The Mechanism Of Intranasal Insulin Improves Propofol Induced Cognitive Dysfunction

Background: Postoperative cognitive dysfunction(POCD)manifests itself as a series of complications that mainly consist of memory damage after anesthesia and surgery.POCD is also one of the major risk factors for Alzheimer’s disease(AD).Animal experiments have shown that after anesthesia,their cognitive function is impaired and the level of tau protein phosphorylation in the brain is significantly increased.Daily intranasal administration of insulin prior to anesthesia can effectively improve this cognitive dysfunction and reduce the phosphorylation level of tau protein.However,the specific mechanism of how insulin increase cognitive function and reduce the phosphorylation level of tau protein has not been fully elucidated.Purpose: To reveal the mechanism underlying intranasal insulin administration improving cognitive function induced by anesthesia in aged mice.Methods: In the study,we used 17~18 months aged mice as research subjects and injected propofol(160 mg / kg)intraperitoneally for 5 days to construct POCD.And insulin(1.75 U)was administered intranasally one week prior to anesthesia until the end of anesthesia as the prevention group and on the 15 th day after anesthesia as the prevention and treatment group.We performed novel object recognition test and contextual fear-conditioning test to detect the cognitive function changes in each group of mice.We applied western blotting to evaluate the level of synapse-related proteins such as post-synaptic density protein 95(PSD95),NMDAR2A(NR2A)in the postsynapse and synaptophysin(syp),synaptotagmin(syt)in the presynapse.Meanwhile we investigated the distribution of Microtubule-associated protein-2(MAP-2)by immunofluorescence.To explore the relationship between insulin ameliorating memory impairment caused by anesthesia and tau hyperphosphorylation in aged mice,we used western blotting to evaluate the level of tau hyperphosphorylation,glycogen synthase kinase-3β(GSK-3β)and the expression level of GSK-3β phosphorylation at serine 9(p-Ser9)both in the prefrontal cortex and hippocampus.To further validate whether insulin ameliorating memory impairment caused by anesthesia through the insulin signaling pathway,we detected the total level of the signaling pathway,including insulin receptor β(IRβ),insulin-like growth factor-1 receptor β(IGF-1Rβ),insulin receptor substrate-1(IRS-1),c-Jun N-terminal kinase(JNK),also named stress-activated protein kinase(SAPK),the regulation subunit of phosphatidylinositide 3-kinases(PI3K)(p85),3-phosphoinositide-dependent protein kinase-1(PDK1)and protein kinase B(AKT).We also assessed the activation of these proteins by measuring their phosphorylation levels at the activity-dependent sites,including phosphoylation of SAPK/JNK at threonine 183/tyrosine 185(p-JNK),phosphorylation of IRS-1 at serine 307(p-IRS1),phosphorylation of PDK1 at serine 241(p-PDK1),phosphorylation of Akt at threonine 308(p-AKT).To further explore whether neuronal loss is related to memory impairment caused by anesthesia,we used Nissl staining to detect the amount of neuron in hippocampus.Results: 1.Insulin rescues cognitive defects induced by anesthesia in aged mice.2.Insulin rescues the loss of synaptic proteins and dendrites impairment caused by anesthesia in aged mice.3.Intranasal administration of insulin reduces anesthesia-induced tau hyperphosphorylation by inhibiting GSK-3β activity in aged mice.4.Insulin antagonizes the down-regulation of PI3K/PDK1/AKT signaling pathways caused by anesthesia in aged mice 5.Anesthesia dose not affect neuron density of the hippocampus in aged mice.Conclusion: Insulin may up-regulate PI3 K / PDK1 / AKT signaling pathway,increase GSK-3β phosphorylation at serine 9,there by inhibits GSK-3β activity,decreases tau hyperphosphorylation and attenuates the loss of synaptic proteins and dendritic impairment induced by anesthesia in aged mice.