LW-AFC, a new formula derived from Liuwei Dihuang decoction, ameliorates behavioral and pathological deterioration via modulating the neuroendocrine-immune system in PrP-hAβPPswe/PS1ΔE9 transgenic mice

BACKGROUND

Accumulating evidence implicates the neuroendocrine immunomodulation (NIM) network in the physiopathological mechanism of Alzheimer's disease (AD). Notably, we previously revealed that the NIM network is dysregulated in the PrP-hAβPPswe/PS1ΔE9 (APP/PS1) transgenic mouse model of AD.

METHODS

After treatment with a novel Liuwei Dihuang formula (LW-AFC), mice were cognitively evaluated in behavioral experiments. Neuron loss, amyloid-β (Aβ) deposition, and Aβ level were analyzed using Nissl staining, immunofluorescence, and an AlphaLISA assay, respectively. Multiplex bead analysis, a radioimmunoassay, immunochemiluminometry, and an enzyme-linked immunosorbent assay (ELISA) were used to measure cytokine and hormone levels. Lymphocyte subsets were detected using flow cytometry. Data between two groups were compared using a Student's t test. Comparison of the data from multiple groups against one group was performed using a one-way analysis of variance (ANOVA) followed by a Dunnett's post hoc test or a two-way repeated-measures analysis of variance with a Tukey multiple comparisons test.

RESULTS

LW-AFC ameliorated the cognitive impairment observed in APP/PS1 mice, including the impairment of object recognition memory, spatial learning and memory, and active and passive avoidance. In addition, LW-AFC alleviated the neuron loss in the hippocampus, suppressed Aβ deposition in the brain, and reduced the concentration of Aβ1-42 in the hippocampus and plasma of APP/PS1 mice. LW-AFC treatment also significantly decreased the secretion of corticotropin-releasing hormone and gonadotropin-releasing hormone in the hypothalamus, and adrenocorticotropic hormone, luteinizing hormone, and follicle-stimulating hormone in the pituitary. Moreover, LW-AFC increased CD8+CD28+ T cells, and reduced CD4+CD25+Foxp3+ T cells in the spleen lymphocytes, downregulated interleukin (IL)-1β, IL-2, IL-6, IL-23, granulocyte-macrophage colony stimulating factor, and tumor necrosis factor-α and -β, and upregulated IL-4 and granulocyte colony stimulating factor in the plasma of APP/PS1 mice.

CONCLUSIONS

LW-AFC ameliorated the behavioral and pathological deterioration of APP/PS1 transgenic mice via the restoration of the NIM network to a greater extent than either memantine or donepezil, which supports the use of LW-AFC as a potential agent for AD therapy.

Inhibiting TLR2 activation attenuates amyloid accumulation and glial activation in a mouse model of Alzheimer's disease

The effects of Toll-like receptor (TLR) activation in peripheral cells are well characterized but, although several TLRs are expressed on cells of the brain, the consequences of their activation on neuronal function remain to be fully investigated, particularly in the context of assessing their potential as therapeutic targets in neurodegenerative diseases. Several endogenous TLR ligands have been identified, many of which are soluble factors released from cells exposed to stressors. In addition, amyloid-β (Aβ) the main constituent of the amyloid plaques in Alzheimer's disease (AD), activates TLR2, although it has also been shown to bind to several other receptors. The objective of this study was to determine whether activation of TLR2 played a role in the developing inflammatory changes and Aβ accumulation in a mouse model of AD. Wild type and transgenic mice that overexpress amyloid precursor protein and presenilin 1 (APP/PS1 mice) were treated with anti-TLR2 antibody for 7months from the age of 7-14months. We demonstrate that microglial and astroglial activation, as assessed by MHCII, CD68 and GFAP immunoreactivity was decreased in anti-TLR2 antibody-treated compared with control (IgG)-treated mice. This was associated with reduced Aβ plaque burden and improved performance in spatial learning. The data suggest that continued TLR2 activation contributes to the developing neuroinflammation and pathology and may be provide a strategy for limiting the progression of AD.

Intranasal insulin alleviates cognitive deficits and amyloid pathology in young adult APPswe/PS1dE9 mice

Brain insulin signaling deficits contribute to multiple pathological features of Alzheimer's disease (AD). Although intranasal insulin has shown efficacy in patients with AD, the underlying mechanisms remain largely unillustrated. Here, we demonstrate that intranasal insulin improves cognitive deficits, ameliorates defective brain insulin signaling, and strongly reduces β‐amyloid (Aβ) production and plaque formation after 6 weeks of treatment in 4.5‐month‐old APPswe/PS1dE9 (APP/PS1) mice. Furthermore, c‐Jun N‐terminal kinase activation, which plays a pivotal role in insulin resistance and AD pathologies, is significantly inhibited. The alleviation of amyloid pathology by intranasal insulin results mainly from enhanced nonamyloidogenic processing and compromised amyloidogenic processing of amyloid precursor protein (APP), and from a reduction in apolipoprotein E protein which is involved in Aβ metabolism. In addition, intranasal insulin effectively promotes hippocampal neurogenesis in APP/PS1 mice. This study, exploring the mechanisms underlying the beneficial effects of intranasal insulin on Aβ pathologies in vivo for the first time, highlights important preclinical evidence that intranasal insulin is potentially an effective therapeutic method for the prevention and treatment of AD.

Neuroinflammatory challenges compromise neuronal function in the aging brain: Postoperative cognitive delirium and Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that targets memory and cognition, and is the most common form of dementia among the elderly. Although AD itself has been extensively studied, very little is known about early-stage preclinical events and/or mechanisms that may underlie AD pathogenesis. Since the majority of AD cases are sporadic in nature, advancing age remains the greatest known risk factor for AD. However, additional environmental and epigenetic factors are thought to accompany increasing age to play a significant role in the pathogenesis of AD. Postoperative cognitive delirium (POD) is a behavioral syndrome that primarily occurs in elderly patients following a surgical procedure or injury and is characterized by disruptions in cognition. Individuals that experience POD are at an increased risk for developing dementia and AD compared to normal aging individuals. One way in which cognitive function is affected in cases of POD is through activation of the inflammatory cascade following surgery or injury. There is compelling evidence that immune challenges (surgery and/or injury) associated with POD trigger the release of pro-inflammatory cytokines into both the periphery and central nervous system. Thus, it is possible that cognitive impairments following an inflammatory episode may lead to more severe forms of dementia and AD pathogenesis. Here we will discuss the inflammation associated with POD, and highlight the advantages of using POD as a model to study inflammation-evoked cognitive impairment. We will explore the possibility that advancing age and immune challenges may provide mechanistic evidence correlating early life POD with AD. We will review and propose neural mechanisms by which cognitive impairments occur in cases of POD, and discuss how POD may augment the onset of AD.

BACE1 in the retina: a sensitive biomarker for monitoring early pathological changes in Alzheimer's disease

Because of a lack of sensitive biomarkers, the diagnosis of Alzheimer's disease (AD) cannot be made prior to symptom manifestation. Therefore, it is crucial to identify novel biomarkers for the presymptomatic diagnosis of AD. While brain lesions are a major feature of AD, retinal pathological changes also occur in patients. In this study, we investigated the temporal changes in β-site APP-cleaving enzyme 1 (BACE1) expression in the retina and brain to determine whether it could serve as a suitable biomarker for early monitoring of AD. APP/PS-1 transgenic mice, 3, 6 and 8 months of age, were used as an experimental group, and age-matched C57/BL6 wild-type mice served as the control group. In the Morris water maze test, there were no significant differences in escape latency or in the number of crossings in the target area among mice of different ages. Compared with wild-type mice, no changes in learning or memory abilities were detected in transgenic mice at 3 months of age. However, compared with wild-type mice, the escape latency was significantly increased in transgenic mice at 6 months, starting on day 3, and at 8 months, starting on day 2, during Morris water maze training. In addition, the number of crossings of the target area was significantly decreased in transgenic mice. The learning and memory abilities of transgenic mice were further worsened at 8 months of age. Immunohistochemical staining revealed no BACE1 plaques in wild-type mice at 3, 6 or 8 months or in transgenic mice at 3 months, but they were clearly found in the entorhinal cortex, hippocampus and prefrontal cortex of transgenic mice at 6 and 8 months. BACE1 expression was not detected in the retina of wild-type mice at 3 months, but weak BACE1 expression was detected in the ganglion cell layer, inner plexiform layer and outer plexiform layer at 6 and 8 months. In transgenic mice, BACE1 expression in the ganglion cell layer was increased at 3 months, and BACE1 expression in the ganglion cell layer, inner plexiform layer and outer plexiform layer was significantly increased at 6 and 8 months, compared with age-matched wild-type mice. Taken together, these results indicate that changes in BACE1 expression appear earlier in the retina than in the brain and precede behavioral deficits. Our findings suggest that abnormal expression of BACE1 in the retina is an early pathological change in APP/PS-1 transgenic mice, and that BACE1 might have potential as a biomarker for the early diagnosis of AD in humans.

Traditional Chinese Nootropic Medicine Radix Polygalae and Its Active Constituent Onjisaponin B Reduce β-Amyloid Production and Improve Cognitive Impairments

Decline of cognitive function is the hallmark of Alzheimer’s disease (AD), regardless of the pathological mechanism. Traditional Chinese medicine has been used to combat cognitive impairments and has been shown to improve learning and memory. Radix Polygalae (RAPO) is a typical and widely used herbal medicine. In this study, we aimed to follow the β-amyloid (Aβ) reduction activity to identify active constituent(s) of RAPO. We found that Onjisaponin B of RAPO functioned as RAPO to suppress Aβ production without direct inhibition of β-site amyloid precursor protein cleaving enzyme 1 (BACE1) and γ-secretase activities. Our mechanistic study showed that Onjisaponin B promoted the degradation of amyloid precursor protein (APP). Further, oral administration of Onjisaponin B ameliorated Aβ pathology and behavioral defects in APP/PS1 mice. Taken together, our results indicate that Onjisaponin B is effective against AD, providing a new therapeutic agent for further drug discovery.

Cognitive improvement of compound danshen in an Aβ25-35 peptide-induced rat model of Alzheimer's disease

BACKGROUND

Senile dementia mainly includes Alzheimer' s disease (AD) and vascular dementia (VD). AD is a progressive and irreversible neurodegenerative disorder that is accompanied with a great deal of social burden. The aim of this study was to investigate the effect of Compound Danshen (CDS) on learning and memory of alzheimer's disease (AD) rat model, as well as to explore the possible connection between CDS and the associated molecules of amyloid beta (Aβ).

METHODS

Rats were injected with Aβ25-35 peptide intracerebroventricularly and CDS were subsequently administered once daily for 23 days. Rats' behavior was monitored using Morris water maze and passive avoidance. Real time PCR and Western blotting were used in determining amyloid precursor protein (APP), β-site APP cleaved enzyme-1(BACE1), Presenilin-1 (PS1), Insulin-degrading enzyme (IDE) and neprilysin (NEP) in hippocampus.

RESULTS

The AD model group presented with spatial learning and memory impairments. CDS and donepezil administration significantly ameliorated the Aβ25-35 peptide-induced memory impairment in both Morris water maze (P < 0.05) and passive avoidance task (P < 0.01) compared to the AD model group. Real time PCR results suggested that CDS significantly decreased APP mRNA, PS1 mRNA and increased IDE and NEP mRNA levels. Western blotting analyses showed that CDS decreased the protein expression of APP and PS1 and increased IDE expression.

CONCLUSION

CDS improved spatial learning and memory by down-regulating APP, PS1 levels and up-regulating IDE. In future, CDS may have significant therapeutic potential in the treatment of AD patients.

Linking insulin with Alzheimer's disease: emergence as type III diabetes

Alzheimer's disease (AD) has characteristic neuropathological abnormalities including regionalized neurodegeneration, neurofibrillary tangles, amyloid beta (Aβ) deposition, activation of pro-apoptotic genes, and oxidative stress. As the brain functions continue to disintegrate, there is a decline in person's cognitive abilities, memory, mood, spontaneity, and socializing behavior. A framework that sequentially interlinks all these phenomenons under one event is lacking. Accumulating evidence has indicated the role of insulin deficiency and insulin resistance as mediators of AD neurodegeneration. Herein, we reviewed the evidence stemming from the development of diabetes agent-induced AD animal model. Striking evidence has attributed loss of insulin receptor-bearing neurons to precede or accompany initial stage of AD. This state seems to progress with AD such that, in the terminal stages, it worsens and becomes global. Oxidative stress, tau hyperphosphorylation, APP-Aβ deposition, and impaired glucose and energy metabolism have all been linked to perturbation in insulin/IGF signaling. We conclude that AD could be referred to as "type 3 diabetes". Moreover, owing to common pathophysiology with diabetes common therapeutic regime could be effective for AD patients.

α-TLR2 antibody attenuates the Aβ-mediated inflammatory response in microglia through enhanced expression of SIGIRR

The immunoregulatory function of single-Ig-interleukin-1 related receptor (SIGIRR) is derived from its ability to constrain the inflammatory consequences of interleukin (IL)-1R and toll-like receptor (TLR)4 activation. This role extends to the brain, where SIGIRR deficiency increases the synaptic and cognitive dysfunction associated with IL-1R- and TLR4-mediated signalling. The current study set out to investigate the interaction between SIGIRR and TLR2 in brain tissue and the data demonstrate that the response to the TLR2 agonist, Pam3CysSK4 (Pam3Cys4), is enhanced in glial cells from SIGIRR(-/-) animals. Consistent with the view that β-amyloid peptide (Aβ) signals through activation of TLR2, the data also show that Aβ-induced changes are exaggerated in glia from SIGIRR(-/-) animals. We report that microglia, rather than astrocytes, are the primary glial cell expressing both TLR2 and SIGIRR. While Aβ increased TLR2 expression, it decreased SIGIRR expression in microglia. This was mimicked by direct activation of TLR2 with Pam3Cys4. We investigated the effect of an anti-TLR2 antibody (αTLR2) on the Aβ-induced inflammatory responses and demonstrate that it prevented the expression and release of the pro-inflammatory cytokines TNFα and IL-6 from microglia. In addition, application of αTLR2 alleviated the Aβ-mediated impairment in long-term potentiation (LTP) of hippocampal synaptic activity. The protective effects of αTLR2 were accompanied by an up-regulation in SIGIRR expression. We propose that a mechanism involving activation of PI3 kinase/Akt and the transcription factor peroxisome proliferator-activated receptor (PPAR)γ may facilitate this increase in SIGIRR. These findings highlight a novel role of SIGIRR as a negative regulator of TLR2-mediated inflammation in the brain.

Genetic manipulation of adult-born hippocampal neurons rescues memory in a mouse model of Alzheimer's disease

In adult mammals, neural progenitors located in the dentate gyrus retain their ability to generate neurons and glia throughout lifetime. In rodents, increased production of new granule neurons is associated with improved memory capacities, while decreased hippocampal neurogenesis results in impaired memory performance in several memory tasks. In mouse models of Alzheimer's disease, neurogenesis is impaired and the granule neurons that are generated fail to integrate existing networks. Thus, enhancing neurogenesis should improve functional plasticity in the hippocampus and restore cognitive deficits in these mice. Here, we performed a screen of transcription factors that could potentially enhance adult hippocampal neurogenesis. We identified Neurod1 as a robust neuronal determinant with the capability to direct hippocampal progenitors towards an exclusive granule neuron fate. Importantly, Neurod1 also accelerated neuronal maturation and functional integration of new neurons during the period of their maturation when they contribute to memory processes. When tested in an APPxPS1 mouse model of Alzheimer's disease, directed expression of Neurod1 in cycling hippocampal progenitors conspicuously reduced dendritic spine density deficits on new hippocampal neurons, to the same level as that observed in healthy age-matched control animals. Remarkably, this population of highly connected new neurons was sufficient to restore spatial memory in these diseased mice. Collectively our findings demonstrate that endogenous neural stem cells of the diseased brain can be manipulated to become new neurons that could allow cognitive improvement.

Prediabetes-induced vascular alterations exacerbate central pathology in APPswe/PS1dE9 mice

Age remains the main risk factor for developing Alzheimer's disease (AD) although certain metabolic alterations, including prediabetes and hyperinsulinemia, also increase this risk. We present a mouse model of AD (APPswe/PS1dE9 mouse) with severe hyperinsulinemia induced by long-term high fat diet (HFD) treatment. After 23 weeks on HFD learning and memory processes were compromised. We observed a significant increase in tau hyperphosphorylation and Aβ pathology, including Aβ levels and amyloid burden. Microglia activation was also significantly increased in HFD-treated mice, both in close proximity to and far from senile plaques. Insulin degrading enzyme and neprilysin levels were not affected, suggesting that Aβ degradation pathways were preserved, whereas we detected an increase in spontaneous cortical bleeding that could underlay an impairment of Aβ interstitial fluid drainage, contributing to the increase in Aβ deposition in APP/PS1-HFD mice. Altogether our data suggest that early hyperinsulinemia is enough to exacerbate AD pathology observed in APP/PS1 mice, and supports the role of insulin-resistance therapies to stop or delay central complications associated.

The role of hippocampal tau protein phosphorylation in isoflurane-induced cognitive dysfunction in transgenic APP695 mice

BACKGROUND

Previous studies have shown that exposure to inhaled anesthetics can cause cognitive dysfunction, suggesting that general anesthesia might be a risk factor for the development of Alzheimer disease. However, the underlying mechanisms remain to be elucidated. In the present study, we tested our hypothesis that enhanced tau protein phosphorylation in hippocampus contributes to isoflurane-induced cognitive dysfunction in a mouse model of Alzheimer disease.

METHODS

Fifty-four male wild-type (WT) mice (12 months old) and 54 male amyloid precursor protein 695 (APP695) mice (12 months old) were either anesthetized for 4 hours with 1.0 minimum alveolar concentration isoflurane or sham-anesthetized (control). Learning and memory behaviors were measured using the Morris Water Maze test for mice. Phosphorylation of hippocampal tau protein at Ser262 site was analyzed with quantitative Western blotting.

RESULTS

In the Morris Water Maze test, both WT and transgenic APP695 mice showed decreased latency times during a 4-day training period. Isoflurane exposure significantly increased the latency times on days 2 and 3 in WT mice as well as on days 3 and 4 in APP695 mice (WT: P = 0.005 for day 2 and P = 0.002 for day 3; APP695: P = 0.001 for day 3 and P < 0.0001 for day 4) and reduced platform quadrant times (WT: P < 0.0001; APP695: P < 0.0001) in both types of mice. Compared with WT mice, transgenic APP695 mice displayed worse learning and memory behaviors after isoflurane exposure (P = 0.0005 for escape latency testing on day 4 training; P = 0.009 for platform probe testing). Western blot analysis showed that the levels of phosphorylation of hippocampal tau protein at Ser262 site (tau[pS262]) in the transgenic APP695 mice were higher than those in WT mice (P < 0.0001) and that isoflurane exposure time dependently enhanced the hippocampal tau[pS262] levels in both types of mice, but this effect was much more significant in the transgenic APP695 mice (P < 0.0001). Our data also showed that isoflurane exposure had no effect on the expression of total tau protein in the hippocampi of all mice (P ≥ 0.54).

CONCLUSIONS

Isoflurane may induce cognitive dysfunction by enhancing phosphorylation of hippocampal tau protein at Ser262 site, and this effect is more significant in transgenic APP695 mice.

Neuroinflammatory changes negatively impact on LTP: A focus on IL-1β

In recent years it has become clear that neuroinflammatory changes develop in the brain with age and that similar, though more profound changes, occur in neurodegenerative conditions and in animal models of neurodegeneration. These changes are linked with deterioration in plasticity and the evidence suggests that a key causative factor is microglial activation and the associated increase in production and release of inflammatory cytokines. Several groups have reported that interleukin (IL)-1β negatively impacts on hippocampal-dependent learning and has an inhibitory effect on LTP although this is concentration-dependent. Similarly other inflammatory cytokines, which are also produced by microglia similarly decrease LTP. The evidence supporting these findings will be reviewed here and will be discussed in the context of considering mechanisms by which the negative impact of neuroinflammation can be ameliorated. This article is part of a Special Issue entitled SI: Brain and Memory.

How dependent is synaptic plasticity on microglial phenotype?

Microglia are particularly plastic cells which can be shifted from their resting state by numerous factors and adopt distinct phenotypes. The cells are multifunctional, though their main role is probably maintenance of homoeostasis. Resting cells are responsible for surveillance, whereas activation induces the cells to adopt neuroprotective or neurodetrimental roles, which are anti-inflammatory or pro-inflammatory respectively. The evidence indicates that activated cells with a pro-inflammatory phenotype predominate in neurodegenerative diseases and models of neurodegeneration and that this may significantly contribute to the deteriorating neuronal function. This question is considered in this review, in particular in the context of animal models of Alzheimer's disease (AD). This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.

The impact of neuroimmune changes on development of amyloid pathology; relevance to Alzheimer's disease

Neuroinflammatory changes are a characteristic of several, if not all, neurodegenerative diseases including Alzheimer's disease and are typified by increased microglial activation. Microglia express several receptors making them highly reactive and plastic cells, and, at least in vitro, they adopt different phenotypes in a manner analogous to their peripheral counterparts, macrophages. Microglia also express numerous cell surface proteins enabling them to interact with cells and the evidence indicates that maintenance of microglia in a quiescent state relies, at least to some extent, on an interaction with neurons by means of specific ligand-receptor pairs, for example CD200-CD200R. It is clear that microglia also interact with T cells and recent evidence indicates that co-incubation of microglia with T helper type 1 cells markedly increases their activation. Under normal conditions, small numbers of activated T cells gain entry to the brain and are involved in immune surveillance but infiltration of significant numbers of T cells occurs in disease and following injury. The consequences of T cell infiltration appear to depend on the conditions, with descriptions of both neurodestructive and neuroprotective effects in animal models of different diseases. This review will discuss the modulatory effect of T cells on microglia and the impact of infiltration of T cells into the brain with a focus on Alzheimer's disease, and will propose that infiltration of interferon-γ-producing cells may be an important factor in triggering inflammation that is pathogenic and destructive.

Puerarin alleviates cognitive impairment and oxidative stress in APP/PS1 transgenic mice

Increasing evidence demonstrates that β-amyloid (Aβ) elicits oxidative stress, which contributes to the pathogenesis and disease progression of Alzheimer's disease (AD). Thus, there is interest in developing antioxidant therapies for the prevention/treatment of cognitive decline during AD. We reported previously that puerarin has antioxidative properties in vitro. Therefore, the aim of the present study was to determine whether puerarin improves cognitive function and reduces oxidative stress in amyloid precursor protein/presenilin-1 (APP/PS1) mice, a well established AD mouse model, and explore its potential mechanism. Our results show that oral administration of puerarin significantly ameliorates cognitive impairment in APP/PS1 mice assessed by the Morris water maze (MWM) test. This was accompanied by a significant decrease in the levels of lipid peroxidation (LPO) through, at least in part, induction of nuclear factor erythroid 2-related factor 2 (Nrf2) target gene heme oxygenase 1 (HO-1) in the hippocampus of APP/PS1 transgenic mice at 9 months of age, but without altering brain Aβ burden. Furthermore, puerarin significantly activated Akt, reduced activation of glycogen synthase kinase 3β (GSK-3β), and induced nuclear translocation of Nrf2 in the hippocampus of APP/PS1 mice but did not alter ERK1/2 phosphorylation. Thus, puerarin may improve cognitive performance in APP/PS1 mice through activation of the Akt/GSK-3β signaling pathway. These findings suggest that puerarin might be an attractive agent for prevention and treatment of cognitive impairment and dementia.

α-Asarone Ameliorates Memory Deficit in Lipopolysaccharide-Treated Mice via Suppression of Pro-Inflammatory Cytokines and Microglial Activation

α-Asarone exhibits a number of pharmacological actions including neuroprotective, anti-oxidative, anticonvulsive, and cognitive enhancing action. The present study investigated the effects of α-asarone on pro-inflammatory cytokines mRNA, microglial activation, and neuronal damage in the hippocampus and on learning and memory deficits in systemic lipopolysaccharide (LPS)-treated C57BL/6 mice. Varying doses of α-asarone was orally administered (7.5, 15, or 30 mg/kg) once a day for 3 days before the LPS (3 mg/kg) injection. α-Asarone significantly reduced TNF-α and IL-1β mRNA at 4 and 24 hours after the LPS injection at dose of 30 mg/kg. At 24 hours after the LPS injection, the loss of CA1 neurons, the increase of TUNEL-labeled cells, and the up-regulation of BACE1 expression in the hippocampus were attenuated by 30 mg/kg of α-asarone treatment. α-Asarone significantly reduced Iba1 protein expression in the hippocampal tissue at a dose of 30 mg/kg. α-Asarone did not reduce the number of Iba1-expressing microglia on immunohistochemistry but the average cell size and percentage areas of Iba1-expressing microglia in the hippocampus were significantly decreased by 30 mg/kg of α-asarone treatment. In the Morris water maze test, α-asarone significantly prolonged the swimming time spent in the target and peri-target zones. α-Asarone also significantly increased the number of target heading and memory score in the Morris water maze. The results suggest that inhibition of pro-inflammatory cytokines and microglial activation in the hippocampus by α-asarone may be one of the mechanisms for the α-asarone-mediated ameliorating effect on memory deficits.

Neural stem cell transplants improve cognitive function without altering amyloid pathology in an APP/PS1 double transgenic model of Alzheimer's disease

Neural stem cells (NSCs) are capable of self-renewal and are multipotent. Transplantation of NSCs may represent a promising approach for treating neurodegenerative disorders associated with cognitive decline, such as Alzheimer disease (AD) characterized by extensive loss of neurons. In this study, we investigated the effect of NSC transplantation on cognitive function in the amyloid precursor protein/presenilin-1 (APP/PS1) transgenic mouse, an AD mouse model with age-dependent cognitive deficits. We found that NSCs bilaterally transplanted into hippocampal regions improved spatial learning and memory function in these mice, but did not alter Aβ pathology. Immunohistochemical analyses determined that NSCs proliferated, migrated, and differentiated into three neuronal cell types. The improvement in cognitive function was correlated with enhanced long-term potentiation (LTP) and an increase in the neuron expression of proteins related to cognitive function: N-methyl-D-aspartate (NMDA) 2B unit, synaptophysin (SYP), protein kinase C ζ subtypes (PKCζ), tyrosine receptor kinase B (TrkB), and brain-derived neurotrophic factor (BDNF). Taken together, our data indicated that injected NSCs can rescue cognitive deficits in APP/PS1 transgenic mice by replacing neuronal cell types expressing multiple cognition-related proteins that enhance LTP.

Cholinergic degeneration is associated with increased plaque deposition and cognitive impairment in APPswe/PS1dE9 mice

Cholinergic dysfunction and deposition of plaques containing amyloid β-peptides (Aβ) are two of the characteristics of Alzheimer's disease. Here, we combine APPswe/PS1dE9 (APP/PS1) mice with the cholinergic immunotoxin mu p75-saporin (SAP) to integrate partial basal forebrain cholinergic degeneration and the neuropathology of APP/PS1 mice. By 6 months of age, APP/PS1 mice and wild type littermates (Wt) received intracerebroventricular injection of 0.6 μg SAP (lesion) or PBS (sham). Two months following surgery, APP/PS1 mice treated with SAP were significantly impaired compared to sham treated APP/PS1 mice in a behavioural paradigm addressing working memory. Conversely, the performance of Wt mice was unaffected by SAP treatment. Choline acetyltransferase activity was reduced in the hippocampus and frontal cortex following SAP treatment. The selective effect of a mild SAP lesion in APP/PS1 mice was not due to a more extensive cholinergic degeneration since the reduction in choline acetyltransferase activity was similar following SAP treatment in APP/PS1 mice and Wt. Interestingly, plaque load was significantly increased in SAP treated APP/PS1 mice relative to sham lesioned APP/PS1 mice. Additionally, APP/PS1 mice treated with SAP showed a tendency towards an increased level of soluble and insoluble Aβ1-40 and Aβ1-42 measured in brain tissue homogenate. Our results suggest that the combination of cholinergic degeneration and Aβ overexpression in the APP/PS1 mouse model results in cognitive decline and accelerated plaque burden. SAP treated APP/PS1 mice might thus constitute an improved model of Alzheimer's disease-like neuropathology and cognitive deficits compared to the conventional APP/PS1 model without selective removal of basal forebrain cholinergic neurons.