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.


CONCLUSIONS
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.
Department of Neurosurgery, Beijing Tongren Hospital, Capital University of Medical Sciences, Beijing, China.
Shangfeng
S
Zhao
Jidi
J
Fu
Xiangrong
X
Liu
Tony
T
Wang
Jialiang
J
Zhang
Yuanli
Y
Zhao
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D015153:Blotting, Western; D001930:Brain Injuries / Q000378:metabolism*; D002470:Cell Survival / Q000502:physiology; D004195:Disease Models, Animal; D005455:Fluorescent Antibody Technique; D038362:Glycogen Synthase Kinase 3 / Q000096:biosynthesis*; D000071679:Glycogen Synthase Kinase 3 beta; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D008297:Male; D009410:Nerve Degeneration / Q000378:metabolism; D009474:Neurons / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000096:biosynthesis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology*; D051176:beta Catenin / Q000096:biosynthesis
C495268:Ctnnb1 protein, rat; D051176:beta Catenin; D000071679:Glycogen Synthase Kinase 3 beta; C000605508:Gsk3b protein, rat; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3