Amyloid-precursor-protein-lowering small molecules for disease modifying therapy of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly with progressive cognitive decline and memory loss. According to the amyloid-hypothesis, AD is caused by generation and subsequent cerebral deposition of β-amyloid (Aβ). Aβ is generated through sequential cleavage of the transmembrane Amyloid-Precursor-Protein (APP) by two endoproteinases termed beta- and gamma-secretase. Increased APP-expression caused by APP gene dosage effects is a risk factor for the development of AD. Here we carried out a large scale screen for novel compounds aimed at decreasing APP-expression. For this we developed a screening system employing a cell culture model of AD. A total of 10,000 substances selected for their ability of drug-likeness and chemical diversity were tested for their potential to decrease APP-expression resulting in reduced Aβ-levels. Positive compounds were further evaluated for their effect at lower concentrations, absence of cytotoxicity and specificity. The six most promising compounds were characterized and structure function relationships were established. The novel compounds presented here provide valuable information for the development of causal therapies for AD

Preclinical Deposition of Pathological Prion Protein in Muscle of Experimentally Infected Primates

Prion diseases are transmissible fatal neurodegenerative disorders affecting humans and animals. A central step in disease progression is the accumulation of a misfolded form (PrPSc) of the host encoded prion protein (PrPC) in neuronal and non-neuronal tissues. The involvement of peripheral tissues in preclinical states increases the risk of accidental transmission. On the other hand, detection of PrPSc in non-neuronal easy-accessible compartments such as muscle may offer a novel diagnostic tool. Primate models have proven invaluable to investigate prion diseases. We have studied the deposition of PrPSc in muscle and central nervous system of rhesus monkeys challenged with sporadic Creutzfeldt-Jakob disease (sCJD), variant CJD (vCJD) and bovine spongiform encephalopathy (BSE) in preclinical and clinical stage using biochemical and morphological methods. Here, we show the preclinical presence of PrPSc in muscle and central nervous system of rhesus monkeys experimentally infected with vCJD

N-Glycans and Glycosylphosphatidylinositol-Anchor Act on Polarized Sorting of Mouse PrPC in Madin-Darby Canine Kidney Cells

The cellular prion protein (PrPC) plays a fundamental role in prion disease. PrPC is a glycosylphosphatidylinositol (GPI)-anchored protein with two variably occupied N-glycosylation sites. In general, GPI-anchor and N-glycosylation direct proteins to apical membranes in polarized cells whereas the majority of mouse PrPC is found in basolateral membranes in polarized Madin-Darby canine kidney (MDCK) cells. In this study we have mutated the first, the second, and both N-glycosylation sites of PrPC and also replaced the GPI-anchor of PrPC by the Thy-1 GPI-anchor in order to investigate the role of these signals in sorting of PrPC in MDCK cells. Cell surface biotinylation experiments and confocal microscopy showed that lack of one N-linked oligosaccharide leads to loss of polarized sorting of PrPC. Exchange of the PrPC GPI-anchor for the one of Thy-1 redirects PrPC to the apical membrane. In conclusion, both N-glycosylation and GPI-anchor act on polarized sorting of PrPC, with the GPI-anchor being dominant over N-glycans

A bovine cell line that can be infected by natural sheep scrapie prions.

Cell culture systems represent a crucial part in basic prion research; yet, cell lines that are susceptible to prions, especially to field isolated prions that were not adapted to rodents, are very rare. The purpose of this study was to identify and characterize a cell line that was susceptible to ruminant-derived prions and to establish a stable prion infection within it. Based on species and tissue of origin as well as PrP expression rate, we pre-selected a total of 33 cell lines that were then challenged with natural and with mouse propagated BSE or scrapie inocula. Here, we report the successful infection of a non-transgenic bovine cell line, a sub-line of the bovine kidney cell line MDBK, with natural sheep scrapie prions. This cell line retained the scrapie infection for more than 200 passages. Selective cloning resulted in cell populations with increased accumulation of PrPres, although this treatment was not mandatory for retaining the infection. The infection remained stable, even under suboptimal culture conditions. The resulting infectivity of the cells was confirmed by mouse bioassay (Tgbov mice, Tgshp mice). We believe that PES cells used together with other prion permissive cell lines will prove a valuable tool for ongoing efforts to understand and defeat prions and prion diseases

Amyloid-precursor-protein-lowering small molecules for disease modifying therapy of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia in the elderly with progressive cognitive decline and memory loss. According to the amyloid-hypothesis, AD is caused by generation and subsequent cerebral deposition of β-amyloid (Aβ). Aβ is generated through sequential cleavage of the transmembrane Amyloid-Precursor-Protein (APP) by two endoproteinases termed beta- and gamma-secretase. Increased APP-expression caused by APP gene dosage effects is a risk factor for the development of AD. Here we carried out a large scale screen for novel compounds aimed at decreasing APP-expression. For this we developed a screening system employing a cell culture model of AD. A total of 10,000 substances selected for their ability of drug-likeness and chemical diversity were tested for their potential to decrease APP-expression resulting in reduced Aβ-levels. Positive compounds were further evaluated for their effect at lower concentrations, absence of cytotoxicity and specificity. The six most promising compounds were characterized and structure function relationships were established. The novel compounds presented here provide valuable information for the development of causal therapies for AD

Thy-1-GPI anchor redirects PrP^C to the apical site.

<p>(A) Cells stably expressing PrP^CWT and PrP^C-GPIThy-1 were grown in Transwells for 4 to 5 days, processed for immunocytochemistry, and analyzed with confocal microscopy. YZ sections (left) and view on the membrane (right) at the level of tight junctions stained for ZO-1 (red) confirm both polarization and confluency of cells and show increased apical signal for PrP^C-GPIThy-1 (green). (B) After staining with PrP 3F4 antibody under non-permeabilizing conditions, serial Z-stacks from the bottom to the top were taken. YZ sections show transversal cut through cells at the level of the dashed line in mid. PrP^C-GPIThy-1 was found at the apical membrane when compared to PrP^CWT. Scale bars are 10 µm. (C) Cells grown in Transwells labeled with EZ-Link Sulfo-NHS-SS-Biotin either apically (a) or basolaterally (b) were processed for Western blotting for PrP^C and E-Cadherin (as control of cell polarization) in parallel. The graph (three independent experiments) shows mean percentages ± SEM of apical (a) or basolateral (b) amount of protein when compared to the total amount which is set at 100%.</p

Schematic drawing of constructs used in this study.

<p>Shown are the maps of PrP^CWT, PrP^CG1, PrP^CG2, and PrP^CG3 with N-terminal signal sequence (ss) and C-terminal GPI-anchor signal (ss GPI-anchor) (dark boxes) and the mutations introduced to delete N-gylcosylation sites.</p