Interaction Of Aβ Research Articles

Discovery of Chemicals to Either Clear or Indicate Amyloid Aggregates by Targeting Memory-Impairing Anti-Parallel Aβ Dimers.

Amyloid-β (Aβ) oligomers are implicated in Alzheimer disease (AD). However, their unstable nature and heterogeneous state disrupts elucidation of their explicit role in AD progression, impeding the development of tools targeting soluble Aβ oligomers. Herein parallel and anti-parallel variants of Aβ(1-40) dimers were designed and synthesized, and their pathogenic properties in AD models characterized. Anti-parallel dimers induced cognitive impairments with increased amyloidogenesis and cytotoxicity, and this dimer was then used in a screening platform. Through screening, two FDA-approved drugs, Oxytetracycline and Sunitinib, were identified to dissociate Aβ oligomers and plaques to monomers in 5XFAD transgenic mice. In addition, fluorescent Astrophloxine was shown to detect aggregated Aβ in brain tissue and cerebrospinal fluid samples of AD mice. This screening platform provides a stable and homogeneous environment for observing Aβ interactions with dimer-specific molecules.

Discovery of Chemicals to Either Clear or Indicate Amyloid Aggregates by Targeting Memory‐Impairing Anti‐Parallel Aβ Dimers

AbstractAmyloid‐β (Aβ) oligomers are implicated in Alzheimer disease (AD). However, their unstable nature and heterogeneous state disrupts elucidation of their explicit role in AD progression, impeding the development of tools targeting soluble Aβ oligomers. Herein parallel and anti‐parallel variants of Aβ(1–40) dimers were designed and synthesized, and their pathogenic properties in AD models characterized. Anti‐parallel dimers induced cognitive impairments with increased amyloidogenesis and cytotoxicity, and this dimer was then used in a screening platform. Through screening, two FDA‐approved drugs, Oxytetracycline and Sunitinib, were identified to dissociate Aβ oligomers and plaques to monomers in 5XFAD transgenic mice. In addition, fluorescent Astrophloxine was shown to detect aggregated Aβ in brain tissue and cerebrospinal fluid samples of AD mice. This screening platform provides a stable and homogeneous environment for observing Aβ interactions with dimer‐specific molecules.

Amyloid Beta Peptide Is an Endogenous Negative Allosteric Modulator of Leptin Receptor

Introduction: Metabolic dysfunction is now recognized as a pivotal component of Alzheimer’s disease (AD), the most common dementia worldwide. However, the precise molecular mechanisms linking metabolic dysfunction to AD remain elusive. Objective: Here, we investigated the direct impact of soluble oligomeric amyloid beta (Aβ) peptides, the main molecular hallmark of AD, on the leptin system, a major component of central energy metabolism regulation. Methods: We developed a new time-resolved fluorescence resonance energy transfer-based Aβ binding assay for the leptin receptor (LepR) and studied the effect of Aβ on LepR function in several in vitro assays. The in vivo effect of Aβ on LepR function was studied in an Aβ-specific AD mouse model and in pro-opiomelanocortin (POMC) neurons of the hypothalamic arcuate nucleus. Results: We revealed specific and high-affinity (K_i = 0.1 nM) binding of Aβ to LepR. Pharmacological characterization of this interaction showed that Aβ binds allosterically to the extracellular domain of LepR and negatively affects receptor function. Negative allosteric modulation of LepR by Aβ was detected at the level of signaling pathways (STAT-3, AKT, and ERK) in vitroand in vivo. Importantly, the leptin-induced response of POMC neurons, key players in the regulation of metabolic function, was completely abolished in the presence of Aβ. Conclusion: Our data indicate that Aβ is a negative allosteric modulator of LepR, resulting in impaired leptin action, and qualify LepR as a new and direct target of Aβ oligomers. Preventing the interaction of Aβ with LepR might improve both the metabolic and cognitive dysfunctions in AD condition.

In silico design of peptide inhibitors of tubulin: amyloid-β as a lead compound

Microtubule is one of the most studied targets in cancer research. Stabilizing and destabilizing of the microtubule by targeting its building block tubulin are common mechanisms of microtubule targeting agents. Cancer associates inversely with Alzheimer’s disease (AD). So the rate of developing AD is significantly slower in patients with cancer and vice versa. Amyloid-β (Aβ) peptide inhibits tubulin polymerization and induces apoptotic death of cancer cells. We studied the interactions of Aβ with tubulin using protein-protein docking and MD simulation. Aβ bond to the vicinity of the vinblastine binding site and interacted with the H6-H7 loop. Interaction of Aβ with H6-H7 loop blocked nucleotide exchange and may be attributed as a possible reason for blocking of tubulin polymerization. We designed new Aβ-based peptidic inhibitors of tubulin using visual inspection and alanine scanning method. P1 (FRHYHHFFELV) and P9 (HYHHF) bound efficiently to tubulin and also interacted with the H6-H7 loop. Obtained results indicated that proposed peptides could potentially inhibit nucleotide exchange as Aβ. Communicated by Ramaswamy H. Sarma

Methionine Oxidation Alters the Mechanism of Aβ Interaction with DMPC Bilayers

The binding of Aβ peptides to neuronal membranes may constitute a molecular basis for Alzheimer's disease. Oxygen-rich brain tissues create an environment that readily oxidizes Met35 of the Aβ peptide, bringing the fraction of oxidized species to 10-50% of all Aβ peptides in the brain. Due to this chemical diversity, it is imperative to understand the differences in the interactions of reduced (wild-type) and oxidized Aβ with membranes. To address this, we have executed replica-exchange molecular dynamics simulations to probe the binding of reduced and oxidized peptides to the DMPC bilayer. We found that oxidation lowers the peptide's hydrophobic moment resulting in an unraveling of the helix structure present in the wild-type bound peptide. Furthermore, oxidation destabilizes intrapeptide interactions causing the bound peptide to expand and form stronger interactions with the bilayer. Unexpectedly, we established that oxidation promotes better mixing of Aβ with lipids. As a result, the oxidized peptide does not perturb the bilayer and does not deplete its density as much as the reduced form. Exhaustive replica exchange simulations allowed us to compute the free energy of binding via the MM-GBSA framework, revealing that the oxidized peptide has lower binding affinity to the DMPC bilayer than the wild-type peptide. The primary origin for this decreased affinity is the loss of favorable intrapeptide contacts. We propose that the decreased affinity of binding to the lipid bilayer explains the diminished cytotoxic effect of oxidized Aβ peptides.

Amyloid-Beta Peptides Trigger Aggregation of Alpha-Synuclein In Vitro.

Alzheimer’s disease (AD) and Parkinson’s disease (PD), including dementia with Lewy bodies (DLB), account for the majority of dementia cases worldwide. Interestingly, a significant number of patients have clinical and neuropathological features of both AD and PD, i.e., the presence of amyloid deposits and Lewy bodies in the neocortex. The identification of α-synuclein peptides in amyloid plaques in DLB brain led to the hypothesis that both peptides mutually interact with each other to facilitate neurodegeneration. In this article, we report the influence of Aβ(1–42) and pGlu-Aβ(3–42) on the aggregation of α-synuclein in vitro. The aggregation of human recombinant α-synuclein was investigated using thioflavin-T fluorescence assay. Fibrils were investigated by means of antibody conjugated immunogold followed by transmission electron microscopy (TEM). Our data demonstrate a significantly increased aggregation propensity of α-synuclein in the presence of minor concentrations of Aβ(1–42) and pGlu-Aβ(3–42) for the first time, but without effect on toxicity on mouse primary neurons. The analysis of the composition of the fibrils by TEM combined with immunogold labeling of the peptides revealed an interaction of α-synuclein and Aβ in vitro, leading to an accelerated fibril formation. The analysis of kinetic data suggests that significantly enhanced nucleus formation accounts for this effect. Additionally, co-occurrence of α-synuclein and Aβ and pGlu-Aβ, respectively, under pathological conditions was confirmed in vivo by double immunofluorescent labelings in brains of aged transgenic mice with amyloid pathology. These observations imply a cross-talk of the amyloid peptides α-synuclein and Aβ species in neurodegeneration. Such effects might be responsible for the co-occurrence of Lewy bodies and plaques in many dementia cases.

Direct Interaction between the β-Amyloid Core and Tau Facilitates Cross-Seeding: A Novel Target for Therapeutic Intervention.

The deposition of amyloid-β (Aβ) plaques and tau-based neurofibrillary tangles is a neuropathological feature of Alzheimer's disease (AD). While studies have shown that the Aβ and tau interaction results in elevated AD pathology, the molecular linkage and mechanism of interaction of Aβ and tau are unclear. A recent study demonstrated the direct interaction between the Aβ core and specific regions of tau that facilitates pathological cross-seeding via a shared epitope. The data suggest that targeting the common epitope could be a more effective treatment strategy rather than targeting only Aβ or only tau. The findings have an important clinical significance for AD and related tauopathies.

Role of Oxidized Gly25, Gly29, and Gly33 Residues on the Interactions of Aβ1-42 with Lipid Membranes.

Oxidative stress is known to play an important role in the pathogenesis of Alzheimer's disease. Moreover, it is becoming increasingly evident that the plasma membrane of neurons plays a role in modulating the aggregation and toxicity of Alzheimer's amyloid-β peptide (Aβ). In this study, the combined and interdependent effects of oxidation and membrane interactions on the 42 residues long Aβ isoform are investigated using molecular simulations. Hamiltonian replica exchange molecular dynamics simulations are utilized to elucidate the impact of selected oxidized glycine residues of Aβ42 on the interactions of the peptide with a model membrane comprised of 70% POPC, 25% cholesterol, and 5% of the ganglioside GM1. The main findings are that, independent of the oxidation state, Aβ prefers binding to GM1 over POPC, which is further enhanced by the oxidation of Gly29 and Gly33 and reduced the formation of β-sheet. Our results suggest that the differences observed in Aβ42 conformations and its interaction with a lipid bilayer upon oxidation originate from the position of the oxidized Gly residue with respect to the hydrophobic sequence of Aβ42 involving the Gly29-XXX-Gly33-XXX-Gly37 motif and from specific interactions between the peptide and the terminal sugar groups of GM1.

Molecular crowding effects on the biochemical properties of amyloid β–heme, Aβ–Cu and Aβ–heme–Cu complexes

Heme as a cofactor has been proposed to bind with β-amyloid peptide (Aβ) and the formed Aβ–heme complex exhibits enhanced peroxidase-like activity. So far, in vitro studies on the interactions between heme, Cu and Aβ have been exclusively performed in dilute solution. However, the intracellular environment is highly crowded with biomolecules. Therefore, exploring how Aβ–heme–Cu complexes behave under molecular crowding conditions is critical for understanding the mechanism of Aβ neurotoxicity in vivo. Herein, we selected PEG-200 as a crowding agent to mimic the crowded cytoplasmic environment for addressing the contributions of crowded physiological environments to the biochemical properties of Aβ–heme, Aβ–Cu and Aβ–heme–Cu complexes. Surprisingly, experimental studies and theoretical calculations revealed that molecular crowding weakened the stabilization of the Aβ–heme complex and decreased its peroxidase activity. Our data attributed this consequence to the decreased binding affinity of heme to Aβ as a result of the alterations in water activity and Aβ conformation. Our findings highlight the significance of hydration effects on the interaction of Aβ–heme and Aβ–Cu and their peroxidase activities. Molecular crowding inside cells may potentially impose a positive effect on Aβ–Cu but a negative effect on the interaction of Aβ with heme. This indicates that Aβ40–Cu but not Aβ40–heme may play more important roles in the oxidative damage in the etiology of AD. Therefore, this work provides a new clue for understanding the oxidative damage occurring in AD.

Interactions between Soluble Species of β-Amyloid and α-Synuclein Promote Oligomerization while Inhibiting Fibrillization.

Aggregations of β-amyloid (Aβ) and α-synuclein (αS) into oligomeric and fibrillar assemblies are the pathological hallmarks of Alzheimer's and Parkinson's diseases, respectively. Although Aβ and αS affect different regions of the brain and are separated at the cellular level, there is evidence of their eventual interaction in the pathology of both disorders. Characterization of interactions of Aβ and αS at various stages of their aggregation pathways could reveal mechanisms and therapeutic targets for the prevention and cure of these neurodegenerative diseases. In this study, we comprehensively examined the interactions and their molecular manifestations using an array of characterization tools. We show for the first time that αS monomers and oligomers, but not αS fibrils, inhibit Aβ fibrillization while promoting oligomerization of Aβ monomers and stabilizing preformed Aβ oligomers via coassembly, as judged by Thioflavin T fluorescence, transmission electron microscopy, and SDS- and native-PAGE with fluorescently labeled peptides/proteins. In contrast, soluble Aβ species, such as monomers and oligomers, aggregate into fibrils, when incubated alone under the otherwise same condition. Our study provides evidence that the interactions with αS soluble species, responsible for the effects, are mediated primarily by the C-terminus of Aβ, when judged by competitive immunoassays using antibodies recognizing various fragments of Aβ. We also show that the C-terminus of Aβ is a primary site for its interaction with αS fibrils. Collectively, these data demonstrate aggregation state-specific interactions between αS and Aβ and offer insight into a molecular basis of synergistic biological effects between the two polypeptides.

β-Amyloid Peptide: the Cell Compartment Multi-faceted Interaction in Alzheimer's Disease.

Alzheimer's disease (AD) is the most widespread form of dementia, characterized by memory loss and reduction of cognitive functions that strongly interfere with normal daily life. Numerous evidences show that aggregates of the amyloid beta peptide, formed by 39 to 42 amino acid residues (Aβ39-43), from soluble small oligomers to large fibrils are characteristic markers of this pathology. However, AD is a complex disease and its neurodegenerative molecular mechanism is not yet fully understood. Growing evidence suggests a link between Aβ polymorphic nature, oligomers and fibrils, and specific mechanisms of neurodegeneration. The Aβ variable nature and its multiplicity of interactions with different proteins and organelles reflect the complexity of this pathology. In this review, we analyze the effects of the interaction between Aβ peptide and different cellular compartments in relation to the different kinds and sizes of amyloid aggregates. In particular, Aβ interaction with different cell structures such as the plasma membrane, mitochondria, lysosomes, nucleus, and endoplasmic reticulum is discussed. Further, we analyze the Aβ peptide ability to modify the structure and function of the target organelle, inducing alteration of its physiological role thus contributing to the pathological event. Dysfunction of cellular components terminating with the activation of the cellular death mechanism and subsequent neurodegeneration is also taken into consideration.

Colorimetric Detection of Mutant β-Amyloid(1-40) Membrane-Active Aggregation with Biosensing Vesicles.

Alzheimer's disease (AD) is a protein misfolding disease commonly characterized by neuritic amyloid plaques and proteinaceous fibrillar aggregate deposits composed of β-amyloid (Aβ) aggregates. The dynamic aggregation of Aβ forms toxic, nanoscale aggregate species which proceed from oligomers to fibrils. Currently, there is need for rapid and direct detection of Aβ peptide aggregation and interaction with lipid membranes, as detecting an interaction with various lipid environments will provide insights to better understand how interactions may modulate membrane function on cellular surfaces, leading to the progression of AD. The goal of this study was to utilize a colorimetric, biomimetic, vesicle-binding assay as a biosensor to detect and investigate the occurrence of neurodegenerative disease-associated protein aggregation and interaction with lipid membranes. Lipid/polydiacetylene (PDA) vesicles were exposed to monomeric preparations of Wild Type Aβ(1-40) or point mutations in Aβ with amino acid substitutions that are commonly associated with familial AD (E22G Arctic, E22Q Dutch, A21G Flemish, D23N Iowa, and E22K Italian). We investigated how these substitutions affect Aβ(1-40) aggregation and interaction with lipid vesicles designed to mimic biological membranes. Time-resolved colorimetric measurements were obtained and reveal that exposure to lipid/PDA vesicle biosensors results in the direct detection of mutant Aβ(1-40) peptide-lipid interaction events. Aβ(1-40) peptide aggregate membrane activity varies among Aβ peptide variants and lipid composition. In addition, we used atomic force microscopy and Thioflavin T fluorescence assays to distinguish the stages of Aβ(1-40) aggregate formation, morphology, and membrane activity. These studies provide a simple means of aggregate detection and insight into the role of cellular surfaces in the mechanism of AD aggregation.

Identification of a Novel Multifunctional Ligand for Simultaneous Inhibition of Amyloid-Beta (Aβ42) and Chelation of Zinc Metal Ion

Zinc binding to β-amyloid structure could promote amyloid-β aggregation, as well as reactive oxygen species (ROS) production, as suggested in many experimental and theoretical studies. Therefore, the introduction of multifunctional drugs capable of chelating zinc metal ion and inhibiting Aβ aggregation is a promising strategy in the development of AD treatment. The present study has evaluated the efficacy of a new bifunctional peptide drug using molecular docking and molecular dynamics (MD) simulations. This drug comprises two different domains, an inhibitor domain, obtained from the C-terminal hydrophobic region of Aβ, and a Zn2+ chelating domain, derived from rapeseed meal, merge with a linker. The multifunctionality of the ligand was evaluated using a comprehensive set of MD simulations spanning up to 3.2 μs including Aβ relaxation, ligand-Zn2+ bilateral interaction, and, more importantly, ligand-Zn2+-Aβ42 trilateral interactions. Analysis of the results strongly indicated that the bifunctional ligand can chelate zinc metal ion and avoid Aβ aggregation simultaneously. The present study illustrated that the proposed ligand has considerable hydrophobic interactions and hydrogen bonding with monomeric Aβ in the presence of zinc metal ion. Therefore, in light of these considerable interactions and contacts, the α-helical structure of Aβ has been enhanced, while the β-sheet formation is prevented and the α-helix native structure is protected. Furthermore, the analysis of interactions between Aβ and ligand-zinc complex revealed that the zinc metal ion is coordinated to Met13, the ending residue of the ligand and merely one residue in Aβ. The results have proven the previous experimental and theoretical findings in the literature about Aβ interactions with zinc metal ion and also Aβ interactions with the first domain of the proposed ligand. Moreover, the current research has evaluated the chelation using MD simulation and linear interaction energy (LIE) methods, and the result has been satisfactorily verified with previous experimental and theoretical (DFT) studies.

Computational Study of Natural Compounds for the Clearance of Amyloid-Βeta: A Potential Therapeutic Management Strategy for Alzheimer's Disease.

Alzheimer’s disease (AD) is a widespread dynamic neurodegenerative malady. Its etiology is still not clear. One of the foremost pathological features is the extracellular deposits of Amyloid-beta (Aβ) peptides in senile plaques. The interaction of Aβ and the receptor for advanced glycation end products at the blood-brain barrier is also observed in AD, which not only causes the neurovascular anxiety and articulation of proinflammatory cytokines, but also directs reduction of cerebral bloodstream by upgrading the emission of endothelin-1 to induce vasoconstriction. In this process, RAGE is deemed responsible for the influx of Aβ into the brain through BBB. In the current study, we predicted the interaction potential of the natural compounds vincamine, ajmalicine and emetine with the Aβ peptide concerned in the treatment of AD against the standard control, curcumin, to validate the Aβ peptide–compounds results. Protein-protein interaction studies have also been carried out to see their potential to inhibit the binding process of Aβ and RAGE. Moreover, the current study verifies that ligands are more capable inhibitors of a selected target compared to positive control with reference to ΔG values. The inhibition of Aβ and its interaction with RAGE may be valuable in proposing the next round of lead compounds for effective Alzheimer’s disease treatment.

Amyloid β and Tumorigenesis: Amyloid β-Induced Telomere Dysfunction in Tumor Cells

Amyloid β and Tumorigenesis: Amyloid β-Induced Telomere Dysfunction in Tumor Cells

Associations among amyloid status, age, and longitudinal regional brain atrophy in cognitively unimpaired older adults

The goal of this study was to compare regional brain atrophy patterns in cognitively unimpaired (CU) older adults with and without brain accumulation of amyloid-β (Aβ) to elucidate contributions of Aβ, age, and other variables to atrophy rates. In 80 CU participants from the Alzheimer's Disease Neuroimaging Initiative, we determined effects of Aβ and age on longitudinal, regional atrophy rates, while accounting for confounding variables including sex, APOE ε4 genotype, white matter lesions, and cerebrospinal fluid total and phosphorylated tau levels. We not only found overlapping patterns of atrophy in Aβ+ versus Aβ− participants but also identified regions where atrophy pattern differed between the 2 groups. Higher Aβ load was associated with increased longitudinal atrophy in the entorhinal cortex, amygdala, and hippocampus, even when accounting for age and other variables. Age was associated with atrophy in insula, fusiform gyrus, and isthmus cingulate, even when accounting for Aβ. We found age by Aβ interactions in the postcentral gyrus and lateral orbitofrontal cortex. These results elucidate the separate and related effects of age, Aβ, and other important variables on longitudinal brain atrophy rates in CU older adults.

Effect of melatonin on Aβ42 induced changes in the mitochondrial function related to Alzheimer’s disease in Drosophila melanogaster

Alzheimers’s disease is one of the alarming neurodegenerative disease and it is of global concern.The hallmarks of the disease are the amyloid beta (Aβ) aggregation and presence of neurofibrillary tangles (NFTs). The interaction of Aβ with macromolecular targets affects the normal cellular functions. The amyloid peptide interaction with cellular surfaces may trigger the intracellular cascades of signalling. Interaction of Aβ with mitochondria leads to the generation of free radicals. Many studies have suggested the involvement of mitochondrial dysfunction in Alzheimer’s disease. Melatonin prevents mitochondria stress and by means of activating the antioxidant systems it protects the death of neurons. Although the study have been already conducted on Aβ42 infused or injury induced animal models but till date there is no reports of such studies on transgenic model of Drosophila melanogaster. In the present study, we have taken UAS/Gal4 system for the development of transgenic flies that overexpress Aβ42 in the brain of Drosophila. With the help of these transgenic flies we have analyse different experiments like behavioural parameters, oxidative stress parameters and protein expression through western blotting in the presence of melatonin. We have found that melatonin significantly ameliorated the toxicity caused by the Aβ42 overexpression. Thus the present study could be beneficial to find out the role of melatonin in transgenic flies overexpressing human Aβ42.

Amyloid Beta 25-35 induces blood-brain barrier disruption in vitro.

The amyloid β-peptide (Aβ) is transported across the blood-brain barrier (BBB) by binding with the receptor for advanced glycation end products (RAGE). Previously, we demonstrated that the Aβ fraction 25-35 (Aβ25-35) increases RAGE expression in the rat hippocampus, likely contributing to its neurotoxic effects. However, it is still debated if the interaction of Aβ with RAGE compromises the BBB function in Alzheimer' disease (AD). Here, we evaluated the effects of Aβ25-35 in an established in vitro model of the BBB. Rat brain microvascular endothelial cells (rBMVECs) were treated with 20μM active Aβ25-35 or the inactive Aβ35-25 (control), for 24h. Exposure to Aβ25-35 significantly decreased cell viability, increased cellular necrosis, and increased the production of reactive oxygen species (ROS), which triggered a decrease in the enzyme glutathione peroxidase when compared to the control condition. Aβ25-35 also increased BBB permeability by altering the expression of tight junction proteins (decreasing zonula occludens-1 and increasing occludin). Aβ25-35 induced monolayer disruption and cellular disarrangement of the BBB, with RAGE being highly expressed in the zones of disarrangement. Together, these data suggest that Aβ25-35-induces toxicity by compromising the functionality and integrity of the BBB in vitro. Graphical abstract Aβ25-35 induces BBB dysfunction in vitro, wich is likely mediated by OS and ultimately leads to disruption of BBB integrity and cell death.

THE ROLE OF ASTROCYTIC α7 NICOTINIC ACETYLCHOLINE RECEPTORS IN NEUROINFLAMMATION-MEDIATED COGNITIVE IMPAIRMENT

An important component of Alzheimer's disease (AD) is neuroinflammation. In the periphery, α7 nAChR activation inhibits macrophage production of pro-inflammatory cytokines. In the CNS, α7 nAChRs are enriched in brain regions affected early in AD. However, α7 nAChR expression is not restricted to neurons; these receptors are highly enriched within the CNS immune system. We have previously reported important roles for astrocytic α7 nicotinic acetylcholine receptor (nAChR)-Aβ interaction with subsequent effects on cognition. To refine these studies, we sought to test the hypothesis that astrocytic α7 nAChRs serve an analogous anti-inflammatory role to that in the periphery. To test our hypothesis, we generated mice in which the fourth exon of the α7 nAChR gene (Chrna7) is flanked by loxP sites (α7nAChRflox). We then crossed α7nAChRflox mice with mice expressing Cre recombinase driven by the glial acidic fibrillary protein (GFAP) and studied neuroinflammatory responses and cognition following intracerebroventricular (ICV) injection of LPS (10 ng); a dose that induces transient neuroinflammatory responses without measurable peripheral inflammation. We studied hemizygous astrocytic α7nAChR (GFAP-A7+/-) knockdown mice compared to α7nAChRflox+/- littermates. Whereas sham and LPS ICV-injected α7nAChRflox+/- littermates performed similarly in hippocampus-dependent associative learning and memory, GFAP-A7+/- mice were impaired. Bio-Plex analysis of serum, hippocampus and cholinergic basal forebrain revealed that α7nAChRflox+/- littermates mounted both a pro- and anti-inflammatory response to ICV LPS; GFAP-A7+/- mice did not. However, GFAP-A7+/- mice exhibited pronounced microglia activation and tau hyperphosphorylation in hippocampal structures. Morphometric analysis showed that GFAP-A7+/- mice presented with blunted astrocyte response to LPS challenge. Currently, we are using cultured astrocytes from hemizygous GFAP-Cre α7nAChR knockdown mice and α7nAChRflox littermates to decipher mechanistic details. Blunted astrocyte response, absence of an anti-inflammatory response, microglia activation and tau pathology resulting from ICV LPS injection suggests that knockdown of α7 nAChRs in astrocytes triggers a feed-forward pro-inflammatory response to elicit AD-like cognitive deficits. Thus, similar to their role in the periphery, astrocytic α7 nAChRs serve an anti-inflammatory role in the CNS. This has significant implications for AD since Aβ binds α7 nAChRs to silence these receptors.

Glycopeptide Nanofiber Platform for Aβ-Sialic Acid Interaction Analysis and Highly Sensitive Detection of Aβ.

The variation of amyloid β peptide (Aβ) concentration and Aβ aggregation are closely associated with the etiology of Alzheimer's diseases (AD). The interaction of Aβ with the monosialoganglioside-rich neuronal cell membrane has been suggested to influence Aβ aggregation. Therefore, studies on the mechanism of Aβ and sialic acids (SA) interaction would greatly contribute to better understanding the pathogenesis of AD. Herein, we report a novel approach for Aβ-SA interaction analysis and highly sensitive Aβ detection by mimicing the cell surface presentation of SA clusters through engineering of SA-modified peptide nanofiber (SANF). The SANF displayed well-ordered 1D nanostructure with high density of SA on surface. Using FAM-labeled Aβ fragments of Aβ1-16, Aβ16-23, and Aβ24-40, the interaction between Aβ and SA was evaluated by the fluorescence titration experiments. It was found that the order of the SA-binding affinity was Aβ1-16 > Aβ24-40 > Aβ16-23. Importantly, the presence of full-length Aβ1-40 monomer triggered a significant fluorescence enhancement due to the multivalent binding of Aβ1-40 to the nanofiber. This fluorescent turn-on response showed high selectivity and sensitivity for Aβ1-40 detection and the method was further used for Aβ aggregation process monitoring and inhibitor screening. The results suggest the proposed strategy is promising to serve as a tool for mechanism study and the early diagnosis of Alzheimer's disease.