Increased vulnerability of hippocampal neurons to excitotoxic necrosis in presenilin-1 mutant knock-in mice

Increased localization of APP-C99 in mitochondria-associated ER membranes causes mitochondrial dysfunction in Alzheimer disease

In the amyloidogenic pathway associated with Alzheimer disease (AD), the amyloid precursor protein (APP) is cleaved by β‐secretase to generate a 99‐aa C‐terminal fragment (C99) that is then cleaved by γ‐secretase to generate the β‐amyloid (Aβ) found in senile plaques. In previous reports, we and others have shown that γ‐secretase activity is enriched in mitochondria‐associated endoplasmic reticulum (ER) membranes (MAM) and that ER–mitochondrial connectivity and MAM function are upregulated in AD. We now show that C99, in addition to its localization in endosomes, can also be found in MAM, where it is normally processed rapidly by γ‐secretase. In cell models of AD, however, the concentration of unprocessed C99 increases in MAM regions, resulting in elevated sphingolipid turnover and an altered lipid composition of both MAM and mitochondrial membranes. In turn, this change in mitochondrial membrane composition interferes with the proper assembly and activity of mitochondrial respiratory supercomplexes, thereby likely contributing to the bioenergetic defects characteristic of AD.

Store-Operated Calcium Channel Complex in Postsynaptic Spines: A New Therapeutic Target for Alzheimer's Disease Treatment

Mushroom dendritic spine structures are essential for memory storage and the loss of mushroom spines may explain memory defects in aging and Alzheimer's disease (AD). The stability of mushroom spines depends on stromal interaction molecule 2 (STIM2)-mediated neuronal-store-operated Ca²⁺ influx (nSOC) pathway, which is compromised in AD mouse models, in aging neurons, and in sporadic AD patients. Here, we demonstrate that the Transient Receptor Potential Canonical 6 (TRPC6) and Orai2 channels form a STIM2-regulated nSOC Ca²⁺ channel complex in hippocampal mushroom spines. We further demonstrate that a known TRPC6 activator, hyperforin, and a novel nSOC positive modulator, NSN21778 (NSN), can stimulate activity of nSOC pathway in the spines and rescue mushroom spine loss in both presenilin and APP knock-in mouse models of AD. We further show that NSN rescues hippocampal long-term potentiation impairment in APP knock-in mouse model. We conclude that the STIM2-regulated TRPC6/Orai2 nSOC channel complex in dendritic mushroom spines is a new therapeutic target for the treatment of memory loss in aging and AD and that NSN is a potential candidate molecule for therapeutic intervention in brain aging and AD.

SIGNIFICANCE STATEMENT

Mushroom dendritic spine structures are essential for memory storage and the loss of mushroom spines may explain memory defects in Alzheimer's disease (AD). This study demonstrated that Transient Receptor Potential Canonical 6 (TRPC6) and Orai2 form stromal interaction molecule 2 (STIM2)-regulated neuronal-store-operated Ca²⁺ influx (nSOC) channel complex in hippocampal synapse and the resulting Ca²⁺ influx is critical for long-term maintenance of mushroom spines in hippocampal neurons. A novel nSOC-positive modulator, NSN21778 (NSN), rescues mushroom spine loss and synaptic plasticity impairment in AD mice models. The TRPC6/Orai2 nSOC channel complex is a new therapeutic target and NSN is a potential candidate molecule for therapeutic intervention in brain aging and AD.

APP mouse models for Alzheimer's disease preclinical studies

Animal models of human diseases that accurately recapitulate clinical pathology are indispensable for understanding molecular mechanisms and advancing preclinical studies. The Alzheimer's disease (AD) research community has historically used first‐generation transgenic (Tg) mouse models that overexpress proteins linked to familial AD (FAD), mutant amyloid precursor protein (APP), or APP and presenilin (PS). These mice exhibit AD pathology, but the overexpression paradigm may cause additional phenotypes unrelated to AD. Second‐generation mouse models contain humanized sequences and clinical mutations in the endogenous mouse App gene. These mice show Aβ accumulation without phenotypes related to overexpression but are not yet a clinical recapitulation of human AD. In this review, we evaluate different APP mouse models of AD, and review recent studies using the second‐generation mice. We advise AD researchers to consider the comparative strengths and limitations of each model against the scientific and therapeutic goal of a prospective preclinical study.

Synthesis and Biological Evaluation of Novel Multi-target-Directed Benzazepines Against Excitotoxicity

Excitotoxicty, a key pathogenic event is characteristic of the onset and development of neurodegeneration. The glutamatergic neurotransmission mediated through different glutamate receptor subtypes plays a pivotal role in the onset of excitotoxicity. The role of NMDA receptor (NMDAR), a glutamate receptor subtype, has been well established in the excitotoxicity pathogenesis. NMDAR overactivation triggers excessive calcium influx resulting in excitotoxic neuronal cell death. In the present study, a series of benzazepine derivatives, with the core structure of 3-methyltetrahydro-3H-benzazepin-2-one, were synthesised in our laboratory and their NMDAR antagonist activity was determined against NMDA-induced excitotoxicity using SH-SY5Y cells. In order to assess the multi-target-directed potential of the synthesised compounds, Aβ_1-42 aggregation inhibitory activity of the most potent benzazepines was evaluated using thioflavin T (ThT) and Congo red (CR) binding assays as Aβ also imparts toxicity, at least in part, through NMDAR overactivation. Furthermore, neuroprotective, free radical scavenging, anti-oxidant and anti-apoptotic activities of the two potential test compounds (7 and 14) were evaluated using primary rat hippocampal neuronal culture against Aβ_1-42-induced toxicity. Finally, in vivo neuroprotective potential of 7 and 14 was assessed using intracerebroventricular (ICV) rat model of Aβ_1-42-induced toxicity. All of the synthesised benzazepines have shown significant neuroprotection against NMDA-induced excitotoxicity. The most potent compound (14) showed relatively higher affinity for the glycine binding site as compared with the glutamate binding site of NMDAR in the molecular docking studies. 7 and 14 have been shown experimentally to abrogate Aβ_1-42 aggregation efficiently. Additionally, 7 and 14 showed significant neuroprotective, free radical scavenging, anti-oxidant and anti-apoptotic properties in different in vitro and in vivo experimental models. Finally, 7 and 14 attenuated Aβ_1-42-induced tau phosphorylation by abrogating activation of tau kinases, i.e. MAPK and GSK-3β. Thus, the results revealed multi-target-directed potential of some of the synthesised novel benzazepines against excitotoxicity.

AF710B, a Novel M1/σ1 Agonist with Therapeutic Efficacy in Animal Models of Alzheimer’s Disease

We previously developed orthosteric M1 muscarinic agonists (e.g. AF102B, AF267B and AF292), which act as cognitive enhancers and potential disease modifiers. We now report on a novel compound, AF710B, a highly potent and selective allosteric M1 muscarinic and σ1 receptor agonist. AF710B exhibits an allosteric agonistic profile on the M1 muscarinic receptor; very low concentrations of AF710B significantly potentiated the binding and efficacy of carbachol on M1 receptors and their downstream effects (p-ERK1/2, p-CREB). AF710B (1-30 µg/kg, p.o.) was a potent and safe cognitive enhancer in rats treated with the M1 antagonist trihexyphenidyl (passive avoidance impairment). These effects of AF710B involve σ1 receptor activation. In agreement with its antiamnesic properties, AF710B (at 30 nM), via activation of M1 and a possible involvement of σ1 receptors, rescued mushroom synapse loss in PS1-KI and APP-KI neuronal cultures, while AF267B (1 µM) was less potent in PS1-KI and ineffective in APP-KI models, respectively. In female 3xTg-AD mice, AF710B (10 µg/kg, i.p./daily/2 months) (i) mitigated cognitive impairments in the Morris water maze; (ii) decreased BACE1, GSK3β activity, p25/CDK5, neuroinflammation, soluble and insoluble Aβ40, Aβ42, plaques and tau pathologies. AF710B differs from conventional σ1 and M1 muscarinic (orthosteric, allosteric or bitopic) agonists. These results highlight AF710B as a potential treatment for Alzheimer's disease (e.g. improving cognitive deficits, synaptic loss, amyloid and tau pathologies, and neuroinflammation) with a superior profile over a plethora of other therapeutic strategies.

Ca2+-permeable AMPA receptor: A new perspective on amyloid-beta mediated pathophysiology of Alzheimer's disease

α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) are the primary conduits of excitatory synaptic transmission. AMPARs are predominantly Ca²⁺-impermeable in the matured excitatory synapse, except under certain circumstances. Growing evidence implicates the Ca²⁺ permeability of AMPARs in the regulation of long-term synaptic plasticity and in the pathophysiology of several neurological disorders. Therefore, the Ca²⁺ conductance of AMPARs may have both physiological and pathological roles at synapses. However, our understanding of the role of Ca²⁺ permeable AMPARs (CP-AMPARs) in Alzheimer's disease is limited. Here we discuss insights into the potential CP-AMPAR mediated pathophysiology of Alzheimer's disease, including: 1. Ca²⁺-mediated aberrant regulation of synapse weakening mechanisms, and 2. neuronal network dysfunction in the brain. Consideration of CP-AMPARs as primary drivers of pathophysiology could help in understanding synaptopathologies, and highlights the potential of CP-AMPARs as therapeutic targets in Alzheimer's disease. This article is part of the Special Issue entitled 'Ionotropic glutamate receptors'.

Long-term dantrolene treatment reduced intraneuronal amyloid in aged Alzheimer triple transgenic mice

In this study, we investigated the long-term treatment of dantrolene on amyloid and tau neuropathology, brain volume, and cognitive function in aged triple transgenic Alzheimer (3xTg-AD) mice. Fifteen-month old 3xTg-AD mice and wild-type controls were treated with oral dantrolene (5 mg/kg) or vehicle control twice a week for 6 months. Learning and memory were examined using the Morris Water Maze at 21 and 22 months of age. After the behavioral testing, hippocampal and cortical brain volumes were calculated with magnetic resonance imaging and motor function was evaluated using the rotorod. The amyloid burden and tau neurofibrillary tangles in the hippocampus were determined using immunohistochemistry. We found that dantrolene significantly decreased the intraneuronal amyloid accumulation by as much as 76% compared with its corresponding vehicle control, together with a trend to reduce phosphorylated tau in the hippocampus. No significant differences could be detected in hippocampal or cortical brain volume, motor function or cognition among all experimental groups, indicating that the mice were still presymptomatic for Alzheimer disease. Thus, presymptomatic and long-term dantrolene treatment significantly decreased the intraneuronal amyloid burden in aged 3xTg-AD mice before significant changes in brain volume, or cognition.

■ REVIEW : The Presenilins

Presenilin-1 and presenilin-2 are highly homologous genes located on chromosomes 14 and 1, respectively, that have recently been linked to some cases of early-onset autosomal dominant inherited forms of Alzhei mer's disease (AD). Presenilins are integral membrane proteins localized in the endoplasmic reticulum of neurons throughout the nervous system. Studies of presenilin-1 knockout mice, and of invertebrate homo logues of presenilins and their interacting proteins, suggest major roles for presenilins in normal develop ment. Presenilin-1 mutant knockin mice do not exhibit developmental abnormalities, which indicates that the pathogenic mechanism of presenilin mutations involves gain of an adverse property of the mutant protein. Expression of presenilin mutations in cultured neurons and transgenic mice results in increased sensitivity to apoptosis induced by trophic factor withdrawal and exposure to oxidative and metabolic insults, and also alters gene expression. The pathogenic mechanism of presenilin mutations may involve perturbed endo plasmic reticulum calcium homeostasis resulting in enhanced oxidative stress, altered proteolytic processing of the amyloid precursor protein (APP), and increased neuronal vulnerability to excitotoxicity. Studies of presenilins are rapidly increasing our understanding the molecular and cellular underpinnings of AD and are also elucidating novel roles of the endoplasmic reticulum in neuronal plasticity and cell death. NEURO SCIENTIST 5:112-124, 1999

Calcium Dysregulation, IP3 Signaling, and Alzheimer’s Disease

Ca2+ ions subserve complex signaling roles in neurons, regulating functions ranging from gene transcription to modulation of membrane excitability. Ca2+ ions enter the cytosol from extracellular sources, such as entry through voltage-gated channels, and by liberation from intracellular endoplasmic reticulum (ER) stores through inositol triphosphate (IP3) receptors and/or ryanodine (RyR) receptors. Disruptions of intracellular Ca2+ signaling are proposed to underlie the pathophysiology of Alzheimer’s disease (AD), and recent studies examining AD-linked mutations in the presenilin genes demonstrate enhanced ER Ca2+ release in a variety of cell types and model systems. The development of transgenic AD mouse models provides a means to study the mechanisms and downstream effects of neuronal ER Ca2+-signaling alterations on AD pathogenesis and offers insight into potential novel therapeutic strategies. The author discusses recent findings in both the physiological functioning of the IP3-signaling pathway in neurons and the involvement of ERCa2+ disruptions in the pathogenesis of AD.

Presenilin 1 promotes trypsin-induced neuroprotection via the PAR2/ERK signaling pathway. Effects of presenilin 1 FAD mutations

Mutants of presenilin 1 (PS1) increase neuronal cell death causing autosomal-dominant familial Alzheimer's disease (FAD). Recent literature shows that treatment of neuronal cultures with low concentrations of trypsin, a member of the serine family of proteases, protects neurons from toxic insults by binding to the proteinase-activated receptor 2 and stimulating survival kinase extracellular signal-regulated kinase (ERK 1/2). Other studies show that PS1 is necessary for the neuroprotective activity of specific neurotrophic factors, such as brain-derived neurotrophic factor, against excitotoxicity and oxidative stress. Here, we show that treatment of mouse cortical neuronal cultures with trypsin activates ERK1/2 and protects neurons against glutamate excitoxicity. The trypsin-dependent ERK activation and neuroprotection requires both alleles of PS1 because neither PS1 knockout nor PS1 hemizygous neuronal cultures can use exogenous trypsin to activate ERK1/2 or increase neuronal survival. The protective effect of PS1 does not depend on its γ-secretase activity because inhibitors of γ-secretase have no effect on trypsin-mediated neuroprotection. Importantly, cortical neuronal cultures either heterozygous or homozygous for PS1 FAD mutants are unable to use trypsin to activate ERK1/2 and rescue neurons from excitotoxicity, indicating that FAD mutants inhibit trypsin-dependent neuroprotection in an autosomal-dominant manner. Furthermore, our data support the theory that PS FAD mutants increase neurodegeneration by inhibiting the ability of neurons to use cellular factors as protective agents against toxic insults.

Loss of presenilin function is associated with a selective gain of APP function

Presenilin 1 (PS1) is an essential γ-secretase component, the enzyme responsible for amyloid precursor protein (APP) intramembraneous cleavage. Mutations in PS1 lead to dominant-inheritance of early-onset familial Alzheimer’s disease (FAD). Although expression of FAD-linked PS1 mutations enhances toxic Aβ production, the importance of other APP metabolites and γ-secretase substrates in the etiology of the disease has not been confirmed. We report that neurons expressing FAD-linked PS1 variants or functionally deficient PS1 exhibit enhanced axodendritic outgrowth due to increased levels of APP intracellular C-terminal fragment (APP-CTF). APP expression is required for exuberant neurite outgrowth and hippocampal axonal sprouting observed in knock-in mice expressing FAD-linked PS1 mutation. APP-CTF accumulation initiates CREB signaling cascade through an association of APP-CTF with Gαs protein. We demonstrate that pathological PS1 loss-of-function impinges on neurite formation through a selective APP gain-of-function that could impact on axodendritic connectivity and contribute to aberrant axonal sprouting observed in AD patients.

DOI:http://dx.doi.org/10.7554/eLife.15645.001

One of the hallmarks of Alzheimer’s disease is the accumulation within the brain of sticky deposits called plaques. These plaques form from clumps of molecules called amyloid-beta peptide. An enzyme called gamma-secretase generates the amyloid-beta peptide, by cutting it from a membrane-associated protein called APP. This enzyme consists of multiple subunits, and a mutation in one of these – presenilin-1 – causes a particularly severe form of Alzheimer’s disease.

For decades, research into Alzheimer’s disease has focused on the harmful effects of amyloid-beta peptides and plaques. However, Deyts et al. now argue that the protein that gives rise to amyloid-beta peptides has a more direct role in Alzheimer’s disease than previously thought. Specifically, APP may contribute to the harmful effects of the presenilin-1 mutations.

By studying genetically modified mice carrying a human presenilin-1 mutation, Deyts et al. show that some of these animals’ nerve cells grow abnormally. Their cell bodies sprout too many branches, while their nerve fibers – which carry electrical signals away from the cell body – become too long. These abnormalities resemble changes seen in the brain in Alzheimer’s disease. Unexpectedly, however, deleting the gene for APP in the presenilin-1 mutant mice prevents the changes from occurring. This suggests that APP must be present for the presenilin-1 mutation to exert this unwanted effect.

An increase in APP-driven signaling within cells seems to trigger the observed abnormalities in nerve cells. The presenilin-1 mutation modifies how gamma-secretase cuts APP at the cell membrane to produce amyloid-beta peptides. This frees up the APP to instead interact with signaling cascades inside the cell. Given that gamma-secretase is a key therapeutic target in Alzheimer’s disease, further work is needed to explore the implications of these protein interactions for potential treatments.

DOI:http://dx.doi.org/10.7554/eLife.15645.002

Murine Aβ over-production produces diffuse and compact Alzheimer-type amyloid deposits

INTRODUCTION

Transgenic overexpression of amyloid precursor protein (APP) genes that are either entirely human in sequence or have humanized Aβ sequences can produce Alzheimer-type amyloidosis in mice, provided the transgenes also encode mutations linked to familial Alzheimer's Disease (FAD). Although transgenic mice have been produced that overexpress wild-type mouse APP, no mice have been generated that express mouse APP with FAD mutations. Here we describe two different versions of such mice that produce amyloid deposits consisting of entirely of mouse Aβ peptides. One line of mice co-expresses mouse APP-Swedish (moAPPswe) with a human presenilin exon-9 deleted variant (PS1dE9) and another line expresses mouse APP-Swedish/Indiana (APPsi) using tetracycline-regulated vectors (tet.moAPPsi).

RESULTS

Both lines of mice that produce mouse Aβ develop amyloid deposits, with the moAPPswe/PS1dE9 mice developing extracellular compact, cored, neuritic deposits that primarily localize to white matter tracts and meningial layers, whereas the tet.moAPPsi mice developed extracellular diffuse cortical/hippocampal deposits distributed throughout the parenchyma.

CONCLUSIONS

These findings demonstrate that murine Aβ peptides have the capacity to produce amyloid deposits that are morphologically similar to deposits found in human AD provided the murine APP gene harbors mutations linked to human FAD.

Luteinizing hormone as a key player in the cognitive decline of Alzheimer's disease

This article is part of a Special Issue "SBN 2014". Alzheimer's disease is one of the most prevalent and costly neurological diseases in the world. Although decades of research have focused on understanding Alzheimer's disease pathology and progression, there is still a great lack of clinical treatments for those who suffer from it. One of the factors most commonly associated with the onset of Alzheimer's disease is a decrease in levels of gonadal hormones, such as estrogens and androgens. Despite the correlational and experimental data which support the role of these hormones in the etiology of Alzheimer's disease, clinical trials involving their reintroduction through hormone therapy have had varied results and these gonadal hormones often have accompanying health risks. More recently, investigation has turned toward other hormones in the hypothalamic-pituitary-gonadal axis that are disrupted by age-related decreases in gonadal hormones. Specifically, luteinizing hormone, which is increased with age in both men and women (in response to removal of negative feedback), has surfaced as a potentially powerful player in the risk and onset of Alzheimer's disease. Mounting evidence in basic research and epidemiological studies supports the role of elevated luteinizing hormone in exacerbating age-related cognitive decline in both males and females. This review summarizes the recent developments involving luteinizing hormone in increasing the cognitive deficits and molecular pathology characteristic of Alzheimer's disease.

Analyzing and Quantifying the Gain-of-Function Enhancement of IP3 Receptor Gating by Familial Alzheimer's Disease-Causing Mutants in Presenilins

Familial Alzheimer’s disease (FAD)-causing mutant presenilins (PS) interact with inositol 1,4,5-trisphosphate (IP₃) receptor (IP₃R) Ca²⁺ release channels resulting in enhanced IP₃R channel gating in an amyloid beta (Aβ) production-independent manner. This gain-of-function enhancement of IP₃R activity is considered to be the main reason behind the upregulation of intracellular Ca²⁺ signaling in the presence of optimal and suboptimal stimuli and spontaneous Ca²⁺ signals observed in cells expressing mutant PS. In this paper, we employed computational modeling of single IP₃R channel activity records obtained under optimal Ca²⁺ and multiple IP₃ concentrations to gain deeper insights into the enhancement of IP₃R function. We found that in addition to the high occupancy of the high-activity (H) mode and the low occupancy of the low-activity (L) mode, IP₃R in FAD-causing mutant PS-expressing cells exhibits significantly longer mean life-time for the H mode and shorter life-time for the L mode, leading to shorter mean close-time and hence high open probability of the channel in comparison to IP₃R in cells expressing wild-type PS. The model is then used to extrapolate the behavior of the channel to a wide range of IP₃ and Ca²⁺ concentrations and quantify the sensitivity of IP₃R to its two ligands. We show that the gain-of-function enhancement is sensitive to both IP₃ and Ca²⁺ and that very small amount of IP₃ is required to stimulate IP₃R channels in the presence of FAD-causing mutant PS to the same level of activity as channels in control cells stimulated by significantly higher IP₃ concentrations. We further demonstrate with simulations that the relatively longer time spent by IP₃R in the H mode leads to the observed higher frequency of local Ca²⁺ signals, which can account for the more frequent global Ca²⁺ signals observed, while the enhanced activity of the channel at extremely low ligand concentrations will lead to spontaneous Ca²⁺ signals in cells expressing FAD-causing mutant PS.

Aberrant Ca²⁺ signaling caused by IP₃R gating dysregulation is implicated in many neurodegenerative diseases such as Alzheimer’s, Huntington’s, Spinocerebellar ataxias, and endoplasmic reticulum stress-induced brain damage. Thus understanding IP₃R dysfunction is important for the etiology of these diseases. It was previously shown that FAD-causing mutant PS interacts with the IP₃R, leading to its gain-of-function enhancement in optimal Ca²⁺ and sub-saturating IP₃ concentrations. Here, we use data-driven modeling to provide deeper insights into the upregulation of IP₃R gating in a wide range of ligand concentrations and quantify the sensitivity of the channel to its ligands in the presence of mutant PS. Our simulations demonstrate that these changes can alter the statistics of local Ca²⁺ events and we speculate that they lead to Ca²⁺ signaling dysregulations at the whole cell level observed in FAD cells. These models will provide the foundation for future data-driven computational framework for local and global Ca²⁺ signals that will be used to judiciously isolate the primary pathways causing Ca²⁺ dysregulation in FAD from those that are downstream, and to study the effects of upregulation of IP₃R activity on cell function.

Colocalization of phosphorylated forms of WAVE1, CRMP2, and tau in Alzheimer's disease model mice: Involvement of Cdk5 phosphorylation and the effect of ATRA treatment

Alzheimer's disease (AD) is the most common type of dementia among the elderly. Neurofibrillary tangles (NFTs), a major pathological hallmark of AD, are composed of tau protein that is hyperphosphorylated by cyclin-dependent kinase 5 (Cdk5) and glycogen synthase kinase 3β (GSK3β). NFTs also contain Wiskott-Aldrich syndrome protein family verprolin-homologous protein 1 (WAVE1) and collapsin response-mediator protein 2 (CRMP2). Although Cdk5 is known to phosphorylate tau, WAVE1, and CRMP2, the significance of this with respect to NFT formation remains to be elucidated. This study examines the involvement of phosphorylated (p-) CRMP2 and WAVE1 in p-tau aggregates using a triple-transgenic (3×Tg; APPswe/PS1M146V/tauP301L) AD mouse model. First, we verified the colocalization of p-WAVE1 and p-CRMP2 with aggregated hyperphosphorylated tau in the hippocampus at 23 months of age. Biochemical analysis revealed the inclusion of p-WAVE1, p-CRMP2, and tau in the sarkosyl-insoluble fractions of hippocampal homogenates. To test the significance of phosphorylation of these proteins further, we administered all-trans-retinoic acid (ATRA) to the 3×Tg mice, which downregulates Cdk5 and GSK3β activity. In ATRA-treated mice, fewer and smaller tau aggregates were observed compared with non-ATRA-treated mice. These results suggest the possibility of novel therapeutic target molecules for preventing tau pathology.

Reduction of increased calcineurin activity rescues impaired homeostatic synaptic plasticity in presenilin 1 M146V mutant

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases characterized by memory loss and cognitive impairment. Whereas most AD cases are sporadic, some are caused by mutations in early-onset familial AD (FAD) genes. One FAD gene encodes presenilin 1 (PS1), and a PS1 mutation in methionine 146 impairs homeostatic synaptic plasticity (HSP). We have previously shown that Ca(2+) and calcineurin activity are critical regulators of HSP. Here, we confirm that endoplasmic reticulum-mediated Ca(2+) signals are increased in mutant PS1 neurons. We further show that calcineurin activity is abnormally elevated in the mutant and that inhibition of increased calcineurin activity stabilizes GluA1 phosphorylation, promoting synaptic trafficking of Ca(2+)-permeable α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, contributing to the recovery of impaired HSP found in the mutant. Because HSP is suggested to have roles during learning and memory formation, increased calcineurin activity-induced impairment of HSP can cause cognitive decline in FAD. Thus, reducing abnormally increased calcineurin activity in AD brain may be beneficial for improving AD-related cognitive decline.

Being human: The role of pluripotent stem cells in regenerative medicine and humanizing Alzheimer's disease models

Human pluripotent stem cells (PSCs) have the capacity to revolutionize medicine by allowing the generation of functional cell types such as neurons for cell replacement therapy. However, the more immediate impact of PSCs on treatment of Alzheimer's disease (AD) will be through improved human AD model systems for mechanistic studies and therapeutic screening. This review will first briefly discuss different types of PSCs and genome-editing techniques that can be used to modify PSCs for disease modeling or for personalized medicine. This will be followed by a more in depth analysis of current AD iPSC models and a discussion of the need for more complex multicellular models, including cell types such as microglia. It will finish with a discussion on current clinical trials using PSC-derived cells and the long-term potential of such strategies for treating AD.

Presenilin-1 knockin mice reveal loss-of-function mechanism for familial Alzheimer's disease

Presenilins play essential roles in memory formation, synaptic function, and neuronal survival. Mutations in the Presenilin-1 (PSEN1) gene are the major cause of familial Alzheimer's disease (FAD). How PSEN1 mutations cause FAD is unclear, and pathogenic mechanisms based on gain or loss of function have been proposed. Here, we generated Psen1 knockin (KI) mice carrying the FAD mutation L435F or C410Y. Remarkably, KI mice homozygous for either mutation recapitulate the phenotypes of Psen1(-/-) mice. Neither mutation altered Psen1 mRNA expression, but both abolished γ-secretase activity. Heterozygosity for the KI mutation decreased production of Aβ40 and Aβ42, increased the Aβ42/Aβ40 ratio, and exacerbated Aβ deposition. Furthermore, the L435F mutation impairs hippocampal synaptic plasticity and memory and causes age-dependent neurodegeneration in the aging cerebral cortex. Collectively, our findings reveal that FAD mutations can cause complete loss of Presenilin-1 function in vivo, suggesting that clinical PSEN mutations produce FAD through a loss-of-function mechanism.

Ca2+ dysregulation in the endoplasmic reticulum related to Alzheimer's disease: A review on experimental progress and computational modeling

Alzheimer's disease (AD) is a devastating, incurable neurodegenerative disease affecting millions of people worldwide. Dysregulation of intracellular Ca(2+) signaling has been observed as an early event prior to the presence of clinical symptoms of AD and is believed to be a crucial factor contributing to its pathogenesis. The progressive and sustaining increase in the resting level of cytosolic Ca(2+) will affect downstream activities and neural functions. This review focuses on the issues relating to the increasing Ca(2+) release from the endoplasmic reticulum (ER) observed in AD neurons. Numerous research papers have suggested that the dysregulation of ER Ca(2+) homeostasis is associated with mutations in the presenilin genes and amyloid-β oligomers. These disturbances could happen at many different points in the signaling process, directly affecting ER Ca(2+) channels or interfering with related pathways, which makes it harder to reveal the underlying mechanisms. This review paper also shows that computational modeling is a powerful tool in Ca(2+) signaling studies and discusses the progress in modeling related to Ca(2+) dysregulation in AD research.

ATF4: a Novel Potential Therapeutic Target for Alzheimer's Disease

Activating transcription factor 4 (ATF4) belongs to the activating transcription factor family and its expression is increased upon the stimulation of a diverse array of microenvironmental stresses. ATF4 plays a major role in the development, metabolism, and memory formation. Alzheimer's disease (AD) is a prevalent neurodegenerative disease in aged population. The dominant pathological changes in AD brain, including the neurofibrillary tangles, consist of hyperphosphorylated tau protein, senile plaques composed of β-amyloid proteins, loss of neurons in the whole brain, and dysfunction of synapses. The protein level of ATF4 is upregulated in both AD brain and AD mouse model, indicating its latent roles in the pathogenesis of this disease. In this paper, we reviewed the related literatures about the interaction of ATF4 with the different types of pathological changes in AD brain and pointed out some unsolved problems in this area. We also proposed that a fine regulation of ATF4 in separate neurons or brain regions might be benefit to the therapy of AD.

Vascular and parenchymal amyloid pathology in an Alzheimer disease knock-in mouse model: interplay with cerebral blood flow

Background

Accumulation and deposition of β-amyloid peptides (Aβ) in the brain is a central event in the pathogenesis of Alzheimer’s disease (AD). Besides the parenchymal pathology, Aβ is known to undergo active transport across the blood–brain barrier and cerebral amyloid angiopathy (CAA) is a prominent feature in the majority of AD. Although impaired cerebral blood flow (CBF) has been implicated in faulty Aβ transport and clearance, and cerebral hypoperfusion can exist in the pre-clinical phase of Alzheimer’s disease (AD), it is still unclear whether it is one of the causal factors for AD pathogenesis, or an early consequence of a multi-factor condition that would lead to AD at late stage. To study the potential interaction between faulty CBF and amyloid accumulation in clinical-relevant situation, we generated a new amyloid precursor protein (APP) knock-in allele that expresses humanized Aβ and a Dutch mutation in addition to Swedish/London mutations and compared this line with an equivalent knock-in line but in the absence of the Dutch mutation, both crossed onto the PS1M146V knock-in background.

Results

Introduction of the Dutch mutation results in robust CAA and parenchymal Aβ pathology, age-dependent reduction of spatial learning and memory deficits, and CBF reduction as detected by fMRI. Direct manipulation of CBF by transverse aortic constriction surgery on the left common carotid artery caused differential changes in CBF in the anterior and middle region of the cortex, where it is reduced on the left side and increased on the right side. However these perturbations in CBF resulted in the same effect: both significantly exacerbate CAA and amyloid pathology.

Conclusions

Our study reveals a direct and positive link between vascular and parenchymal Aβ; both can be modulated by CBF. The new APP knock-in mouse model recapitulates many symptoms of AD including progressive vascular and parenchymal Aβ pathology and behavioral deficits in the absence of APP overexpression.

Age-Dependent Modifications of AMPA Receptor Subunit Expression Levels and Related Cognitive Effects in 3xTg-AD Mice

GluA1, GluA2, GluA3, and GluA4 are the constitutive subunits of amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), the major mediators of fast excitatory transmission in the mammalian central nervous system. Most AMPARs are Ca²⁺-impermeable because of the presence of the GluA2 subunit. GluA2 mRNA undergoes an editing process that results in a Q–R substitution, a key factor in the regulation of AMPAR Ca²⁺-permeability. AMPARs lacking GluA2 or containing the unedited subunit are permeable to Ca²⁺ and Zn²⁺. The phenomenon physiologically modulates synaptic plasticity while, in pathologic conditions, leads to increased vulnerability to excitotoxic neuronal death. Given the importance of these subunits, we have therefore evaluated possible associations between changes in expression levels of AMPAR subunits and development of cognitive deficits in 3xTg-AD mice, a widely investigated transgenic mouse model of Alzheimer’s disease (AD). With quantitative real-time PCR analysis, we assayed hippocampal mRNA expression levels of GluA1–4 subunits occurring in young [3 months of age (m.o.a.)] and old (12 m.o.a) Tg-AD mice and made comparisons with levels found in age-matched wild type (WT) mice. Efficiency of GluA2 RNA editing was also analyzed. All animals were cognitively tested for learning short- and long-term spatial memory with the Morris Water Maze (MWM) navigation task. 3xTg-AD mice showed age-dependent decreases of mRNA levels for all the AMPAR subunits, with the exception of GluA2. Editing remained fully efficient with aging in 3xTg-AD and WT mice. A one-to-one correlation analysis between MWM performances and GluA1–4 mRNA expression profiles showed negative correlations between GluA2 levels and MWM performances in young 3xTg-AD mice. On the contrary, positive correlations between GluA2 mRNA and MWM performances were found in young WT mice. Our data suggest that increases of AMPARs that contain GluA1, GluA3, and GluA4 subunits may help in maintaining cognition in pre-symptomatic 3xTg-AD mice.

Suppression of InsP3 receptor-mediated Ca2+ signaling alleviates mutant presenilin-linked familial Alzheimer's disease pathogenesis

Exaggerated intracellular Ca(2+) signaling is a robust proximal phenotype observed in cells expressing familial Alzheimer's disease (FAD)-causing mutant presenilins (PSs). The mechanisms that underlie this phenotype are controversial and their in vivo relevance for AD pathogenesis is unknown. Here, we used a genetic approach to identify the mechanisms involved and to evaluate their role in the etiology of AD in two FAD mouse models. Genetic reduction of the type 1 inositol trisphosphate receptor (InsP3R1) by 50% normalized exaggerated Ca(2+) signaling observed in cortical and hippocampal neurons in both animal models. In PS1M146V knock-in mice, reduced InsP3R1 expression restored normal ryanodine receptor and cAMP response element-binding protein (CREB)-dependent gene expression and rescued aberrant hippocampal long-term potentiation (LTP). In 3xTg mice, reduced InsP3R1 expression profoundly attenuated amyloid β accumulation and tau hyperphosphorylation and rescued hippocampal LTP and memory deficits. These results indicate that exaggerated Ca(2+) signaling, which is associated with FAD PS, is mediated by InsP3R and contributes to disease pathogenesis in vivo. Targeting the InsP3 signaling pathway could be considered a potential therapeutic strategy for patients harboring mutations in PS linked to AD.

Reduced synaptic STIM2 expression and impaired store-operated calcium entry cause destabilization of mature spines in mutant presenilin mice

Mushroom dendritic spine structures are essential for memory storage, and the loss of mushroom spines may explain memory defects in Alzheimer's disease (AD). Here we show a significant reduction in the fraction of mushroom spines in hippocampal neurons from the presenilin-1 M146V knockin (KI) mouse model of familial AD (FAD). The stabilization of mushroom spines depends on STIM2-mediated neuronal store-operated calcium influx (nSOC) and continuous activity of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). We demonstrate that STIM2-nSOC-CaMKII pathway is compromised in KI neurons, in aging neurons, and in sporadic AD brains due to downregulation of STIM2 protein. We further establish that overexpression of STIM2 rescues synaptic nSOC, CaMKII activity, and mushroom spine loss in KI neurons. Our results identify STIM2-nSOC-CaMKII synaptic maintenance pathway as a novel potential therapeutic target for treatment of AD and age-related memory decline.

Genetic suppression of transgenic APP rescues Hypersynchronous network activity in a mouse model of Alzeimer's disease

Alzheimer's disease (AD) is associated with an elevated risk for seizures that may be fundamentally connected to cognitive dysfunction. Supporting this link, many mouse models for AD exhibit abnormal electroencephalogram (EEG) activity in addition to the expected neuropathology and cognitive deficits. Here, we used a controllable transgenic system to investigate how network changes develop and are maintained in a model characterized by amyloid β (Aβ) overproduction and progressive amyloid pathology. EEG recordings in tet-off mice overexpressing amyloid precursor protein (APP) from birth display frequent sharp wave discharges (SWDs). Unexpectedly, we found that withholding APP overexpression until adulthood substantially delayed the appearance of epileptiform activity. Together, these findings suggest that juvenile APP overexpression altered cortical development to favor synchronized firing. Regardless of the age at which EEG abnormalities appeared, the phenotype was dependent on continued APP overexpression and abated over several weeks once transgene expression was suppressed. Abnormal EEG discharges were independent of plaque load and could be extinguished without altering deposited amyloid. Selective reduction of Aβ with a γ-secretase inhibitor has no effect on the frequency of SWDs, indicating that another APP fragment or the full-length protein was likely responsible for maintaining EEG abnormalities. Moreover, transgene suppression normalized the ratio of excitatory to inhibitory innervation in the cortex, whereas secretase inhibition did not. Our results suggest that APP overexpression, and not Aβ overproduction, is responsible for EEG abnormalities in our transgenic mice and can be rescued independently of pathology.

Apoptosis signal regulating kinase 1 (ASK1): potential as a therapeutic target for Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia, characterized by a decline in memory and cognitive function. Clinical manifestations of AD are closely associated with the formation of senile plaques and neurofibrillary tangles, neuronal loss and cognitive decline. Apoptosis signal regulating kinase 1 (ASK1) is a mediator of the MAPK pathway, which regulates various cellular responses such as apoptosis, cell survival, and differentiation. Accumulating evidence indicates that ASK1 plays a key role in the pathogenesis of neurodegenerative disorders such as Huntington's disease and AD. Of particular interest, ASK1 is associated with many signaling pathways, which include endoplasmic reticulum (ER) stress-mediated apoptosis, Aβ-induced neurotoxicity, tau protein phosphorylation, and insulin signal transduction. Here, we review experimental evidence that links ASK1 signaling and AD pathogenesis and propose that ASK1 might be a new point of therapeutic intervention to prevent or treat AD.

L-type Ca2+ currents at CA1 synapses, but not CA3 or dentate granule neuron synapses, are increased in 3xTgAD mice in an age-dependent manner

Abnormal neuronal excitability and impaired synaptic plasticity might occur before the degeneration and death of neurons in Alzheimer's disease (AD). To elucidate potential biophysical alterations underlying aberrant neuronal network activity in AD, we performed whole-cell patch clamp analyses of L-type (nifedipine-sensitive) Ca(2+) currents (L-VGCC), 4-aminopyridine-sensitive K(+) currents, and AMPA (2-amino-3-(3-hydroxy-5-methyl-isoxazol-4-yl)propanoic acid) and NMDA (N-methyl-D-aspartate) currents in CA1, CA3, and dentate granule neurons in hippocampal slices from young, middle-age, and old 3xTgAD mice and age-matched wild type mice. 3xTgAD mice develop progressive widespread accumulation of amyloid β-peptide, and selective hyperphosphorylated tau pathology in hippocampal CA1 neurons, which are associated with cognitive deficits, but independent of overt neuronal degeneration. An age-related elevation of L-type Ca(2+) channel current density occurred in CA1 neurons in 3xTgAD mice, but not in wild type mice, with the magnitude being significantly greater in older 3xTgAD mice. The NMDA current was also significantly elevated in CA1 neurons of old 3xTgAD mice compared with in old wild type mice. There were no differences in the amplitude of K(+) or AMPA currents in CA1 neurons of 3xTgAD mice compared with wild type mice at any age. There were no significant differences in Ca(2+), K(+), AMPA, or NMDA currents in CA3 and dentate neurons from 3xTgAD mice compared with wild type mice at any age. Our results reveal an age-related increase of L-VGCC density in CA1 neurons, but not in CA3 or dentate granule neurons, of 3xTgAD mice. These findings suggest a potential contribution of altered L-VGCC to the selective vulnerability of CA1 neurons to tau pathology in the 3xTgAD mice and to their degeneration in AD patients.

Modeling Alzheimer's disease in mouse without mutant protein overexpression: cooperative and independent effects of Aβ and tau

Background

Alzheimer’s disease (AD), the most common cause of dementia in the elderly, has two pathological hallmarks: Aβ plaques and aggregation of hyperphosphorylated tau (p-tau). Aβ is a cleavage product of Amyloid Precursor Protein (APP). Presenilin 1 (PS1) and presenilin 2 (PS2) are the catalytic subunit of γ-secretase, which cleaves APP and mediates Aβ production. Genetic mutations in APP, PSEN1 or PSEN2 can lead to early onset of familial AD (FAD). Although mutations in the tau encoding gene MAPT leads to a subtype of frontotemporal dementia and these mutations have been used to model AD tauopathy, no MAPT mutations have been found to be associated with AD.

Results

To model AD pathophysiology in mice without the gross overexpression of mutant transgenes, we created a humanized AD mouse model by crossing the APP and PSEN1 FAD knock-in mice with the htau mice which express wildtype human MAPT genomic DNA on mouse MAPT null background (APP/PS1/htau). The APP/PS1/htau mice displayed mild, age-dependent, Aβ plaques and tau hyperphosphorylation, thus successfully recapitulating the late-onset AD pathological hallmarks. Selected biochemical analyses, including p-tau western blot, γ-secretase activity assay, and Aβ ELISA, were performed to study the interaction between Aβ and p-tau. Subsequent behavioral studies revealed that the APP/PS1/htau mice showed reduced mobility in old ages and exaggerated fear response. Genetic analysis suggested that the fear phenotype is due to a synergic interaction between Aβ and p-tau, and it can be completely abolished by tau deletion.

Conclusion

The APP/PS1/htau model represents a valuable and disease-relevant late-onset pre-clinical AD animal model because it incorporates human AD genetics without mutant protein overexpression. Analysis of the mice revealed both cooperative and independent effects of Aβ and p-tau.

Endogenous expression of FAD-linked PS1 impairs proliferation, neuronal differentiation and survival of adult hippocampal progenitors

BACKGROUND

Alzheimer's disease (AD) is characterized by progressive memory loss and impaired cognitive function. Early-onset familial forms of the disease (FAD) are caused by inheritance of mutant genes encoding presenilin 1 (PS1) variants. We have demonstrated that prion promoter (PrP)-driven expression of human FAD-linked PS1 variants in mice leads to impairments in environmental enrichment (EE)-induced adult hippocampal neural progenitor cell (AHNPC) proliferation and neuronal differentiation, and have provided evidence that accessory cells in the hippocampal niche expressing PS1 variants may modulate AHNPC phenotypes, in vivo. While of significant interest, these latter studies relied on transgenic mice that express human PS1 variant transgenes ubiquitously and at high levels, and the consequences of wild type or mutant PS1 expressed under physiologically relevant levels on EE-mediated AHNPC phenotypes has not yet been tested.

RESULTS

To assess the impact of mutant PS1 on EE-induced AHNPC phenotypes when expressed under physiological levels, we exposed adult mice that constitutively express the PSEN1 M146V mutation driven by the endogenous PSEN1 promoter (PS1 M146V "knock-in" (KI) mice) to standard or EE-housed conditions. We show that in comparison to wild type PS1 mice, AHNPCs in mice carrying homozygous (PS1M146V/M146V) or heterozygous (PS1M146V/+) M146V mutant alleles fail to exhibit EE-induced proliferation and commitment towards neurogenic lineages. More importantly, we report that the survival of newborn progenitors are diminished in PS1 M146V KI mice exposed to EE-conditions compared to respective EE wild type controls.

CONCLUSIONS

Our findings reveal that expression at physiological levels achieved by a single PS1 M146V allele is sufficient to impair EE-induced AHNPC proliferation, survival and neuronal differentiation, in vivo. These results and our finding that microglia expressing a single PS1 M146V allele impairs the proliferation of wild type AHNPCs in vitro argue that expression of mutant PS1 in the AHNPC niche impairs AHNPCs phenotypes in a dominant, non-cell autonomous manner.

Longitudinal study of differential protein expression in an Alzheimer's mouse model lacking inducible nitric oxide synthase

Alzheimer's disease (AD) is a complex neurodegenerative process that involves altered brain immune, neuronal and metabolic functions. Understanding the underlying mechanisms has relied on mouse models that mimic components of AD pathology. We used gel-free, label-free LC-MS/MS to quantify protein and phosphopeptide levels in brains of APPSwDI/NOS2-/- (CVN-AD) mice. CVN-AD mice show a full spectrum of AD-like pathology, including amyloid deposition, hyperphosphorylated and aggregated tau, and neuronal loss that worsens with age. Tryptic digests, with or without phosphopeptide enrichment on an automated titanium dioxide LC system, were separated by online two-dimensional LC and analyzed on a Waters Synapt G2 HDMS, yielding relative expression for >950 proteins and >1100 phosphopeptides. Among differentially expressed proteins were known markers found in humans with AD, including GFAP and C1Q. Phosphorylation of connexin 43, not previously described in AD, was increased at 42 weeks, consistent with dysregulation of gap junctions and activation of astrocytes. Additional alterations in phosphoproteins suggests dysregulation of mitochondria, synaptic transmission, vesicle trafficking, and innate immune pathways. These data validate the CVN-AD mouse model of AD, identify novel disease and age-related changes in the brain during disease progression, and demonstrate the utility of integrating unbiased and phosphoproteomics for understanding disease processes in AD.

Rare variants in calcium homeostasis modulator 1 (CALHM1) found in early onset Alzheimer's disease patients alter calcium homeostasis

Calcium signaling in the brain is fundamental to the learning and memory process and there is evidence to suggest that its dysfunction is involved in the pathological pathways underlying Alzheimer’s disease (AD). Recently, the calcium hypothesis of AD has received support with the identification of the non-selective Ca²⁺-permeable channel CALHM1. A genetic polymorphism (p. P86L) in CALHM1 reduces plasma membrane Ca²⁺ permeability and is associated with an earlier age-at-onset of AD. To investigate the role of CALHM1 variants in early-onset AD (EOAD), we sequenced all CALHM1 coding regions in three independent series comprising 284 EOAD patients and 326 controls. Two missense mutations in patients (p.G330D and p.R154H) and one (p.A213T) in a control individual were identified. Calcium imaging analyses revealed that while the mutation found in a control (p.A213T) behaved as wild-type CALHM1 (CALHM1-WT), a complete abolishment of the Ca²⁺ influx was associated with the mutations found in EOAD patients (p.G330D and p.R154H). Notably, the previously reported p. P86L mutation was associated with an intermediate Ca²⁺ influx between the CALHM1-WT and the p.G330D and p.R154H mutations. Since neither expression of wild-type nor mutant CALHM1 affected amyloid ß-peptide (Aß) production or Aß-mediated cellular toxicity, we conclude that rare genetic variants in CALHM1 lead to Ca²⁺ dysregulation and may contribute to the risk of EOAD through a mechanism independent from the classical Aß cascade.

Presenilins regulate the cellular activity of ryanodine receptors differentially through isotype-specific N-terminal cysteines

Presenilins (PS), endoplasmic reticulum (ER) transmembrane proteins, form the catalytic core of γ-secretase, an amyloid precursor protein processing enzyme. Mutations in PS lead to Alzheimer's disease (AD) by altering γ-secretase activity to generate pathologic amyloid beta and amyloid plaques in the brain. Here, we identified a novel mechanism where binding of a soluble, cytosolic N-terminal domain fragment (NTF) of PS to intracellular Ca(2+) release channels, ryanodine receptors (RyR), controls Ca(2+) release from the ER. While PS1NTF decreased total RyR-mediated Ca(2+) release, PS2NTF had no effect at physiological Ca(2+) concentrations. This differential function and isotype-specificity is due to four cysteines absent in PS1NTF, present, however, in PS2NTF. Site-directed mutagenesis targeting these cysteines converted PS1NTF to PS2NTF function and vice versa, indicating differential RyR binding. This novel mechanism of intracellular Ca(2+) regulation through the PS-RyR interaction represents a novel target for AD drug development and the treatment of other neurodegenerative disorders that critically depend on RyR and PS signaling.

Transient knockdown of presenilin-1 provokes endoplasmic reticulum stress related formation of autophagosomes in HepG2 cells

The involvement of presenilins in the endoplasmic reticulum (ER) related autophagy was investigated by their transient knockdown in HepG2 cells. The silencing of PSEN1 but not of PSEN2 led to cell growth impairment and decreased viability. PSEN1 silencing resulted in ER stress response as evidenced by the elevated levels of glucose regulated protein 78 (Grp78), protein disulfide isomerase (PDI), and CCAAT/enhancer-binding protein homologous protein (CHOP) and by the activation of activating transcription factor 6 (ATF6). The activation of autophagy was indicated by the increased procession of microtubule-associated light chain 3 protein isoform B (LC3B) and by decreased phosphorylation of mammalian target of rapamycin (mTOR) and 70kDa ribosomal protein S6 kinase (p70S6K). Formation of ER-related cytoplasmic vacuolization colocalizing with the autophagic marker LC3B was also observed. The morphological effects and LC3B activation in presenilin-1 knockdown cells could be prevented by using the phosphoinositide 3-kinase (PI3K) inhibitor wortmannin or by calcium chelation. The results show that presenilin-1 hampers the ER stress dependent initiation of macroautophagy.

Curcumin and its derivatives: their application in neuropharmacology and neuroscience in the 21st century

Curcumin (diferuloylmethane), a polyphenol extracted from the plant Curcuma longa, is widely used in Southeast Asia, China and India in food preparation and for medicinal purposes. Since the second half of the last century, this traditional medicine has attracted the attention of scientists from multiple disciplines to elucidate its pharmacological properties. Of significant interest is curcumin's role to treat neurodegenerative diseases including Alzheimer's disease (AD), and Parkinson's disease (PD) and malignancy. These diseases all share an inflammatory basis, involving increased cellular reactive oxygen species (ROS) accumulation and oxidative damage to lipids, nucleic acids and proteins. The therapeutic benefits of curcumin for these neurodegenerative diseases appear multifactorial via regulation of transcription factors, cytokines and enzymes associated with (Nuclear factor kappa beta) NFκB activity. This review describes the historical use of curcumin in medicine, its chemistry, stability and biological activities, including curcumin's anti-cancer, anti-microbial, anti-oxidant, and anti-inflammatory properties. The review further discusses the pharmacology of curcumin and provides new perspectives on its therapeutic potential and limitations. Especially, the review focuses in detail on the effectiveness of curcumin and its mechanism of actions in treating neurodegenerative diseases such as Alzheimer's and Parkinson's diseases and brain malignancies.

Exenatide promotes cognitive enhancement and positive brain metabolic changes in PS1-KI mice but has no effects in 3xTg-AD animals

Recent studies have shown that type 2 diabetes mellitus (T2DM) is a risk factor for cognitive dysfunction or dementia. Insulin resistance is often associated with T2DM and can induce defective insulin signaling in the central nervous system as well as increase the risk of cognitive impairment in the elderly. Glucagone like peptide-1 (GLP-1) is an incretin hormone and, like GLP-1 analogs, stimulates insulin secretion and has been employed in the treatment of T2DM. GLP-1 and GLP-1 analogs also enhance synaptic plasticity and counteract cognitive deficits in mouse models of neuronal dysfunction and/or degeneration. In this study, we investigated the potential neuroprotective effects of long-term treatment with exenatide, a GLP-1 analog, in two animal models of neuronal dysfunction: the PS1-KI and 3xTg-AD mice. We found that exenatide promoted beneficial effects on short- and long-term memory performances in PS1-KI but not in 3xTg-AD animals. In PS1-KI mice, the drug increased brain lactate dehydrogenase activity leading to a net increase in lactate levels, while no effects were observed on mitochondrial respiration. On the contrary, exenatide had no effects on brain metabolism of 3xTg-AD mice. In summary, our data indicate that exenatide improves cognition in PS1-KI mice, an effect likely driven by increasing the brain anaerobic glycolysis rate.

Glutamate system, amyloid ß peptides and tau protein: functional interrelationships and relevance to Alzheimer disease pathology

Alzheimer disease is the most prevalent form of dementia globally and is characterized premortem by a gradual memory loss and deterioration of higher cognitive functions and postmortem by neuritic plaques containing amyloid ß peptide and neurofibrillary tangles containing phospho-tau protein. Glutamate is the most abundant neurotransmitter in the brain and is essential to memory formation through processes such as long-term potentiation and so might be pivotal to Alzheimer disease progression. This review discusses how the glutamatergic system is impaired in Alzheimer disease and how interactions of amyloid ß and glutamate influence synaptic function, tau phosphorylation and neurodegeneration. Interestingly, glutamate not only influences amyloid ß production, but also amyloid ß can alter the levels of glutamate at the synapse, indicating that small changes in the concentrations of both molecules could influence Alzheimer disease progression. Finally, we describe how the glutamate receptor antagonist, memantine, has been used in the treatment of individuals with Alzheimer disease and discuss its effectiveness.

Effects of long-term treatment with pioglitazone on cognition and glucose metabolism of PS1-KI, 3xTg-AD, and wild-type mice

In this study, we investigated the effects of long-term (9-month) treatment with pioglitazone (PIO; 20 mg/kg/d) in two animal models of Alzheimer's disease (AD)-related neural dysfunction and pathology: the PS1-KI(M146V) (human presenilin-1 (M146V) knock-in mouse) and 3xTg-AD (triple transgenic mouse carrying AD-linked mutations) mice. We also investigated the effects on wild-type (WT) mice. Mice were monitored for body mass changes, fasting glycemia, glucose tolerance, and studied for changes in brain mitochondrial enzyme activity (complexes I and IV) as well as energy metabolism (lactate dehydrogenase (LDH)). Cognitive effects were investigated with the Morris water maze (MWM) test and the object recognition task (ORT). Behavioral analysis revealed that PIO treatment promoted positive cognitive effects in PS1-KI female mice. These effects were associated with normalization of peripheral gluco-regulatory abnormalities that were found in untreated PS1-KI females. PIO-treated PS1-KI females also showed no statistically significant alterations in brain mitochondrial enzyme activity but significantly increased reverse LDH activity.PIO treatment produced no effects on cognition, glucose metabolism, or mitochondrial functioning in 3xTg-AD mice. Finally, PIO treatment promoted enhanced short-term memory performance in WT male mice, a group that did not show deregulation of glucose metabolism but that showed decreased activity of complex I in hippocampal and cortical mitochondria. Overall, these results indicate metabolically driven cognitive-enhancing effects of PIO that are differentially gender-related among specific genotypes.

Potential moderators of physical activity on brain health

Age-related cognitive decline is linked to numerous molecular, structural, and functional changes in the brain. However, physical activity is a promising method of reducing unfavorable age-related changes. Physical activity exerts its effects on the brain through many molecular pathways, some of which are regulated by genetic variants in humans. In this paper, we highlight genes including apolipoprotein E (APOE), brain derived neurotrophic factor (BDNF), and catechol-O-methyltransferase (COMT) along with dietary omega-3 fatty acid, docosahexaenoic acid (DHA), as potential moderators of the effect of physical activity on brain health. There are a growing number of studies indicating that physical activity might mitigate the genetic risks for disease and brain dysfunction and that the combination of greater amounts of DHA intake with physical activity might promote better brain function than either treatment alone. Understanding whether genes or other lifestyles moderate the effects of physical activity on neurocognitive health is necessary for delineating the pathways by which brain health can be enhanced and for grasping the individual variation in the effectiveness of physical activity interventions on the brain and cognition. There is a need for future research to continue to assess the factors that moderate the effects of physical activity on neurocognitive function.

Calcium homeostasis in aging neurons

The nervous system becomes increasingly vulnerable to insults and prone to dysfunction during aging. Age-related decline of neuronal function is manifested by the late onset of many neurodegenerative disorders, as well as by reduced signaling and processing capacity of individual neuron populations. Recent findings indicate that impairment of Ca(2+) homeostasis underlies the increased susceptibility of neurons to damage, associated with the aging process. However, the impact of aging on Ca(2+) homeostasis in neurons remains largely unknown. Here, we survey the molecular mechanisms that mediate neuronal Ca(2+) homeostasis and discuss the impact of aging on their efficacy. To address the question of how aging impinges on Ca(2+) homeostasis, we consider potential nodes through which mechanisms regulating Ca(2+) levels interface with molecular pathways known to influence the process of aging and senescent decline. Delineation of this crosstalk would facilitate the development of interventions aiming to fortify neurons against age-associated functional deterioration and death by augmenting Ca(2+) homeostasis.

Endoplasmic reticulum enrollment in Alzheimer's disease

Alzheimer's disease (AD) poses a huge challenge for society and health care worldwide as molecular pathogenesis of the disease is poorly understood and curative treatment does not exist. The mechanisms leading to accelerated neuronal cell death in AD are still largely unknown, but accumulation of misfolded disease-specific proteins has been identified as potentially involved. In the present review, we describe the essential role of endoplasmic reticulum (ER) in AD. Despite the function that mitochondria may play as the central major player in the apoptotic process, accumulating evidence highlights ER as a critical organelle in AD. Stress that impairs ER physiology leads to accumulation of unfolded or misfolded proteins, such as amyloid β (Aβ) peptide, the major component of amyloid plaques. In an attempt to ameliorate the accumulation of unfolded proteins, ER stress triggers a protective cellular mechanism, which includes the unfolded protein response (UPR). However, when activation of the UPR is severe or prolonged enough, the final cellular outcome is pathologic apoptotic cell death. Distinct pathways can be activated in this process, involving stress sensors such as the JNK pathway or ER chaperones such as Bip/GRP94, stress modulators such as Bcl-2 family proteins, or even stress effectors such as caspase-12. Here, we detail the involvement of the ER and associated stress pathways in AD and discuss potential therapeutic strategies targeting ER stress.