Astrocyte-expressed STAT3 regulates glutamate homeostasis and binge ethanol drinking in mice

Abstract

Astrocytes play an important role in neuronal health. A critical function of astrocytes is to clear excess extracellular glutamate and prevent excitotoxicity. STAT3 is a transcription factor that promotes astrocyte development and astrocyte reactivity in neurodegenerative diseases and following central nervous system injury. To determine the innate molecular and behavioral functions of adult astrocyte-expressed STAT3 in a non-pathological state, we created conditional Stat3 astrocyte knockout mice (Stat3 aKO) using Stat3flox and the tamoxifen-activated Cre line, Aldh1l1-Cre/ERT2. We measured transcript levels of Gfap, a known STAT3 target gene, and glutamate transporter genes in the medial prefrontal cortex (PFC) of Stat3 aKO. Gfap, Slc1a2 and Slc17a8 transcripts were decreased in the PFC of Stat3 aKO of both sexes. GLT-1 protein, encoded by Slc1a2, was also reduced in the PFC of male Stat3 aKO. We recorded spontaneous excitatory post-synaptic currents (sEPSCs) in male Stat3 aKO and control prelimbic pyramidal neurons and found increased sEPSC amplitude, consistent with a hyper-glutamatergic state due to impaired glutamate clearance. To determine the behavioral consequences of STAT3 depletion in astrocytes, Stat3 aKO were tested for locomotor activity, anxiety-like behavior and binge ethanol consumption, behaviors linked to dysregulation of glutamate homeostasis. Stat3 aKO mice did not differ in locomotor activity or anxiety-like behavior; however, male Stat3 aKO mice consumed significantly less ethanol than controls. These results indicate that STAT3 in adult astrocytes is crucial for maintaining glutamate transporter levels in the adult brain and that astrocytic STAT3 promotes ethanol consumption in male mice. Main pointsO_LIGfap, Slc1a2 and Slc17a8 expression are lower in the cortex of Stat3 astrocyte knockout mice (Stat3 aKO) C_LIO_LIGLT-1 protein is decreased and glutamate neurotransmission is elevated in the cortex of male Stat3 aKO C_LIO_LIMale Stat3 aKO consume less ethanol C_LI