Hippocampal PI₃K/AKT-Warburg Axis Mediates The Antagonistic Role Of Hydrogen Sulfide In Diabetes-associated Cognitive Dysfunction

[Background and Objective]It has been previously demonstrated that hydrogen sulfide（H₂S）ameliorates cognitive dysfunction in STZ-induced diabetic rats,but the exact mechanisms underlying this protection remain to be fully elucidated.Warburg effect in brain plays a key role in regulating synaptic plasticity and learning and memory.Interestingly,our previous works have confirmed that H₂S enhances Warburg effect in the hippocampus of diabetic rats.The activation of PI₃K/AKT signal promotes Warburg effect and H₂S activates PI₃K/AKT signal in brain.Therefore,we will explore whether the hippocampal PI₃K/AKT-Warburg axis mediates the antagonistic role of H₂S in diabetes-associated cognitive dysfunction（DACD）.[Methods]1.Diabetic rats were induced by intraperitoneal injection of streptozotocin（STZ,55mg/kg）for once.2.The cognitive function of rats were evaluated by Y-maze test,novel objective recognition（NOR）test,and Morris water maze（MWM）test.3.The ultrastructure of hippocampal synapses were detected by transmission electron microscopy（TEM）4.The expressions of Warburg effect-associated kinases [Hexokinase II（HK-II）、Pyruvate kinase M2（PKM2）、Pyruvate dehydrogenase kinase 1（PDK-1）、Pyruvate dehydrogenase（PDH）、Lactate dehydrogenase A（LDHA）]and synaptic plasticity-related proteins[Postsynaptic density protein-95（PSD95）and Synapsin-1)]were detected by western blot.5.The content of lactate in hippocampus was determined by Lactate Assay Kit.[Results]1.Dichloroacetate（DCA）,an inhibitor of Warburg effect,abolished the enhancing role of H₂S on hippocampal Warburg effect of STZ-induced diabetic rats.DCA reversed the up-regulatory role of NaHS in the expressions of PDK-1 and LDHA,the down-regulatory role of NaHS in the expression of PDH,the increasing role of NaHS in the content of lactate,in the hippocampus of STZ-induced diabetic rats.DCA did not affect the upregulation of NaHS on the expressions of HK-2 and PKM2（located upstream of PDK1）in the hippocampus of STZ-induced diabetic rats.These results suggested that DCA abolishes H₂S-enhanced hippocampal Warburg effect in STZ-induced diabetic rats.2.DCA abolished the ameliorative role of H₂S in the cognitive function of STZ-induced diabetic ratsDCA reversed the up-regulatory action of NaHS on the alternation in Y-maze and the discrimination index in NOR of STZ-induced diabetic rats.In MWM,DCA reversed the simplify role of NaHS on the swimming tracks and the reducing role of NaHS on escape the latency to find platform,in acquisition phase.In addition,DCA eliminates the increasing role of NaHS in the times across platform and percentage of time expended in the target quadrant in probe trial.These data indicated that inhibition of hippocampal Warburg effect abolishes the H₂S-ameliorated cognitive behavior in STZ-induced diabetic rats.3.DCA abolished the ameliorative role of H₂S in hippocampal synaptic plasticity of STZ-induced diabetic ratsDCA not only reversed the up-regulatory role of NaHS in the expressions of hippocampal Synapsin-1 and PSD-95,but also reversed the increasing role of NaHS in the synaptic density、the postsynaptic density（PSD）thickness、the length of synaptic active zone,and the reducing role of NaHS in the width of synaptic gap,in hippocampal CA1,CA3 region.These data indicated that inhibited hippocampal Warburg effect abolishes H₂S-ameliorated synaptic plasticity in STZ-induced diabetic rats.4.LY294002,an inhibitor of PI₃K/AKT pathway,abolished the enhancing role of H₂S in hippocampal Warburg effect of STZ-induced diabetic rats.LY294002 reversed the up-regulatory role of NaHS in the expressions of HK-2、PKM2、PDK-1 and LDHA,the down-regulatory role of NaHS in the expression of PDH,the increasing role of NaHS in the content of lactate,in the hippocampus of STZ-induced diabetic rats.These results suggested that inhibited hippocampal PI₃K/AKT pathway abolishes H₂S-enhanced hippocampal Warburg effect in STZ-induced diabetic rats.5.LY294002 abolished the ameliorative role of H₂S in the cognitive function of STZ-induced diabetic ratsLY294002 reversed the up-regulatory role of NaHS in the alternation in Y-maze and the discrimination index in NOR of STZ-induced diabetic rats.In MWM,LY294002 reversed the simplify role of NaHS on swimming tracks and the reducing role of NaHS in the escape latency to find platform,in the acquisition phase.In addition,LY294002 eliminates the increasing role of NaHS in the times across platform and the percentage of time expended in the target quadrant in the probe trial.These data indicated that inhibition of hippocampal PI₃K/AKT pathway abolishes H₂S-ameliorated cognitive behavior in STZ-induced diabetic rats.6.LY294002 abolished the ameliorative role of H₂S on hippocampal synaptic plasticity of STZ-induced diabetic ratsLY294002 not only reversed the up-regulatory role of NaHS in the expressions of hippocampal Synapsin-1 and PSD-95,but also reversed the increasing role of NaHS in the synaptic density、the PSD thickness、the length of synaptic active zone,and the reducing role of NaHS in the width of synaptic gap,in hippocampal CA1,CA3 region.These data indicated that inhibition of hippocampal PI₃K/AKT pathway abolishes H₂S-ameliorated synaptic plasticity in STZ-induced diabetic rats.[Conclusion] Hippocampal PI₃K/AKT-Warburg axis mediates the antagonistic action of H₂S in DACD.