The Role And Mechanism Of MTOR-autophagy In Diabetes Mellitus Aggravating Perioperative Neurocognitive Disorders

ObjectiveDiabetes mellitus(DM)is an independent risk factor of perioperative neurocognitive disorders(PND).This study was designed to investigate the role of m TOR-autophagy signal pathway in the cognitive impairment of orthopedic surgery in DM rats.Methods1.Successful establishment of animal model of DM and PNDStreptozotocin was injected intraperitoneally to establish DM model and internal fixation of left tibial fracture with 2% isoflurane anesthesia was used to establish PND model.2.Diabetes Aggravated PND via m TOR / Autophagy PathwayTo investigate the role of m TOR-autophagy signal pathway in the cognitive impairment of orthopedic surgery in DM rats,male adult Sprague Dawley(SD)rats were divided into 4 groups randomly(n = 45): Control group(C group),Diabetes group(DM group),Surgery group(PND group),DM + PND group.3.Diabetes aggravated PND by activating m TOR to inhibit autophagyTo further confirmed the role of m TOR-autophagy signal pathway in the cognitive impairment of orthopedic surgery in DM rats,SD rats were randomly divided into 8groups(n = 45): Solvent group(DMSO group),DM group,Diabetes +Dimethylsulfoxide group(DM + DMSO group),Diabetes + Rapamycin group(DM +Rapa group),Surgery + DMSO group(PND + DMSO group),PND + Rapa group,DM+ PND + DMSO group and DM + PND + Rapa group.Rapamycin(0.5mg / kg *d)was injected intraperitoneally for three days and the operation followed two hours after the last injection.Learning and memory function were determined by Morris Water Maze test at 3rd,7th,and 14 th day after surgery,respectively.The expression of cleaved caspase3,Bax and Bcl-2 were detected by Western blot(WB)to determine neuronal apoptosis.Aβ and p-tau(Ser 396),which is neurotoxic,were detected by immunohistochemistry(IHC)and WB.The expression of Beclin1 and LC3 were detected by WB to determine the autophagic flux and p-m TOR(Ser 2448)were detected by IHC and WB.P <0.05 was considered statistically significant.Result1.Successful establishment of DM SD rats model1)Elevated blood glucose and weight loss were observed after STZ injection.2)Rats in PND shown longer escape latency,fewer platform crossings,shorter stay time in the target quadrant.2.Diabetes Aggravated PND via m TOR / Autophagy Pathway1)Diabetes aggravated cognitive impairment in PND rats: longer escape latency,fewer platform crossings,shorter stay time in the target quadrant were observed in DM+PND group;2)DM promoted Aβ and p-tau(Ser 396)accumulation in the hippocampus of PND rats;3)DM activated m TOR to inhibit autophagy in PND rats: Beclin-1,LC3 expression decreased and p-m TOR(Ser 2448)content increased(p <0.05).3.Diabetes aggravated PND by activating m TOR to inhibit autophagy1)Rapamycin and solvent had no effect on body weight and blood glucose in rats;2)Rapamycin reversed the suppression of autophagy caused by orthopedic surgery in DM rats though inhibiting the abnormal m TOR signaling: rats in the rapamycin-treated group decreased the content of p-m TOR(Ser 2448)while increased the expression of Beclin1 and the ratio of LC3Ⅱ/LC3Ⅰ;3)Rapamycin treatment reduced neuronal apoptosis due to orthopedic surgery of DM rats: the expression of Cleaved Caspase3 and Bax markedly reduced with the expression Bcl-2 increase after rapamycin treatment;4)Rapamycin treatment attenuated Aβ accumulation and the hyperphosphorylation of tau induced by surgery in DM rats;5)Rapamycin treatment improved cognitive dysfunction induced by orthopedic surgery in DM rats: rats with rapamycin treatment showed shorter escape latency,increased number of platform crossings,increased time in the target quadrant.Conclusion(s)Diabetes mellitus aggravated perioperative neurocognitive disorders by inhibiting autophagy via the m TOR signaling pathway to promote Aβ deposition and tau phosphorylation,and aggravate hippocampal neuron apoptosis.