Hippocampal Amyloid Precursor Protein Research Articles

Alcohol-drinking during later life by C57BL/6J mice induces sex- and age-dependent changes in hippocampal and prefrontal cortex expression of glutamate receptors and neuropathology markers

Heavy drinking can induce early-onset dementia and increase the likelihood of the progression and severity of Alzheimer's Disease and related dementias (ADRD). Recently, we showed that alcohol-drinking by mature adult C57BL/6J mice induces more signs of cognitive impairment in females versus males without worsening age-related cognitive decline in aged mice. Here, we immunoblotted for glutamate receptors and protein markers of ADRD-related neuropathology within the hippocampus and prefrontal cortex (PFC) of these mice after three weeks of alcohol withdrawal to determine protein correlates of alcohol-induced cognitive decline. Irrespective of alcohol history, age-related changes in protein expression included a male-specific decline in hippocampal glutamate receptors and an increase in the expression of a beta-site amyloid precursor protein cleaving enzyme (BACE) isoform in the PFC as well as a sex-independent increase in hippocampal amyloid precursor protein. Alcohol-drinking was associated with altered expression of glutamate receptors in the hippocampus in a sex-dependent manner, while all glutamate receptor proteins exhibited significant alcohol-related increases in the PFC of both sexes. Expression of BACE isoforms and phosphorylated tau varied in the PFC and hippocampus based on age, sex, and drinking history. The results of this study indicate that withdrawal from a history of alcohol-drinking during later life induces sex- and age-selective effects on glutamate receptor expression and protein markers of ADRD-related neuropathology within the hippocampus and PFC of potential relevance to the etiology, treatment and prevention of alcohol-induced dementia and Alzheimer's Disease.

Acute interleukin-6 modulates key enzymes involved in prefrontal cortex and hippocampal amyloid precursor protein processing.

Exercise is beneficial for individuals with Alzheimer's disease (AD). In rodent models of AD, exercise decreases the amyloidogenic processing of the amyloid precursor protein (APP). Although, it remains unclear how exercise is promoting this shift away from pathological APP processing, there is emerging evidence that exercise-induced factors released from peripheral tissues may facilitate these alterations in brain APP processing. Interleukin-6 (IL-6) is released from multiple organs into peripheral circulation during exercise and is among the most characterized exerkines. The purpose of this study is to examine if acute IL-6 can modulate key enzymes responsible for APP processing, namely a disintegrin and metalloproteinase 10 (ADAM10) and beta-site amyloid precursor protein cleaving enzyme 1 (BACE1), which initiate the non-amyloidogenic and amyloidogenic cascades respectively. Male 10-week-old C57BL/6J mice underwent and acute treadmill exercise bout or were either injected with IL-6 or a PBS control 15 min prior to tissue collection. ADAM10 and BACE1 enzyme activity, mRNA, and protein expression, as well as downstream markers of both cascades, including sAPPa and sAPPβ, were examined. Exercise increased circulating IL-6 and brain IL-6 signaling (pSTAT3 and Socs3 mRNA). This occurred alongside a reduction in BACE1 activity and an increase in ADAM10 activity. IL-6 injection reduced BACE1 activity and increased sAPPa protein content in the prefrontal cortex. In the hippocampus, IL-6 injection decreased BACE1 activity and sAPPβ protein content. Our results show that acute IL-6 injection increases markers of the non-amyloidogenic cascade and decreases markers of the amyloidogenic cascade in the cortex and hippocampus of the brain.

Effects of Steroidal Na/K‐ATPase Inhibitor Marinobufagenin on Neurodegeneration, Neuroinflammation and Cognition in a Mouse Model of Alzheimer's Disease and Cardiovascular Amyloidosis

Background Na/K-ATPase is a keystone enzyme in all living cells. Steroidal inhibitor of Na/K-ATPase, marinobufagenin (MBG), participates in regulating cardiac function, vessel architecture, intracellular signaling transduction, and anti-neuroinflammatory response. The aged double-transgene APPswe/PS1dE9 mice, a model of Alzheimer's disease (AD), exhibit lower levels of urine MBG compared to wild-type (WT) mice, impairments in cognitive function and amyloid β (Aβ) pathologies. Compromised blood supply to the brain may contribute to AD development and Aβ pathologies. Here we examined Aβ pathology in the cerebral and central vasculature of aged AD mice and whether MBG treatment affects neuroinflammation, neurodegeneration, and cognitive function. Methods To aged male AD (n=8; 15-mo old) and age-matched WT mice (n=4) MBG (100 µg/day/kg body weight) was administered via subcutaneous ALZET minipumps for 3-mo. Age-matched control mice received saline (AD-C, n=8; WT-C, n=4). Systolic blood pressure (SBP; by tail cuff plethysmography), cognitive flexibility (reversal learning in a water T-maze), plasma (for MBG measurement), brain and tissue samples (for qPCR, 3D green light laser microscopy and immunohistochemistry analysis) were collected at 18-mo. Data was analyzed by 2-way ANOVA and presented as mean±SE. Results In aged AD mice, we observed granulated Aβ plaques and Aβ localization around small cerebral blood vessels (Fig 1B; white arrows). Aβ protein was also found in significantly larger abundance in aortae vessel wall of old AD mice vs. WT mice (Fig 2; blue stain). SBP was not affected by treatment and did not differ between AD and WT mice. Endogenous plasma MBG was lower in AD-C vs. WT-C (125±21 vs. 223±41 pmol/L; p<0.05). Plasma MBG was elevated in both WT-MBG and AD-MBG (483±116 and 657±176 pmol/L; p<0.05 vs. WT-C and AD-C, correspondently). Hippocampal mRNA expression of inflammatory marker IL6 was upregulated 1.5-fold in AD-C vs. WT-C (p<0.05); MBG reduced this expression in AD-MBG vs. AD-C (p<0.01). Hippocampal mRNA expression of amyloid precursor protein (APP) was upregulated 2.6-fold in AD-C vs. WT-C (p<0.01); MBG reduced this expression in AD-MBG vs. AD-C (p<0.01). AD mice showed normal learning for a turn-based discrimination rule but were impaired during the reversal phase vs. WT mice. MBG treatment did not affect the amount of Aβ plaque load in the brains of AD-MBG vs. AD-C. Conclusion Old AD mice exhibited lower endogenous plasma MBG, impaired cognitive flexibility, higher hippocampal IL6 and APP mRNAs, and Aβ accumulation in cerebral vessels and aortae relative to WT counterparts. MBG treatment significantly reduced hippocampal APP and inflammatory mRNA markers; however, it had no effect on existing Aβ load. In future experiments, we will examine how MBG treatment affects the formation of brain Aβ plaques in younger AD mice.

Brain Training Improves Cigarette Smoke Induced Dementia in Female C57 Black 6 Mice

Alzheimer’s disease is a chronic neurodegenerative disease among the elderly population. Various genetic, environmental and lifestyle factors have been associated with the etiology of Alzheimer’s disease. Cigarette smoke has been reported to be a major predisposing factor for Alzheimer’s disease and contributes to disease development. Conversely, studies have reported beneficial effects of brain training on the disease condition. The purpose of this study was to evaluate the effect of a brain training task in cigarette smoke induced dementia. Three groups of female C57 black 6 mice were used in the study with two of the groups subjected to cigarette smoke exposure. The third group was subjected to a novel object test immediately after the exposure. Brain training improved the cognitive domains of the smoke exposed mice. Brain training could also regain the neurotransmitter imbalances induced by cigarette smoke, importantly, decreased the glutamate levels in the hippocampus. Brain training also significantly decreased the hippocampal amyloid precursor protein expression levels by reducing the reactive oxygen species production. Additionally, the improved hippocampal neuronal count, post training supported the findings. The results indicated that brain training significantly decreased the deleterious effects of cigarette smoke in hippocampus tissue and improved dementia symptoms.

Kidney-reinforcing and Governor Vessel-regulating EA Intervention May Improve Learningmemory Possibly by Suppressing Formation of Senile Plaques in Hippocampus in APP/PS 1 Double Transgenic Alzheimer's Disease Mice

To observe the effect of electroacupuncture (EA) intervention on learning-memory ability and the expression of senile plaques (SP), amyloid precursor protein (APP), β-secretase 1(BACE 1) and insulin degrading enzyme (IDE) in the hippocampus in APP/presenilin 1 (PS 1) double transgenic Alzheimer's disease (AD) mice, so as to reveal its mechanisms underlying improvement of AD. A total of 18 male APP/PS 1 double transgenic AD mice were randomly divided into model, EA-2-week and EA-3-week groups (n=6 in each). The control group was consisted of 6 male wild mice. EA (2 Hz, 2 mA) was applied to "Baihui" (GV 20) and bilateral "Shenshu" (BL 23) for 15 min, once a day, with 7 days being a therapeutic course, 2 or 3 courses altogether and with an one day's interval between every two courses. The spatial learning-memory ability was assessed using Morris water maze test during 5 days' training. The immunoactivity of SP in the hippocampus tissue was detected by immunohistochemistry, and the expression levels of APP, BACE 1 and IDE in the hippocampus were analyzed by Western blot. Following modeling, the escape latency and path length of hidden platform tests were significantly increased (P<0.01, P<0.05), and the platform crossing time of spatial probing test significantly decreased (P<0.01) in the model group compared with the control group. After EA intervention, the escape latency on the 5th day of training, and the path length on the 4th and 5th day of training in both EA-2-week and EA-3-week groups were significantly shorter relevant to the model group (P<0.01), and those of the EA-3-week group were considerably shorter than those of the EA-2-week group in the escape latency and path length (P<0.05, P<0.01). The platform crossing times of spatial probing test were significanthy increased in both EA-2-week and EA-3-week groups in comparison with the model group (P<0.01), and that of the EA-3-week group was considerably increased compared with the EA-2-week group (P<0.05). Immunohistochemical staining showed that the number of SP in the hippocampus was markedly increased in the model group compared with the control group (P<0.01), and was markedly reduced in both EA-2-week and EA-3-week groups (P<0.01), and that of the EA-3-week group was significantly decreased compared with the EA-2-week group (P<0.01). The expression levels of hippocampal APP and BACE 1 proteins were significantly higher in the model group than in the control group (P<0.01), and that of hippocampal IDE was markedly lower in the model group than in the control group (P<0.01). After EA, the increased expression levels of APP and BACE 1 proteins and the decreased expression level of IDE in the EA-2-week and EA-3-week groups were significantly inhibited (P<0.01). The effects of EA-3-week were significantly stronger than those of EA-2-week in down-regulating the expression of APP and BACE 1 proteins and up-regulating the expression of IDE (P<0.01, P<0.05). EA stimulation of GV 20 and BL 23 can improve the learning-memory ability in APP/PS 1 double transgenic AD mice, which may be related to its effects in down-regulating the expression of SP, APP and BACE 1 proteins and up-regulating the expression of IDE protein in the hippocampus.

Matrix metalloproteinase 14 modulates diabetes and Alzheimer's disease cross-talk: a meta-analysis.

Diabetes mellitus is associated with dementia, but whether diabetes is associated with Alzheimer's disease remains controversial. Alzheimer's disease is characterized by amyloid beta aggregation. We hypothesized that genes, involved in amyloid beta degradation, may be altered due to diabetes and thus participate in progression of Alzheimer's disease. Expression profiling of amyloid beta-degrading enzymes in streptozotocin-induced diabetic mice and their correlation with expression of amyloid precursor protein in hippocampus of Alzheimer's disease patients were accessed. We found that matrix metalloproteinase 14 decreased in brain but not in other tissues of streptozotocin-induced diabetic mice, and was negatively correlated with expression of amyloid precursor protein in hippocampus of Alzheimer's disease patients. These findings suggested matrix metalloproteinase 14 may link insulin-deficient diabetes to Alzheimer's disease.

Similarities in lindane induced alterations in protein expression profiling in different brain regions with neurodegenerative diseases

Previous studies have reported that lindane, an organochlorine pesticide induces oxidative stress in rat brain that may lead to neurodegeneration. However, as the proteins involved in lindane induced neurodegeneration are yet to be identified, the present study aims to identify the proteins that may regulate lindane induced neurotoxicity. The data showed that repeated exposure of lindane (2.5 mg/kg) for 21 days to adult rats significantly increased the reactive oxygen species and lipid peroxidation in different brain regions. Proteomic study revealed that lindane induces major dysregulation in the ubiquitin proteasome pathway. Alterations in the expression of molecular chaperones in brain regions and an increase in the expression of α-synuclein in substantia-nigra and corpus-striatum and amyloid precursor protein in hippocampus and frontal-cortex suggests the accumulation of proteins in these brain regions. Western blotting also revealed alterations in the dopaminergic and cholinergic pathways in hippocampus and substantia-nigra isolated from lindane treated rats. Neurobehavioural data indicating alterations in learning and working memory, conditioned avoidance response and motor function, supports the proteomic data. The data suggest that repeated exposure of lindane to adult rats induces alterations, which are similar to that seen in neurodegenerative diseases.

Enduring Elevations of Hippocampal Amyloid Precursor Protein and Iron Are Features of β-Amyloid Toxicity and Are Mediated by Tau.

The amyloid cascade hypothesis of Alzheimer's disease (AD) positions tau protein as a downstream mediator of β-amyloid (Aβ) toxicity This is largely based on genetic cross breeding, which showed that tau ablation in young (3-7-month-old) transgenic mice overexpressing mutant amyloid precursor protein (APP) abolished the phenotype of the APP AD model. This evidence is complicated by the uncertain impact of overexpressing mutant APP, rather than Aβ alone, and for potential interactions between tau and overexpressed APP. Cortical iron elevation is also implicated in AD, and tau promotes iron export by trafficking APP to the neuronal surface. Here, we utilized an alternative model of Aβ toxicity by directly injecting Aβ oligomers into the hippocampus of young and old wild-type and tau knockout mice. We found that ablation of tau protected against Aβ-induced cognitive impairment, hippocampal neuron loss, and iron accumulation. Despite injected human Aβ being eliminated after 5weeks, enduring changes, including increased APP levels, tau reduction, tau phosphorylation, and iron accumulation, were observed. While the results from our study support the amyloid cascade hypothesis, they also suggest that downstream effectors of Aβ, which propagate toxicity after Aβ has been cleared, may be tractable therapeutic targets.

Folic acid administration inhibits amyloid β-peptide accumulation in APP/PS1 transgenic mice

Alzheimer's disease (AD) is associated with malnutrition, altered one-carbon metabolism and increased hippocampal amyloid-β peptide (Aβ) accumulation. Aberrant DNA methylation may be an epigenetic mechanism that underlies AD pathogenesis. We hypothesized that folic acid acts through an epigenetic gene silencing mechanism to lower Aβ levels in the APP/PS1 transgenic mouse model of AD. APP/PS1 mice were fed either folate-deficient or control diets and gavaged daily with 120μg/kg folic acid, 13.3mg/kg S-adenosylmethionine (SAM) or both. Examination of the mice after 60days of treatment showed that serum folate concentration increased with intake of folic acid but not SAM. Folate deficiency lowered endogenous SAM concentration, whereas neither intervention altered S-adenosylhomocysteine concentration. DNA methyltransferase (DNMT) activity increased with intake of folic acid raised DNMT activity in folate-deficient mice. DNA methylation rate was stimulated by folic acid in the amyloid precursor protein (APP) promoter and in the presenilin 1 (PS1) promoter. Folate deficiency elevated hippocampal APP, PS1 and Aβ protein levels, and these rises were prevented by folic acid. In conclusion, these findings are consistent with a mechanism in which folic acid increases methylation potential and DNMT activity, modifies DNA methylation and ultimately decreases APP, PS1 and Aβ protein levels.

Lead-induced morphological changes and amyloid precursor protein accumulation in adult rat hippocampus

Lead is an important environmental pollutant that exerts potent toxic effects on many organs. The toxic effects of lead are less well known for adult brain than for children. We investigated the morphological changes and amyloid precursor protein (APP) accumulation in the adult rat hippocampus following exposure to lead. Forty rats were divided into two groups of 20. One group was exposed to 580 parts per million (ppm) lead acetate and other group to an identical concentration of sodium acetate as a control group. After exposure to lead for 3 months, the hippocampus was examined by electron microscopy and APP levels in the hippocampus were detected using immunohistochemistry. Lead levels in the blood of rats exposed to lead were significantly higher than in the controls. The morphological changes in the hippocampus included mitochondrial degeneration, apoptosis and abnormal synapses in the rats exposed to lead. APP in hippocampus was increased significantly in the group exposed to lead compared to controls. We determined that lead exposure causes accumulation of APP and morphological changes in the adult rat hippocampus.

Systemic immune challenges trigger and drive Alzheimer-like neuropathology in mice

BackgroundAlzheimer’s disease (AD) is the most prevalent form of age-related dementia, and its effect on society increases exponentially as the population ages. Accumulating evidence suggests that neuroinflammation, mediated by the brain’s innate immune system, contributes to AD neuropathology and exacerbates the course of the disease. However, there is no experimental evidence for a causal link between systemic inflammation or neuroinflammation and the onset of the disease.MethodsThe viral mimic, polyriboinosinic-polyribocytidilic acid (PolyI:C) was used to stimulate the immune system of experimental animals. Wild-type (WT) and transgenic mice were exposed to this cytokine inducer prenatally (gestation day (GD)17) and/or in adulthood. Behavioral, immunological, immunohistochemical, and biochemical analyses of AD-associated neuropathologic changes were performed during aging.ResultsWe found that a systemic immune challenge during late gestation predisposes WT mice to develop AD-like neuropathology during the course of aging. They display chronic elevation of inflammatory cytokines, an increase in the levels of hippocampal amyloid precursor protein (APP) and its proteolytic fragments, altered Tau phosphorylation, and mis-sorting to somatodendritic compartments, and significant impairments in working memory in old age. If this prenatal infection is followed by a second immune challenge in adulthood, the phenotype is strongly exacerbated, and mimics AD-like neuropathologic changes. These include deposition of APP and its proteolytic fragments, along with Tau aggregation, microglia activation and reactive gliosis. Whereas Aβ peptides were not significantly enriched in extracellular deposits of double immune-challenged WT mice at 15 months, they dramatically increased in age-matched immune-challenged transgenic AD mice, precisely around the inflammation-induced accumulations of APP and its proteolytic fragments, in striking similarity to the post-mortem findings in human patients with AD.ConclusionChronic inflammatory conditions induce age-associated development of an AD-like phenotype in WT mice, including the induction of APP accumulations, which represent a seed for deposition of aggregation-prone peptides. The PolyI:C mouse model therefore provides a unique tool to investigate the molecular mechanisms underlying the earliest pathophysiological changes preceding fibrillary Aβ plaque deposition and neurofibrillary tangle formations in a physiological context of aging. Based on the similarity between the changes in immune-challenged mice and the development of AD in humans, we suggest that systemic infections represent a major risk factor for the development of AD.

Nicotine modifies in vivo and in vitro rat hippocampal amyloid precursor protein processing in young but not old rats

Previous studies have shown that administration of nicotine modifies the expression and secretion of amyloid precursor protein (APP) in various cell lines. The present study investigated the extent to which chronic subcutaneous nicotine administration influences APP levels and processing in cerebral cortex, striatum and hippocampus of young and old rat brains. The results showed that constant nicotine infusion (0.25 or 4.00mg/kg/day) increased the levels of particulate APP (APPp) but not secreted APP (APPs) in the hippocampus of young rats in vivo. This response to nicotine was not observed in the striatum or cerebral cortex of young rats or in any of the brain regions examined in old animals. Subsequent in vitro analysis demonstrated that nicotine enhanced the release of APPs from hippocampal slice preparations and that this increase was attenuated by mecamylamine, a non-selective nicotinic acetylcholine receptor (nAChR) antagonist. The in vitro effect of nicotine on APPs was age-related, being only detected from hippocampal slices derived from the young but not the older animals. These results suggest that nicotine modulates APP expression and secretion in the hippocampus and that the responses observed to the drug are age-dependent being only detected in younger rats.

Activation of nicotinic cholinergic receptors modifies the processing of rat hippocampal amyloid precursor protein both in vivo and in vitro

oligomers on p75 expression in mouse hippocampus and SH-SY5Y cells. Methods: As-derived diffusible ligands (ADDLs) were prepared by incubation of As1-42 at 4 C for 24h. ADDLs were microinjected into mouse hippocampus region and 6-24 later hippocampus from ipsilateral and contra lateral sideswere analyzed. SH-SY5Ycells were treatedwithADDLs in the presence and absence of inhibitor and the effects on p75expression were determined. Results: Western blot analysis showed that ADDLs were heterogeneous mixtures, predominantly made up of As1-42 dimers and oligomers. After microinjection of ADDLs into mouse brain, p expression in ipsilateralhippocampus was increased by 1.4-fold in 24hrs compared to contra lateral hippocampus. No significant difference was observed at 6hrs. Anti-As antibody (6E10)-positive As1-42 was not detected in significant amounts in contralateralhippocampus by immunohistochemistry, suggesting that diffusion into the contralateral side from the injection site is limited. ADDLs (1 uM) increased (1.4-fold) p75 expression in SH-SY5Y cells 24hrs after incubation as previously reported. Insulin-like growth factor I receptor (IGF1R) is reported to be involved in the induction of p expression inSH-SY5Y cells. ADDL-induced p75 expression was inhibited by PPP, a selective IGF1R inhibitor. Moreover, ADDLs induced phosphorylation of IGF1R in SH-SY5Y cells in 30 min. Conclusions: The present study indicates that As1-42 oligomersinduce p75 NTR expression in mouse hippocampus and suggests that IGF1Rsignaling pathway contributes to As1-42 oligomer-mediated induction of p75 expression in neurons.

MicroRNA-101 Regulates Amyloid Precursor Protein Expression in Hippocampal Neurons

The amyloid precursor protein (APP) and its proteolytic product amyloid beta (Abeta) are associated with both familial and sporadic forms of Alzheimer disease (AD). Aberrant expression and function of microRNAs has been observed in AD. Here, we show that in rat hippocampal neurons cultured in vitro, the down-regulation of Argonaute-2, a key component of the RNA-induced silencing complex, produced an increase in APP levels. Using site-directed mutagenesis, a microRNA responsive element (RE) for miR-101 was identified in the 3'-untranslated region (UTR) of APP. The inhibition of endogenous miR-101 increased APP levels, whereas lentiviral-mediated miR-101 overexpression significantly reduced APP and Abeta load in hippocampal neurons. In addition, miR-101 contributed to the regulation of APP in response to the proinflammatory cytokine interleukin-1beta (IL-lbeta). Thus, miR-101 is a negative regulator of APP expression and affects the accumulation of Abeta, suggesting a possible role for miR-101 in neuropathological conditions.

Tetrahydroxy stilbene glucoside reduces the cognitive impairment and overexpression of amyloid precursor protein induced by aluminum exposure

Excessive aluminum (Al) exposure impairs neurocognitive function in humans and animals. Epidemiologic studies have shown a potential linkage between chronic Al exposure and Alzheimer's disease. The present study aims to evaluate the effects of tetrahydroxy stilbene glucoside (TSG), the extract from herbal medicine Polygoni Multiflori, on cognitive impairment and the over-expression of hippocampal amyloid precursor protein (APP) induced by chronic exposure to Al in rats. Rats were treated with 0.3% aluminum chloride (AlCl3) prepared in the drinking water for 90 d. AlCl3-treated animals were then randomly assigned to receive vehicle, TSG (4 g/kg), or Vitamin E (VE; 40 mg/kg) treatment for 5 months. VE served as a positive control. The effect of TSG was evaluated by passive avoidance task, and APP expression was evaluated by Western blotting. Following exposure to AlCl3 for 90 d, animals displayed a striking decrease (> 80%) in step-through latency in the passive avoidance task and a significant increase in the expression of APP in the hippocampus. Both TSG and VE significantly ameliorated the performance impairment in the passive avoidance task, and suppressed the over-expression of APP. Moreover, the effects of TSG, but not of VE, were in a time-dependent manner. TSG may possess therapeutic effects against Alzheimer's disease.

Abnormal APP, cholinergic and cognitive function in Ts65Dn Down's model mice

We evaluated Ts65Dn Down's syndrome mice and their littermates (LM) at 1–2, 4, and 12 months of age to determine amyloid precursor protein (APP)-related cellular and biochemical changes associated with cognitive deficits. Ts65Dn mice showed cognitive deficits in the Morris water maze compared to LM mice at 4 and 12 months of age. Ts65Dn, but not LM mice, developed a septohippocampal cholinergic neuronal degeneration of choline acetyltransferase (ChAT)-positive neurons at 12 months of age. These cellular changes were compensated by increases in ChAT enzyme activity of remaining cholinergic terminals in the hippocampus. By 12 months of age, Ts65Dn mice had elevations of APP protein levels in the hippocampus compared to their LM. At this age, both Ts65Dn mice and their LM abnormally responded to cholinergic muscarinic M1 agonist treatment in terms of hippocampal APP, nerve growth factor (NGF), and brain-derived neurotrophic factor (BDNF) levels compared to young adult C57BL/6 mice. In summary, the Ts65Dn mice show developmental and progressive age-related behavioral deficits, hippocampal APP, and cholinergic pathology. The relatively better cognitive spatial performance in LM compared to Ts65Dn mice suggests that high APP levels combined with progressive degeneration of the cholinergic system are critical to the pathology and cognitive deficits seen in Ts65Dn mice.

Apolipoprotein e4 decreases whereas apolipoprotein e3 increases the level of secreted amyloid precursor protein after closed head injury

Apolipoprotein E (apoE4) and head trauma are important genetic and environmental risk factors for Alzheimer's disease. Furthermore, apoE4 increases both the acute and chronic consequences of head trauma. The latter are associated with the deposition of amyloid-β, which is particularly elevated in apoE4 subjects. The short-term effects of head injury are associated with transiently increased metabolism of amyloid precursor protein (APP) and its secreted fragment, APPs. In the present study, we examined the possibility that the acute, short-term pathological effects of apoE4 following head trauma and the corresponding neuroprotective effects of apoE3 are related to isoform-specific effects of apoE on APP metabolism. Accordingly, male transgenic mice expressing human apoE3 or apoE4 on a null mouse apoE background and apoE-deficient and control mice were subjected to closed head injury (CHI). The resulting effects on brain APP, and on its secreted products, APPs and secreted product of the α-cleavage of APP (APPsα) were then determined 24 h following injury. Immunoblotting revealed no significant differences between the basal APP, APPs and APPsα levels of the hippocampus or the cortex of the control and the apoE3 and ApoE4 transgenic mice. The apoE-deficient mice also had similar cortical basal levels of APP and its metabolites, whereas their corresponding basal hippocampal APP and APPs levels were lower than those of the other groups. CHI lowered the hipppocampal APPs and APPsα levels of the apoE4 transgenic mice, whereas those of the apoE3 transgenic mice and of the control and apoE-deficient mice were not affected by this insult. In contrast, CHI raised the cortical APP and APPs levels of the apoE3 transgenic mice but had no significant effect on those of the other mice groups. These animal model findings suggest that the acute, short-term pathological effects of apoE4 following CHI and the corresponding neuroprotective effects of apoE3 may be mediated by their opposing effects on the expression and cleavage of cortical and hippocampal APP. Similar isoform-specific interactions between apoE and APP may play a role in the acute, short-term effects of head trauma in humans.

Fimbria–Fornix Lesion Does Not Affect APP Levels and Amyloid Deposition in the Hippocampus of APP+PS1 Double Transgenic Mice

The deposition of amyloid β peptides (Aβ) and cholinergic dysfunction are two characteristic features of Alzheimer's disease. Several studies have suggested that a compromised cholinergic transmission can increase the amount of amyloid precursor protein (APP) in the denervated cortex (or hippocampus); however, whether this will increase Aβ production is unknown. To investigate the relation between cholinergic neurotransmission and APP metabolism, and the possible role of cholinergic dysfunction in the development of amyloid neuropathology, we lesioned the fimbria–fornix pathway in APP+PS1 double transgenic mice, at 5 and 7 months of age. Three months and 11 months postlesion, the mice were sacrificed for biochemical and histopathological analyses. The fimbria–fornix transection resulted in a substantial depletion of cholinergic markers in the hippocampus at both time points. Three months postlesion, hippocampal APP and Aβ levels were not significantly changed. At 11 months postlesion, the fimbria–fornix lesion did not result in an alteration in either the hippocampal Aβ levels or the extent of Aβ deposition, as assessed by amyloid plaque counts and image analysis of Aβ load in the 18-month-old APP+PS1 mice. Our findings indicate that APP metabolism in mice may be dissociated from cholinergic neurotransmission rather than related as previously suggested in other mammalian species.

Spatial memory testing decreases hippocampal amyloid precursor protein in young, but not aged, female rats

Using young and aged rats, we investigated relationships between amyloid precursor protein (APP) and working or reference memory, as well as assessed whether cognitive testing altered APP levels. In young rats, higher APP levels were related to more working memory errors as a linear function. Aged rats exhibited a curvilinear relationship between APP and working memory, with moderate APP levels associated with better relative performance. A comparison of rats that received cognitive testing with those that did not showed that testing decreased APP levels in young, but not aged, rats. Collectively, the data suggest that young and aged rats exhibit different relationships between APP and working memory, and that aged rats do not maintain the capacity to decrease APP in response to cognitive testing.

Selective Antibody-Induced Cholinergic Cell and Synapse Loss Produce Sustained Hippocampal and Cortical Hypometabolism with Correlated Cognitive Deficits

The physiological interrelationships between cognitive impairments, neurotransmitter loss, amyloid processing and energy metabolism changes in AD, cholinergic dementia and Down's syndrome are largely unknown to date. This report contains novel studies into the association between cognitive function and cerebral metabolism after long-term selective CNS cholinergic neuronal and synaptic loss in a rodent model. We measured local cerebral rates of glucose utilization (14C-2-deoxyglucose) throughout the brains of awake rats 4.5 months after bilateral intraventricular injections of a cholinotoxic antibody directed against the low-affinity NGF receptor (p75 NGF) associated with cholinergic neurons (192 IgG-saporin). Permanent cholinergic synapse loss was demonstrated by [3H]-vesamicol in vitro autoradiography defining presynaptic vesicular acetylcholine (ACh) transport sites. While other metabolic studies have defined acute and transient glucose use changes after relatively nonspecific lesions of anatomical regions containing cholinergic neurons, our results show sustained reductions in glucose utilization in brain regions impacted by cholinergic synapse loss, including frontal cortical and hippocampal regions, relative to glucose use levels in control rats. In the same animals, impaired cognitive spatial performance in a Morris water maze was correlated with reduced glucose use rates in the cortex and hippocampus at this time point, which is consistent with increased postmortem cortical and hippocampal amyloid precursor protein (APP) levels (45, 46). These results are consistent with the view of cholinergic influence over metabolism, APP processing, and cognition in the cortex and hippocampus.