GPI-anchor signal sequence influences PrPC sorting, shedding and signalling, and impacts on different pathomechanistic aspects of prion disease in mice.

The cellular prion protein (PrPC) is a cell surface glycoprotein attached to the membrane by a glycosylphosphatidylinositol (GPI)-anchor and plays a critical role in transmissible, neurodegenerative and fatal prion diseases. Alterations in membrane attachment influence PrPC-associated signaling, and the development of prion disease, yet our knowledge of the role of the GPI-anchor in localization, processing, and function of PrPC in vivo is limited We exchanged the PrPC GPI-anchor signal sequence of for that of Thy-1 (PrPCGPIThy-1) in cells and mice. We show that this modifies the GPI-anchor composition, which then lacks sialic acid, and that PrPCGPIThy-1 is preferentially localized in axons and is less prone to proteolytic shedding when compared to PrPC.

The phospholipase A pathway controls a synaptic cholesterol ester cycle and synapse damage.

The cellular prion protein (PrP) acts as a scaffold protein that organises signalling complexes. In synaptosomes, the aggregation of PrP by amyloid-β (Aβ) oligomers attracts and activates cytoplasmic phospholipase A (cPLA), leading to synapse degeneration. The signalling platform is dependent on cholesterol released from cholesterol esters by cholesterol ester hydrolases (CEHs).

Monomeric amyloid-β reduced amyloid-β oligomer-induced synapse damage in neuronal cultures.

Alzheimer's disease is a progressive neurodegenerative disease characterized by the accumulation of amyloid-β (Aβ) in the brain. Aβ oligomers are believed to cause synapse damage resulting in the memory deficits that are characteristic of this disease. Since the loss of synaptic proteins in the brain correlates closely with the degree of dementia in Alzheimer's disease, the process of Aβ-induced synapse damage was investigated in cultured neurons by measuring the loss of synaptic proteins.

Cholesterol ester hydrolase inhibitors reduce the production of synaptotoxic amyloid-β oligomers.

The production of amyloid-β (Aβ) is the key factor driving pathogenesis in Alzheimer's disease (AD). Increasing concentrations of Aβ within the brain cause synapse degeneration and the dementia that is characteristic of AD. Here the factors that affect the release of disease-relevant forms Aβ were studied in a cell model.

Breaking the Cycle, Cholesterol Cycling, and Synapse Damage in Response to Amyloid-β.

Soluble amyloid-β (Aβ) oligomers, a key driver of pathogenesis in Alzheimer disease, bind to cellular prion proteins (PrP) expressed on synaptosomes resulting in increased cholesterol concentrations, movement of cytoplasmic phospholipase A (cPLA) to lipid rafts and activation of cPLA. The formation of Aβ-PrP-cPLA complexes was controlled by the cholesterol ester cycle. Thus, Aβ activated cholesterol ester hydrolases which released cholesterol from stores of cholesterol esters; the increased cholesterol concentrations stabilised Aβ-PrP-cPLA complexes.

Valproic acid and its congener propylisopropylacetic acid reduced the amount of soluble amyloid-β oligomers released from 7PA2 cells.

The amyloid hypothesis of Alzheimer's disease suggests that synaptic degeneration and pathology is caused by the accumulation of amyloid-β (Aβ) peptides derived from the amyloid precursor protein (APP). Subsequently, soluble Aβ oligomers cause the loss of synaptic proteins from neurons, a histopathological feature of Alzheimer's disease that correlates with the degree of dementia. In this study, the production of toxic forms of Aβ was examined in vitro using 7PA2 cells stably transfected with human APP.

The cholesterol ester cycle regulates signalling complexes and synapse damage caused by amyloid-β.

Cholesterol is required for the formation and function of some signalling platforms. In synaptosomes, amyloid-β (Aβ) oligomers, the causative agent in Alzheimer's disease, bind to cellular prion proteins (PrP) resulting in increased cholesterol concentrations, translocation of cytoplasmic phospholipase A (cPLA, also known as PLA2G4A) to lipid rafts, and activation of cPLA The formation of Aβ-PrP complexes is controlled by the cholesterol ester cycle. In this study, Aβ activated cholesterol ester hydrolases, which released cholesterol from stores of cholesterol esters and stabilised Aβ-PrP complexes, resulting in activated cPLA Conversely, cholesterol esterification reduced cholesterol concentrations causing the dispersal of Aβ-PrP complexes.

Sialylated glycosylphosphatidylinositols suppress the production of toxic amyloid-β oligomers.

The production of amyloid-β (Aβ) is a key factor driving pathogenesis in Alzheimer's disease (AD). Increasing concentrations of soluble Aβ oligomers within the brain lead to synapse degeneration and the progressive dementia characteristic of AD. Since Aβ exists in both disease-relevant (toxic) and non-toxic forms, the factors that affected the release of toxic Aβ were studied in a cell model.

Sialic Acid within the Glycosylphosphatidylinositol Anchor Targets the Cellular Prion Protein to Synapses.

Although the cellular prion protein (PrP(C)) is concentrated at synapses, the factors that target PrP(C) to synapses are not understood. Here we demonstrate that exogenous PrP(C) was rapidly targeted to synapses in recipient neurons derived from Prnp knock-out((0/0)) mice. The targeting of PrP(C) to synapses was dependent upon both neuronal cholesterol concentrations and the lipid and glycan composition of its glycosylphosphatidylinositol (GPI) anchor.

Glycosylphosphatidylinositols: More than just an anchor?

There is increasing interest in the role of glycosylphosphatidylinositol (GPI) anchors that attach some proteins to cell membranes. Far from being biologically inert, GPIs influence the targeting, intracellular trafficking and function of the attached protein. Our recent paper demonstrated the role of sialic acid on the GPI of the cellular prion protein (PrP(C)).

Does the tail wag the dog? How the structure of a glycosylphosphatidylinositol anchor affects prion formation.

There is increasing interest in the role of the glycosylphosphatidylinositol (GPI) anchor attached to the cellular prion protein (PrP(C)). Since GPI anchors can alter protein targeting, trafficking and cell signaling, our recent study examined how the structure of the GPI anchor affected prion formation. PrP(C) containing a GPI anchor from which the sialic acid had been removed (desialylated PrP(C)) was not converted to PrP(Sc) in prion-infected neuronal cell lines and in scrapie-infected primary cortical neurons.

Sialic Acid on the Glycosylphosphatidylinositol Anchor Regulates PrP-mediated Cell Signaling and Prion Formation.

The prion diseases occur following the conversion of the cellular prion protein (PrP(C)) into disease-related isoforms (PrP(Sc)). In this study, the role of the glycosylphosphatidylinositol (GPI) anchor attached to PrP(C) in prion formation was examined using a cell painting technique. PrP(Sc) formation in two prion-infected neuronal cell lines (ScGT1 and ScN2a cells) and in scrapie-infected primary cortical neurons was increased following the introduction of PrP(C).

Glimepiride protects neurons against amyloid-β-induced synapse damage.

Alzheimer's disease is associated with the accumulation within the brain of amyloid-β (Aβ) peptides that damage synapses and affect memory acquisition. This process can be modelled by observing the effects of Aβ on synapses in cultured neurons. The addition of picomolar concentrations of soluble Aβ derived from brain extracts triggered the loss of synaptic proteins including synaptophysin, synapsin-1 and cysteine string protein from cultured neurons.

cAMP-Inhibits Cytoplasmic Phospholipase A₂ and Protects Neurons against Amyloid-β-Induced Synapse Damage.

A key event in Alzheimer's disease (AD) is the production of amyloid-β (Aβ) peptides and the loss of synapses. In cultured neurons Aβ triggered synapse damage as measured by the loss of synaptic proteins. α-synuclein (αSN), aggregates of which accumulate in Parkinson's disease, also caused synapse damage.

An in vitro model for synaptic loss in neurodegenerative diseases suggests a neuroprotective role for valproic acid via inhibition of cPLA2 dependent signalling.

Many neurodegenerative diseases present the loss of synapses as a common pathological feature. Here we have employed an in vitro model for synaptic loss to investigate the molecular mechanism of a therapeutic treatment, valproic acid (VPA). We show that amyloid-β (Aβ), isolated from patient tissue and thought to be the causative agent of Alzheimer's disease, caused the loss of synaptic proteins including synaptophysin, synapsin-1 and cysteine-string protein from cultured mouse neurons.

Monoacylated Cellular Prion Proteins Reduce Amyloid-β-Induced Activation of Cytoplasmic Phospholipase A2 and Synapse Damage.

Alzheimer's disease (AD) is a progressive neurodegenerative disease characterized by the accumulation of amyloid-β (Aβ) and the loss of synapses. Aggregation of the cellular prion protein (PrPC) by Aβ oligomers induced synapse damage in cultured neurons. PrPC is attached to membranes via a glycosylphosphatidylinositol (GPI) anchor, the composition of which affects protein targeting and cell signaling.

α-Synuclein-induced synapse damage in cultured neurons is mediated by cholesterol-sensitive activation of cytoplasmic phospholipase A2.

The accumulation of aggregated forms of the α-synuclein (αSN) is associated with the pathogenesis of Parkinson's disease (PD) and Dementia with Lewy Bodies. The loss of synapses is an important event in the pathogenesis of these diseases. Here we show that aggregated recombinant human αSN, but not βSN, triggered synapse damage in cultured neurons as measured by the loss of synaptic proteins.

Glimepiride reduces CD14 expression and cytokine secretion from macrophages.

Background: Activated microglia are associated with deposits of aggregated proteins within the brains of patients with Alzheimer's disease (AD), Parkinson's disease (PD) and prion diseases. Since the cytokines secreted from activated microglia are thought to contribute to the pathogenesis of these neurodegenerative diseases, compounds that suppress cytokine production have been identified as potential therapeutic targets. CD14 is a glycosylphosphatidylinositol (GPI)- anchored protein that is part of a receptor complex that mediates microglial responses to peptides that accumulate in prion disease (PrP82-146), AD (amyloid-β (Aβ)42) and PD (α-synuclein (αSN)).

Platelet-activating factor antagonists enhance intracellular degradation of amyloid-β42 in neurons via regulation of cholesterol ester hydrolases.

Introduction: The progressive dementia that is characteristic of Alzheimer's disease is associated with the accumulation of amyloid-beta (Aβ) peptides in extracellular plaques and within neurons. Aβ peptides are targeted to cholesterol-rich membrane micro-domains called lipid rafts. Observations that many raft proteins undertake recycling pathways that avoid the lysosomes suggest that the accumulation of Aβ in neurons may be related to Aβ targeting lipid rafts.

The N-methylated peptide SEN304 powerfully inhibits Aβ(1-42) toxicity by perturbing oligomer formation.

Oligomeric forms of β-amyloid (Aβ) have potent neurotoxic activity and are the primary cause of neuronal injury and cell death in Alzheimer's disease (AD). Compounds that perturb oligomer formation or structure may therefore be therapeutic for AD. We previously reported that d-[(chGly)-(Tyr)-(chGly)-(chGly)-(mLeu)]-NH(2) (SEN304) is able to inhibit Aβ aggregation and toxicity, shown primarily by thioflavin T fluorescence and MTT (Kokkoni, N.

Clustering of sialylated glycosylphosphatidylinositol anchors mediates PrP-induced activation of cytoplasmic phospholipase A 2 and synapse damage.

Precisely how the accumulation of PrP (Sc) causes the neuronal degeneration that leads to the clinical symptoms of prion diseases is poorly understood. Our recent paper showed that the clustering of specific glycosylphosphatidylinositol (GPI) anchors attached to PrP proteins triggered synapse damage in cultured neurons. First, we demonstrated that small, soluble PrP (Sc) oligomers caused synapse damage via a GPI-dependent process.

Neurodegeneration induced by clustering of sialylated glycosylphosphatidylinositols of prion proteins.

The transmissible spongiform encephalopathies, more commonly known as the prion diseases, are associated with the production and aggregation of disease-related isoforms of the prion protein (PrP(Sc)). The mechanisms by which PrP(Sc) accumulation causes neurodegeneration in these diseases are poorly understood. In cultured neurons, the addition of PrP(Sc) alters cell membranes, increasing cholesterol, activating cytoplasmic phospholipase A(2) (cPLA(2)), and triggering synapse damage.

Ethanol protects cultured neurons against amyloid-β and α-synuclein-induced synapse damage.

The loss of synapses and a corresponding reduction in synaptic proteins are histopathological features of Alzheimer's disease that correlate strongly with dementia. Here we report that stable Aβ oligomers secreted by 7PA2 cells reduced the amount of synaptophysin, a protein used as an indicator of synapse density, in cultured cortical and hippocampal neurons. Pre-treatment with physiologically relevant concentrations of ethanol (0.