Browsing by Author "Stys, Peter K."

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    Copper ions, prion protein and Aβ modulate Ca levels in central nervous system myelin in an NMDA receptor-dependent manner
    (2022-07-26) Tsutsui, Shigeki; Morgan, Megan; Tedford, Hugo; You, Haitao; Zamponi, Gerald W.; Stys, Peter K.
    Abstract As in neurons, CNS myelin expresses N-Methyl-D-Aspartate Receptors (NMDARs) that subserve physiological roles, but have the potential to induce injury to this vital element. Using 2-photon imaging of myelinic Ca in live ex vivo mouse optic nerves, we show that Cu ions potently modulate Ca levels in an NMDAR-dependent manner. Chelating Cu in the perfusate induced a substantial increase in Ca levels, and also caused significant axo-myelinic injury. Myelinic NMDARs are shown to be regulated by cellular prion protein; only in prion protein KO optic nerves does application of NMDA + D-serine induce a large Ca increase, consistent with strong desensitization of these receptors in the presence of prion protein limiting Ca overload. Aβ1-42 peptide induced a large Ca increase that was also Cu-dependent, and was blocked by NMDAR antagonism. Our results indicate that like in neurons, myelinic NMDARs permeate potentially injurious amounts of Ca, and are also potently regulated by micromolar Cu and activated by Aβ1-42 peptides. These findings shed mechanistic light on the important primary white matter injury frequently observed in Alzheimer's brain.
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    Copper-dependent regulation of NMDA receptors by cellular prion protein: implications for neurodegenerative disorders
    (The Physiological Society, 2012-02-06) Stys, Peter K.; You, Haitao; Zamponi, Gerald W.
    N-Methyl-D-aspartate (NMDA) receptors mediate a wide range of important nervous system functions. Conversely, excessive NMDA receptor activity leads to cytotoxic calcium overload and neuronal damage in a wide variety of CNS disorders. It is well established that NMDA receptors are tightly regulated by a number of cell signalling pathways. Recently, it has been shown that NMDA receptor activity is modulated by cellular prion protein (PrP(C)) in a copper-dependent manner. Here we give an overview of the current state of knowledge concerning the novel concept of potent modulation of this receptor's kinetics by copper ions, and the interplay between NMDA receptors and PrP(C) in the context of neurological diseases such as Alzheimer's disease, epilepsy, pain and depression.
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    Dual-probe fluorescence spectroscopy for sensitive quantitation of Alzheimer’s amyloid pathology
    (2022-10-28) Stepanchuk, Anastasiia A.; Morgan, Megan L.; Joseph, Jeffrey T.; Stys, Peter K.
    Abstract Protein misfolding is a prominent pathological hallmark of neurodegenerative disorders, including Alzheimer’s disease (AD). Studies have shown that the diversity of β sheet-rich protein deposits (such as amyloid β plaques and neurofibrillary tangles), present across different brain regions, might underlie different disease phenotypes and only certain types of aggregates might be associated with cognitive decline. Conformationally sensitive fluorescent amyloid probes have the ability to report different structures of protein aggregates by virtue of their shifting emission spectra. Here we defined the binding affinity of the fluorescent amyloid probes BSB and MCAAD to disease-relevant protein aggregates, and combined the two probes to examine formalin-fixed paraffin-embedded mouse and human brain samples. Coupled with quantitative spectral phasor analysis, the dual-probe staining approach revealed remarkable heterogeneity of protein aggregates across the samples. Distinct emission spectra were consistent with certain types of deposits present in the mouse and human brain sections. The sensitivity of this staining, imaging and analysis approach outperformed conventional immunohistochemistry with the detected spectral differences between the greater parenchyma of cognitively normal and AD cases indicating a subtle yet widespread proteopathy associated with disease. Our method offers more sensitive, objective, and quantitative examination of protein misfolding pathology using conventional tissue sections.
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    Excitatory glycine responses of CNS myelin mediated by NR1/NR3 "NMDA" receptor subunits
    (Society for Neuroscience, 2010-08-25) Piña-Crespo, Juan C.; Talantova, Maria V.; Micu, Ileana; States, Bradley A.; Chen, Huei Sheng Vincent; Tu, Shichun; Nakanishi, Nobuki; Tong, Gary G.; Zhang, Dongxian; Heinemann, Stephen F.; Zamponi, Gerald W.; Stys, Peter K.; Lipton, Stuart A.
    NMDA receptors are typically excited by a combination of glutamate and glycine. Here we describe excitatory responses in CNS myelin that are gated by a glycine agonist alone and mediated by NR1/NR3 "NMDA" receptor subunits. Response properties include activation by d-serine, inhibition by the glycine-site antagonist CNQX, and insensitivity to the glutamate-site antagonist d-APV. d-Serine responses were abrogated in NR3A-deficient mice. Our results suggest the presence of functional NR1/NR3 receptors in CNS myelin.
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    Glutamate receptors on myelinated spinal cord axons: I. GluR6 kainate receptors
    (Wiley-Liss, Inc., 2009-02) Ouardouz, Mohamed; Basak, Ajoy; Chen, Andrew; Rehak, Renata; Yin, Xinghua; Coderre, Elaine M.; Zamponi, Gerald W.; Hameed, Shahid; Trapp, Bruce D. T.; Stys, Peter K.
    The deleterious effects of glutamate excitotoxicity are well described for central nervous system gray matter. Although overactivation of glutamate receptors also contributes to axonal injury, the mechanisms are poorly understood. Our goal was to elucidate the mechanisms of kainate receptor-dependent axonal Ca(2+) deregulation.
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    Glutamate receptors on myelinated spinal cord axons: II. AMPA and GluR5 receptors
    (Wiley-Liss Inc., 2009-02-01) Ouardouz, Mohamed; Hameed, Shameed; Yin, Xinghua; Zamponi, Gerald W.; Coderre, Elaine M.; Trapp, Bruce D. T.; Stys, Peter K.
    Glutamate receptors, which play a major role in the physiology and pathology of central nervous system gray matter, are also involved in the pathophysiology of white matter. However, the cellular and molecular mechanisms responsible for excitotoxic damage to white matter elements are not fully understood. We explored the roles of AMPA and GluR5 kainate receptors in axonal Ca(2+) deregulation.
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    Mutation of copper binding sites on cellular prion protein abolishes its inhibitory action on NMDA receptors in mouse hippocampal neurons
    (2021-07-19) Huang, Sun; Black, Stefanie A.; Huang, Junting; Stys, Peter K.; Zamponi, Gerald W.
    Abstract We have previously reported that cellular prion protein (PrPC) can down-regulate NMDA receptor activity and in a copper dependent manner. Here, we employed AAV9 to introduce murine cellular prion protein into mouse hippocampal neurons in primary cultures from PrP null mice to determine the role of the six copper binding motifs located within the N-terminal domain of PrPC. The results demonstrate that viral expression of wild type PrPC lowers NMDAR activity in PrP null mouse hippocampal neurons by reducing the magnitude of non-desensitizing currents. Elimination of the last two copper binding sites alone, or in combination with the remaining four attenuates this protective effect. Thus our data suggest that copper ion interactions with specific binding sites on PrPC are critical for PrPC dependent modulation of NMDA receptor function.
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    Polarization Controlled Coherent Anti-Stokes Raman Scattering Microscopy for Determination of Structural Order of the Myelin Sheath
    (2018-05-17) Brideau, Craig; Stys, Peter K.; Frayne, Richard; Barclay, Paul; Colicos, Michael A.; Fear, Elise C.; Potma, Eric Olaf
    Coherent Anti-Stokes Raman Scattering (CARS) is a laser-scanning microscopy technique that generates a strong label-free signal in lipid. The myelin sheath surrounding nerves is up to 80% lipid, and therefore is an ideal candidate for CARS imaging. The long lipid chains forming the myelin wraps have a directional preference when the myelin is healthy, with CH2 bonds aligned parallel to the axis of the nerve. The optical polarization dependence of the CARS signal can be used to probe the orientation of CH2 bonds in the sheath and determine their nanoscopic orientation. As myelin becomes unhealthy the organization of the lipids begins to loosen from their native organized packing structure. In the early stages this is not visible by conventional microscopy, however polarization-resolved CARS can measure the increasing disorder in the arrangement of the bonds before obvious morphological changes can occur. The degree of disorder is also measured to provide a metric of myelin disorganization in disease models.
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    The Presynaptic and Postsynaptic Signaling of Amyloid β Protein During Ischemia
    (2019-06-11) Palmer, Laura Ann; Thompson, Roger J.; Teskey, G. Campbell; Stys, Peter K.
    Amyloid β has been implicated in the pathophysiology of Alzheimer disease (AD) by disrupting synapses and enhancing cell death. Genetic mutations that are causative of familial Alzheimer disease are associated with enhanced Aβ burden. Since only 5% of AD cases are genetic, efforts must be made to understand environmental risk factors and other co-morbidities that could elevate Aβ. For instance, ischemic stroke is associated with increased risk of developing AD, which is thought to be due to enhanced production of Aβ. Loss of key energy substrates during ischemia initiate overactive synaptic glutamate release, reversed glutamate uptake, ionic dysregulation, and the anoxic depolarization. The anoxic depolarization is mediated by a number of channels, including NMDARs and pannexin-1 (Panx1) to induce Ca2+ dysregulation and downstream cell death. The role of Aβ during the events of acute ischemia is unknown, and is assumed to be pathological due to similar features of ischemia and AD. However, Aβ has been shown to depress synapses and enhance cell survival during excitotoxicity. The overarching hypothesis of this thesis is that Aβ acts to depress aberrant synaptic events during ischemia and reduces excitotoxicity. Here, I show that Aβ potently reduces excitotoxic currents during the anoxic depolarization and prevents Panx1-dependent secondary currents in response to NMDA overstimulation. Aβ does not directly inhibit Panx1 but regulates its opening by acting as an antagonist for mGluR1. This Aβ-mGluR1 interaction also enhances GABAergic signalling to reduce excitotoxic glutamate release, however, presynaptic release does not determine the magnitude of the anoxic depolarization. These data reveal a novel modulation of Panx1 opening by mGluR1, which is regulated by Aβ. Aβ production could be increased during hypoxia to reduce activation of Panx1, thereby attenuating the anoxic depolarization and downstream cell death pathways. With prolonged/repeated ischemic events, Aβ could reach toxic levels and coincide with hallmark pathophysiology of AD.
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    Role of prions in neuroprotection and neurodegeneration: a mechanism involving glutamate receptors?
    (Prion, 2009-12-01) Zamponi, Gerald W.; Stys, Peter K.
    There is increasing evidence that cellular prion protein plays important roles in neurodegeneration and neuroprotection. One of the possible mechanism by which this may occur is a functional inhibition of ionotropic glutamate receptors, including N-Methyl-D-Aspartate (NMDA) receptors. Here we review recent evidence implicating a possible interplay between NMDA receptors and prions in the context of neurodegenerative disorders. Such is a functional link between NMDA receptors and normal prion protein, and therefore possibly between these receptors and pathological prion isoforms, raises interesting therapeutic possibilities for prion diseases.
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    Will the real multiple sclerosis please stand up?
    (Macmillan Publishers Limited, 2012-06-20) Stys, Peter K.; Zamponi, Gerald W.; Geurts, Jeroen J. G.; Van-Minnen, Jan
    Multiple sclerosis (MS) is considered to be an autoimmune, inflammatory disease of the CNS. In most patients, the disease follows a relapsing-remitting course and is characterized by dynamic inflammatory demyelinating lesions in the CNS. Although on the surface MS may appear consistent with a primary autoimmune disease, questions have been raised as to whether inflammation and/or autoimmunity are really at the root of the disease, and it has been proposed that MS might in fact be a degenerative disorder. We argue that MS may be an 'immunological convolution' between an underlying primary degenerative disorder and the host's aberrant immune response. To better understand this disease, we might need to consider non-inflammatory primary progressive MS as the 'real' MS, with inflammatory forms reflecting secondary, albeit very important, reactions.