Postoperative Cognitive Dysfunction In Mice Research Articles

Macrophage-derived exosomes exacerbate postoperative cognitive dysfunction in mice through inflammation

This study investigated the impact of two-hit inflammation on postoperative cognitive dysfunction (POCD) in mice and the role of macrophage-derived exosomes in regulating this process. Mice models were used to mimic the state of two-hit inflammation, and cognitive function was assessed through behavioral experiments. Proinflammatory cytokine expression levels and blood-brain barrier (BBB)-associated functional proteins were measured using ELISA and Western blot, respectively. An in vitro macrophage inflammation two-hit model was created, and the role of exosomes was examined using the previously mentioned assays. Additionally, exosomes were injected into mice to further understand their impact in the two-hit inflammation model. Mice exposed to two-hit inflammation experienced impaired cognitive function, increased BBB permeability, and elevated levels of proinflammatory cytokines. Macrophages subjected to two-hit inflammation released higher levels of proinflammatory cytokines compared to the control group and other treatment groups. Treatment with an exosome inhibitor GW4869 effectively reduced the expression levels of proinflammatory cytokines in macrophages exposed to two-hit inflammation. Moreover, injection of macrophage-released exosomes into healthy mice induced inflammation, hippocampal damage, and cognitive disorders, which were mitigated by treatment with GW4869. In mice with two-hit inflammation, macrophage-released exosomes worsened cognitive disorders by promoting inflammation in the peripheral blood and central nervous system. However, treatment with GW4869 protected cognitive function by suppressing exosome release. These findings highlight the importance of two-hit inflammation in POCD and emphasize the critical role of exosomes as regulatory factors. This research provides valuable insights into the pathogenesis of POCD and potential intervention strategies.

Sirtuin 3 (SIRT3) improves sevoflurane-induced postoperative cognitive impairment by regulating mitochondrial oxidative stress.

One of the most prevalent co-operative disorders is postoperative cognitive dysfunction (POCD), however, its pathogenesis remains unclear. Thus, the aim of this work was to evaluate SIRT3's impact on cognitive decline in aged mice under anesthesia. Adeno-associated virus SIRT3 vector (AAV-SIRT3) or empty vector (AAV-VEH) was injected into the hippocampal region of aged mice after sevoflurane induction in order to upregulate the expression of SIRT3. The expression levels of SIRT3, pro-inflammatory cytokines, and apoptotic factors in hippocampus tissues were identified by PCR, Western blotting, TUNEL staining, and enzyme-linked immunosorbent assay (ELISA), and the cognitive function of mice was assessed. The SIRT3 expression was down-regulated in the hippocampal tissue of anesthetized mice. SIRT3 overexpression can improve the learning and memory ability, reduce the escape latency, and increase the residence time in the platform and platform crossing ability of mice. The overexpression of SIRT3 in hippocampus can reduce the oxidative stress response and inflammatory response induced by anesthesia in mice, increase the superoxide dismutase (SOD) expression level, and decrease the expression level of MDA and inflammatory factors in hippocampus. In addition, SIRT3 overexpression can also reduce anesthetic-induced hippocampal cell apoptosis. By reducing the hippocampus mitochondrial oxidative stress response, SIRT3 plays a significant role in the pathophysiology of POCD in mice and is a potential target for POCD treatment and diagnosis.

Study on the Mechanism of Eerdun Wurile's Effects on Post-operative Cognitive Dysfunction by the TLR4/NF-κB Pathway.

The object of our work was to observe whether the Mongolian medicine Eerdun Wurile (EW) improve postoperative cognitive dysfunction (POCD) by affecting the TLR4/NF-κB. Mice (6-8-week-old male C57BL/6J) were selected to establish an animal model of POCD by combining intracerebroventricular injection of lipopolysaccharide and nephrectomy; EW formulation and EW basic formulation were administered intra-gastrically for 7 consecutive days. The cognitive performance was assessed by Morris water maze test. H&E staining was examined to detect alterations in hippocampal tissue. Immunohistochemical staining was performed to evaluate MyD88, NF-κB, TLR4, iNOS, and IBA-1 expressions; Western blotting and RT-qPCR were performed to evaluate MyD88, NF-κB, and TLR4. The expressions of IL-6, IL-1β, and TNF-α were evaluated by ELISA. Intracerebroventricular injection of lipopolysaccharide combined with nephrectomy induced cognitive dysfunction in mice, stimulated TLR4/NF-κB and microglia, and promoted the secretion of murine TNF-α, IL-1β, and IL-6. EW formulation and EW basic formulation treatment are able to suppress the TLR4/NF-κB pathway activation and microglia, and the serum cytokine secretions related to proinflammation, and restore the cognitive performance. EW formulation and EW basic formulation can improve POCD in mice, and TLR4/NF-κB pathway seems to be one of the important mechanisms in EW's improvement of POCD.

TL1A promotes the postoperative cognitive dysfunction in mice through NLRP3-mediated A1 differentiation of astrocytes.

We investigated the mechanism, whereby tumor necrosis factor-like ligand 1A (TL1A) mediates the A1 differentiation of astrocytes in postoperative cognitive dysfunction (POCD). The cognitive and behavioral abilities of mice were assessed by Morris water maze and open field tests, while the levels of key A1 and A2 astrocyte factors were detected by RT-qPCR. Immunohistochemical (IHC) staining was used to examine the expression of GFAP, western blot was used to assay the levels of related proteins, and enzyme-linked immunosorbent assay (ELISA) was used to detect the levels of inflammatory cytokines. The results showed that TL1A could promote the progression of cognitive dysfunction in mice. Astrocytes differentiated into A1 phenotype, while unobvious changes were noted in astrocyte A2 biomarkers. Knockout of NLRP3 or intervention with NLRP3 inhibitor could inhibit the effect of TL1A, improving the cognitive dysfunction and suppressing the A1 differentiation. Our results demonstrate that TL1A plays an important role in POCD in mice, which promotes the A1 differentiation of astrocytes through NLRP3, thereby exacerbating the progression of cognitive dysfunction.

Involvement of microRNA-138-5p in cardiac surgery-induced postoperative cognitive dysfunction

Background: Despite being one of the main concerns in cardiac surgery, the molecular basis and regulatory mechanisms of postoperative cognitive dysfunction (POCD) are still unclear. In this study, we demonstrate the critical role of miR-138-5p in POCD in mice.
 Methods: We first established an animal model for POCD caused by cardiac surgery. We then used quantitative reverse transcription polymerase chain reaction to examine the expression levels of miR-138-5p and its target mRNAs. The protein level of sirtuin 1 (SIRT1) was determined using Western blot assays. To assess the mice’s recognition abilities, we performed the Morris water maze (MWM) test. Enzyme-linked immunosorbent assays were used to evaluate the expression levels of hippocampal inflammatory cytokines. Finally, we used a luciferase assay to confirm that miR-138-5p directly targeted the mRNA of SIRT1.
 Results: MiR-138-5p was upregulated in the hippocampus of mice following cardiac surgery. Inhibiting miR-138-5p reduced the occurrence of POCD and the hippocampus inflammation in the mice. MiR-138-5p targeted the mRNA of SIRT1, thereby suppressing its expression in the hippocampus of mice following cardiac surgery.
 Conclusion: Our findings suggest that miR-138-5p contributes to cardiac surgery-induced POCD by directly targeting and suppressing the expression of SIRT1 in the hippocampus.

Small extracellular vesicles secreted by induced pluripotent stem cell-derived mesenchymal stem cells improve postoperative cognitive dysfunction in mice with diabetes.

Postoperative cognitive dysfunction (POCD) is a common surgical complication. Diabetes mellitus (DM) increases risk of developing POCD after surgery. DM patients with POCD seriously threaten the quality of patients' life, however, the intrinsic mechanism is unclear, and the effective treatment is deficiency. Previous studies have demonstrated neuronal loss and reduced neurogenesis in the hippocampus in mouse models of POCD. In this study, we constructed a mouse model of DM by intraperitoneal injection of streptozotocin, and then induced postoperative cognitive dysfunction by transient bilateral common carotid artery occlusion. We found that mouse models of DM-POCD exhibited the most serious cognitive impairment, as well as the most hippocampal neural stem cells (H-NSCs) loss and neurogenesis decline. Subsequently, we hypothesized that small extracellular vesicles secreted by induced pluripotent stem cell-derived mesenchymal stem cells (iMSC-sEVs) might promote neurogenesis and restore cognitive function in patients with DM-POCD. iMSC-sEVs were administered via the tail vein beginning on day 2 after surgery, and then once every 3 days for 1 month thereafter. Our results showed that iMSC-sEVs treatment significantly recovered compromised proliferation and neuronal-differentiation capacity in H-NSCs, and reversed cognitive impairment in mouse models of DM-POCD. Furthermore, miRNA sequencing and qPCR showed miR-21-5p and miR-486-5p were the highest expression in iMSC-sEVs. We found iMSC-sEVs mainly transferred miR-21-5p and miR-486-5p to promote H-NSCs proliferation and neurogenesis. As miR-21-5p was demonstrated to directly targete Epha4 and CDKN2C, while miR-486-5p can inhibit FoxO1 in NSCs. We then demonstrated iMSC-sEVs can transfer miR-21-5p and miR-486-5p to inhibit EphA4, CDKN2C, and FoxO1 expression in H-NSCs. Collectively, these results indicate significant H-NSC loss and neurogenesis reduction lead to DM-POCD, the application of iMSC-sEVs may represent a novel cell-free therapeutic tool for diabetic patients with postoperative cognitive dysfunction.

SVCAM1 in the Hippocampus Contributes to Postoperative Cognitive Dysfunction in Mice by Inducing Microglial Activation Through the VLA-4 Receptor.

Postoperative cognitive dysfunction (POCD) is a severe postsurgical complication, but its underlying mechanisms remain unclear. Neuroinflammation mediated by microglial activation plays a major role in POCD pathophysiology. Upregulation of vascular cell adhesion molecule 1 (VCAM1) on brain endothelial cells is closely correlated with microglial activation in the mouse hippocampus. However, the role of VCAM1 upregulation in microglial activation remains unknown. Soluble VCAM1 (sVCAM1) activates the very late antigen-4 (VLA-4) receptor under inflammatory conditions. Therefore, we hypothesized that sVCAM1 which is shed from VCAM1 contributes to POCD by triggering hippocampal microglial activation through the VLA-4 receptor. We found that VCAM1 and sVCAM1 expression in the mouse hippocampus was upregulated after surgery, and the upregulation was accompanied by hippocampal microglial activation. sVCAM1 levels in mouse and human serum were increased after surgery. Anti-VCAM1 treatment inhibited microglial activation, proinflammatory cytokine production, VLA-4 expression and P38 mitogen-associated protein kinase (MAPK) pathway activation and attenuated hippocampal-dependent cognitive dysfunction. In vitro, recombinant sVCAM1 promoted M1 polarization in BV2 cells, increased VLA-4 expression and activated the P38 MAPK pathway. These effects were reversed by VLA-4 receptor blockade. Anti-VLA-4 treatment ameliorated hippocampal-dependent cognitive dysfunction after surgery by inhibiting microglial activation, proinflammatory cytokine production and P38 pathway activation. In conclusion, increased sVCAM1 in the hippocampus is involved in microglial activation and cognitive dysfunction induced by surgery. Inhibiting the sVCAM1-VLA-4 interaction in microglia may be a therapeutic strategy for POCD.

Activation of the Lateral Habenula‐Ventral Tegmental Area Neural Circuit Contributes to Postoperative Cognitive Dysfunction in Mice

Postoperative cognitive dysfunction (POCD) is common and is associated with poor outcome. Neural circuit involvement in POCD is unknown. Lateral habenula (LHb) that regulates coping and depression‐like behaviors after aversive stimuli is activated by surgery in the previous study. Here, surgery activated LHb and ventral tegmental area (VTA) are presented. VTA is known to receive projections from LHb and project to the prefrontal cortex and hippocampus. Direct chemogenetic inhibition of LHb or damaging LHb attenuates surgery‐induced learning and memory impairment, N‐methyl‐d‐aspartate (NMDA) receptor activation, endoplasmic reticulum stress, inflammatory responses and cell injury in the VTA, and activation of rostromedial tegmental nucleus, an intermediate station to connect LHb with VTA. LHb inhibition preserves dendritic spine density in the prefrontal cortex and hippocampus. Retrograde inhibition of LHb via its projections to VTA attenuated surgery‐induced learning and memory dysfunction is observed. Retrograde activation of LHb induced learning and memory dysfunction is observed. Inhibition of NMDA receptors, dopamine synthesis, and endoplasmic reticulum stress in the VTA reduced surgery‐induced learning and memory impairment, inflammatory responses, and cell injury are observed. These results suggest that surgery activates the LHb‐VTA neural circuit, which contributes to POCD and neuropathological changes in the brain. These novel findings represent initial evidence for neural circuit involvement in surgery effects.

Preoperative environment enrichment preserved neuroligin 1 expression possibly via epigenetic regulation to reduce postoperative cognitive dysfunction in mice.

AimsPostoperative cognitive dysfunction (POCD) is a common and significant syndrome. Our previous studies have shown that surgery reduces dendritic arborization and spine density and that environment enrichment (EE) reduces POCD. Neuroligin 1 is a postsynaptic protein involved in the formation of postsynaptic protein complex. This study was designed to determine the role of neuroligin 1 in the protection of EE against POCD and the mechanisms for EE to affect neuroligin 1 expression.MethodsEight‐week‐old C57BL/6J male mice with or without EE for 3, 7, or 14 days had right carotid artery exposure under isoflurane anesthesia. An anti‐neuroligin 1 antibody at 1.5 µg/mouse was injected intracerebroventricularly at one and two weeks before the surgery. Mice were subjected to the Barnes maze and fear conditioning tests from one week after the surgery. Cerebral cortex and hippocampus were harvested after surgery.ResultsMice with surgery had poorer performance in the Barnes maze and fear conditioning tests than control mice. EE for 2 weeks, but not EE for 3 or 7 days, improved the performance of surgery mice in these tests. Surgery reduced neuroligin 1 in the hippocampus. Preoperative EE for 2 weeks attenuated this reduction. The anti‐neuroligin 1 antibody worsened the performance of mice with surgery plus EE in the Barnes maze and fear conditioning tests. Surgery increased histone deacetylase activity and decreased the acetylated histone in the hippocampus. EE attenuated these surgery effects.ConclusionOur results suggest that preoperative EE for 2 weeks reduces POCD. This effect may be mediated by preserving neuroligin 1 expression via attenuating surgery‐induced epigenetic dysregulation in the brain.

Role of Sox2 in Learning, Memory, and Postoperative Cognitive Dysfunction in Mice.

Postoperative cognitive dysfunction (POCD) is a significant clinical issue. Its neuropathogenesis has not been clearly identified and effective interventions for clinical use to reduce POCD have not been established. This study was designed to determine whether environmental enrichment (EE) or cognitive enrichment (CE) reduces POCD and whether sex-determining region Y-box-2 regulated by sirtuin 1, plays a role in the effect. Eighteen-month-old male mice were subjected to right-common-carotid-artery exposure under sevoflurane anesthesia. Some of them stayed in cages with EE or CE after the surgery. Learning and memory of mice were tested by a Barnes maze and fear conditioning, starting 2 weeks after the surgery. Sex-determining region Y-box-2 (Sox2) in the brain was silenced by small hairpin RNA (shRNA). Immunofluorescent staining was used to quantify Sox2-positive cells. Surgery reduced Sox2-positive cells in the hippocampus (64 ± 9 cells vs. 91 ± 9 cells in control group, n = 6, p < 0.001) and impaired learning and memory (time to identify target box one day after training sessions in the Barnes maze test: 132 ± 53 s vs. 79 ± 53 s in control group, n = 10, p = 0.040). EE or CE applied after surgery attenuated this reduction of Sox2 cells and POCD. Surgery reduced sirtuin 1 activity and CE attenuated this reduction. Resveratrol, a sirtuin 1 activator, attenuated POCD and surgery-induced decrease of Sox2-positive cells. Silencing shRNA reduced the Sox2-positive cells in the hippocampus and impaired learning and memory in mice without surgery. These results suggest a role of Sox2 in learning, memory, and POCD. EE and CE attenuated POCD via maintaining Sox2-positive cells in the hippocampus.

Surgery Trauma Severity but not Anesthesia Length Contributes to Postoperative Cognitive Dysfunction in Mice.

Perioperative, modifiable factors contributing to perioperative neurocognitive disorders (PND) have not been clearly defined. To determine the contribution of anesthesia lengths and the degrees of surgical trauma to PND and neuroinflammation, a critical process for PND. Three-month-old C57BL/6J mice were subjected to 2 h or 6 h isoflurane anesthesia plus a 5 min or 15 min left common carotid artery exposure (surgery) in a factorial design (two factors: anesthesia with two levels and surgery with three levels). Their learning and memory were tested by Barnes maze and novel object recognition paradigms. Blood, spleen, and hippocampus were harvested for measuring interleukin (IL)-6 and IL-1β. Eighteen-month-old C57BL/6J mice (old mice) were subjected to 6 h isoflurane anesthesia or 2 h isoflurane anesthesia plus 15 min surgery and then had learning and memory tested. Three-month-old mice with 15 min surgery (long surgery) under 2 h or 6 h anesthesia performed poorly in the learning and memory tests compared with controls. Anesthesia alone or anesthesia plus 5 min surgery did not affect mouse performance in these tests. Similarly, only mice with long surgery but not mice with other experimental conditions had increased IL-6 and IL-1β in the blood, spleen, and hippocampus and decreased spleen weights. Splenocytes were found in the hippocampus after surgery. Similarly, old mice with long surgery but not the mice with isoflurane anesthesia alone had poor performance in the Barnes maze and novel object recognition tests. Surgical trauma, but not anesthesia, contributes to the development of PND and neuroinflammation. Splenocytes may modulate these processes.

A Novel Individual-based Determination of Postoperative Cognitive Dysfunction in Mice.

Postoperative cognitive dysfunction (POCD) is a significant clinical issue. Aging is a risk factor for POCD. It is known that not every patient develops POCD. This situation shall be similar in animals. Determination of POCD is individual-based in humans but group-based in animal studies. This difference prevents effective evaluation of biomarkers and interventions for POCD in preclinical studies. The objective of this study was to determine whether individual animal could be assessed for POCD by a system similar to that for patients. Seven-week old CD1 and 18-month old C57BL/6 male mice were subjected to right carotid arterial exposure under isoflurane anesthesia. Mice were evaluated by Barnes maze and fear conditioning either post-surgery alone or both prior to surgery and post-surgery. Surgery increased the time to identify the target box in Barnes maze when tested one day or 8 days after the training sessions and reduced freezing behavior in fear conditioning test. This phenomenon occurred in 7-week old animals with and without evaluation before the surgery and in 18-month old mice evaluated before and after surgery. Based on the method and criteria used for a human whose cognition was evaluated before and after surgery to assess individual decline of cognition, 7 in 21 mice in the surgical group and 1 in 21 mice in control group of 7-week old mice had cognitive dysfunction. Among 18-month old mice, 13 in 21 mice in the surgical group and 2 in 20 mice in the control group had cognitive dysfunction. The incidence of cognitive dysfunction in mice with surgery was higher than that in control mice no matter whether young adult (P = 0.045) or old mice (P < 0.001) were considered. These results indicate that surgery induces POCD in mice. Individual animal-based assessment can be used to identify animals with POCD.

Fingolimod (FTY720) improves postoperative cognitive dysfunction in mice subjected to D-galactose-induced aging.

Neurocognitive dysfunction is a common postoperative complication, especially in older adult patients. Fingolimod (FTY720) is a sphingosine-1-phosphate receptor modulator that has been found to be neuroprotective in several animal models of central nervous system disease. However, few reports have examined whether FTY720 could mitigate postoperative cognitive dysfunction. In this study, we investigated whether FTY720 could prevent postoperative neurocognitive impairment in mice subjected to D-galactose-induced aging. We induced an accelerated model of aging by administering an intraperitoneal injection of D-galactose. Subsequently, we performed a partial hepatolobectomy under sevoflurane anesthesia. FTY720 (1 mg/kg) was administered intraperitoneally 3 hours before and 24 hours after anesthesia and surgery. Our results indicated that anesthesia and surgery significantly impaired spatial memory in the Y-maze test 6 hours after surgery. We also found that problem solving ability and long-term memory in the puzzle box test on postoperative days 2-4 were significantly improved by FTY720 treatment. Immunohistochemical staining and western blot assay demonstrated that FTY720 significantly inhibited microglial activation in the hippocampal CA1 region of mice 6 hours and 3 days after anesthesia, and down-regulated the expression of synaptic-related proteins postsynaptic density protein 95 and GluR2 in the hippocampus. These results indicate that FTY720 improved postoperative neurocognitive dysfunction in mice subjected to D-galactose-induced aging. This study was approved by the Experimental Animal Ethics Committee of the Third Xiangya Hospital of Central South University of China (approval No. LLSC (LA) 2016-025) on September 27, 2016.

Regulation and molecular mechanism of histone acetylation modification in sevoflurane-induced POCD in mice

ObjectiveThe objective is to explore the effect of sevoflurane anesthesia on histone acetylation and the mechanism of learning and memory ability in mice, so as to provide reference for the development of drugs with cognitive protection and brain injury reduction. Method: In this study, 40 healthy male BALB/c mice are selected as the study subjects and randomly divided into four groups: control group (group A), sevoflurane group (group B), sevoflurane + SAHA group (group C) and SAHA group (group D). A postoperative cognitive dysfunction (POCD) model induced by sevoflurane is established. After extracting the hippocampus, Morris water maze test is used to detect the spatial learning and memory ability of mice, and conditioned fear test is used to detect conditioned fear memory ability. The expression of brain derived neural factor (BDNF) and synaptotagmin-1 (SYT-I) mRNA in hippocampus is detected by real-time fluorescence quantitative PCR. Western blotting is used to detect the expression of Acetylated histone-3 (Ac-H3), BDNF and SYT-I in mouse hippocampus. Results: After sevoflurane anesthesia, the escape latency of mice in Morris water maze experiment is significantly prolonged, and the target quadrant time ratio is significantly reduced. Compared with group A, the time ratio and times of stiffness in group B are significantly lower (P < 0.05). There is no significant difference between group C and group A (P > 0.05). The expression level of Ac-H3, BDNF and SYT-I protein in group B is significantly lower than that in group A (P < 0.05). Compared with group B, the expression level of Ac-H3, BDNF and SYT-I protein in group D is significantly higher, and the difference is statistically significant (P < 0.05), while the effect of sevoflurane anesthesia might be weakened by using the histone deacetylase inhibitor SAHA. Conclusion: Sevoflurane anesthesia can inhibit the expression of BDNF and SYT-I by inhibiting the acetylation of histone-3 in the hippocampus of mice, thus leading to POCD.

SIRT1 mediates improvement of cardiac surgery-induced postoperative cognitive dysfunction via the TLR4/NF-κB pathway

Objectives Clinically, there is no effective therapy for postoperative cognitive dysfunction (POCD). Inflammation after surgery is closely associated with POCD. Methods In this study, we explored the role of sirtuin 1 (SIRT1) in POCD. POCD in mice was induced by cardiac surgery. The mRNA and protein levels of related genes were determined by real-time polymerase chain reaction and western blot, respectively. Plasma concentrations of inflammatory factors were measured using an ELISA kit. Novel object and novel location recognition tests were carried out to measure recognition ability. The Morris water maze (MWM) test was performed to measure learning and memory ability. Results There was a clear decrease in SIRT1 expression after POCD. The SIRT1 activator SRT1720 promoted recognition, learning, and memory ability of mice with POCD. Moreover, SRT1720 treatment greatly inhibited plasma inflammatory cytokine levels and TLR4 and P65 protein expression in the hippocampus of POCD mice. The effect of SRT1720 on POCD was in a TLR4-dependent manner. Conclusions SIRT1 mediates the improvement of cardiac surgery-induced postoperative cognitive dysfunction via the TLR4/NF-κB pathway.

Amelioration of postoperative cognitive dysfunction in mice by mesenchymal stem cell-conditioned medium treatments is associated with reduced inflammation, oxidative stress and increased BDNF expression in brain tissues

ObjectiveMesenchymal stem cells (MSCs) are widely used in regeneration and repair of various tissues and organs, and whether MSC-conditioned medium (MSC-CM) has protective effects in postoperative cognitive dysfunction (POCD) remains largely unknown. We aimed to assess the therapeutic effect and explore the mechanisms of MSC-CM therapy in a POCD mouse model. MethodsSixty C57BL/6 mice were randomly assigned to 3 groups: control, POCD and POCD + MSC-CM. The POCD mouse model was established by left liver lobectomy. While mice in the control group were sham-operated, mice in the POCD + MSC-CM group were immediately administrated with MSC-CM after operation. The Morris water maze was used to determine cognitive function of mice at 1, 3, and 7 days after operation. The levels of IL-1β, IL-6, TNF-α and malondialdehyde in brain tissues at 3 days after operation were assessed by ELISA, while the protein level of brain derived neurotrophic factor (BDNF) was determined by western blot. ResultsLeft liver lobectomy induced POCD in mice resulted in decrease of cognitive function, increase of brain IL-1β, IL-6, TNF-α and malondialdehyde levels, and decreased BDNF expression, while administration of MSC-CM significantly reversed these changes. ConclusionMSC-CM ameliorates POCD in mice, and its protective roles are associated with reduced levels of inflammatory factors, attenuated oxidative stress, and increased BDNF expression.

Effect of exogenous miR-181b on postoperative cognitive dysfunction in mice

Objective To evaluate the effect of exogenous miR-181b on postoperative cognitive dysfunction (POCD) in mice. Methods A total of 108 clean-grade healthy male C57BL/6 mice, weighing 25-30 g, were divided into 4 groups (n=27 each) using a random number table method: control group (group C), POCD group, miR-181b agonist agomir group (group Ag), and agomir negative control group (group AC). POCD was induced by open tibial fracture in 2.1% isoflurane-anesthetized mice.A total volume of miR-181b agomir 4 μl (0.25 nmol/μl) was injected into bilateral hippocampi at 2 days before establishing the model in group Ag.Agomir negative control solution 4 μl was given at 2 days before establishing the model in group AC.Eighteen mice were selected at days 1, 3 and 7 after surgery, and contextual fear conditioning test was performed to assess cognitive function.Nine mice in each group were sacrificed at 6, 12 and 24 h after surgery (3 mice at each time point), and the hippocampus was isolated for determination of miR-181b expression (by quantitative real-time polymerase chain reaction) and interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α) contents (by enzyme-linked immunosorbent assay). Results Compared with group C, the percentage of time spent freezing in the contextual fear conditioning test was significantly decreased at 1, 3 and 7 days after surgery, and the expression of miR-181b was down-regulated and the contents of IL-1β and TNF-α were increased at 6, 12 and 24 h after surgery in POCD and AC groups (P<0.05). Compared with POCD and AC groups, the percentage of time spent freezing in the contextual fear conditioning test was significantly increased 1, 3 and 7 days after surgery, and the expression of miR-181b was up-regulated and the contents of IL-1β and TNF-α were decreased at 6, 12 and 24 h after surgery in group Ag (P<0.05). Conclusion Exogenous miR-181b can mitigate POCD, and the mechanism may be related to inhibiting inflammatory responses in the hippocampus of mice. Key words: MicroRNAs; Cognition disorders; Hippocampus; Neuroinflammation

Role of hippocampal cannabinoid receptor 2 in postoperative cognitive dysfunction in mice

Objective To investigate the role of hippocampal cannabinoid receptor 2 (CB2R) in postoperative cognitive dysfunction (POCD) in mice. Methods Fifty-four healthy male C57BL/6 mice, aged 12-16 weeks, weighing 20-30 g, were divided into 3 groups (n=18 each) using a random number table: control group (group C), group POCD and POCD plus CB2R agonist JWH133 group (group POCD+ J). The mice were subjected to an intramedullary fixation for tibial fracture under 1.5% isoflurane anesthesia to establish POCD model.In group POCD+ J, 2 mg/kg JWH133 was injected intraperitoneally at a total volume of 10 ml/kg after emergence from anesthesia and then the injection was repeated once a day until the 7th day after surgery.Open field test was carried out on 1 day before surgery and 1, 3 and 7 days after surgery to evaluate the locomotor activity.Fear conditioning test was carried out at 15 min after completion of open field test.Mice were sacrificed at 2 h after the end of behavioral test, and the hippocampus was harvested for determination of the expression of tumor necrosis factor-alpha (TNF-α), interleukin-1beta (IL-1β), monocyte chemotactic protein-1 (MCP-1) and CB2R (by Western blot) and expression of CD11b in hippocampal tissues (by immunofluorescence). Results There was no significant difference in the total exploring distance in open field test, percentage of freezing time in contextual fear conditioning test or percentage of freezing time in tone-fear conditioning text at each time point among the three groups (P>0.05). Compared with group C, the percentage of freezing time in contextual fear conditioning test was significantly decreased, and the expression of TNF-α, IL-1β, MCP-1, CD11b and CB2R was up-regulated after surgery in group S (P<0.05). Compared with group S, the percentage of freezing time in contextual fear conditioning test was significantly increased, and the expression of TNF-α, IL-1β, MCP-1, CD11b and CB2R was down-regulated after surgery in group S+ J (P<0.05). Conclusion Activation of hippocampal CB2R may be involved in the endogenous protective mechanism of POCD in mice, and the mechanism is related to inhibiting activation of hippocampal microglia and attenuating central inflammatory responses. Key words: Receptor, cannabinoid, CB2; Cognition disorders; Postoperative complications; Hippocampus

Pre-existing weakness is critical for the occurrence of postoperative cognitive dysfunction in mice of the same age.

Occurrence of postoperative cognitive dysfunction (POCD) is age-dependent and heterogenous. Factors deciding the occurrence of POCD in patients of the same age undergone same surgeries remain unclear. Here we investigated the effects of pre-existing weakness on the occurrence of POCD in mice of the same age. Pre-existing weakness of mice was induced by intraperitoneal injection of lipopolysaccharide (8mg/kg) and was evaluated by physical frailty index (by open field test), neuroinflammation level (by Iba1 immunostaining and inflammatory factors TNF-α and IL-1β), and neuronal activity (by p-CREB immunostaining). POCD was induced by partial hepatolobectomy and was evaluated by puzzle box test and Morris water maze test. The brains were collected to detect the levels of neuroinflammation, synaptophysin and NMDA receptor subunits NR2A, NR2B and NR1 (by western blot), and oxidative stress (by Dihydroethidium). Compared to the normal adult mice of the same age, LPS pretreated mice had increased physical frailty index, higher levels of neuroinflammation, and lower neuronal activity. Partial hepatolobectomy induced obvious impairments in executive function, learning and memory in LPS pretreated mice after surgery, but not in normal mice of the same age. Partial hepatolobectomy also induced heightened neuroinflammation, obvious loss of NMDA receptor subunits, strong oxidative stress in LPS pretreated mice on the 1st and 3rd postoperative day. However, the POCD-associated pathological changes didn’t occur in normal mice of the same age after surgery. These results suggest that pre-existing weakness is critical for the occurrence of POCD in mice of the same age.

S100A8 contributes to postoperative cognitive dysfunction in mice undergoing tibial fracture surgery by activating the TLR4/MyD88 pathway.

Neuro-inflammation plays a key role in the occurrence and development of postoperative cognitive dysfunction (POCD). Although S100A8 and Toll-like receptor 4 (TLR4) have been increasingly recognized to contribute to neuro-inflammation, little is known about the interaction between S100A8 and TLR4/MyD88 signaling in the process of systemic inflammation that leads to neuro-inflammation. Firstly, we demonstrated that C57BL/6 wide-type mice exhibit cognitive deficit 24h after the tibial fracture surgery. Subsequently, increased S100A8 and S100A9 expression was found in the peripheral blood mononuclear cells (PBMCs), spleen, and hippocampus of C57BL/6 wide-type mice within 48h after the surgery. Pre-operative administration of S100A8 antibody significantly inhibited hippocampal microgliosis and improved cognitive function 24h after the surgery. Secondly, we also observed TLR4/MyD88 activation in the PBMCs, spleen, and hippocampus after the surgery. Compared with those in their corresponding wide-type mice, TLR4(-/-) and MyD88(-/-) mice showed lower immunoreactive area of microglia in the hippocampal CA3 region after operation. TLR4 deficiency also led to reduction of CD45(hi)CD11b(+) cells in the brain and better performance in both Y maze and open field test after surgery, suggesting a new regulatory mechanism of TLR4-dependent POCD. At last, the co-location of S100A8 and TLR4 expression in spleen after operation suggested a close relationship between them. On the one hand, S100A8 could induce TLR4 activation of CD11b(+) cells in the blood and hippocampus via intraperitoneal or intracerebroventricular injection. On the other hand, TLR4 deficiency conversely alleviated S100A8 protein-induced hippocampal microgliosis. Furthermore, the increased expression of S100A8 protein in the hippocampus induced by surgery sharply decreased in both TLR4 and MyD88 genetically deficient mice. Taken together, these data suggest that S100A8 exerts pro-inflammatory effect on the occurrence and development of neuro-inflammation and POCD by activating TLR4/MyD88 signaling in the early pathological process of the postoperative stage.