Redox Modulation Of Long-term Potentiation In The Hippocampus Via Regulation Of Glycogen Synthase Kinase-3β Pathway

PartⅠRedox modulation of long-term potentiation in the hippocampusBackground:Alzheimer's disease (AD) is an age-related neurodegenerative disorder, characterized by a progressive loss of memory and cognitive functions. There is now considerable evidence that impaired redox regulation is implicated in AD with a synaptic failure, and in particular, that amyloid beta (Aβ) and ROS induced dysfunction of synaptic plasticity contributes to early memory loss that precedes neuronal degeneration. A prominent form of synaptic plasticity known as long-term potentiation (LTP) has consolidated its status as the preeminent synaptic model for investigating the molecular and cellular basis of learning and memory. ROS particularly hydrogen peroxide (H2O2) and modulation of LTP has been proposed. Millimolar concentrations of H2O2 irreversibly suppress synaptic transmission and plasticity, whereas micromolar concentrations enhance LTP. Methods:Field potentials were evoked by a constant stimulation in the Schaffer collaterals with a bipolar electrode and recorded in the stratum radiatum layer of CA1 with a glass micropipette. Results:In the present study, we find that membrane-permeable oxidizing agent CH-T inhibits the induction of LTP in CA1 region of hippocampus in vitro, which can be restored by pretreatment with DTT but not by TCEP. In contrast, membrane-permeable reducing agent DTT enhanced the induction of LTP in CA1 region of hippocampus, which can be reversed by pretreatment with CH-T but not by DTNB. However, neither membrane-impermeable oxidizing agent DTNB nor membrane-impermeable reducing agent TCEP can affect the induction of LTP. The concentrations of redox agents used did not affect the basic synaptic transmission and PPF. Conclusion:The characteristics of their membrane-permeable or membrane-impermeable ability may contribute to explain their different effects on LTP. These results also demonstrated that the targets of redox regulation are not on the surface of cell membrane, but located in the intracellular structures or internal surface of cell membrane.PartⅡRedox modulation of long-term potentiation in the hippocampus via regulation of GSK-3βpathwayBackground:GSK-3βis well known to play critical roles in oxidative stress-induced neurodegenerative disease such as AD. Recent study shows that phosphorylation at the inhibitory Ser9 site on GSK-3βis increased upon induction of LTP in both hippocampal CA1 and dentate gyrus (DG). In order to explore a role for GSK-3βin redox modulation of LTP, we investigated the phosphorylation status of GSK-3βin CA1 area of hippocampal slices after HFS. Methods:Field potentials recordings and Western Blot were used to evaluate the effects of GSK-3β. Results:HFS induction caused an increase in the phosphorylation of GSK-3βser9, but with no change in total GSK-3β. Treatment with CH-T decreased the ratio of pGSK-3βto total GSK-3β. In contrast, the ratio of pGSK-3βto total GSK-3βwas increased markedly in DTT-treated slices. No significant changes were found in relative ratio of pGSK-3βto total GSK-3βin DTNB or TCEP-treated slices. To directly examine the possibility that GSK-3βinactivity may be required for the redox modulation of LTP, we then determined the effects of LiCl, an inhibitor of GSK-3β, on LTP modulation by CH-T. LiCl (10 mM) completely blocked the inhibitory effects of CH-T on LTP. There were no significant differences of LTP magnitudes between control group and LiCl combined CH-T group. Next, we sought to determine whether LiCl mimicked the effects of DTT on the induction of LTP. We found that preincubation of LiCl increased the magnitudes of LTP similar to that of DTT alone. Furthermore, after incubation of LiCl, application of DTT produced a significant increase in LTP magnitude, which was similar to that of LiCl alone. We then measured the phosphorylation of GSK-3β in presence of LiCl alone or LiCl plus redox agents. Preincubation with LiCl before CH-T reversed the decrease ratio of pGSK-3βto total GSK-3βas found in CH-T group. There was no difference in the ratio of pGSK-3βto total GSK-3βbetween LiCl group and DTT group. Preincubation of LiCl increased the ratio of pGSK-3βto total GSK-3βsimilar to that of LiCl plus DTT group. Conclusion:The effects of these membrane-permeable redox agents are at least partially attributed to the modification of GSK-3β. These findings are benefit for understanding of redox contribution to mechanisms underlying AD pathogenesis and its promising therapeutic target.