Altered Astrocytic Swelling in the Cortex of [alpha]-Syntrophin-Negative GFAP/EGFP Mice

Brain edema accompanying ischemic or traumatic brain injuries, originates from a disruption of ionic/neurotransmitter homeostasis that leads to accumulation of K.sup.+ and glutamate in the extracellular space. Their increased uptake, predominantly provided by astrocytes, is associated with water influx via aquaporin-4 (AQP4). As the removal of perivascular AQP4 via the deletion of [alpha]-syntrophin was shown to delay edema formation and K.sup.+ clearance, we aimed to elucidate the impact of [alpha]-syntrophin knockout on volume changes in individual astrocytes in situ evoked by pathological stimuli using three dimensional confocal morphometry and changes in the extracellular space volume fraction ([alpha]) in situ and in vivo in the mouse cortex employing the real-time iontophoretic method. RT-qPCR profiling was used to reveal possible differences in the expression of ion channels/transporters that participate in maintaining ionic/neurotransmitter homeostasis. To visualize individual astrocytes in mice lacking [alpha]-syntrophin we crossbred GFAP/EGFP mice, in which the astrocytes are labeled by the enhanced green fluorescent protein under the human glial fibrillary acidic protein promoter, with [alpha]-syntrophin knockout mice. Three-dimensional confocal morphometry revealed that [alpha]-syntrophin deletion results in significantly smaller astrocyte swelling when induced by severe hypoosmotic stress, oxygen glucose deprivation (OGD) or 50 mM K.sup.+ . As for the mild stimuli, such as mild hypoosmotic or hyperosmotic stress or 10 mM K.sup.+, [alpha]-syntrophin deletion had no effect on astrocyte swelling. Similarly, evaluation of relative [alpha] changes showed a significantly smaller decrease in [alpha]-syntrophin knockout mice only during severe pathological conditions, but not during mild stimuli. In summary, the deletion of [alpha]-syntrophin markedly alters astrocyte swelling during severe hypoosmotic stress, OGD or high K.sup.+.