Preliminary Study On The Anti-apoptosis Mechanism Via Pi3k/akt Signal Pathway Induced By Gaba_b Receptor In Cerebella Granule Neurons

GABAB receptor which belongs to the class C of G-protein-coupled receptors is broadly distributed in neurons. After activated by major inhibitory neurotransmitterγ-aminobutyric acid (GABA), it mediates slow and prolonged synaptic transmission and modulates neuronal excitability and synaptic plasticity. Recent studies suggest GABAB receptor may promote neuronal survival, but the molecular mechanism underlying this neuroprotection is poorly characterized.Our previous published article confirmed that GABAB receptor activation leads to increased ERK1/2 phosphorylation via PI3K. But the effect of GABAB receptor on the activity of Akt and the mechanism are not clear.Using induction of apoptosis in cerebellar granule neurons(CGNs) by low K+ as a model, we investigate the neuroprotection of GABAB receptor by TUNEL assay, Hoechst 33258 stainning and caspase-3 activity assay. It shows that GABAB-selective agonist baclofen and positive allosteric regulator CGP7930 have a significant protective effect on CGN in low K+, and this effect isn't mediated by GABAA receptor or GABAC receptor.Furthermore, we study and elucidate the preliminary anti-apoptosis mechanism of GABAB receptor. Our data show that Gi/o inhibitory pertussis toxin (PTX) and PI3K inhibitor LY294002 not only suppress the neuroprotection of activated GABAB receptor but also significantly reverse the inhibition of caspase-3 activation, which indicate that the neuroprotection mediated by GABAB receptor is dependent on Gi/o protein and PI3K. Moveover, it demonstrates that GABA, baclofen and CGP7930 induce a rapidly activation of Akt. GABAB receptor-mediated-Akt phosphorylation can be suppressed by inhibitors of signal proteins such as PTX and LY294002, which suggests the involvement of Gi/o protein and PI3K. In conclusion, in CGN,the activation of GABAB receptor activates Akt signal pathway via Gi/o protein and PI3K,then inhibits caspase-3 activity through relative downstream signal pathways ,eventually leads to the neuroprotection. The present study reveals a new function of GABAB receptor in neurons and establishes a theory basis for screening and developing drugs which target at GABAB receptor and its relative downstream signal proteins.