investigated whether raloxifene affected the glutamate-induced calcium (Ca2+) overload in rat cultured cortical neurons. The bulk cytosolic intracellular Ca2+ level was measured by using confocal microscopy with fluorescent Ca2+ probe fluo3. Whole-cell recording technique was used to observe the effects of raloxifene on N-methyl-D-aspartate (NMDA)-evoked and voltage-activated Ca2+ currents in cultured cortical neurons. Pre-exposure of cortical neurons to raloxifene (0.5 microM-10 microM) for 3 min attenuated intracellular Ca2+ increase induced by application of glutamate (300 microM) for 1 min. The action of raloxifene was reversible after washout. ICI 182,780 and thapsigargin did not block the action of raloxifene. In whole-cell recording experiments, raloxifene (10 microM) significantly reduced the amplitude of the high-voltage-activated Ca2+ current but had no effect on NMDA-evoked Ca2+ current. The present study demonstrates that raloxifene acutely reduces glutamate-induced intracellular Ca2+ increase probably via inhibition of high-voltage-activated calcium channels.

Calcium and neurodegeneration

When properly controlled, Ca2+ fluxes across the plasma membrane and between intracellular compartments play critical roles in fundamental functions of neurons, including the regulation of neurite outgrowth and synaptogenesis, synaptic transmission and plasticity, and cell survival. During aging, and particularly in neurodegenerative disorders, cellular Ca2+-regulating systems are compromised resulting in synaptic dysfunction, impaired plasticity and neuronal degeneration. Oxidative stress, perturbed energy metabolism and aggregation of disease-related proteins (amyloid beta-peptide, alpha-synuclein, huntingtin, etc.) adversely affect Ca2+ homeostasis by mechanisms that have been elucidated recently. Alterations of Ca2+-regulating proteins in the plasma membrane (ligand- and voltage-gated Ca2+ channels, ion-motive ATPases, and glucose and glutamate transporters), endoplasmic reticulum (presenilin-1, Herp, and ryanodine and inositol triphosphate receptors), and mitochondria (electron transport chain proteins, Bcl-2 family members, and uncoupling proteins) are implicated in age-related neuronal dysfunction and disease. The adverse effects of aging on neuronal Ca2+ regulation are subject to modification by genetic (mutations in presenilins, alpha-synuclein, huntingtin, or Cu/Zn-superoxide dismutase; apolipoprotein E isotype, etc.) and environmental (dietary energy intake, exercise, exposure to toxins, etc.) factors that may cause or affect the risk of neurodegenerative disease. A better understanding of the cellular and molecular mechanisms that promote or prevent disturbances in cellular Ca2+ homeostasis during aging may lead to novel approaches for therapeutic intervention in neurological disorders such as Alzheimer's and Parkinson's diseases and stroke.

Expansion of the calcium hypothesis of brain aging and Alzheimer's disease: minding the store

Evidence accumulated over more than two decades has implicated Ca²⁺ dysregulation in brain aging and Alzheimer's disease (AD), giving rise to the Ca²⁺ hypothesis of brain aging and dementia. Electrophysiological, imaging, and behavioral studies in hippocampal or cortical neurons of rodents and rabbits have revealed aging-related increases in the slow afterhyperpolarization, Ca²⁺ spikes and currents, Ca²⁺ transients, and L-type voltage-gated Ca²⁺ channel (L-VGCC) activity. Several of these changes have been associated with age-related deficits in learning or memory. Consequently, one version of the Ca²⁺ hypothesis has been that increased L-VGCC activity drives many of the other Ca²⁺-related biomarkers of hippocampal aging. In addition, other studies have reported aging- or AD model-related alterations in Ca²⁺ release from ryanodine receptors (RyR) on intracellular stores. The Ca²⁺-sensitive RyR channels amplify plasmalemmal Ca²⁺ influx by the mechanism of Ca²⁺-induced Ca²⁺ release (CICR). Considerable evidence indicates that a preferred functional link is present between L-VGCCs and RyRs which operate in series in heart and some brain cells. Here, we review studies implicating RyRs in altered Ca²⁺ regulation in cell toxicity, aging, and AD. A recent study from our laboratory showed that increased CICR plays a necessary role in the emergence of Ca²⁺-related biomarkers of aging. Consequently, we propose an expanded L-VGCC/Ca²⁺ hypothesis, in which aging/pathological changes occur in both L-type Ca²⁺ channels and RyRs, and interact to abnormally amplify Ca²⁺ transients. In turn, the increased transients result in dysregulation of multiple Ca²⁺-dependent processes and, through somewhat different pathways, in accelerated functional decline during aging and AD.

Ischemia-induced neuronal cell death and stress response

Neuronal cell death is a major feature of various diseases, including brain ischemia, neuronal degenerative diseases, and traumatic injury, suggesting the importance of investigating the mechanisms that mediate neuronal cell death. Although the various factors that contribute to brain ischemia have been defined and the mechanism through which each factor causes neuronal cell death has been investigated, definite strategies have not been established. In this brief review, we focus on two important mechanisms that contribute to the pathogenesis of brain ischemia. First, we discuss the glutamate theory, a proposed mechanism for the understanding of ischemia-induced neuronal cell death. Second, an accumulation of recent molecular neurobiology evidence regarding the dysfunction of a cellular organelle, the endoplasmic reticulum (ER), suggests that it plays a major role in the pathogenesis of neuronal cell death. Whereas the former theory reflects the role of neuron-specific factors in the induction of cell death, the stress response of the ER for maintenance of its function is regarded as a defense mechanism. Because hypoxia, another major factor in ischemia, results in further dysfunction of the ER, studies on the malfunction of this cellular organelle may facilitate the development of novel strategies to block ischemia-induced cell death.

Alterations in presenilin 1 processing by amyloid-beta peptide in the rat retina

Accumulating evidence indicates that mutations in the presenilin 1 (PS1) gene are responsible for most cases of familial Alzheimer's disease (AD). Although its biological functions are not yet fully understood, it appears that PS1 plays a role in the processing and trafficking of the amyloid precursor protein (APP). However, little is known about factors that are involved in regulating the metabolism of PS1 especially in relation to AD pathology. In this study, we have examined the effect of optic nerve crush, intravitreal injection of the inflammatory agent lipopolysaccharide (LPS) or injection of amyloid beta(1-42) (A beta(1-42)) on the expression and processing of PS1 in the rat retina. We found that 48 h after injection of A beta(1-42) there was a dramatic alteration in the banding pattern of PS1 on Western blots, as indicated by marked changes in the levels of expression of some of its C- and N-terminal fragments in retinal homogenates. These results suggest an A beta(1-42)-induced potentiation of a non-specific stress-related but inflammation-independent alteration of processing of PS1 in this in vivo model.

Relationship between antihypertensive drug therapy and cognitive function in elderly hypertensive patients with memory complaints

OBJECTIVE

To evaluate the relationship between antihypertensive treatments and cognitive function in elderly hypertensive patients with memory complaints.

METHODS

The association between cognitive function and antihypertensive drug therapy was studied in 1241 hypertensive elderly patients with memory complaints attending a geriatric outpatient clinic. Cognitive function was assessed using the Mini Mental State Examination (MMSE) and validated neuropsychological tests (Cognitive Efficiency Profile; CEP). Patients were classified into four categories according to their cognitive status: normal cognitive function, mild cognitive impairment (MCI), Alzheimer's disease (AD) or vascular dementia (VaD).

RESULTS

In this population aged 78 +/- 8 years, with a mean blood pressure of 152 +/- 19/86 +/- 12 mmHg, antihypertensive treatment was prescribed for 57% of patients. After adjustment for age, sex and education, treated hypertensive patients had better cognitive function than untreated patients (MMSE score 23.9 +/- 5.6/30 versus 22.7 +/- 6.4/30, P < 0.001, CEP score 49.1 +/- 24.9/100 versus 45.4 +/- 23.7/100, P < 0.001). This association was observed independently of the cognitive status, both in normal, MCI, AD and VaD hypertensive patients. The odds ratio (OR) for AD was 0.58 [95% confidence interval (CI) 0.42-0.81] in treated compared with untreated hypertensive patients. In patients on antihypertensive therapy, higher cognitive function was observed in patients using calcium antagonists compared with those without calcium antagonists (CEP 52.9 +/- 24.6/100 versus 46.4 +/- 23.4/100, P < 0.001; OR for AD 0.67; 95% CI 0.45-0.99), independently of blood pressure level.

CONCLUSIONS

Antihypertensive therapy was associated with a lower risk of cognitive impairment and AD. In particular, the use of calcium antagonists was associated with a decreased risk of cognitive impairment and AD independently of the blood pressure level, suggesting a specific neuroprotective effect of these antihypertensive agents.

Hypocapnia induces caspase-3 activation and increases Abeta production

BACKGROUND

At least half of all cases of early onset (<60) familial Alzheimer's disease (FAD) are caused by any of over 150 mutations in three genes: the amyloid precursor protein (APP), presenilin 1 (PS1), and presenilin 2 (PS2). Mutant forms of PS1 have been shown to sensitize cells to apoptotic cell death.

OBJECTIVE

We investigated the effects of hypocapnia, a risk factor for both cognitive and neurodevelopment deficits, on caspase-3 activation, apoptosis, and amyloid beta-protein (Abeta) production, and assessed the influence of the PS1Delta9 FAD mutation on these effects.

METHOD

For this purpose, we exposed stably transfected H4 human neuroglioma cells to conditions consistent with hypocapnia (PCO2<40 mm Hg) and hypocapnia plus hypoxia (PO2<21%).

RESULTS

Hypocapnia (20 mm Hg CO2 for 6 h) induced caspase-3 activation and apoptosis; the PS1Delta9 FAD mutation significantly potentiated these effects. Moreover, the combination of hypocapnia (20 mm Hg CO2) and hypoxia (5%O2) induced caspase-3 activation and apoptosis in a synergistic manner. Hypocapnia (5 and 20 mm Hg CO2 for 6 h) also led to an increased Abeta production.

CONCLUSION

The findings suggest that hypocapnia (e.g. during general anesthesia) could exacerbate AD neuropathogenesis.

Alzheimer's Disease Pathogenesis: Role of Aging

Alzheimer's disease (AD) is the chief cause of dementia, and age is its major risk factor. The majority of cases (90-95%) are sporadic (SAD), and the remainder are familial (FAD). AD is characterized by two brain lesions, intraneuronal fibrillary tangles and extracellular plaques. The lesions are identical in SAD and FAD as well as to those in persons with Down's syndrome (DS). The same lesions are also observed frequently in elderly non-demented individuals (E-ND). Both AD lesions may stem from the normal progressive increases in oxidative stress (OxS) throughout the body with age. Onset of dementia due to the accumulating lesions is around 40 years for DS, 40-60 years for FAD, over about 65 years for SAD, while that for E-ND is unknown. The lesions are made clinically manifest with time by the normal increase with age of OxS, "the dementia of old age," or by a process specific for each AD category, which enhances the normal OxS so as to lower the unknown onset age of dementia for E-ND individuals to that associated with the AD category. A plausible process can be advanced for each AD category. The hypothesis suggests convenient, effective measures to prevent and treat, for example, by decreasing brain OxS levels with oral antioxidants such as lipoic or dehydroascorbic acids that are capable of passing the blood-brain barrier.

Alzheimer's disease and post-operative cognitive dysfunction

Alzheimer's disease (AD), an insidious and progressive neurodegenerative disorder accounting for the vast majority of dementia, is characterized by global cognitive decline and the robust accumulation of amyloid deposits and neurofibrillary tangles in the brain. This review article is based on the currently published literature regarding molecular studies of AD and the potential involvement of AD neuropathogenesis in post-operative cognitive dysfunction (POCD). Genetic evidence, confirmed by neuropathological and biochemical studies, indicates that excessive beta-amyloid protein (Abeta) generated from amyloidogenic processing of the beta-amyloid precursor protein (APP) plays a fundamental role in the AD neuropathogenesis. Abeta is produced from APP by beta-secretase, and then gamma-secretase complex, consisting of presenilins, nicastrin (NCSTN), APH-1 and PEN-2. Additionally, Abeta clearance and APP adaptor proteins can contribute to AD neuropathogenesis via affecting Abeta levels. Finally, cellular apoptosis may also be involved in AD neuropathogenesis. Surgery and anesthesia can cause cognitive disorders, especially in elderly patients. Even the molecular mechanisms underlying these disorders are largely unknown; several perioperative factors such as hypoxia, hypocapnia and anesthetics may be associated with AD and render POCD via trigging AD neuropathogenesis. More studies to assess the potential relationship between anesthesia/surgery and AD dementia are, therefore, urgently needed.

Inositol phosphates and phosphoinositides in health and disease

In the past two decades, considerable progress has been made toward understanding inositol phosphates and PI metabolism. However, there is still much to learn. The present challenge is to understand how inositol phosphates and PIs are compartmentalized, identify new targets of inositol phosphates and PIs, and elucidate the mechanisms underlying spatial and temporal regulation of the enzymes that metabolize inositol phosphates and PIs. Answers to these questions will help clarify the mechanisms of the diseases associated with these molecules and identify new possibilities for drug design.

Perturbations in calcium-mediated signal transduction in microglia from Alzheimer's disease patients

Calcium-sensitive fluorescence microscopy has been used to study Ca2+-dependent signal transduction pathways in microglia obtained from Alzheimer's disease (AD) patients and non-demented (ND) individuals. Data were obtained from nine AD cases and seven ND individuals and included basal levels of intracellular Ca2+ [Ca2+]i, peak amplitudes (Delta[Ca2+]i) and time courses of adenosine triphosphate (ATP) responses and amplitudes of an initial transient response and a subsequent second component of Ca2+ influx through store-operated channels (SOC) induced by platelet-activating factor (PAF). Overall, AD microglia were characterized by significantly higher (20%) basal Ca2+ [Ca2+]i relative to ND cells. The Delta[Ca2+]i of ATP and initial phase of PAF responses, which reflect rapid depletion of Ca2+ from endoplasmic reticulum stores, were reduced by respective values of 63% and 59% in AD cells relative to amplitudes recorded from ND microglia. Additionally, AD microglia showed diminished amplitudes (reduction of 61%) of SOC-mediated Ca2+ entry induced by PAF and prolonged time courses (increase of 60%) of ATP responses with respect to ND microglia. We have generally replicated these results with exposure of human fetal microglia to beta amyloid (5 microM Abeta1-42 applied for 24 hr). Overall, these data indicate significant abnormalities are present in Ca2+-mediated signal transduction in microglia isolated from AD patients.

Endoplasmic reticulum stress response and neurodegeneration

The endoplasmic reticulum (ER) is a subcellular compartment playing a central role in calcium storage and signaling. Disturbances of ER calcium homeostasis constitute a severe form of stress interfering with central functions of this structure including the folding and processing of newly synthesized membrane and secretory proteins. Blocking the folding and processing reactions results in the accumulation of unfolded proteins forming potentially toxic aggregates. To restore ER functioning, specific stress responses are activated one of which is the unfolded protein response (UPR). UPR is characterized by a shutdown of global protein synthesis and activation of expression of genes coding for ER-resident proteins that are involved in the folding and processing reactions. ER calcium homeostasis is therefore inevitably associated with major cellular functions, including gene transcription and translation. ER calcium homeostasis und ER functions are believed to be impaired in various degenerative diseases of the brain including Alzheimer's, Parkinson's and Huntington's disease, and amyotrophic lateral sclerosis. ER functioning has also been shown to be disturbed in acute pathological states of the brain such as ischemia and trauma, which have been identified as risk factors for the development of degenerative diseases. This implies that there are common underlying pathomechanisms. This review will summarize new observations suggesting that impairment of ER functioning may be a common denominator of pathological processes resulting in neuronal cell injury in acute disorders and degenerative diseases of the brain.

Effects of azumolene on Ca2+ sparks in skeletal muscle fibers

Azumolene is an analog of dantrolene, the only approved medicine for treatment of malignant hyperthermia (MH). The pharmacological mechanism of these drugs is to inhibit skeletal muscle sarcoplasmic reticulum (SR) Ca2+ release by modulating the activity of the SR ryanodine receptor (RyR) Ca2+ release channel. To investigate the effects of azumolene on SR Ca2+ channel gating within skeletal muscle fibers, we monitored Ca2+ sparks in permeabilized frog skeletal muscle fibers. Application of 0.0001 to 10 microM azumolene suppressed the frequency of spontaneous Ca2+ sparks in a dose-dependent manner (EC50 = 0.25 microM; Hill coefficient = 1.44), but it did not cause systematic dose-dependent effects on the properties of the Ca2+ sparks. These results suggest that azumolene decreases the likelihood of Ca2+ release channel openings that initiate Ca2+ sparks, thereby decreasing spark frequency, but it has little effect on aggregate Ca2+ channel open times during a spark. To assess azumolene inhibition of RyRs activated in a manner analogous to those activated during an MH episode, we applied DP4, a synthetic peptide corresponding to a central region of RyR1 (Leu2442 to Pro2477), which mimics an MH modification. Azumolene also decreased Ca2+ spark frequency in a dose-dependent manner without altering spark properties in the DP4 MH model. We conclude that azumolene suppresses the opening rate but not the open time of RyR Ca2+ release channels within skeletal fibers.

The protective effect of dantrolene on ischemic neuronal cell death is associated with reduced expression of endoplasmic reticulum stress markers

The endoplasmic reticulum (ER) plays an important role in ischemic neuronal cell death. In order to determine the effect of dantrolene, a ryanodine receptor antagonist, on ER stress response and ischemic brain injury, we investigated changes in ER stress-related molecules, that is phosphorylated form of double-stranded RNA-activated protein kinase (PKR)-like ER kinase (p-PERK), phosphorylated form of eukaryotic initiation factor 2alpha (p-eIF2alpha), activating transcription factor-4 (ATF-4), and C/EBP-homologous protein (CHOP), as well as terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) in the peri-ischemic area and ischemic core region of rat brain after transient middle cerebral artery occlusion (MCAO). In contrast to the cases treated with vehicle, the infarct volume and TUNEL-positive cells were significantly reduced at 24 h of reperfusion by treatment with dantrolene. The immunoreactivities for p-PERK, p-eIF2alpha, ATF-4, and CHOP were increased at the ischemic peripheral region after MCAO, which were partially inhibited by dantrolene treatment. The present results suggest that dantrolene significantly decreased infarct volume and provided neuroprotective effect on rats after transient MCAO by reducing ER stress-mediated apoptotic signal pathway activation in the ischemic area.

Interaction of presenilins with FKBP38 promotes apoptosis by reducing mitochondrial Bcl-2

Presenilins 1 and 2 (PS1/2), causative molecules for familial Alzheimer's disease (FAD), are multipass transmembrane proteins localized predominantly in the endoplasmic reticulum (ER) and Golgi apparatus. Heteromeric protein complexes containing PS1/2 are thought to participate in several functions, including intramembrane proteolysis mediated by their gamma-secretase activities. Previous studies have shown that PS1/2 are also involved in the regulation of apoptotic cell death, although the underlying mechanism remains unknown. Here, we demonstrate that FKBP38, an immunophilin family member residing in the mitochondrial membrane, is an authentic PS1/2-interacting protein. PS1/2 and FKBP38 form macromolecular complexes together with anti-apoptotic Bcl-2. PS1/2 promote the degradation of FKBP38 and Bcl-2 and sequester these proteins in the ER/Golgi compartments, thereby inhibiting FKBP38-mediated mitochondrial targeting of Bcl-2 via a gamma-secretase-independent mechanism. Thus, PS1/2 increase the susceptibility to apoptosis by antagonizing the anti-apoptotic function of FKBP38. In contrast, C-terminal fragments of caspase-processed PS1/2 redistribute Bcl-2 to the mitochondria by abrogating the activity of full-length PS1/2, resulting in a dominant-negative anti-apoptotic effect. In cultured cells and mutant PS1-knockin mice brains, FAD-linked PS1/2 mutants enhance the pro-apoptotic activity by causing a more efficient reduction in mitochondrial Bcl-2 than wild-type PS1/2. These results suggest a novel molecular mechanism for the regulation of mitochondria-mediated apoptosis by competition between PS1/2 and FKBP38 for subcellular targeting of Bcl-2. Excessive pro-apoptotic activity of PS1/2 may play a role in the pathogenesis of FAD.

Temporary focal ischemia in the mouse: Technical aspects and patterns of Fluoro-Jade evident neurodegeneration

Animal models of cerebral infarction are crucial to understanding the mechanisms of neuronal survival following ischemic brain injury and to the development of therapeutic interventions for victims of all types of stroke. Rodents have been used extensively in such research. One rodent model of stroke utilizes either permanent or temporary occlusion of the middle cerebral artery (MCAO) to produce ischemia. Since the development of an endovascular method for this was published in 1989, MCAO has been applied commonly to the rat, and often paired with 2, 3, 5-triphenyltetrazolium chloride (TTC) staining for stroke volume measurement. Meanwhile, advances in the ability to genetically alter mice have allowed exciting lines of research into ischemia. Because of technical demands and issues with survival, relatively few laboratories have investigated the MCAO method in the mouse. Our present work utilizes a mouse middle cerebral occlusion (MCAO) model of embolic stroke to study neuronal degeneration following temporary focal cerebral ischemia. C57Bl/6J mice were used to examine the exact effects of MCAO using Fluoro-Jade, a marker of neurodegeneration that allows observation of specific brain regions and cells destined to die. A time course of escalating neuronal degeneration from 10 min to 7 days following MCAO was established. Technical aspects of this popular method for transient focal ischemia as it applies to the mouse are discussed.

Anti-oxidant gene expression imbalance, aging and Down syndrome

The expression of copper zinc superoxide dismutase (SOD1), manganese superoxide dismutase (SOD2), glutathione peroxidase (GPx), and catalase (CAT) genes have been detected in human skin fibroblast cells for 2 year normal child (control), 50 year old normal male and female and a 1 year old Down Syndrome (DS) male and female with established trisomy karyotype using the RT-PCR technique. Differential expression of these genes is quantified individually against a beta-Actin gene that has been employed as an internal control. The immunoblotting of cell lysate proteins with polyclonal antibodies exhibit SOD1 (16 kD), SOD2 (40 kD), GPx (23 and 92 kD), CAT (64 kD), and Actin (43 kD) as translational products. The results demonstrate that the enhancement in the level of mRNAs encoding SOD1 in DS male and female, as well as aged male and female are 51, 21, 31 and 50% respectively compared to the normal child (control). In SOD2, DS male and female display higher (176%) and lower (26%) levels of expression whereas aged male and female exhibit enhanced levels of expression (66 and 119%) respectively compared to the control. This study demonstrates that DS affects the female less than the male whereas in the aging process, the female is more prone to oxidative damage than the male. These results not only indicate that the level of GPx mRNA is constant except in DS male, which shows a downward regulation but that even CAT mRNA is upward regulated in aged as well as in DS males and females. These disproportionate changes in anti-oxidant genes, which are incapable of coping with over expressed genes, may contribute towards the aging process, dementia and Down syndrome.

Coenzyme Q10 protects SHSY5Y neuronal cells from beta amyloid toxicity and oxygen-glucose deprivation by inhibiting the opening of the mitochondrial permeability transition pore

Coenzyme Q10 (CoQ10) is an essential biological cofactor which increases brain mitochondrial concentration and exerts neuroprotective effects. In the present study, we exposed SHSY5Y neuroblastoma cells to neurotoxic beta amyloid peptides (Abeta) and oxygen glucose deprivation (OGD) to investigate the neuroprotective effect of 10 microM CoQ10 by measuring (i) cell viability by the MTT assay, (ii) opening of the mitochondrial permeability transition pore via the fluorescence intensity of calcein-AM, and (iii) superoxide anion concentration by hydroethidine. Cell viability (mean +/- S.E.M.) was 55.5 +/- 0.8% in the group exposed to Abeta + OGD, a value lower than that in the Abeta or OGD group alone (P < 0.01). CoQ10 had no neuroprotective effect on cell death induced by either Abeta or OGD, but increased cell survival in the Abeta + OGD group to 57.3 +/- 1.7%, which was higher than in the group treated with vehicle (P < 0.05). The neuroprotective effect of CoQ10 was blocked by administration of 20 microM atractyloside. Pore opening and superoxide anion concentration were increased in the Abeta + OGD group relative to sham control (P < 0.01), and were attenuated to the sham level (P > 0.05) when CoQ10 was administered. Our results demonstrate that CoQ10 protects neuronal cells against Abeta neurotoxicity together with OGD by inhibiting the opening of the pore and reducing the concentration of superoxide anion.

Physiology and Pathophysiology of the Calcium Store in the Endoplasmic Reticulum of Neurons

The endoplasmic reticulum (ER) is the largest single intracellular organelle, which is present in all types of nerve cells. The ER is an interconnected, internally continuous system of tubules and cisterns, which extends from the nuclear envelope to axons and presynaptic terminals, as well as to dendrites and dendritic spines. Ca2+release channels and Ca2+pumps residing in the ER membrane provide for its excitability. Regulated ER Ca2+release controls many neuronal functions, from plasmalemmal excitability to synaptic plasticity. Enzymatic cascades dependent on the Ca2+concentration in the ER lumen integrate rapid Ca2+signaling with long-lasting adaptive responses through modifications in protein synthesis and processing. Disruptions of ER Ca2+homeostasis are critically involved in various forms of neuropathology.

Prevention of dementia: lessons from SYST-EUR and PROGRESS

Hypertension is one of the principal risk factors for cerebrovascular diseases, closely correlated also with cognitive decline and dementia. Data from recent therapeutic trials (SYST-EUR, PROGRESS) open the way toward the prevention of dementia (vascular or Alzheimer's type) by antihypertensive treatments. The results of these two studies suggest different mechanisms of action of antihypertensive drugs in the prevention of cognitive decline. The use of angiotensin converting enzyme (ACE) inhibitors, with or without diuretics, resulted in decrease incidence of stroke-related dementia, but dementia without stroke was not reduced. With the dihydropyridine calcium antagonists, a reduction in both Alzheimer's type and vascular dementia was demonstrated.

Ischemia-induced neuronal cell death is mediated by the endoplasmic reticulum stress pathway involving CHOP

Brain ischemia induces apoptosis in neuronal cells, but the mechanism is not well understood. When wild-type mice were subjected to bilateral common carotid arteries occlusion (BCCAO) for 15 min, apoptosis-associated morphological changes and appearance of TUNEL-positive cells were observed in the striatum and in the hippocampus at 48 h after occlusion. RT-PCR analysis revealed that mRNAs for ER stress-associated proapoptotic factor CHOP and an ER chaperone BiP are markedly induced at 12 h after BCCAO. Immunohistochemical analysis showed that CHOP protein is induced in nuclei of damaged neurons at 24 h after occlusion. In contrast, ischemia-associated apoptotic loss of neurons was decreased in CHOP(-/-) mice. Primary hippocampal neurons from CHOP(-/-) mice were more resistant to hypoxia-reoxygenation-induced apoptosis than those from wild-type animals. These results indicate that ischemia-induced neuronal cell death is mediated by the ER stress pathway involving CHOP induction.

Prevention of dementia and cerebroprotection with antihypertensive drugs

High blood pressure is a major risk factor for stroke and is also closely correlated with cognitive decline and dementia. Indeed, most longitudinal studies showed that cognitive functioning is often inversely proportional to blood pressure values measured 15 or 20 years previously. Because of the aging of the population, the frequency of stroke and dementia will dramatically increase in the coming years. Therefore, the prevention of cerebrovascular and cognitive disorders represents a major challenge. Antihypertensive drugs have shown clinical benefits in both primary and secondary prevention of strokes. Consensus is generally that blood-pressure lowering represents the major determinant of the benefit conferred by the antihypertensive treatment for stroke prevention; however, recent studies have suggested some differences between classes of antihypertensive drugs. The results of therapeutic trials (Systolic Hypertension in Europe, Perindopril Protection Against Recurrent Stroke Study [PROGRESS]) open the way to the prevention of dementia (vascular or Alzheimer's type) by antihypertensive treatments. These two studies suggest different mechanisms for the prevention of cognitive decline using antihypertensive drugs. In this context, reduced incidence of dementia should be the primary outcome of future trials comparing different classes of antihypertensive drugs.

Calcium dyshomeostasis in beta-amyloid and tau-bearing skeletal myotubes

The relative scarcity of inclusion-affected muscle cells or markers of cell death in inclusion body myositis (IBM) is in distinction to the specific and early intracellular deposition of several Alzheimer's Disease (AD)-related proteins. The current study examined the possible correlation between myotube beta-amyloid and/or Tau accumulations and a widespread mishandling of intracellular muscle calcium concentration that could potentially account for the unrelenting weakness in affected patients. Cultured myogenic cells (C(2)C(12)) expressed beta-amyloid-42 (Abeta(42)) and fetal Tau peptides, as human transgenes encoded by herpes simplex virus, either individually or concurrently. Co-expression of Abeta(42) in C(2)C(12) myotubes resulted in hyperphosphorylation of Tau protein that was not observed when Tau was expressed alone. Resting calcium concentration and agonist-induced RyR-mediated Ca(2+) release were examined using calcium-specific microelectrodes and Fluo-4 epifluorescence, respectively. Co-expression of Abeta(42) and Tau cooperatively elevated basal levels of myoplasmic-free calcium, an effect that was accompanied by depolarization of the plasma membrane. Sarcoplasmic reticulum (SR) calcium release, induced by KCl depolarization, was not affected by Abeta(42) or Tau. In contrast, expression of Abeta(42), Tau, or Abeta(42) together with Tau resulted in enhanced sensitivity of ryanodine receptors to activation by caffeine. Notably, expression of beta-amyloid, alone, was sufficient to result in an increased sensitivity to direct activation by caffeine. Current results indicate that amyloid proteins cooperate to raise resting calcium levels and that these effects are associated with a passive SR Ca(2+) leak and Tau hyperphosphorylation in skeletal muscle.

Potential roles for presenilin-1 in oxygen sensing and in glial-specific gene expression

The integral membrane glycoprotein presenilin-1 (PS1), in concert with beta-secretase and beta amyloid precursor protein (betaAPP), orchestrate cleavage of betaAPP into amyloidogenic Abeta peptides. To gain further insight into PS1 function, we undertook a gene expression profiling study that interrogated the expression of 12,000 genes in the forebrain of PS1-hypomorphic mice that exhibit highly attenuated PS1 activity. Using stringent RNA screening, DNA array and Northern assay, we report significant down-regulation in the expression of betaAPP and hypoxia inducible factor-1 alpha (HIF-1alpha), and a marked up-regulation in the expression of glial-specific markers that include S100beta protein, glycerol phosphate dehydrogenase, and glial fibrillary acidic protein. These data suggest potential roles for PS1 in the cellular response to hypoxia and glial-specific gene expression.

Effects of RNA Interference-mediated Silencing of γ-Secretase Complex Components on Cell Sensitivity to Caspase-3 Activation

Familial Alzheimer's disease mutations in the presenilin 1 gene (PSEN1) have been previously shown to potentiate caspase activation and apoptosis in transfected cells and transgenic mice. However, the mechanism underlying this effect is not known. We set out to determine whether cellular sensitivity to caspase activation could be affected by modulating presenilin 1 (PS1) processing. PS1 processing was altered using RNA interference (RNAi) aimed at silencing the expression of the genes encoding the four components of the gamma-secretase complex, PSEN1, APH-1, PEN-2, and nicastrin. RNAi for these genes was carried out in naive H4 human neuroglioma cells, as well as H4 cell lines overexpressing either wild-type PSEN1 or the Familial Alzheimer's disease mutant PSEN1-Delta9 (PS1-mutant), that were induced to undergo apoptosis. In wild-type PSEN1 cells, RNAi for PEN-2, as expected, increased levels of full-length PS1 (PS1-FL) and decreased PS1 endoproteolysis. This was accompanied by potentiated caspase-3 activation in response to an apoptotic stimulus. In contrast, nicastrin RNAi, which only decreased levels of PS1-amino-terminal fragment and did not affect PS1-FL levels, had no effect on caspase-3 activation during apoptosis. Surprisingly, in the PS1-mutant cells, RNAi for PEN-2 (and APH-1) did not increase but instead reduced the levels of PS1-FL deleted for exon 9. In turn, this was accompanied by attenuated caspase-3 activation in response to an apoptotic stimulus. Finally, in naive H4 cells, PSEN1 RNAi also attenuated caspase-3 activation in response to an apoptotic stimulus. Collectively, these findings indicate that cellular sensitivity to caspase activation correlates with overall PS1 protein levels, particularly with levels of FL-PS1.

Metal-catalyzed disruption of membrane protein and lipid signaling in the pathogenesis of neurodegenerative disorders

Membrane lipid peroxidation and oxidative modification of various membrane and associated proteins (e.g., receptors, ion transporters and channels, and signal transduction and cytoskeletal proteins) occur in a range of neurodegenerative disorders. This membrane-associated oxidative stress (MAOS) is promoted by redox-active metals, most notably iron and copper. The mechanisms whereby different genetic and environmental factors initiate MAOS in specific neurological disorders are being elucidated. In Alzheimer's disease (AD), the amyloid beta-peptide generates reactive oxygen species and induces MAOS, resulting in disruption of cellular calcium homeostasis. In Parkinson's disease (PD), mitochondrial toxins and perturbed ubiquitin-dependent proteolysis may impair ATP production and increase oxyradical production and MAOS. The inheritance of polyglutamine-expanded huntingtin may promote neuronal degeneration in Huntington's disease (HD), in part, by increasing MAOS. Increased MAOS occurs in amyotrophic lateral sclerosis (ALS) as the result of genetic abnormalities (e.g., Cu/Zn-superoxide dismutase mutations) or exposure to environmental toxins. Levels of iron are increased in vulnerable neuronal populations in AD and PD, and dietary and pharmacological manipulations of iron and copper modify the course of the disease in mouse models of AD and PD in ways that suggest a role for these metals in disease pathogenesis. An increasing number of pharmacological and dietary interventions are being identified that can suppress MAOS and neuronal damage and improve functional outcome in animal models of AD, PD, HD, and ALS. Novel preventative and therapeutic approaches for neurodegenerative disorders are emerging from basic research on the molecular and cellular actions of metals and MAOS in neural cells.

Role of AIF in caspase-dependent and caspase-independent cell death

The major challenge in treating cancer is that many tumor cells carry mutations in key apoptotic genes such as p53, Bcl family proteins or those affecting caspase signaling. Such defects render treatment with traditional chemotherapeutic agents ineffective. Many studies have demonstrated the importance of caspase-independent cell death pathways in injury, degenerative diseases and tumor tissue. It is now recognized that in addition to their critical role in the production of cellular energy, mitochondria are also the source of key proapoptotic molecules involved in caspase activation. More recently, it has been discovered that in response to apoptotic stimuli, mitochondria can also release caspase-independent cell death effectors such as AIF and Endonuclease G. In this review, we examine the role of Bcl family proteins and poly(ADP-ribose) polymerase-1 signaling in the regulation of these apoptotic pathways and address the ongoing controversies in this field. Continued study of the mechanisms of apoptosis including caspase-independent death processes are likely to reveal novel therapeutic targets for the treatment of diverse human pathologies including cancer, neurodegenerative diseases and acute injuries such as stroke or myocardial infarction.

Alzheimer's disease: the two-hit hypothesis

There are many lines of evidence showing that oxidative stress and aberrant mitogenic changes have important roles in the pathogenesis of Alzheimer's disease (AD). However, although both oxidative stress and cell cycle-related abnormalities are early events, occurring before any cytopathology, the relation between these two events, and their role in pathophysiology was, until recently, unclear. However, on the basis of studies of mitogenic and oxidative stress signalling pathways in AD, we proposed a "two-hit hypothesis" which states that although either oxidative stress or abnormalities in mitotic signalling can independently serve as initiators, both processes are necessary to propagate disease pathogenesis. In this paper, we summarise evidence for oxidative stress and abnormal mitotic alterations in AD and explain the two-hit hypothesis by describing how both mechanisms are necessary and invariant features of disease.

A potentially critical role of phospholipases in central nervous system ischemic, traumatic, and neurodegenerative disorders

Phospholipases are a diverse group of enzymes whose activation may be responsible for the development of injury following insult to the brain. Amongst the numerous isoforms of phospholipase proteins expressed in mammals are 19 different phospholipase A2's (PLA2s), classified functionally as either secretory, calcium dependent, or calcium independent, 11 isozymes belonging to three structural groups of PLC, and 3 PLD gene products. Many of these phospholipases have been identified in selected brain regions. Under normal conditions, these enzymes regulate the turnover of free fatty acids (FFAs) in membrane phospholipids affecting membrane stability, fluidity, and transport processes. The measurement of free fatty acids thus provides a convenient method to follow phospholipase activity and their regulation. Phospholipase activity is also responsible for the generation of an extensive list of intracellular messengers including arachidonic acid metabolites. Phospholipases are regulated by many factors including selective phosphorylation, intracellular calcium and pH. However, under abnormal conditions, excessive phospholipase activation, along with a decreased ability to resynthesize membrane phospholipids, can lead to the generation of free radicals, excitotoxicity, mitochondrial dysfunction, and apoptosis/necrosis. This review evaluates the critical contribution of the various phospholipases to brain injury following ischemia and trauma and in neurodegenerative diseases.

Hypoxic remodelling of Ca2+ mobilization in type I cortical astrocytes: involvement of ROS and pro-amyloidogenic APP processing

Chronic hypoxia (CH) alters Ca2+ homeostasis in various cells and may contribute to disturbed Ca2+ homeostasis of Alzheimer's disease. Here, we have employed microfluorimetric measurements of [Ca2+]i to investigate the mechanism underlying augmentation of Ca2+ signalling by chronic hypoxia in type I cortical astrocytes. Application of bradykinin evoked significantly larger rises of [Ca2+]i in hypoxic cells as compared with control cells. This augmentation was prevented fully by either melatonin (150 micro m) or ascorbic acid (200 micro m), indicating the involvement of reactive oxygen species. Given the association between hypoxia and increased production of amyloid beta peptides (AbetaPs) of Alzheimer's disease, we performed immunofluorescence studies to show that hypoxia caused a marked and consistent increased staining for AbetaPs and presenilin-1 (PS-1). Western blot experiments also confirmed that hypoxia increased PS-1 protein levels. Hypoxic increases of AbetaP production was prevented with inhibitors of either gamma- or beta-secretase. These inhibitors also partially prevented the augmentation of Ca2+ signalling in astrocytes. Our results indicate that chronic hypoxia enhances agonist-evoked rises of [Ca2+]i in cortical astrocytes, and that this can be prevented by antioxidants and appears to be associated with increased AbetaP formation.

Magnetic resonance imaging shows delayed ischemic striatal neurodegeneration

Brief focal ischemia leading to temporary neurological deficits induces delayed hyperintensity on T1-weighted magnetic resonance imaging (MRI) in the striatum of humans and rats. The T1 hyperintensity may stem from biochemical alterations including manganese (Mn) accumulation after ischemia. To clarify the significance of this MRI modification, we investigated the changes in the dorsolateral striatum of rats from 4 hours through 16 weeks after a 15-minute period of middle cerebral artery occlusion (MCAO), for MRI changes, Mn concentration, neuronal number, reactivities of astrocytes and microglia/macrophages, mitochondrial Mn-superoxide dismutase (Mn-SOD), glutamine synthetase (GS), and amyloid precursor protein. The cognitive and behavioral studies were performed in patients and rats and compared with striatal T1 hyperintensity to show whether alteration in brain function correlated with MRI and histological changes. The T1-weighted MRI signal intensity of the dorsolateral striatum increased from 5 days to 4 weeks after 15-minute MCAO, and subsequently decreased until 16 weeks. The Mn concentration of the dorsolateral striatum increased after ischemia in concert with induction of Mn-SOD and GS in reactive astrocytes. The neuronal survival ratio in the dorsolateral striatum decreased significantly from 4 hours through 16 weeks, accompanied by extracellular amyloid precursor protein accumulation and chronic glial/inflammatory responses. The patients and rats with neuroradiological striatal degeneration had late-onset cognitive and/or behavioral declines after brief focal ischemia. This study suggests that (1) the hyperintensity on T1-weighted MRI after mild ischemia may involve tissue Mn accumulation accompanied by Mn-SOD and GS induction in reactive astrocytes, (2) the MRI changes correspond to striatal neurodegeneration with a chronic inflammatory response and signs of oxidative stress, and (3) the subjects with these MRI changes are at risk for showing a late impairment of brain function even though the transient ischemia is followed by total neurological recovery.

Neuronal and glial calcium signaling in Alzheimer's disease

Cognitive impairment and emotional disturbances in Alzheimer's disease (AD) result from the degeneration of synapses and death of neurons in the limbic system and associated regions of the cerebral cortex. An alteration in the proteolytic processing of the amyloid precursor protein (APP) results in increased production and accumulation of amyloid beta-peptide (Abeta) in the brain. Abeta has been shown to cause synaptic dysfunction and can render neurons vulnerable to excitotoxicity and apoptosis by a mechanism involving disruption of cellular calcium homeostasis. By inducing membrane lipid peroxidation and generation of the aldehyde 4-hydroxynonenal, Abeta impairs the function of membrane ion-motive ATPases and glucose and glutamate transporters, and can enhance calcium influx through voltage-dependent and ligand-gated calcium channels. Reduced levels of a secreted form of APP which normally regulates synaptic plasticity and cell survival may also promote disruption of synaptic calcium homeostasis in AD. Some cases of inherited AD are caused by mutations in presenilins 1 and 2 which perturb endoplasmic reticulum (ER) calcium homeostasis such that greater amounts of calcium are released upon stimulation, possibly as the result of alterations in IP(3) and ryanodine receptor channels, Ca(2+)-ATPases and the ER stress protein Herp. Abnormalities in calcium regulation in astrocytes, oligodendrocytes, and microglia have also been documented in studies of experimental models of AD, suggesting contributions of these alterations to neuronal dysfunction and cell death in AD. Collectively, the available data show that perturbed cellular calcium homeostasis plays a prominent role in the pathogenesis of AD, suggesting potential benefits of preventative and therapeutic strategies that stabilize cellular calcium homeostasis.

The NMDA receptor antagonist memantine as a symptomatological and neuroprotective treatment for Alzheimer's disease: preclinical evidence

There is increasing evidence for the involvement of glutamate-mediated neurotoxicity in the pathogenesis of Alzheimer's disease (AD). We suggest that glutamate receptors of the N-methyl-D-aspartate (NMDA) type are overactivated in a tonic rather than a phasic manner in this disorder. This continuous mild activation may lead to neuronal damage and impairment of synaptic plasticity (learning). It is likely that under such conditions Mg(2+) ions, which block NMDA receptors under normal resting conditions, can no longer do so. We found that overactivation of NMDA receptors using a direct agonist or a decrease in Mg(2+) concentration produced deficits in synaptic plasticity (in vivo: passive avoidance test and/or in vitro: LTP in the CA1 region). In both cases, memantine-an uncompetitive NMDA receptor antagonists with features of an 'improved' Mg(2+) (voltage-dependency, kinetics, affinity)-attenuated this deficit. Synaptic plasticity was restored by therapeutically-relevant concentrations of memantine (1 microM). Moreover, doses leading to similar brain/serum levels provided neuroprotection in animal models relevant for neurodegeneration in AD such as neurotoxicity produced by inflammation in the NBM or beta-amyloid injection to the hippocampus. As such, if overactivation of NMDA receptors is present in AD, memantine would be expected to improve both symptoms (cognition) and to slow down disease progression because it takes over the physiological function of magnesium.

Neuroprotection by complement (C1) inhibitor in mouse transient brain ischemia

The authors investigated the effect of the C1 inhibitor (C1-INH), the only known inhibitor of complement C1, in a murine model of transient focal ischemia. Ischemia was induced by intraluminal occlusion of the middle cerebral artery. After 2 hours, reperfusion was produced by removing the nylon monofilament occluding the artery. The effect of 15 U C1-INH (intravenously) was evaluated in terms of general and focal neurologic deficits, ischemic volume, neutral red staining (to identify the brain areas subject to ischemic damage), and glial fibrillary acidic protein immunoreactivity (to show astrocytic response). Forty-eight hours after ischemia, C1-INH significantly improved general and focal deficits by 36% and 54%, respectively, and significantly reduced infarct volume (CI-INH, 6.69% +/- 2.93%; saline, 24.24% +/- 8.24%) of total brain. Neutral red staining further showed the strong protective effect of C1-INH in cortex, hippocampus, and striatum. Astrocyte activation induced by ischemia was not affected by C1-INH. These findings show that C1-INH displayed a potent neuroprotective action by effectively reducing ischemia-reperfusion injury.

The Yin and Yang of NMDA receptor signalling

Ca(2+) entry through the NMDA subtype of glutamate receptors has the power to determine whether neurons survive or die. Too much NMDA receptor activity is harmful to neurons - but so is too little. Is it a case of too much or too little Ca(2+) influx causing cell death or do other factors, such as receptor location or receptor-associated proteins, play a role? Understanding the mechanisms behind this dichotomous signalling is an important area of molecular neuroscience with direct clinical implications.

Presenilins and APP in neuritic and synaptic plasticity: implications for the pathogenesis of Alzheimer's disease

A key neuropathological hallmark of Alzheimer's disease (AD) is the loss of neocortical and hippocampal synapses, which is closely correlated with the degree of memory impairment. Mutations in the genes encoding the amyloid precursorprotein (APP) and presenilins are responsible from some cases of early-onset autosomal-dominant AD. This article reviews the current understanding of how alterations in the cellular functions of APP and presenilins may result in the dysfunction and degeneration of synapses in AD. APP mutations result in increased production/aggregation of amyloid beta-peptide (Abeta), which induces oxidative stress, resulting in the impairment of synaptic membrane ion, glutamate, and glucose transporters. APP mutations may also compromise the production and/or function of secreted forms of APP that are believed to play important roles in learning and memory processes. Presenilin (PS1) mutations result in a major defect in endoplasmic reticulum (ER) calcium regulation, which may perturb synaptic function in ways that lead to impaired synaptic plasticity and neuronal degeneration. Studies in transgenic mice that express APP and PS1 mutations have provided evidence that the mutations result in altered cellular calcium homeostasis and synaptic plasticity, and impaired learning and memory. This article provides a brief review of the pathophysiological interactions of APP and presenilins with synaptic proteins, and discusses how AD-linked mutations in APP and PS1 may disrupt synaptic processes that contribute to memory formation.

Differential display analysis of presenilin 1-deficient mouse brains

Missense mutations in presenilin 1 (PS1) gene are the most common cause of early onset familial Alzheimer's disease (FAD). AD pathogenic PS1 mutations result in elevated gamma-secretase cleavage of APP and diminished S3-site cleavage of Notch. We have previously described a PS1-hypomorphic mouse line that could survive postnatally with markedly reduced gamma-secretase cleavage of APP and S3-site cleavage of Notch, resulting in a Notch developmental phenotype similar to PS1-null mice. This model was exploited to identify genes whose expression is altered due to the loss of PS1. A global gene expression study by differential display was performed on whole brains of PS1-hypomorphic mice and their wild type siblings. In total, more than 16,000 bands corresponding to cDNAs were compared between the mutant and wild-type brains. This analysis identified 19 cDNAs showing significantly altered expression resulting from PS1 deficiency. Four of the identified cDNAs corresponded to genes that could be associated with AD or presenilin function. Hypoxia inducible factor 1a (Hif1a), NPRAP (delta-catenin) and cell division cycle 10 (CDC10) showed significantly reduced expression in the PS1-hypomorphic compared to wild-type brains, whereas expression of nucleoside diphosphate kinase sub-unit A (NDPK-A) was markedly elevated in the respective brains. Clarification of the possible role of these genes in AD and the basis for their differential expression induced by PS1-deficiency may provide insight into the disease, presenilin function and consequences of its loss, as well as possible deleterious effects of AD therapeutics aimed at inhibiting PS1.

The novel presenilin-1-associated protein is a proapoptotic mitochondrial protein

Recent studies have suggested a possible role for presenilin proteins in apoptotic cell death observed in Alzheimer's disease. The mechanism by which presenilin proteins regulate apoptotic cell death is not well understood. Using the yeast two-hybrid system, we previously isolated a novel protein, presenilin-associated protein (PSAP) that specifically interacts with the C terminus of presenilin 1 (PS1), but not presenilin 2 (PS2). Here we report that PSAP is a mitochondrial resident protein sharing homology with mitochondrial carrier protein. PSAP was detected in a mitochondria-enriched fraction, and PSAP immunofluorescence was present in a punctate pattern that colocalized with a mitochondrial marker. More interestingly, overexpression of PSAP caused apoptotic death. PSAP-induced apoptosis was documented using multiple independent approaches, including membrane blebbing, chromosome condensation and fragmentation, DNA laddering, cleavage of the death substrate poly(ADP-ribose) polymerase, and flow cytometry. PSAP-induced cell death was accompanied by cytochrome c release from mitochondria and caspase-3 activation. Moreover, the general caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone, which blocked cell death, did not block the release of cytochrome c from mitochondria caused by overexpression of PSAP, indicating that PSAP-induced cytochrome c release was independent of caspase activity. The mitochondrial localization and proapoptotic activity of PSAP suggest that it is an important regulator of apoptosis.

Effects of immunosuppressants, calcineurin inhibition, and blockade of endoplasmic reticulum calcium channels on free fatty acid efflux from the ischemic/reperfused rat cerebral cortex

Elevated levels of free fatty acids (FFA) have been implicated in the pathogenesis of neuronal injury and death induced by cerebral ischemia. This study evaluated the effects of immunosuppressants agents, calcineurin inhibitors and blockade of endoplasmic reticulum (ER) calcium channels on free fatty acid formation and efflux in the ischemic/reperfused (I/R) rat brain. Changes in the extracellular levels of arachidonic, docosahexaenoic, linoleic, myristic, oleic and palmitic acids in cerebral cortical superfusates during four-vessel occlusion-elicited global cerebral ischemia were examined using a cortical cup technique. A 20-min period of ischemia elicited large increases in the efflux of all six FFAs, which were sustained during the 40 min of reperfusion. Cyclosporin A (CsA) and trifluoperazine, which reportedly inhibit the I/R elicited opening of a mitochondrial permeability transition (MPT) pore, were very effective in suppressing ischemia/reperfusion evoked release of all six FFAs. FK506, an immunosuppressant which does not directly affect the MPT, but is a calcineurin inhibitor, also suppressed the I/R-evoked efflux of FFAs, but less effectively than CsA. Rapamycin, a derivative of FK506 which does not inhibit calcineurin, did not suppress I/R-evoked FFA efflux. Gossypol, a structurally unrelated inhibitor of calcineurin, was also effective, significantly reducing the efflux of docosahexaenoic, arachidonic and oleic acids. As previous experiments had implicated elevated Ca(2+) levels in the activation of phospholipases with FFA formation, agents affecting endoplasmic reticulum stores were also evaluated. Dantrolene, which blocks the ryanodine receptor (RyR) channel of the ER, significantly inhibited I/R-evoked release of docosahexaenoic, arachidonic, linoleic and oleic acids. Ryanodine, which can either accentuate or block Ca(2+) release, significantly enhanced ischemia/reperfusion-elicited efflux of linoleic acid, with non-significant increases in the efflux of myristic, arachidonic, palmitic and oleic acids. Xestospongin C, an inhibitor of the inositol triphosphate (IP(3)R) channel, failed to affect I/R-evoked FFA efflux. Thapsigargin, an inhibitor of the Ca(2+)-ATPase ER uptake pump, elicited significant elevations in the efflux of myristic, arachidonic and linoleic acids, in the absence of ischemia. Collectively, the data suggest an involvement of both ER and mitochondrial Ca(2+) stores in the chain of events which lead to PLA(2) activation and FFA formation.

Acute and chronic alterations in calcium homeostasis in 3-nitropropionic acid-treated human NT2-N neurons

3-Nitropropionic acid (3-NP), an irreversible inhibitor of succinate dehydrogenase, induced ATP depletion and both necrosis and apoptosis in human NT2-N neurons. Necrosis occurred predominantly within the first two days, and increased in a dose-dependent fashion with the concentration of 3-NP, whereas apoptosis was observed after 24 h or later at a similar rate in 0.1 mM and 5 mM 3-NP. We focused our efforts on intracellular calcium homeostasis during the first 48 h in 1 mM 3-NP, a period during which 10% of the neurons died by necrosis and 3% by apoptosis. All NT2-N neurons showed a stereotyped [Ca(2+)](i) rise, from 48+/-2 to 140+/-12 nM (mean +/-S.E.M.), during the first 2 h in 3-NP. Despite severe ATP depletion, however, [Ca(2+)](i) remained above 100 nM in only 17% and 25% of the NT2-N neurons after 24 and 48 h in 3-NP, respectively, indicating that most neurons were able to recover from acute [Ca(2+)](i) rise, and suggesting that chronic [Ca(2+)](i) dysregulation is a better indicator of subsequent necrosis. Blockade of N-methyl-D-aspartate-glutamate receptor by MK-801 substantially ameliorated 3-NP-induced ATP depletion, subsequent chronic [Ca(2+)](i) elevation, and survival. Moreover, xestospongin C, an inhibitor of endoplasmic reticulum Ca(2+) release, enhanced the capacity of NT2-N neurons to maintain [Ca(2+)](i) homeostasis and resist necrosis while subjected to sustained energy deprivation. As far as we know, this report is the first to employ human neurons to study the pathophysiology of 3-NP neurotoxicity.

Tau-mediated cytotoxicity in a pseudohyperphosphorylation model of Alzheimer's disease

Aggregation and increased phosphorylation of tau at selected sites ("hyperphosphorylation") are histopathological hallmarks of Alzheimer's disease (AD). However, it is not known whether the tau pathology has a primary role during neuronal degeneration. To determine the role of tau hyperphosphorylation in AD, pseudohyperphosphorylated tau (PHP-tau) that simulates disease-like permanent, high stoichiometric tau phosphorylation and mimics structural and functional aspects of hyperphosphorylated tau was expressed in neural cells. In differentiated PC12 cells, PHP-tau exhibited reduced microtubule interaction and failed to stabilize the microtubule network compared with exogenously expressed wild-type tau (wt-tau). During longer culture, PHP-tau exerted a cytotoxic effect, whereas wt-tau was neutral. PHP-tau-mediated cytotoxicity was associated with an induction of apoptotic cell death as characterized by chromatin condensation, DNA fragmentation, and caspase-3 activation in the absence of detectable protein aggregates. Furthermore, PHP-tau expression specifically sensitized the cells for other apoptotic stimuli (colchicine and staurosporine). Herpes simplex virus-mediated overexpression of PHP-tau induced degeneration associated with an induction of apoptotic mechanisms also in terminally differentiated human CNS model neurons. Partially pseudophosphorylated constructs caused an intermediate toxicity. The data provide evidence for a neurotoxic "gain of function" of soluble tau during AD as a result of structural changes that are induced by a cumulative, high stoichiometric tau phosphorylation. PHP-tau-expressing cells and organisms could provide a useful system to identify mechanisms that contribute to tau-mediated toxicity.