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

Volatile oil of Acori tatarinowii rhizoma: potential candidate drugs for mitigating dementia

Objective

This study aims to elucidate the mitigating effects of the volatile oil of Acori tatarinowii rhizoma (ATR) on dementia, in order to provide a reference for future research and applications of the volatile oil of ATR in the field of dementia.

Materials and methods

A search strategy was developed using terms such as "Acori tatarinowii rhizoma," "Acorus tatarinowii Schott," "Asarone," and "Dementia." The literature search was conducted in PubMed, Web of Science, and Google Scholar, and studies not meeting the inclusion criteria were excluded. This study summarizes the main metabolites, active ingredients, toxicological properties, and pharmacokinetic characteristics of the volatile oil from ATR in mitigating dementia, with a particular focus on its potential mechanisms of action. Furthermore, the study highlights the limitations of existing research and offers insights into future research directions.

Results

The volatile oil of ATR mitigates dementia through multiple pathways, including reducing abnormal protein aggregation, promoting neurogenesis, inhibiting neuronal apoptosis, regulating neurotransmitters, improving synaptic function, modulating autophagy, countering cellular stress, reducing neuroinflammation, and alleviating vascular risk factors.

Conclusion

The multi-pathway pharmacological effects of the volatile oil of ATR are well-aligned with the complex mechanisms of dementia progression, highlighting its significant therapeutic potential for anti-dementia applications. This provides new perspectives for the development of more effective anti-dementia drugs. Nonetheless, further rigorous and high-quality preclinical and clinical investigations are required to address key issues, including the chemical characterization of the volatile oil of ATR, potential synergistic effects among active ingredients, toxicity profiles, and definitive clinical efficacy.

Deletion of Dcf1 Reduces Amyloid-β Aggregation and Mitigates Memory Deficits

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disease. One of the pathologies of AD is the accumulation of amyloid-β (Aβ) to form senile plaques, leading to a decline in cognitive ability and a lack of learning and memory. However, the cause leading to Aβ aggregation is not well understood. Dendritic cell factor 1 (Dcf1) shows a high expression in the entorhinal cortex neurons and neurofibrillary tangles in AD patients.

OBJECTIVE

Our goal is to investigate the effect of Dcf1 on Aβ aggregation and memory deficits in AD development.

METHODS

The mouse and Drosophila AD model were used to test the expression and aggregation of Aβ, senile plaque formation, and pathological changes in cognitive behavior during dcf1 knockout and expression. We finally explored possible drug target effects through intracerebroventricular delivery of Dcf1 antibodies.

RESULTS

Deletion of Dcf1 resulted in decreased Aβ42 level and deposition, and rescued AMPA Receptor (GluA2) levels in the hippocampus of APP-PS1-AD mice. In Aβ42 AD Drosophila, the expression of Dcf1 in Aβ42 AD flies aggravated the formation and accumulation of senile plaques, significantly reduced its climbing ability and learning-memory. Data analysis from all 20 donors with and without AD patients aged between 80 and 90 indicated a high-level expression of Dcf1 in the temporal neocortex. Dcf1 contributed to Aβ aggregation by UV spectroscopy assay. Intracerebroventricular delivery of Dcf1 antibodies in the hippocampus reduced the area of senile plaques and reversed learning and memory deficits in APP-PS1-AD mice.

CONCLUSION

Dcf1 causes Aβ-plaque accumulation, inhibiting dcf1 expression could potentially offer therapeutic avenues.

Elevating the Levels of Calcium Ions Exacerbate Alzheimer's Disease via Inducing the Production and Aggregation of β-Amyloid Protein and Phosphorylated Tau

Alzheimer’s disease (AD) is a neurodegenerative disease with a high incidence rate. The main pathological features of AD are β-amyloid plaques (APs), which are formed by β-amyloid protein (Aβ) deposition, and neurofibrillary tangles (NFTs), which are formed by the excessive phosphorylation of the tau protein. Although a series of studies have shown that the accumulation of metal ions, including calcium ions (Ca²⁺), can promote the formation of APs and NFTs, there is no systematic review of the mechanisms by which Ca²⁺ affects the development and progression of AD. In view of this, the current review summarizes the mechanisms by which Ca²⁺ is transported into and out of cells and organelles, such as the cell, endoplasmic reticulum, mitochondrial and lysosomal membranes to affect the balance of intracellular Ca²⁺ levels. In addition, dyshomeostasis of Ca²⁺ plays an important role in modulating the pathogenesis of AD by influencing the production and aggregation of Aβ peptides and tau protein phosphorylation and the ways that disrupting the metabolic balance of Ca²⁺ can affect the learning ability and memory of people with AD. In addition, the effects of these mechanisms on the synaptic plasticity are also discussed. Finally, the molecular network through which Ca²⁺ regulates the pathogenesis of AD is introduced, providing a theoretical basis for improving the clinical treatment of AD.

Maternal antibodies facilitate Amyloid-β clearance by activating Fc-receptor-Syk-mediated phagocytosis

Maternal antibodies (MAbs) protect against infections in immunologically-immature neonates. Maternally transferred immunity may also be harnessed to target diseases associated with endogenous protein misfolding and aggregation, such as Alzheimer's disease (AD) and AD-pathology in Down syndrome (DS). While familial early-onset AD (fEOAD) is associated with autosomal dominant mutations in the APP, PSEN1,2 genes, promoting cerebral Amyloid-β (Aβ) deposition, DS features a life-long overexpression of the APP and DYRK1A genes, leading to a cognitive decline mediated by Aβ overproduction and tau hyperphosphorylation. Although no prenatal screening for fEOAD-related mutations is in clinical practice, DS can be diagnosed in utero. We hypothesized that anti-Aβ MAbs might promote the removal of early Aβ accumulation in the central nervous system of human APP-expressing mice. To this end, a DNA-vaccine expressing Aβ1-11 was delivered to wild-type female mice, followed by mating with 5xFAD males, which exhibit early Aβ plaque formation. MAbs reduce the offspring's cortical Aβ levels 4 months after antibodies were undetectable, along with alleviating short-term memory deficits. MAbs elicit a long-term shift in microglial phenotype in a mechanism involving activation of the FcγR1/Syk/Cofilin pathway. These data suggest that maternal immunization can alleviate cognitive decline mediated by early Aβ deposition, as occurs in EOAD and DS.

The effect of phloretin on synaptic proteins and adult hippocampal neurogenesis in Aβ (1-42)-injected male Wistar rats

Objectives

Considering the deleterious effect of Aβ1-42, a study was designed to evaluate the effect of phloretin on altered synaptic proteins and adult hippocampal neurogenesis in Aβ1-42-injected Wistar rats.

Methods

The rats were pretreated with 5 mg/kg p.o dose of phloretin and donepezil (positive control) for 28 days, followed by intrahippocampal injections of aggregated Aβ1-42. After termination, perfused brains were isolated and subjected to Western blot and immunohistochemistry (IHC) analysis.

Key findings

The Western blot revealed that Aβ1-42-injected rats had significantly low levels of synaptophysin as compared to sham control. Phloretin pretreatment significantly protected the presynaptic protein synaptophysin against the effects of Aβ1-42. There were no significant changes in the levels of PSD95 between different groups. The IHC findings showed that Aβ1-42 significantly reduced the Ki67 and DCX in the dentate gyrus as compared to sham control. However, phloretin significantly improved the number of Ki67- and DCX-positive neurons in the dentate gyrus region as compared to Aβ1-42 group.

Conclusions

This study demonstrated the protective effect of phloretin on synaptophysin and adult neuronal proliferating cells in Aβ1-42-injected rats. The encouraging findings highlight the potential of phloretin as a dietary supplement targeting key therapeutic mechanisms in neurodegenerative disorders such as AD.

Neuroprotective effect of β-asarone against Alzheimer's disease: regulation of synaptic plasticity by increased expression of SYP and GluR1

Aim

β-asarone, an active component of Acori graminei rhizome, has been reported to have neuroprotective effects in Alzheimer’s disease. As the underlying mechanism is not known, we investigated the neuroprotective effects of β-asarone in an APP/PS1 double transgenic mouse model and in NG108 cells.

Materials and methods

APPswe/PS1dE9 double transgenic male mice were randomly assigned to a model group, β-asarone treatment groups (21.2, 42.4, or 84.8 mg/kg/d), or donepezil treatment group (2 mg/kg/d). Donepezil treatment was a positive control, and background- and age-matched wild-type B6 mice were an external control group. β-asarone (95.6% purity) was dissolved in 0.8% Tween 80 and administered by gavage once daily for 2.5 months. Control and model animals received an equal volume of vehicle. After 2.5 months of treatment, behavior of all animals was evaluated in a Morris water maze. Expression of synaptophysin (SYP) and glutamatergic receptor 1 (G1uR1) in the hippocampus and cortex of the double transgenic mice was assayed by Western blotting. The antagonistic effects of β-asarone against amyloid-β peptide (Aβ) were investigated in vitro in the NG108-15 cell line. After 24 hours of incubation, cells were treated with 10 μm Aβ with or without β-asarone at different concentrations (6.25, 12.5, or 25 μM) for an additional 36 hours. The cytotoxicity of β-asarone was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay of cell viability, and cell morphology was evaluated by bright-field microscopy after 24 hours of treatment. The expression of SYP and GluR1 in cells was detected by Western blot assay in the hippocampus and brain cortex tissues of mice.

Results

β-asarone at a high dose reduced escape latency and upregulated SYP and GluR1 expression at both medium and high doses. Cell morphology evaluation showed that β-asarone treatment did not result in obvious cell surface spots and cytoplasmic granularity. β-asarone had a dose-dependent effect on cell proliferation.

Conclusion

β-asarone antagonized the Aβ neurotoxicity in vivo, improved the learning and memory ability of APP/PS1 mice, and increased the expression of SYP and GluR1 both in vivo and in vitro. Thus, β-asarone may be a potential drug for the treatment of Alzheimer’s disease.

Developmental perfluorooctane sulfonate exposure results in tau hyperphosphorylation and β-amyloid aggregation in adults rats: Incidence for link to Alzheimer's disease

With regard to the defects of the cognitive function observed after developmental exposure to perfluorooctane sulfonate (PFOS), and earlier studies on the developmental neurotoxicology, the aim of this study was to investigate the role of developmental PFOS exposure in neurodegenerative disorders in later life. Two pathological hallmarks of Alzheimer's disease (AD), Tau hyperphosphorylation and β-amyloid (Aβ) aggregation, were examined. SD rats were exposed to PFOS during only prenatal and/or postnatal period. Tau mRNA and protein levels were elevated by PFOS exposure. The phosphorylation of Tau at S199, T231 and S396 sites were also increased. Besides, PFOS exposure increased the Aβ1-42 levels, as well as the amyloid precursor protein (APP) regulation. The prenatal PFOS exposure caused alterations in the involved proteins at comparable levels with the postnatal and both prenatal and postnatal exposure. Thus, it has raised some evidence that early PFOS exposure can affect processes linked to neurodegeneration, enhancing the AD pathological risk. And PFOS exposures in early life may be of particular etiologic importance of neurodegenerative diseases.

Can BACE1 inhibition mitigate early axonal pathology in neurological diseases?

β-Secretase-1 (BACE1) is the rate-limiting enzyme for the genesis of amyloid-β (Aβ) peptides, the main constituents of the amyloid plaques in the brains of Alzheimer's disease (AD) patients. BACE1 is being evaluated as an anti-Aβ target for AD therapy. Recent studies indicate that BACE1 elevation is associated with axonal and presynaptic pathology during plaque development. Evidence also points to a biological role for BACE1 in axonal outgrowth and synapse formation during development. Axonal, including presynaptic, pathology exists in AD as well as many other neurological disorders such as Parkinson's disease, epilepsy, stroke, and trauma. In this review, we discuss pharmaceutical BACE1 inhibition as a therapeutic option for axonal pathogenesis, in addition to amyloid pathology. We first introduce the amyloidogenic processing of amyloid-β protein precursor and describe the normal expression pattern of the amyloidogenic proteins in the brain, with an emphasis on BACE1. We then address BACE1 elevation relative to amyloid plaque development, followed by updating recent understanding of a neurotrophic role of BACE1 in axon and synapse development. We further elaborate the occurrence of axonal pathology in some other neurological conditions. Finally, we propose pharmacological inhibition of excessive BACE1 activity as an option to mitigate early axonal pathology occurring in AD and other neurological disorders.

Altered processing of amyloid precursor protein in cells undergoing apoptosis

Altered proteolysis of amyloid precursor protein is an important determinant of pathology development in Alzheimer's disease. Here, we describe the detection of two novel fragments of amyloid precursor protein in H4 neuroglioma cells undergoing apoptosis. Immunoreactivity of these 25-35 kDa fragments to two different amyloid precursor protein antibodies suggests that they contain the amyloid-β region and an epitope near the C-terminus of amyloid precursor protein. Generation of these fragments is associated with cleavage of caspase-3 and caspase-7, suggesting activation of these caspases. Studies in neurons undergoing DNA damage-induced apoptosis also showed similar results. Inclusion of caspase inhibitors prevented the generation of these novel fragments, suggesting that they are generated by a caspase-dependent mechanism. Molecular weight prediction and immunoreactivity of the fragments generated suggested that such fragments could not be generated by cleavage at any previously identified caspase, secretase, or calpain site on amyloid precursor protein. Bioinformatic analysis of the amino acid sequence of amyloid precursor protein revealed that fragments fitting the observed size and immunoreactivity could be generated by either cleavage at a novel, hitherto unidentified, caspase site or at a previously identified matrix metalloproteinase site in the extracellular domain. Proteolytic cleavage at any of these sites leads to a decrease in the generation of α-secretase cleaved secreted APP, which has both anti-apoptotic and neuroprotective properties, and thus may contribute to neurodegeneration in Alzheimer's disease.

Should Alzheimer's disease be equated with human brain ageing? A maladaptive interaction between brain evolution and senescence

In this review Alzheimer's disease is seen as a maladaptive interaction between human brain evolution and senescence. It is predicted to occur in everyone although does not necessarily lead to dementia. The pathological process is initiated in relation to a senescence mediated functional down-regulation in the posteromedial cortex (Initiation Phase). This leads to a loss of glutamatergic excitatory input to layer II entorhinal cortex neurons. A human specific maladaptive neuroplastic response is initiated in these neurons leading to neuronal dysfunction, NFT formation and death. This leads to further loss of glutamatergic excitatory input and propagation of the maladaptive response along excitatory pathways linking evolutionary progressed vulnerable neurons (Propagation Phase). Eventually neurons are affected in many brain areas resulting in dementia. Possible therapeutic approaches include enhancing glutamatergic transmission. The theory may have implications with regards to how Alzheimer's disease is classified.

13-Desmethyl spirolide-C is neuroprotective and reduces intracellular Aβ and hyperphosphorylated tau in vitro

Spirolides are marine compounds of the cyclic imine group. Although the mechanism of action is not fully elucidated yet, cholinergic (muscarinic and nicotinic) receptors have been proposed as the main targets of these toxins. In this study we examined the effect of 13-desmethyl spirolide-C (SPX) on amyloid-beta (Aβ) accumulation and tau hyperphosphorylation in a neuronal model from triple transgenic mice (3xTg) for Alzheimer disease (AD). In vitro treatment of 3xTg cortical neurons with SPX reduced intracellular Aβ accumulation and the levels of phosphorylated tau. SPX treatment did not affect the steady-state levels of neither the M1 and M2 muscarinic nor the α7 nicotinic acetylcholine receptors (AChRs), while it decreased the amplitude of acetylcholine-evoked responses and increased ACh (acetylcholine) levels in 3xTg neurons. Additionally, SPX treatment decreased the levels of two protein kinases involved in tau phosphorylation, glycogen synthase kinase 3β (GSK-3β) and extracellular-regulated kinase (ERK). Also SPX abolished the glutamate-induced neurotoxicity in both control and 3xTg neurons. The results presented here constitute the first report indicating that exposure of 3xTg neurons to nontoxic concentrations of SPX produces a simultaneous reduction in the main pathological characteristics of AD. In spite of the few reports analyzing the mode of action of the toxin we suggest that SPX could ameliorate AD pathology increasing the intracellular ACh levels and simultaneously diminishing the levels of kinases involved in tau phosphorylation.

Downregulation of genes with a function in axon outgrowth and synapse formation in motor neurones of the VEGFdelta/delta mouse model of amyotrophic lateral sclerosis

Background

Vascular endothelial growth factor (VEGF) is an endothelial cell mitogen that stimulates vasculogenesis. It has also been shown to act as a neurotrophic factor in vitro and in vivo. Deletion of the hypoxia response element of the promoter region of the gene encoding VEGF in mice causes a reduction in neural VEGF expression, and results in adult-onset motor neurone degeneration that resembles amyotrophic lateral sclerosis (ALS). Investigating the molecular pathways to neurodegeneration in the VEGF^δ/δ mouse model of ALS may improve understanding of the mechanisms of motor neurone death in the human disease.

Results

Microarray analysis was used to determine the transcriptional profile of laser captured spinal motor neurones of transgenic and wild-type littermates at 3 time points of disease. 324 genes were significantly differentially expressed in motor neurones of presymptomatic VEGF^δ/δ mice, 382 at disease onset, and 689 at late stage disease. Massive transcriptional downregulation occurred with disease progression, associated with downregulation of genes involved in RNA processing at late stage disease. VEGF^δ/δ mice showed reduction in expression, from symptom onset, of the cholesterol synthesis pathway, and genes involved in nervous system development, including axonogenesis, synapse formation, growth factor signalling pathways, cell adhesion and microtubule-based processes. These changes may reflect a reduced capacity of VEGF^δ/δ mice for maintenance and remodelling of neuronal processes in the face of demands of neural plasticity. The findings are supported by the demonstration that in primary motor neurone cultures from VEGF^δ/δ mice, axon outgrowth is significantly reduced compared to wild-type littermates.

Conclusions

Downregulation of these genes involved in axon outgrowth and synapse formation in adult mice suggests a hitherto unrecognized role of VEGF in the maintenance of neuronal circuitry. Dysregulation of VEGF may lead to neurodegeneration through synaptic regression and dying-back axonopathy.

The metabolic enhancer piracetam ameliorates the impairment of mitochondrial function and neurite outgrowth induced by beta-amyloid peptide

BACKGROUND AND PURPOSE

beta-Amyloid peptide (Abeta) is implicated in the pathogenesis of Alzheimer's disease by initiating a cascade of events from mitochondrial dysfunction to neuronal death. The metabolic enhancer piracetam has been shown to improve mitochondrial dysfunction following brain aging and experimentally induced oxidative stress.

EXPERIMENTAL APPROACH

We used cell lines (PC12 and HEK cells) and murine dissociated brain cells. The protective effects of piracetam in vitro and ex vivo on Abeta-induced impairment of mitochondrial function (as mitochondrial membrane potential and ATP production), on secretion of soluble Abeta and on neurite outgrowth in PC12 cells were investigated.

KEY RESULTS

Piracetam improves mitochondrial function of PC12 cells and acutely dissociated brain cells from young NMRI mice following exposure to extracellular Abeta(1-42). Similar protective effects against Abeta(1-42) were observed in dissociated brain cells from aged NMRI mice, or mice transgenic for mutant human amyloid precursor protein (APP) treated with piracetam for 14 days. Soluble Abeta load was markedly diminished in the brain of those animals after treatment with piracetam. Abeta production by HEK cells stably transfected with mutant human APP was elevated by oxidative stress and this was reduced by piracetam. Impairment of neuritogenesis is an important consequence of Abeta-induced mitochondrial dysfunction and Abeta-induced reduction of neurite growth in PC12 cells was substantially improved by piracetam.

CONCLUSION AND IMPLICATIONS

Our findings strongly support the concept of improving mitochondrial function as an approach to ameliorate the detrimental effects of Abeta on brain function.

Mitochondrial medicine for aging and neurodegenerative diseases

Mitochondria are key cytoplasmic organelles, responsible for generating cellular energy, regulating intracellular calcium levels, altering the reduction-oxidation potential of cells, and regulating cell death. Increasing evidence suggests that mitochondria play a central role in aging and in neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, and Freidriech ataxia. Further, several lines of evidence suggest that mitochondrial dysfunction is an early event in most late-onset neurodegenerative diseases. Biochemical and animal model studies of inherited neurodegenerative diseases have revealed that mutant proteins of these diseases are associated with mitochondria. Mutant proteins are reported to block the transport of nuclear-encoded mitochondrial proteins to mitochondria, interact with mitochondrial proteins and disrupt the electron transport chain, induce free radicals, cause mitochondrial dysfunction, and, ultimately, damage neurons. This article discusses critical issues of mitochondria causing dysfunction in aging and neurodegenerative diseases, and discusses the potential of developing mitochondrial medicine, particularly mitochondrially targeted antioxidants, to treat aging and neurodegenerative diseases.

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.

FAD mutants unable to increase neurotoxic Abeta 42 suggest that mutation effects on neurodegeneration may be independent of effects on Abeta

Strong support for a primary causative role of the Abeta peptides in the development of Alzheimer's disease (AD) neurodegeneration derives from reports that presenilin familial AD (FAD) mutants alter amyloid precursor protein processing, thus increasing production of neurotoxic Abeta 1-42 (Abeta 42). This effect of FAD mutants is also reflected in an increased ratio of peptides Abeta 42 over Abeta 1-40 (Abeta 40). In the present study, we show that several presenilin 1 FAD mutants failed to increase production of Abeta 42 or the Abeta 42/40 ratio. Our data suggest that the mechanism by which FAD mutations promote neurodegeneration and AD may be independent of their effects on Abeta production.

Alzheimer's disease-like tau neuropathology leads to memory deficits and loss of functional synapses in a novel mutated tau transgenic mouse without any motor deficits

Tau transgenic mice are valuable models to investigate the role of tau protein in Alzheimer's disease and other tauopathies. However, motor dysfunction and dystonic posture interfering with behavioral testing are the most common undesirable effects of tau transgenic mice. Therefore, we have generated a novel mouse model (THY-Tau22) that expresses human 4-repeat tau mutated at sites G272V and P301S under a Thy1.2-promotor, displaying tau pathology in the absence of any motor dysfunction. THY-Tau22 shows hyperphosphorylation of tau on several Alzheimer's disease-relevant tau epitopes (AT8, AT100, AT180, AT270, 12E8, tau-pSer396, and AP422), neurofibrillary tangle-like inclusions (Gallyas and MC1-positive) with rare ghost tangles and PHF-like filaments, as well as mild astrogliosis. These mice also display deficits in hippocampal synaptic transmission and impaired behavior characterized by increased anxiety, delayed learning from 3 months, and reduced spatial memory at 10 months. There are no signs of motor deficits or changes in motor activity at any age investigated. This mouse model therefore displays the main features of tau pathology and several of the pathophysiological disturbances observed during neurofibrillary degeneration. This model will serve as an experimental tool in future studies to investigate mechanisms underlying cognitive deficits during pathogenic tau aggregation.

Amyloid precursor protein is involved in staurosporine induced glial differentiation of neural progenitor cells

Staurosporine (STS) has been reported as not only a pro-apoptotic agent, but also a terminal differentiation inducer in several neuroblastoma cell lines. Here, we report involvement of amyloid precursor protein (APP) in a STS induced astrocytic differentiation of human neural progenitor cells (NT-2/D1). We found that STS-treated NT-2/D1 cells expressed astrocyte-specific glial fibrillary acidic protein (GFAP), aspartate transporter, and glutamate transporter-1 with a distinctive astrocytic morphology. STS treatment increased GFAP promoter activity and increased expression and secretion of APP in NT-2/D1 cell culture. Overexpressed APP enhanced GFAP promoter activity and expression of GFAP, while gene silencing of APP by RNA interference decreased GFAP expression. These results indicate involvement of APP in STS induced astrocytic differentiation of NT-2/D1 cells. Furthermore, suppression of ERK1/2 phosphorylation, which is known to regulate APP expression by a MEK1 inhibitor, PD098059, reduced both APP and GFAP expression in STS treated NT-2/D1 cells. Thus, STS may induce astrocytic differentiation of NT-2/D1 by increasing APP levels associate with activation of ERK pathway.

Age-related loss of synaptophysin immunoreactive presynaptic boutons within the hippocampus of APP751SL, PS1M146L, and APP751SL/PS1M146L transgenic mice

Neuron and synapse loss are important features of the neuropathology of Alzheimer's disease (AD). Recently, we observed substantial age-related hippocampal neuron loss in APP751SL/PS1M146L transgenic mice but not in PS1M146L mice. Here, we investigated APP751SL mice, PS1M146L mice, and APP751SL/PS1M146L mice for age-related alterations in synaptic integrity within hippocampal stratum moleculare of the dentate gyrus (SM), stratum lucidum of area CA3 (SL), and stratum radiatum of area CA1-2 (SR) by analyzing densities and numbers of synaptophysin-immunoreactive presynaptic boutons (SIPBs). Wild-type mice, APP751SL mice and PS1M146L mice showed similar amounts of age-related SIPB loss within SM, and no SIPB loss within SL. Both APP751SL mice and PS1M146L mice showed age-related SIPB loss within SR. Importantly, APP751SL/PS1M146L) mice displayed the severest age-related SIPB loss within SM, SL, and SR, even in regions free of extracellular Abeta deposits. Together, these mouse models offer a unique framework to study the impact of several molecular and cellular events caused by mutant APP and/or mutant PS1 on age-related alterations in synaptic integrity. The observation of age-related SIPB loss within SR of PS1M146L mice supports a role of mutant PS1 in neurodegeneration apart from its contribution to alterations in Abeta generation.

Overexpression of calsenilin enhances γ-secretase activity

Presenilin/gamma-secretase is a membrane-associated protease that cleaves within the transmembrane region of the amyloid precursor protein (APP) to generate amyloid-beta peptide (Abeta) whose deposition in the brain is a characteristic of Alzheimer's disease (AD). Calsenilin, a calcium binding protein that has been shown to interact with the C-termini of both presenilin 1 (PS1) and presenilin 2 (PS2), appears to play a role in transcriptional regulation and apoptosis and to bind to A-type voltage-gated potassium channels. Here, we report that overexpression of calsenilin enhanced gamma-secretase activity in cells. The effect of calsenilin on the gamma-cleavage of substrates was blocked by the selective gamma-secretase inhibitor L-685,458. We also employed a cellular gamma-cleavage GFP-reporter assay to demonstrate the effect of calsenilin on gamma-secretase activity. To establish a direct role for calsenilin in regulating gamma-secretase activity, we incubated purified calsenilin with isolated membrane fractions and found increased Abeta production in a cell free system. These data suggest that calsenilin may be one of the regulatory factors for gamma-secretase.

Secreted β-amyloid precursor protein activates microglia via JNK and p38-MAPK

Reactive microglia are thought to play a role in the pathogenesis of Alzheimer's disease (AD) and are localized to the senile plaques that are associated with cognitive decline. The beta-amyloid precursor protein (betaAPP) is over-expressed in the dystrophic neurites near such plaques, and secreted forms of betaAPP (sAPPalpha) activate inflammatory responses in microglia. To characterize the mechanisms by which sAPPalpha activates microglia, we assayed its effects on MAP kinases, including c-Jun N-terminal kinases (JNK), extracellular signal-regulated protein kinases (ERK), and p38-MAPK. sAPPalpha was found to rapidly activate JNKs, ERKs and p38-MAPK in a dose-dependent manner. The JNK inhibitor SP600125 and the p38 inhibitor SB203580 independently reduced both nitrite accumulation and induction of inflammatory nitric oxide synthase (iNOS). By contrast, inhibition of the ERK pathway with U0126 did not appreciably affect either outcome measure. These findings suggest that sAPP activates the ERK, JNK and p38 classes of MAP kinases but that only JNK and p38-MAPK are critical for activation of microglia by sAPPalpha, a process that compromises neuronal function and survival.

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.

Pathways towards and away from Alzheimer's disease

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

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.

Cycles of aberrant synaptic sprouting and neurodegeneration in Alzheimer's and dementia with Lewy bodies

Alzheimer's disease (AD) and dementia with Lewy bodies (DLB) are the most common neurodegenerative disorders affecting the elderly. The cognitive and motor deficits in these diseases are associated with the disruption of neuritic substructure, loss of synaptic contacts in selectively vulnerable circuitries, and aberrant sprouting. Where as in AD, accumulation of misfolded forms of Abeta triggers neurodegeneration, in DLB accumulation of alpha-synuclein might play a central role. The mechanisms by which oligomeric forms of these proteins might lead to cycles of synapse loss and aberrant sprouting are currently under investigation. Several possibilities are being considered, including mitochondrial damage, caspase activation, lysosomal leakage, fragmentation of the Golgi apparatus, interference with synaptic vesicle transport and function, and interference with gene transcription and signaling. Among them, recent lines of research support the possibility that alterations in signaling pathways such extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38 relevant to synaptic plasticity and cell survival might play a pivotal role. A wide range of cellular functions are affected by the accumulation of misfolded Abeta and alpha-synuclein; thus it is possible that a more fundamental cellular alteration may underlie the mechanisms of synaptic pathology in these disorders. Among them, one possibility is that scaffold proteins, such as caveolin and JNK-interacting protein (JIP), which are necessary to integrate signaling pathways, are affected, leading to cycles of synapse loss and aberrant sprouting. This is significant because both caveolar dysfunction and altered axonal plasticity might be universally important in the pathogenesis of various neurodegenerative disorders, and therefore these signaling pathways might be common therapeutic targets for these devastating diseases.

Regulatory roles of presenilin-1 and nicastrin in neuronal differentiation during in vitro neurogenesis

Presenilin (PS) in association with nicastrin (NICA) forms a gamma-secretase complex that plays a crucial role in facilitating intramembranous processing of Notch, a signaling receptor that is essential for neuronal fate specification and differentiation. Loss of function studies have implicated a role for PS1 in regulating neuronal differentiation in association with the down-regulation of Notch signaling during neurogenesis. By using a system for stable, as well as tetracycline-inducible expression of interfering RNAs (RNAi), we studied the functions of PS1 during neuronal differentiation in the murine pluripotent p19 embryonic carcinoma cell line. After retinoic acid (RA) treatment and in the absence of doxycycline, neuronal progenitor cells in the p19 clone were found to extend their processes towards the neighboring colony to form network-like connections, as revealed by neuron-specific microtubule-associated protein 2 staining and laser scanning confocal microscopy. However, doxycycline-induced expression of PS1 small interfering RNA (siRNA) in the p19 clone resulted in a severe defect in the formation of network-like connections. Expression of the NICA and Notch down-stream effector genes Hes1 and Hes5 was unaffected in p19 cells expressing doxycycline-induced PS1 siRNA. In contrast to PS1, constitutive inactivation of NICA by siRNA in p19 cells resulted in premature and partial differentiation without RA treatment. In these NICA siRNA-expressing p19 cells the expression of the Notch1 down-stream effector Hes1 gene was substantially reduced. After RA treatment the NICA siRNA clone failed to differentiate completely into networks of neurons. These results taken together provide direct evidence that PS1 and NICA may participate in neuronal differentiation during neurogenesis in vitro.

Mitochondria in cell death: novel targets for neuroprotection and cardioprotection

Post-mitotic neurons and heart muscle cells undergo apoptotic cell death in a variety of acute and chronic degenerative diseases. The intrinsic pathway of apoptosis involves the permeabilization of mitochondrial membranes, which leads to the release of protease and nuclease activators, and to bioenergetic failure. Mitochondrial permeabilization is induced by a variety of pathologically relevant second messengers, including reactive oxygen species, calcium, stress kinases and pro-apoptotic members of the Bcl-2 family. Several pharmacological agents act on mitochondria to prevent the permeabilization of their membranes, thereby inhibiting apoptosis. Such agents include inhibitors of the permeability transition pore complex (in particular ligands of cyclophilin D), openers of mitochondrial ATP-sensitive or Ca(2+)-activated K(+) channels, and proteins from the Bcl-2 family engineered to cross the plasma membrane. In addition, manipulations that modulate the expression or activity of mitochondrial uncoupling proteins can prevent the death of post-mitotic cells. Such agents hold promise for use in clinical neuroprotection and cardioprotection.