Neuroprotective Role of Astrocytic Gap Junctions in Ischemic Stroke

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Abstract
The role of astrocytic gap junctions in ischemia remains controversial. Several studies support that astrocytic gap junctions play a role in the spread of hypoxic injury, while other reports have demonstrated that blocking astrocytic gap junctions increases neuronal death. Using a stroke model on animals in which the astrocytic gap junction protein connexin43 (Cx43) was compromised, we explored the neuroprotective role of astrocytic gap junctions. A focal brain stroke was performed on heterozygous Cx43 null [Cx43(+/−)] mice, wild type [Cx43(+/+)] mice, astrocyte-directed Cx43 deficient [Cx43fl/ fl/hGFAP-cre] mice (here designated as Cre(+) mice), and their corresponding controls [Cx43fl/fl] (here designated as Cre(−) mice). Four days following stroke, ischemic lesions were measured for size and analyzed immunohistochemically. Stroke volume was significantly larger in Cx43(+/−) and Cre(+) mice compared to Cx43(+/+) and Cre(−) mice, respectively. Apoptosis as detected by TUNEL labeling and caspase-3 immunostaining was amplified in Cx43(+/−) and Cre(+) mice compared to their control groups. Furthermore, increased inflammation as characterized by the immunohistochemical staining of the microglial marker CD11b was observed in the Cre(+) mice penumbra. Astrocytic gap junctions may reduce apoptosis and inflammation in the penumbra following ischemic insult, suggesting that coupled astrocytes fulfill a neuroprotective role under ischemic stroke conditions.