Lamotrigine attenuates deficits in synaptic plasticity and accumulation of amyloid plaques in APP/PS1 transgenic mice

Inhibition of sphingomyelin synthase 1 ameliorates alzheimer-like pathology in APP/PS1 transgenic mice through promoting lysosomal degradation of BACE1

Sphingolipids emerge as essential modulators in the etiology of Alzheimer's disease (AD) with unclear mechanisms. Elevated levels of SM synthase 1 (SMS1), which catalyzes the synthesis of SM from ceramide and phosphatidylcholine, have been observed in the brains of Alzheimer's disease (AD), where expression of β-site APP cleaving enzyme 1 (BACE1), a rate limiting enzyme in amyloid-β (Aβ) generation, are upregulated. In the present study, we show knockdown of SMS1 via andeno associated virus (serotype 8, AAV8) in the hippocampus of APP/PS1 transgenic mice, attenuates the densities of Aβ plaques, neuroinflammation, synaptic loss and thus rescuing cognitive deficits of these transgenic mice. We further describe that knockdown or inhibition of SMS1 decreases BACE1 stability, which is accompanied with decreased BACE1 levels in the Golgi, whereas enhanced BACE1 levels in the early endosomes and the lysosomes. The reduction of BACE1 levels induced by knockdown or inhibition of SMS1 is prevented by inhibition of lysosomes. Therefore, knockdown or inhibition of SMS1 promotes lysosomal degradation of BACE1 via modulating the intracellular trafficking of BACE1. Knockdown of SMS1 attenuates AD-like pathology through promoting lysosomal degradation of BACE1.

Long-term social isolation inhibits autophagy activation, induces postsynaptic dysfunctions and impairs spatial memory

. Moreover, we found that L-PWSI increased the protein expression of p-AKT/AKT, p-mTOR/mTOR and p62, whereas the protein levels of LC3B and Beclin1 were decreased indicating an inhibition in autophagy activity. Intraperitoneal injection of rapamycin significantly potentiated fEPSP slope and cognition-related proteins expression in the L-PWSI mice. These results therefore suggest that L-PWSI induces postsynaptic dysfunction by disrupting the interaction between AMPAR, NMDAR and PSD-95, and inhibit the autophagy activity which led to impaired spatial memory and cognitive function.

Altered glutamate clearance in ascorbate deficient mice increases seizure susceptibility and contributes to cognitive impairment in APP/PSEN1 mice

Ascorbate (vitamin C) is critical as a first line of defense antioxidant within the brain, and specifically within the synapse. Ascorbate is released by astrocytes during glutamate clearance and disruption of this exchange mechanism may be critical in mediating glutamate toxicity within the synapse. This is likely even more critical in neurodegenerative disorders with associated excitotoxicity and seizures, in particular Alzheimer's disease, in which ascorbate levels are often low. Using Gulo^-/- mice that are dependent on dietary ascorbate, we established that low brain ascorbate increased sensitivity to kainic acid as measured via behavioral observations, electroencephalography (EEG) measurements, and altered regulation of several glutamatergic system genes. Kainic acid-induced immobility was improved in wild-type mice following treatment with ceftriaxone, which upregulates glutamate transporter GLT-1. The same effect was not observed in ascorbate-deficient mice in which sufficient ascorbate is not available for release. A single, mild seizure event was sufficient to disrupt performance in the water maze in low-ascorbate mice and in APP_SWE/PSEN1_dE9 mice. Together, the data support the critical role of brain ascorbate in maintaining protection during glutamatergic hyperexcitation events, including seizures. The study further supports a role for mild, subclinical seizures in cognitive decline in Alzheimer's disease.

A role for astrocyte-derived amyloid β peptides in the degeneration of neurons in an animal model of temporal lobe epilepsy

Kainic acid, an analogue of the excitatory neurotransmitter glutamate, can trigger seizures and neurotoxicity in the hippocampus and other limbic structures in a manner that mirrors the neuropathology of human temporal lobe epilepsy (TLE). However, the underlying mechanisms associated with the neurotoxicity remain unclear. Since amyloid-β (Aβ) peptides, which are critical in the development of Alzheimer's disease, can mediate toxicity by activating glutamatergic NMDA receptors, it is likely that the enhanced glutamatergic transmission that renders hippocampal neurons vulnerable to kainic acid treatment may involve Aβ peptides. Thus, we seek to establish what role Aβ plays in kainic acid-induced toxicity using in vivo and in vitro paradigms. Our results show that systemic injection of kainic acid to adult rats triggers seizures, gliosis and loss of hippocampal neurons, along with increased levels/processing of amyloid precursor protein (APP), resulting in the enhanced production of Aβ-related peptides. The changes in APP levels/processing were evident primarily in activated astrocytes, implying a role for astrocytic Aβ in kainic acid-induced toxicity. Accordingly, we showed that treating rat primary cultured astrocytes with kainic acid can lead to increased Aβ production/secretion without any compromise in cell viability. Additionally, we revealed that kainic acid reduces neuronal viability more in neuronal/astrocyte co-cultures than in pure neuronal culture, and this is attenuated by precluding Aβ production. Collectively, these results indicate that increased production/secretion of Aβ-related peptides from activated astrocytes can contribute to neurotoxicity in kainic acid-treated rats. Since kainic acid administration can lead to neuropathological changes resembling TLE, it is likely that APP/Aβ peptides derived from astrocytes may have a role in TLE pathogenesis.

Brain-Specific SNAP-25 Deletion Leads to Elevated Extracellular Glutamate Level and Schizophrenia-Like Behavior in Mice

Several studies have associated reduced expression of synaptosomal-associated protein of 25 kDa (SNAP-25) with schizophrenia, yet little is known about its role in the illness. In this paper, a forebrain glutamatergic neuron-specific SNAP-25 knockout mouse model was constructed and studied to explore the possible pathogenetic role of SNAP-25 in schizophrenia. We showed that SNAP-25 conditional knockout (cKO) mice exhibited typical schizophrenia-like phenotype. A significantly elevated extracellular glutamate level was detected in the cerebral cortex of the mouse model. Compared with Ctrls, SNAP-25 was dramatically reduced by about 60% both in cytoplasm and in membrane fractions of cerebral cortex of cKOs, while the other two core members of SNARE complex: Syntaxin-1 (increased ~80%) and Vamp2 (increased ~96%) were significantly increased in cell membrane part. Riluzole, a glutamate release inhibitor, significantly attenuated the locomotor hyperactivity deficits in cKO mice. Our findings provide in vivo functional evidence showing a critical role of SNAP-25 dysfunction on synaptic transmission, which contributes to the developmental of schizophrenia. It is suggested that a SNAP-25 cKO mouse, a valuable model for schizophrenia, could address questions regarding presynaptic alterations that contribute to the etiopathophysiology of SZ and help to consummate the pre- and postsynaptic glutamatergic pathogenesis of the illness.

Amyloid precursor protein has clinical and prognostic significance in AML1-ETO-positive acute myeloid leukemia

Amyloid precursor protein (APP) has been reported to be highly expressed in acute myeloid leukemia (AML)1-eight-twenty one (ETO)-positive AML. In the present study, the clinical and prognostic significance of APP expression was assessed in 65 patients with AML1-ETO-positive AML using reverse transcription-quantitative polymerase chain reaction. The patients were divided into an APP-high expression (APP-H) group (n=32) and an APP-low expression (APP-L) group (n=33) according to the cut-off value of APP relative expression, which was calculated by receiver operating characteristic curve analysis. It was observed that C-KIT mutations (14/32 vs. 3/33, P=0.009), white blood cell count (median, 23.2×10⁹ vs. 12.4×10⁹ cells/l; P=0.011) and bone marrow cellularity (median, 91.0 vs. 84.0%; P=0.039) and incidence of extramedullary leukemia (11/32 vs. 3/33, P=0.013) were all significantly increased in the APP-H group compared with the APP-L group. Furthermore, significantly lower rate of cumulative two-cycle complete remission (83.9 vs. 100%, P=0.016), major molecular remission following two courses of consolidation (34.5 vs. 71.4%, P=0.005), and poorer relapse-free survival (RFS) (33.5±5.2% vs. 76.3±6.9%, P<0.001) and overall survival (OS) (44.5±7.0% vs. 81.9±5.8%, P=0.002) were associated with APP overexpression. Multivariate analysis revealed that APP overexpression was a significant adverse factor affecting both RFS and OS. Taken together, these data suggest that APP may be correlated with C-KIT mutations and involved in leukemia cell proliferation, and its overexpression has an adverse effect on the prognosis in AML1-ETO-positive AML.

Dianxianning improved amyloid β-induced pathological characteristics partially through DAF-2/DAF-16 insulin like pathway in transgenic C. elegans

Dianxianning (DXN) is a traditional Chinese formula, and has been approved in China for treating epilepsy since 1996. Here anti-Alzheimer's disease activity of DXN has been reported. DXN improved AD-like symptoms of paralysis and 5-HT sensitivity of transgenic Aβ1-42 C. elegans. In worms, DXN significantly increased Aβ monomers and decreased the toxic Aβ oligomers, thus reducing Aβ toxicity. DXN significantly suppressed the expression of hsp-16.2 induced by juglone, and up-regulated sod-3 expression. These results indicated that DXN increased stress resistance and protected C. elegans against oxidative stress. Furthermore, DXN could significantly promote DAF-16 nuclear translocation, but it did not activate SKN-1. The inhibitory effect of DXN on the Aβ toxicity was significantly reverted by daf-16 RNAi, rather than skn-1 RNAi or hsf-1 RNAi. These results indicated that DAF-16 is at least partially required for the anti-AD effect of DXN. In conclusion, DXN improved Aβ-induced pathological characteristics partially through DAF-2/DAF-16 insulin like pathway in transgenic worms. Together with our data obtained by Morris water maze test, the results showed that DXN markedly ameliorated cognitive performance impairment induced by scopolamine in mice. All the results support that DXN is a potential drug candidate to treat Alzheimer's diseases.

Epileptic activity in Alzheimer's disease: causes and clinical relevance

Epileptic activity is frequently associated with Alzheimer's disease; this association has therapeutic implications, because epileptic activity can occur at early disease stages and might contribute to pathogenesis. In clinical practice, seizures in patients with Alzheimer's disease can easily go unrecognised because they usually present as non-motor seizures, and can overlap with other symptoms of the disease. In patients with Alzheimer's disease, seizures can hasten cognitive decline, highlighting the clinical relevance of early recognition and treatment. Some evidence indicates that subclinical epileptiform activity in patients with Alzheimer's disease, detected by extended neurophysiological monitoring, can also lead to accelerated cognitive decline. Treatment of clinical seizures in patients with Alzheimer's disease with select antiepileptic drugs (AEDs), in low doses, is usually well tolerated and efficacious. Moreover, studies in mouse models of Alzheimer's disease suggest that certain classes of AEDs that reduce network hyperexcitability have disease-modifying properties. These AEDs target mechanisms of epileptogenesis involving amyloid β and tau. Clinical trials targeting network hyperexcitability in patients with Alzheimer's disease will identify whether AEDs or related strategies could improve their cognitive symptoms or slow decline.

Amniotic Mesenchymal Stem Cells Decrease Aβ Deposition and Improve Memory in APP/PS1 Transgenic Mice

Transplantation of human amniotic mesenchymal stem cells (hAM-MSCs) seems to be a promising strategy for the treatment of neurodegenerative disorders, including Alzheimer's disease (AD). However, the clinical therapeutic effects of hAM-MSCs and their mechanisms of action in AD remain to be determined. Here, we used amyloid precursor protein (APP) and presenilin1 (PS1) double-transgenic mice to evaluate the effects of hAM-MSC transplantation on AD-related neuropathology and cognitive dysfunction. We found that hAM-MSC transplantation into the hippocampus dramatically reduced amyloid-β peptide (Aβ) deposition and rescued spatial learning and memory deficits in APP/PS1 mice. Interestingly, these effects were associated with increasing in Aβ-degrading factors, elevations in activated microglia, and the modulation of neuroinflammation. Furthermore, enhanced hippocampal neurogenesis in the subgranular zone (SGZ) of the dentate gyrus (DG) and enhanced synaptic plasticity following hAM-MSC treatment could be another important factor in reversing the cognitive decline in APP/PS1 mice. Instead, the mechanism underlying the improved cognition apparently involves a robust increase in hippocampal synaptic density and neurogenesis that is mediated by brain-derived neurotrophic factor (BDNF). In conclusion, our data suggest that hAM-MSCs may be a new and effective therapy for the treatment of AD.

Lamotrigine Reduces Inflammatory Response and Ameliorates Executive Function Deterioration in an Alzheimer's-Like Mouse Model

Alzheimer's disease (AD) has been described in the literature, to be associated with impairment of executive function which develops early in the course of disease, and an effective treatment for this clinical feature remains elusive. Preclinical studies have implied that lamotrigine, an antiepileptic agent, could be a potential treatment for executive dysfunction in AD patients. Although there have been promising results in previous studies with lamotrigine, executive function has never been measured using animal models. The aim of the present study was to evaluate the effects of lamotrigine on executive function and determine whether lamotrigine can attenuate inflammatory response in an AD mouse model. Nontransgenic and transgenic mice were treated with lamotrigine (0 or 30 mg/kg/day) in a standard laboratory chow diet starting at 3 months of age. After 6 months of continuous lamotrigine administration, there was a marked improvement in executive function and a significant attenuation in the expression of proinflammatory cytokines. These results suggest that lamotrigine could ameliorate executive dysfunction and brain inflammatory response in the mouse model of AD and early lamotrigine intervention may be a promising therapeutic strategy for AD.

Incidence and impact of subclinical epileptiform activity in Alzheimer's disease

OBJECTIVE

Seizures are more frequent in patients with Alzheimer's disease (AD) and can hasten cognitive decline. However, the incidence of subclinical epileptiform activity in AD and its consequences are unknown. Motivated by results from animal studies, we hypothesized higher than expected rates of subclinical epileptiform activity in AD with deleterious effects on cognition.

METHODS

We prospectively enrolled 33 patients (mean age, 62 years) who met criteria for AD, but had no history of seizures, and 19 age-matched, cognitively normal controls. Subclinical epileptiform activity was assessed, blinded to diagnosis, by overnight long-term video-electroencephalography (EEG) and a 1-hour resting magnetoencephalography exam with simultaneous EEG. Patients also had comprehensive clinical and cognitive evaluations, assessed longitudinally over an average period of 3.3 years.

RESULTS

Subclinical epileptiform activity was detected in 42.4% of AD patients and 10.5% of controls (p = 0.02). At the time of monitoring, AD patients with epileptiform activity did not differ clinically from those without such activity. However, patients with subclinical epileptiform activity showed faster declines in global cognition, determined by the Mini-Mental State Examination (3.9 points/year in patients with epileptiform activity vs 1.6 points/year in patients without; p = 0.006), and in executive function (p = 0.01).

INTERPRETATION

Extended monitoring detects subclinical epileptiform activity in a substantial proportion of patients with AD. Patients with this indicator of network hyperexcitability are at risk for accelerated cognitive decline and might benefit from antiepileptic therapies. These data call for more sensitive and comprehensive neurophysiological assessments in AD patient evaluations and impending clinical trials. Ann Neurol 2016;80:858-870.

Amyloid precursor protein cooperates with c-KIT mutation/overexpression to regulate cell apoptosis in AML1-ETO-positive leukemia via the PI3K/AKT signaling pathway

It has been reported that amyloid precursor protein (APP) promotes cell proliferation and metastasis in various types of solid cancers. In our previous study, we showed that APP is highly expressed and regulates leukemia cell migration in AML1‑ETO-positive (AE) leukemia. Whether APP is involved in the regulation of AE leukemia cell proliferation or apoptosis is unclear. In the present study we focused on the correlation of APP with c-KIT mutation/overexpression and cell proliferation and apoptosis in AE leukemia. APP and c-KIT expression detected by quantitative real-time (qPCR) method, and c-KIT mutations screened using PCR in bone marrow cells from 65 patients with AE leukemia before their first chemotherapy, were simultaneously assessed. Furthermore, the Kasumi-1 cell line was chosen as the cell model, and the APP gene was knocked down using siRNA technology. The correlation of cell cycle distribution and apoptosis and c-Kit expression with APP expression levels, as well as the regulation of the PI3K/AKT signaling pathway by APP were analyzed in the Kasumi-1 cell line. The results showed that peripheral white blood cell counts (P=0.008) and bone marrow cellularity (P=0.031), but not bone marrow blasts, were correlated with APP expression. Moreover, the patients with APP high expression had a significantly higher incidence of c-KIT mutations (P<0.001) and increased levels of c-KIT expression (P=0.001) and poorer disease outcome. In the Kasumi-1 cell line, as compared with the wild-type and negative control cells, cell apoptosis, both early (P<0.001) and late (P<0.001), was significantly increased when the APP gene was knocked down, concomitant with reduced levels of anti-apoptotic protein Bcl-2 and increased levels of caspase-3 and -9, however, no apparent change was observed in the cell cycle distribution (P>0.05). Moreover, the knockdown of APP markedly decreased c-KIT expression at both the transcription (as evidenced by qPCR analysis) and translation (as confirmed by CD117 assay and western blot analysis) levels, as well as p-AKT and its downstream targets including NF-κB, p53 and Bcl-2. In conclusion, APP may cooperate with c-KIT mutation/overexpression in the regulation of cell apoptosis but not proliferation in AE leukemia via the PI3K/AKT signaling pathway.

Stereotactic Administration of Edaravone Ameliorates Collagenase-Induced Intracerebral Hemorrhage in Rat

Background

Edaravone is widely used for treating ischemic stroke, but it is not still confirmed in intracerebral hemorrhage (ICH) as an ideal medication targeting the brain parenchyma. We aimed to investigate the neuroprotective effects of stereotactic administration of edaravone (SI) into the brain parenchyma.

Methods

Intracerebral hemorrhage rat models were established by infusion of collagenase into the caudate nucleus. Neural functional recovery was assessed using modified neurological severity scores (mNSS). A comparative study of therapeutic effects between SI and intraperitoneal injection of edaravone (IP) involved in cerebral edema, blood–brain barrier (BBB) permeability, hematoma absorption, inflammatory response and neuronal apoptosis.

Results

Compared with IP, the mNSS was significantly (P < 0.05) improved by SI; cerebral edema and BBB permeability were dramatically ameliorated (P < 0.05); IL‐4 and IL‐10 levels increased, but IL‐1β and TNF‐α levels significantly decreased; neuron apoptosis decreased markedly (P < 0.05); and caspase‐3 and Bax expression significantly dropped, but Bcl‐2 increased in SI group (P < 0.05).

Conclusion

SI markedly improved neurological deficits in ICH rat models via antiinflammatory and antiapoptosis mechanisms and promoted M2‐type microglia differentiation. SI was effective in rats with collagenase‐induced ICH.

Lamotrigine Reduces β-Site AβPP-Cleaving Enzyme 1 Protein Levels Through Induction of Autophagy

Lamotrigine (LTG), a broad-spectrum anti-epileptic drug widely used in treatment for seizures, shows potential efficacy in Alzheimer's disease (AD) therapy. Chronic LTG treatment rescues the suppressed long-term potentiation, loss of spines and cognitive deficits in AβPP/PS1 mice, known to overexpress a chimeric mouse/human mutant amyloid-β protein precursor (AβPP) and a mutant human presenilin 1 (PS1). These changes are accompanied by reduction of amyloid-β (Aβ) plaques density and of levels of β-C-terminal fragment of AβPP (β-CTF), a fragment of AβPP cleaved by β-secretase. These results suggest LTG treatment reduces Aβ production, possibly through modulation of cleavage of AβPP by β-secretase. However, the underlying mechanisms still remain unclear. In this study, decreased protein levels, but not mRNA levels of β-site AβPP-cleaving enzyme 1 (BACE1), were observed in cultured HEK293 cells and the brains of AβPP/PS1 transgenic mice upon LTG treatment. Moreover, LTG treatment suppressed mammalian target of rapamycin (mTOR) signaling, while enhancing activation of cAMP response element binding protein (CREB), two signaling pathways essential for autophagy induction. LTG treatment increased the numbers of LC3-GFP + puncta and LC3-II levels in HEK293 cells, indicating an induction of autophagy. The downregulation of BACE1 by LTG treatment was prevented by the autophagy inhibitor 3-Methyladenine. Therefore, this study shows that LTG treatment reduces the protein levels of BACE1 through activation of autophagy, possibly via inhibition of mTOR signaling and activation of CREB.

The flavonoid baicalein rescues synaptic plasticity and memory deficits in a mouse model of Alzheimer's disease

Increasing evidence suggests that disruptions of synaptic functions correlate with the severity of cognitive deficit in Alzheimer's disease (AD). Our previous study demonstrated that baicalein enhances long-term potentiation (LTP) in acute rat hippocampal slices and improves hippocampus-dependent contextual fear conditioning in rats. Given that baicalein possess various biological activities, especially its effects on synaptic plasticity and cognitive function, we examined the effect of baicalein on synaptic function both in vitro and in vivo in AD model. The effect of baicalein on Aβ42 oligomer impaired LTP was investigated by electrophysiological methods. Baicalein was administered orally via drinking water to the APP/PS1 mice and sex- and age-matched wild-type mice. Treatment started at 5 months of age and mice were assessed for cognition and AD-like pathology at 7-month-old. Cognition was analyzed by Morris water maze test, fear conditioning test, and novel object recognition test. Changes in hippocampal 12/15 Lipoxygenase (12/15LO) and glycogen synthase kinase 3β (GSK3β) activity, Aβ production, tau phosphorylation, synaptic plasticity, and dendritic spine density were evaluated. Baicalein prevented Aβ-induced impairments in hippocampal LTP through activation of serine threonine Kinase (Akt) phosphorylation. Long-term oral administration of baicalein inhibited 12/15LO and GSK3β activity, reduced β-secretase enzyme (BACE1), decreased the concentration of total Aβ, and prevented phosphorylation of tau in APP/PS1 mice. Meanwhile, baicalein restored spine number, synaptic plasticity, and memory deficits. Our results strengthen the potential of the flavonoid baicalein as a novel and promising oral bioactive therapeutic agent that prevents memory deficits in AD.

Levetiracetam mitigates doxorubicin-induced DNA and synaptic damage in neurons

Neurotoxicity may occur in cancer patients and survivors during or after chemotherapy. Cognitive deficits associated with neurotoxicity can be subtle or disabling and frequently include disturbances in memory, attention, executive function and processing speed. Searching for pathways altered by anti-cancer treatments in cultured primary neurons, we discovered that doxorubicin, a commonly used anti-neoplastic drug, significantly decreased neuronal survival. The drug promoted the formation of DNA double-strand breaks in primary neurons and reduced synaptic and neurite density. Pretreatment of neurons with levetiracetam, an FDA-approved anti-epileptic drug, enhanced survival of chemotherapy drug-treated neurons, reduced doxorubicin-induced formation of DNA double-strand breaks, and mitigated synaptic and neurite loss. Thus, levetiracetam might be part of a valuable new approach for mitigating synaptic damage and, perhaps, for treating cognitive disturbances in cancer patients and survivors.

Elevated Neuronal Excitability Due to Modulation of the Voltage-Gated Sodium Channel Nav1.6 by Aβ1-42

Aberrant increases in neuronal network excitability may contribute to the cognitive deficits in Alzheimer's disease (AD). However, the mechanisms underlying hyperexcitability are not fully understood. Such overexcitation of neuronal networks has been detected in the brains of APP/PS1 mice. In the present study, using current-clamp recording techniques, we observed that 12 days in vitro (DIV) primary cultured pyramidal neurons from P0 APP/PS1 mice exhibited a more prominent action potential burst and a lower threshold than WT littermates. Moreover, after treatment with Aβ₁₋₄₂ peptide, 12 DIV primary cultured neurons showed similar changes, to a greater degree than in controls. Voltage-clamp recordings revealed that the voltage-dependent sodium current density of neurons incubated with Aβ₁₋₄₂ was significantly increased, without change in the voltage-dependent sodium channel kinetic characteristics. Immunohistochemistry and western blot results showed that, after treatment with Aβ₁₋₄₂, expressions of Nav and Nav1.6 subtype increased in cultured neurons or APP/PS1 brains compared to control groups. The intrinsic neuronal hyperexcitability of APP/PS1 mice might thus be due to an increased expression of voltage-dependent sodium channels induced by Aβ₁₋₄₂. These results may illuminate the mechanism of aberrant neuronal networks in AD.

Disrupted-in-Schizophrenia-1 Attenuates Amyloid-β Generation and Cognitive Deficits in APP/PS1 Transgenic Mice by Reduction of β-Site APP-Cleaving Enzyme 1 Levels

Disrupted-in-Schizophrenia-1 (DISC1) is a genetic risk factor for a wide range of major mental disorders, including schizophrenia, major depression, and bipolar disorders. Recent reports suggest a potential role of DISC1 in the pathogenesis of Alzheimer's disease (AD), by referring to an interaction between DISC1 and amyloid precursor protein (APP), and to an association of a single-nucleotide polymorphism in a DISC1 intron and late onset of AD. However, the function of DISC1 in AD remains unknown. In this study, decreased levels of DISC1 were observed in the cortex and hippocampus of 8-month-old APP/PS1 transgenic mice, an animal model of AD. Overexpression of DISC1 reduced, whereas knockdown of DISC1 increased protein levels, but not mRNA levels of β-site APP-Cleaving Enzyme 1 (BACE1), a key enzyme in amyloid-β (Aβ) generation. Reduction of BACE1 protein levels by overexpression of DISC1 was accompanied by an accelerating decline rate of BACE1, and was blocked by the lysosomal inhibitor chloroquine, rather than proteasome inhibitor MG-132. Moreover, overexpression of DISC1 in the hippocampus with an adeno-associated virus reduced the levels of BACE1, soluble Aβ40/42, amyloid plaque density, and rescued cognitive deficits of APP/PS1 transgenic mice. These results indicate that DISC1 attenuates Aβ generation and cognitive deficits of APP/PS1 transgenic mice through promoting lysosomal degradation of BACE1. Our findings provide new insights into the role of DISC1 in AD pathogenesis and link a potential function of DISC1 to the psychiatric symptoms of AD.

Antiepileptic drugs as a new therapeutic concept for the prevention of cognitive impairment and Alzheimer’s disease. Recent advances

Introduction.Excessive accumulation of amyloid-beta (Aβ) peptides in the brain results initially in mild cognitive impairment (MCI) and finally in Alzheimer’s disease (AD). Evidences from experimental and clinical studies show that pathological hyperexcitability of hippocampal neurons is a very early functional impairment observed in progressive memory dysfunctions. Therefore, antiepileptic drugs (AEDs) whose mechanism of action is aimed at inhibition of such neuronal hyperexcitability, seems to be an rationale choice for MCI and AD treatment.

Aim.To provide data from experimental and clinical studies on: 1. The unfavorable impact of neuronal hyperexcitability, mainly within the hippocampus, on cognitive processes. 2. Efficacy of AEDs against such abnormally elevated neuronal activity for the prevention of progressive cognitive impairment.

Methods.A literature review of publications published within the last fifteen years, was conducted using the PubMed database.

Review.The authors describe Aβ-induced hyperexcitability of hippocampal nerve cells as the cause of cognitive deficits, the connection of such activity with an increased risk of seizures and epilepsy in patients with MCI/AD, and finally the efficacy of AEDs: valproic acid (VPA), phenytoin (PHT), topiramate (TPM), lamotrigine (LTG), ethosuximide (ESM) and levetiracetam (LEV) in the prevention of cognitive impairment in experimental models and patients with MCI/AD.

Conclusions.The majority of the studied AEDs improve cognitive dysfunction in various experimental models of Aβ-induced brain pathology with accompanied neuronal hyperexcitability. The promising results achieved for LEV in animal models of cognitive impairment were also confirmed in patients with MCI/AD. LEV was well-tolerated and it’s beneficial antidementive effect was confirmed by memory tests and fMRI examination. In conclusion, the use of AEDs could be a novel therapeutic concept for preventing cognitive impairment in patients with Aβ-associated brain pathology.

Ethosuximide Induces Hippocampal Neurogenesis and Reverses Cognitive Deficits in an Amyloid-β Toxin-induced Alzheimer Rat Model via the Phosphatidylinositol 3-Kinase (PI3K)/Akt/Wnt/β-Catenin Pathway

Neurogenesis involves generation of new neurons through finely tuned multistep processes, such as neural stem cell (NSC) proliferation, migration, differentiation, and integration into existing neuronal circuitry in the dentate gyrus of the hippocampus and subventricular zone. Adult hippocampal neurogenesis is involved in cognitive functions and altered in various neurodegenerative disorders, including Alzheimer disease (AD). Ethosuximide (ETH), an anticonvulsant drug is used for the treatment of epileptic seizures. However, the effects of ETH on adult hippocampal neurogenesis and the underlying cellular and molecular mechanism(s) are yet unexplored. Herein, we studied the effects of ETH on rat multipotent NSC proliferation and neuronal differentiation and adult hippocampal neurogenesis in an amyloid β (Aβ) toxin-induced rat model of AD-like phenotypes. ETH potently induced NSC proliferation and neuronal differentiation in the hippocampus-derived NSC in vitro. ETH enhanced NSC proliferation and neuronal differentiation and reduced Aβ toxin-mediated toxicity and neurodegeneration, leading to behavioral recovery in the rat AD model. ETH inhibited Aβ-mediated suppression of neurogenic and Akt/Wnt/β-catenin pathway gene expression in the hippocampus. ETH activated the PI3K·Akt and Wnt·β-catenin transduction pathways that are known to be involved in the regulation of neurogenesis. Inhibition of the PI3K·Akt and Wnt·β-catenin pathways effectively blocked the mitogenic and neurogenic effects of ETH. In silico molecular target prediction docking studies suggest that ETH interacts with Akt, Dkk-1, and GSK-3β. Our findings suggest that ETH stimulates NSC proliferation and differentiation in vitro and adult hippocampal neurogenesis via the PI3K·Akt and Wnt·β-catenin signaling.

Paeoniflorin Atttenuates Amyloidogenesis and the Inflammatory Responses in a Transgenic Mouse Model of Alzheimer's Disease

Alzheimer's disease (AD) is associated with the inflammatory response in response to amyloid β-peptide (Aβ). Previous studies have suggested that paeoniflorin (PF) shows anti-inflammatory and neuroprotective effects in inflammation-related diseases. However, the impacts of PF on AD have not been investigated. In the present study, we showed that a 4-week treatment with PF could significantly inhibit Aβ burden, Aβ-induced over activation of astrocytes and microglia, downregulation of proinflammatory cytokines, and upregulation of anti-inflammatory cytokines in the brain. In addition, we demonstrated that chronic treatment with PF inhibited the activation of glycogen synthase kinase 3β (GSK-3β) and reversed neuroinflammtory-induced activation of nuclear factor-kappa B (NF-κB) signaling pathways. Moreover, PF exerted inhibitory effects on NALP3 inflammasome, caspase-1, and IL-1β. Collectively, in the present study, we demonstrated that PF exhibits neuroprotective effects in amyloid precursor protein (APP) and presenilin 1 (PS1) double-transgenic (APP/PS1) mice via inhibiting neuroinflammation mediated by the GSK-3β and NF-κB signaling pathways and nucleotide-binding domain-like receptor protein 3 inflammasome. Thus, these results suggest that PF might be useful to intervene in development or progression of neurodegeneration in AD through its anti-inflammatory and anti-amyloidogenic effects.

Rodent models for Alzheimer's disease drug discovery

INTRODUCTION

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by memory loss and personality changes, leading to dementia. Histopathological hallmarks are represented by aggregates of beta-amyloid peptide (Aβ) in senile plaques and deposition of hyperphosphorylated tau protein in neurofibrillary tangles in the brain. Rare forms of early onset familial Alzheimer's disease are due to gene mutations. This has prompted researchers to develop genetically modified animals that could recapitulate the main features of the disease. The use of these models is complemented by non-genetically modified animals.

AREAS COVERED

This review summarizes the characteristics of the most used transgenic (Tg) and non-Tg models of AD. The authors have focused on models mainly used in their laboratories including amyloid precursor protein (APP) Tg2576, APP/presenilin 1, 3xAD, single h-Tau, non-Tg mice treated with acute injections of Aβ or tau, and models of physiological aging.

EXPERT OPINION

Animal models of disease might be very useful for studying the pathophysiology of the disease and for testing new therapeutics in preclinical studies but they do not reproduce the entire clinical features of human AD. When selecting a model, researchers should consider the various factors that might influence the phenotype. They should also consider the timing of testing/treating animals since the age at which each model develops certain aspects of the AD pathology varies.

Regional and sub-regional differences in hippocampal GABAergic neuronal vulnerability in the TgCRND8 mouse model of Alzheimer's disease

Hippocampal network activity is predominantly coordinated by γ-amino-butyric acid (GABA)ergic neurons. We have previously hypothesized that the altered excitability of hippocampal neurons in Alzheimer's disease (AD), which manifests as increased in vivo susceptibility to seizures in the TgCRND8 mouse model of AD, may be related to disruption of hippocampal GABAergic neurons. In agreement, our previous study in TgCRND8 mice has shown that hippocampal GABAergic neurons are more vulnerable to AD-related neuropathology than other types of neurons. To further explore the mechanisms behind the observed decrease of GABAergic neurons in 6 month-old TgCRND8 mice, we assessed the relative proportion of somatostatin (SOM), neuropeptide Y (NPY) and paravalbumin (PV) sub-types of GABAergic neurons at the regional and sub-regional level of the hippocampus. We found that NPY expressing GABAergic neurons were the most affected, as they were decreased in CA1-CA2 (pyramidal-, stratum oriens, stratum radiatum and molecular layers), CA3 (specifically in the stratum oriens) and dentate gyrus (specifically in the polymorphic layer) in TgCRND8 mice as compared to non-transgenic controls. SOM expressing GABAergic neurons were decreased in CA1-CA2 (specifically in the stratum oriens) and in the stratum radiatum of CA3, whereas PV neurons were significantly altered in stratum oriens sub-region of CA3. Taken together, these data provide new evidence for the relevance of hippocampal GABAergic neuronal network disruption as a mechanism underlying AD sequelae such as aberrant neuronal excitability, and further point to complex hippocampal regional and sub-regional variation in susceptibility to AD-related neuronal loss.