Inhibition of connexin43 improves functional recovery after ischemic brain injury in neonatal rats.

Connexin43 (Cx43) is one of the most abundant gap junction proteins in the central nervous system. Abnormal opening of Cx43 hemichannels after ischemic insults causes apoptotic cell death. In this study, we found persistently increased expression of Cx43 8 h to 7 d after hypoxia/ischemia (HI) injury in neonatal rats. Pre-treatment with Gap26 and Gap27, two Cx43 mimetic peptides, significantly reduced cerebral infarct volume. Gap26 treatment at 24 h after ischemia improved functional recovery on muscle strength, motor coordination, and spatial memory abilities. Further, Gap26 inhibited Cx43 expression and reduced active astrogliosis. Gap26 interacted and co-localized with Cx43 together in brain tissues and cultured astrocytes. After oxygen glucose deprivation, Gap26 treatment reduced the total Cx43 level in cultured astrocytes; but Cx43 level in the plasma membrane was increased. Degradation of Cx43 in the cytoplasm was mainly via the ubiquitin proteasome pathway. Concurrently, phosphorylated Akt, which phosphorylates Cx43 on Serine(373) and facilitates the forward transport of Cx43 to the plasma membrane, was increased by Gap26 treatment. Microdialysis showed that increased membranous Cx43 causes glutamate release by opening Cx43 hemichannels. Extracellular glutamate concentration was significantly decreased by Gap26 treatment in vivo. Finally, we found that cleaved caspase-3, an apoptosis marker, was attenuated after HI injury by Gap26 treatment. Effects of Gap27 were analogous to those of Gap26. In summary, our findings demonstrate that modulation of Cx43 expression and astroglial function is a potential therapeutic strategy for ischemic brain injury.

7,8-Dihydroxy-4-methylcoumarin provides neuroprotection by increasing hippocalcin expression.

7,8-Dihydroxy-4-methylcoumarin (Dhmc) is a precursor in the synthesis of derivatives of 4-methyl coumarin, which has excellent radical scavenging properties. In this study, we investigated whether Dhmc protects against oxidative stress and ischemic brain injury. We found that Dhmc protected against glutamate toxicity in hippocampal HT-22 cells in a concentration-dependent manner in vitro. Dhmc inhibited glutamate-induced glutathione depletion and generation of reactive oxygen species, suggesting that Dhmc has an antioxidant effect. In addition, Dhmc inhibited glutamate-induced depletion of hippocalcin, a protein that buffers intracellular calcium and prevents calcium-induced cell death. In our in vivo studies, Dhmc reduced infarct volume in neonatal rats when administered 4 h after cerebral hypoxia/ischemia injury and attenuated the hypoxia/ischemia injury-induced decrease of hippocalcin expression in neonatal rats. Taken together, these results suggest that Dhmc prevents glutamate-induced toxicity by scavenging free radicals and regulating hippocalcin expression. Dhmc may represent a promising agent in the treatment of acute and chronic neurological disorders induced by oxidative stress.