The Role Of Hippocampal NF-κB-MMP-9Signaling Pathway In Memory Consolidation And Postoperative Cognitive Dysfunction

Section1：The role of MMP-9in propofol-induced spatial memoryconsolidation impairmentObjective: We sought to determine the effect of propofol anesthesia on memoryconsolidation and its relation to hippocampal MMP-9protein expression.Methods: Four-month-old male Sprague Dawley (SD) rats were randomly assignedinto three groups (n=12per group): the control group received10%intralipid15ml/kg asvehicle, intraperitoneal, the P75group received propofol75mg/kg, intraperitoneal, andthe P150group received propofol150mg/kg, intraperitoneal, immediately after training.All rats underwent a single Morris water maze training session. After completion oftraining, the rats were given relevant dose of propofol or10%intralipid in three groups,and then returned to their home cages unitil probe test24hours later. Next, the separategroups of rats from the control, P75and P150(n=6/group/time point), and home cage (HC)group (n=6) were sacrificed at1,3,6, and12hours after training for MMP-9immnunoblotting. The rats in the HC group were neither exposed to Morris water mazetraining apparatus nor received either propofol or intralipid.Results:①During spatial training (trials1-8), two-way repeated measures ANOVAshowed no significant main effects of experimental group for escape latency (F2,287=0.927,P=0.409). However, the main effects of training trials were significant for escape latency(F7,287=117.28, P<0.001). The group×trial interaction was not significant(F14,287=0.538,P=0.908). Moreover, there were no significant differences in escape latency by the end of spatial training (trial8) between the three groups(One-way ANOVA: F2,35=0.7851,P=0.3261). In probe test, one-way ANOVA for time in the target quadrant showed asignificant effect of propofol treatment (F2,35=6.931, P=0.006). Tukey’s post-hoc analysisshowed that rats receiving150mg/kg propofol (18.1±4.6s) but not75mg/kg propofol(26.0±5.3s) spent less time in the target quadrant when compared with the control group(28.1±5.9s)(F2,35=5.712, P=0.0038). Importantly, there were no significant differences inanimals’swimming speed(One-way ANOVA: F2,35=0.8527, P=0.477) between the controland the propofol-treated groups.②In the control group, one-way ANOVA forpro-MMP-9(F4,29=45.4, P<0.001) and active-MMP-9(F4,29=37.3, P<0.001) showed asignificant effect of time points. Tukey’s post-hoc analysis showed that protein levels ofpro-MMP-9and active-MMP-9became significantly elevated between3and6hours aftertraining in comparison with those of HC control rats (P<0.05), and then decreased tobaseline values by12hours after training. In75mg/kg propofol-treated group, proteinlevels of pro-MMP-9and active-MMP-9showed a time-dependent process similar to thatof the control group. However, in the150mg/kg propofol-treated group, the levels ofpro-MMP-9were not significantly different from the HC control levels at all time points(One-way ANOVA: F4,29=1.588, P=0.216). Although there was a transient elevation in theactive-MMP-9protein level at3hours after training (One-way ANOVA: F4,29=7.562,P<0.001), the levels of both pro and active forms of MMP-9were significantly less thanthose of the control and the75mg/kg propofol-treated group at3and6h after training(P<0.05).Conclusion: The amnestic effect of propofol stems at least partially from itsimpairement of memory consolidation, which parallels with reduced activity ofhippocampal MMP-9. Section2：The role of NF-κB-MMP-9signaling pathway in postoperativecognitive dysfunctionObjective: To investigate the role of NF-κB-MMP-9signaling pathway insurgery-induced blood–brain disruption, neuroinflammation and subsequent postoperativecognitive dysfunction.Methods: Four-month-old male Fischer344rats were randomly assigned into fivegroups: the control group, anesthesisa group received propofol-buprenorphine anesthesiafor2hours, surgery group undergone right carotid exploration underpropofol-buprenorphine anesthesia received same volume of normal saline as PDTC plussurgery group, PDTC group received two doses of50mg/kg PDTC just like PDTC plussurgery group, PDTC plus surgery group received two doses of50mg/kg PDTC givenintraperitoneally30minutes before and6hours after the surgery.①All rats in fivegroups (n=8-12per group) were tested in the Barnes maze and fear conditioning paradigmbegun7days after the surgery to assess the effect of above-mentioned five treatements onpostoperative coginitve profiles.②The Ig G extravasation, expressions of IL-1β、IL-6、nuclear NF-κ-p65、MMP-9, and microglia activation in hippocampusat24hours after thesurgery were assessed using either Western blotting or immunohistochemistry (Ig Gextravastion and Iba-1) in five groups undergone above-mentioned five treatements(n=5-12per group).③The expressions of IL-1β、IL-6proteins and microglia activation(Iba-1) in hippocampus at20days after the surgery were assessed in three groups (Controlgroup, anesthesia group, and anesthesia plus surgery group, n=6per group).Results:①During the Barnes maze test, training sessions had a main effect on thetime to identify the target hole (F1,3=10.692, P<0.001), surgery also had a significanteffect on this latency (F1,24=6.544, P=0.017). This surgical effect was abolished by PDTC(F1,3=0.127, P=0.725). Surgery also significantly increased the latency to identify the target hole when tested at8days after the training sessions (F4,52=8.75, P<0.001). Thiseffect was also abolished by PDTC(P<0.05). Rats in the surgery group had decreasedfreezing behavior in context-related fear conditioning test when compared with controlanimals (F4,52=14.871, P<0.001). This decrease was attenuated by PDTC(P<0.05).However, the tone-related freezing behavior was not affected by any experimentalconditions (F4,52=1.853, P=0.134).②Surgery, but not anesthesia or PDTC alone,significantly increased the expressions of IL-1β(F4,24=29.263,P<0.001)、IL-6(F4,24=43.846,P<0.001)、nuclear NF-κ-p65(F4,24=42.694, P<0.001)、active-MMP-9(F4,24=49.568,P<0.001) in hippocampus, Ig G extravasation in hippocampal CA3area (F4,44=11.687,P<0.001), and Iba-1immune intensity in hippocampal dentate gyrus and CA3(F4,24=0.127,P<0.001；F4,59=13.298, P<0.001). This increase was attenuated by PDTC(P<0.05).③Neither anesthesia nor surgery plus anesthesia affected the Iba-1immune intensity indentate gyrus and CA3(F2,17=0.341, P=0.716；F2,17=0.38, P=0.69) and the expressions ofIL-1βand IL-6(F2,17=0.444, P=0.65；F2,17=0.26, P=0.775) in the hippocampus at20daysafter the surgery.Conclusion: Surgery, but not propofol-buprenorphine anesthesia, induces thedisruption of blood-brain barrier, hippocampal microglia activation, neuroinflammationand postoperative cognitive deficit. PDTC attenuates these effects possibly by inhibitingNF-κB activation and the downstream MMP-9activity. The NF-κB-MMP-9signalingpathway may be involved in postoperative cognitive dysfunction.