Astrocytic Gap Junctions Composed of Connexin 43 Reduce Apoptotic Neuronal Damage in Cerebral Ischemia

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Abstract
Background and Purpose— Astrocytes may play a vital role in neuroprotection by providing energy substrates to neurons and regulating the concentration of K+ and neurotransmitters through gap junctions. Connexin 43 (Cx43) is one of the major gap junction proteins in astrocytes. We have shown that, after focal stroke, heterozygote Cx43 null (Cx43+/−) mice exhibited larger infarction volumes than wild-type (Cx43+/+) mice. We explored the underlying mechanism by which gap junctional intercellular communication influences astrocytic activation and neuroprotection in ischemia. Methods— Both Cx43+/− and Cx43+/+ mice underwent right side permanent middle cerebral artery occlusion (MCAO). Mice were prepared by transcardial perfusion, and at 24 hours and 4 days after surgery, brains were prepared for immunohistochemistry or Western blot analysis. Results— Four days after MCAO, Cx43+/− mice showed severe apoptosis in the penumbral lesion compared with Cx43+/+ mice. The level of caspase-3 was significantly higher in the stroke lesion of Cx43+/− mice than in Cx43+/+ mice. Four days after MCAO, Cx43+/− mice showed a significantly larger infarct volume but a smaller area of astrogliosis than did Cx43+/+ mice. The penumbra of Cx43+/− mice showed an increased level of Cx30 compared with Cx43+/+ mice. Conclusions— Gap junctions may play an important role in astrocytic activation. Reactive astrocytes may reduce neuronal apoptosis under ischemia by regulating extracellular conditions through their gap junction.