It has recently been reported that
melatonin protects neuronal cells from damage by enhancing Akt activation, thus mediating antiapoptosis signals. However, there is little information regarding the effects of
melatonin on the activation of genes further downstream in the Akt signaling pathway in ischemic
brain injury. This study investigated whether
melatonin modulates the antiapoptotic signal through Akt and its downstream targets, Bad and 14-3-3. Adult male rats were treated with
melatonin (5 mg/kg) prior to
middle cerebral artery occlusion (MCAO). Brains were collected at 24 hr after MCAO and
infarct volumes were analyzed. Our results confirm that
melatonin significantly reduces
infarct volume and decreases the positive reaction of TUNEL staining in the cerebral cortex. Signal pathway activation was measured by phosphorylation of Akt at Ser(473) and Bad at Ser(136) using Western blot analysis.
Melatonin prevented the injury-induced decrease of pAkt and pBad levels. However,
melatonin did not affect the expression of 14-3-3, which acts as an antiapoptotic factor through interaction with Bad. Immunoprecipitation analysis showed that the interaction between pBad and 14-3-3 increased in the presence of
melatonin, compared to that of control animals. Our findings suggest that
melatonin prevents cell death because of
brain injury and that these protective effects are mediated through maintaining the interaction between pBad and 14-3-3, thus blocking activation of the apoptotic pathway.