17 β‐Estradiol prevents focal cerebral ischemic damages via activation of Akt and CREB in association with reduced PTEN phosphorylation in rats

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Abstract
This study aimed to assess the signaling pathway of the neuroprotective action of estrogen in the cerebral ischemic injury evoked by subjecting rats to 2‐h occlusion of the middle cerebral artery (MCA) followed by 24‐h reperfusion. Rats received 17 β‐estradiol (1, 4 and 10 mg/kg, i.p.) 24 h before and 5 min after the completion of 2‐h MCA occlusion. The cerebral infarct area was consistently observed in the cortex and striatum of the left hemisphere. Increased terminal deoxynucleotidyl transferase‐mediated deoxyuridine–biotin nick‐end labeling (TUNEL)‐positive cells and DNA fragmentation in the penumbral zone were significantly reduced by 17 β‐estradiol. In line with these results, 17 β‐estradiol significantly increased Akt and cyclic AMP response element binding protein (CREB) with increased Bcl‐2 protein in the ischemic area, whereas the elevated the phosphatase and tensin homolog deleted from chromosome10 (PTEN) phosphorylation was significantly reduced with decreased Bax protein and cytochrome c release. Inhibition of DNA fragmentation, PTEN phosphorylation, and Akt activation by 17 β‐estradiol were antagonized by iberiotoxin, a maxi‐K channel blocker. Taken together, it is suggested that suppression of cerebral ischemic injury by 17 β‐estradiol may be ascribed to the maxi‐K channel opening‐coupled downregulation of PTEN phosphorylation and upregulation of Akt and CREB phosphorylation with resultant increase in Bcl‐2 protein and decrease in Bax protein and cytochrome c release.