Domenica Donatella Li Puma1,2, Cristian Ripoli1,2, Giulia Puliatti1, Francesco Pastore1, Giacomo Lazzarino3, Barbara Tavazzi3, Ottavio Arancio4, Roberto Piacentini1,2, Claudio Grassi1,2. 1. Department of Neuroscience, Università Cattolica del Sacro Cuore, Rome, Italy. 2. Fondazione Policlinico Universitario A. Gemelli IRCCS, Rome, Italy. 3. UniCamillus - Saint Camillus International University of Health Sciences, Rome, Italy. 4. Department of Pathology and Cell Biology, Taub Institute for Research on Alzheimer's Disease and the Aging Brain, and Department of Medicine, Columbia University, New York, NY, USA.
Abstract
AIMS: Several studies reported that astrocytes support neuronal communication by the release of gliotransmitters, including ATP and glutamate. Astrocytes also play a fundamental role in buffering extracellular glutamate in the synaptic cleft, thus limiting the risk of excitotoxicity in neurons. We previously demonstrated that extracellular tau oligomers (ex-oTau), by specifically targeting astrocytes, affect glutamate-dependent synaptic transmission via a reduction in gliotransmitter release. The aim of this work was to determine if ex-oTau also impair the ability of astrocytes to uptake extracellular glutamate, thus further contributing to ex-oTau-dependent neuronal dysfunction. METHODS: Primary cultures of astrocytes and organotypic brain slices were exposed to ex-oTau (200 nM) for 1 h. Extracellular glutamate buffering by astrocytes was studied by: Na+ imaging; electrophysiological recordings; high-performance liquid chromatography; Western blot and immunofluorescence. Experimental paradigms avoiding ex-oTau internalisation (i.e. heparin pre-treatment and amyloid precursor protein knockout astrocytes) were used to dissect intracellular vs extracellular effects of oTau. RESULTS: Ex-oTau uploading in astrocytes significantly affected glutamate-transporter-1 expression and function, thus impinging on glutamate buffering activity. Ex-oTau also reduced Na-K-ATPase activity because of pump mislocalisation on the plasma membrane, with no significant changes in expression. This effect was independent of oTau internalisation and it caused Na+ overload and membrane depolarisation in ex-oTau-targeted astrocytes. CONCLUSIONS: Ex-oTau exerted a complex action on astrocytes, at both intracellular and extracellular levels. The net effect was dysregulated glutamate signalling in terms of both release and uptake that relied on reduced expression of glutamate-transporter-1, altered function and localisation of NKA1A1, and NKA1A2. Consequently, Na+ gradients and all Na+ -dependent transports were affected.
AIMS: Several studies reported that astrocytes support neuronal communication by the release of gliotransmitters, including ATP and glutamate. Astrocytes also play a fundamental role in buffering extracellular glutamate in the synaptic cleft, thus limiting the risk of excitotoxicity in neurons. We previously demonstrated that extracellular tau oligomers (ex-oTau), by specifically targeting astrocytes, affect glutamate-dependent synaptic transmission via a reduction in gliotransmitter release. The aim of this work was to determine if ex-oTau also impair the ability of astrocytes to uptake extracellular glutamate, thus further contributing to ex-oTau-dependent neuronal dysfunction. METHODS: Primary cultures of astrocytes and organotypic brain slices were exposed to ex-oTau (200 nM) for 1 h. Extracellular glutamate buffering by astrocytes was studied by: Na+ imaging; electrophysiological recordings; high-performance liquid chromatography; Western blot and immunofluorescence. Experimental paradigms avoiding ex-oTau internalisation (i.e. heparin pre-treatment and amyloid precursor protein knockout astrocytes) were used to dissect intracellular vs extracellular effects of oTau. RESULTS: Ex-oTau uploading in astrocytes significantly affected glutamate-transporter-1 expression and function, thus impinging on glutamate buffering activity. Ex-oTau also reduced Na-K-ATPase activity because of pump mislocalisation on the plasma membrane, with no significant changes in expression. This effect was independent of oTau internalisation and it caused Na+ overload and membrane depolarisation in ex-oTau-targeted astrocytes. CONCLUSIONS: Ex-oTau exerted a complex action on astrocytes, at both intracellular and extracellular levels. The net effect was dysregulated glutamate signalling in terms of both release and uptake that relied on reduced expression of glutamate-transporter-1, altered function and localisation of NKA1A1, and NKA1A2. Consequently, Na+ gradients and all Na+ -dependent transports were affected.
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Authors: M Fá; D Puzzo; R Piacentini; A Staniszewski; H Zhang; M A Baltrons; D D Li Puma; I Chatterjee; J Li; F Saeed; H L Berman; C Ripoli; W Gulisano; J Gonzalez; H Tian; J A Costa; P Lopez; E Davidowitz; W H Yu; V Haroutunian; L M Brown; A Palmeri; E M Sigurdsson; K E Duff; A F Teich; L S Honig; M Sierks; J G Moe; L D'Adamio; C Grassi; N M Kanaan; P E Fraser; O Arancio Journal: Sci Rep Date: 2016-01-20 Impact factor: 4.379