Effects of dexmedetomidine on the release of glial cell line-derived neurotrophic factor from rat astrocyte cells

Dexmedetomidine (DEX) has been found to improve neuronal survival after transient global or focal cerebral ischemia in rats. Astrocyte cells may possess beneficial properties that promote neuronal recovery by secreting neurotrophic factors, such as glial cell line-derived neurotrophic factor (GDNF). The purpose of this study was to investigate the effects of DEX on GDNF release from astrocytes and the possible mechanisms involved. Astrocyte cells were treated with DEX, and GDNF level in the conditioned media was determined by ELISA assay. The expression of CREB, p-CREB and PKCα was analyzed by Western blotting to explore the mechanisms involved in GDNF release. Our results showed that DEX stimulated GDNF release in a time- and dose-dependent manner; and this stimulation was blocked by the α2-adrenoreceptor antagonist yohimbine, but not by α1-adrenoreceptor antagonist prasozin, demonstrating that DEX induced GDNF release likely acts via activating the α2A adrenoreceptor. In addition, DEX-stimulated GDNF release was also blocked by the universal PKC inhibitor Ro-318220 and PKCα/β inhibitor Gö 6976, but not by PKCδ inhibitor rottlerin and PKCβ inhibitor LY333531. Interestingly, DEX also activated CREB phosphorylation, which was inhibited by Ro-318220, Gö 697 and ERK kinase inhibitor PD98059. Silencing CREB by siRNA decreased the DEX-stimulated GDNF release. In addition, the membrane translocation of PKCα was enhanced following DEX treatment. Furthermore, we found that DEX stimulated GDNF release rescued neurons against OGD-induced neurotoxicity; this effect was partly abolished by GDNF antibody. Thus, through α2A adrenergic receptors, DEX may activate astrocytes, and promote GDNF release to protect neurons after stroke, and this signaling is possibly dependent on PKCα and CREB activation.

Research highlights
► Dexmedetomidine (DEX) stimulated GDNF release in a time- and dose-dependent manner; and this stimulation was blocked by the α2-adrenoreceptor antagonist yohimbine and α2-adrenoreceptor siRNA, but not by α1-adrenoreceptor antagonist prasozin.
► DEX-stimulated GDNF release was also blocked by the universal PKC inhibitor Ro-318220 and PKCα/β inhibitor Gö 6976, but not by PKCδ inhibitor rottlerin and PKCβ inhibitor LY333531.
► DEX also activated CREB phosphorylation, which was inhibited by Ro-318220, Gö 6976 and ERK kinase inhibitor PD98059. And silencing CREB by siRNA decreased the DEX-stimulated GDNF release.
► The membrane translocation of PKCα was enhanced following DEX treatment.
► DEX stimulated GDNF release rescued neurons against OGD-induced neurotoxicity.