Phosphatidylinositol-3-kinase/Akt/glycogen synthase kinase-3 beta and ERK1/2 pathways mediate protective effects of acylated and unacylated ghrelin against oxygen-glucose deprivation-induced apoptosis in primary rat cortical neuronal cells.
Only acylated ghrelin (AG) binds GH secretagog receptor 1a (GHS-R1a) and has central endocrine activities. An anti-apoptotic effect of AG in neuronal cells has recently been reported. However, whether there is a neuroprotective effect of unacylated ghrelin (UAG), the most abundant form of ghrelin in plasma, is still unknown. Therefore, we investigated whether UAG was neuroprotective against ischemic neuronal injury using primary cultured rat cortical neurons exposed to oxygen and glucose deprivation (OGD). Both AG and UAG inhibited OGD-induced apoptosis. Exposure of cells to the receptor-specific antagonist D-Lys-3-GHRH-6 abolished the protective effects of AG against OGD, whereas those of UAG were preserved, suggesting the involvement of a receptor that is distinct from GHS-R1a. Chemical inhibition of MAPK and phosphatidylinositol-3-kinase (PI3K) blocked the anti-apoptotic effects of AG and UAG. Ghrelin siRNA enhanced apoptosis either during OGD or even in normoxic conditions. The protective effects of AG and UAG were accompanied by an increased phosphorylation of extracellular signal-regulated kinase (ERK)1/2, Akt, and glycogen synthase kinase-3beta (GSK-3beta). Furthermore, treatment of cells with AG or UAG resulted in nuclear translocation of beta-catenin. In addition, both AG and UAG increased the Bcl-2/Bax ratio, prevented cytochrome c release, and inhibited caspase-3 activation. The data indicate that, independent of acylation, ghrelin can function as a neuroprotective agent that inhibits apoptotic pathways. These effects may be mediated via activation of the MAPK and PI3K/Akt pathways. Our data also suggest that PI3K/Akt-mediated inactivation of GSK-3beta and stabilization of beta-catenin contribute to the anti-apoptotic effects of ghrelin.
Department of Pharmacology and Medical Research Center for Bioreaction to ROS and Biomedical Science Institute, Kyunghee University School of Medicine, Seoul 130-701, South Korea.
Hyunju
H
Chung
Sanghee
S
Seo
Minho
M
Moon
Seungjoon
S
Park
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D053148:Caspase 3 / Q000378:metabolism; D015687:Cell Hypoxia / Q000502:physiology; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology* / Q000378:metabolism; D002867:Chromones / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D054439:Ghrelin / Q000378:metabolism / Q000494:pharmacology*; D005947:Glucose / Q000172:deficiency; D038362:Glycogen Synthase Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D007150:Immunohistochemistry; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009025:Morpholines / Q000494:pharmacology; D009474:Neurons / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism*; D034741:RNA, Small Interfering; D051381:Rats; D017207:Rats, Sprague-Dawley; D054440:Receptors, Ghrelin / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000187:drug effects; D000077191:Wortmannin
D000730:Androstadienes; D002867:Chromones; D005419:Flavonoids; D054439:Ghrelin; D009025:Morpholines; D034741:RNA, Small Interfering; D054440:Receptors, Ghrelin; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D000071679:Glycogen Synthase Kinase 3 beta; C000605508:Gsk3b protein, rat; D051057:Proto-Oncogene Proteins c-akt; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D038362:Glycogen Synthase Kinase 3; D053148:Caspase 3; D005947:Glucose; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D000077191:Wortmannin