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

Let-7b-TLR7 Signaling Axis Contributes to the Anesthesia/Surgery-Induced Cognitive Impairment

Perioperative neurocognitive disorders (PNDs) are severe and common neurological complications among elderly patients following anesthesia and surgery. As the first line of defense of the innate immune system, Toll-like receptors (TLRs) have been found to be involved in the occurrence of neurodegenerative diseases in recent years. However, the role of TLR7 in the pathology and development of PNDs remains largely unclear. In our current study, we hypothesized that increased microRNA let-7b (let-7b) during anesthesia and surgical operation would activate TLR7 signaling pathways and mediate PNDs. Using a mouse model of PNDs, 18-20 months wild-type (WT) mice were undergoing unilateral nephrectomy, and increased TLR7 and let-7b expression levels were found in the surgery group compared with the Sham group. Of note, increased TLR7 was found to be co-localized with let-7b in the hippocampal area CA1 in the PNDs model. In addition, TLR7 and let-7b inhibition could improve hippocampus-dependent memory and attenuate the production of inflammatory cytokines. Together, our results indicated that TLR7 activation and up-regulation might be triggered by increased let-7b under stressful conditions and initiated the downstream inflammatory signaling, playing a substantial role in the development of PNDs.

The cold-inducible RNA-binding protein-Thioredoxin 1 pathway ameliorates mitochondrial dysfunction and mitochondrial dynamin-related protein 1 level in the hippocampus of aged mice with perioperative neurocognitive dysfunction

BACKGROUND

As a multi-disease model, neuroinflammation, mitochondrial dysfunction, and oxidative stress might be involved in the pathogenic process of perioperative neurocognitive dysfunction (PND). Dynamin-related protein 1 (Drp1) could mediate mitochondrial fission and play important roles in mitochondrial dynamic homeostasis and mitochondria function. The Drp1 may be involved in PND development. The cold-inducible RNA-binding protein (Cirbp) could bind to the 3'-UTR of the thioredoxin 1 (Trx1) mRNA, control oxidative stress, and improve mitochondrial function. In this study, we hypothesized that the Cirbp-Trx1 pathway could ameliorate mitochondrial dysfunction and Drp1 levels in PND mice.

METHODS

Differentially expressed genes were screened using the Gene Expression Omnibus (GEO) database GSE95426 and validated using PCR. Eighteen-month-old C57BL/6 mice were subjected to tibial fracture surgery to generate a PND model. Cirbp was upregulated by hippocampal stereotaxic injections of over-Cirbp plasmid according to the manufacturer's instructions for the in vivo DNA transfection reagent. Cirbp expression was measured using western blot (WB) and immunofluorescence (IF). The Morris water maze (MWM) was used to assess cognitive function. After behavioral testing, the hippocampal tissue was extracted to examine changes in mitochondrial Drp1, mitochondrial function, neuroinflammation, and oxidative stress.

RESULTS

Differential gene screening showed that Cirbp expression was significantly downregulated (fold change >1.5, p = 0.003272) in the PND model. In this study, we also found that Cirbp protein levels were downregulated, accompanied by an impairment of cognition, a decrease in superoxide dismutase (SOD) activity, and an increase in malondialdehyde (MDA) content, mitochondrial Drp1 levels, neuroinflammation, and apoptosis. Cirbp overexpression increased Trx1 protein levels and reversed the damage. However, this protective effect was abolished by PX-12 treatment with a Trx1 inhibitor.

CONCLUSIONS

The Cirbp-Trx1 pathway may regulate mitochondrial dysfunction and mitochondrial Drp1 expression in the hippocampus of PND mice to ameliorate cognitive dysfunction.

Unveiling the role of astrocytes in postoperative cognitive dysfunction

Alzheimer's disease (AD) is the most common neurodegenerative disorder, characterized by progressive cognitive decline and the accumulation of amyloid-beta plaques, tau tangles, and neuroinflammation in the brain. Postoperative cognitive dysfunction (POCD) is a prevalent and debilitating condition characterized by cognitive decline following neuroinflammation and oxidative stress induced by procedures. POCD and AD are two conditions that share similarities in the underlying mechanisms and pathophysiology. Compared to normal aging individuals, individuals with POCD are at a higher risk for developing AD. Emerging evidence suggests that astrocytes, the most abundant glial cells in the central nervous system, play a critical role in the pathogenesis of these conditions. Comprehensive functions of astrocyte in AD has been extensively explored, but very little is known about POCD may experience late-onset AD pathogenesis. Herein, in this context, we mainly explore the multifaceted roles of astrocytes in the context of POCD, highlighting their involvement in neuroinflammation, neurotransmitter regulation, synaptic plasticity and neurotrophic support, and discuss how POCD may augment the onset of AD. Additionally, we discuss potential therapeutic strategies targeting astrocytes to mitigate or prevent POCD, which hold promise for improving the quality of life for patients undergoing surgeries and against AD in the future.

Role and mechanism of esketamine in improving postoperative cognitive dysfunction in aged mice through the TLR4/MyD88/p38 MAPK pathway

Postoperative cognitive dysfunction (POCD) is a significant concern for the elderly population worldwide. This study explored the effects of esketamine on aged mice with POCD and investigate its mechanism of action involving the TLR4/MyD88/MAPK pathway. We administrated esketamine, along with lipopolysaccharide or anisomycin, to the aged POCD mouse models. We assessed their cognitive function using the Morris water maze test. Additionally, we evaluated histopathological changes/neuronal apoptosis in the mouse hippocampal CA1 area through HE/TUNEL stainings. Furthermore, we measured IL-1β/IL-6/TNF-α/TLR4/MyD88/MAPK (p-p38/p38) levels in mouse hippocampal tissues using ELISA/RT-qPCR/Western blotting. Lastly, we analyzed the interaction between TLR4 and MyD88 using a co-immunoprecipitation assay. Our findings showed that esketamine effectively mitigated POCD in aged mice. This was evident from the improved cognitive performance observed in the Morris water maze test, characterized by reduced escape latency/increased number of platform crossing/a higher percentage of time spent in the target quadrant. Furthermore, esketamine exhibited a protective effect against neuronal apoptosis and reduced the levels of inflammatory factors. These findings suggest that esketamine exerts an anti-inflammatory effect by downregulating TLR4/MyD88, thereby attenuating the inflammatory response associated with POCD. Additionally, esketamine suppressed the p38 MAPK pathway by inhibiting the TLR4/MyD88 signaling cascade. Esketamine demonstrated its efficacy in improving postoperative inflammation and cognitive impairment in aged mice by inhibiting the TLR4/MyD88 pathway. The activation of p38 MAPK signaling diminished the beneficial effects of esketamine in aged POCD mice. Collectively, the underlying mechanism of esketamine in mitigating POCD in aged mice involves the suppression of the TLR4/MyD88/p38 MAPK pathway.

Activation of the CD200/CD200R1 axis attenuates neuroinflammation and improves postoperative cognitive dysfunction via the PI3K/Akt/NF-κB signaling pathway in aged mice

BACKGROUND

Postoperative cognitive dysfunction (POCD) is a neurological complication occurring after anesthesia and surgery. Neuroinflammation plays a critical role in the pathogenesis of POCD, and the activation of the cluster of differentiation 200 (CD200)/CD200R1 axis improves neurological recovery in various neurological disorders by modulating inflammation. The aim of this study was to investigate the impact and underlying mechanism of CD200/CD200R1 axis on POCD in aged mice.

METHODS

The model of POCD was established in aged mice. To assess the learning and memory abilities of model mice, the Morris water maze test was implemented. CD200Fc (CD200 fusion protein), CD200R1 Ab (anti-CD200R1 antibody), and 740Y-P (a specific PI3K activator) were used to evaluate the effects of the CD200/CD200R1/PI3K/Akt/NF-κB signaling pathway on hippocampal microglial polarization, neuroinflammation, synaptic activity, and cognition in mice.

RESULTS

It was observed that anesthesia/surgery induced cognitive decline in aged mice, increased the levels of tumor necrosis factor alpha (TNF-α), interleukin (IL)-6, IL-1 β and decreased the levels of postsynaptic density protein 95 (PSD-95), synaptophysin (SYN) in the hippocampus. Moreover, CD200Fc and 740Y-P attenuated neuroinflammation and synaptic deficits and reversed cognitive impairment via the phosphatidylinositol 3-kinase (PI3K)/ protein kinase B (Akt)/nuclear factor-kappa B (NF-κB) signaling pathway, whereas CD200R1 Ab administration exerted the opposite effects. Our results further show that the CD200/CD200R1 axis modulates M1/M2 polarization in hippocampal microglia via the PI3K/Akt/NF-κB signaling pathway.

CONCLUSIONS

Our findings indicate that the activation of the CD200/CD200R1 axis reduces neuroinflammation, synaptic deficits, and cognitive impairment in the hippocampus of aged mice by regulating microglial M1/M2 polarization via the PI3K/Akt/NF-κB signaling pathway.

Neuroinflammation: The central enabler of postoperative cognitive dysfunction

The proportion of advanced age patients undergoing surgical procedures is on the rise owing to advancements in surgical and anesthesia technologies as well as an overall aging population. As a complication of anesthesia and surgery, older patients frequently suffer from postoperative cognitive dysfunction (POCD), which may persist for weeks, months or even longer. POCD is a complex pathological process involving multiple pathogenic factors, and its mechanism is yet unclear. Potential theories include inflammation, deposition of pathogenic proteins, imbalance of neurotransmitters, and chronic stress. The identification, prevention, and treatment of POCD are still in the exploratory stages owing to the absence of standardized diagnostic criteria. Undoubtedly, comprehending the development of POCD remains crucial in overcoming the illness. Neuroinflammation is the leading hypothesis and a crucial component of the pathological network of POCD and may have complex interactions with other mechanisms. In this review, we discuss the possible ways in which surgery and anesthesia cause neuroinflammation and investigate the connection between neuroinflammation and the development of POCD. Understanding these mechanisms may likely ensure that future treatment options of POCD are more effective.

Toll-Like Receptor 4 Plays a Significant Role in the Biochemical and Neurological Alterations Observed in Two Distinct Mice Models of Huntington's Disease

Toll-like receptors (TLRs) are central players in innate immunity responses. They are expressed in glial cells and neurons, and their overactivation leads to the production of proinflammatory molecules, neuroinflammation, and neural damage associated with many neurodegenerative pathologies, such as Huntington's disease (HD). HD is an inherited disorder caused by a mutation in the gene coding for the protein Huntingtin (Htt). Expression of mutated Htt (mHtt) causes progressive neuronal degeneration characterized by striatal loss of GABAergic neurons, oxidative damage, neuroinflammatory processes, and impaired motor behavior. The main animal models to study HD are the intrastriatal injection of quinolinic acid (QA) and the transgenic B6CBA-Tg (HDexon1)61Gpb/1 J mice (R6/1). Those models mimic neuronal damage and systemic manifestations of HD. The objective of this work was to study the participation of TLR4 in the manifestations of neuronal damage and HD symptoms in the two mentioned models. For this purpose, C57BL6/J and TLR4-KO mice were administered with QA, and after that motor activity, and neuronal and oxidative damages were measured. R6/1 and TLR4-KO were mated to study the effect of low expression of TLR4 on the phenotype manifestation in R6/1 mice. We found that TLR4 is involved in motor activity, and neurological and oxidative damage induced by intrastriatal injection of QA, and the low expression of TLR4 causes a delay in the onset of phenotypic manifestations by the mHtt expression in R6/1 mice. Our results show that TLR4 is involved in both models of HD and focuses then as a therapeutic target for some deleterious reactions in HD.

Stellate ganglion block alleviates postoperative cognitive dysfunction via inhibiting TLR4/NF-κB signaling pathway

Postoperative cognitive dysfunction (POCD) is common in aged patients after major surgery and is associated with increased risk of long-term morbidity and mortality. However, the underlying mechanism remains largely unknown and the clinical management of POCD is still controversial. Stellate ganglion block (SGB) is a clinical treatment for nerve injuries and circulatory issues. Recent evidence has identified the benefits of SGB in promoting learning and memory. We thus hypothesize that SGB could be effective in improving cognitive function after surgery. In present study, we established POCD model in aged rats via partial liver resection surgery. We found that the development of POCD was associated with the activation of toll-like receptor 4/nuclear factor kapa-B (TLR4/NF-κB) signaling pathway in the microglia in dorsal hippocampus, which induced the production of pro-inflammatory mediators (TNF-α, IL-1β, IL-6) and promoted neuroinflammation. More importantly, we showed evidence that preoperative treatment with SGB could inhibit microglial activation, suppress TLR4/NF-κB-mediated neuroinflammation and effectively attenuate cognitive decline after the surgery. Our study suggested that SGB may serve as a novel treatment to prevent POCD in elderly patients. As SGB is safe procedure widely used in clinic, our findings can be easily translated into clinical practice and benefit more patients.

Abdominal surgery plus sevoflurane exposure induces abnormal emotional changes and cognitive dysfunction in aged rats

BACKGROUND

Cognitive impairment, which includes perioperative psychological distress and cognitive dysfunction, can be determined by preoperative and post-operative neuropsychological tests. Several mechanisms have been proposed regarding the two-way communication between the immune system and the brain after surgery. We aimed to understand the mechanisms underlying perioperative neurocognitive disorders (PND) in elderly rats using an experimental abdominal surgery model.

METHODS

24-month-old SD rats were exposed to the abdominal surgery model (AEL) under 3% anesthesia. On day 15 and day 30 post-surgery, fractional anisotropy (FA) using diffusion kurtosis imaging (DKI) was measured. From day 25 to day 30 post-surgery, behavioral tests, including open field test (OFT), Morris water maze (MWM), novel object recognition (NOR), force swimming test (FST), and elevated plus maze (EPM), were performed. Then, the rats were euthanized to perform pathological analysis and western blot measurement.

RESULTS

The rats exposed to AEL surgical treatment demonstrated significantly decreased time crossing the platform in the MWM, decreased recognition index in the NOR, reduced time in the open arm in the EPM, increased immobility time in the FST, and increased number of crossings in the OFT. Aged rats, after AEL exposure, further demonstrated decreased FA in the mPFC, nucleus accumbens (NAc), and hippocampus, together with reduced MAP2 intensity, attenuation of GAD65, VGlut2, CHAT, and phosphorylated P38MAPK expression, and increased reactive astrocytes and microglia.

CONCLUSIONS

In this study, the aged rats exposed to abdominal surgery demonstrated both emotional changes and cognitive dysfunction, which may be associated with neuronal degeneration and reduced phosphorylated P38MAPK.

Caffeic Acid Phenethyl Ester Suppresses Oxidative Stress and Regulates M1/M2 Microglia Polarization via Sirt6/Nrf2 Pathway to Mitigate Cognitive Impairment in Aged Mice following Anesthesia and Surgery

Postoperative cognitive dysfunction (POCD) is a severe neurological complication after anesthesia and surgery. However, there is still a lack of effective clinical pharmacotherapy due to its unclear pathogenesis. Caffeic acid phenethyl ester (CAPE), which is obtained from honeybee propolis and medicinal plants, shows powerful antioxidant, anti-inflammatory, and immunomodulating properties. In this study, we aimed to evaluate whether CAPE mitigated cognitive impairment following anesthesia and surgery and its potential underlying mechanisms in aged mice. Here, isoflurane anesthesia and tibial fracture surgery were used as the POCD model, and H2O2-induced BV2 cells were established as the microglial oxidative stress model. We revealed that CAPE pretreatment suppressed oxidative stress and promoted the switch of microglia from the M1 to the M2 type in the hippocampus, thereby ameliorating cognitive impairment caused by anesthesia and surgery. Further investigation indicated that CAPE pretreatment upregulated hippocampal Sirt6/Nrf2 expression after anesthesia and surgery. Moreover, mechanistic studies in BV2 cells demonstrated that the potent effects of CAPE pretreatment on reducing ROS generation and promoting protective polarization were attenuated by a specific Sirt6 inhibitor, OSS_128167. In summary, our findings opened a promising avenue for POCD prevention through CAPE pretreatment that enhanced the Sirt6/Nrf2 pathway to suppress oxidative stress as well as favor microglia protective polarization.

Selective TLR4 Antagonism Prevents and Reverses Morphine-Induced Persistent Postoperative Cognitive Dysfunction, Dysregulation of Synaptic Elements, and Impaired BDNF Signaling in Aged Male Rats

Perioperative neurocognitive disorders (PNDs) are characterized by confusion, difficulty with executive function, and episodic memory impairment in the hours to months following a surgical procedure. Postoperative cognitive dysfunction (POCD) represents such impairments that last beyond 30 d postsurgery and is associated with increased risk of comorbidities, progression to dementia, and higher mortality. While it is clear that neuroinflammation plays a key role in PND development, what factors underlie shorter self-resolving versus persistent PNDs remains unclear. We have previously shown that postoperative morphine treatment extends POCD from 4 d (without morphine) to at least 8 weeks (with morphine) in aged male rats, and that this effect is likely dependent on the proinflammatory capabilities of morphine via activation of toll-like receptor 4 (TLR4). Here, we extend these findings to show that TLR4 blockade, using the selective TLR4 antagonist lipopolysaccharide from the bacterium Rhodobacter sphaeroides (LPS-RS Ultrapure), ameliorates morphine-induced POCD in aged male rats. Using either a single central preoperative treatment or a 1 week postoperative central treatment regimen, we demonstrate that TLR4 antagonism (1) prevents and reverses the long-term memory impairment associated with surgery and morphine treatment, (2) ameliorates morphine-induced dysregulation of the postsynaptic proteins postsynaptic density 95 and synaptopodin, (3) mitigates reductions in mature BDNF, and (4) prevents decreased activation of the BDNF receptor TrkB (tropomyosin-related kinase B), all at 4 weeks postsurgery. We also reveal that LPS-RS Ultrapure likely exerts its beneficial effects by preventing endogenous danger signal HMGB1 (high-mobility group box 1) from activating TLR4, rather than by blocking continuous activation by morphine or its metabolites. These findings suggest TLR4 as a promising therapeutic target to prevent or treat PNDs.SIGNIFICANCE STATEMENT With humans living longer than ever, it is crucial that we identify mechanisms that contribute to aging-related vulnerability to cognitive impairment. Here, we show that the innate immune receptor toll-like receptor 4 (TLR4) is a key mediator of cognitive dysfunction in aged rodents following surgery and postoperative morphine treatment. Inhibition of TLR4 both prevented and reversed surgery plus morphine-associated memory impairment, dysregulation of synaptic elements, and reduced BDNF signaling. Together, these findings implicate TLR4 in the development of postoperative cognitive dysfunction, providing mechanistic insight and novel therapeutic targets for the treatment of cognitive impairments following immune challenges such as surgery in older individuals.

Preventing postoperative cognitive dysfunction using anesthetic drugs in elderly patients undergoing noncardiac surgery: a systematic review and meta-analysis

Postoperative cognitive dysfunction (POCD) is a common neurological system disorder in surgical patients. The choice of anesthetic can potentially reduce POCD. The authors performed this network meta-analysis to compare different anesthetic drugs in reducing the incidence of POCD for elderly people undergoing noncardiac surgery. We searched MEDLINE, EMBASE, the Cochrane Library, and the Web of Science for randomized controlled trials comparing the different anesthetic drugs for noncardiac surgery in elderly from inception until July, 2022. The protocol was registered on the PROSPERO database (CRD#42020183014). A total of 34 trials involving 4314 patients undergoing noncardiac surgery in elderly were included. The incidence of POCD for each anesthetic drug was placebo (27.7%), dexmedetomidine (12.9%), ketamine (15.2%), propofol (16.8%), fentanyl (23.9%), midazolam (11.3%), sufentanil (6.3%), sevoflurane (24.0%), and desflurane (28.3%). Pairwise and network meta-analysis showed dexmedetomidine was significantly reducing the incidence of POCD when compared with placebo. Network meta-analysis also suggested dexmedetomidine was significantly reducing the incidence of POCD when compared with sevoflurane. Sufentanil and dexmedetomidine ranked the first and second in reducing the incidence of POCD with the surface under the cumulative ranking curve value of 87.4 and 81.5%. Sufentanil and dexmedetomidine had the greatest possibility to reduce the incidence of POCD for elderly people undergoing noncardiac surgery.

Postoperative Delirium in Neurosurgical Patients: Recent Insights into the Pathogenesis

Postoperative delirium (POD) is a complication characterized by disturbances in attention, awareness, and cognitive function that occur shortly after surgery or emergence from anesthesia. Since it occurs prevalently in neurosurgical patients and poses great threats to the well-being of patients, much emphasis is placed on POD in neurosurgical units. However, there are intricate theories about its pathogenesis and limited pharmacological interventions for POD. In this study, we review the recent insights into its pathogenesis, mainly based on studies within five years, and the five dominant pathological theories that account for the development of POD, with the intention of furthering our understanding and boosting its clinical management.

Effects of different types of non-cardiac surgical trauma on hippocampus-dependent memory and neuroinflammation

Background

Older individuals have been reported to suffer from cognitive disorders after surgery. Various types of surgical trauma have been used to establish postoperative cognitive dysfunction (POCD) animal models in preclinical studies. However, few comparative analyses of these animal models were conducted.

Methods

Tibial surgery, abdominal surgery, and extended abdominal surgery were performed on aged ICR mice to establish POCD models. Behavioral tests included open field, novel object recognition, fear conditioning, and Morris water maze tests. The Z-score methodology was adopted to obtain a comprehensive and integrated memory performance profile. The changes in hippocampal neuroinflammation were analyzed by ELISA, PCR, and immunofluorescence.

Results

In this study, we found that each type of non-cardiac surgical trauma has a different effects on locomotor activity. Tibial and extended abdominal surgeries led to more significant cognitive impairment than abdominal surgery. Inflammatory cytokines peaked on postoperative day 1 and decreased to control levels on days 3 and 7. Hippocampal neuroinflammation indicators between the three surgery types on postoperative day 1 had no statistical differences.

Conclusion

Overall, the type and intensity of non-cardiac surgical trauma can affect cognitive behavioral outcomes and central inflammation. The shortcomings and emerging issues of POCD animal research methods need to be further studied and solved.

Network Biology Approaches to Uncover Therapeutic Targets Associated with Molecular Signaling Pathways from circRNA in Postoperative Cognitive Dysfunction Pathogenesis

Postoperative cognitive dysfunction (POCD) is a cognitive deterioration and dementia that arise after a surgical procedure, affecting up to 40% of surgery patients over the age of 60. The precise etiology and molecular mechanisms underlying POCD remain uncovered. These reasons led us to employ integrative bioinformatics and machine learning methodologies to identify several biological signaling pathways involved and molecular signatures to better understand the pathophysiology of POCD. A total of 223 differentially expressed genes (DEGs) comprising 156 upregulated and 67 downregulated genes were identified from the circRNA microarray dataset by comparing POCD and non-POCD samples. Gene ontology (GO) analyses of DEGs were significantly involved in neurogenesis, autophagy regulation, translation in the postsynapse, modulating synaptic transmission, regulation of the cellular catabolic process, macromolecule modification, and chromatin remodeling. Pathway enrichment analysis indicated some key molecular pathways, including mTOR signaling pathway, AKT phosphorylation of cytosolic targets, MAPK and NF-κB signaling pathway, PI3K/AKT signaling pathway, nitric oxide signaling pathway, chaperones that modulate interferon signaling pathway, apoptosis signaling pathway, VEGF signaling pathway, cellular senescence, RANKL/RARK signaling pathway, and AGE/RAGE pathway. Furthermore, seven hub genes were identified from the PPI network and also determined transcription factors and protein kinases. Finally, we identified a new predictive drug for the treatment of SCZ using the LINCS L1000, GCP, and P100 databases. Together, our results bring a new era of the pathogenesis of a deeper understanding of POCD, identified novel therapeutic targets, and predicted drug inhibitors in POCD.

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.

Annexin-A1 Tripeptide Attenuates Surgery-Induced Neuroinflammation and Memory Deficits Through Regulation the NLRP3 Inflammasome

Neuroinflammation is a growing hallmark of perioperative neurocognitive disorders (PNDs), including delirium and longer-lasting cognitive deficits. We have developed a clinically relevant orthopedic mouse model to study the impact of a common surgical procedure on the vulnerable brain. The mechanism underlying PNDs remains unknown. Here we evaluated the impact of surgical trauma on the NLRP3 inflammasome signaling, including the expression of apoptosis-associated speck-like protein containing a CARD (ASC), caspase-1, and IL-1β in the hippocampus of C57BL6/J male mice, adult (3-months) and aged (>18-months). Surgery triggered ASC specks formation in CA1 hippocampal microglia, but without inducing significant morphological changes in NLRP3 and ASC knockout mice. Since no therapies are currently available to treat PNDs, we assessed the neuroprotective effects of a biomimetic peptide derived from the endogenous inflammation-ending molecule, Annexin-A1 (ANXA1). We found that this peptide (ANXA1sp) inhibited postoperative NLRP3 inflammasome activation and prevented microglial activation in the hippocampus, reducing PND-like memory deficits. Together our results reveal a previously under-recognized role of hippocampal ANXA1 and NLRP3 inflammasome dysregulation in triggering postoperative neuroinflammation, offering a new target for advancing treatment of PNDs through the resolution of inflammation.

Neuroinflammation as the Underlying Mechanism of Postoperative Cognitive Dysfunction and Therapeutic Strategies

Postoperative cognitive dysfunction (POCD) is a common neurological complication following surgery and general anesthesia, especially in elderly patients. Severe cases delay patient discharge, affect the patient’s quality of life after surgery, and are heavy burdens to society. In addition, as the population ages, surgery is increasingly used for older patients and those with higher prevalences of complications. This trend presents a huge challenge to the current healthcare system. Although studies on POCD are ongoing, the underlying pathogenesis is still unclear due to conflicting results and lack of evidence. According to existing studies, the occurrence and development of POCD are related to multiple factors. Among them, the pathogenesis of neuroinflammation in POCD has become a focus of research in recent years, and many clinical and preclinical studies have confirmed the correlation between neuroinflammation and POCD. In this article, we reviewed how central nervous system inflammation occurred, and how it could lead to POCD with changes in peripheral circulation and the pathological pathways between peripheral circulation and the central nervous system (CNS). Furthermore, we proposed some potential therapeutic targets, diagnosis and treatment strategies at the cellular and molecular levels, and clinical applications. The goal of this article was to provide a better perspective for understanding the occurrence of POCD, its development, and preventive strategies to help manage these vulnerable geriatric patients.

An Update on Postoperative Cognitive Dysfunction Following Cardiac Surgery

Postoperative cognitive dysfunction is extremely prevalent following cardiac surgery. The increasing patient age and comorbidity profile increases their susceptibility to cognitive impairment. The underlying pathophysiological mechanisms leading to cognitive impairment are not clearly elucidated. Using the contemporary literature (2015-present), this narrative review has three aims. Firstly, to provide an overview of postoperative cognitive impairment. Secondly, to analyse the predominant pathophysiological mechanisms leading to cognitive dysfunction following cardiac surgery such as inflammation, cerebral hypoperfusion, cerebral microemboli, glycaemic control and anaesthesia induced neurotoxicity. Lastly, to assess the current therapeutic strategies of interest to address these pathophysiological mechanisms, including the administration of dexamethasone, the prevention of prolonged cerebral desaturations and the monitoring of cerebral perfusion using near-infrared spectroscopy, surgical management strategies to reduce the neurological effects of microemboli, intraoperative glycaemic control strategies, the effect of volatile vs. intravenous anaesthesia, and the efficacy of dexmedetomidine.

Prophylactic Effects of Sub-anesthesia Ketamine on Cognitive Decline, Neuroinflammation, and Oxidative Stress in Elderly Mice

Cognitive dysfunction is a very common postoperative complication. The study aimed at investigating the effects of ketamine on the cognition of elderly mice after anesthesia and surgery (AS). We reported that AS impaired the cognition of elderly mice, while ketamine helped to maintain the cognitive function. Ketamine decreased the levels of TNF-α, IL-6, IL-1β and the expression of p-TAU, S100B in hippocampal induced by AS. In addition, AS triggered severe oxidative stress in hippocampal, while ketamine inhibited it. Oxidative stress induced autophagy of hippocampal neurons via inhibiting PI3K/AKT/mTOR pathway. Ketamine could activate PI3K pathway and inhibit autophagy in hippocampal, thus maintain the loss of hippocampal neurons. The study suggested that ketamine inhibited the neuroinflammation and oxidative stress, reduced the autophagy of hippocampal neurons via PI3K/AKT/mTOR pathway. It may provide novel methods for the protection of cognitive function in elderly during perioperative period.

Hypercholesterolemia and 27-Hydroxycholesterol Increase S100A8 and RAGE Expression in the Brain: a Link Between Cholesterol, Alarmins, and Neurodegeneration

Alterations in cholesterol metabolism in the brain have a major role in the physiology of Alzheimer's disease (AD). Oxysterols are cholesterol metabolites with multiple implications in memory functions and in neurodegeneration. Previous studies have shown detrimental effects of cholesterol metabolites in neurons, but its effect in glial cells is unknown. We used a high-fat/high-cholesterol diet in mice to study the effects of hypercholesterolemia over the alarmin S100A8 cascade in the hippocampus. Using CYP27Tg, a transgenic mouse model, we show that the hypercholesterolemia influence on the brain is mediated by the excess of 27-hydroxycholesterol (27-OH), a cholesterol metabolite. We also employed an acute model of 27-OH intraventricular injection in the brain to study RAGE and S100A8 response. We used primary cultures of neurons and astrocytes to study the effect of high levels of 27-OH over the S100A8 alarmin cascade. We report that a high-fat/high-cholesterol diet leads to an increase in S100A8 production in the brain. In CYP27Tg, we report an increase of S100A8 and its receptor RAGE in the hippocampus under elevated 27-OH in the brain. Using siRNA, we found that 27-OH upregulation of RAGE in astrocytes and neurons is mediated by the nuclear receptor RXRγ. Silencing RXRγ in neurons prevented 27-OH-mediated upregulation of RAGE. These results show that S100A8 alarmin and RAGE respond to high levels of 27-OH in the brain in both neurons and astrocytes through RXRγ. Our study supports the notion that 27-OH mediates detrimental effects of hypercholesterolemia to the brain via alarmin signaling.

Progress of research in postoperative cognitive dysfunction in cardiac surgery patients: A review article

BACKGROUND

Postoperative cognitive dysfunction (POCD) is a common complication of central nervous system in middle-aged and elderly patients after cardiac surgery. The purpose of this study was to review the progress in diagnosis, pathogenesis and risk factors and control strategy of POCD.

METHODS

A systematic literature search was conducted using Pubmed and EMBASE, using the Mesh terms and key words "POCD", "diagnostic criteria", "pathogenesis", "influencing factors" and "prevention strategies". Studies were retained for review after meeting strict inclusion criteria that included only prospective studies evaluating risk factors for POCD in patients who had elective cardiac surgery. Diagnosis of POCD needed to be confirmed using the Diagnostic and Statistical Manual of Montreal Cognitive Assessment (MoCA) Scale and other criteria.

RESULTS

"Twenty two articles were selected for inclusion. The incidence of POCD across the studies ranged from 9% to 54%. Multiple factors have been associated with the pathogenesis and increased risk of POCD, including neuroinflammation, dysfunction of cholinergic system, abnormal protein function (β-amyloid), old age, anesthetic, surgical and other factors."

CONCLUSIONS

POCD is a common complication after cardiac surgery in elderly. The highest POCD incidence was observed after open aortic, TAVI and CABG surgery. Age, cognitive function, depression, CPB and anesthetic use are leading risk factors. Further research is needed in determining interventions that will be effective in preventing and treating POCD in cardiac surgical setting.

miRNA-124-3p targeting of LPIN1 attenuates inflammation and apoptosis in aged male rats cardiopulmonary bypass model of perioperative neurocognitive disorders

Perioperative neurocognitive disorder (PND) is recently recommended to define the cognitive decrease during the perioperative period. However, the disease's underlying mechanisms remain unclear. MicroRNAs (miRNAs) are noncoding RNAs that play a vital role in regulating neuroregeneration and neuronal apoptosis. In this study, miR-124-3p was significantly reduced in the PND rat model after a cardiopulmonary bypass (CPB) procedure. MicroRNA-124 (miR-124)-3p-overexpressed lentivirus was constructed and injected via the intracerebroventricular method before CPB. Morris Water Maze test (WMW) and the Open-Field test (OFT) were used to measure behavior changes, data shows decline of cognitive function of rats after CPB. PND rats expressed higher Aβ and p-Tau Protein by using immunohistochemistry (IHC) analyses and Enzyme-Linked Immune Sorbent Assay (ELISA). Moreover, the results of IHC, ELISA, Western Blot analysis (WB) and Terminal-deoxynucleotidyl Transferase Mediated Nick End Labeling Assay (TUNEL) showed CPB procedure induced inflammation and apoptosis in rats with PND. The data also revealed the protective function of miR-124-3p overexpression against PND in relieving inflammation, cell apoptosis, and alleviating repaired cognitive function. Moreover, miR-124-3p was predicted by directly targeting LPIN1. This study gives a novel viewpoint that miR-124-3p could improve the state of PND via modulating LPIN1, therefore providing a new strategy for preventing and treating PND in a preclinical application.

MD2 contributes to the pathogenesis of perioperative neurocognitive disorder via the regulation of α5GABAA receptors in aged mice

BACKGROUND

Perioperative neurocognitive disorder (PND) is a long-term postoperative complication in elderly surgical patients. The underlying mechanism of PND is unclear, and no effective therapies are currently available. It is believed that neuroinflammation plays an important role in triggering PND. The secreted glycoprotein myeloid differentiation factor 2 (MD2) functions as an activator of the Toll-like receptor 4 (TLR4) inflammatory pathway, and α5GABA_A receptors (α5GABA_ARs) are known to play a key role in regulating inflammation-induced cognitive deficits. Thus, in this study, we aimed to investigate the role of MD2 in PND and determine whether α5GABA_ARs are involved in the function of MD2.

METHODS

Eighteen-month-old C57BL/6J mice were subjected to laparotomy under isoflurane anesthesia to induce PND. The Barnes maze was used to assess spatial reference learning and memory, and the expression of hippocampal MD2 was assayed by western blotting. MD2 expression was downregulated by bilateral injection of AAV-shMD2 into the hippocampus or tail vein injection of the synthetic MD2 degrading peptide Tat-CIRP-CMA (TCM) to evaluate the effect of MD2. Primary cultured neurons from brain tissue block containing cortices and hippocampus were treated with Tat-CIRP-CMA to investigate whether downregulating MD2 expression affected the expression of α5GABA_ARs. Electrophysiology was employed to measure tonic currents. For α5GABA_ARs intervention experiments, L-655,708 and L-838,417 were used to inhibit or activate α5GABA_ARs, respectively.

RESULTS

Surgery under inhaled isoflurane anesthesia induced cognitive impairments and elevated the expression of MD2 in the hippocampus. Downregulation of MD2 expression by AAV-shMD2 or Tat-CIRP-CMA improved the spatial reference learning and memory in animals subjected to anesthesia and surgery. Furthermore, Tat-CIRP-CMA treatment decreased the expression of membrane α5GABA_ARs and tonic currents in CA1 pyramidal neurons in the hippocampus. Inhibition of α5GABA_ARs by L-655,708 alleviated cognitive impairments after anesthesia and surgery. More importantly, activation of α5GABA_ARs by L-838,417 abrogated the protective effects of Tat-CIRP-CMA against anesthesia and surgery-induced spatial reference learning and memory deficits.

CONCLUSIONS

MD2 contributes to the occurrence of PND by regulating α5GABA_ARs in aged mice, and Tat-CIRP-CMA is a promising neuroprotectant against PND.

BoDV-1 infection induces neuroinflammation by activating the TLR4/MyD88/IRF5 signaling pathway, leading to learning and memory impairment in rats

Borna disease virus (BoDV-1) can infect the hippocampus and limbic lobes of newborn rodents, causing cognitive deficits and abnormal behavior. Studies have found that neuroinflammation caused by viral infection in early life can affect brain development and impair learning and memory function, revealing the important role of neuroinflammation in cognitive impairment caused by viral infection. However, there is no research to explore the pathogenic mechanism of BoDV-1 in cognition from the direction of neuroinflammation. We established a BoDV-1 infection model in rats, and tested the learning and memory impairment by Morris water maze (MWM) experiment. RNAseq was introduced to detect changes in the gene expression profile of BoDV-1 infection, focusing on inflammation factors and related signaling pathways. BoDV-1 infection impairs the learning and memory of Sprague-Dawley rats in the MWM test and increases the expression of inflammatory cytokines in the hippocampus. RNAseq analysis found 986 differentially expressed genes (DEGs), of which 845 genes were upregulated and 141 genes were downregulated, and 28 genes were found to be enriched in the toll-like receptor (TLR) pathway. The expression of TLR4, MyD88, and IRF5 in the hippocampus was significantly changed in the BoDV-1 group. Our results indicate that BoDV-1 infection stimulates TLR4/MyD88/IRF5 pathway activation, causing the release of downstream inflammatory factors, which leads to neuroinflammation in rats. Neuroinflammation may play a significant role in learning and memory impairment caused by BoDV-1 infection.

Toll-like receptor 2 activation and up-regulation by high mobility group box-1 contribute to post-operative neuroinflammation and cognitive dysfunction in mice

Post-operative cognitive dysfunction (POCD) is common and is associated with poor clinical outcome. Toll-like receptor (TLR) 3 and 4 have been implied in the development of POCD. The role of TLR2, a major brain TLR, in POCD is not clear. High mobility group box-1 (HMGB1) is a delayed inflammatory mediator and may play a role in POCD. The interaction between HMGB1 and TLRs in the perioperative period is not known. We hypothesize that TLR2 contributes to the development of POCD and that HMGB1 regulates TLR2 for this effect. To test these hypotheses, 6- to 8-week old male mice were subjected to right carotid artery exposure under isoflurane anesthesia. CU-CPT22, a TLR1/TLR2 inhibitor, at 3 mg/kg was injected intraperitoneally 30 min before surgery and 1 day after surgery. Glycyrrhizin, a HMGB1 antagonist, at 200 mg/kg was injected intraperitoneally 30 min before surgery. Mice were subjected to Barnes maze and fear conditioning tests from 1 week after surgery. Hippocampus and cerebral cortex were harvested 6 hr or 12 hr after the surgery for Western blotting, ELISA, immunofluorescent staining, and chromatin immunoprecipitation. There were neuroinflammation and impairment of learning and memory in mice with surgery. Surgery increased the expression of TLR2 and TLR4 but not TLR9 in the brain of CD-1 male mice. CU-CPT22 attenuated surgery-induced neuroinflammation and cognitive impairment. Similarly, surgery induced neuroinflammation and cognitive dysfunction in C57BL/6J mice but not in TLR2^-/- mice. TLR2 staining appeared in neurons and microglia. Surgery increased HMGB1 in the cell nuclei of the cerebral cortex and hippocampus. Glycyrrhizin ameliorated this increase and the increase of TLR2 in the hippocampus after surgery. Surgery also increased the amount of tlr2 DNA precipitated by an anti-HMGB1 antibody in the hippocampus. Our results suggest that TLR2 contributes to surgery-induced neuroinflammation and cognitive impairment. HMGB1 up-regulates TLR2 expression in the hippocampus after surgery to facilitate this contribution. Thus, TLR2 and HMGB1 are potential targets for reducing 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.

TLR4-mediated hippocampal MMP/TIMP imbalance contributes to the aggravation of perioperative neurocognitive disorder in db/db mice

Although type 2 diabetes is an important predictor of perioperative neurocognitive disorder (PND), little is currently known about its mechanism of action. Adult male db/db and db/m mice were subjected to four different treatments, including either sham or tibial fracture surgery as well as intraperitoneal injection of vehicle or TAK-242 (the selective inhibitor of TLR4) at 1, 24, and 48 h after surgery. The fear conditioning test was performed to detect cognitive impairment on post-operative day (POD) 3. The hippocampus was collected on POD 1 for western-blots and on POD 3 for western-blots, transmission electron microscopy, and electrophysiological experiments. Toll-like receptor 4 (TLR4) inhibition reversed more profound decline in the freezing behavior of db/db mice on POD 3. The surgery reduced the slope of hippocampal field excitatory postsynaptic potentials, and induced blood-brain barrier (BBB) damage in db/db mice on POD 3. The surgery also increased protein levels of TLR4, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, albumin, matrix metalloproteinase (MMP)-2, and MMP-9, and decreased protein levels of claudin-5, occludin, tissue inhibitor of matrix metalloproteinase (TIMP)-1, and TIMP-2 in the hippocampus of db/db and db/m mice. These changes were all reversed by TAK-242 treatment. At last, compared with those in post-operative db/m mice, the surgery increased protein levels of TLR4, TNF-α, and IL-1β, decreased protein levels of claudin-5 and occludin, and sustained the MMP/TIMP imbalance in the hippocampus of db/db mice on POD 3. Our results suggest that TLR4-mediated aggravated hippocampal MMP/TIMP imbalance, BBB disruption, sustained inflammatory cytokine release, and impairment of long-term potentiation play a key role in tibial fracture surgery-induced persistent PND in db/db mice.

Neuroinflammation after surgery: from mechanisms to therapeutic targets

Injury is a key driver of inflammation, a critical yet necessary response involving several mediators that is aimed at restoring tissue homeostasis. Inflammation in the central nervous system can be triggered by a variety of stimuli, some intrinsic to the brain and others arising from peripheral signals. Fine-tuned regulation of this response is crucial in a system that is vulnerable due to, for example, aging and ongoing neurodegeneration. In this context, seemingly harmless interventions like a common surgery to repair a broken limb can overwhelm the immune system and become the driver of further complications such as delirium and other perioperative neurocognitive disorders. Here, we discuss potential mechanisms by which the immune system affects the central nervous system after surgical trauma. Together, these neuroimmune interactions are becoming hallmarks of and potential therapeutic targets for multiple neurologic conditions, including those affecting the perioperative space.

NLRP3 inflammasomes are involved in the progression of postoperative cognitive dysfunction: from mechanism to treatment

Postoperative cognitive dysfunction (POCD) involves patient memory and learning decline after surgery. POCD not only presents challenges for postoperative nursing and recovery but may also cause permanent brain damage for patients, including children and the aged, with vulnerable central nervous systems. Its occurrence is mainly influenced by surgical trauma, anesthetics, and the health condition of the patient. There is a lack of imaging and experimental diagnosis; therefore, patients can only be diagnosed by clinical observation, which may underestimate the morbidity, resulting in decreased treatment efficacy. Except for symptomatic support therapy, there is a relative lack of effective drugs specific for the treatment of POCD, because the precise mechanism of POCD remains to be determined. One current hypothesis is that postoperative inflammation promotes the progression of POCD. Accumulating research has indicated that overactivation of NOD-, LRR- and pyrin domain-containing protein 3 (NLRP3) inflammasomes contribute to the POCD progression, suggesting that targeting NLRP3 inflammasomes may be an effective therapy to treat POCD. In this review, we summarize recent studies and systematically describe the pathogenesis, treatment progression, and potential treatment options of targeting NLRP3 inflammasomes in POCD patients.

Sevoflurane-induced cognitive decline in aged mice: Involvement of toll-like receptors 4

Toll-like receptors 4 (TLR4) contributes to the pathogenesis of some neurodegenerative diseases. However, little is known about whether TLR4 is associated with sevoflurane-induced cognitive decline. This investigation aims to address the effect of global TLR4 gene knockout on cognitive decline following sevoflurane exposure to mice. Wild-type and TLR4^-/- mice were exposed to 3% sevoflurane. Novel object recognition test and Y-maze test were used to analyze cognitive function. Tumor necrosis factor α (TNF-α), interleukin-1β (IL-1β) and interleukin-6 (IL-6) in plasma and hippocampus were measured by ELISA. Peripheral administration of recombinant TNF-α to TLR4^-/- mice was used to observed the role of TNF-α in cognitive function following sevoflurane. Our results showed that, in contrast to wild-type mice, TLR4 deficiency protected against the cognitive function impairment following sevoflurane exposure, and abrogated IL-1β, IL-6 and TNF-α response to sevoflurane in the system and the hippocampus. Subcutaneous administration of recombinant TNF-α elevated these cytokine levels in the hippocampus, and resulted in cognitive decline in TLR4^-/- mice exposed to sevoflurane. Taken together, our results identify the crucial role of TLR4 in sevoflurane-induced cognitive decline, and showed that TLR4 mediated pro-inflammatory cytokine response to sevoflurane, and consequent cognitive decline in aged mice exposed to sevoflurane, and imply a novel target for improvement and therapy of sevoflurane-associated cognitive decline.

Modulation of KDM1A with vafidemstat rescues memory deficit and behavioral alterations

Transcription disequilibria are characteristic of many neurodegenerative diseases. The activity-evoked transcription of immediate early genes (IEGs), important for neuronal plasticity, memory and behavior, is altered in CNS diseases and governed by epigenetic modulation. KDM1A, a histone 3 lysine 4 demethylase that forms part of transcription regulation complexes, has been implicated in the control of IEG transcription. Here we report the development of vafidemstat (ORY-2001), a brain penetrant inhibitor of KDM1A and MAOB. ORY-2001 efficiently inhibits brain KDM1A at doses suitable for long term treatment, and corrects memory deficit as assessed in the novel object recognition testing in the Senescence Accelerated Mouse Prone 8 (SAMP8) model for accelerated aging and Alzheimer’s disease. Comparison with a selective KDM1A or MAOB inhibitor reveals that KDM1A inhibition is key for efficacy. ORY-2001 further corrects behavior alterations including aggression and social interaction deficits in SAMP8 mice and social avoidance in the rat rearing isolation model. ORY-2001 increases the responsiveness of IEGs, induces genes required for cognitive function and reduces a neuroinflammatory signature in SAMP8 mice. Multiple genes modulated by ORY-2001 are differentially expressed in Late Onset Alzheimer’s Disease. Most strikingly, the amplifier of inflammation S100A9 is highly expressed in LOAD and in the hippocampus of SAMP8 mice, and down-regulated by ORY-2001. ORY-2001 is currently in multiple Phase IIa studies.

Anesthesia and surgery induce cognitive dysfunction in elderly male mice: the role of gut microbiota

It is well known that the incidence of postoperative cognitive dysfunction (POCD) is high in elderly patients. The pathogenesis and therapeutic mechanisms of POCD, however, have not yet been completely elucidated. The effects of gut microbiota, particularly in terms of regulating brain function, have gradually attracted increasing attention. In this study, we investigated the potential role of gut microbiota in POCD in aged male mice and attempted to determine whether alterations in gut microbiota would be helpful in the diagnosis of POCD. POCD and non-POCD mice were classified by hierarchical cluster analysis of behavioral results. Additionally, α- and β-diversity of gut microbiota showed a differential profile between the groups. In total, 24 gut bacteria were significantly altered in POCD mice compared with those in non-POCD mice, in which 13 gut bacteria were significantly correlated with escape latency in the Morris water maze test (MWMT). Remarkably, receiver operating characteristic curves revealed that the Dehalobacteriaceae family and Dehalobacterium genus are potentially important bacteria for the diagnosis of POCD. These findings indicate that alterations in the composition of gut microbiota are probably involved in the pathogenesis of POCD in aged mice. Novel therapeutic strategies regulating specific gut bacteria may be helpful for the prevention and treatment of POCD.

Toll-like receptor 4 deficiency ameliorates β2-microglobulin induced age-related cognition decline due to neuroinflammation in mice

Toll-like receptor 4 (TLR4) is a crucial receptor in neuroinflammation and apoptotic neuronal death, and increasing evidences indicated that β2-microglobulin (B2M) is thought to be a major contributor to age-related cognitive decline. In present study, we designed to investigate the effects of TLR4 on B2M-induced age-related cognitive decline. Wild-type (WT) C57BL/6, TLR4 knockout (TLR4 -KO) mice and hippocampal neurons from the two type mice were respectively divided into two groups: (1) Veh group; (2) B2M-treated group. The behavioral responses of mice were measured using Morris Water Maze. Hippocampal neurogenesis and neuronal damage, inflammatory response, apoptosis, synaptic proteins and neurotrophic factors, and TLR4/MyD88/NF-κB signaling pathway proteins were examined using molecular biological or histopathological methods. The results showed that WT mice received B2M in the DG exhibited age-related cognitive declines, increased TLR4 mRNA expression and high levels of interleukin-1β (IL-1β), tumor necrosis factor-alpha (TNF-α) and apoptotic neuronal death in the hippocampus, which were partially attenuated in TLR4-KO mice. Moreover, in absence of TLR4, B2M treatment improved hippocampus neurogenesis and increased synaptic related proteins. Our cell experiments further demonstrated that deletion of TLR4 could significantly increase synaptic related protein, decrease neuroinflammatory fators, inhibited apoptotic neuronal death, and regulated MyD88/NF-κB signal pathway after B2M treatment. In summary, our results support the TLR4 contributes to B2M-induced age-related cognitive decline due to neuroinflammation and apoptosis through TLR4/MyD88/NF-κB signaling pathway via a modulation of hippocampal neurogenesis and synaptic function. This may provide an important neuroprotective mechanism for improving age-related cognitive decline.

Inflammasome and Cognitive Symptoms in Human Diseases: Biological Evidence from Experimental Research

Cognitive symptoms are prevalent in the elderly and are associated with an elevated risk of developing dementia. Disease-driven changes can cause cognitive disabilities in memory, attention, and language. The inflammasome is an innate immune intracellular complex that has a critical role in the host defense system, in that it senses infectious pathogen-associated and endogenous danger-associated molecular patterns. An unbalanced or dysregulated inflammasome is associated with infectious, inflammatory, and neurodegenerative diseases. Due to its importance in such pathological conditions, the inflammasome is an emerging drug target for human diseases. A growing number of studies have revealed links between cognitive symptoms and the inflammasome. Several studies have shown that reducing the inflammasome component mitigates cognitive symptoms in diseased states. Therefore, understanding the inflammasome regulatory mechanisms may be required for the prevention and treatment of cognitive symptoms. The purpose of this review is to discuss the current understanding of the inflammasome and its relationships with cognitive symptoms in various human diseases.

Dexmedetomidine May Reduce IL-6 Level and the Risk of Postoperative Cognitive Dysfunction in Patients After Surgery: A Meta-Analysis

Dexmedetomidine (DEX) was widely used in clinical work. However, the effectiveness of DEX on postoperative cognitive dysfunction (POCD) was still need to be confirmed. The aim of this meta-analysis was to explore whether DEX can reduce the incidence of POCD on the first day and seventh postoperative day. The results showed that lower incidence of POCD associated with DEX treatment on the first (odds ratio [OR]: 0.41; 95% confidence interval [CI]: 0.31-0.54) or seventh postoperative day (OR: 0.53; 95% CI: 0.36-0.77). Mini-Mental State Examination scores on the first (mean difference [MD]: 4.67; 95% CI: 1.72-7.63) and seventh postoperative days (MD: 3.71; 95% CI: 2.51-4.90) were higher in DEX use group than that in physiological saline group. Meanwhile, neuron-specific enolase (NSE; MD: −3.99; 95% CI: −6.20 to −1.78) and interleukin 6 (IL-6) levels (MD: −17.53; 95% CI: −21.51 to −13.54) on the first postoperative day in DEX group were lower than that in the physiological saline group. This meta-analysis suggested that DEX use could reduce the risk of POCD and the reduction in levels of NSE and IL-6 can improve long-term cognitive dysfunction and anti-inflammation.

Extracellular RNAs-TLR3 signaling contributes to cognitive decline in a mouse model of postoperative cognitive dysfunction

Postoperative cognitive dysfunction (POCD) is considered a severe complication after surgery among elderly patients. Toll-like receptor 3 (TLR3) has recently been reported to play an important role in hippocampus-dependent working memory. However, the role of TLR3 in the development of POCD remains unclear. In the current study, we hypothesized that increased extracellular RNAs (exRNAs) during anesthesia and surgical operation, especially double stranded RNAs (dsRNAs), would activate TLR3 signaling pathways and mediate POCD. Using a mouse model of POCD, 20-22 months wild-type (WT) mice were undergoing unilateral nephrectomy and increased TLR3 expression levels and co-localization with neuronal and microglial cells were found in the surgery group compared with the sham group. Compared with WT mice, TLR3 knockout (KO, ^-/-) mice had improved hippocampus-dependent memory and attenuated production of inflammatory cytokines and apoptosis. Increased exRNAs and/or co-localization with TLR3 were found in both in vitro and in vivo models. Of note, TLR3/dsRNA complex inhibitor administration reduced hippocampal dsRNA level and TLR3 expression, attenuated hippocampal inflammatory cytokines production and apoptosis, and thus improved hippocampus-dependent memory. Our results indicate that exRNAs, especially dsRNAs, present under stressful conditions may trigger TLR3 activation and initiate the downstream inflammatory and apoptotic signaling, and play a substantial role in the development of POCD.

Neuroprotective effects of a Smoothened receptor agonist against postoperative cognitive dysfunction by promoting autophagy in the dentate gyrus of aged rats

Objectives: To investigate the effect of purmorphamine (PUR), a Shh co-receptor Smoothened (Smo) agonist, on postoperative cognitive dysfunction (POCD) rat models. Methods: Eighteen-month-old male Sprague-Dawley rats were subjected to intramedullary fixation of a tibial fracture with 7% chloral hydrate anesthesia to mimic human clinical surgery. PUR was administered via an intraperitoneal injection at a dose of 15mg/kg/day for 3 consecutive days at 6 h after surgery. The aged rats were sacrificed after performing a Morris water maze test 1, 3, and 7 days postoperatively to evaluate the expression of related proteins at the appointed time. Results: Compared to the POCD + vehicle group and sham + PUR group, the POCD + PUR group restored neurological deficit (P = 0.01). PUR administration induced upregulation of Shh expression on postoperative day 1 (P = 0.02), which continued on the third day (P = 0.008) but dropped by the 7th day (P = 0.03). Immunofluorescent analysis, similar to western blot analysis, showed a significant increase in the autophagy-marker LC3 (P = 0.006) as well as p62 degradation (P = 0.000) in the dentate gyrus of the aged rats (P = 0.000) after PUR treatment. Importantly, LC3 was mainly found in the presynaptic and postsynaptic membranes of the hippocampus. Conclusions: These results indicate a link between Shh and autophagy in the rat model of POCD, providing new insights into Shh signaling pathway-mediated mechanisms of neuroprotection and cognitive repair after POCD. It also provides a potential entry point for the development of clinical drugs.

Stabilization of Brain Mast Cells Alleviates LPS-Induced Neuroinflammation by Inhibiting Microglia Activation

Background

The functional aspects of mast cell-microglia interactions are important in neuroinflammation. Our previous studies have demonstrated that mast cell degranulation can directly induce microglia activation. However, the role of mast cells in Lipopolysaccharide (LPS)-induced microglia activation, neuroinflammation and cognitive impairment has not been clarified.

Methods

This study investigated the interaction between brain microglia and mast cells in vivo through site-directed injection of cromolyn into rat right hypothalamus using stereotaxic techniques. Cognitive function was subsequently assessed using trace fear conditioning and Y maze tests. Mast cells in rat brain were stained with toluidine blue and counted using Cell D software. Microglia activation was assessed by Iba1 immunohistochemistry both in rat brain and in mast cell-deficient Kit^W-sh/W-sh mice. Receptor expression in rat microglia was determined using flow cytometry analysis. Cytokine levels in rat brain tissue and cell supernatant were measured using high-throughput ELISA. Western blotting was used to analyze Cell signaling proteins.

Results

In this study, intraperitoneal injection of 1 mg/kg LPS induced mast cell activation in hypothalamus and cognitive dysfunction in rats, and that this process can be repressed by the mast cell stabilizer cromolyn (200 μg). Meanwhile, in mice, LPS IP injection induced significant microglia activation 24 h later in the hypothalamus of wild-type (WT) mice, but had little effect in Kit^W-sh/W-sh mice. The stabilization of mast cells in rats inhibited LPS-induced microglia activation, inflammatory factors release, and the activation of MAPK, AKT, and NF-κB signaling pathways. We also found that LPS selectively provokes upregulation of H₁R, H₄R, PAR2, and TLR4, but downregulation of H₂R and H₃R, in ipsilateral hypothalamus microglia; these effects were partially inhibited by cromolyn. In addition, LPS was also found to induce activation of P815 cells in vitro, consistent with findings from in vivo experiments. These activated P815 cells also induced cytokine release from microglia, which was mediated by the MAPK signaling pathway.

Conclusion

Taken together, our results demonstrate that stabilization of mast cells can inhibit LPS-induced neuroinflammation and memory impairment, suggesting a novel treatment strategy for neuroinflammation-related diseases.

MicroRNA-146a protects against cognitive decline induced by surgical trauma by suppressing hippocampal neuroinflammation in mice

Postoperative cognitive dysfunction (POCD) is a common postoperative complication that is associated with increased morbidity and mortality. However, the neuropathogenesis of this complication remains largely unknown. Neuroinflammation, in particular hippocampal inflammation, contributes to POCD. Recently, increasing evidence has supported the involvement of microRNAs (miRNAs) in the regulation of neuroinflammation in human neurological disorders. In the present study, we investigated the role of miR-146a, a key regulator of the innate immune response, in surgery-induced hippocampal inflammation and cognitive impairment. The expression of miR-146a was measured in BV-2 microglial cells stimulated with lipopolysaccharide (LPS) and hippocampal tissues of mice with POCD. Loss of function and overexpression studies were performed via transfection with miR-146a mimic/inhibitor in cultured BV-2 cell lines and intrahippocampal injection of miR-146a agomir/antagomir before surgery/anesthesia to identify the role of miR-146a in neuroinflammation and cognitive impairment. QPCR, Western blot and ELISA were used to determine the expression levels of downstream adaptor proteins and proinflammatory cytokines. Immunofluorescence staining was applied to evaluate the activation of microglia. Increased expression of miR-146a was observed in BV-2 microglial cells stimulated with LPS and hippocampal tissues of mice with POCD. Modulation of miR-146a expression via transfection of microglia with miR-146a mimic or inhibitor regulated the mRNA and protein expression levels of downstream targets of miR-146a (IRAK1 and TRAF6) as well as the release of proinflammatory cytokines (TNF-α, IL-1β and IL-6). In addition, overexpression of miR-146a attenuated hippocampus-dependent learning and memory impairment in mice with POCD, which was accompanied by decreased expression of the IRAK1/TRAF6/nuclear factor (NF)-κB pathway and downregulation of microglial activation in the hippocampus. Conversely, knockdown of miR-146a expression may exacerbate hippocampus-dependent learning and memory deficiency and hippocampal inflammation in mice with POCD. Collectively, our findings demonstrate the important role of miR-146a in the neuropathogenesis of POCD and suggest that miR-146a may be a potential therapeutic target for POCD.

Preoperative Sleep Disturbance Exaggerates Surgery-Induced Neuroinflammation and Neuronal Damage in Aged Mice

Postoperative cognitive dysfunction (POCD) is defined as new cognitive impairment (memory impairment and impaired performance) after surgery, especially in aged patients. Sleep disturbance is a common phenomenon before surgery that has been increasingly thought to affect patient recovery. However, little is known about the functional impact of preoperative sleep disturbance on POCD. Here, we showed that tibial fracture surgery induced cognitive deficit and production of proinflammatory cytokines interleukin-6 (IL-6) and IL-1β, along with microglia and astrocyte activation, neuronal damage, and blood-brain barrier (BBB) disruption. Preoperative sleep disturbance enhanced the surgery-induced neuroinflammation, neuronal damage, BBB disruption, and memory impairment 24 h after surgery. Taken together, these results demonstrated that preoperative sleep disturbance aggravated postoperative cognitive function in aged mice and the mechanism may be related to central nervous system (CNS) inflammation and neuronal damage.

Effects of Memantine in a Mouse Model of Postoperative Cognitive Dysfunction

Persistent impairment in cognitive functioning postoperatively is reported by clinical and animal studies, and is labeled as postoperative cognitive dysfunction (POCD). Evidence points to an exaggerated neuroinflammatory response resulting from peripheral systemic inflammation after surgery, with subsequent cytokine-induced glutamatergic excitotoxicity and synaptic impairment. These immunological changes, among many others, are also observed in Alzheimer’s disease. Memantine is an N-methyl-D-aspartate receptor (NMDAR) antagonist commonly used to treat Alzheimer’s disease. Surprisingly, little research exists on the role of memantine in preventing POCD. The purpose of this study is to investigate the effects of memantine on a spectrum of cognitive functions postoperatively. Mice were divided into 3 groups and each received treatment for 4 weeks. Placebo groups received a placebo then underwent either a sham procedure or a laparotomy procedure. The memantine group received memantine hydrochloride then underwent a laparotomy procedure. Cognitive tests were performed on postoperative days (POD) 1 and 7. Compared to sham-operated mice, placebo groups that underwent a laparotomy procedure showed impaired memory in the Morris water maze test, higher anxiety-like behavior in the open field and the elevated plus maze tests, increased depression-like behavior in the tail suspension test, and lack of preference for social novelty in the three-chamber test. On the other hand, memantine-treated mice that underwent a laparotomy procedure showed enhanced memory on POD7, improved depression-like behavior on POD1 and POD7, enhanced preference for social novelty on POD1, and no improvement in anxiety-like behavior. These findings suggest a potential protective effect of memantine in mice postoperatively on memory, depression-like behavior, and preference for social novelty.

Surgery, neuroinflammation and cognitive impairment

Trauma experienced during surgery can contribute to the development of a systemic inflammatory response that can cause multi-organ dysfunction or even failure. Post-surgical neuroinflammation is a documented phenomenon that results in synaptic impairment, neuronal dysfunction and death, and impaired neurogenesis. Various pro-inflammatory cytokines, such as TNFα, maintain a state of chronic neuroinflammation, manifesting as post-operative cognitive dysfunction and post-operative delirium. Furthermore, elderly patients with post-operative cognitive dysfunction or delirium are three times more likely to experience permanent cognitive impairment or dementia. We conducted a narrative review, considering evidence extracted from various databases including Pubmed, MEDLINE and EMBASE, as well as journals and book reference lists. We found that further pre-clinical and well-powered clinical studies are required to delineate the precise pathogenesis of post-operative delirium and cognitive dysfunction. Despite the burden of post-operative neurological sequelae, clinical studies investigating therapeutic agents, such as dexmedetomidine, ibuprofen and statins, have yielded conflicting results. In addition, evidence supporting novel therapeutic avenues, such as nicotinic and HMGB-1 targeting and remote ischaemic pre-conditioning, is limited and necessitates further investigation.

The neurotoxicity induced by PM2.5 might be strongly related to changes of the hippocampal tissue structure and neurotransmitter levels

Objective: The complex components of PM2.5 including metal elements transported through the blood brain barrier could induce nervous system damage. This study discusses the relationship between rats' learning and memory and changes in the hippocampal neuron histomorphology and neurotransmitter levels induced by PM2.5 exposure. Methods: Male rats were treated with different concentrations of PM2.5 by tracheal perfusion once per week for up to 12 weeks. After the rats were sacrificed, the main metal element contents (Al, Pb, Cu, Mn, As, Cr, Cd, and Ni) of the blood and whole hippocampus, levels of neurotransmitters released in the whole hippocampus and relative receptors, and changes in the hippocampal structure were detected. Results: The results showed that PM2.5 significantly reduced the cognitive learning abilities of rats. PM2.5 exposure increased the contents of hippocampal lead, manganese, and aluminum. The level of glutamic acid was increased in the hippocampal tissues of the 20 mg kg-1 group, in combination with the decreased N-methyl-d-aspartate glutamate receptor (NMDAR) and increased metabotropic glutamate receptor type1 (mGluR1) expression. Increased clearance, a mild disorder of arrangement, and mild edema could be observed in the rat hippocampal neurons treated with PM2.5. Conclusion: PM2.5-induced defects in learning and memory may be related to the morphological abnormalities of the hippocampus and the abnormal expression of neurotransmitters and their receptors.

Ulinastatin May Significantly Improve Postoperative Cognitive Function of Elderly Patients Undergoing Spinal Surgery by Reducing the Translocation of Lipopolysaccharide and Systemic Inflammation

Background: Studies have shown that perioperative inflammatory response is one of the important factors that caused postoperative cognitive dysfunction (POCD). Ulinastatin is a broad-spectrum protease inhibitor that inhibits inflammatory. We investigated the effects of ulinastatin on inflammatory response and early postoperative cognitive function in elderly patients undergoing spinal surgery.

Methods: This clinical trial was approved by the Xuanwu Hospital Ethical Committee (Registration number: ChiCTR-IPR-16008931). Sixty elderly patients undergoing elective spinal surgery with American Society of Anesthesiologists (ASA) status of I–II were randomized into ulinastatin and control groups; total intravenous anesthesia was performed. The elderly patients in ulinastatin group underwent intravenous infusion of ulinastatin 10,000 units/kg following anesthesia induction and before surgical incision, and 5000 units/kg on post-operative days 1 and 2. Cognitive function was determined with Montreal Cognitive Assessment (MOCA) test preoperatively and on post-operative day 7 by a neurologist. Serum lipopolysaccharide (LPS), interleukin-6 (IL-6), C-reactive protein (CRP), and matrix metalloprotease-9 (MMP-9) concentration levels were measured at baseline, the end of surgery, and on post-operative days 1 and 3.

Results: All elderly patients completed the study. Ulinastatin infusion significantly reduced the incidence of POCD in elderly patients undergoing spine surgery (ulinastatin group 16% vs. control group 43%, χ² = 5.079, P = 0.024, P < 0.05). The elderly patients in ulinastatin group exhibited lower serum LPS, IL-6, CRP, and MMP-9 concentrations, as well as a shortened peak value duration, compared with those in the control group following surgery (P < 0.05).

Conclusion: Systemic inflammation and translocation of LPS were inhibited by the infusion of ulinastatin in elderly patients undergoing spinal surgery. The anti-inflammation intervention with ulinastatin can significantly improve the elderly patients’ postoperative cognitive function.

Microarray Expression Profiles of lncRNAs and mRNAs in Postoperative Cognitive Dysfunction

Postoperative cognitive dysfunction (POCD) is serious disorder in the central nervous system common in aged patients after anesthesia. Although its clinical symptoms are well recognized, however, the molecular etiology of the POCD remains unrevealed. Similarly, neither gold standard molecular diagnosis nor effective treatment is available for POCD until the present. Therefore, we aimed to explore the molecular mechanism of this disorder through investigating lncRNAs and mRNAs associated with POCD human patients and investigate their underlying regulatory pathways. In this study, we recruited 200 patients requiring hip or knee replacement surgery. Their neurological functions were assessed at two time points, 1 day before the surgery and 30 days post-surgery. In parallel, serum samples were collected from the participants to analyze lncRNAs and mRNAs differential expression profile between POCD and non-POCD patients using microarray analysis. To further investigate the role differentially expressed mRNA and lncRNAs, Gene Ontology (GO), pathway analyses on mRNAs and lncRNA-mRNA interaction network were performed. As a result, 68 lncRNAs and 115 mRNAs were dysregulated in the POCD group compared to non-POCD group. Among them, the top 10 upregulated lncRNAs and 10 downregulated lncRNAs were listed for enrichment analysis. Interestingly, we found that these lncRNA and mRNA are involved in biological process, molecular function, and cellular component in addition to various signaling pathways, suggesting that the pathogenesis of POCD involves lncRNAs and mRNAs differential expression. Consequently, the genetic dysregulation between the non-POCD and POCD patients participates in the occurrence and development of POCD, and could be served as diagnostic biomarkers and drug targets for POCD treatment.