Details

Autor(en) / Beteiligte

• Li Puma, Domenica Donatella
• Ripoli, Cristian
• Puliatti, Giulia
• Pastore, Francesco
• Lazzarino, Giacomo
• Tavazzi, Barbara
• Arancio, Ottavio
• Piacentini, Roberto
• Grassi, Claudio

Titel

Extracellular tau oligomers affect extracellular glutamate handling by astrocytes through downregulation of GLT‐1 expression and impairment of NKA1A2 function

Ist Teil von

• Neuropathology and applied neurobiology, 2022-08, Vol.48 (5), p.e12811-n/a

Ort / Verlag

England: Wiley Subscription Services, Inc

Erscheinungsjahr

2022

Quelle

Wiley Online Library - AutoHoldings Journals

Beschreibungen/Notizen

• 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. Extracellularly, tau oligomers cause NKAs mislocalisation on the plasma membrane inducing intracellular Na+ overload in astrocytes leading to reduced Na+ gradient across the membrane. Intracellularly, tau oligomers downregulate GLT‐1 expression. The net effects of extracellular tau oligomers are a reduction of Na+‐driven uploading of extracellular glutamate from astrocytes.