Expression of acetylcholinesterase in alzheimer's disease brain: Role in neuritic dystrophy and synaptic scaling

Not availabl

The beta-amyloid protein of Alzheimer's disease increases neuronal CRMP-2 phosphorylation by a Rho-GTP mechanism

Neuritic abnormalities are a major hallmark of Alzheimer's disease (AD) pathology. Accumulation of ?-amyloid protein (A?) in the brain causes changes in neuritic processes in individuals with this disease. In this study, we show that A? decreases neurite outgrowth from SH-SY5Y human neuroblastoma cells. To explore molecular pathways by which A? alters neurite outgrowth, we examined the activation and localization of RhoA and Rac1 which regulate the level and phosphorylation of the collapsin response mediator protein-2 (CRMP-2). A? increased the levels of the GTP-bound (active) form of RhoA in SH-SY5Y cells. This increase in GTP-RhoA correlated with an increase in an alternatively spliced form of CRMP-2 (CRMP-2A) and its threonine phosphorylated form. Both a constitutively active form of Rac1 (CA-Rac1) and the Rho kinase inhibitor, Y27632, decreased levels of the CRMP-2A variant and decreased threonine phosphorylation caused by A? stimulation. The amount of tubulin bound to CRMP-2 was decreased in the presence of A? but Y27632 increased the levels of tubulin bound to CRMP-2. Increased levels of both RhoA and CRMP-2 were found in neurons surrounding amyloid plaques in the cerebral cortex of the APP(Swe) Tg2576 mice. We found that there was an increase in threonine phosphorylation of CRMP-2 in Tg2576 mice and the increase correlated with a decrease in the ability of CRMP-2 to bind tubulin. The results suggest that A?-induced neurite outgrowth inhibition may be initiated through a mechanism in which A? causes an increase in Rho GTPase activity which, in turn, phosphorylates CRMP-2 to interfere with tubulin assembly in neurites

The crystal structure of diadenosine tetraphosphate hydrolase from Caenorhabditis elegans in free and binary complex forms

AbstractThe crystal structure of C. elegans Ap4A hydrolase has been determined for the free enzyme and a binary complex at 2.0 Å and 1.8 Å, respectively. Ap4A hydrolase has a key role in regulating the intracellular Ap4A levels and hence potentially the cellular response to metabolic stress and/or differentiation and apoptosis via the Ap3A/Ap4A ratio. The structures reveal that the enzyme has the mixed α/β fold of the Nudix family and also show how the enzyme binds and locates its substrate with respect to the catalytic machinery of the Nudix motif. These results suggest how the enzyme can catalyze the hydrolysis of a range of related dinucleoside tetraphosphate, but not triphosphate, compounds through precise orientation of key elements of the substrate

The beta-amyloid protein of Alzheimer's disease does not bind to the alpha7 nicotinic acetylcholine receptor

Accumulation of the amyloid protein (Aß) in the brain is an important step in the pathogenesis of Alzheimer's disease. However, the mechanism by which Aß exerts its neurotoxic effect is largely unknown. It has been suggested that the peptide can bind to the a7 nicotinic acetylcholine receptor (a7nAChR). In this study, we examined the binding of Aß1-42 to endogenous and recombinantly expressed a7nAChRs. Aß1-42 did neither inhibit the specific binding of a7nAChR ligands to rat brain homogenate or slice preparations, nor did it influence the activity of a7nAChRs expressed in Xenopus oocytes. Similarly, Aß1-42 did not compete for a-bungarotoxin-binding sites on SH-SY5Y cells stably expressing a7nAChRs. The effect of the Aß1-42 on tau phosphorylation was also examined. Although Aß1-42 altered tau phosphorylation in a7nAChR-transfected SH-SY5Y cells, the effect of the peptide was unrelated to a7nAChR expression or activity. Binding studies using surface plasmon resonance indicated that the majority of the Aß bound to membrane lipid, rather than to a protein component. Fluorescence anisotropy experiments indicated that Aß may disrupt membrane lipid structure or fluidity. We conclude that the effects of Aß are unlikely to be mediated by direct binding to the a7nAChR. Instead, we speculate that Aß may exert its effects by altering the packing of lipids within the plasma membrane, which could, in turn, influence the function of a variety of receptors and channels on the cell surface. © 2007 The Author

Monitoring of chromatin organization in live cells by FRIC. Effects of the inner nuclear membrane protein Samp1

In most cells, transcriptionally inactive heterochromatin is preferentially localized in the nuclear periphery and transcriptionally active euchromatin is localized in the nuclear interior. Different cell types display characteristic chromatin distribution patterns, which change dramatically during cell differentiation, proliferation, senescence and different pathological conditions. Chromatin organization has been extensively studied on a cell population level, but there is a need to understand dynamic reorganization of chromatin at the single cell level, especially in live cells. We have developed a novel image analysis tool that we term Fluorescence Ratiometric Imaging of Chromatin (FRIC) to quantitatively monitor dynamic spatiotemporal distribution of euchromatin and total chromatin in live cells. A vector (pTandemH) assures stoichiometrically constant expression of the histone variants Histone 3.3 and Histone 2B, fused to EGFP and mCherry, respectively. Quantitative ratiometric (H3.3/H2B) imaging displayed a concentrated distribution of heterochromatin in the periphery of U2OS cell nuclei. As proof of concept, peripheral heterochromatin responded to experimental manipulation of histone acetylation. We also found that peripheral heterochromatin depended on the levels of the inner nuclear membrane protein Samp1, suggesting an important role in promoting peripheral heterochromatin. Taken together, FRIC is a powerful and robust new tool to study dynamic chromatin redistribution in live cells