Activation of the L voltage-sensitive calcium channel by mitogen-activated protein (MAP) kinase following exposure of neuronal cells to beta-amyloid. MAP kinase mediates beta-amyloid-induced neurodegeneration

Role of Calcium Modulation in the Pathophysiology and Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disease and the most frequent cause of progressive dementia in senior adults. It is characterized by memory loss and cognitive impairment secondary to cholinergic dysfunction and N-methyl-D-aspartate (NMDA)-mediated neurotoxicity. Intracellular neurofibrillary tangles, extracellular plaques composed of amyloid-β (Aβ), and selective neurodegeneration are the anatomopathological hallmarks of this disease. The dysregulation of calcium may be present in all the stages of AD, and it is associated with other pathophysiological mechanisms, such as mitochondrial failure, oxidative stress, and chronic neuroinflammation. Although the cytosolic calcium alterations in AD are not completely elucidated, some calcium-permeable channels, transporters, pumps, and receptors have been shown to be involved at the neuronal and glial levels. In particular, the relationship between glutamatergic NMDA receptor (NMDAR) activity and amyloidosis has been widely documented. Other pathophysiological mechanisms involved in calcium dyshomeostasis include the activation of L-type voltage-dependent calcium channels, transient receptor potential channels, and ryanodine receptors, among many others. This review aims to update the calcium-dysregulation mechanisms in AD and discuss targets and molecules with therapeutic potential based on their modulation.

Modulation of L-type calcium channels in Alzheimer's disease: A potential therapeutic target

Calcium plays a fundamental role in various signaling pathways and cellular processes in the human organism. In the nervous system, voltage-gated calcium channels such as L-type calcium channels (LTCCs) are critical elements in mediating neurotransmitter release, synaptic integration and plasticity. Dysfunction of LTCCs has been implicated in both aging and Alzheimer's Disease (AD), constituting a key component of calcium hypothesis of AD. As such, LTCCs are a promising drug target in AD. However, due to their structural and functional complexity, the mechanisms by which LTCCs contribute to AD are still unclear. In this review, we briefly summarize the structure, function, and modulation of LTCCs that are the backbone for understanding pathological processes involving LTCCs. We suggest targeting molecular pathways up-regulating LTCCs in AD may be a more promising approach, given the diverse physiological functions of LTCCs and the ineffectiveness of LTCC blockers in clinical studies.

Synaptogenic effect of APP-Swedish mutation in familial Alzheimer's disease

Mutations in β-amyloid (Aβ) precursor protein (APP) cause familial Alzheimer's disease (AD) probably by enhancing Aβ peptides production from APP. An antibody targeting Aβ (aducanumab) was approved as an AD treatment; however, some Aβ antibodies have been reported to accelerate, instead of ameliorating, cognitive decline in individuals with AD. Using conditional APP mutations in human neurons for perfect isogenic controls and translational relevance, we found that the APP-Swedish mutation in familial AD increased synapse numbers and synaptic transmission, whereas the APP deletion decreased synapse numbers and synaptic transmission. Inhibition of BACE1, the protease that initiates Aβ production from APP, lowered synapse numbers, suppressed synaptic transmission in wild-type neurons, and occluded the phenotype of APP-Swedish-mutant neurons. Modest elevations of Aβ, conversely, elevated synapse numbers and synaptic transmission. Thus, the familial AD-linked APP-Swedish mutation under physiologically relevant conditions increased synaptic connectivity in human neurons via a modestly enhanced production of Aβ. These data are consistent with the relative inefficacy of BACE1 and anti-Aβ treatments in AD and the chronic nature of AD pathogenesis, suggesting that AD pathogenesis is not simply caused by overproduction of toxic Aβ but rather by a long-term effect of elevated Aβ concentrations.

The formation of small aggregates contributes to the neurotoxic effects of tau45-230

Intracellular deposits of hyperphosphorylated tau are commonly detected in tauopathies. Furthermore, these aggregates seem to play an important role in the pathobiology of these diseases. In the present study, we determined whether the recently identified neurotoxic tau_45-230 fragment also formed aggregates in neurodegenerative disorders. The presence of such aggregates was examined in brain samples obtained from Alzheimer's disease (AD) subjects by means of Western blot analysis performed under non-denaturing conditions. Our results showed that a mixture of tau_45-230 oligomers of different sizes was easily detectable in brain samples obtained from AD subjects. Our data also suggested that tau_45-230 oligomers could be internalized by cultured hippocampal neurons, mainly through a clathrin-mediated mechanism, triggering their degeneration. In addition, in vitro aggregation studies showed that tau_45-230 modulated full-length tau aggregation thereby inducing the formation of smaller, and potentially more toxic, aggregates of this microtubule-associated protein. Together, these data identified alternative mechanisms underlying the toxic effects of tau_45-230.

The Many Faces of Post-Ischemic Tau Protein in Brain Neurodegeneration of the Alzheimer's Disease Type

Recent data suggest that post-ischemic brain neurodegeneration in humans and animals is associated with the modified tau protein in a manner typical of Alzheimer’s disease neuropathology. Pathological changes in the tau protein, at the gene and protein level due to cerebral ischemia, can lead to the development of Alzheimer’s disease-type neuropathology and dementia. Some studies have shown increased tau protein staining and gene expression in neurons following ischemia-reperfusion brain injury. Recent studies have found the tau protein to be associated with oxidative stress, apoptosis, autophagy, excitotoxicity, neuroinflammation, blood-brain barrier permeability, mitochondrial dysfunction, and impaired neuronal function. In this review, we discuss the interrelationship of these phenomena with post-ischemic changes in the tau protein in the brain. The tau protein may be at the intersection of many pathological mechanisms due to severe neuropathological changes in the brain following ischemia. The data indicate that an episode of cerebral ischemia activates the damage and death of neurons in the hippocampus in a tau protein-dependent manner, thus determining a novel and important mechanism for the survival and/or death of neuronal cells following ischemia. In this review, we update our understanding of proteomic and genomic changes in the tau protein in post-ischemic brain injury and present the relationship between the modified tau protein and post-ischemic neuropathology and present a positive correlation between the modified tau protein and a post-ischemic neuropathology that has characteristics of Alzheimer’s disease-type neurodegeneration.

Hyperactivity Induced by Soluble Amyloid-β Oligomers in the Early Stages of Alzheimer's Disease

Soluble amyloid-beta oligomers (Aβo) start to accumulate in the human brain one to two decades before any clinical symptoms of Alzheimer's disease (AD) and are implicated in synapse loss, one of the best predictors of memory decline that characterize the illness. Cognitive impairment in AD was traditionally thought to result from a reduction in synaptic activity which ultimately induces neurodegeneration. More recent evidence indicates that in the early stages of AD synaptic failure is, at least partly, induced by neuronal hyperactivity rather than hypoactivity. Here, we review the growing body of evidence supporting the implication of soluble Aβo on the induction of neuronal hyperactivity in AD animal models, in vitro, and in humans. We then discuss the impact of Aβo-induced hyperactivity on memory performance, cell death, epileptiform activity, gamma oscillations, and slow wave activity. We provide an overview of the cellular and molecular mechanisms that are emerging to explain how Aβo induce neuronal hyperactivity. We conclude by providing an outlook on the impact of hyperactivity for the development of disease-modifying interventions at the onset of AD.

Oligomer β-amyloid Induces Hyperactivation of Ras to Impede NMDA Receptor-Dependent Long-Term Potentiation in Hippocampal CA1 of Mice

The activity of Ras, a small GTPase protein, is increased in brains with Alzheimer’s disease. The objective of this study was to determine the influence of oligomeric Aβ_1-42 on the activation of Ras, and the involvement of the Ras hyperactivity in Aβ_1-42-induced deficits in spatial cognition and hippocampal synaptic plasticity. Herein, we show that intracerebroventricular injection of Aβ_1-42 in mice (Aβ-mice) enhanced hippocampal Ras activation and expression, while 60 min incubation of hippocampal slices in Aβ_1-42 (Aβ-slices) only elevated Ras activity. Aβ-mice showed deficits in spatial cognition and NMDA receptor (NMDAR)-dependent long-term potentiation (LTP) in hippocampal CA1, but basal synaptic transmission was enhanced. The above effects of Aβ_1-42 were corrected by the Ras inhibitor farnesylthiosalicylic acid (FTS). ERK2 phosphorylation increased, and Src phosphorylation decreased in Aβ-mice and Aβ_1-42-slices. Both were corrected by FTS. In CA1 pyramidal cells of Aβ_1-42-slices, the response of AMPA receptor and phosphorylation of GluR1 were enhanced with dependence on Ras activation rather than ERK signaling. In contrast, NMDA receptor (NMDAR) function and GluN2A/2B phosphorylation were downregulated in Aβ_1-42-slices, which was recovered by application of FTS or the Src activator ouabain, and mimicked in control slices treated with the Src inhibitor PP2. The administration of PP2 impaired the spatial cognition and LTP induction in control mice and FTS-treated Aβ-mice. The treatment of Aβ-mice with ouabain rescued Aβ-impaired spatial cognition and LTP. Overall, the results indicate that the oligomeric Aβ_1-42 hyperactivates Ras and thereby causes the downregulation of Src which impedes NMDAR-dependent LTP induction resulting in cognitive deficits.

Tau as a potential therapeutic target for ischemic stroke

Tau is a protein mainly expressed in adult human brain. It plays important roles both in neurodegenerative diseases and stroke. Stroke is an important cause of adult death and disability, ischemic stroke almost account for 80% in all cases. Abundant studies have proven that the increase of dysfunctional tau may act as a vital factor in pathological changes after ischemic stroke. However, the relationship between tau and ischemic stroke remains ununified. Based on present studies, we firstly introduced the structure and biological function of tau protein. Secondly, we summarized the potential regulatory mechanisms of tau protein in the process of ischemic stroke. Thirdly, we discussed about the findings in therapeutic researches of ischemic stroke. This review may be helpful in implementing new therapies for ischemic stroke and may be beneficial for the clinical and experimental studies.

Single amyloid-beta injection exacerbates 4-aminopyridine-induced seizures and changes synaptic coupling in the hippocampus

Accumulation of amyloid-beta (Aβ) in temporal lobe structures, including the hippocampus, is related to a variety of Alzheimer's disease symptoms and seems to be involved in the induction of neural network hyperexcitability and even seizures. Still, a direct evaluation of the pro-epileptogenic effects of Aβ in vivo, and of the underlying mechanisms, is missing. Thus, we tested whether the intracisternal injection of Aβ modulates 4-aminopyridine (4AP)-induced epileptiform activity, hippocampal network function, and its synaptic coupling. When tested 3 weeks after its administration, Aβ (but not its vehicle) reduces the latency for 4AP-induced seizures, increases the number of generalized seizures, exacerbates the time to fully recover from seizures, and favors seizure-induced death. These pro-epileptogenic effects of Aβ correlate with a reduction in the power of the spontaneous hippocampal network activity, involving all frequency bands in vivo and only the theta band (4-10 Hz) in vitro. The pro-epileptogenic effects of Aβ also correlate with a reduction of the Schaffer-collateral CA1 synaptic coupling in vitro, which is exacerbated by the sequential bath application of 4-AP and Aβ. In summary, Aβ produces long-lasting pro-epileptic effects that can be due to alterations in the hippocampal circuit, impacting its coordinated network activity and its synaptic efficiency. It is likely that normalizing synaptic coupling and/or coordinated neural network activity (i.e., theta activity) may contribute not only to improve cognitive function in Alzheimer's disease but also to avoid hyperexcitation in conditions of amyloidosis.

Anti-apoptotic activity of ETB receptor agonist, IRL-1620, protects neural cells in rats with cerebral ischemia

Endothelin-B receptor agonist, IRL-1620, provides significant neuroprotection following cerebral ischemia in rats. Whether this neuroprotection is due to inhibition of apoptosis is unknown. IRL-1620-treated rats following permanent middle cerebral artery occlusion (MCAO) showed significant improvement in neurological and motor functions along with a decrease in infarct volume at 24 h (-81.3%) and day 7 (-73.0%) compared to vehicle group. Cerebral blood flow (CBF) significantly improved in IRL-1620-treated animals compared to vehicle by day 7 post MCAO. IRL-1620-treated rats showed an increase in phospho-Akt and decrease in Bad level 7 h post-occlusion compared to vehicle, while Akt and Bad expression was similar in cerebral hemispheres at 24 h post-MCAO. The phospho-Bad level was lower in vehicle- but not in IRL-1620-treated rats at 24 h. Anti-apoptotic Bcl-2 expression decreased, while pro-apoptotic Bax expression increased in vehicle-treated MCAO rats, these changes were attenuated (P < 0.01) by IRL-1620. Mitochondrial membrane-bound Bax intensity significantly decreased in IRL-1620 compared to vehicle-treated MCAO rats. IRL-1620 treatment reduced (P < 0.001) the number of TUNEL-positive cells compared to vehicle at 24 h and day 7 post MCAO. The results demonstrate that IRL-1620 is neuroprotective and attenuates neural damage following cerebral ischemia in rats by increasing CBF and reducing apoptosis.

Altered Cytoskeletal Composition and Delayed Neurite Elongation in tau45-230-Expressing Hippocampal Neurons

Calpain-mediated tau cleavage into the neurotoxic tau_45-230 fragment plays an important role in Alzheimer's disease (AD). This tau fragment accumulates mainly in the cytoplasm of degenerating neurons. However, subcellular localization studies indicated that a pool of tau_45-230 associates with the cytoskeleton in hippocampal neurons. In the present study, we assessed whether such localization could underlie tau_45-230 neurotoxic effects. Quantitative Western blot analysis showed decreased levels of full-length tau bound to microtubules in tau_45-230-expressing hippocampal neurons when compared to controls. In addition, the presence of this tau fragment induced a transient increase in tyrosinated tubulin, a marker of unstable microtubules, followed by a significant decrease in the levels of this tubulin isoform. The data obtained also showed a significant reduction in actin filaments in tau_45-230-expressing neurons. These changes in microtubules and actin filaments correlated with delayed neurite elongation and axonal differentiation in the presence of this tau fragment. Together, these results suggest that tau_45-230 could exert its toxic effects, at least in part, by modifying the composition of the neuronal cytoskeleton and impairing neurite elongation in neurons undergoing degeneration.

Ca2+ homeostasis dysregulation in Alzheimer's disease: a focus on plasma membrane and cell organelles

Emerging evidence indicates that Ca²⁺ is a vital factor in modulating the pathogenesis of Alzheimer's disease (AD). In healthy neurons, Ca²⁺ concentration is balanced to maintain a lower level in the cytosol than in the extracellular space or certain intracellular compartments such as endoplasmic reticulum (ER) and the lysosome, whereas this homeostasis is broken in AD. On the plasma membrane, the AD hallmarks amyloid-β (Aβ) and tau interact with ligand-gated or voltage-gated Ca²⁺-influx channels and inhibit the Ca²⁺-efflux ATPase or exchangers, leading to an elevated intracellular Ca²⁺ level and disrupted Ca²⁺ signal. In the ER, the disabled presenilin "Ca²⁺ leak" function and the direct implications of Aβ and presenilin mutants contribute to Ca²⁺-signal disorder. The enhanced ryanodine receptor (RyR)-mediated and inositol 1,4,5-trisphosphate receptor (IP₃R)-mediated Ca²⁺ release from the ER aggravates cytosolic Ca²⁺ disorder and triggers apoptosis; the down-regulated ER Ca²⁺ sensor, stromal interaction molecule (STIM), alleviates store-operated Ca²⁺ entry in plasma membrane, leading to spine loss. The increased transfer of Ca²⁺ from ER to mitochondria through mitochondria-associated ER membrane (MAM) causes Ca²⁺ overload in the mitochondrial matrix and consequently opens the cellular damage-related channel, mitochondrial permeability transition pore (mPTP). In this review, we discuss the effects of Aβ, tau and presenilin on neuronal Ca²⁺ signal, focusing on the receptors and regulators in plasma membrane and ER; we briefly introduce the involvement of MAM-mediated Ca²⁺ transfer and mPTP opening in AD pathogenesis.-Wang, X., Zheng, W. Ca²⁺ homeostasis dysregulation in Alzheimer's disease: a focus on plasma membrane and cell organelles.

Panax ginseng components and the pathogenesis of Alzheimer's disease (Review)

Ginseng is one of the main representatives of traditional Chinese medicine and presents a wide range of pharmacological actions. Ginsenosides are the main class of active compounds found in ginseng. They demonstrate unique biological activity and medicinal value, namely anti-tumour, anti-inflammatory and antioxidant properties, as well as anti-apoptotic properties. Increasing levels of stress in life are responsible for the increased incidence of nervous system diseases. Neurological diseases create a huge burden on the lives and health of individuals. In recent years, studies have indicated that ginsenosides play a pronounced positive role in the prevention and treatment of neurological diseases. Nevertheless, research is still at an early stage of development, and the complex mechanisms of action involved remain largely unknown. This review aimed to shed light into what is currently known about the mechanisms of action of ginsenosides in relation to Alzheimer's disease. Scientific material and theoretical bases for the treatment of nervous system diseases with purified Panax ginseng extracts are also discussed.

While I Still Remember: 30 Years of Alzheimer's Disease Research

Turns out I have been a major contributor to the Journal of Alzheimer's Disease over its 20-year history. As such, I was invited to provide a review of my work over the years. What follows is a retrospective of how the Alzheimer-related research of a Ph.D. (i.e., not an M.D.) transitioned from basic to clinical, and moved from bench to bedside and back again.I have included some of the more humorous and poignant twists along the way that some older players may find familiar and I hope might inspire some younger players to hang in there.

Activation of Ras-ERK Signaling and GSK-3 by Amyloid Precursor Protein and Amyloid Beta Facilitates Neurodegeneration in Alzheimer's Disease

It is widely accepted that amyloid β (Aβ) generated from amyloid precursor protein (APP) oligomerizes and fibrillizes to form neuritic plaques in Alzheimer’s disease (AD), yet little is known about the contribution of APP to intracellular signaling events preceding AD pathogenesis. The data presented here demonstrate that APP expression and neuronal exposure to oligomeric Aβ42 enhance Ras/ERK signaling cascade and glycogen synthase kinase 3 (GSK-3) activation. We find that RNA interference (RNAi)-directed knockdown of APP in B103 rat neuroblastoma cells expressing APP inhibits Ras-ERK signaling and GSK-3 activation, indicating that APP acts upstream of these signal transduction events. Both ERK and GSK-3 are known to induce hyperphosphorylation of tau and APP at Thr668, and our findings suggest that aberrant signaling by APP facilitates these events. Supporting this notion, analysis of human AD brain samples showed increased expression of Ras, activation of GSK-3, and phosphorylation of APP and tau, which correlated with Aβ levels in the AD brains. Furthermore, treatment of primary rat neurons with Aβ recapitulated these events and showed enhanced Ras-ERK signaling, GSK-3 activation, upregulation of cyclin D1, and phosphorylation of APP and tau. The finding that Aβ induces Thr668 phosphorylation on APP, which enhances APP proteolysis and Aβ generation, denotes a vicious feedforward mechanism by which APP and Aβ promote tau hyperphosphorylation and neurodegeneration in AD. Based on these results, we hypothesize that aberrant proliferative signaling by APP plays a fundamental role in AD neurodegeneration and that inhibition of this would impede cell cycle deregulation and neurodegeneration observed in AD.

The Function of the Mitochondrial Calcium Uniporter in Neurodegenerative Disorders

The mitochondrial calcium uniporter (MCU)-a calcium uniporter on the inner membrane of mitochondria-controls the mitochondrial calcium uptake in normal and abnormal situations. Mitochondrial calcium is essential for the production of adenosine triphosphate (ATP); however, excessive calcium will induce mitochondrial dysfunction. Calcium homeostasis disruption and mitochondrial dysfunction is observed in many neurodegenerative disorders. However, the role and regulatory mechanism of the MCU in the development of these diseases are obscure. In this review, we summarize the role of the MCU in controlling oxidative stress-elevated mitochondrial calcium and its function in neurodegenerative disorders. Inhibition of the MCU signaling pathway might be a new target for the treatment of neurodegenerative disorders.

Dose-response analysis indicating time-dependent neurotoxicity caused by organic and inorganic mercury-Implications for toxic effects in the developing brain

A latency period preceding neurotoxicity is a common characteristic in the dose-response relationship induced by organic mercury. Latency periods have typically been observed with genotoxicants in carcinogenesis, with cancer being manifested a long time after the initiating event. These observations indicate that even a very small dose may cause extensive adverse effects later in life, so the toxicity of the genotoxic compound is dose and time-dependent. In children, methylmercury exposure during pregnancy (in utero) has been associated with delays in reaching developmental milestones (e.g., age at first walking) and decreases in intelligence, increasing in severity with increasing exposure. Ethylmercury exposure from thimerosal in some vaccines has been associated, in some studies, with autism and other neurological disorders in children. In this paper, we have examined whether dose-response data from in vitro and in vivo organic mercury toxicity studies fit the Druckrey-Küpfmüller equation c·t(n)=constant (c=exposure concentration, t=latency period), first established for genotoxic carcinogens, and whether or not irreversible effects are enhanced by time of exposure (n≥1), or else toxic effects are dose-dependent while time has only minor influence on the adverse outcome (n<1). The mode of action underlying time-dependent toxicity is irreversible binding to critical receptors causing adverse and cumulative effects. The results indicate that the Druckrey-Küpfmüller equation describes well the dose-response characteristics of organic mercury induced neurotoxic effects. This amounts to a paradigm shift in chemical risk assessment of mercurial compounds and highlights that it is vital to perform toxicity testing geared to investigate time-dependent effects.

Ginsenoside Rg1 inhibits high-voltage-activated calcium channel currents in hippocampal neurons of beta-amyloid peptide-exposed rat brain slices

OBJECTIVE

To examine whether ginsenoside Rg1 (Rg1) inhibits the high-voltage-activated calcium currents (ICa,HVA) via mitogen-activated protein kinase (MAPK) in hippocampal neurons in rat brain slices exposed to beta-amyloid peptide 25-35 (Aβ25-35).

METHODS

An experimental Alzheimer disease (AD) model was prepared by exposure of rat brain slices to Aβ25-35 (10 µmol/L). After treatment with Rg1 (20 µmol/L), the ICa,HVA elicited in hippocampal neurons in these rat brain slices upon depolarization from-40 to 40 mV for 200 ms was recorded by a whole-cell patch clamp to analyze the changes in the peak current density, I-V curve, activation-V curve, and inactivation-V curve.

RESULTS

Exposure of rat brain slices to Aβ led to a significant increase in ICa,HVA, enhancement of the voltage sensitivity of channel activation, and reduction of the voltage sensitivity of channel inactivation in neurons in the hippocampus of rat brain slices. Rg1 treatment significantly inhibited these changes. These effects of Rg1 could be effectively inhibited by the MAPK inhibitor PD98059.

CONCLUSION

Rg1 can inhibit Ica,HVA via MAPK in hippocampal neurons in Aβ-exposed rat brain slices.

Nutritional supplementation for Alzheimer's disease?

PURPOSE OF REVIEW

Evidence for the benefit of nutrition in Alzheimer's disease continues to accumulate. Many studies with individual vitamins or supplements show marginal, if any, benefit. However, new findings with combinatorial formulations demonstrate improvement in cognitive performance and behavioral difficulties that accompany Alzheimer's disease. Herein, we review some of the most recent clinical advances and summarize supportive preclinical studies.

RECENT FINDINGS

We present novel positive effects on Alzheimer's disease derived from diet, trace elements, vitamins and supplements. We discuss the inherent difficulty in conducting nutritional studies because of the variance in participants' nutritional history, versus pharmacological interventions in which participants are naive to the intervention. We examine the evidence that epigenetics play a role in Alzheimer's disease and how nutritional intervention can modify the key epigenetic events to maintain or improve cognitive performance.

SUMMARY

Overall consideration of the most recent collective evidence suggests that the optimal approach for Alzheimer's disease would seem to combine early, multicomponent nutritional approaches (a Mediterranean-style diet, multivitamins and key combinatorial supplements), along with lifestyle modifications such as social activity and mental and physical exercise, with ultimate addition of pharmacological agents when warranted.

Neuronal degeneration, synaptic defects, and behavioral abnormalities in tau₄₅₋₂₃₀ transgenic mice

The complement of mechanisms underlying tau pathology in neurodegenerative disorders has yet to be elucidated. Among these mechanisms, abnormal tau phosphorylation has received the most attention because neurofibrillary tangles present in Alzheimer's disease (AD) and related disorders known as tauopathies are composed of hyperphosphorylated forms of this microtubule-associated protein. More recently, we showed that calpain-mediated cleavage leading to the generation of the 17kDa tau₄₅₋₂₃₀ fragment is a conserved mechanism in these diseases. To obtain insights into the role of this fragment in neurodegeneration, we generated transgenic mice that express tau₄₅₋₂₃₀ and characterized their phenotype. Our results showed a significant increase in cell death in the hippocampal pyramidal cell layer of transgenic tau₄₅₋₂₃₀ mice when compared to wild-type controls. In addition, significant synapse loss was detected as early as six months after birth in transgenic hippocampal neurons. These synaptic changes were accompanied by alterations in the expression of the N-methyl-d-aspartate glutamate (NMDA) receptor subunits. Furthermore, functional abnormalities were detected in the transgenic mice using Morris Water Maze and fear conditioning tests. These results suggest that the accumulation of tau₄₅₋₂₃₀ is responsible, at least in part, for neuronal degeneration and some behavioral changes in AD and other tauopathies. Collectively, these data provide the first direct evidence of the toxic effects of a tau fragment biologically produced in the context of these diseases in vertebrate neurons that develop in situ.

The dendritic hypothesis for Alzheimer's disease pathophysiology

Converging evidence indicates that processes occurring in and around neuronal dendrites are central to the pathogenesis of Alzheimer's disease. These data support the concept of a "dendritic hypothesis" of AD, closely related to the existing synaptic hypothesis. Here we detail dendritic neuropathology in the disease and examine how Aβ, tau, and AD genetic risk factors affect dendritic structure and function. Finally, we consider potential mechanisms by which these key drivers could affect dendritic integrity and disease progression. These dendritic mechanisms serve as a framework for therapeutic target identification and for efforts to develop disease-modifying therapeutics for Alzheimer's disease.

The changing landscape of voltage-gated calcium channels in neurovascular disorders and in neurodegenerative diseases

It is a common belief that voltage-gated calcium channels (VGCC) cannot carry toxic amounts of Ca²⁺ in neurons. Also, some of them as L-type channels are essential for Ca²⁺-dependent regulation of prosurvival gene-programs. However, a wealth of data show a beneficial effect of drugs acting on VGCCs in several neurodegenerative and neurovascular diseases. In the present review, we explore several mechanisms by which the “harmless” VGCCs may become “toxic” for neurons. These mechanisms could explain how, though usually required for neuronal survival, VGCCs may take part in neurodegeneration. We will present evidence showing that VGCCs can carry toxic Ca²⁺ when: a) their density or activity increases because of aging, chronic hypoxia or exposure to β-amyloid peptides or b) Ca²⁺-dependent action potentials carry high Ca²⁺ loads in pacemaker neurons. Besides, we will examine conditions in which VGCCs promote neuronal cell death without carrying excess Ca²⁺. This can happen, for instance, when they carry metal ions into the neuronal cytoplasm or when a pathological decrease in their activity weakens Ca²⁺-dependent prosurvival gene programs. Finally, we will explore the role of VGCCs in the control of nonneuronal cells that take part to neurodegeneration like those of the neurovascular unit or of microglia.

Calpain dysregulation in Alzheimer's disease

Alzheimer's disease (AD) is characterized by the presence of senile plaques and neurofibrillary tangles in the neocortex and hippocampus of AD patients. In addition, a marked decrease in synaptic contacts has been detected in these affected brain areas. Due to its prevalence in the aging population, this disease has been the focus of numerous studies. The data obtained from those studies suggest that the mechanisms leading to the formation of the hallmark lesions of AD might be linked. One of such mechanisms seems to be the dysregulation of calcium homeostasis that results in the abnormal activation of calpains. Calpains are a family of Ca(2+)-dependent cysteine proteases that play a key role in multiple cell functions including cell development, differentiation and proliferation, axonal guidance, growth cone motility, and cell death, among others. In this paper, we briefly reviewed data on the structure of these proteases and their regulation under normal conditions. We also summarized data underscoring the participation of calpains in the neurodegenerative mechanisms associated with AD.

Inhaled essential oil from Chamaecyparis obtuse ameliorates the impairments of cognitive function induced by injection of β-amyloid in rats

CONTEXT

Chamaecyparis obtusa Sieb. & Zucc., Endlicher (Cupressaceae) forest bathing or aromatherapy has been shown in various studies to have biological functions such as anticancer, antiallergies, antiinflammatory, and antioxidant activity. However, no reports exist on the pharmacological or biological activities of the essential oil of C. obtusa (EOCO) or its effects on central nervous system.

OBJECTIVE

The aggregation and formation of β-amyloid peptides (Aβ) into fibrils are central events in the pathogenesis of Alzheimer's disease (AD), and overproduction and aggregation of Aβ into oligomers have been known to trigger neurotoxicity. In this study, we investigated the effects of inhaled EOCO on cognitive function and neuronal apoptosis in rats intrahippocampally injected with Aβ.

MATERIALS AND METHODS

To model AD, 4 μg of aggregated Aβ was injected into the hippocampus. To test the effects of EOCO, behavioral performance in the Morris water maze was tested 4 days after injection. After behavioral testing, brain sections were prepared for TTC staining and TUNEL assay.

RESULTS

Inhaled EOCO protected spatial learning and memory from the impairments induced by Aβ(1-40) injection. In addition, the behavioral deficits accompanying Aβ(1-40)-induced AD were attenuated by inhalation of EOCO. Furthermore, acetylcholinesterase (AChE) activity and neuronal apoptosis were significantly inhibited in rats treated with Aβ(1-40) and EOCO compared to rats treated only with Aβ(1-40).

DISCUSSION AND CONCLUSION

EOCO suppressed both AD-related neuronal cell apoptosis and AD-related dysfunction of the memory system. Thus, the results of this study support EOCO as a candidate drug for the treatment of AD.

Changes in the physiology of CA1 hippocampal pyramidal neurons in preplaque CRND8 mice

Amyloid-β protein (Aβ) is thought to play a central pathogenic role in Alzheimer's disease. Aβ can impair synaptic transmission, but little is known about the effects of Aβ on intrinsic cellular properties. Here we compared the cellular properties of CA1 hippocampal pyramidal neurons in acute slices from preplaque transgenic (Tg+) CRND8 mice and wild-type (Tg-) littermates. CA1 pyramidal neurons from Tg+ mice had narrower action potentials with faster decays than neurons from Tg- littermates. Action potential-evoked intracellular Ca(2+) transients in the apical dendrite were smaller in Tg+ than in Tg- neurons. Resting calcium concentration was higher in Tg+ than in Tg- neurons. The difference in action potential waveform was eliminated by low concentrations of tetraethylammonium ions and of 4-aminopyridine, implicating a fast delayed-rectifier potassium current. Consistent with this suggestion, there was a small increase in immunoreactivity for Kv3.1b in stratum radiatum in Tg+ mice. These changes in intrinsic properties may affect information flow through the hippocampus and contribute to the behavioral deficits observed in mouse models and patients with early-stage Alzheimer's disease.

4-O-methylhonokiol attenuated β-amyloid-induced memory impairment through reduction of oxidative damages via inactivation of p38 MAP kinase

Oxidative stress induced neuronal cell death by accumulation of β-amyloid (Aβ) is a critical pathological mechanism of Alzheimer's disease (AD). Intracerebroventrical infusion of Aβ(1-42) (300 pmol/day per mouse) for 14 days induced neuronal cell death and memory impairment, but pre-treatment of 4-O-methylhonokiol (4-O-MH), a novel compound extracted from Magnolia officinalis for 3 weeks (0.2, 0.5 and 1.0 mg/kg) prior to the infusion of Aβ(1-42) and during the infusion dose dependently improved Aβ(1-42)-induced memory impairment and prevented neuronal cell death. Additionally, 4-O-MH reduced Aβ(1-42) infusion-induced oxidative damages of protein and lipid but reduced glutathione levels in the cortex and hippocampus. Aβ(1-42) infusion-induced activation of astrocytes and p38 mitogenic activated protein (MAP) kinase was also prevented by 4-O-MH in mice brains. In further study using culture cortical neurons, p38 MAP kinase inhibitor abolished the inhibitory effect of 4-O-MH (10 μM) on the Aβ(1-42) (5 μM)-induced reactive oxidative species generation and neuronal cell death. These results suggest that 4-O-MH might prevent the development and progression of AD through the reduction of oxidative stress and neuronal cell death via inactivation of p38 MAP kinase pathway.

Oligomerisation differentially affects the acute and chronic actions of amyloid-beta in vitro

Key neuropathological hallmarks of Alzheimer's disease include the accumulation of amyloid-beta (Abeta), disruption of Ca(2+) homeostasis and neurodegeneration. However, the physical nature of the toxic Abeta species is controversial. Here, we examined the effect of aging on acute and chronic actions of Abeta peptides: changes in intracellular Ca(2+) and toxic responses, respectively. Acute application of Abeta(1-42) to PC12 cells potentiated KCl-evoked increases in Ca(2+), while chronic application decreased mitochondrial function with concomitant perturbation of membrane integrity and activation of apoptosis in PC12 cells, and reduced neurite length and synaptogenesis in rat cortical neurons. Both the acute and chronic effects of Abeta(1-42) were prevented by the anti-oligomerisation peptide D-KLVFFA, implicating oligomeric structures. The generation of a range of oligomeric species by aging Abeta(1-42) at 37 degrees C for different times was supported by thioflavin T fluorescence and atomic force microscopy. Abeta(1-42) aged for 24 h maximally potentiated KCl-evoked increases in Ca(2+), and this correlated with oligomers composed of 3-6 monomers, as judged by size exclusion filtration. Aging for 72 or 96 h, which generated fibrillar structures, was less efficacious. The Abeta(25-35) fragment that lacks the self-recognition element targeted by D-KLVFFA failed to potentiate KCl-evoked increases in Ca(2+). However, Abeta(25-35) was more efficacious than Abeta(1-42) at decreasing cellular functions when applied chronically. The acute and chronic effects of Abeta(1-42) also showed differential sensitivity to blockade of voltage operated Ca(2+) channels. These results suggest that the acute effects of Abeta(1-42) on Ca(2+) signals do not underpin the toxic responses measured, although both acute and chronic effects are promoted by small oligomeric species.

Amyloid precursor protein regulates Cav1.2 L-type calcium channel levels and function to influence GABAergic short-term plasticity

Amyloid precursor protein (APP) has been strongly implicated in the pathogenesis of Alzheimer's disease (AD). Although impaired synaptic function is believed to be an early and causative event in AD, how APP physiologically regulates synaptic properties remains poorly understood. Here, we report a critical role for APP in the regulation of L-type calcium channels (LTCC) in GABAergic inhibitory neurons in striatum and hippocampus. APP deletion in mice leads to an increase in the levels of Ca(v)1.2, the pore-forming subunit of LTCCs, and subsequent increases in GABAergic calcium currents (I(Ca(2+))) that can be reversed by reintroduction of APP. Upregulated levels of Ca(v)1.2 result in reduced GABAergic paired-pulse inhibition and increased GABAergic post-tetanic potentiation in both striatal and hippocampal neurons, indicating that APP modulates synaptic properties of GABAergic neurons by regulating Ca(v)1.2. Furthermore, APP physically interacts with Ca(v)1.2, suggesting a mechanism in which loss of APP leads to an inappropriate accumulation and aberrant activity of Ca(v)1.2. These results provide a direct link between APP and calcium signaling and might help explain how altered APP regulation leads to changes in synaptic function that occur with AD.

Mitochondrial permeability transition pore in Alzheimer's disease: cyclophilin D and amyloid beta

Amyloid beta (Abeta) plays a critical role in the pathophysiology of Alzheimer's disease. Increasing evidence indicates mitochondria as an important target of Abeta toxicity; however, the effects of Abeta toxicity on mitochondria have not yet been fully elucidated. Recent biochemical studies in vivo and in vitro implicate mitochondrial permeability transition pore (mPTP) formation involvement in Abeta-mediated mitochondrial dysfunction. mPTP formation results in severe mitochondrial dysfunction such as reactive oxygen species (ROS) generation, mitochondrial membrane potential dissipation, intracellular calcium perturbation, decrease in mitochondrial respiration, release of pro-apoptotic factors and eventually cell death. Cyclophilin D (CypD) is one of the more well-known mPTP components and recent findings reveal that Abeta has significant impact on CypD-mediated mPTP formation. In this review, the role of Abeta in the formation of mPTP and the potential of mPTP inhibition as a therapeutic strategy in AD treatment are examined.

Aβ toxicity in primary cultured neurons

The aggregation of beta-amyloid (Aβ) into soluble oligomers is considered an early event in Alzheimer's disease. Furthermore, the presence of these aggregates seems to lead to neurodegeneration in the context of this disease. However, the mechanisms underlying Aβ-induced neurotoxicity are not completely understood. Primary cultures of pyramidal neurons have proven to be an excellent model system for the study of such mechanisms. These cultures provide a homogenous population of neurons that extend and differentiate axons and dendrites and that establish functional synapses among them. In addition, the neurotoxic effects of preaggregated Aβ can be easily analyzed both morphologically and biochemically. Here, we describe in detail the materials and methods used for the preparation and maintenance of primary cultures of hippocampal pyramidal neurons, as well as for the aggregation of and treatment with Aβ.

Calcium dysregulation in Alzheimer's disease: from mechanisms to therapeutic opportunities

Calcium is involved in many facets of neuronal physiology, including activity, growth and differentiation, synaptic plasticity, and learning and memory, as well as pathophysiology, including necrosis, apoptosis, and degeneration. Though disturbances in calcium homeostasis in cells from Alzheimer's disease (AD) patients have been observed for many years, much more attention was focused on amyloid-beta (Abeta) and tau as key causative factors for the disease. Nevertheless, increasing lines of evidence have recently reported that calcium dysregulation plays a central role in AD pathogenesis. Systemic calcium changes accompany almost the whole brain pathology process that is observed in AD, including synaptic dysfunction, mitochondrial dysfunction, presenilins mutation, Abeta production and Tau phosphorylation. Given the early and ubiquitous involvement of calcium dysregulation in AD pathogenesis, it logically presents a variety of potential therapeutic targets for AD prevention and treatment, such as calcium channels in the plasma membrane, calcium channels in the endoplasmic reticulum membrane, Abeta-formed calcium channels, calcium-related proteins. The review aims to provide an overview of the current understanding of the molecular mechanisms involved in calcium dysregulation in AD, and an insight on how to exploit calcium regulation as therapeutic opportunities in AD.

Calcium in the initiation, progression and as an effector of Alzheimer's disease pathology

The cause(s) of sporadic Alzheimer’s disease (sAD) are complex and currently poorly understood. They likely result from a combination of genetic, environmental, proteomic and lipidomic factors that crucially occur only in the aged brain. Age-related changes in calcium levels and dynamics have the potential to increase the production and accumulation of both amyloid-β peptide (Aβ) and τ pathologies in the AD brain, although these two pathologies themselves can induce calcium dyshomeostasis, particularly at synaptic membranes. This review discuses the evidence for a role for calcium dyshomeostasis in the initiation of pathology, as well as the evidence for these pathologies themselves disrupting normal calcium homeostasis, which lead to synaptic and neuronal dysfunction, synaptotoxicity and neuronal loss, underlying the dementia associated with the disease.

Expression of human amyloid precursor protein in rat cortical neurons inhibits calcium oscillations

Synchronous calcium oscillations are observed in primary cultures of rat cortical neurons when mature networks are formed. This spontaneous neuronal activity needs an accurate control of calcium homeostasis. Alteration of intraneuronal calcium concentration is described in many neurodegenerative disorders, including Alzheimer disease (AD). Although processing of amyloid precursor protein (APP) that generates Abeta peptide has critical implications for AD pathogenesis, the neuronal function of APP remains unclear. Here, we report that expression of human APP (hAPP) in rat cortical neurons increases L-type calcium currents, which stimulate SK channels, calcium-dependent K(+) channels responsible for medium afterhyperpolarization (mAHP). In a neuronal network, increased mAHP in some neurons expressing hAPP leads to inhibition of calcium oscillations in all the cells of the network. This inhibition is independent of production and secretion of Abeta and other APP metabolites. In a neuronal network, reduction of endogenous APP expression using shRNA increases the frequency and reduces the amplitude of calcium oscillations. Altogether, these data support a key role for APP in the control of neuronal excitability.

Role of methionine 35 in the intracellular Ca2+ homeostasis dysregulation and Ca2+-dependent apoptosis induced by amyloid beta-peptide in human neuroblastoma IMR32 cells

Amyloid beta-peptide (Abeta) plays a fundamental role in the pathogenesis of Alzheimer's disease. We recently reported that the redox state of the methionine residue in position 35 of amyloid beta-peptide (Abeta) 1-42 (Met35) strongly affects the peptide's ability to trigger apoptosis and is thus a major determinant of its neurotoxicity. Dysregulation of intracellular Ca(2+) homeostasis resulting in the activation of pro-apoptotic pathways has been proposed as a mechanism underlying Abeta toxicity. Therefore, we investigated correlations between the Met35 redox state, Abeta toxicity, and altered intracellular Ca(2+) signaling in human neuroblastoma IMR32 cells. Cells incubated for 6-24 h with 10 microM Abeta1-42 exhibited significantly increased KCl-induced Ca(2+) transient amplitudes and resting free Ca(2+) concentrations. Nifedipine-sensitive Ca(2+) current densities and Ca(v)1 channel expression were markedly enhanced by Abeta1-42. None of these effects were observed when cells were exposed to Abeta containing oxidized Met35 (Abeta1-42(Met35-Ox)). Cell pre-treatment with the intracellular Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid acetoxymethyl ester (1 microM) or the Ca(v)1 channel blocker nifedipine (5 microM) significantly attenuated Abeta1-42-induced apoptosis but had no effect on Abeta1-42(Met35-Ox) toxicity. Collectively, these data suggest that reduced Met35 plays a critical role in Abeta1-42 toxicity by rendering the peptide capable of disrupting intracellular Ca(2+) homeostasis and thereby provoking apoptotic cell death.

Abeta plaques lead to aberrant regulation of calcium homeostasis in vivo resulting in structural and functional disruption of neuronal networks

Alzheimer's disease is characterized by the deposition of senile plaques and progressive dementia. The molecular mechanisms that couple plaque deposition to neural system failure, however, are unknown. Using transgenic mouse models of AD together with multiphoton imaging, we measured neuronal calcium in individual neurites and spines in vivo using the genetically encoded calcium indicator Yellow Cameleon 3.6. Quantitative imaging revealed elevated [Ca(2+)]i (calcium overload) in approximately 20% of neurites in APP mice with cortical plaques, compared to less than 5% in wild-type mice, PS1 mutant mice, or young APP mice (animals without cortical plaques). Calcium overload depended on the existence and proximity to plaques. The downstream consequences included the loss of spinodendritic calcium compartmentalization (critical for synaptic integration) and a distortion of neuritic morphologies mediated, in part, by the phosphatase calcineurin. Together, these data demonstrate that senile plaques impair neuritic calcium homeostasis in vivo and result in the structural and functional disruption of neuronal networks.

Modified Ca(v)1.4 expression in the Cacna1f(nob2) mouse due to alternative splicing of an ETn inserted in exon 2

The Cacna1f^nob2 mouse is reported to be a naturally occurring null mutation for the Ca_v1.4 calcium channel gene and the phenotype of this mouse is not identical to that of the targeted gene knockout model. We found two mRNA species in the Cacna1f^nob2 mouse: approximately 90% of the mRNA represents a transcript with an in-frame stop codon within exon 2 of CACNA1F, while approximately 10% of the mRNA represents a transcript in which alternative splicing within the ETn element has removed the stop codon. This latter mRNA codes for full length Ca_v1.4 protein, detectable by Western blot analysis that is predicted to differ from wild type Ca_v1.4 protein in a region of approximately 22 amino acids in the N-terminal portion of the protein. Electrophysiological analysis with either mouse Ca_v1.4^wt or Ca_v1.4^nob2 cDNA revealed that the alternatively spliced protein does not differ from wild type with respect to activation and inactivation characteristics; however, while the wild type N-terminus interacted with filamin proteins in a biochemical pull-down experiment, the alternatively spliced N-terminus did not. The Cacna1f^nob2 mouse electroretinogram displayed reduced b-wave and oscillatory potential amplitudes, and the retina was morphologically disorganized, with substantial reduction in thickness of the outer plexiform layer and sprouting of bipolar cell dendrites ectopically into the outer nuclear layer. Nevertheless, the spatial contrast sensitivity (optokinetic response) of Cacna1f^nob2 mice was generally similar to that of wild type mice. These results suggest the Cacna1f^nob2 mouse is not a CACNA1F knockout model. Rather, alternative splicing within the ETn element can lead to full-length Ca_v1.4 protein, albeit at reduced levels, and the functional Ca_v1.4 mutant may be incapable of interacting with cytoskeletal filamin proteins. These changes, do not alter the ability of the Cacna1f^nob2 mouse to detect and follow moving sine-wave gratings compared to their wild type counterparts.

The novel calpain inhibitor A-705253 potently inhibits oligomeric beta-amyloid-induced dynamin 1 and tau cleavage in hippocampal neurons

We have previously shown that beta-amyloid (Abeta) oligomers induced dynamin 1 and tau cleavage in cultured hippocampal neurons. As a result of this cleavage, dynamin 1 levels decreased and a toxic tau fragment was generated. Abeta-induced cleavage of these proteins was calpain-mediated and impacted both synaptic vesicle recycling and the integrity of neuronal processes [Kelly, B.L., Vassar, R., Ferreira, A., 2005. Beta-amyloid-induced dynamin 1 depletion in hippocampal neurons. A potential mechanism for early cognitive decline in Alzheimer disease. J. Biol. Chem. 280, 31746-31753; Park, S.Y., Ferreira, A., 2005. The generation of a 17kDa neurotoxic fragment: an alternative mechanism by which tau mediates beta-amyloid-induced neurodegeneration. J. Neurosci. 25, 5365-5375; Kelly, B.L., Ferreira, A., 2006. Beta-amyloid-induced dynamin 1 degradation is mediated by N-methyl-d-aspartate receptors in hippocampal neurons. J. Biol. Chem. 281, 28079-28089, Kelly, B.L., Ferreira, A., 2007. Beta-amyloid disrupted synaptic vesicle endocytosis in cultured hippocampal neurons. Neuroscience 147, 60-70]. Building on previous reports, these results identified calpain as a potential target for therapeutic intervention in Alzheimer's disease. In the present study, we tested the ability of A-705253, a novel water-soluble calpain inhibitor with oral availability and enhanced metabolic stability, to prevent Abeta-induced dynamin 1 and tau cleavage in cultured hippocampal neurons. Quantitative Western blot analysis indicated that the incubation of these cells with A-705253 prior to the addition of oligomeric Abeta reduced both dynamin 1 and tau cleavage in a dose-dependent manner. In addition, our results showed that this calpain inhibitor significantly ameliorated the cleavage of these proteins when added simultaneously with oligomeric Abeta. Furthermore, our data indicated that the use of this calpain inhibitor could have some beneficial effects even when added after the cleavage of these proteins have been triggered by Abeta. Collectively, these results suggest that, indeed, specific calpain inhibitors could play an important role in the treatment of Alzheimer's disease.

Tournefolic acid B attenuates amyloid beta protein-mediated toxicity by abrogating the calcium overload in mitochondria and retarding the caspase 8-truncated Bid-cytochrome c pathway in rat cortical neurons

The effect of tournefolic acid B (TAB) on amyloid beta protein-mediated neurotoxicity and the underlying mechanisms were investigated. Amyloid beta protein 25-35 elicited neuronal death as determined by calcein/ethidium homodimer-1 staining. 10 microM amyloid beta protein 25-35 caused cell death at a level of 41.5+/-3.8% by MTT reduction. 50 microM TAB attenuated the amyloid beta protein 25-35-induced cell death by 49.7+/-11.1%. TAB also abrogated amyloid beta protein-induced activation of caspases 8 and 9 by about 50-60%. Furthermore, TAB significantly diminished the amyloid beta protein 25-35-induced elevation of calcium level in mitochondria, whereas it did not affect the calcium level in cytosol or endoplasmic reticulum. TAB markedly retarded the amyloid beta protein-mediated release of cytochrome c from mitochondria. Amyloid beta protein 25-35 elevated mitochondrial truncated BH3 interacting domain death agonist (tBid) and decreased the level of B-cell leukemia/lymphoma-2alpha (Bcl-2alpha) in mitochondria. Moreover, amyloid beta protein induced a slight up-regulation of Bcl-2 agonist killer 1 (Bak) in cytosol. 50 microM TAB decreased the amyloid beta protein-induced elevation of mitochondrial tBid and the level of Bak, whereas it did not affect the amyloid beta protein-mediated decrease in mitochondrial Bcl-2alpha. Caspase 8 inhibitor significantly inhibited the amyloid beta protein-mediated increase in mitochondrial tBid and the release of cytochrome c. Therefore, TAB blocked the overload of calcium in mitochondria and impaired the amyloid beta protein-mediated activation of the caspase 8-tBid-cytochrome c pathway, thereby conferring its neuroprotective effects on amyloid beta protein-mediated neurotoxicity.

Role of calcium in the pathogenesis of Alzheimer's disease and transgenic models

Alzheimer's disease (AD) is a progressive neurodegenerative disorder of the elderly that is characterized by memory loss. Neuropathologically, the AD brain is marked by an increased AP burden, hyperphosphorylated tau aggregates, synaptic loss, and inflammatory responses. Disturbances in calcium homeostasis are also one of the earliest molecular changes that occur in AD patients, alongside alterations in calcium-dependent enzymes in the post-mortem brain. The sum of these studies suggests that calcium dyshomeostasis is an integral part of the pathology, either influencing AP production, mediating its effects or both. Increasing evidence from in vitro studies demonstrates that the AP peptide could modulate a number of ion channels increasing calcium influx, including voltage-gated calcium and potassium channels, the NMDA receptor, the nicotinic receptor, as well as forming its own calcium-conducting pores. In vivo evidence has shown that A3 impairs both LTP and cognition, whereas all of these ion channels cluster at the synapse and underlie synaptic transmission and hence cognition. Here we consider the evidence that AP causes cognitive deficits through altering calcium homeostasis at the synapse, thus impairing synaptic transmission and LTP. Furthermore, this disruption appearr to occur without overt or extensive neuronal loss, as it is observed in transgenic mouse models of AD, but may contribute to the synaptic loss, which is an early event that correlates best with cognitive decline.

3,4-Dihydroxybenzoic acid from Smilacis chinae rhizome protects amyloid β protein (25–35)-induced neurotoxicity in cultured rat cortical neurons

The neuroprotective effect of 3,4-dihydroxybenzoic acid (3,4-DHBA) isolated from Smilacis chinae rhizome against Abeta (25-35)-induced neurotoxicity on cultured rat cortical neurons was found in this study. The protective effect of 3,4-DHBA against Abeta (25-35)-induced neuronal cell death was investigated by measuring cell viability via a 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide (MTT) assay and Hoechst 33342 staining. 3,4-DHBA (1 and 10 microM) concentration-dependently inhibited 10 microM Abeta (25-35)-induced neuronal apoptotic death. 3,4-DHBA (1 and 10 microM) inhibited 10 microM Abeta (25-35)-induced elevation of cytosolic Ca(2+) concentration ([Ca(2+)](c)), which was measured by a fluorescent dye, Fluo-4 AM. 3,4-DHBA also inhibited glutamate release into medium, reactive oxygen species (ROS) generation, and caspase-3 activation, which were induced by 10 microM Abeta (25-35). These results suggest that 3,4-DHBA prevents Abeta (25-35)-induced neuronal cell damage by interfering with the increase of [Ca(2+)](c), and then by inhibiting glutamate release, generation of ROS and caspase-3 activity.