Neuroinflammation-induced acceleration of amyloid deposition in the APPV717F transgenic mouse

It has been postulated that neuroinflammation plays a critical role in the pathogenesis of Alzheimer's disease (AD). To directly test whether an inflammatory stimulus can accelerate amyloid deposition in vivo, we chronically administered the bacterial endotoxin, lipopolysaccharide (LPS), intracerebroventricularly (i.c.v.) to 2-month-old APPV717F+/+ transgenic (TG) mice, which overexpress a mutant human amyloid precursor protein (APP 717V-F) with or without apolipoprotein E (apoE) for 2 weeks. Two weeks following central LPS administration a striking global reactive astrocytosis with increased GFAP immunoreactivity was found throughout the brains of all LPS-treated wild-type and transgenic mice including the contralateral brain hemisphere. Localized microglial activation was also evident from lectin immunostaining adjacent to the cannula track of LPS-treated mice. Quantification of thioflavine-S-positive Abeta deposits revealed a marked acceleration of amyloid deposition in LPS-treated APPV717F+/+-apoE+/+ mice compared to nontreated or vehicle-treated APPV717F+/+-apoE+/+ mice (P = 0.005). By contrast, no amyloid deposits were detected by thioflavine-S staining in LPS or vehicle-treated apoE-deficient APPV717F TG mice. Our data suggest that neuroinflammation can accelerate amyloid deposition in the APPV717F+/+ mouse model of AD and that this process requires the expression of apoE.     

Behavioral deficits in APP(V717F) transgenic mice deficient for the apolipoprotein E gene

Both the beta-amyloid precursor protein (APP) and the apoliprotein E (apoE) genes are involved in the pathogenesis of Alzheimer's disease (AD). We previously showed that mice over-expressing a human mutated form of APP (APP(V717F)) display age-dependent recognition memory deficits associated with the progression of amyloid deposition. Here, we asked whether 10- to 12-month-old APP(V717F) mice lacking the apoE gene, which do not present obvious amyloid deposition, differ from APP(V717F) mice in the object recognition task. The recognition performance is decreased in both transgenic mouse groups compared to control groups. Moreover, some behavioral disturbances displayed by APP mice lacking apoE are even more pronounced than those of APP mice expressing apoE. Our results suggest that the recognition memory deficits are related to high levels of soluble Abeta rather than to amyloid deposits.     

Reducing human apolipoprotein E levels attenuates age-dependent Aβ accumulation in mutant human amyloid precursor protein transgenic mice

Apolipoprotein E4 (apoE4) plays a major role in the pathogenesis of Alzheimer's disease. Brain amyloid-β (Aβ) accumulation depends on age and apoE isoforms (apoE4 > apoE3) both in humans and in transgenic mouse models. Brain apoE levels are also isoform dependent, but in the opposite direction (apoE4 < apoE3). Thus, one prevailing hypothesis is to increase brain apoE expression to reduce Aβ levels. To test this hypothesis, we generated mutant human amyloid precursor protein transgenic mice expressing one or two copies of the human APOE3 or APOE4 gene that was knocked in and flanked by LoxP sites. We report that reducing apoE3 or apoE4 expression by 50% in 6-month-old mice results in efficient Aβ clearance and does not increase Aβ accumulation. However, 12-month-old mice with one copy of the human APOE gene had significantly reduced Aβ levels and plaque loads compared with mice with two copies, regardless of which human apoE isoform was expressed, suggesting a gene dose-dependent effect of apoE on Aβ accumulation in aged mice. Additionally, 12-month-old mice expressing one or two copies of the human APOE4 gene had significantly higher levels of Aβ accumulation and plaque loads than age-matched mice expressing one or two copies of the human APOE3 gene, suggesting an isoform-dependent effect of apoE on Aβ accumulation in aged mice. Moreover, Cre-mediated APOE4 gene excision in hippocampal astrocytes significantly reduced insoluble Aβ in adult mice. Thus, reducing, rather than increasing, apoE expression is an attractive approach to lowering brain Aβ levels.     

Dendritic spine loss in the hippocampus of young PDAPP and Tg2576 mice and its prevention by the ApoE2 genotype

Postmortem AD brains exhibit dendritic spine loss in the hippocampus. To determine whether this pathology may be associated with amyloid burden, the present study used the Golgi stain technique to assess age- and genotype-dependent changes in dendritic spine density in CA1 hippocampus of two transgenic mouse lines that produce high levels of Abeta. Tg2576 and PDAPP mice, as well as a group of Tg2576 mice crossed with human apoE2-expressing transgenic mice, were compared to respective transgene-negative controls. Since the time course of amyloid plaque deposition in the PDAPP and Tg2576 mice is well characterized, we examined changes in spine density at ages that corresponded to different levels of amyloid plaque load. The data show age- and genotype-dependent reductions in spine density in both Tg2576 and PDAPP mice, albeit at somewhat different time courses. The spine loss occurred prior to plaque deposition and was ameliorated by the overexpression of human apoE2. These results suggest that a soluble Abeta species may affect hippocampal synapses and thereby contribute to functional deficits evident in these animals.     

Amyloid beta40/42 clearance across the blood-brain barrier following intra-ventricular injections in wild-type,apoE knock-out and human apoE3 or E4 expressing transgenic mice

An important event in the pathogenesis of Alzheimer's disease (AD) is the deposition of the amyloid beta (Abeta)1-40 and 1-42 peptides in a fibrillar form, with Abeta42 typically having a greater propensity to undergo this conformational change. A major risk factor for late-onset AD is the inheritance of the apolipoprotein E (apoE) 4 allele [3,14,31]. We previously proposed that apoE may function as a "pathological chaperone" in the pathogenesis of AD (i.e. modulate the structure of Abeta, promoting or stabilizing a beta-sheet conformation), prior to the discovery of this linkage [7,40,41,42]. Data from apoE knockout / AbetaPP^(V717F) mice, has shown that the presence of apoE is necessary for cerebral amyloid formation [1,2], consistent with our hypothesis. However, in betaPP^(V717F) mice expressing human apoE3 or E4 early Abeta deposition at 9 months is suppressed, but by 15 months both human apoE expressing mice had significant fibrillar Abeta deposits with the apoE4 expressing mice having a 10 fold greater amyloid burden [8,9]. This and other data has suggested that apoE, in addition to having a facilitating role in fibril formation, may also influence clearance of Abeta peptides. In order to address if apoE affects the clearance of Abeta peptides across the blood-brain barrier (BBB) and whether there are differences in the clearance of Abeta40 versus Abeta42, we performed stereotactic, intra-ventricular micro-injections of Abeta40, Abeta42 or control peptides in wild-type, apoE knock-out (KO) or human apoE3 or apoE4 expressing transgenic mice. We found that consistent with other studies [5], Abeta40 is rapidly cleared from the brain across the BBB; however, Abeta42 is cleared much less effectively. This clearance of exogenous Abeta peptides across the BBB does not appear to be affected by apoE expression. This data suggests that Abeta42 production may favor amyloid deposition due to a reduced clearance across the BBB, compared to Abeta40. In addition, our experiments support a role of apoE as a pathological chaperone, and do not suggest an isotype specific role of apoE in exogenous Abeta peptide clearance from the CSF across the BBB.     

Apolipoprotein E affects the amount, form, and anatomical distribution of amyloid β-peptide deposition in homozygous APPV717F transgenic mice

Apolipoprotein E (apoE) has been implicated as a risk factor for Alzheimer’s disease and in the deposition, fibrillogenesis, and clearance of the amyloid β-peptide (Aβ). To examine the in vivo interactions between apoE and Aβ deposition, we examined 12-month-old transgenic (tg) mice expressing human amyloid precursor protein (APP) with the V717F mutation (APP^V717F homozygous) on an APOE null background. Elimination of APOE resulted in a redistribution and alteration in the character of Aβ deposition in homozygous APP^V717F tg mice, with a dramatic reduction in cortical and dentate gyrus deposition, prominent increase in diffuse CA1 and CA3 deposition, and prevention of the formation of thioflavin-S-positive deposits. These alterations in Aβ deposition were not mediated by significant changes in regional APP expression, low-density lipoprotein receptor-related protein expression, or soluble Aβ levels. Thus, apoE in APP^V717F tg mice not only affects the amount and form of Aβ deposition, but also the anatomical distribution of diffuse Aβ deposits. The APP^V717F tg mouse can serve as a model to investigate genetic influences on the vulnerability of specific neuroanatomical regions to Aβ deposition. Received: 11 April 2000 / Revised, accepted: 25 May 2000     

Human and murine ApoE markedly alters A beta metabolism before and after plaque formation in a mouse model of Alzheimer's disease

The epsilon4 allele of apolipoprotein E (apoE) is a risk factor for Alzheimer's disease (AD), perhaps through effects on amyloid-beta (Abeta) metabolism. Detailed analyses of various Abeta parameters in aging APP(V717F+/-) transgenic mice expressing mouse apoE, no apoE, or human apoE2, apoE3, or apoE4 demonstrate that apoE facilitates, but is not required for, Abeta fibril formation in vivo. Human apoE isoforms markedly delayed Abeta deposition relative to mouse apoE, with apoE2 (and apoE3 to a lesser extent) having a prolonged ability to prevent Abeta from converting into fibrillar forms. Isoform-specific effects of human apoE on Abeta levels and neuritic plaque formation mimicked that observed in AD (E4 > E3 > E2). Importantly, observation of an apoE-dependent decrease in percent soluble Abeta and enrichment of Abeta in membrane microdomains prior to Abeta deposition indicates that apoE influences Abeta metabolism early in the amyloidogenic process and provides a possible novel mechanism by which apoE affects AD pathogenesis.     

Behavioral phenotype and BDNF differences related to apoE isoforms and sex in young transgenic mice

Human apolipoprotein E (apoE) plays an important role in lipid transport and distribution, being involved in neurite growth and neuroprotection in the brain. In humans, the apoE4 isoform is a risk factor for developing Azheimer's disease (AD), while apoE2 seems to provide neuroprotection. However, very little information is available on apoE2 genotype. In the present study, we have characterized behavioral and learning phenotypes in young transgenic mice apoE2, apoE3 and apoE4 of both sexes. We have also determined the levels of brain-derived neurotrophic factor (BDNF) and its receptor TrkB in cortex and hippocampus of male and female mice carrying either genotype. Our results show a worse performance of apoE4 and apoE2 mice in the acquisition of a spatial task compared to apoE3 mice, and a worse retention in apoE2 mice compared to the other two genotypes. On the other hand, an increase in the exploration of an open-field, which is compatible with a hyperactive behavior, was found in apoE2 females, while a decreased activity was observed in apoE4 mice. Increased BDNF levels in the frontal cortex were observed in apoE2 mice compared to apoE3. These results underscore behavioral differences between apoE genotypes in young mice, as well as the existence of interactions between genotype and gender, providing new valuable information on the apoE2 genotype.     

Modulation of apolipoprotein D and apolipoprotein E expression in rat hippocampus after entorhinal cortex lesion.

Apolipoprotein (apo) D is a member of the lipocalin family of proteins. Although its physiological function is unknown, apoD is thought to transport one or more small hydrophobic ligands. A second apolipoprotein, apoE is known to play an important role in lipid transport, and apoE genetic polymorphism has been shown to be associated with susceptibility to Alzheimer's disease. Both apoD and apoE are expressed in the central nervous system (CNS) and both proteins accumulate at sites of peripheral nerve injury due to increased local synthesis. The two proteins may have overlapping or complementary functions within nervous tissue. In order to define the role of apoD within the CNS, we have studied the regional distribution of apoD and apoE mRNA and protein within the normal rat brain and the changes in apoD and apoE expression in the hippocampus of rats after entorhinal cortex lesion (EC lesion). Within the brains of normal rats, apoD expression in the hippocampus was as high as 180-fold that of the liver. ApoD mRNA levels in other areas of the rat brain ranged from 40 to 120 times the hepatic levels. The distribution of apoE gene expression within the brain was similar to that of apoD, but was much lower than hepatic apoE expression. When rats were subjected to EC lesion, the apoD message increased by 54% at 4 days post lesion (DPL) in the ipsilateral region of hippocampus while apoE mRNA levels (ipsilateral and contralateral) decreased by 43%. At 6 to 8 DPL apoD mRNA in the ipsilateral hippocampus remained elevated (42% above controls) whereas the apoE mRNA levels increased to about 15% above those of controls. At 14 and 31 DPL, both apoD and apoE expression was similar to controls. The increase in immunoreactive apoD in hippocampal extracts was more dramatic. At 1 DPL, immunoreactive apoD levels were already 16-fold higher than those in extracts of non-lesioned animals and, at 31 DPL, levels were still 8-fold higher than those of control animals. Finally, we have demonstrated that the levels of apoD in the brains of apoE-deficient mice are 50-fold those of wildtype control mice. ApoD clearly has an important function within the CNS in both normal and pathological situations.     

The PDAPP mouse model of Alzheimer's disease: locus coeruleus neuronal shrinkage

Alzheimer's disease is characterized by neuronal degeneration in the cerebral cortex and hippocampus and subcortical neuronal degeneration in such nuclei as the locus coeruleus (LC). Transgenic mice overexpressing mutant human amyloid precursor protein V717F, PDAPP mice, develop several Alzheimer's disease-like lesions. The present study sought to determine whether there is also loss of LC noradrenergic neurons or evidence of degenerative changes in these animals. PDAPP hemizygous and wild-type littermate control mice were examined at 23 months of age, at a time when there are numerous amyloid-beta (Abeta) plaques in the neocortex and hippocampus. Tissue sections were stained immunohistochemically with an antibody against tyrosine hydroxylase (TH) to identify LC neurons. Computer imaging procedures were used to count the TH-immunoreactive somata in sections through the rostral-caudal extent of the nucleus. There was no loss of LC neurons in the hemizygous mice. In a second experiment, homozygous PDAPP and wild-type mice were examined, at 2 months and 24 months of age. Again there was no age-related loss of neurons in the homozygous animals. In the portion of the LC where neurons reside that project to the cortex and hippocampus, however, the neurons were decreased in size selectively in the 24-month-old transgenic animals. These data indicate that overt LC cell loss does not occur following abundant overexpression of Abeta peptide. However, the selective size reduction of the LC neuronal population projecting to cortical and hippocampal regions containing Abeta-related neuropathology implies that these cells may be subjected to a retrograde-mediated stress.     

Early dysregulation of hippocampal proteins in transgenic rats with Alzheimer's disease-linked mutations in amyloid precursor protein and presenilin 1

The response of the hippocampal proteome to expression of mutant proteins present in familial forms of Alzheimer's disease (AD) was studied using transgenic rats. These animals carry both the amyloid precursor protein Swedish and 717 mutation (APP(SW+717)) as well as the presenilin 1 Finnish mutation (PS1(FINN)). This transgenic rat model displays intracellular amyloid beta (Abeta) in neurons of the neocortex and the hippocampus (CA2 and CA3). The hippocampus was selected as it is one of the first brain regions affected in AD and is involved in the processing of short-term memory and spatial memory. Applying a proteomic approach, we demonstrate that the expression of APP(SW+717) and PS1(FINN) transgenes causes changes in expression of hippocampal proteins, some of which have been previously linked to learning and memory formation. The protein alterations documented here occur in the absence of plaque formation and prior to the onset of cognitive deficits later observed in these transgenic rats. This indicates that molecular changes take place in the hippocampal neurons in response to expression of mutant proteins APP(SW+717) and PS1(FINN), which precede the occurrence of overt extracellular accumulation of extracellular amyloid. The implications of these findings on our understanding of the early stages of AD are discussed.     

Human apoE3 but not apoE4 rescues impaired astrocyte activation in apoE null mice

The allele E4 of apolipoprotein E (apoE) is an important risk factor for Alzheimer's disease (AD) and the chronic brain inflammation which is associated with AD is more pronounced in subjects who carry this allele. In the present study, we employed mice transgenic for the human apoE isoforms apoE3 or apoE4 on a null mouse apoE background and intracerebroventricular injection of LPS to investigate the possibility that the regulation of brain inflammation is affected by the apoE genotype. LPS treatment of control mice resulted in activation of brain astrocytes and microglia whose extent decreased with age. LPS treatment of 6-month-old apoE transgenic and control mice resulted in marked activation of brain astrocytes in the control and apoE3 transgenic mice but had no effect on astrogliosis of age-matched apoE-deficient and apoE4 transgenic mice. In contrast, there were no significant differences between the levels of activated microglia of the apoE3 and apoE4 transgenic mice following LPS treatment. Immunoblot assays revealed that the apoE4 and apoE3 transgenic mice had the same levels of brain apoE, which were similarly increased following LPS treatment. These results show that LPS-induced astrogliosis in apoE transgenic mice is regulated isoform-specifically by apoE3 and not by apoE4 and suggest that similar mechanisms may mediate the phenotypic expression of the apoE4 genotype in AD and in other neurodegenerative diseases.     

High frequency stimulation of the subthalamic nucleus impacts adult neurogenesis in a rat model of Parkinson's disease

APP.V717I and Tau.P301L transgenic mice develop Alzheimer's disease pathology comprising important aspects of human disease including increased levels of amyloid peptides, cognitive and motor impairment, amyloid plaques and neurofibrillary tangles. The combined model, APP.V717I × Tau.P301L bigenic mice (biAT mice) exhibit aggravated amyloid and tau pathology with severe cognitive and behavioral defects. In the present study, we investigated early changes in synaptic function in the CA1 and CA3 regions of acute hippocampal slices of young APP.V717I, Tau.P301L and biAT transgenic animals. We have used planar multi-electrode arrays (MEA) and improved methods for simultaneous multi-site recordings from two hippocampal sub-regions. In the CA1 region, long-term potentiation (LTP) was severely impaired in all transgenic animals when compared with age-matched wild-type controls, while basal synaptic transmission and paired-pulse facilitation were minimally affected. In the CA3 region, LTP was normal in Tau.P301L and APP.V717I but clearly impaired in biAT mice. Surprisingly, frequency facilitation in CA3 was significantly enhanced in Tau.P301L mice, while not affected in APP.V717I mice and depressed in biAT mice. The findings demonstrate important synaptic changes that differ considerably in the hippocampal sub-regions already at young age, well before the typical amyloid or tau pathology is evident.     

Impaired eyeblink conditioning and decreased hippocampal volume in PDAPP V717F mice

We examined heterozygous transgenic (Tg) mice that overexpress V717F amyloid precursor protein (APP) for delay eyeblink conditioning (EBC) and hippocampal volume with magnetic resonance imaging (MRI). Platelet-derived APP mice were significantly impaired on EBC relative to wild type (WT) litter-mate controls. T2-weighted spin echo images (62.5 x 125 x 500 microm) of the same mice were acquired under anesthesia using a 9.4T magnet. Tg mice had hippocampal to brain volume ratios that were significantly smaller than WT controls (31% smaller in the rostral dorsal hippocampus, 13-22% smaller among equal dorsal-ventral thirds of a caudal section). These results indicate that overexpression of APP or beta amyloid profoundly affects learning and memory and hippocampal volume. The results also indicate that eyeblink conditioning and quantitative MRI in mice may be useful assays to follow the progression of disease-related changes, and to test the effectiveness of potential therapeutics against Alzheimer's disease.     

Aging increased amyloid peptide and caused amyloid plaques in brain of old APP/V717I transgenic mice by a different mechanism than mutant presenilin1.

Aging of transgenic mice that overexpress the London mutant of amyloid precursor protein (APP/V717I) (Moechars et al., 1999a) was now demonstrated not to affect the normalized levels of alpha- or beta-cleaved secreted APP nor of the beta-C-terminal stubs. This indicated that aging did not markedly disturb either alpha- or beta-secretase cleavage of APP and failed to explain the origin of the massive amounts of amyloid peptides Abeta40 and Abeta42, soluble and precipitated as amyloid plaques in the brain of old APP/V717I transgenic mice. We tested the hypothesis that aging acted on presenilin1 (PS1) to affect gamma-secretase-mediated production of amyloid peptides by comparing aged APP/V717I transgenic mice to double transgenic mice coexpressing human PS1 and APP/V717I. In double transgenic mice with mutant (A246E) but not wild-type human PS1, brain amyloid peptide levels increased and resulted in amyloid plaques when the mice were only 6-9 months old, much earlier than in APP/V717I transgenic mice (12-15 months old). Mutant PS1 increased mainly brain Abeta42 levels, whereas in aged APP/V717I transgenic mice, both Abeta42 and Abeta40 increased. This resulted in a dramatic difference in the Abeta42/Abeta40 ratio of precipitated or plaque-associated amyloid peptides, i.e., 3.11+/-0.22 in double APP/V717I x PS1/A246E transgenic mice compared with 0.43 +/- 0.07 in aged APP/V717I transgenic mice, and demonstrated a clear difference between the effect of aging and the effect of the insertion of a mutant PS1 transgene. In conclusion, we demonstrate that aging did not favor amyloidogenic over nonamyloidogenic processing of APP, nor did it exert a mutant PS1-like effect on gamma-secretase. Therefore, the data are interpreted to suggest that parenchymal and vascular accumulation of amyloid in aging brain resulted from failure to clear the amyloid peptides rather than from increased production.     

Overexpression of apolipoprotein E4 increases kainic-acid-induced hippocampal neurodegeneration

Apolipoprotein E (apoE) has an intricate biological function in modulating immune responses and apoE isoforms exhibit diverse effects on neurodegenerative and neuroinflammatory disorders. In the present study, we investigated the individual roles of apoE isoforms in the kainic acid (KA)-induced hippocampal neurodegeneration with focus on immune response and microglia functions. ApoE2, 3 and 4 transgenic mice as well as wild-type (WT) mice were treated with KA by intranasal route. ApoE4 overexpressing mice revealed several peculiarities as compared with other transgenic mice and WT mice, i.e. (1) they had more severe KA-induced seizures than apoE2 and 3 mice, (2) they exhibited neuron loss in hippocampus that was higher than in apoE2, 3 and WT mice, (3) KA administration resulted in higher counts of their head drops in the cross-area of elevated plus-maze, (4) they showed lower KA-induced rearing activity than apoE2 mice in the open-field test, (5) their KA-induced microglial expression of MHC-II and CD86 was elevated compared to apoE3 mice, (6) the KA-induced increase of microglial iNOS was higher than that in the other groups of mice, and (7) the TNF-α and IL-6 expression was decreased 7 days after KA application compared to untreated mice and mice treated 1 day with KA. However, the signaling pathway of NFκB or Akt seemed not to be involved in apoE-isoform dependent susceptibility to KA-induced neurotoxicity. In conclusion, over-expression of apoE4 deteriorated KA-induced hippocampal neurodegeneration in C57BL/6 mice, which might result from a higher up-regulation of microglia activation compared to apoE2 and 3 transgenic mice and WT mice.     

ApoE4 impairs hippocampal plasticity isoform-specifically and blocks the environmental stimulation of synaptogenesis and memory

Alzheimer's disease (AD) is associated with genetic risk factors, of which the allele E4 of apolipoprotein E (apoE4) is the most prevalent, and is affected by environmental factors that include education early in life and socioeconomic background. The extent to which environmental factors affect the phenotypic expression of the AD genetic risk factors is not known. Here we show that the neuronal and cognitive stimulations, which are elicited by environmental enrichment at a young age, are markedly affected by the apoE genotype. Accordingly, exposure to an enriched environment of young mice transgenic for human apoE3, which is the benign AD apoE allele, resulted in improved learning and memory, whereas mice transgenic for human apoE4 were unaffected by the enriched environment and their learning and memory were similar to those of the nonenriched apoE3 transgenic mice. These cognitive effects were associated with higher hippocampal levels of the presynaptic protein synaptophysin and of NGF in apoE3 but not apoE4 transgenic mice. In contrast, cortical synaptophysin and NGF levels of the apoE3 and apoE4 transgenic mice were similarly elevated by environmental enrichment. These findings show that apoE4 impairs hippocampal plasticity and isoform-specifically blocks the environmental stimulation of synaptogenesis and memory. This provides a novel mechanism by which environmental factors can modulate the function and phenotypic expression of the apoE genotype.     

BACE/APPV717F double-transgenic mice develop cerebral amyloidosis and inflammation

Most of the transgenic mice generated to model Alzheimer's disease express human amyloid precursor protein (APP) mutants alone or in conjunction with presenilin mutants. We have generated a mouse model by overexpressing human BACE and human APP with the V717F mutation. The combination of a mutation at the gamma-secretase cleavage site of APP and of increased beta-secretase activity should favour the production of amyloid peptides. We analysed double BACE/APPIn and single APPIn transgenic mice at 16-18 months for amyloid load, brain histopathology and behavioural deficits. We show that overexpression of BACE induces an increase in APP CTFbeta and total brain Abeta peptides. Brain histopathology shows clearly enhanced amyloid deposits in the cortex, hippocampus and in brain vasculature when compared to single APPIn transgenic mice. Amyloid deposits are mostly diffuse and predominantly composed of Abeta(42). A strong inflammatory reaction is evidenced by the presence of microglial cells around the most mature amyloid deposits and astrocytosis over the entire cerebral cortex. At the same age, the APPIn single-transgenic mice show only very limited pathology. When assessed for their cognitive performance at 12 months, BACE/APPIn mice show impaired spatial acquisition in the Morris water maze test. However, these deficits are not greater than those observed in the APPIn single-transgenic animals.     

Time course of response to estradiol replacement in ovariectomized mice: brain apolipoprotein E and synaptophysin transiently increase and glial fibrillary acidic protein is suppressed

The current study examined the effect of long-term estradiol replacement in ovariectomized mice. Estradiol-17beta (E2) pellets or vehicle pellets were implanted at the time of ovariectomy (OVX) in young adult female mice. Five mice from each group were sacrificed at 5, 14, 28 and 49 days after OVX and pellet replacement. Western blotting of homogenates from somatosensory cortex, hippocampus, olfactory bulb and cerebellum was performed to obtain concentrations of glial fibrillary acidic protein (GFAP), apolipoprotein E (apoE) and synaptophysin (SYN). At 5 days after OVX, GFAP levels were not affected by E2 replacement. In contrast to GFAP, synaptophysin and apoE concentrations were significantly elevated by 15% and 25%, respectively, in the E2-replaced group compared to the vehicle-replaced group at 5 days but by 14 days concentrations were equivalent. Late in the time course of this study, at 49 days, GFAP concentrations were higher in the E2-deprived mice but did not increase in the E2-replaced group. Immunocytochemistry for GFAP confirmed this observation. Of note was that these effects occurred in all four brain regions measured. These observations suggest that estradiol is able to suppress reactive gliosis. In addition, E2 replacement in OVX mice is associated with transiently higher levels of apoE and synaptophysin.