The amyloid-␤ peptide (A␤) plays a major role in neuronal dysfunction and neurotoxicity in Alzheimer disease. However, the signal transduction mechanisms involved in A␤-induced neuronal dysfunction remain to be fully elucidated. A major current unknown is the identity of the protein receptor(s) involved in neuronal A␤ binding. Using phage display of peptide libraries, we have identified a number of peptides that bind A␤ and are homologous to neuronal receptors putatively involved in A␤ interactions. We report here on a cysteine-linked cyclic heptapeptide (denominated cSP5) that binds A␤ with high affinity and is homologous to the extracellular cysteine-rich domain of several members of the Frizzled (Fz) family of Wnt receptors. Based on this homology, we investigated the interaction between A␤ and Fz. The results show that A␤ binds to the Fz cysteine-rich domain at or in close proximity to the Wnt-binding site and inhibits the canonical Wnt signaling pathway. Interestingly, the cSP5 peptide completely blocks A␤ binding to Fz and prevents inhibition of Wnt signaling. These results indicate that the A␤-binding site in Fz is homologous to cSP5 and that this is a relevant target for A␤-instigated neurotoxicity. Furthermore, they suggest that blocking the interaction of A␤ with Fz might lead to novel therapeutic approaches to prevent neuronal dysfunction in Alzheimer disease. Alzheimer disease (AD)2 is a progressive neurodegenerative disorder characterized, in its early stages, by a striking inability to form new memories. Recent work indicates that cognitive and memory impairments in early AD are caused by synaptic dysfunction instigated by pathological assemblies of the amyloid-␤ peptide (A␤) (for recent reviews, see Refs. 1-3). Neuropathological hallmarks of AD include increased brain levels and extracellular build-up of A␤ aggregates, intraneuronal neurofibrillary tangles composed of hyperphosphorylated Tau, and, notably, synaptic loss (1). Despite the fact that A␤ has been strongly implicated in neuronal dysfunction and neurotoxicity in AD, the signal transduction mechanisms involved in the neuronal impact of A␤ remain to be fully elucidated. A major current unknown is the identity of the neuronal receptor(s) that bind A␤ and mediate neuronal dysfunction. Identification of such receptor(s) would provide considerable insight into mechanisms of pathogenesis and might reveal novel opportunities for the development of strategies to combat AD.The Wnt signaling pathway has been recently proposed to play a role in AD (for a review, see Ref. 4). Wnts are secreted glycoproteins that bind to and signal through Frizzled (Fz) receptors and mediate cell-cell communication (5). Wnt signaling regulates a variety of biological processes, including development, cell movement, polarity, axon guidance, and synapse formation (6). Different types of Wnt⅐Fz complexes may signal through the so-called canonical or noncanonical Wnt pathways. Canonical Wnt/Fz signaling results in stabilization and increased intracellular levels of ␤-cate...

In the past two decades, a large body of evidence has established a causative role for the beta-amyloid peptide (Abeta) in Alzheimer's disease (AD). However, recent debate has focused on whether amyloid fibrils or soluble oligomers of Abeta are the main neurotoxic species that contribute to neurodegeneration and dementia. Considerable early evidence has indicated that amyloid fibrils are toxic, but some recent studies support the notion that Abeta oligomers are the primary neurotoxins. While this crucial aspect of AD pathogenesis remains controversial, effective therapeutic strategies should ideally target both oligomeric and fibrillar species of Abeta. Here, we describe the anti-amyloidogenic and neuroprotective actions of some di- and tri-substituted aromatic compounds. Inhibition of the formation of soluble Abeta oligomers was monitored using a specific antibody-based assay that discriminates between Abeta oligomers and monomers. Thioflavin T and electron microscopy were used to screen for inhibitors of fibril formation. Taken together, these results led to the identification of compounds that more effectively block Abeta oligomerization than fibrillization. It is significant that such compounds completely blocked the neurotoxicity of Abeta to rat hippocampal neurons in culture. These findings provide a basis for the development of novel small molecule Abeta inhibitors with potential applications in AD.

Prions, the etiological agents for infectious degenerative encephalopathies, act by entering the cell and inducing conformational changes in PrPC (a normal cell membrane sialoglycoprotein), which result in cell death. A specific cell-surface receptor to mediate PrPC and prion endocytosis has been predicted. Complementary hydropathy let us generate a hypothetical peptide mimicking the receptor binding site. Antibodies raised against this peptide stain the surface of mouse neurons and recognize a 66-kDa membrane protein that binds PrPC both in vitro and in vivo. Furthermore, both the complementary prion peptide and antiserum against it inhibit the toxicity of a prion-derived peptide toward neuronal cells in culture. Such reagents might therefore have therapeutic applications.

Regional astrocyte cultures were obtained by dissecting and dissociating medial and lateral sectors of the midbrain from 14-day Swiss mouse embryos. Once confluent, these cultures were tested by glial fibrillary acidic protein (GFAP) immunocytochemistry to confirm their astrocyte composition and for 2'-3' cyclic nucleotide 3'-phosphohydrolase (CNPase) and microtubule-associated protein 2 (MAP2) immunocytochemistry to rule out oligodendroglial and neuronal components, respectively. In confluent astrocyte cultures from either sector, virtually all cells were GFAP-positive elements, most of which were flat cells accompanied by smaller numbers of flat cells with processes. Confluent astrocyte cultures, derived from medial (M) or lateral (L) sectors, were used as substrata for culturing dissociated cells from medial (m) or lateral (l) sectors of 14-day embryonic midbrains. Fixed cocultures (Ll, Lm, Mm, Ml) were stained with an anti-MAP2 antibody to verify neuronal aggregation and neuritic morphology. In spite of the morphological constancy of glial substrata at plating, MAP2-positive cells in cocultures showed differences in the aggregation of somata and in the length, caliber, and branching of neurites. These differences, which depend mostly on the sector of origin of astrocytes, suggest that the substrata may differ in adhesiveness and/or growth-promoting vs. growth-interfering properties. Together with evidence for sectorial heterogeneity in brainstem radial glia, the present results raise the possibility that cultured astrocytes have properties that reflect the roles played by their parent radial glia in the developing brain.