Amyloid beta mediated glutamate release from astrocytes

SANZ BLASCO S; PIÑA-CRESPO JC; TALANTOVA M; CAO G; LIPTON SA

San Diego

Congreso; Society for Neuroscience 2010; 2010

Society for Neuroscience

Background: Excitotoxicity is caused by excessive exposure to glutamate or overstimulation of its membrane receptors. Several lines of evidence indicate that synaptic damage and neuronal loss can result from excessive NMDA-type glutamate receptor (NMDAR)-dependent Ca2+ entry. Dysregulation of intracellular Ca2+ homeostasis and glutamate-dependent excitotoxic injury has been suggested to underlie amyloid β-peptide (Aβ) toxicity in Alzheimer?s disease (AD), but the exact mechanism remains unknown. We used the glutamate sensing fluorescent reporter (SuperGluSnFR) developed by Roger Tsien?s laboratory to perform quantitative optical measurements of glutamate release in response to oligomerized Aβ peptide in cultures of rodent astrocytes. Astrocytes are known to modulate neuronal excitability and synaptic transmission.  We extend these findings here by showing that astrocytes can release toxic levels of glutamate in response to oligomerized Aβ.   Objective: The main objective of this project was to directly measure and quantify glutamate release in from purified rat cortical astrocytes in response to Aβ oligomers.  Methods: We performed Foerster resonance energy transfer (FRET) microscopy to image glutamate release using the glutamate ?sniffer? SuperGluSnFR. This probe provides a sensitive fluorescent readout of glutamate concentration by FRET-dependent changes in the CFP/YFP emission ratio.  We co-transfected HEK 293T cells with SuperGluSnFr and Neuroligin, and then co-cultured these ?glutamate-sensing cells? with purified rat cortical astrocytes. We used the protein Neuroligin, which is known to induce functional synaptic contacts between cells, to allow the ?probe? HEK cells to come into close contact with astrocytes that were suspected of releasing glutamate. Aβ oligomers, as well as Aβ in its non-oligomerized form as a control, were applied during FRET measurements. Results: As monitored with the glutamate ?sniffer? SuperGlu, nanomolar concentrations of Aβ oligomers induced glutamate release from astrocytes at concentrations of a few hundred micromolar.  These levels of glutamate are known to cause synaptic loss and excitotoxic damage in neurons. Conclusions.  Taken together with prior studies, this work suggests that the toxic effects of Ab oligomers on neurons may be mediated at least in part by local release of glutamate from astrocytes.