Alzheimer Disease: Klein WL

Lambert MP, Velasco PT, Viola KL, Klein WL. · Northwestern University, Dept. of Neurobiology and Physiology, and the Cognitive Neurology and Alzheimer's Disease Center, Evanston, IL 60208, USA. · CNS Neurol Disord Drug Targets. · Pubmed #19275637 No free full text.

Abstract: Individuals with early Alzheimer's disease (AD) suffer from a selective and profound failure to form new memories. A novel molecular mechanism with implications for therapeutics and diagnostics is now emerging in which the specificity of AD for memory derives from disruption of plasticity at synapses targeted by toxic Abeta oligomers (also known as ADDLs). ADDLs accumulate in AD brain and constitute long-lived alternatives to the disease-defining Abeta fibrils deposited in amyloid plaques. The AD-like cellular pathologies induced by ADDLs suggest their impact could provide a unifying mechanism for AD pathogenesis, explaining why early stage disease is specific for memory and accounting for major facets of AD neuropathology. Discovery of these new toxins has provided an appealing target for disease-modifying immunotherapy. For optimal protection against these toxins, antibodies should bind to the pathological oligomers without being depleted by their monomeric subunits, which are rapidly generated by membrane protein turnover. A solution to this problem is likely to come from the continued development of conformation-specific antibodies, as described here. Prototype conformation-specific antibodies, not yet in the clinic, have been introduced and utilized in multiple applications for their ability to bind with high specificity and affinity to ADDLs. It can be anticipated that further development of such antibodies for use in clinical trials will come in the near future.

Viola KL, Velasco PT, Klein WL. · Department of Neurobiology and Physiology, Cognitive Neurology and Alzheimer's Disease Center, Northwestern University, Evanston, IL 60208, USA. · J Nutr Health Aging. · Pubmed #18165846 No free full text.

Abstract: Individuals with early-stage Alzheimer's disease (AD) suffer from profound failure to form new memories. A novel molecular mechanism with implications for therapeutics and diagnostics is now emerging in which the specificity of AD for memory derives from disruption of plasticity at synapses targeted by neurologically active A beta oligomers (1). We have named these oligomers "ADDLs" (for pathogenic A beta-Derived Diffusible Ligands). ADDLs constitute metastable alternatives to the disease-defining A beta fibrils deposited in amyloid plaques. In AD brain, ADDLs accumulate primarily as A beta 12mers (2) (approximately 54 kDa) and can be found in dot-like clusters distinct from senile plaques (3). Oligomers of equal mass have been reported to occur in tgmouse AD models where they emerge concomitantly with memory failure (4), consistent with ADDL inhibition of LTP (1). In cell biology studies, ADDLs act as pathogenic gain-of-function ligands that target particular synapses, binding to synaptic spines at or near NMDA receptors (5,6). Binding produces ectopic expression of the memory-linked immediate early gene Arc. Subsequent ADDL-induced abnormalities in spine morphology and synaptic receptor composition (7) are predicted consequences of Arc overexpression, a pathology associated with memory dysfunction in tg-Arc mice. Significantly, the attack on synapses provides a plausible mechanism unifying memory dysfunction with major features of AD neuropathology; recent findings show that ADDL binding instigates synapse loss, oxidative damage, and AD-type tau hyperphosphorylation. Acting as novel neurotoxins that putatively account for memory loss and neuropathology, ADDLs present significant targets for disease-modifying therapeutics in AD.

De Felice FG, Wasilewska-Sampaio AP, Barbosa AC, Gomes FC, Klein WL, Ferreira ST. · Instituto de Bioquímica Médica, Programa de Bioquímica e Biofísica Celular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21944-590, Brazil. · Curr Alzheimer Res. · Pubmed #17627483 No free full text.

Abstract: One of the earliest manifestations of Alzheimer's disease (AD) is the characteristic inability of affected individuals to form new memories. Memory impairment appears to significantly predate the death of nerve cells, implying that neuronal dysfunction is responsible for the pathophysiology of early stage AD. Mounting evidence now indicates that soluble oligomers of the amyloid-beta peptide (Abeta) are the main neurotoxins that lead to early neuronal dysfunction and memory deficits in AD. Cyclic AMP (cAMP) is a central component of intracellular signaling pathways that regulate a wide range of biological functions, including memory. Among other actions, cAMP triggers the phosphorylation and activation of the cAMP responsive element binding protein (CREB), a transcription factor that regulates the expression of genes that are important for long-term memory. Here, we discuss recent evidence suggesting that cAMP enhancing compounds may find applications as neurocognitive enhancers in AD and in other neurological disorders, as well as possible roles of cAMP in the regulation of neuronal regeneration. In particular, we review recent results showing that low concentrations of 2,4-dinitrophenol (DNP) upregulate neuronal cAMP and tau levels, promote neurite outgrowth and neuronal differentiation and block the oligomerization and neurotoxicity of Abeta. Possible implications of these findings in the development of novel therapeutic approaches in AD are discussed.

Klein WL, Stine WB, Teplow DB. · Department of Neurobiology and Physiology, Cognitive Neurology and Alzheimer's Disease Center, Northwestern University Institute for Neuroscience, Evanston, IL, USA. · Neurobiol Aging. · Pubmed #15172732 No free full text.

Abstract: Pioneering work in the 1950s by Christian Anfinsen on the folding of ribonuclease has shown that the primary structure of a protein "encodes" all of the information necessary for a nascent polypeptide to fold into its native, physiologically active, three-dimensional conformation (for his classic review, see [Science 181 (1973) 223]). In Alzheimer's disease (AD), the amyloid beta-protein (Abeta) appears to play a seminal role in neuronal injury and death. Recent data have suggested that the proximate effectors of neurotoxicity are oligomeric Abeta assemblies. A fundamental question, of relevance both to the development of therapeutic strategies for AD and to understanding basic laws of protein folding, is how Abeta assembly state correlates with biological activity. Evidence suggests, as argued by Anfinsen, that the formation of toxic Abeta structures is an intrinsic feature of the peptide's amino acid sequence-one requiring no post-translational modification or invocation of peptide-associated enzymatic activity.

Klein WL. · Department of Neurobiology and Physiology, Cognitive Neurology and Alzheimer's Disease Center, Northwestern University Institute for Neuroscience, 2153 North Campus Drive, 60208, Evanston, IL, USA. · Neurochem Int. · Pubmed #12176077 No free full text.

Abstract: Over the past several years, experiments with synthetic amyloid-beta peptide (Abeta) and animal models have strongly suggested that pathogenesis of Alzheimer's disease (AD) involves soluble assemblies of Abeta peptides (Trends Neurosci. 24 (2001) 219). These soluble neurotoxins (known as ADDLs and protofibrils) seem likely to account for the imperfect correlation between insoluble fibrillar amyloid deposits and AD progression. Recent experiments have detected the presence of ADDLs in AD-afflicted brain tissue and in transgenic-mice models of AD. The presence of high affinity ADDL binding proteins in hippocampus and frontal cortex but not cerebellum parallels the regional specificity of AD pathology and suggests involvement of a toxin receptor-mediated mechanism. The properties of ADDLs and their presence in AD-afflicted brain are consistent with their putative role even in the earliest stages of AD, including forms of mild cognitive impairment.

Klein WL, Krafft GA, Finch CE. · Northwestern University Institute for Neuroscience and Dept of Neurobiology and Physiology, Northwestern University, 2153 N Campus Drive, Evanston, IL 60208, USA. · Trends Neurosci. · Pubmed #11250006 No free full text.

Abstract: Amyloid beta (Abeta) is a small self-aggregating peptide produced at low levels by normal brain metabolism. In Alzheimer's disease (AD), self-aggregation of Abeta becomes rampant, manifested most strikingly as the amyloid fibrils of senile plaques. Because fibrils can kill neurons in culture, it has been argued that fibrils initiate the neurodegenerative cascades of AD. An emerging and different view, however, is that fibrils are not the only toxic form of Abeta, and perhaps not the neurotoxin that is most relevant to AD: small oligomers and protofibrils also have potent neurological activity. Immuno-neutralization of soluble Abeta-derived toxins might be the key to optimizing AD vaccines that are now on the horizon.

Zhao WQ, Lacor PN, Chen H, Lambert MP, Quon MJ, Krafft GA, Klein WL. · From the Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208. · J Biol Chem. · Pubmed #19406747 No free full text.

Abstract: Accumulation of amyloid beta (Abeta) oligomers in the brain is toxic to synapses and may play an important role in memory loss in Alzheimer disease. However, how these toxins are built up in the brain is not understood. In this study we investigate whether impairments of insulin and insulin-like growth factor-1 (IGF-1) receptors play a role in aggregation of Abeta. Using primary neuronal culture and immortal cell line models, we show that expression of normal insulin or IGF-1 receptors confers cells with abilities to reduce exogenously applied Abeta oligomers (also known as ADDLs) to monomers. In contrast, transfection of malfunctioning human insulin receptor mutants, identified originally from patient with insulin resistance syndrome, or inhibition of insulin and IGF-1 receptors via pharmacological reagents increases ADDL levels by exacerbating their aggregation. In healthy cells, activation of insulin and IGF-1 receptor reduces the extracellular ADDLs applied to cells via seemingly the insulin-degrading enzyme activity. Although insulin triggers ADDL internalization, IGF-1 appears to keep ADDLs on the cell surface. Nevertheless, both insulin and IGF-1 reduce ADDL binding, protect synapses from ADDL synaptotoxic effects, and prevent the ADDL-induced surface insulin receptor loss. Our results suggest that dysfunctions of brain insulin and IGF-1 receptors contribute to Abeta aggregation and subsequent synaptic loss.

De Felice FG, Vieira MN, Bomfim TR, Decker H, Velasco PT, Lambert MP, Viola KL, Zhao WQ, Ferreira ST, Klein WL. · Department of Neurobiology and Physiology, Northwestern University, Evanston, IL 60208, USA. · Proc Natl Acad Sci U S A. · Pubmed #19188609 links to  free full text

Abstract: Synapse deterioration underlying severe memory loss in early Alzheimer's disease (AD) is thought to be caused by soluble amyloid beta (Abeta) oligomers. Mechanistically, soluble Abeta oligomers, also referred to as Abeta-derived diffusible ligands (ADDLs), act as highly specific pathogenic ligands, binding to sites localized at particular synapses. This binding triggers oxidative stress, loss of synaptic spines, and ectopic redistribution of receptors critical to plasticity and memory. We report here the existence of a protective mechanism that naturally shields synapses against ADDL-induced deterioration. Synapse pathology was investigated in mature cultures of hippocampal neurons. Before spine loss, ADDLs caused major downregulation of plasma membrane insulin receptors (IRs), via a mechanism sensitive to calcium calmodulin-dependent kinase II (CaMKII) and casein kinase II (CK2) inhibition. Most significantly, this loss of surface IRs, and ADDL-induced oxidative stress and synaptic spine deterioration, could be completely prevented by insulin. At submaximal insulin doses, protection was potentiated by rosiglitazone, an insulin-sensitizing drug used to treat type 2 diabetes. The mechanism of insulin protection entailed a marked reduction in pathogenic ADDL binding. Surprisingly, insulin failed to block ADDL binding when IR tyrosine kinase activity was inhibited; in fact, a significant increase in binding was caused by IR inhibition. The protective role of insulin thus derives from IR signaling-dependent downregulation of ADDL binding sites rather than ligand competition. The finding that synapse vulnerability to ADDLs can be mitigated by insulin suggests that bolstering brain insulin signaling, which can decline with aging and diabetes, could have significant potential to slow or deter AD pathogenesis.

Hirata-Fukae C, Li HF, Hoe HS, Gray AJ, Minami SS, Hamada K, Niikura T, Hua F, Tsukagoshi-Nagai H, Horikoshi-Sakuraba Y, Mughal M, Rebeck GW, LaFerla FM, Mattson MP, Iwata N, Saido TC, Klein WL, Duff KE, Aisen PS, Matsuoka Y. · Department of Neurology, Georgetown University Medical Center, Washington, DC 20057, USA. · Brain Res. · Pubmed #18486110 No free full text.

Abstract: Epidemiological studies indicate that women have a higher risk of Alzheimer's disease (AD) even after adjustment for age. Though transgenic mouse models of AD develop AD-related amyloid beta (Abeta) and/or tau pathology, gender differences have not been well documented in these models. In this study, we found that female 3xTg-AD transgenic mice expressing mutant APP, presenilin-1 and tau have significantly more aggressive Abeta pathology. We also found an increase in beta-secretase activity and a reduction of neprilysin in female mice compared to males; this suggests that a combination of increased Abeta production and decreased Abeta degradation may contribute to higher risk of AD in females. In contrast to significantly more aggressive Abeta pathology in females, gender did not affect the levels of phosphorylated tau in 3xTg-AD mice. These results point to the involvement of Abeta pathways in the higher risk of AD in women. In addition to comparison of pathology between genders at 9, 16 and 23 months of age, we examined the progression of Abeta pathology at additional age points; i.e., brain Abeta load, intraneuronal oligomeric Abeta distribution and plaque load, in male 3xTg-AD mice at 3, 6, 9, 12, 16, 20 and 23 months of age. These findings confirm progressive Abeta pathology in 3xTg-AD transgenic mice, and provide guidance for their use in therapeutic research.

McKee AC, Carreras I, Hossain L, Ryu H, Klein WL, Oddo S, LaFerla FM, Jenkins BG, Kowall NW, Dedeoglu A. · Department of Neurology, Boston University School of Medicine, Boston, MA, USA. · Brain Res. · Pubmed #18374906 links to  free full text

Abstract: We examined the effects of ibuprofen on cognitive deficits, Abeta and tau accumulation in young triple transgenic (3xTg-AD) mice. 3xTg-AD mice were fed ibuprofen-supplemented chow between 1 and 6 months. Untreated 3xTg-AD mice showed significant impairment in the ability to learn the Morris water maze (MWM) task compared to age-matched wild-type (WT) mice. The performance of 3xTg-AD mice was significantly improved with ibuprofen treatment compared to untreated 3xTg-AD mice. Ibuprofen-treated transgenic mice showed a significant decrease in intraneuronal oligomeric Abeta and hyperphosphorylated tau (AT8) immunoreactivity in the hippocampus. Confocal microscopy demonstrated co-localization of conformationally altered (MC1) and early phosphorylated tau (CP-13) with oligomeric Abeta, and less co-localization of oligomeric Abeta and later forms of phosphorylated tau (AT8 and PHF-1) in untreated 3xTg-AD mice. Our findings show that prophylactic treatment of young 3xTg-AD mice with ibuprofen reduces intraneuronal oligomeric Abeta, reduces cognitive deficits, and prevents hyperphosphorylated tau immunoreactivity. These findings provide further support for intraneuronal Abeta as a cause of cognitive impairment, and suggest that pathological alterations of tau are associated with intraneuronal oligomeric Abeta accumulation.

De Felice FG, Wu D, Lambert MP, Fernandez SJ, Velasco PT, Lacor PN, Bigio EH, Jerecic J, Acton PJ, Shughrue PJ, Chen-Dodson E, Kinney GG, Klein WL. · Department of Neurobiology and Physiology, Northwestern University, 2205 Tech Drive, Evanston, IL 60208, USA. · Neurobiol Aging. · Pubmed #17403556 No free full text.

Abstract: Alzheimer's disease (AD) is characterized by presence of extracellular fibrillar A beta in amyloid plaques, intraneuronal neurofibrillary tangles consisting of aggregated hyperphosphorylated tau and elevated brain levels of soluble A beta oligomers (ADDLs). A major question is how these disparate facets of AD pathology are mechanistically related. Here we show that, independent of the presence of fibrils, ADDLs stimulate tau phosphorylation in mature cultures of hippocampal neurons and in neuroblastoma cells at epitopes characteristically hyperphosphorylated in AD. A monoclonal antibody that targets ADDLs blocked their attachment to synaptic binding sites and prevented tau hyperphosphorylation. Tau phosphorylation was blocked by the Src family tyrosine kinase inhibitor, 4-amino-5-(4-chlorophenyl)-7(t-butyl)pyrazol(3,4-D)pyramide (PP1), and by the phosphatidylinositol-3-kinase inhibitor LY294002. Significantly, tau hyperphosphorylation was also induced by a soluble aqueous extract containing A beta oligomers from AD brains, but not by an extract from non-AD brains. A beta oligomers have been increasingly implicated as the main neurotoxins in AD, and the current results provide a unifying mechanism in which oligomer activity is directly linked to tau hyperphosphorylation in AD pathology.

De Felice FG, Velasco PT, Lambert MP, Viola K, Fernandez SJ, Ferreira ST, Klein WL. · Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208, USA. · J Biol Chem. · Pubmed #17308309 links to  free full text

Abstract: Oxidative stress is a major aspect of Alzheimer disease (AD) pathology. We have investigated the relationship between oxidative stress and neuronal binding of Abeta oligomers (also known as ADDLs). ADDLs are known to accumulate in brain tissue of AD patients and are considered centrally related to pathogenesis. Using hippocampal neuronal cultures, we found that ADDLs stimulated excessive formation of reactive oxygen species (ROS) through a mechanism requiring N-methyl-d-aspartate receptor (NMDA-R) activation. ADDL binding to neurons was reduced and ROS formation was completely blocked by an antibody to the extracellular domain of the NR1 subunit of NMDA-Rs. In harmony with a steric inhibition of ADDL binding by NR1 antibodies, ADDLs that were bound to detergent-extracted synaptosomal membranes co-immunoprecipitated with NMDA-R subunits. The NR1 antibody did not affect ROS formation induced by NMDA, showing that NMDA-Rs themselves remained functional. Memantine, an open channel NMDA-R antagonist prescribed as a memory-preserving drug for AD patients, completely protected against ADDL-induced ROS formation, as did other NMDA-R antagonists. Memantine and the anti-NR1 antibody also attenuated a rapid ADDL-induced increase in intraneuronal calcium, which was essential for stimulated ROS formation. These results show that ADDLs bind to or in close proximity to NMDA-Rs, triggering neuronal damage through NMDA-R-dependent calcium flux. This response provides a pathologically specific mechanism for the therapeutic action of memantine, indicates a role for ROS dysregulation in ADDL-induced cognitive impairment, and supports the unifying hypothesis that ADDLs play a central role in AD pathogenesis.

Lacor PN, Buniel MC, Furlow PW, Clemente AS, Velasco PT, Wood M, Viola KL, Klein WL. · Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208, USA. · J Neurosci. · Pubmed #17251419 links to  free full text

Abstract: The basis for memory loss in early Alzheimer's disease (AD) seems likely to involve synaptic damage caused by soluble Abeta-derived oligomers (ADDLs). ADDLs have been shown to build up in the brain and CSF of AD patients and are known to interfere with mechanisms of synaptic plasticity, acting as gain-of-function ligands that attach to synapses. Because of the correlation between AD dementia and synaptic degeneration, we investigated here the ability of ADDLs to affect synapse composition, structure, and abundance. Using highly differentiated cultures of hippocampal neurons, a preferred model for studies of synapse cell biology, we found that ADDLs bound to neurons with specificity, attaching to presumed excitatory pyramidal neurons but not GABAergic neurons. Fractionation of ADDLs bound to forebrain synaptosomes showed association with postsynaptic density complexes containing NMDA receptors, consistent with observed attachment of ADDLs to dendritic spines. During binding to hippocampal neurons, ADDLs promoted a rapid decrease in membrane expression of memory-related receptors (NMDA and EphB2). Continued exposure resulted in abnormal spine morphology, with induction of long thin spines reminiscent of the morphology found in mental retardation, deafferentation, and prionoses. Ultimately, ADDLs caused a significant decrease in spine density. Synaptic deterioration, which was accompanied by decreased levels of the spine cytoskeletal protein drebrin, was blocked by the Alzheimer's therapeutic drug Namenda. The observed disruption of dendritic spines links ADDLs to a major facet of AD pathology, providing strong evidence that ADDLs in AD brain cause neuropil damage believed to underlie dementia.

Lambert MP, Velasco PT, Chang L, Viola KL, Fernandez S, Lacor PN, Khuon D, Gong Y, Bigio EH, Shaw P, De Felice FG, Krafft GA, Klein WL. · Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208, USA. · J Neurochem. · Pubmed #17116235 No free full text.

Abstract: Amyloid beta (Abeta) immunotherapy for Alzheimer's disease has shown initial success in mouse models of Alzheimer's disease and in human patients. However, because of meningoencephalitis in clinical trials of active vaccination, approaches using therapeutic antibodies may be preferred. As a novel antigen to generate monoclonal antibodies, the current study has used Abeta oligomers (amyloid beta-derived diffusible ligands, ADDLs), pathological assemblies known to accumulate in Alzheimer's disease brain. Clones were selected for the ability to discriminate Alzheimer's disease from control brains in extracts and tissue sections. These antibodies recognized Abeta oligomers and fibrils but not the physiologically prevalent Abeta monomer. Discrimination derived from an epitope found in assemblies of Abeta1-28 and ADDLs but not in other sequences, including Abeta1-40. Immunoneutralization experiments showed that toxicity and attachment of ADDLs to synapses in culture could be prevented. ADDL-induced reactive oxygen species (ROS) generation was also inhibited, establishing this response to be oligomer-dependent. Inhibition occurred whether ADDLs were prepared in vitro or obtained from Alzheimer's disease brain. As conformationally sensitive monoclonal antibodies that selectively immunoneutralize binding and function of pathological Abeta assemblies, these antibodies provide tools by which pathological Abeta assemblies from Alzheimer's disease brain might be isolated and evaluated, as well as offering a valuable prototype for new antibodies useful for Alzheimer's disease therapeutics.

Ohno M, Chang L, Tseng W, Oakley H, Citron M, Klein WL, Vassar R, Disterhoft JF. · Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA. · Eur J Neurosci. · Pubmed #16420434 No free full text.

Abstract: Transgenic mouse models of Alzheimer's disease (AD) exhibit amyloid-beta (Abeta) accumulation and related cognitive impairments. Although deficits in hippocampus-dependent place learning have been well characterized in Alzheimer's transgenic mice, little is known about temporal memory function in these AD models. Here, we applied trace fear conditioning to two different Alzheimer's mouse models and investigated the relationship between pathogenic Abeta and temporal memory deficits. This behavioral test requires hippocampus-dependent temporal memory processing as the conditioned and unconditioned stimuli are separated by a trace interval of 30 s. We found that both amyloid precursor protein (APP) transgenic (Tg2576) and APP/presenilin (PS)1 transgenic (Tg6799) mice were impaired in memorizing this association across the time gap. Both transgenic groups performed as well as wild-type control mice in delay fear conditioning when the trace interval was removed, indicating that the trace conditioning deficits are hippocampus-specific. Importantly, Tg6799 mice engineered to lack the major Alzheimer's beta-secretase (beta-site APP-cleaving enzyme 1: BACE1) showed behavioral rescue from temporal memory deficits. Elevated levels of soluble Abeta oligomers found in Tg6799+ mouse brains returned to wild-type control levels without changes in APP/PS1 transgene expression in BACE1-/- * Tg6799+ bigenic mouse brains, suggesting Abeta oligomers as potential mediators of memory loss. Thus, trace fear conditioning is a useful assay to test the mechanisms and therapeutic interventions for Abeta-dependent deficits in temporal associative memory. Our gene-based approach suggests that lowering soluble Abeta oligomers by inhibiting BACE1 may be beneficial for alleviating cognitive disorders in AD.

Oddo S, Caccamo A, Tran L, Lambert MP, Glabe CG, Klein WL, LaFerla FM. · Department of Neurobiology and Behavior, University of California, Irvine, California 92697-4545, USA. · J Biol Chem. · Pubmed #16282321 links to  free full text

Abstract: Accumulation of amyloid-beta (Abeta) is one of the earliest molecular events in Alzheimer disease (AD), whereas tau pathology is thought to be a later downstream event. It is now well established that Abeta exists as monomers, oligomers, and fibrils. To study the temporal profile of Abeta oligomer formation in vivo and to determine their interaction with tau pathology, we used the 3xTg-AD mice, which develop a progressive accumulation of plaques and tangles and cognitive impairments. We show that SDS-resistant Abeta oligomers accumulate in an age-dependent fashion, and we present evidence to show that oligomerization of Abeta appears to first occur intraneuronally. Finally, we show that a single intrahippocampal injection of a specific oligomeric antibody is sufficient to clear Abeta pathology, and more importantly, tau pathology. Therefore, Abeta oligomers may play a role in the induction of tau pathology, making the interference of Abeta oligomerization a valid therapeutic target.

Haes AJ, Chang L, Klein WL, Van Duyne RP. · Department of Chemistry, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208-3113, USA. · J Am Chem Soc. · Pubmed #15713105 links to  free full text

Abstract: A nanoscale optical biosensor based on localized surface plasmon resonance (LSPR) spectroscopy has been developed to monitor the interaction between the antigen, amyloid-beta derived diffusible ligands (ADDLs), and specific anti-ADDL antibodies. Using the sandwich assay format, this nanosensor provides quantitative binding information for both antigen and second antibody detection that permits the determination of ADDL concentration and offers the unique analysis of the aggregation mechanisms of this putative Alzheimer's disease pathogen at physiologically relevant monomer concentrations. Monitoring the LSPR-induced shifts from both ADDLs and a second polyclonal anti-ADDL antibody as a function of ADDL concentration reveals two ADDL epitopes that have binding constants to the specific anti-ADDL antibodies of 7.3 x 10(12) M(-1) and 9.5 x 10(8) M(-1). The analysis of human brain extract and cerebrospinal fluid samples from control and Alzheimer's disease patients reveals that the LSPR nanosensor provides new information relevant to the understanding and possible diagnosis of Alzheimer's disease.

Georganopoulou DG, Chang L, Nam JM, Thaxton CS, Mufson EJ, Klein WL, Mirkin CA. · Department of Chemistry and Institute of Nanotechnology, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USA. · Proc Natl Acad Sci U S A. · Pubmed #15695586 links to  free full text

Abstract: The recently developed ultrasensitive bio-barcode assay was used to measure the concentration of amyloid-beta-derived diffusible ligands (ADDLs), a potential soluble pathogenic Alzheimer's disease (AD) marker, in the cerebrospinal fluid (CSF) of 30 individuals. ADDL concentrations for the subjects diagnosed with AD were consistently higher than the levels in the CSF taken from nondemented age-matched controls. Studies of ADDLs or for any other potential pathogenic AD markers in CSF have not been possible because of their low concentration in CSF (<1 pM). This study is a step toward a diagnostic tool, based on soluble pathogenic markers for the debilitating disease.

Lacor PN, Buniel MC, Chang L, Fernandez SJ, Gong Y, Viola KL, Lambert MP, Velasco PT, Bigio EH, Finch CE, Krafft GA, Klein WL. · Neurobiology and Physiology Department, Northwestern University, Evanston, Illinois 60208, USA5. · J Neurosci. · Pubmed #15537891 links to  free full text

Abstract: The cognitive hallmark of early Alzheimer's disease (AD) is an extraordinary inability to form new memories. For many years, this dementia was attributed to nerve-cell death induced by deposits of fibrillar amyloid beta (Abeta). A newer hypothesis has emerged, however, in which early memory loss is considered a synapse failure caused by soluble Abeta oligomers. Such oligomers rapidly block long-term potentiation, a classic experimental paradigm for synaptic plasticity, and they are strikingly elevated in AD brain tissue and transgenic-mouse AD models. The current work characterizes the manner in which Abeta oligomers attack neurons. Antibodies raised against synthetic oligomers applied to AD brain sections were found to give diffuse stain around neuronal cell bodies, suggestive of a dendritic pattern, whereas soluble brain extracts showed robust AD-dependent reactivity in dot immunoblots. Antigens in unfractionated AD extracts attached with specificity to cultured rat hippocampal neurons, binding within dendritic arbors at discrete puncta. Crude fractionation showed ligand size to be between 10 and 100 kDa. Synthetic Abeta oligomers of the same size gave identical punctate binding, which was highly selective for particular neurons. Image analysis by confocal double-label immunofluorescence established that >90% of the punctate oligomer binding sites colocalized with the synaptic marker PSD-95 (postsynaptic density protein 95). Synaptic binding was accompanied by ectopic induction of Arc, a synaptic immediate-early gene, the overexpression of which has been linked to dysfunctional learning. Results suggest the hypothesis that targeting and functional disruption of particular synapses by Abeta oligomers may provide a molecular basis for the specific loss of memory function in early AD.

De Felice FG, Vieira MN, Saraiva LM, Figueroa-Villar JD, Garcia-Abreu J, Liu R, Chang L, Klein WL, Ferreira ST. · Departamento de Bioquímica Médica, Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ 21944-590, Brazil. · FASEB J. · Pubmed #15333579 links to  free full text

Abstract: 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.

Chang L, Bakhos L, Wang Z, Venton DL, Klein WL. · Department of Neurobiology and Physiology, Northwestern University, Evanston, IL 60208, USA. · J Mol Neurosci. · Pubmed #14501013 No free full text.

Abstract: Alzheimer's disease (AD) is a fatal, progressive dementia for which there is no cure and for which a molecular basis has yet to be established. However, considerable evidence suggests that AD is linked to neurotoxic assemblies of the 42-amino-acid peptide amyloid beta (Abeta). There is now a clear body of evidence that shows this neurotoxicity resides not only in insoluble fibrils of Abeta but also in soluble Abeta ADDLs (Abeta-derived diffusible ligands) and larger protofibrils. Further, anti-Abeta antibodies have been reported to reverse memory failure in human amyloid precursor protein (hAPP)-expressed transgenic mice in a manner that suggests symptom reversal is attributable to targeting of ADDLs. Clearly, a search for drugs targeting the assembly of these soluble Abeta species represents a new and potentially important approach to the treatment of AD. In this work we describe the development of a dot-blot immunoassay to measure ADDL at the femtomole level, its use in defining the time course of ADDL formation, and its use in determining the presence of ADDLs in the hAPP transgenic mouse brain. Discussion of a protocol to screen agents for inhibition of neurotoxic ADDLformation both in vivo and in vitro is also presented. The methods are suitable for screening combinatorial libraries and, importantly, provide the potential for simultaneous information on candidate transport across the blood-brain barrier.

Gong Y, Chang L, Viola KL, Lacor PN, Lambert MP, Finch CE, Krafft GA, Klein WL. · Department of Neurobiology and Physiology, Northwestern University, Evanston, IL 60208, USA. · Proc Natl Acad Sci U S A. · Pubmed #12925731 links to  free full text

Abstract: A molecular basis for memory failure in Alzheimer's disease (AD) has been recently hypothesized, in which a significant role is attributed to small, soluble oligomers of amyloid beta-peptide (A beta). A beta oligomeric ligands (also known as ADDLs) are known to be potent inhibitors of hippocampal long-term potentiation, which is a paradigm for synaptic plasticity, and have been linked to synapse loss and reversible memory failure in transgenic mouse AD models. If such oligomers were to build up in human brain, their neurological impact could provide the missing link that accounts for the poor correlation between AD dementia and amyloid plaques. This article, using antibodies raised against synthetic A beta oligomers, verifies the predicted accumulation of soluble oligomers in AD frontal cortex. Oligomers in AD reach levels up to 70-fold over control brains. Brain-derived and synthetic oligomers show structural equivalence with respect to mass, isoelectric point, and recognition by conformation-sensitive antibodies. Both oligomers, moreover, exhibit the same striking patterns of attachment to cultured hippocampal neurons, binding on dendrite surfaces in small clusters with ligand-like specificity. Binding assays using solubilized membranes show oligomers to be high-affinity ligands for a small number of nonabundant proteins. Current results confirm the prediction that soluble oligomeric A beta ligands are intrinsic to AD pathology, and validate their use in new approaches to therapeutic AD drugs and vaccines.

Kim HJ, Chae SC, Lee DK, Chromy B, Lee SC, Park YC, Klein WL, Krafft GA, Hong ST. · Research Division, Jinis Biopharmaceuticals Co., Chonju, Chonbuk, South Korea. · FASEB J. · Pubmed #12424218 links to  free full text

Abstract: The prevailing amyloid hypothesis for Alzheimer's disease (AD) holds that amyloid beta-protein (Abeta) causes neuronal degeneration by forming neurotoxic fibrillar structures. Yet, many aspects of AD pathology and symptoms are not well explained by this hypothesis. Here, we present evidence that neurotoxicity of soluble oligomeric Abeta closely corresponds to the selective neurodegeneration so distinctly manifest in AD. Selectivity was first observed in vitro, where only the human central nervous system neuronal cells were susceptible to soluble oligomeric Abeta. Furthermore, in mouse cerebral slice treated with soluble oligomeric Abeta, selective regiospecific toxicity was evident in the hippocampal CA1, a division important for memory, but not in the CA3 subfield. The fibrillar Abeta, however, killed neurons in all regions of the cerebral slice cultures and also in cerebellar slices. Remarkably, even at the highest soluble oligomeric Abeta concentrations, cerebellar neurons were completely spared, consistent with one of the hallmark features of AD pathology. Our observation of the selective neurodegeneration of soluble oligomeric Abeta to neurons involved in cognitive function may provide a new opportunity for the development of an effective AD therapy as well as elucidating the pathological mechanism of AD.

Yu J, Bakhos L, Chang L, Holterman MJ, Klein WL, Venton DL. · Department of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, The University of Illinois at Chicago, 60612, USA. · J Mol Neurosci. · Pubmed #12212793 No free full text.

Abstract: Alzheimer's disease is the most common cause of dementia in older individuals with compelling evidence favoring neuron dysfunction and death triggered by assembled forms of A beta(1-42). While large neurotoxic amyloid fibrils have been known for years, recent studies show that soluble protofibril and A beta(1-42)-derived diffusible ligands (ADDLs) may also be involved in neurotoxicity. In the present work, dot-blot immunoassays discriminating ADDLs from monomers were used to screen libraries of per-substituted beta-cyclodextrin (beta-CD) derivatives for inhibition of ADDLs formation. Libraries were prepared from per-6-iodo-beta-CD by treatment with various amine nucleophiles. The most active library tested (containing >2000 derivatives) was derived from imidazole, N, N-dimethylethylenediamine and furfurylamine, which at 10 microM total library, inhibited ADDLs formation (10 nM A beta(1-42)) over a period of 4 hours. The latter was confirmed by a western blot assay showing decreased amounts of the initially formed A beta(1-42) tetramer. These preliminary experiments suggest that derivatized forms of beta-CD can interfere with the oligomerization process of A beta(1-42).

Klein WL. · Cognitive Neurology and Alzheimer's Disease Center, Northwestern University Institute for Neuroscience, Evanston, IL 60208, USA. · Neurobiol Aging. · Pubmed #11804707 No free full text.

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