Decreased Aβ Deposition Research Articles

Synaptic Released Zinc Promotes Tau Hyperphosphorylation by Inhibition of Protein Phosphatase 2A (PP2A)

Hyperphosphorylated tau is the major component of neurofibrillary tangles in Alzheimer disease (AD), and the tangle distribution largely overlaps with zinc-containing glutamatergic neurons, suggesting that zinc released in synaptic terminals may play a role in tau phosphorylation. To explore this possibility, we treated cultured hippocampal slices or primary neurons with glutamate or Bic/4-AP to increase the synaptic activity with or without pretreatment of zinc chelators, and then detected the phosphorylation levels of tau. We found that glutamate or Bic/4-AP treatment caused tau hyperphosphorylation at multiple AD-related sites, including Ser-396, Ser-404, Thr-231, and Thr-205, while application of intracellular or extracellular zinc chelators, or blockade of zinc release by extracellular calcium omission almost abolished the synaptic activity-associated tau hyperphosphorylation. The zinc release and translocation of excitatory synapses in the hippocampus were detected, and zinc-induced tau hyperphosphorylation was also observed in cultured brain slices incubated with exogenously supplemented zinc. Tau hyperphosphorylation induced by synaptic activity was strongly associated with inactivation of protein phosphatase 2A (PP2A), and this inactivation can be reversed by pretreatment of zinc chelator. Together, these results suggest that synaptically released zinc promotes tau hyperphosphorylation through PP2A inhibition.

Changes in Brain β-Amyloid Deposition and Aquaporin 4 Levels in Response to AlteredAgrinExpression in Mice

Conditions that compromise the blood-brain barrier (BBB) have been increasingly implicated in the pathogenesis of Alzheimer disease (AD). AGRIN is a heparan sulfate proteoglycan found abundantly in basement membranes of the cerebral vasculature, where it has been proposed to serve a functional role in the BBB. Furthermore, AGRIN is the major heparan sulfate proteoglycan associated with amyloid plaques in AD brains. To examine the relationship of AGRIN, the BBB, and AD-related pathologies, we generated mice in which the Agrn gene was deleted from either endothelial cells or neurons using gene targeting or was overexpressed using a genomic transgene construct. These mice were combined with a transgenic model of AD that over expresses disease-associated forms of amyloid precursor protein and presenilin 1. In mice lacking endothelial cell expression of Agrn, the BBB remained intact but aquaporin 4 levels were reduced, indicating that the loss of AGRIN affects BBB-associated components. This change in Agrn resulted in an increase in β-amyloid (Aβ) in the brain. Conversely, overexpression of Agrn decreased Aβ deposition, whereas elimination of Agrn from neurons did not change Aβ levels. These results indicate that AGRIN is important for maintaining BBB composition and that changes in Agrn expression (particularly vessel-associated AGRIN) influence Aβ homeostasis in mouse models of AD.

The effect of normobaric hyperoxia on the spatial learning and memory of APP/PS1 double transgenic mice

Objective To investigate whether normobaric hyperoxia exert neuroproteetive effect on APP/ PS1 double transgenic AD mouse model. Methods 20 APP/PS1 transgenic mice were randomly divided into 2 groups(A, B). Mice in group A were treated with 40% oxygen for 8 h per day, and lasted 8 weeks. Mice in group B were treated with normal air, as control. ELISA assay as well as behavioral test were used in the present study. Results Compared with normoxia-treated control, hyperoxia-treated mice had a significant lesser (P 0.05 ). EL1SA showed that Aβ40(783.64±97.21)pg/ml and Aβ42(175.30 ± 17.09) pg/ml were significantly decreased in hyperoxia-treated mice, compared with control[Aβ40 (1251.59 ± 42.29 ) pg/ml and Aβ42 (286.83 ± 12.96) pg/ml] (P< 0.01 ). Conclusion Treatment with hyperoxia significantly decreases Aβ deposition, and remarkably improves the capability of spatial learning and memory of APP/PS1 transgenic mice. Hyperoxia may exert its neuroprotective effect through decreasing Aβ generation or enhancing clearance of Aβ by endothelial cells. Key words: Normobaric hyperoxia; Alzheimer's disease; Learning and memory; Aβ amyloid

DHA and cholesterol containing diets influence Alzheimer-like pathology, cognition and cerebral vasculature in APP swe/PS1 dE9 mice

Cholesterol and docosahexenoic acid (DHA) may affect degenerative processes in Alzheimer's Disease (AD) by influencing Aβ metabolism indirectly via the vasculature. We investigated whether DHA-enriched diets or cholesterol-containing Typical Western Diets (TWD) alter behavior and cognition, cerebral hemodynamics (relative cerebral blood volume (rCBV)) and Aβ deposition in 8- and 15-month-old APP swe/PS1 dE9 mice. In addition we investigated whether changes in rCBV precede changes in Aβ deposition or vice versa. Mice were fed regular rodent chow, a TWD-, or a DHA-containing diet. Behavior, learning and memory were investigated, and rCBV was measured using contrast-enhanced MRI. The Aβ load was visualized immunohistochemically. We demonstrate that DHA altered rCBV in 8-month-old APP/PS1 and wild type mice[AU1]. In 15-month-old APP/PS1 mice DHA supplementation improved spatial memory, decreased Aβ deposition and slightly increased rCBV, indicating that a DHA-enriched diet can diminish AD-like pathology. In contrast, TWD diets decreased rCBV in 15-month-old mice. The present data indicate that long-term dietary interventions change AD-like pathology in APP/PS1 mice. Additionally, effects of the tested diets on vascular parameters were observed before effects on Aβ load were noted. These data underline the importance of vascular factors in the APP/PS1 mouse model of AD pathology.

Aβ40 Inhibits Amyloid DepositionIn Vivo

Numerous studies have established a pivotal role for Abeta42 in Alzheimer's disease (AD) pathogenesis. In contrast, although Abeta40 is the predominant form of amyloid beta (Abeta) produced and accumulates to a variable degree in the human AD brain, its role in AD pathogenesis has not been established. It has generally been assumed that an increase in Abeta40 would accelerate amyloid plaque formation in vivo. We have crossed BRI-Abeta40 mice that selectively express high levels of Abeta40 with both Tg2576 (APPswe, K670N+M671L) mice and BRI-Abeta42A mice expressing Abeta42 selectively and analyzed parenchymal and cerebrovascular Abeta deposition in the bitransgenic mice compared with their singly transgenic littermates. In the bitransgenic mice, the increased steady-state levels of Abeta40 decreased Abeta deposition by 60-90%. These results demonstrate that Abeta42 and Abeta40 have opposing effects on amyloid deposition: Abeta42 promotes amyloid deposition but Abeta40 inhibits it. In addition, increasing Abeta40 levels protected BRI-Abeta40/Tg2576 mice from the premature-death phenotype observed in Tg2576 mice. The protective properties of Abeta40 with respect to amyloid deposition suggest that strategies that preferentially target Abeta40 may actually worsen the disease course and that selective increases in Abeta40 levels may actually reduce the risk for development of AD.

Intracranial Adeno-Associated Virus-Mediated Delivery of Anti-Pan Amyloid β, Amyloid β40, and Amyloid β42 Single-Chain Variable Fragments Attenuates Plaque Pathology in Amyloid Precursor Protein Mice

Accumulation of amyloid beta protein (Abeta) aggregates is hypothesized to trigger a pathological cascade that causes Alzheimer's disease (AD). Active or passive immunizations targeting Abeta are therefore of great interest as potential therapeutic strategies. We have evaluated the use of recombinant anti-Abeta single-chain variable fragments (scFvs) as a potentially safer form of anti-Abeta immunotherapy. We have generated and characterized three anti-Abeta scFvs that recognize Abeta 1-16, Abeta x-40, or Abeta x-42. To achieve widespread brain delivery, constructs expressing these anti-Abeta scFvs were packaged into adeno-associated virus (AAV) vectors and injected into the ventricles of postnatal day 0 (P0) amyloid precursor protein CRND8-transgenic mice. Intracranial delivery of AAV to neonatal mice resulted in widespread neuronal delivery. In situ expression of each of the anti-Abeta scFvs after intracerebroventricular AAV serotype 1 delivery to P0 pups decreased Abeta deposition by 25-50%. These data suggest that intracranial anti-Abeta scFv expression is an effective strategy to attenuate amyloid deposition. As opposed to transgenic approaches, these studies also establish a "somatic brain transgenic" paradigm to rapidly and cost-effectively evaluate potential modifiers of AD-like pathology in AD mouse models.

Deletion of Abca1 Increases Aβ Deposition in the PDAPP Transgenic Mouse Model of Alzheimer Disease

Apolipoprotein E (apoE) genotype has a major influence on the risk for Alzheimer disease (AD). Different apoE isoforms may alter AD pathogenesis via their interactions with the amyloid beta-peptide (Abeta). Mice lacking the lipid transporter ABCA1 were found to have markedly decreased levels and lipidation of apoE in the central nervous system. We hypothesized that if Abca1-/- mice were bred to the PDAPP mouse model of AD, PDAPP Abca1-/ mice would have a phenotype similar to that of PDAPP Apoe+/- and PDAPP Apoe-/- mice, which develop less amyloid deposition than PDAPP Apoe+/+ mice. In contrast to this prediction, 12-month-old PDAPP Abca -/- mice had significantly higher levels of hippocampal Abeta, and cerebral amyloid angiopathy was significantly more common compared with PDAPP Abca1+/+ mice. Amyloid precursor protein (APP) C-terminal fragments were not different between Abca1 genotypes prior to plaque deposition in 3-month-old PDAPP mice, suggesting that deletion of Abca1 did not affect APP processing or Abeta production. As expected, 3-month-old PDAPP Abca1-/- mice had decreased apoE levels, but they also had a higher percentage of carbonate-insoluble apoE, suggesting that poorly lipidated apoE is less soluble in vivo. We also found that 12-month-old PDAPP Abca1-/- mice had a higher percentage of carbonate-insoluble apoE and that apoE deposits co-localize with amyloid plaques, demonstrating that poorly lipidated apoE co-deposits with insoluble Abeta. Together, these data suggest that despite substantially lower apoE levels, poorly lipidated apoE produced in the absence of ABCA1 is strongly amyloidogenic in vivo.

Methylation of the Imidazole Side Chains of the Alzheimer Disease Amyloid-β Peptide Results in Abolition of Superoxide Dismutase-like Structures and Inhibition of Neurotoxicity

The toxicity of the amyloid-beta peptide (Abeta) is thought to be responsible for the neurodegeneration associated with Alzheimer disease. Generation of hydrogen peroxide has been implicated as a key step in the toxic pathway. Abeta coordinates the redox active metal ion Cu2+ to catalytically generate H2O2. Structural studies on the interaction of Abeta with Cu have suggested that the coordination sphere about the Cu2+ resembles the active site of superoxide dismutase 1. To investigate the potential role for such structures in the toxicity of Abeta, two novel Abeta40 peptides, Abeta40(HistauMe) and Abeta40(HispiMe), have been prepared, in which the histidine residues 6, 13, and 14 have been substituted with modified histidines where either the pi- or tau-nitrogen of the imidazole side chain is methylated to prevent the formation of bridging histidine moieties. These modifications did not inhibit the ability of these peptides to form fibrils. However, the modified peptides were four times more effective at generating H2O2 than the native sequence. Despite the ability to generate more H2O2, these peptides were not neurotoxic. Whereas the modifications to the peptide altered the metal binding properties, they also inhibited the interaction between the peptides and cell surface membranes. This is consistent with the notion that Abeta-membrane interactions are important for neurotoxicity and that inhibiting these interactions has therapeutic potential.

A novel recombinant adeno-associated virus vaccine reduces behavioral impairment and β-amyloid plaques in a mouse model of Alzheimer's disease

Memory impairment progressing to dementia is the main clinical symptom of Alzheimer's disease (AD). Deposition of the amyloid-β peptide (Aβ) in brain, particularly its 42-amino acid isoform (Aβ42), has been shown to play a primary and crucial role in the pathogenesis of AD. In this study we have developed a recombinant adeno-associated virus (AAV) vaccine against AD. This vaccine could express CB-Aβ42 (cholera toxin B subunit and Aβ42 fusion protein) in vivo. A single administration of the AAV-CB-Aβ42 vaccine induced a prolonged, strong production of Aβ-specific serum IgG in transgenic mice that overexpressed the London mutant of amyloid precursor protein (APP/V717I), and resulted in improved ability of memory and cognition, decreased Aβ deposition in the brain, and a resultant decrease in plaque-associated astrocytosis. Our results extended the immunological approaches for the treatment and prevention of AD to an oral, intranasal, or intramuscular route that might be better tolerated in human patients than repetitive parental immunizations in the presence of adjuvant. AAV has attracted tremendous interest as a promising vector for gene delivery. Our results raised the possibility that AAV-CB-Aβ42 vector immunization may provide the basis of a novel and promising Alzheimer's disease vaccination program.