Fluoxetine affects GluK2 editing, glutamate-evoked Ca2+ influx and extracellular signal-regulated kinase phosphorylation in mouse astrocytes

Abstract

Background: We sought to study the effects of chronic exposure to fluoxetine - a selective serotonin reuptake inhibitor (SSRI) and specific 5-HT2B receptor agonist in astrocytes - on the expression of kainate receptors (GluK1-5) in cultured astrocytes and in intact brains in mice and on GluK2 editing by adenosine deaminase acting on RNA (ADAR), as well as the ensuing effects of fluoxetine on glutamate-mediated Ca2+ influx and extracellular signal-regulated kinase (ERK)1/2 phosphorylation in astrocytes. Methods: We performed reverse transcription-polymerase chain reaction (PCR) to assess mRNA expression. We analyzed RNA editing with amplification refractory mutation system PCR and complementary DNA sequencing. Protein expression and ERK phosphorylation were assessed using Western blots. We studied gene silencing with specific small interfering RNAs (siRNA), and we studied intracellular Ca2+ using fluorometry. Results: All GluK subunits were present in the brain in vivo, and GluK2-5 subunits were present in cultured astrocytes. Fluoxetine upregulated GluK2 and ADAR2. Enhanced GluK2 editing by fluoxetine abolished glutamate-mediated increases in intra cellular Ca2+ and ERK1/2 phosphorylation. Enhanced editing of GluK2 was prevented by siRNA against the 5-HT2B receptor or ADAR2. Limitations: Limitations of our study include the use of an in vitro system, but our cultured cells in many respects behave like in vivo astrocytes. Conclusion: Fluoxetine alters astrocytic glutamatergic function. © 2011 Canadian Medical Association.