Human apolipoprotein E4 accelerates beta-amyloid deposition in APPsw transgenic mouse brain

The human apolipoprotein E4 (ApoE4) isoform is associated with genetic risk for Alzheimer's disease. To assess the effects of different ApoE isoforms on amyloid plaque formation, human ApoE3 and ApoE4 were expressed in the brains of transgenic mice under the control of the human transferrin promoter. Mice were crossed with transgenic mice expressing human amyloid precursor protein containing the Swedish mutation (APPsw), which facilitates amyloid beta peptide (A beta) production. The following progeny were selected for characterization: APPsw+/- x ApoE3+/- and APPsw+/-, APPsw+/- x ApoE4+/- and APPsw+/- littermates. All mice analyzed were wild type for the endogenous mouse APP and ApoE genes. Mice expressing ApoE4 in combination with APPsw have accelerated A beta deposition in the brain as assessed by enzyme immunoassay for A beta40 and A beta42 extractable in 70% formic acid, by assessment of amyloid plaque formation using thioflavin-S staining, and by immunohistochemical staining with antibodies specific for A beta40 or A beta42 and the 4G8 monoclonal or 162 polyclonal antibody. No difference in the rate of A beta deposition in the brain was seen in mice expressing ApoE3 in combination with APPsw. Thus, our data are consistent with the observation in Alzheimer's disease that ApoE4 is associated with increased accumulation of A beta in the brain relative to ApoE3.     

Nilvadipine antagonizes both Abeta vasoactivity in isolated arteries, and the reduced cerebral blood flow in APPsw transgenic mice

The development of Alzheimer's disease (AD) is generally thought to correlate with cerebral accumulation of Abeta. It has previously been shown that Abeta peptides enhance vasoconstriction in isolated arteries and oppose certain vasorelaxants. Moreover, exogenous application of Abeta peptides causes cerebral vasoconstriction in rodents and in transgenic mouse models of AD that overexpress Abeta there is reduced cerebral blood flow. In the present study, we investigated the effect of nilvadipine, a dihydropyridine-type calcium channel blocker, on Abeta induced vasoconstriction in isolated arteries and in vivo on cerebral blood flow (CBF) of an AD transgenic mouse model overexpressing Abeta (Tg APPsw line 2576). Nilvadipine completely inhibited the vasoactivity elicited by Abeta in rat aortae and in human middle cerebral arteries. The effect of a short treatment duration (2 weeks) with nilvadipine on regional CBF was investigated in 13-month-old Tg APPsw mice and control littermates using a laser Doppler imager. Additionally, CBF was also measured in 20-month-old Tg APPsw mice and control littermates that were chronically treated with nilvadipine for 7 months. Untreated Tg APPsw mice showed a reduction of regional CBF compared to their untreated control littermates. Nilvadipine restored cortical perfusion levels in Tg APPsw to values similar to those observed in control littermates without notably affecting the CBF of control mice. All together, these data suggest that nilvadipine might be useful for the treatment of oligemia associated with AD.     

Neuropathological Characterization of Mutant Amyloid Precursor Protein Yeast Artificial Chromosome Transgenic Mice

Mutations in the amyloid precursor protein (APP) gene result in elevated production and deposition of the 42 amino acid beta-amyloid (Abeta1-42) peptide and early-onset Alzheimer's disease (AD). To accurately examine the effect of the APP FAD mutations in vivo, we introduced yeast artificial chromosomes (YACs) containing the entire genomic copy of human APP harboring FAD mutations into transgenic mice. Our current results demonstrate that mutant APP YAC transgenic mice exhibit many features characteristic of human AD, including regional deposition of Abeta with preferential deposition of Abeta1-42, extensive neuritic abnormalities as evidenced by staining with APP, ubiquitin, neurofilament, and hyperphosphorylated tau antibodies, increased markers of inflammation, and the overlapping deposition of Abeta with apolipoproteins E and J. Our results also suggest that APP YAC transgenic mice possess unique pathological attributes when compared to other transgenic mouse models of AD that may reflect the experimental design of each model.     

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.     

Lipoprotein effects on Abeta accumulation and degradation by microglia in vitro.

An inflammatory response involving activated microglia in neuritic beta-amyloid plaques is found in Alzheimer's disease (AD) brain. Because HDL lipoproteins have been shown to carry the beta-amyloid peptide (Abeta) in plasma and CSF, we have investigated the influence of plasma high-density lipoprotein (HDL) and lipidated ApoE and ApoJ particles on the interaction of cultured rat microglia with Abeta1-42. Microglia degraded Abeta via a pathway sensitive to cytochalasin D and the scavenger receptor inhibitor, fucoidan. HDL increased the degradation of Abeta and the ratio of multimeric/monomeric Abeta in a dose-dependent manner. In contrast, lipidated ApoJ and ApoE decreased the degradation of Abeta, and the effects were ApoE isoform-dependent. Immuno-electron microscopy revealed internalized Abeta in endosomes and lysosomes as well as cell-associated Abeta in deep invaginations, which may be related to caveolae and surface-connected compartments. These data suggest that lipoprotein-dependent Abeta trafficking to microglia could be relevant to plaque pathogenesis in AD.     

Cholinergic neuropathology in a mouse model of Alzheimer's disease

Transgenic mice overexpressing mutant human amyloid precursor protein (PDAPP mice) develop several Alzheimer's disease (AD)-like lesions including an age-related accumulation of amyloid-beta (Abeta)-containing neuritic plaques. Although aged, heterozygous PDAPP mice also exhibit synaptic and glial cell changes characteristic of AD pathology, no evidence of widespread neuronal loss has been observed. The present study sought to determine whether homozygous PDAPP mice, which express very high levels of Abeta peptide, exhibit AD-like cholinergic degenerative changes, and whether the changes parallel the deposition of Abeta plaques. Mice were examined at 2 and 4 months and at 1 and 2 years of age. There was an age-related increase in the density of Abeta plaques in the cortex and hippocampus of the PDAPP animals; at 4 months of age there were very few plaques, and at 2 years there was a very high density of plaques. There was an age-related reduction in the density of cholinergic nerve terminals in the cerebral cortex; at 2 months there was a normal density of nerve terminals, but as early as age 4 months there was an approximately 50% reduction. However, at age 2 years there was no difference in the number or size of basal forebrain cholinergic somata compared with 2-month-old PDAPP mice. These data indicated that the homozygous PDAPP mouse exhibits cholinergic nerve terminal degenerative pathology and that the cortical neurodegenerative changes occur before the deposition of Abeta-containing neuritic plaques.     

Apolipoprotein Serum Amyloid A in Alzheimer's Disease

Alzheimer's disease is characterized by the tissue deposition of beta-amyloid peptide (Abeta) in the brain. Recent studies have shown apoproteins (apo) in amyloid plaques and associated with high-density lipoprotein (HDL) particles in the cerebrospinal fluid (CSF). Western blot analysis revealed that serum amyloid A (apoSAA) protein was present in control and AD patients at low levels compared to apoE and apoA-I, however, AD brains showed a significant increase over control values. Analysis of CSF-HDL from control and AD individuals showed that apoA-I, apoE and apoSAA were on the particle. Immuno-cytochemical analysis showed that SAA was detected in senile plaques in AD tissue, but was predominantly localized to neuritic plaques. ApoE staining of AD brain confirmed that most plaques contained the apoprotein, similar to Abeta immunoreactivity, whereas apoA-I expressed little staining of senile plaques. No significant differences were detected in the level of apoSAA when compared to APOE genotype in AD samples, suggesting that interactions with apoE were non-specific. These data imply that the specific interactions of SAA with Abeta in the neuritic plaques may play a role in AD.     

CD40 promotion of amyloid beta production occurs via the NF-kappaB pathway

The CD40 receptor is a member of the tumor necrosis factor (TNF) super-family of trans-membrane receptors. Interaction of CD40 with its ligand CD40L mediates a broad range of immune and inflammatory responses in the periphery and in the central nervous system. Recently it has been suggested that CD40/CD40L interaction is involved in amyloid precursor protein (APP) processing and Alzheimer's disease (AD)-like pathology in transgenic mouse models of AD. We have previously shown that pharmacologically inhibiting CD40/CD40L interaction improves memory deficits in the PSAPP AD mouse model. We have also recently shown that CD40 deficiency mitigates amyloid deposition in APPsw and PSAPP mouse models. In the present report, using human embryonic kidney cells (HEK293) over-expressing both the APPsw mutation and CD40, we demonstrate that CD40/CD40L interaction directly increases the production of APP metabolites (Abeta 1-40, Abeta 1-42, CTFs, sAPPbeta and sAPPalpha). The results also show that CD40/CD40L interaction affects APP processing via the NF-kappaB pathway. Using NFkappaB inhibitors and SiRNAs to silence diverse elements of the NFkappaB pathway, we observe a reduction in levels of both Abeta 1-40 and Abeta 1-42. Taken together, our results further suggest that CD40L stimulation may be a key component in AD pathology and that elements of the NF-kappaB pathway may be suitable targets for therapeutic approaches against AD.     

Alzheimer beta amyloid deposition enhanced by apoE epsilon4 gene precedes neurofibrillary pathology in the frontal association cortex of nondemented senior subjects.

To clarify how Alzheimer disease pathology develops in the brains of nondemented subjects, we examined the interrelations among the amounts and morphology of Abeta deposition, neurofibrillary pathology, and apolipoprotein E (ApoE) genotype in the frontal association cortex of 101 autopsy brains from patients aged between 40 to 83. Senile plaque density correlated well with the logarithmic data of insoluble Abeta measured by enzyme immunoassay (EIA). The amounts of Abeta42-ETA increased dramatically in the late preclinical stage, whereas the AP42+ plaque density increased in the early preclinical stage. Neurofibrillary pathology appeared only in the areas with severe Abeta deposition and in subjects aged over 70. The ApoE epsilon4 allele enhanced the Abeta3 deposition in presenile subjects. Plaque-associated glial Abeta was prominent in subjects with mild to moderate Abeta deposition. The morphology of cerebral Abeta deposition changed from diffuse plaques with small amounts of Abeta in each plaque in the early preclinical stage to primitive/neuritic plaques with larger amounts of Abeta in each plaque in the late preclinical stage. Our findings suggest that the prevention of Abeta deposition in the late preclinical stage can be a rational therapeutic target, especially in elderly people with ApoE epsilon4 allele.     

Normal cognitive behavior in two distinct congenic lines of transgenic mice hyperexpressing mutant APP SWE

Amyloid deposition appears to be an early and crucial event in Alzheimer's disease (AD). To generate animal models of AD, mice expressing full-length amyloid precursor protein (APP), with mutations linked to FAD, have been created. These animals exhibit abnormalities characteristic of AD, including deposits of beta-amyloid (Abeta), neuritic plaques, and glial responses. In studies of cognition in these animals, there have been several reports of memory disturbances well before the appearance of amyloid deposits. We have developed two distinct lines of transgenic mice (C3-3 and E1-2) that express the "Swedish" variant of APP (APP(SWE)) at levels that are approximately three-fold higher than endogenous mouse APP. Both lines have been backcrossed to C57BL/6J mice for 10 generations. Here, we use longitudinal and cross-sectional studies to evaluate the cognitive performance of our animals, where the concentration of Abeta1-42 in brain increases with aging from low levels (2-10 pmol/g) at 6-14 months of age to relatively high levels (60-100 pmol/g) at 24-26 months, when deposits of Abeta were beginning to form. When 12-month-old mice were tested in tasks that assess reference and working memory, transgenic mice from both lines could not be distinguished from nontransgenic littermates. Further study of 24- to 26-month-old transgenic mice (C3-3 line) found no evidence of memory impairment despite the presence of high levels of human Abeta (60-100 pmol/g). Thus, the expression of APP(SWE) at approximately three-fold over endogenous levels, which is sufficient to induce amyloid deposition at advanced ages, does not significantly erode cognitive performance in aged mice.     

Aberrant expressions of pathogenic phenotype in Alzheimer's diseased transgenic mice carrying NSE-controlled APPsw

Mutations in the APP gene lead to enhanced cleavage by the beta- and gamma-secretase, and increased Abeta formation, which are tightly associated with Alzheimer's disease (AD)-like neuropathological changes. To examine whether depositions of Abeta by APP mutations are increased, and if this is associated with potential pathogenic phenotypes, the APPsw was expressed in a transgenic line under the control of the neuron-specific enolase (NSE) promoter. A behavioral dysfunction was shown at 12 months, and intensive staining bands, with APP and Abeta-42 antibodies, were visible in the brains of transgenic mice. Of the MAPK family, both JNK and p38 were activated in the brains of transgenic mice, whereas there was no significant activation of the ERK. In parallel, tau phosphorylation was also enhanced in the transgenic relative to the control mice. Moreover, the Cox-2 levels, from Western blot and immunostaining, were increased in the brains of the transgenic line. Furthermore, there were significant caspase-3- and TUNEL-stained nuclei in the transgenic line compared to the age-matched control mice. Thus, these results suggest that NSE-controlled APPsw transgenic mice appear to be a more relevant model in neuropathological phenotypes of AD, and thus could be useful in developing new therapeutic treatments for targeting the aberrant phenotypes that appear in these mice.     

Reduced levels of amyloid beta-peptide antibody in Alzheimer disease

OBJECTIVE: To investigate whether it was possible to detect the presence and different levels of naturally occurring anti-beta-amyloid (Abeta) antibodies in the CSF of patients with AD and age-matched controls by employing a sensitive ELISA. BACKGROUND: Immunization with preaggregated amyloid beta-peptide (Abeta(1-42)) and administration of antibodies against Abeta into amyloid precursor protein APP(V717F)- transgenic mice (an animal model of AD) have recently been reported to dramatically reduce amyloid plaque deposition, neuritic dystrophy, and astrogliosis, most likely by enhancing Abeta clearance from brain. METHODS: A sensitive ELISA was performed to detect levels of naturally occurring anti-Abeta antibodies in the CSF of patients with AD and age-matched controls. Additionally, an immunoprecipitation assay was performed to confirm that naturally occurring anti-Abeta antibodies also exist in the human blood. RESULT: - Naturally occurring antibodies directed against Abeta were found in the CSF and plasma of patients with AD and healthy control subjects. Moreover, CSF anti-Abeta antibody titers are significantly lower in patients with AD compared with healthy control subjects. CONCLUSION: Naturally occurring antibodies directed against Abeta exist in human CSF and plasma. The CSF anti-Abeta antibody titers may be helpful in better understanding the effects of future immunologic therapies for AD.     

LRP and senile plaques in Alzheimer's disease: colocalization with apolipoprotein E and with activated astrocytes

The low density lipoprotein receptor-related protein (LRP) is a multifunctional receptor which is present on senile plaques in Alzheimer's disease (AD). It is suggested to play an important role in the balance between amyloid beta (Abeta) synthesis and clearance mechanisms. One of its ligands, apolipoprotein E (apoE), is also present on senile plaques and has been implicated as a risk factor for AD, potentially affecting the deposition, fibrillogenesis and clearance of Abeta. Using immunohistochemistry we show that LRP was present only on cored, apoE-containing senile plaques, in both PDAPP transgenic mice and human AD brains. We detected strong LRP staining in neurons and in reactive astrocytes, and immunostaining of membrane-bound LRP showed colocalization with fine astrocytic processes surrounding senile plaques. LRP was not present in plaques in young transgenic mice or in plaques of APOE-knockout mice. As LRP ligands associated with Abeta deposits in AD brain may play an important role in inducing levels of LRP in both neurons and astrocytes, our findings support the idea that apoE might be involved in upregulation of LRP (present in fine astrocytic processes) and act as a local scaffolding protein for LRP and Abeta. The upregulation of LRP would allow increased clearance of LRP ligands as well as clearance of Abeta/ApoE complexes.     

Decreased neprilysin immunoreactivity in Alzheimer disease, but not in pathological aging

Although evidence suggests that extensive cortical beta-amyloid (Abeta) deposition is essential in Alzheimer disease (AD), it is also detected in nondemented elderly individuals with pathologic aging (PA). Given evidence that neutral endopeptidase (NEP) or neprilysin, a key enzyme for clearance of Abeta, is decreased in AD, the goal of the present study was to determine if NEP was also decreased in PA. We measured NEP immunoreactivity in frontal cortex of 12 AD and six PA cases and compared this with 10 normal (N) elderly individuals. None had any significant other pathology, and they were similar with respect to age, sex, and postmortem delay. In addition, Abeta1-40 and Abeta1-42 were measured by enzyme-linked immunosorbent assay (ELISA), whereas tau, synaptophysin, and alpha-synuclein were measured on Western blots. The AD cases had more neuritic plaques, neurofibrillary tangles, higher Braak stage, and more tau immunoreactivity in frontal cortex than both PA and N. In contrast, both PA and AD had more senile plaques and Abeta1-42 than N. NEP immunoreactivity was decreased in AD but not in PA. The decrease was unlikely the result of neuronal or synaptic loss because NEP immunoreactivity in frontotemporal degeneration with comparable degrees of synaptic loss as the AD cases was not different from control subjects. Although NEP enzyme activity was decreased in approximately half the AD cases, on average, it was not decreased compared with N or PA. The results add further evidence that PA is distinct from AD and indicate that decreased Abeta degradation by NEP is unlikely to contribute significantly to amyloid deposition in PA or, in many cases, of AD.     

An increase in Abeta42 in the prefrontal cortex is associated with a reversal-learning impairment in Alzheimer's disease model Tg2576 APPsw mice

The medial temporal lobe-dependent memory loss associated with Alzheimer's disease (AD) is often accompanied by a loss of prefrontal cortex-dependent cognitive domains that fall under the broad category of executive function. In this study, we examined the relationship between one type of prefrontal-dependent executive function, discrimination reversal-learning, and levels of the amyloid beta protein (Abeta) of 40 and 42 residues in a transgenic mouse model (Tg2576) of the over-expression of the familial AD mutant form of the amyloid precursor protein (APPsw). Tg2576 and their non-transgenic (NTg) littermates were assessed at 3 and 6 months of age when there is little to no amyloid plaque deposition. After reversal-learning assessment, Abeta40 and Abeta42 were quantified in the prefrontal cortex and hippocampus. Tg2576 mice were impaired in reversal-learning at 6 but not 3 months of age when compared to the NTg group. Coincidently, there was a corresponding approximately 3-fold increase of Abeta42 levels in the prefrontal cortex of 6- compared to 3-month-old Tg2576 mice. In addition, the prefrontal cortex contained higher levels of Abeta42 compared to the hippocampus at both 3 and 6 months of age, regardless of genotype, indicating a high vulnerability of this brain region to Abeta42 accumulation. These data suggest that the early emergence of reversal-learning deficits in the Tg2576 mouse may be due to the localized increase of Abeta42 in the prefrontal cortex.     

Gene vaccination to bias the immune response to amyloid-beta peptide as therapy for Alzheimer disease

BACKGROUND: The amyloid-beta (Abeta) peptide has a central role in the neurodegeneration of Alzheimer disease (AD). Immunization of AD transgenic mice with Abeta(1-42) (Abeta(42)) peptide reduces both the spatial memory impairments and AD-like neuropathologic changes in these mice. Therapeutic immunization with Abeta in patients with AD was shown to be effective in reducing Abeta deposition, but studies were discontinued owing to the development of an autoimmune, cell-mediated meningoencephalitis. We hypothesized that gene vaccination could be used to generate an immune response to Abeta(42) that produced antibody response but avoided an adverse cell-mediated immune effect. OBJECTIVE: To develop an effective genetic immunization approach for treatment and prevention of AD without causing an autoimmune, cell-mediated meningoencephalitis. METHODS: Mice were vaccinated with a plasmid that encodes Abeta(42), administered by gene gun. The immune response of the mice to Abeta(42) was monitored by measurement of (1) antibody levels by enzyme-linked immunosorbent assay (ELISA) and Western blot and (2) Abeta(42)-specific T-cell response as measured by interferon-gamma enzyme-linked immunospot (ELISPOT) assay. RESULTS: Gene-gun delivery of the mouse Abeta(42) dimer gene induced significant humoral immune responses in BALB/c wild-type mice after 3 vaccinations in 10-day intervals. All 3 mice in the treated group showed significant humoral immune responses. The ELISPOT assay for interferon-gamma release with mouse Abeta(42) peptide and Abeta(9-18) showed no evident cytotoxic T-lymphocyte response. We further tested the responses of wild-type BALB/c mice to the monomer Abeta(42) gene vaccine. Western blot evaluation showed both human and mouse Abeta monomer gene vaccine elicited detectable humoral immune responses. We also introduced the human Abeta(42) monomer gene vaccine into AD double transgenic mice APPswe/PSEN1(A246E). Mice were vaccinated with plasmids that encode Abeta(1-42) and Abeta(1-16), or with plasmid without the Abeta gene. Treated mice showed significant humoral immune responses as demonstrated by ELISA and by Western blot. These mice also showed no significant cellular immune response as tested by ELISPOT. One of the treated mice was killed at 7 months of age for histological observations, and scattered amyloid plaques were noted in all layers of the cerebral cortex and in the hippocampus in both Abeta(42)- and control-vaccinated mice. No definite difference was discerned between the experimental and control animals. CONCLUSIONS: Gene-gun-administered genetic immunization with the Abeta(42) gene in wild-type BALB/c and AD transgenic mice can effectively elicit humoral immune responses without a significant T-cell-mediated immune response to the Abeta peptide. This immunotherapeutic approach could provide an alternative active immunization method for therapy and prevention of AD.     

Environmental enrichment improves cognition in aged Alzheimer's transgenic mice despite stable beta-amyloid deposition

Environmental enrichment (EE) has been shown to improve cognitive performance and brain indices of cognition in normal mice and rats. Because the therapeutic potential of intensive, long-term EE to benefit patients with Alzheimer's disease (AD) has yet to be explored, the present study evaluated the effect of long-term EE on cognition in an animal model of AD, the APPsw transgenic mouse. Beginning at 16 months of age, APPsw mice were put into EE or standard housing for 4 months and then tested in four cognitive-based tasks (Morris maze, circular platform, platform recognition, and radial arm water maze) between 20 and 22 months of age. Our results indicate that long-term EE of aged APPsw mice results in global, overall improvement in cognitive function across these tasks without decreasing brain beta-amyloid (A beta) deposition. The results suggest that long-term EE/cognitive stimulation could provide cognitive stabilization or improvement to AD patients through mechanisms independent of A beta deposition and clearance.     

Cerebral ischemia and Alzheimer's disease: the expression of amyloid-beta and apolipoprotein E in human hippocampus

Growing evidence suggests a synergistic and perhaps etiological relationship between vascular disease and Alzheimer's disease (AD), which is characterized by the progressive accumulation of amyloid-beta peptide (Abeta). Moreover, apolipoprotein E (ApoE) has also been shown to be associated with AD and cerebral ischemia. It seems that cerebral ischemia may play an important, both direct and indirect, role in the pathogenesis of AD. We investigated the expression and distribution of Abeta1-40, beta1-42 and ApoE in human hippocampus after cerebral ischemia in this study to determine the role of cerebral ischemia in Alzheimer's disease. Our study has demonstrated that the accumulation of both Abeta1-40 and beta1-42 were increased dramatically and consistently after cerebral ischemia. Neuronal ApoE immunoreactivity was also significantly increased in all ischemic groups compared with controls. The most likely stimulus for the increased Abeta1-40, Abeta1-42 and ApoE immunoreactivity in the CA1 and CA3 neurons is the ischemic conditions, and their upregulation, in turn, may partly explain the contribution of cerebral ischemia to the pathogenesis of AD. Therefore our observations provide a basis for establishing therapeutic strategies aimed at preventing ischemic insults and subsequent neurodegeneration in AD.     

Nasal administration of amyloid-beta peptide decreases cerebral amyloid burden in a mouse model of Alzheimer's disease

Progressive cerebral deposition of amyloid-beta (Abeta) peptide, an early and essential feature of Alzheimer's disease (AD), is accompanied by an inflammatory reaction marked by microgliosis, astrocytosis, and the release of proinflammatory cytokines. Mucosal administration of disease-implicated proteins can induce antigen-specific anti-inflammatory immune responses in mucosal lymphoid tissue which then act systemically. We hypothesized that chronic mucosal administration of Abeta peptide might induce an anti-inflammatory process in AD brain tissue that could beneficially affect the neuropathological findings. To test this hypothesis, we treated PDAPP mice, a transgenic line displaying numerous neuropathological features of AD, between the ages of approximately 5 and approximately 12 months with human Abeta synthetic peptide mucosally each week. We found significant decreases in the cerebral Abeta plaque burden and Abeta42 levels in mice treated intranasally with Abeta peptide versus controls treated with myelin basic protein or left untreated. This lower Abeta burden was associated with decreased local microglial and astrocytic activation, decreased neuritic dystrophy, serum anti-Abeta antibodies of the IgG1 and IgG2b classes, and mononuclear cells in the brain expressing the anti-inflammatory cytokines interleukin-4, interleukin-10, and tumor growth factor-beta. Our results demonstrate that chronic nasal administration of Abeta peptide can induce an immune response to Abeta that decreases cerebral Abeta deposition, suggesting a novel mucosal immunological approach for the treatment and prevention of AD.     

Amyloid beta protein deposition and neuron loss in osteopetrotic (op/op) mice

Formation of senile plaques (SPs) by amyloid beta (Abeta) protein is a neuropathological change which characterizes Alzheimer's disease (AD), and Abeta deposition and neuron loss are essential for the pathological cascade of the disease. Although the mechanism of Abeta deposition remains unclear, it has been suggested that clearance of Abeta protein may be impaired in the AD brain. Previous studies demonstrated that microglia were able to remove Abeta by releasing a metalloprotease or by phagocytosis, suggesting that microglia may play an important role in preventing Abeta deposition in the central nervous system (CNS). On the other hand, it was reported that the number of microglia was reduced in osteopetrotic (op/op) toothless mice resulting from the lack of functional macrophage colony-stimulating factor (M-CSF). The present study was thus designed to examine the Abeta deposition and the number of hippocampal neurons in the brain of op/op mice. A number of fibrillar plaques were detected in the cerebral cortex, hippocampus, amygdala and hypothalamus in op/op mice, however, no quantitative evidence of Abeta deposition was observed in normal mice. Moreover, the total number of pyramidal cells in the hippocampal CA1, and CA3 regions was significantly reduced in op/op mice when compared to the controls. These results demonstrate that Abeta deposition influence neuron loss and it may be suspected that expression of SPs may be in part regulated by microglia under physiological conditions.