Activation of Akt/GSK-3beta/beta-catenin signaling pathway is involved in survival of neurons after traumatic brain injury in rats.

OBJECTIVE

Apoptotic cell death is an important factor influencing the prognosis after traumatic brain injury (TBI). Akt/GSK-3beta/beta-catenin signaling plays a critical role in the apoptosis of neurons in several models of neurodegeneration. The goal of this study was to determine if the mechanism of cell survival mediated by the Akt/GSK-3beta/beta-catenin pathway is involved in a rat model of TBI.

METHODS

TBI was performed by a controlled cortical impact device. Expression of Akt, phospho-Akt, GSK-3beta, phospho-GSK-3beta, beta-catenin, phospho-beta-catenin were examined by immunohistochemistry and Western blot analysis. Double immunofluorenscent staining was used to observe the neuronal expression of the aforementioned subtrates. Terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end-labeling (TUNEL) staining was performed to identify apoptosis.

RESULTS

Western blot analysis showed that phospho-Akt significantly increased at 4 hours post-TBI, but decreased after 72 hours post-TBI. Phospho-GSK-3beta - phosphorylated by phospho-Akt - slightly increased at 4 hours post-TBI and peaked at 72 hours post-TBI. These changes in Phospho-GSK-3beta expression were accompanied by a marked increase in expression of phospho-beta-catenin at 4 hours post-TBI which was sustained until 7 days post-TBI. Double staining of phospho-Akt and NeuN revealed the colocalization of phospho-Akt positive cells and neuronal cells. In addition, double staining of phospho-Akt and TUNEL showed no colocalization of phospho-Akt cells and TUNEL-positive cells.

CONCLUSION

Phosphorylation of Akt (Ser473) and GSK3beta (Ser9) was accelerated in the injured cortex, and involved in the neuronal survival after TBI. Moreover, neuroprotection of beta-catenin against ischemia was partly mediated by enhanced and persistent activation of the Akt/GSK3beta signaling pathway.