The Effect Of Neuroinflammation On The Isoflurane-induced Cognitive Impairment In APP/PSEN1 Transgenic Mice

Objective: In the present study,we use APP/PSEN1 transgenic mice,which has cognitive impairment.APP/PSEN1 transgenic mice and their wildtype(WT)littermates were used.We hypothesized that exposure of APP/ PSEN1 transgenic mice to repeat isoflurane during different process of AD(Alzheimer Disease,AD)would alter the progression of AD.We investigated the effect of isoflurane exposure on learning and memory ability and neuroinflammation,as well as the microglial immunepenotype in Alzheimer’s disease model mice,to provide more experimental basis for safe use of anesthetics on the neurodegenerative diseases including AD and elderly people.Methods:1 Novel object recognition test(NOR)and Morris water maze(MWM)were used to evaluate the effects of isoflurane on non-spatial and spatial cognitive impairment in different process of AD model mice,including 4-month-old,6-month-old and 10-month-old mice.2 Congo-Red staining was used to test the cortical and hippocampal Aβ(β-amyloid)deposition in AD model mice.3 The cortical or hippocampal immunoreactivity of microglia and astrocyte was analyzed with Immunofluorescence experiments targeting Iba1(ionized calcium-binding receptor adapter molecular 1,Iba1)and GFAP(glial fibrillary acidic protein,GFAP).4 The RT-PCR was used to assess the effects of isoflurane on the m RNA levels of IL-6(interleukin-6,IL-6).TNF-α(Tumor Necrosis Factor-α,TNF-α),i NOS(inducible nitric oxide synthase,i NOS),which described as M1 microglia phenotype marker and M2 microglia marker Ym1/2(Chitinase-3 like protein,Ym1/2)in PFC(prefrontal cortex)and HIP(hippocampus)of AD model mice.5 Brd U(bromodeoxyuridine,Brd U)labeling immunohistrochemistry was applied to evaluate hippocampal neurogenesis of APP/PSEN1 mice.Results:1 In NOR,in compared with WT mice,there was no difference of novel object cognitive index(RI)in APP/PSEN1 mice in 4-month-old or in 6-month-old,but the RI of the 10-month-old APP/PSEN1 mice decreased(P <0.05),suggesting that it was 10-month-old APP/PSEN1 mice that have cognitive impairment.Then we use long-term repeated isoflurane or O2 to the mice.Compared to APP/PSEN1+CON,the RI of the 6-month-old isofluranetreated APP/PSEN1 mice APP/PSEN1+ISO decreased(P<0.05).In MWM,6-month-old isoflurane-treated APP/PSEN1 mice has a longer escape latency and less crossing platform number than APP/PSEN1+CON mice(P<0.05,P<0.01).In compared with O2-treated WT+CON mice,there was a statistically decrease of novel object cognitive index in 10-month-old isofluranetreated WT mice WT+ISO(P<0.05),in MWM,10-month-old isoflurane-treated WT mice WT+ISO have a longer escape latency and less crossing platform number than WT+CON(P<0.05,P<0.01).The result suggested that isoflurane can induce the PFC-dependent non-spatial cognitive ability and a dramatically influence on hippocampus-dependent spatial memory disorder of AD model mouse in the early process,while it can also aggravates the cognitive impairment in elderly WT mice;2 Congo-red staining results showed that there were no plaques were observed in O2-treated WT+CON mice.However,Compared to APP/PSEN1+ CON,the plaque number has no difference in 6-month-old and 10-month-old isoflurane-treated APP/PSEN1 mice APP/PSEN1+ISO in cortical and hippocampal,which suggested that isoflurane has no effective on Aβ deposition;3 Compared to O2-treated WT+CON,GFAP immunoreactivity were significantly increased in the cortex area of 6-month and 10-month APP/ PSEN1+CON mice(P<0.01,P<0.001),but it was not statistically different in hippocampus.Compared to O2-treated WT+CON,isoflurane exposure did not influence the GFAP immunofluorescence intensity in both the cortex and hippocampus area in 10-month-old isoflurane-treated WT mice WT+ISO;Compared to O2-treated APP/PSEN1+CON,isoflurane exposure did not influence the GFAP immunofluorescence intensity in both the cortex and hippocampus area in 10-month-old isoflurane-treated APP/PSEN1 mice APP/ PSEN1+ISO.In compared with O2-treated WT+CON mice,Iba1 immunoreactivity significantly increased in the cortex and hippocampus area of 6-month and 10-month APP/PSEN1+CON mice(P<0.05,P<0.01);Compared to APP/ PSEN1+CON,isoflurane exposure significantly increased the Iba1 immunofluorescence intensity in both the cortex and hippocampus area in 6-month-old isoflurane-treated APP/PSEN1 mice APP/PSEN1+ISO(P <0.05).In compared with O2-treated WT+CON mice,isoflurane exposure increased the Iba1 immunofluorescence intensity in both the cortex and hippocampus area in 10-month-old isoflurane-treated WT mice WT+ISO(P<0.05).The results suggested that isoflurane is effective to induce microglial immunoreactivity;4 In compared with O2-treated WT+CON,the m RNA expression level of M1 microglia phenotype marker IL-6、TNF-α、i NOS significantly increased in PFC and hippocampus of 6 and 10-month-old APP/PSEN1+CON mice.Compared to APP/PSEN1+CON,the m RNA expression level of TNF-a 、i NOS m RNA expression level in 6-month-old APP/PSEN1+ISO increased in hippocampus(P<0.05,P<0.01),similar to the expression level of IL-6,but it was not statistically different.Compared to APP/PSEN1+CON,the m RNA expression level of Ym1/2 in 6-month-old APP/PSEN1+ISO has no significant difference.Compared to WT+CON,Isoflurane increased the m RNA expression level of IL-6 m RNA in 10-month-old isoflurane-treated WT mice WT+ISO in PFC;and increased the m RNA expression level of TNF-a m RNA in 10-month-old isoflurane-treated WT mice WT+ISO.Compared to WT+ CON,the m RNA expression level of Ym1/2 in 10-month-old isofluranetreated WT mice WT+ISO decreased(P<0.01).The results Suggested that isoflurane promoted the expression of M1 microglia phenotype,contributed to microglia phenotype transformation from M2 microglia phenotype microglia to M1 microglia phenotype in WT mice,but not in APP/PSEN1 transgenic mice.5 In Brd U labeling staining,compared to WT+CON,it was 10-month rather than 6-month APP/PSEN1+CON mice hippocampal Brd U+ cell number decreased significantly(P<0.001);and Compared to APP/PSEN1+CON,isoflurane counteracted increasing of hippocampal Brd U+ cell number in 6-month-old isoflurane-treated APP/PSEN1 mice APP/PSEN1+ISO,which indicates that isoflurane reduced neurogenesis.In compared with O2-treated WT+CON,isoflurane increased the Brd U+ cell number in 10-month-old isoflurane-treated WT mice WT+ISO in hippocampal.Conclusion: Isoflurane induced non-spatial cognitive impairment and hippocampus-dependent spatial memory disorder of APP/PSEN1 transgenic mice in the early process,similar to the elderly one,but has no effect on the later stage of AD,which may be related with the microglia-mediated neuroinflammation as well as the reduce of neurogenesis.This study provides a new mechanism that Isoflurane can alter the neuroinflammation on different process of AD to induce cognitive impairment.And the neuroinflammation was effected by microglia phenotype transformation in WT mice,but not in APP/PSEN1 transgenic mice.These findings suggested to paying more attention on the safe use of anesthetics on the neurodegenerative diseases including AD and elderly people.