Phosphorylation of astrocytic connexin43 by ERK1/2 impairs blood-brain barrier in acute cerebral ischemia.

Connexins are a family of transmembrane proteins that form gap junctions, which are important for diffusion of cytosolic factors such as ions and second messenger signaling molecules. Our previous study has shown that Connexin40 (Cx40), one dominant connexin expressed in brain, was involved in brain injury. In this study, Cx43, another dominant connexin in brain, was investigated. Using bilateral common carotid artery occlusion-induced ischemia rat model, we tested the expression and phosphorylation level of Cx43 as well as heteromeric Cx40/Cx43 complex formation in brain after ischemia induction. We screened total 16 kinase inhibitors to identify the kinase for Cx43 phosphorylation and confirmed the result using siRNA targeting the specific kinase. Finally, we explored the role of the identified kinase in brain damage using in vivo rat model. We discovered that phosphorylation of Cx43 increased after ischemia. The formation of Cx40/Cx43 heteromeric complex on membrane also increased. Inhibition of ERK activity resulted in inhibition of Cx43 phosphorylation on astrocytes. In in vivo model, application of ERK inhibitor and siRNA prevented brain damage and protected blood-brain barrier integrity in rat. Our study provides evidence that Cx43 phosphorylation by ERK is implicated in ischemia induced brain damage.