GT1b-induced neurotoxicity is mediated by the Akt/GSK-3/tau signaling pathway but not caspase-3 in mesencephalic dopaminergic neurons.
BACKGROUND
Gangliosides, sialic acid-containing glycosphingolipids exist in mammalian cell membranes particularly neuronal membranes. The trisialoganglioside (GT1b) is one of the major brain gangliosides and acts as an endogenous regulator in the brain. We previously showed GT1b induces mesencephalic dopaminergic (DA) neuronal death, both in vivo and in vitro. We further investigate the underlying mechanisms of GT1b neurotoxicity.


RESULTS
Consistent with earlier findings, GT1b attenuated the DA neuron number and dopamine uptake level in mesencephalic cultures. Morphological evidence revealed GT1b-induced chromatin condensation and nuclear fragmentation as well as an increased number of TUNEL-positive cells, compared to control cultures. Interestingly, while GT1b enhanced caspase-3 activity, DEVD, a caspase-3 inhibitor, failed to rescue DA neuronal death. Immunoblot analysis revealed that GT1b inactivates Akt through dephosphorylation at both Ser473 and Thr308, subsequent dephosphorylation of GSK-3beta, a substrate of Akt, and hyperphosphorylation of tau, downstream of GSK-3beta. Moreover, a GSK-3beta specific inhibitor, L803-mt, attenuated tau phosphorylation and rescued DA neurons from cell death in mesencephalic cultures.


CONCLUSIONS
Our data provide novel evidence that a Akt/GSK-3beta/tau-dependent, but not caspase-3 signaling pathway plays a pivotal role in GT1b-mediated neurotoxic actions on mesencephalic DA neurons.
Chung
Eun S
ES
Department of Biochemistry and Molecular Biology, School of Medicine Kyung Hee University, Seoul 130-701, Korea.
Bok
Eugene
E
Sohn
Sunghyang
S
Lee
Young D
YD
Baik
Hyung H
HH
Jin
Byung K
BK
D000704:Analysis of Variance; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D053148:Caspase 3 / Q000378:metabolism; D002452:Cell Count; D002478:Cells, Cultured; D004298:Dopamine / Q000378:metabolism*; D005260:Female; D005732:Gangliosides / Q000494:pharmacology*; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D007150:Immunohistochemistry; D020287:In Situ Nick-End Labeling; D008636:Mesencephalon / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D016253:Microscopy, Immunoelectron; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects*; D016875:tau Proteins / Q000378:metabolism*
D005732:Gangliosides; D016875:tau Proteins; C016481:trisialoganglioside GT1; D051057:Proto-Oncogene Proteins c-akt; D038362:Glycogen Synthase Kinase 3; D053148:Caspase 3; D004298:Dopamine