Abstrakt
Brain edema accompanying ischemic or traumatic brain injuries, originates from a disruption of ionic/neurotransmitter homeostasis that leads to accumulation of K+ 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+ 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+.
As for the mild stimuli, such as mild hypoosmotic or hyperosmotic stress or 10 mM K+, 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+.