Identification of vilazodone as a novel plasminogen activator inhibitor to overcome Alzheimer's disease through virtual screening, molecular dynamics simulation, and biological evaluation.

Urokinase-type plasminogen activator (PLAU), a member of the S1 serine peptidase family in Clan PA, plays a crucial role in the conversion of plasminogen into active plasmin. However, the precise role of PLAU in the central nervous system remains incompletely elucidated, particularly, in relation to Alzheimer's disease (AD). In this study, we successfully identified that PLAU could promote cell senescence in neurons, indicating it as a potential target for AD treatment through a systematic approach, which included both bioinformatics analysis and experimental verification. Subsequently, a structure-based virtual screening approach was employed to identify a potential PLAU inhibitor from the Food and Drug Administration-approved drug database. After analyzing docking scores and thoroughly examining the receptor-ligand complex interaction modes, vilazodone emerges as a highly promising PLAU inhibitor. Additionally, molecular docking and molecular dynamics simulations were performed to generate a complex structure between the relatively stable inhibitor vilazodone and PLAU. Of note, vilazodone exhibited superior cytotoxicity against senescent cells, showing a senolytic activity through targeting PLAU and ultimately producing an anti-AD effect. These findings suggest that targeting PLAU could represent a promising therapeutic strategy for AD. Furthermore, investigating the inhibitory potential and structural modifications based on vilazodone may provide valuable insights for future drug development targeting PLAU in AD disorders.

Pathological Role of Peptidyl-Prolyl Isomerase Pin1 in the Disruption of Synaptic Plasticity in Alzheimer's Disease.

Synaptic loss is the structural basis for memory impairment in Alzheimer's disease (AD). While the underlying pathological mechanism remains elusive, it is known that misfolded proteins accumulate as ß-amyloid (Aß) plaques and hyperphosphorylated Tau tangles decades before the onset of clinical disease. The loss of Pin1 facilitates the formation of these misfolded proteins in AD. Pin1 protein controls cell-cycle progression and determines the fate of proteins by the ubiquitin proteasome system. The activity of the ubiquitin proteasome system directly affects the functional and structural plasticity of the synapse. We localized Pin1 to dendritic rafts and postsynaptic density (PSD) and found the pathological loss of Pin1 within the synapses of AD brain cortical tissues. The loss of Pin1 activity may alter the ubiquitin-regulated modification of PSD proteins and decrease levels of Shank protein, resulting in aberrant synaptic structure. The loss of Pin1 activity, induced by oxidative stress, may also render neurons more susceptible to the toxicity of oligomers of Aß and to excitation, thereby inhibiting NMDA receptor-mediated synaptic plasticity and exacerbating NMDA receptor-mediated synaptic degeneration. These results suggest that loss of Pin1 activity could lead to the loss of synaptic plasticity in the development of AD.

Alzheimer's Toxic Amyloid Beta Oligomers: Unwelcome Visitors to the Na/K ATPase alpha3 Docking Station.

Toxic amyloid beta oligomers (AßOs) are known to accumulate in Alzheimer's disease (AD) and in animal models of AD. Their structure is heterogeneous, and they are found in both intracellular and extracellular milieu. When given to CNS cultures or injected ICV into non-human primates and other non-transgenic animals, AßOs have been found to cause impaired synaptic plasticity, loss of memory function, tau hyperphosphorylation and tangle formation, synapse elimination, oxidative and ER stress, inflammatory microglial activation, and selective nerve cell death. Memory loss and pathology in transgenic models are prevented by AßO antibodies, while Aducanumab, an antibody that targets AßOs as well as fibrillar Aß, has provided cognitive benefit to humans in early clinical trials. AßOs have now been investigated in more than 3000 studies and are widely thought to be the major toxic form of Aß. Although much has been learned about the downstream mechanisms of AßO action, a major gap concerns the earliest steps: How do AßOs initially interact with surface membranes to generate neuron-damaging transmembrane events? Findings from Ohnishi et al (PNAS 2005) combined with new results presented here are consistent with the hypothesis that AßOs act as neurotoxins because they attach to particular membrane protein docks containing Na/K ATPase-α3, where they inhibit ATPase activity and pathologically restructure dock composition and topology in a manner leading to excessive Ca++ build-up. Better understanding of the mechanism that makes attachment of AßOs to vulnerable neurons a neurotoxic phenomenon should open the door to therapeutics and diagnostics targeting the first step of a complex pathway that leads to neural damage and dementia.

Human Alzheimer's disease synaptic O-GlcNAc site mapping and iTRAQ expression proteomics with ion trap mass spectrometry.

Neuronal synaptic functional deficits are linked to impaired learning and memory in Alzheimer's disease (AD). We recently demonstrated that O-GlcNAc, a novel cytosolic and nuclear carbohydrate post-translational modification, is enriched at neuronal synapses and positively regulates synaptic plasticity linked to learning and memory in mice. Reduced levels of O-GlcNAc have been observed in AD, suggesting a possible link to deficits in synaptic plasticity. Using lectin enrichment and mass spectrometry, we mapped several human cortical synaptic O-GlcNAc modification sites. Overlap in patterns of O-GlcNAcation between mouse and human appears to be high, as previously mapped mouse synaptic O-GlcNAc sites in Bassoon, Piccolo, and tubulin polymerization promoting protein p25 were identified in human. Novel O-GlcNAc modification sites were identified on Mek2 and RPN13/ADRM1. Mek2 is a signaling component of the Erk 1/2 pathway involved in synaptic plasticity. RPN13 is a component of the proteasomal degradation pathway. The potential interplay of phosphorylation with mapped O-GlcNAc sites, and possible implication of those sites in synaptic plasticity in normal versus AD states is discussed. iTRAQ is a powerful differential isotopic quantitative approach in proteomics. Pulsed Q dissociation (PQD) is a recently introduced fragmentation strategy that enables detection of low mass iTRAQ reporter ions in ion trap mass spectrometry. We optimized LTQ ion trap settings for PQD-based iTRAQ quantitation and demonstrated its utility in O-GlcNAc site mapping. Using iTRAQ, abnormal synaptic expression levels of several proteins previously implicated in AD pathology were observed in addition to novel changes in synaptic specific protein expression including Synapsin II.

Amyloid Beta Oligomers Target to Extracellular and Intracellular Neuronal Synaptic Proteins in Alzheimer's Disease.

Introduction: ß-Amyloid protein (Aß) putatively plays a seminal role in synaptic loss in Alzheimer's disease (AD). While there is no consensus regarding the synaptic-relevant species of Aß, it is known that Aß oligomers (AßOs) are noticeably increased in the early stages of AD, localizing at or within the synapse. In cell and animal models, AßOs have been shown to attach to synapses and instigate synapse dysfunction and deterioration. To establish the pathological mechanism of synaptic loss in AD, it will be important to identify the synaptic targets to which AßOs attach. Methods: An unbiased approach using far western ligand blots has identified three synaptic proteins to which AßOs specifically attach. These proteins (p100, p140, and p260) were subsequently enriched by detergent extraction, ultracentrifugation, and CHT-HPLC column separation, and sequenced by LC-MS/MS. P100, p140, and p260 were identified. These levels of AßOs targets in human AD and aging frontal cortexes were analyzed by quantitative proteomics and western-blot. The polyclonal antibody to AßOs was developed and used to block the toxicity of AßOs. The data were analyzed with one-way analysis of variance. Results: AßOs binding proteins p100, p140, and p260 were identified as Na/K-ATPase, synGap, and Shank3, respectively. α3-Na/K-ATPase, synGap, and Shank3 proteins showed loss in the postsynaptic density (PSD) of human AD frontal cortex. In short term experiments, oligomers of Aß inhibited Na/K-ATPase at the synapse. Na/K-ATPase activity was restored by an antibody specific for soluble forms of Aß. α3-Na/K-ATPase protein and synaptic ß-amyloid peptides were pulled down from human AD synapses by co-immunoprecipitation. Results suggest synaptic dysfunction in early stages of AD may stem from inhibition of Na/K-ATPase activity by Aß oligomers, while later stages could hypothetically result from disrupted synapse structure involving the PSD proteins synGap and Shank3. Conclusion: We identified three AßO binding proteins as α3-Na/K-ATPase, synGap, and Shank3. Soluble Aß oligomers appear capable of attacking neurons via specific extracellular as well as intracellular synaptic proteins. Impact on these proteins hypothetically could lead to synaptic dysfunction and loss, and could serve as novel therapeutic targets for AD treatment by antibodies or other agents.

Effect of intraperitoneal or intracerebroventricular injection of streptozotocin on learning and memory in mice.

Alteration of behavior and PSD proteins in cerebral cortex and hippocampal synaptosome in the Alzheimer's disease (AD) mouse model were determined. AD was established by intraperitoneal injection of streptozotocin (STZ) in neonatal mice (intraperitoneal AD group) or intracerebroventricular injection of STZ in adult mice (intracerebroventricular AD group). Body weight and blood sugar level were measured. Following Morris water maze (MWM) test and fear-conditioning test, cerebral cortex and hippocampus tissues were collected and the levels of PSD95 and shank3 proteins in these tissues were measured by western blot analysis. The body weight was reduced and the blood sugar concentration was increased in the intraperitoneal AD group compared with the control group. In contrast, the body weight was reduced, while the blood sugar concentration was not increased in the intracerebroventricular AD group compared with the control group. Escape latency in both AD groups was extended compared with the control group. The freezing time in the intraperitoneal AD group was increased, while in the intracerebroventricular AD group, the freezing time was reduced. PSD95 and shank3 proteins in the cerebral cortex in both AD groups were decreased compared with the control group. PSD95 in the hippocampus was reduced in both AD groups compared with the control group. Shank3 in the hippocampus in the intracerebroventricular AD group was significantly reduced compared with the control group. Intraperitoneal injection of STZ in neonatal mice led to elevated blood sugar, impaired spatial memory and enhanced emotional memory when they become adults. In contrast, intracerebroventricular injection of STZ in adults directly led to deteriorated spatial and emotional memory without alteration of blood sugar content, which could be associated with the changes of PSD95 and shank3 proteins in hippocampus.

Synaptic targeting by Alzheimer's-related amyloid beta oligomers.

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.

The Potential Role of Insulin on the Shank-Postsynaptic Platform in Neurodegenerative Diseases Involving Cognition.

Loss of synaptic function is critical in the pathogenesis of Alzheimer's disease (AD) and other central nervous system (CNS) degenerations. A promising candidate in the regulation of synaptic function is Shank, a protein that serves as a scaffold for excitatory synaptic receptors and proteins. Loss of Shank alters structure and function of the postsynaptic density (PSD). Shank proteins are associated with N-methyl-d-aspartate and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor loss at the PSD in AD; mutations in Shank also lead to autism spectrum disorders (ASDs) and schizophrenia, both of which affect cognition, suggesting that Shank may play a common pathologic role in AD, ASD, and schizophrenia. Shank protein directly associates with insulin receptor substrate protein p53 in PSD. Insulin and insulin sensitizers have been used in clinical trials for these diseases; this suggests that insulin signals may alter protein homeostasis at the shank-postsynaptic platform in PSDs; insulin could improve the function of synapses in these diseases.

Review: disruption of the postsynaptic density in Alzheimer's disease and other neurodegenerative dementias.

The most common causes of neurodegenerative dementia include Alzheimer's disease (AD), dementia with Lewy bodies (DLB), and frontotemporal dementia (FTD). We believe that, in all 3, aggregates of pathogenic proteins are pathological substrates which are associated with a loss of synaptic function/plasticity. The synaptic plasticity relies on the normal integration of glutamate receptors at the postsynaptic density (PSD). The PSD organizes synaptic proteins to mediate the functional and structural plasticity of the excitatory synapse and to maintain synaptic homeostasis. Here, we will discuss the relevant disruption of the protein network at the PSD in these dementias and the accumulation of the pathological changes at the PSD years before clinical symptoms. We suggest that the functional and structural plasticity changes of the PSD may contribute to the loss of molecular homeostasis within the synapse (and contribute to early symptoms) in these dementias.

Disruption of glutamate receptors at Shank-postsynaptic platform in Alzheimer's disease.

Synaptic loss underlies the memory deficit of Alzheimer's disease (AD). The molecular mechanism is elusive; however, excitatory synapses organized by the postsynaptic density (PSD) have been used as targets for AD treatment. To identify pathological entities at the synapse in AD, synaptic proteins were screened by quantitative proteomic profiling. The critical proteins were then selected for immunoblot analysis. The glutamate receptors N-methyl-d-aspartate (NMDA) receptor 1 and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor 2 (GluR2) were substantially lost; specifically, the loss of GluR2 was up to 40% at PSD in AD. Shank proteins, the organizers of these glutamate receptors at excitatory synapses, were dramatically altered in AD. The level of Shank2 was increased, whereas the protein level of Shank3 was decreased. Further, the Shank3 protein was modified by ubiquitin, indicating that abnormal activity of the ubiquitin-proteasome system may lead to Shank3 degradation in AD. Our findings suggest that disruption of glutamate receptors at the Shank-postsynaptic platform could contribute to destruction of the PSD which underlies the synaptic dysfunction and loss in AD.

Monoclonal antibodies that target pathological assemblies of Abeta.

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.

Alzheimer's disease-affected brain: presence of oligomeric A beta ligands (ADDLs) suggests a molecular basis for reversible memory loss.

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.