Faculty Bibliography

The cerebral deposition of amyloid beta-peptide, a central event in Alzheimer's disease (AD) pathogenesis, begins several years before the onset of clinical symptoms. Noninvasive detection of AD pathology at this initial stage would facilitate intervention and enhance treatment success. In this study, high-field MRI was used to detect changes in regional brain MR relaxation times in three types of mice: 1). transgenic mice (PS/APP) carrying both mutant genes for amyloid precursor protein (APP) and presenilin (PS), which have high levels and clear accumulation of beta-amyloid in several brain regions, starting from 10 weeks of age; 2). transgenic mice (PS) carrying only a mutant gene for presenilin (PS), which show subtly elevated levels of Abeta-peptide without beta-amyloid deposition; and 3). nontransgenic (NTg) littermates as controls. The transverse relaxation time T(2), an intrinsic MR parameter thought to reflect impaired cell physiology, was significantly reduced in the hippocampus, cingulate, and retrosplenial cortex, but not the corpus callosum, of PS-APP mice compared to NTg. No differences in T(1) values or proton density were detected between any groups of mice. These results indicate that T(2) may be a sensitive marker of abnormalities in this transgenic mouse model of AD

The diagnosis of prion diseases in humans is challenging due to a lack of specific and sensitive non-invasive tests. Many forms of human prion disease including variant Creutzfeldt-Jakob disease (vCJD), Gerstmann-Straussler-Scheinker (GSS) syndrome, and 10% of sporadic CJD cases are associated with amyloid deposition. Several positron emission tomography (PET) ligands have recently been developed to directly image beta-amyloid associated with Alzheimer disease. One of them, methoxy-X04, is a fluorescent derivative of Congo red with high binding affinity toward amyloid fibrils and good blood-brain barrier permeability. Using methoxy-X04, we investigated whether amyloid-targeting ligands can be also employed for direct imaging of amyloid deposits associated with some prion diseases. Such a method could potentially become a novel diagnostic approach for these conditions. Studies were performed on MB mice infected with the 87V mouse-adapted scrapie strain. Labeling of PrP amyloid plaques in brains of presymptomatic and symptomatic mice was demonstrated using in vivo transcranial two-photon microscopy after systemic administration of methoxy-X04. During real-time imaging, PrP amyloid deposits could be clearly distinguished 15 min after intravenous administration of methoxy-X04. The ligand showed rapid clearance from brain areas that did not contain amyloid deposits. PrP amyloid deposits could also be detected by direct application of methoxy-X04 on cerebellar sections from GSS patients. These results suggest that methoxy-X04 or similar derivatives could be used as PET imaging agents to improve the diagnosis of human prion diseases associated with amyloid deposition

Immunization with amyloid-beta (Abeta) 1-42 has been shown to reduce amyloid burden and improve cognition in Alzheimer's disease (AD) model mice. In a human trial, possible cognitive benefit was found but in association with significant toxicity in a minority of patients. We proposed that immunization with nonfibrillogenic Abeta derivatives is much less likely to produce toxicity and have previously shown that one such derivative (K6Abeta1-30) can reduce amyloid burden in mice to a similar extent as Abeta1-42. Here, we immunized AD model mice (Tg2576) with Abeta1-30[E18E19] or with K6Abeta1-30[E18E19]. These peptides were designed to be nontoxic and to produce less T-cell response, which has been linked to toxicity. K6Abeta1-30[E18E19] induced primarily an IgM response, whereas Abeta1-30[E18E19] induced an IgG titer that was lower than previously seen with K6Abeta1-30 or Abeta1-42. However, both treated animal groups performed better than Tg controls in the radial arm maze. Amyloid burden was similar in Abeta1-30[E18E19]-vaccinated mice and their Tg controls, whereas the number of medium and small sized plaques was reduced (29-34%) in K6Abeta1-30[E18E19]-immunized mice compared with Tg controls. Amyloid burden in these mice correlated inversely with plasma IgM levels. The cognitive benefit and amyloid reduction in the K6Abeta1-30[E18E19]-vaccinated mice are likely to be related to peripheral clearance of Abeta, because IgM does not cross the blood-brain barrier because of its large size. Our results indicate that these nontoxic Abeta derivatives produce an attenuated antibody response, which is less likely to be associated with negative side effects while having cognitive benefits

In Alzheimer disease (AD) patients, early memory dysfunction is associated with glucose hypometabolism and neuronal loss in the hippocampus. Double transgenic (Tg) mice co-expressing the M146L presenilin 1 (PS1) and K670N/M671L, the double 'Swedish' amyloid precursor protein (APP) mutations, are a model of AD amyloid-beta deposition (Abeta) that exhibits earlier and more profound impairments of working memory and learning than single APP mutant mice. In this study we compared performance on spatial memory tests, regional glucose metabolism, Abeta deposition, and neuronal loss in APP/PS1, PS1, and non-Tg (nTg) mice. At the age of 2 months no significant morphological and metabolic differences were detected between 3 studied genotypes. By 8 months, however, APP/PS1 mice developed selective impairment of spatial memory, which was significantly worse at 22 months and was accompanied by reduced glucose utilization in the hippocampus and a 35.8% dropout of neurons in the CA1 region. PS1 mice exhibited a similar degree of neuronal loss in CA1 but minimal memory deficit and no impairment of glucose utilization compared to nTg mice. Deficits in 22 month APP/PS1 mice were accompanied by a substantially elevated Abeta load, which rose from 2.5% +/- 0.4% at 8 months to 17.4% +/- 4.6%. These findings implicate Abeta or APP in the behavioral and metabolic impairments in APP/PS1 mice and the failure to compensate functionally for PS1-related hippocampal cell loss

The minibrain kinase (Mnb/Dyrk1A) gene is localized in the Down syndrome (DS) critical region of chromosome 21. This gene encodes a proline-directed serine/threonine protein kinase (minibrain kinase-Mnb/Dyrk1A), which is required for the proliferation of distinct neuronal cell types during postembryonic neurogenesis. To study the distribution of Mnb/Dyrk1A during human brain development and aging, we raised Mnb/Dyrk1A-specific antibody (mAb 7F3) and examined 22 brains of normal subjects from 8 months to 90 years of age. We found that neurons were the only cells showing the presence of 7F3-positive product in both cell nucleus and cytoplasm. Nuclear localization supports the concept that Mnb/Dyrk1A may be involved in control of gene expression. Synaptic localization of Mnb/Dyrk1A also supports our previous studies suggesting that Mnb/Dyrk1A is a regulator of assembly of endocytic apparatus and appears to be involved in synaptic vesicle recycling and synaptic signal transmission. Accumulation of numerous 7F3-positive corpora amylacea in the memory and motor system subdivisions in subjects older than 33 years of age indicates that Mnb/Dyrk1A is colocalized with markers of astrocyte and neuron degeneration. Differences in the topography and the amount of Mnb/Dyrk1A in neurons, astrocytes, and ependymal and endothelial cells appear to reflect cell type- and brain structure-specific patterns in trafficking and utilization of Mnb/Dyrk1A

We used anti-prion (PrP) monoclonal antibodies (Mabs) in different combinations to scan changes in the availability of antibody binding epitopes--using an epitope scanning assay--in brain homogenates from normal mice, and from mice infected with either ME7 or 139 A strains of infectious scrapie prion (PrPSc). In ME7-infected brains, the epitope detected by the Mab pair 8B4/8H4 is reduced, while the epitope detected by the Mab pair 8F9/11G5 is increased. Mab 8F9/11G5 detect a conformational epitope on PrPSc because the rise in Mab 8F9/11G5 binding is sensitive to a denaturing agent but resistant to proteinase K (PK). While the increase in Mab 8F9/11G5 binding correlates with the presence of PK-resistant PrP and clinical signs of infection, the reduction in Mab 8B4/8H4 binding is detected earlier. Fractionation of the ME7-infected brain homogenate in sucrose gradient revealed that the PrPSc species detected by the epitope scanning assay are heterogeneous in size, with a molecular mass of approximately > or = 2000-kDa. We also investigated whether these findings were applicable to two other strains of PrPSc, namely 87 V and 22 L. We found that the decrease in Mab 8B4/8H4 binding detected in ME7-infected brains was also detected in 87 V-infected brains but not in 22 L-infected brains. In contrast, the increase in Mab 8F9/11G5 binding detected in ME7- and 139 A-infected brains was also detected in 22 L-infected brains but not in 87 V-infected brains. Therefore, each prion strain has its unique conformation, and we can monitor the conversion of normal cellular prion (PrPC) to PrPSc based on the changes in the antibody binding patterns. The epitope can be decreased or increased, linear or conformational, detected late or early during infection, in a strain specific manner

A novel presenilin-1 (PS1) mutation (P117S) in an American pedigree is described. We compare clinical, neuropathological and cell culture phenotypes produced by this mutation with another codon 117 mutation that was earlier discovered by our group in a Polish kindred. Both mutations are associated with an unusually severe Alzheimer disease (AD) phenotype, with the onset starting before the third decade of life, rapid disease progression and acute presentation of clinical symptoms. The severity of clinical phenotype was closely correlated with the abundance of pathology: massive deposition of Abeta42 in plaques, severe neurofibrillary degeneration and neuronal loss. When overexpressed in mouse neuroblastoma N2a cells, both mutations caused loss of an ability to promote neurite outgrowth and produced an increase in the ratio of secreted Abeta42/40 amyloid peptides. In stably transfected N2a cell lines only mutant proteins were endoproteolytically cleaved indicating some dependability of this process on the presence of mutation. Taken together, our results show that clinical and cell culture phenotypes produced by these 2 codon 117 mutations are closely related suggesting that the pathogenic action of PS1 may involve effect on neurite outgrowth and endoproteolytic cleavage of the full-length protein. Given the high potency in vivo and in vitro of both codon 117 mutations, this site of PS1 must be particularly important for its normal/pathogenic function