Faculty Bibliography

The prion protein (PrP) binds copper and under some conditions copper can facilitate its folding into a more protease resistant form. Hence, copper levels may influence the infectivity of the scrapie form of prion protein (PrPSc). To determine the feasibility of copper-targeted therapy for prion disease, we treated mice with a copper chelator, D-(-)-penicillamine (D-PEN), starting immediately following intraperitoneal scrapie inoculation. D-PEN delayed the onset of prion disease in the mice by about 11 days (p = 0.002), and reduced copper levels in brain by 29% (p < 0.01) and in blood by 22% (p = 0.03) compared with control animals. Levels of other metals were not significantly altered in the blood or brain. Modest correlation was observed between incubation period and levels of copper in brain (p = 0.08) or blood (p = 0.04), indicating that copper levels are only one of many factors that influence the rate of progression of prion disease. In vitro, copper dose-dependently enhanced the proteinase K resistance of the prion protein, and this effect was counteracted in a dose-dependent manner by co-incubation with D-PEN. Overall, these findings indicate that copper levels can influence the conformational state of PrP, thereby enhancing its infectivity, and this effect can be attenuated by chelator-based therapy

Dendritic spines are postsynaptic sites of excitatory input in the mammalian nervous system. Apolipoprotein (apo) E participates in the transport of plasma lipids and in the redistribution of lipids among cells. A role for apoE is implicated in regeneration of synaptic circuitry after neural injury. The apoE4 allele is a major risk factor for late-onset familial and sporadic Alzheimer's disease (AD) and is associated with a poor outcome after brain injury. ApoE isoforms are suggested to have differential effects on neuronal repair mechanisms. In vitro studies have demonstrated the neurotrophic properties of apoE3 on neurite outgrowth. We have investigated the influence of apoE genotype on neuronal cell dendritic spine density in mice and in human postmortem tissue. In order to compare the morphology of neurons developing under different apoE conditions, gene gun labeling studies of dendritic spines of dentate gyrus (DG) granule cells of the hippocampus were carried out in wild-type (WT), human apoE3, human apoE4 expressing transgenic mice and apoE knockout (KO) mice; the same dendritic spine parameters were also assessed in human postmortem DG from individuals with and without the apoE4 gene. Quantitative analysis of dendritic spine length, morphology, and number was carried out on these mice at 3 weeks, 1 and 2 years of age. Human apoE3 and WT mice had a higher density of dendritic spines than human E4 and apoE KO mice in the 1 and 2 year age groups (P<0.0001), while at 3 weeks there were no differences between the groups. These age dependent differences in the effects of apoE isoforms on neuronal integrity may relate to the increased risk of dementia in aged individuals with the apoE4 allele. Significantly in human brain, apoE4 dose correlated inversely with dendritic spine density of DG neurons cell in the hippocampus of both AD (P=0.0008) and aged normal controls (P=0.0015). Our findings provide one potential explanation for the increased cognitive decline seen in aged and AD patients expressing apoE4

A significant percentage of Alzheimer's disease (AD) patients exhibit concomitant vascular pathology. Epidemiological evidence suggest that vascular disease may not only add to global cognitive impairment but also exacerbate the course of AD pathology. The goal of this study was to analyze the impact of global ischemia on the cellular and amyloid-beta pathology in AD murine transgenic (Tg) models. Seven month old double Tg mice, expressing Swedish amyloid precursor protein (APP) and M146L presenilin 1 (PS1) mutations and single Tg mice (PS1 mutation alone) were subjected to 45 minutes bilateral common carotid artery occlusion or sham surgery. Behavioral testing performed two weeks after the surgery showed impaired learning and memory retention on Morris water maze and Hebb-Williams tests in both single PS1 and double PS1/APP Tg mice which underwent ischemia comparing to sham operated animals (p<0.05). Double Tg mice scored worse than single Tg mice. Animals were sacrificed two months after ischemia. The total brain volume was decreased by 6.5% and 5% and the ventricular volume was increased by 33.7% and 46.4% in single and double operated Tg mice, respectively comparing to sham animals. Unbiased stereological analysis demonstrated a 23% neuronal dropout in the CA1 sector of the cornu Ammonis after ischemia. Increased Abetaburden and plaque density was also observed in APP/PS1 animals which underwent ischemia comparing to sham operated ones. Overall, this data indicate that global ischemia exacerbate both neuronal and Abetarelated pathology in AD Tg animal models

Deposition of amyloid-beta (Abeta) in form of the senile plaques and in vessel walls is a hallmark of Alzheimer's disease (AD). Apolipoprotein E (apoE) is known to act as a pathological chaperone by increasing the beta-sheet content of Abeta, promoting its fibrillization, toxicity, and deposition in the brain. ApoE binds to residues 12-28 of Abeta. We report in vitro and in vivo data on the blocking of the apoE/Abeta interaction by a synthetic peptide homologues to residues 12-28 of Abeta. To eliminate any residual toxicity and fibrillogenic potential the peptide sequence was altered by replacing a valine in position 18 by a proline (Abeta12-28P). On ELISA Abeta12-28P demonstrates high affinity binding to apoE and in competitive binding experiments inhibits the binding of apoE to Abeta42. Abeta12-28P also reduces the toxicity of Abeta in cell culture, as well as blocking the enhanced fibril formation of Abeta in the presence of apoE4, measured by the Thioflavin-T assay. The in vivo effect of Abeta12-28P was assessed in double transgenic (Tg) APP/PS1 AD mice which received 1mg of Abeta12-28P or placebo three times a week for four weeks. There was an approximately five fold reduction of the total and fibrillar Abeta in treated mice comparing to control (p<0.05). Also, Abeta40 and Abeta42 levels in the brain demonstrated a 40-60% reduction of both species in the total Abeta fraction and in the soluble Abeta fraction in treated mice comparing to controls. No significant titer of anti-Abeta antibodies in treated animals was detected, indicating that the effect of Abeta12-28P on Abeta deposition observed in vivo is not immune mediated. Overall, compounds blocking the interaction between Abeta and its pathological chaperones such as apoE (or alpha1anti-chymotrypsin, perlecan etc.) can be considered as an alternative approach for the treatment of beta-amyloidosis in AD

Presenilin 1 (PS1) mutations have been identified in many pedigrees with early-onset familial Alzheimer's disease (FAD). PS1 mutants are known to influence gamma-secretase action and increase amyloid-beta (Abeta) 1-42 production, but there is also evidence suggesting direct involvement of PS1 in the neuronal pathology of AD. Transgenic (Tg) mice expressing the M146L PS1 mutation, associated with FAD symptom onset in the forties, demonstrate no difference in the total number of neurons (fractionator method) in the CA1 sector of the cornu Ammonis comparing with wild type (wt) animals at two months of age. At the age of 9 months and 22 months PS1 M146L Tg mice demonstrated 20% and 29% neuronal dropout comparing to age-matched controls, respectively (p<0.05). Between 2 months and 22 months old wt animals did not show any significant neuronal loss; however, 22 month old M146L PS1 mice showed a 41% neuronal decline compared to 2 month old controls. PS1 M146L Tg animals also exhibited impaired performance of both learning and retention on the Morris water maze test (p<0.05), but not on locomotor testing comparing to wt mice. We have also analyzed another line of Tg mice expressing a P117L PS1 mutation associated with an onset of disease as early as 23 years. These mice at the age of 6 months demonstrate a 17.9% reduction in the total number of CA1 neurons comparing to wt mice and a 26.5% reduction comparing to mice expressing the wt form of human PS1 (p<0.05). Overall, this data suggest that PS1 mutations are directly involved in neuronal pathology which is age-dependant. This process is unrelated to Abeta deposition since PS1 Tg mice do not develop amyloid plaques

According to the amyloid hypothesis, it is the progressive accumulation of beta-amyloid that leads to a cascade of neurodegenerative processes in Alzheimer's disease (AD). Thus, current strategies for diagnosis and treatment evaluation rely on the ability to accurately quantify beta-amyloid burden. It has previously been shown that beta-amyloid plaques can be imaged using Magnetic Resonance Microscopy (MRM) at 40mum isotropic resolution in ex vivo human samples of the hippocampus. Transgenic (Tg) mice have been generated for research as beta-amyloidosis models. Plaque sizes range can from 5mum to 200mum, with an average diameter of approximately 25mum. In the present study, we used high resolution MRM to explore the feasibility of visualizing beta-amyloid plaque deposits in the brain of Tg2576 mice carrying the Swedish mutation of APP. We obtained T2 weighted 3D whole brain MRM data at 20mum and 25mum isotropic resolution. MRM images were compared with histological data to confirm that the signal seen on MRM corresponded to actual beta-amyloid plaque deposits. We conclude that MRM is a practical and useful assay for imaging beta-amyloid plaques with diameters as small as 20mum. These results will aid in the interpretation of MRI data gathered from in-vivo scans of mice, including scans wherein contrast agents are employed. This MRI technique can be easily applied to whole brain plaque quantification studies and for the purpose of studying treatment strategies using mouse models of AD, and may further be extended to in vivo studies tracking amyloid deposit formation and maturation throughout the animals life span