Acetylcholinesterase (AChE), an important component of cholinergic synapses, colocalizes with amyloid-beta peptide (A beta) deposits of Alzheimer's brain. We report here that bovine brain AChE, as well as the human and mouse recombinant enzyme, accelerates amyloid formation from wild-type A beta and a mutant A beta peptide, which alone produces few amyloid-like fibrils. The action of AChE was independent of the subunit array of the enzyme, was not affected by edrophonium, an active site inhibitor, but it was affected by propidium, a peripheral anionic binding site ligand. Butyrylcholinesterase, an enzyme that lacks the peripheral site, did not affect amyloid formation. Furthermore, AChE is a potent amyloid-promoting factor when compared with other A beta-associated proteins. Thus, in addition to its role in cholinergic synapses, AChE may function by accelerating A beta formation and could play a role during amyloid deposition in Alzheimer's brain.

The roles of the Wnt signalling pathway in several developmental processes, including synaptic differentiation, are well characterized. The expression of Wnt ligands and Wnt signalling components in the mature mammalian CNS suggests that this pathway might also play a part in synaptic maintenance and function. In fact, Wnts have a crucial role in synaptic physiology, as they modulate the synaptic vesicle cycle, the trafficking of neurotransmitter receptors and the interaction of these receptors with scaffold proteins in postsynaptic regions. In addition, Wnts participate in adult neurogenesis and protect excitatory synaptic terminals from amyloid-beta oligomer toxicity. Here, the latest insights into the function of Wnt signalling in the adult nervous system and therapeutic opportunities for neurodegenerative diseases such as Alzheimer's and Parkinson's disease are discussed.

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Acetylcholinesterase (AChE) has been found to be associated with the core of senile plaques. We have shown that AChE interacts with the amyloid beta-peptide (Abeta) and promotes amyloid fibril formation by a hydrophobic environment close to the peripheral anionic binding site (PAS) of the enzyme. Here we present evidence for the structural motif of AChE involved in this interaction. First, we modeled the docking of Abeta onto the structure of Torpedo californica AChE, and identified four potential sites for AChE-Abeta complex formation. One of these, Site I, spans a major hydrophobic sequence exposed on the surface of AChE, which had been previously shown to interact with liposomes [Shin et al. (1996) Protein Sci. 5, 42-51]. Second, we examined several AChE-derived peptides and found that a synthetic 35-residue peptide corresponding to the above hydrophobic sequence was able to promote amyloid formation. We also studied the ability to promote amyloid formation of two synthetic 24-residue peptides derived from the sequence of a Omega-loop, which has been suggested as an AChE-Abeta interacting motif. Kinetic analyses indicate that only the 35-residue hydrophobic peptide mimics the effect of intact AChE on amyloid formation. Moreover, RP-HPLC analysis revealed that the 35-residue peptide was incorporated into the growing Abeta-fibrils. Finally, fluorescence binding studies showed that this peptide binds Abeta with a K(d) = 184 microM, independent of salt concentration, indicating that the interaction is primarily hydrophobic. Our results indicate that the homologous human AChE motif is capable of accelerating Abeta fibrillogenesis.

ChileAlzheimer's disease (AD) is a progressive neurodegenerative disorder, which is probably caused by the cytotoxic effect of the amyloid b-peptide (Ab). We report here molecular changes induced by Ab, both in neuronal cells in culture and in rats injected in the dorsal hippocampus with preformed Ab fibrils, as an in vivo model of the disease. Results indicate that in both systems, Ab neurotoxicity resulted in the destabilization of endogenous levels of b-catenin, a key transducer of the Wnt signaling pathway. Lithium chloride, which mimics Wnt signaling by inhibiting glycogen synthase kinase-3b promoted the survival of post-mitotic neurons against Ab neurotoxicity and recovered cytosolic b-catenin to control levels. Moreover, the neurotoxic effect of Ab fibrils was also modulated with protein kinase C agonists/inhibitors and reversed with conditioned medium containing the Wnt-3a ligand. We also examined the spatial memory performance of rats injected with preformed Ab fibrils in the Morris water maze paradigm, and found that chronic lithium treatment protected neurodegeneration by rescuing b-catenin levels and improved the deficit in spatial learning induced by Ab. Our results are consistent with the idea that Ab-dependent neurotoxicity induces a loss of function of Wnt signaling components and indicate that lithium or compounds that mimic this signaling cascade may be putative candidates for therapeutic intervention in Alzheimer's patients.

Amyloid-beta peptide (A beta) consists of a hydrophobic C-terminal domain (residues 29-42) that adopts beta-strand conformation and an N-terminal domain (amino acids 10-24) whose sequence permits the existence of a dynamic equilibrium between an alpha-helix and a beta-strand. In this paper we analyzed the effect of the alternate N-terminal conformations on amyloid fibril formation through the study of the analogous A beta peptides containing single amino acidic substitutions. The single mutation of valine 18 to alanine induces a significant increment of the alpha-helical content of A beta, determined by Fourier transform infrared spectroscopy and circular dichroism and dramatically diminishes fibrillogenesis, measured by turbidity, thioflavine T binding, Congo red staining, and electron microscopic examination. In hereditary Dutch cerebral hemorrhage with amyloidosis (a variant of Alzheimer's disease), the substitution of glutamine for glutamic acid at position 22 decreased the propensity of the A beta N-terminal domain to adopt an alpha-helical structure, with a concomitant increase in amyloid formation. We propose that A beta exists in an equilibrium between two species: one "able" and another "unable" to form amyloid, depending on the secondary structure adopted by the N-terminal domain. Thus, manipulation of the A beta secondary structure with therapeutical compounds that promote the alpha-helical conformation may provides a tool to control the amyloid deposition observed in Alzheimer's disease patients.

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Wnt signaling is essential for neuronal development and the maintenance of the developing nervous system. Recent studies indicated that Wnt signaling modulates long term potentiation in adult hippocampal slices. We report here that different Wnt ligands are present in hippocampal neurons of rat embryo and adult rat, including Wnt-4, -5a, -7a, and -11. Wnt-7a acts as a canonical Wnt ligand in rat hippocampal neurons, stimulates clustering of presynaptic proteins, and induces recycling and exocytosis of synaptic vesicles as studied by FM dyes. Wnt-3a has a moderate effect on recycling of synaptic vesicles, and no effect of Wnt-1 and Wnt-5a was detected. Electrophysiological analysis on adult rat hippocampal slices indicates that Wnt-7a, but not Wnt-5a, increases neurotransmitter release in CA3-CA1 synapses by decreasing paired pulse facilitation and increasing the miniature excitatory post-synaptic currents frequency. These results indicate that the presynaptic function of rat hippocampal neurons is modulated by the canonical Wnt signaling.Wnt signaling regulates crucial processes in all multicellular organisms, including cell proliferation, differentiation, migration, and morphogenesis. Since its discovery about 25 years ago, Wnt signaling has been extensively studied for its diverse roles in embryogenesis and cancer (1) and, more recently, in neural development and synaptic plasticity (2-5). Several studies suggest that Wnt factors play a role in the formation of neuronal connections, and other reports indicate a specific effect on synapse assembly; for example, in Drosophila embryos overexpression of the Wnt gene DWnt-3, encoding a protein localized in axonal processes, disrupted the formation of commissural tracts (6). Wnt-3 also regulates terminal arborization of neurotrophin-3-responsive spinal sensory neurons before the formation of sensory motoneuron synapses (7). In developing cerebellum cortex it has been found that conditioned medium from granule cells increases the diameter of mossy fiber axons and growth cone complexity, a result mimicked by 9). Wingless, the prototypical Drosophila Wnt, and its receptor are localized at the larval neuromuscular junction (10). Wingless is secreted by motoneurons and accumulates at both the pre-and postsynaptic terminals. The loss of Wingless leads to reduction in target-dependent synapse formation (10).The expression of Wnt ligands and proteins of the Wnt signaling machinery in the mature nervous system (11, 12) suggests that Wnt signaling plays a role in neuroprotection and synaptic plasticity in addition to its role in neurite patterning in the developing nervous system (3, 5, 13). Indeed, Wnt ligands can act locally to regulate changes in neuronal cell shape and pre-and postsynaptic terminals, which are thought to underlie changes in synaptic function and learning. Thus, Wnt ligands would appear to be particularly well suited as mediators of synaptic plasticity (5,14,15).In the present study we report that Wnt-7a, a canonical ligand that stimulates vesicle clusteri...