Loss of LAMP5 interneurons drives neuronal network dysfunction in Alzheimer's disease.

In Alzheimer's disease (AD), where amyloid-ß (Aß) and tau deposits in the brain, hyperexcitation of neuronal networks is an underlying disease mechanism, but its cause remains unclear. Here, we used the Collaborative Cross (CC) forward genetics mouse platform to identify modifier genes of neuronal hyperexcitation. We found LAMP5 as a novel regulator of hyperexcitation in mice, critical for the survival of distinct interneuron populations. Interestingly, synaptic LAMP5 was lost in AD brains and LAMP5 interneurons degenerated in different AD mouse models. Genetic reduction of LAMP5 augmented functional deficits and neuronal network hypersynchronicity in both Aß- and tau-driven AD mouse models. To this end, our work defines the first specific function of LAMP5 interneurons in neuronal network hyperexcitation in AD and dementia with tau pathology.

The Amyloid Fibril-Forming ß-Sheet Regions of Amyloid ß and α-Synuclein Preferentially Interact with the Molecular Chaperone 14-3-3ζ.

14-3-3 proteins are abundant, intramolecular proteins that play a pivotal role in cellular signal transduction by interacting with phosphorylated ligands. In addition, they are molecular chaperones that prevent protein unfolding and aggregation under cellular stress conditions in a similar manner to the unrelated small heat-shock proteins. In vivo, amyloid ß (Aß) and α-synuclein (α-syn) form amyloid fibrils in Alzheimer's and Parkinson's diseases, respectively, a process that is intimately linked to the diseases' progression. The 14-3-3ζ isoform potently inhibited in vitro fibril formation of the 40-amino acid form of Aß (Aß40) but had little effect on α-syn aggregation. Solution-phase NMR spectroscopy of 15N-labeled Aß40 and A53T α-syn determined that unlabeled 14-3-3ζ interacted preferentially with hydrophobic regions of Aß40 (L11-H21 and G29-V40) and α-syn (V3-K10 and V40-K60). In both proteins, these regions adopt ß-strands within the core of the amyloid fibrils prepared in vitro as well as those isolated from the inclusions of diseased individuals. The interaction with 14-3-3ζ is transient and occurs at the early stages of the fibrillar aggregation pathway to maintain the native, monomeric, and unfolded structure of Aß40 and α-syn. The N-terminal regions of α-syn interacting with 14-3-3ζ correspond with those that interact with other molecular chaperones as monitored by in-cell NMR spectroscopy.

Oligomeric and Fibrillar Species of Aß42 Diversely Affect Human Neural Stem Cells.

Amyloid-ß 42 peptide (Aß1-42 (Aß42)) is well-known for its involvement in the development of Alzheimer's disease (AD). Aß42 accumulates and aggregates in fibers that precipitate in the form of plaques in the brain causing toxicity; however, like other forms of Aß peptide, the role of these peptides remains unclear. Here we analyze and compare the effects of oligomeric and fibrillary Aß42 peptide on the biology (cell death, proliferative rate, and cell fate specification) of differentiating human neural stem cells (hNS1 cell line). By using the hNS1 cells we found that, at high concentrations, oligomeric and fibrillary Aß42 peptides provoke apoptotic cellular death and damage of DNA in these cells, but Aß42 fibrils have the strongest effect. The data also show that both oligomeric and fibrillar Aß42 peptides decrease cellular proliferation but Aß42 oligomers have the greatest effect. Finally, both, oligomers and fibrils favor gliogenesis and neurogenesis in hNS1 cells, although, in this case, the effect is more prominent in oligomers. All together the findings of this study may contribute to a better understanding of the molecular mechanisms involved in the pathology of AD and to the development of human neural stem cell-based therapies for AD treatment.

Cognitive decline according to amyloid uptake in patients with poststroke cognitive impairment.

BACKGROUND AND PURPOSE: Poststroke cognitive impairment (PSCI) is common, but the impact of ß-amyloid (Aß) on PSCI is uncertain. The proposed study will investigate amyloid pathology in participants with PSCI and how differently their cognition progress according to the amyloid pathology. METHODS: This multicenter study was designed to be prospective and observational based on a projected cohort size of 196 participants with either newly developed cognitive impairment, or rapidly aggravated CI, within 3 months after acute cerebral infarction. They will undergo 18F-flutemetamol positron emission tomography at baseline and will be categorized as either amyloid-positive (A+) or amyloid-negative (A-) by visual rating. The primary outcome measures will be based on Korean Mini-Mental State Examination changes (baseline to 12 months) between the A+ and A- groups. The secondary outcome measures will be the dementia-conversion rate and changes in the Korean version of the Montreal Cognitive Assessment (baseline to 12 months) between the A+ and A- groups. CONCLUSIONS: This study will provide a broadened perspective on the impact of Aß on the cause and outcomes of PSCI in clinical practice. Identifying amyloid pathology in patients with PSCI will help select patients who need more focused treatments such as acetylcholinesterase inhibitors. TRIAL REGISTRATION: Clinical Research Information Service identifier: KCT0005086.

A multifaceted role of progranulin in regulating amyloid-beta dynamics and responses.

Haploinsufficiency of progranulin (PGRN) is a leading cause of frontotemporal lobar degeneration (FTLD). PGRN polymorphisms are associated with Alzheimer's disease. PGRN is highly expressed in the microglia near Aß plaques and influences plaque dynamics and microglial activation. However, the detailed mechanisms remain elusive. Here we report that PGRN deficiency reduces human APP and Aß levels in the young male but not female mice. PGRN-deficient microglia exhibit increased expression of markers associated with microglial activation, including CD68, galectin-3, TREM2, and GPNMB, specifically near Aß plaques. In addition, PGRN loss leads to up-regulation of lysosome proteins and an increase in the nuclear localization of TFE3, a transcription factor involved in lysosome biogenesis. Cultured PGRN-deficient microglia show enhanced nuclear translocation of TFE3 and inflammation in response to Aß fibril treatment. Taken together, our data revealed a sex- and age-dependent effect of PGRN on APP metabolism and a role of PGRN in regulating lysosomal activities and inflammation in plaque-associated microglia.

Microglia show differential transcriptomic response to Aß peptide aggregates ex vivo and in vivo.

Aggregation and accumulation of amyloid-ß (Aß) is a defining feature of Alzheimer's disease pathology. To study microglial responses to Aß, we applied exogenous Aß peptide, in either oligomeric or fibrillar conformation, to primary mouse microglial cultures and evaluated system-level transcriptional changes and then compared these with transcriptomic changes in the brains of CRND8 APP mice. We find that primary microglial cultures have rapid and massive transcriptional change in response to Aß. Transcriptomic responses to oligomeric or fibrillar Aß in primary microglia, although partially overlapping, are distinct and are not recapitulated in vivo where Aß progressively accumulates. Furthermore, although classic immune mediators show massive transcriptional changes in the primary microglial cultures, these changes are not observed in the mouse model. Together, these data extend previous studies which demonstrate that microglia responses ex vivo are poor proxies for in vivo responses. Finally, these data demonstrate the potential utility of using microglia as biosensors of different aggregate conformation, as the transcriptional responses to oligomeric and fibrillar Aß can be distinguished.

Alzheimer amyloid-ß- peptide disrupts membrane localization of glucose transporter 1 in astrocytes: implications for glucose levels in brain and blood.

Alzheimer's disease (AD) is associated with disturbances in blood glucose regulation, and type-2 diabetes elevates the risk for dementia. A role for amyloid-ß peptide (Aß) in linking these age-related conditions has been proposed, tested primarily in transgenic mouse lines that overexpress mutated amyloid precursor protein (APP). Because APP has its own impacts on glucose regulation, we examined the BRI-Aß42 line ("Aß42-tg"), which produces extracellular Aß1-42 in the CNS without elevation of APP. We also looked for interactions with diet-induced obesity (DIO) resulting from a high-fat, high-sucrose ("western") diet. Aß42-tg mice were impaired in both spatial memory and glucose tolerance. Although DIO induced insulin resistance, Aß1-42 accumulation did not, and the impacts of DIO and Aß on glucose tolerance were merely additive. Aß42-tg mice exhibited no significant differences from wild-type in insulin production, body weight, lipidemia, appetite, physical activity, respiratory quotient, an-/orexigenic factors, or inflammatory factors. These negative findings suggested that the phenotype in these mice arose from perturbation of glucose excursion in an insulin-independent tissue. To wit, cerebral cortex of Aß42-tg mice had reduced glucose utilization, similar to human patients with AD. This was associated with insufficient trafficking of glucose transporter 1 to the plasma membrane in parenchymal brain cells, a finding also documented in human AD tissue. Together, the lower cerebral metabolic rate of glucose and diminished function of parenchymal glucose transporter 1 indicate that aberrant regulation of blood glucose in AD likely reflects a central phenomenon, resulting from the effects of Aß on cerebral parenchyma, rather than a generalized disruption of hypothalamic or peripheral endocrinology. The involvement of a specific glucose transporter in this deficit provides a new target for the design of AD therapies.

Cholesterol-lowering drugs reduce APP processing to Aß by inducing APP dimerization.

Amyloid beta (Aß) is a major component of amyloid plaques, which are a key pathological hallmark found in the brains of Alzheimer's disease (AD) patients. We show that statins are effective at reducing Aß in human neurons from nondemented control subjects, as well as subjects with familial AD and sporadic AD. Aß is derived from amyloid precursor protein (APP) through sequential proteolytic cleavage by BACE1 and γ-secretase. While previous studies have shown that cholesterol metabolism regulates APP processing to Aß, the mechanism is not well understood. We used iPSC-derived neurons and bimolecular fluorescence complementation assays in transfected cells to elucidate how altering cholesterol metabolism influences APP processing. Altering cholesterol metabolism using statins decreased the generation of sAPPß and increased levels of full-length APP (flAPP), indicative of reduced processing of APP by BACE1. We further show that statins decrease flAPP interaction with BACE1 and enhance APP dimerization. Additionally, statin-induced changes in APP dimerization and APP-BACE1 are dependent on cholesterol binding to APP. Our data indicate that statins reduce Aß production by decreasing BACE1 interaction with flAPP and suggest that this process may be regulated through competition between APP dimerization and APP cholesterol binding.

Aß Beyond the AD Pathology: Exploring the Structural Response of Membranes Exposed to Nascent Aß Peptide.

The physiological and pathological roles of nascent amyloid beta (Aß) monomers are still debated in the literature. Their involvement in the pathological route of Alzheimer's Disease (AD) is currently considered to be the most relevant, triggered by their aggregation into structured oligomers, a toxic species. Recently, it has been suggested that nascent Aß, out of the amyloidogenic pathway, plays a physiological and protective role, especially in the brain. In this emerging perspective, the study presented in this paper investigated whether the organization of model membranes is affected by contact with Aß in the nascent state, as monomers. The outcome is that, notably, the rules of engagement and the resulting structural outcome are dictated by the composition and properties of the membrane, rather than by the Aß variant. Interestingly, Aß monomers are observed to favor the tightening of adjacent complex membranes, thereby affecting a basic structural event for cell-cell adhesion and cell motility.

Dynamic changes in the brain protein interaction network correlates with progression of Aß42 pathology in Drosophila.

Alzheimer's disease (AD), the most prevalent form of dementia, is a progressive and devastating neurodegenerative condition for which there are no effective treatments. Understanding the molecular pathology of AD during disease progression may identify new ways to reduce neuronal damage. Here, we present a longitudinal study tracking dynamic proteomic alterations in the brains of an inducible Drosophila melanogaster model of AD expressing the Arctic mutant Aß42 gene. We identified 3093 proteins from flies that were induced to express Aß42 and age-matched healthy controls using label-free quantitative ion-mobility data independent analysis mass spectrometry. Of these, 228 proteins were significantly altered by Aß42 accumulation and were enriched for AD-associated processes. Network analyses further revealed that these proteins have distinct hub and bottleneck properties in the brain protein interaction network, suggesting that several may have significant effects on brain function. Our unbiased analysis provides useful insights into the key processes governing the progression of amyloid toxicity and forms a basis for further functional analyses in model organisms and translation to mammalian systems.

Amyloid-ß regulates gap junction protein connexin 43 trafficking in cultured primary astrocytes.

Altered expression and function of astroglial gap junction protein connexin 43 (Cx43) has increasingly been associated to neurotoxicity in Alzheimer disease (AD). Although earlier studies have examined the effect of increased ß-amyloid (Aß) on Cx43 expression and function leading to neuronal damage, underlying mechanisms by which Aß modulates Cx43 in astrocytes remain elusive. Here, using mouse primary astrocyte cultures, we have examined the cellular processes by which Aß can alter Cx43 gap junctions. We show that Aß25-35 impairs functional gap junction coupling yet increases hemichannel activity. Interestingly, Aß25-35 increased the intracellular pool of Cx43 with a parallel decrease in gap junction assembly at the surface. Intracellular Cx43 was found to be partly retained in the endoplasmic reticulum-associated cell compartments. However, forward trafficking of the newly synthesized Cx43 that already reached the Golgi was not affected in Aß25-35-exposed astrocytes. Supporting this, treatment with 4-phenylbutyrate, a well-known chemical chaperone that improves trafficking of several transmembrane proteins, restored Aß-induced impaired gap junction coupling between astrocytes. We further show that interruption of Cx43 endocytosis in Aß25-35-exposed astrocytes resulted in their retention at the cell surface in the form of functional gap junctions indicating that Aß25-35 causes rapid internalization of Cx43 gap junctions. Additionally, in silico molecular docking suggests that Aß can bind favorably to Cx43. Our study thus provides novel insights into the cellular mechanisms by which Aß modulates Cx43 function in astrocytes, the basic understanding of which is vital for the development of alternative therapeutic strategy targeting connexin channels in AD.

Genistein inhibits amyloid peptide 25-35-induced neuronal death by modulating estrogen receptors, choline acetyltransferase and glutamate receptors.

PURPOSE: To explore genistein, the most active component of soy isoflavones, on viability, expression of estrogen receptor (ER) subtypes, choline acetyltransferase (ChAT), and glutamate receptor subunits in amyloid peptide 25-35-induced hippocampal neurons, providing valuable data and basic information for neuroprotective effect of genistein in Aß25-35-induced neuronal injury. METHODS: We established an in vitro model of Alzheimer's disease by exposing primary hippocampal neurons of newborn rats to amyloid peptide 25-35 (20 µM) for 24 h and observing the effects of genistein (10 µM, 3 h) on viability, expression of ER subtypes, ChAT, NMDA receptor subunit NR2B and AMPA receptor subunit GluR2 in Aß25-35-induced hippocampal neurons. RESULTS: We found that amyloid peptide 25-35 exposure reduced the viability of hippocampal neurons. Meanwhile, amyloid peptide 25-35 exposure decreased the expression of ER subtypes, ChAT and GluR2, and increased the expression of NR2B. Genistein at least partially reversed the effects of amyloid peptide 25-35 in hippocampal neurons. CONCLUSION: Genistein could increase the expression of ChAT as a consequence of activating estrogen receptor subtypes, modulating the expression of NR2B and GluR2, and thereby ameliorating the status of hippocampal neurons and exerting neuroprotective effects against amyloid peptide 25-35. Our data suggest that genistein might represent a potential cell-targeted therapy which could be a promising approach to treating AD.

The physiological roles of tau and Aß: implications for Alzheimer's disease pathology and therapeutics.

Tau and amyloid beta (Aß) are the prime suspects for driving pathology in Alzheimer's disease (AD) and, as such, have become the focus of therapeutic development. Recent research, however, shows that these proteins have been highly conserved throughout evolution and may have crucial, physiological roles. Such functions may be lost during AD progression or be unintentionally disrupted by tau- or Aß-targeting therapies. Tau has been revealed to be more than a simple stabiliser of microtubules, reported to play a role in a range of biological processes including myelination, glucose metabolism, axonal transport, microtubule dynamics, iron homeostasis, neurogenesis, motor function, learning and memory, neuronal excitability, and DNA protection. Aß is similarly multifunctional, and is proposed to regulate learning and memory, angiogenesis, neurogenesis, repair leaks in the blood-brain barrier, promote recovery from injury, and act as an antimicrobial peptide and tumour suppressor. This review will discuss potential physiological roles of tau and Aß, highlighting how changes to these functions may contribute to pathology, as well as the implications for therapeutic development. We propose that a balanced consideration of both the physiological and pathological roles of tau and Aß will be essential for the design of safe and effective therapeutics.

Pharmacological Treatment of Alzheimer's Disease: Insights from Drosophila melanogaster.

Aging is an ineluctable law of life. During the process of aging, the occurrence of neurodegenerative disorders is prevalent in the elderly population and the predominant type of dementia is Alzheimer's disease (AD). The clinical symptoms of AD include progressive memory loss and impairment of cognitive functions that interfere with daily life activities. The predominant neuropathological features in AD are extracellular ß-amyloid (Aß) plaque deposition and intracellular neurofibrillary tangles (NFTs) of hyperphosphorylated Tau. Because of its complex pathobiology, some tangible treatment can only ameliorate the symptoms, but not prevent the disease altogether. Numerous drugs during pre-clinical or clinical studies have shown no positive effect on the disease outcome. Therefore, understanding the basic pathophysiological mechanism of AD is imperative for the rational design of drugs that can be used to prevent this disease. Drosophila melanogaster has emerged as a highly efficient model system to explore the pathogenesis and treatment of AD. In this review we have summarized recent advancements in the pharmacological research on AD using Drosophila as a model species, discussed feasible treatment strategies and provided further reference for the mechanistic study and treatment of age-related AD.

The Use of Antimicrobial and Antiviral Drugs in Alzheimer's Disease.

The aggregation and accumulation of amyloid-ß plaques and tau proteins in the brain have been central characteristics in the pathophysiology of Alzheimer's disease (AD), making them the focus of most of the research exploring potential therapeutics for this neurodegenerative disease. With success in interventions aimed at depleting amyloid-ß peptides being limited at best, a greater understanding of the physiological role of amyloid-ß peptides is needed. The development of amyloid-ß plaques has been determined to occur 10-20 years prior to AD symptom manifestation, hence earlier interventions might be necessary to address presymptomatic AD. Furthermore, recent studies have suggested that amyloid-ß peptides may play a role in innate immunity as an antimicrobial peptide. These findings, coupled with the evidence of pathogens such as viruses and bacteria in AD brains, suggests that the buildup of amyloid-ß plaques could be a response to the presence of viruses and bacteria. This has led to the foundation of the antimicrobial hypothesis for AD. The present review will highlight the current understanding of amyloid-ß, and the role of bacteria and viruses in AD, and will also explore the therapeutic potential of antimicrobial and antiviral drugs in Alzheimer's disease.

Three-dimensional real time imaging of amyloid ß aggregation on living cells.

Alzheimer's disease (AD) is a progressive disorder of the brain that gradually decreases thinking, memory, and language abilities. The aggregation process of amyloid ß (Aß) is a key step in the expression of its neurocytotoxicity and development of AD because Aß aggregation and accumulation around neuronal cells induces cell death. However, the molecular mechanism underlying the neurocytotoxicity and cell death by Aß aggregation has not been clearly elucidated. In this study, we successfully visualized real-time process of Aß42 aggregation around living cells by applying our established QD imaging method. 3D observations using confocal laser microscopy revealed that Aß42 preferentially started to aggregate at the region where membrane protrusions frequently formed. Furthermore, we found that inhibition of actin polymerization using cytochalasin D reduced aggregation of Aß42 on the cell surface. These results indicate that actin polymerization-dependent cell motility is responsible for the promotion of Aß42 aggregation at the cell periphery. 3D observation also revealed that the aggregates around the cell remained in that location even if cell death occurred, implying that amyloid plaques found in the AD brain grew from the debris of dead cells that accumulated Aß42 aggregates.

Agmatine reverses memory deficits induced by Aß1-42 peptide in mice: A key role of imidazoline receptors.

Agmatine is a biogenic amine synthesized following decarboxylation of L-arginine by the enzyme arginine decarboxylase and exhibits favourable outcome in neurodegenerative disorders. Present study was designed to examine the relationship between agmatine and the imidazoline receptors in memory deficits induced by Aß1-42 peptide in mice. Mice were treated with single intracerebroventricular (i.c.v.) injection of Aß1-42 peptide (3 µg) and evaluated for learning and memory in Morris water maze (MWM) and subjected to Aß1-42, TNF-α and IL-6 and BDNF immunocontent analysis within the hippocampus. While the learning and memory impairment was evident in the mice subjected to MWM test following Aß1-42 peptide administration, there was a significant increase in Aß1-42, TNF-α and IL-6 and reduction in BDNF immunocontent within the hippocampus. Daily intraperitoneal (i.p.) treatment with agmatine (10 and 20 mg/kg); imidazoline I1 receptor agonist, moxonidine and imidazoline I2 receptor agonist, 2-BFI starting from day 8 to 27 post-Aß1-42 injection, significantly prevented the cognitive deficits and normalized the Aß1-42 peptide, IL-6, TNF-α and BDNF immunocontent in hippocampus. On the other hand, pre-treatment with imidazoline I1 receptor antagonist, efaroxan and imidazoline I2 receptor antagonist, BU 224 attenuated the effects of agmatine on learning and memory in MWM, IL-6, TNF-α and BDNF content. In conclusion, the present study provides functional evidence for the involvement of the imidazoline receptors in agmatine induced reversal of Aß1-42 induced memory deficits in mice. The data projects agmatine and imidazoline receptor agonists as a potential therapeutic target for the treatment of AD.

Copper stabilizes antiparallel ß-sheet fibrils of the amyloid ß40 (Aß40)-Iowa variant.

Cerebral amyloid angiopathy (CAA) is a vascular disorder that primarily involves deposition of the 40-residue-long ß-amyloid peptide (Aß40) in and along small blood vessels of the brain. CAA is often associated with Alzheimer's disease (AD), which is characterized by amyloid plaques in the brain parenchyma enriched in the Aß42 peptide. Several recent studies have suggested a structural origin that underlies the differences between the vascular amyloid deposits in CAA and the parenchymal plaques in AD. We previously have found that amyloid fibrils in vascular amyloid contain antiparallel ß-sheet, whereas previous studies by other researchers have reported parallel ß-sheet in fibrils from parenchymal amyloid. Using X-ray fluorescence microscopy, here we found that copper strongly co-localizes with vascular amyloid in human sporadic CAA and familial Iowa-type CAA brains compared with control brain blood vessels lacking amyloid deposits. We show that binding of Cu(II) ions to antiparallel fibrils can block the conversion of these fibrils to the more stable parallel, in-register conformation and enhances their ability to serve as templates for seeded growth. These results provide an explanation for how thermodynamically less stable antiparallel fibrils may form amyloid in or on cerebral vessels by using Cu(II) as a structural cofactor.