Sirt1 Mediates The Antagonistic Effect Of Hydrogen Sulfide On Cognitive Dysfunction In Streptozotocin-induced Diabetic Rats

[Backgroud and objective] Diabetes mellitus, a chronic metabolic disease, can affect central nervous system and cause cognition impairment. We have demonstrated that hydrogen sulfide(H2S), a new gastransmitter and neuromodulator, attenuates cognitive dysfunction induced by diabetes. But the mechanism is unclear. Silent information regulator 1(SIRT1), plays a critical role in cell survival, neurogenesis, synaptogenesis and synaptic plasticity and is involved in the formation of learning and cognition. Our previous studies have found that H2 S upregulates the expression of hippocampal SIRT1 in the diabetic rats. Therefore, we speculated that SIRT1 mediates the antagonistic effect of hydrogen sulfide on cognitive dysfunction in diabetic rats. In the present work, we further investigated the mediatory role of SIRT1 in the antagonistic effect of hydrogen sulfide on cognitive dysfunction in diabetic rats by exploring the effects of Sirtinol, a inhibitor of SIRT1, on H2S-elicited antagonistic action in cognitive dysfunction and protective effects on hippocampal damage in diabetic rats.[Methods] Learning and memory as well as cognitive function of rats were tested by Y-maze, novel object recognition test and the Morris water maze(MWM).The Expressions of Glucose regulated protein 78(GRP78), C/EBP homologous protein(CHOP), Cleaved caspase-12, pro-apoptotic protein Bax, anti-apoptotic protein Bcl-2 and Synapsin-1 in hippocampus were measured by Western blot. Neuronal apoptosis in hippocampus was analysed by Terminaldeoxynucleotidyl transferase-mediated d UTP nick-end labeling(Tunel) staining. The levels of Malondialdehyde(MDA) and GSH were detected by enzyme-linked immunosorbent assay(Elisa). The viability of SOD in the hippocampus was assayed using Total Superoxide Dismutase Assay Kit with NBT.[Results] 1. Sirtinol, the inhibitor of SIRT1, suppressed H2S-improved cognitive function in diabetic rats. Sirtinol(10 nmol) reduced Na HS(100 mmol/kg/d, 30 d)-induced the increaces in spontaneous alternation of diabetic rats in Y-maze test and in discrimination index of diabetic rats in the novel object recognition test. Sirtinol(10 nmol) reversed Na HS(100 mmol/kg/d, 30 d)-induced decrease in the latency period of diabetic rats in the fifth-day acquisition phase and increases in the times of rat across platform, the time spent in target quadrant, and the proportionality of swimming time in mid-ring of diabetic rats in the spatial search test of MWM test. These data indicated that Sirtinol reversed the inhibitory effect of H2 S in cognitive dysfunction of diabetic rats. 2. SIRT1 abolished the protection of H2 S against hippocampal damage of diabetic rats. Western blot showed that Sirtinol(10 nmol) upregulated Na HS(100 mmol/kg/d, 30 d)-downregulated the expressions of GRP78, CHOP, and Cleaved-caspase-12 in hippocampus of diabetic rats, indicating that Sirtinol reverses the protective effect of H2 S on hippocampal ER stress in diabetic rats. Results of Elisa showed that Sirtinol(10 nmol) inhibited Na HS(100 mmol/kg/d, 30 d)-caused decrease in the level of MDA and increase the level of GSH in hippocampus of diabetic rats. Results of NBT method showed that Sirtinol(10 nmol) suppressed Na HS(100 mmol/kg/d, 30 d)-enhanced in the viability of SOD in hippocampus of diabetic rats. These results suggested that Sirtinol reverses the protective effect of H2 S on diabetes-induced hippocampal oxidative stress. Tunel staining showed that Sirtinol(10 nmol) supperessed Na HS(100 mmol/kg/d, 30 d)-caused decrease in the number of Tunel positive neuron in hippocampus of diabetic rats; Western blot results showed Sirtinol(10 nmol) reversed Na HS(100 mmol/kg/d, 30 d)-exerted downregulation of Bax and upregulation of Bcl-2 in the hippocampus of diabetic rats. These results revealed that Sirtinol reverses the antagonistic action of H2 S in neuronal apoptosis in the hippocmpus of diabetic rats. Western blot results showed that Sirtinol(10 nmol) downregulated Na HS(100 mmol/kg/d, 30 d)-upregulated the expression of Synapsin-1 in the hippocmpus of diabetic rats, which indicating that Sirtinol reverses the inhibitory role of H2 S in the obstacle of hippocampal synaptic formation in diabetic rats.[Conclusion] SIRT1 mediates the antagonistic effect of H2 S on cognitive dysfunction in diabetic rats.