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.

Itaconate alleviates anesthesia/surgery-induced cognitive impairment by activating a Nrf2-dependent anti-neuroinflammation and neurogenesis via gut-brain axis.

BACKGROUND: Postoperative cognitive dysfunction (POCD) is a common neurological complication of anesthesia and surgery in aging individuals. Neuroinflammation has been identified as a hallmark of POCD. However, safe and effective treatments of POCD are still lacking. Itaconate is an immunoregulatory metabolite derived from the tricarboxylic acid cycle that exerts anti-inflammatory effects by activating the nuclear factor erythroid 2-related factor 2 (Nrf2) pathway. In this study, we investigated the effects and underlying mechanism of 4-octyl itaconate (OI), a cell-permeable itaconate derivative, on POCD in aged mice. METHODS: A POCD animal model was established by performing aseptic laparotomy in 18-month-old male C57BL/6 mice under isoflurane anesthesia while maintaining spontaneous ventilation. OI was intraperitoneally injected into the mice after surgery. Primary microglia and neurons were isolated and treated to lipopolysaccharide (LPS), isoflurane, and OI. Cognitive function, neuroinflammatory responses, as well as levels of gut microbiota and their metabolites were evaluated. To determine the mechanisms underlying the therapeutic effects of OI in POCD, ML385, an antagonist of Nrf2, was administered intraperitoneally. Cognitive function, neuroinflammatory responses, endogenous neurogenesis, neuronal apoptosis, and Nrf2/extracellular signal-related kinases (ERK) signaling pathway were evaluated. RESULTS: Our findings revealed that OI treatment significantly alleviated anesthesia/surgery-induced cognitive impairment, concomitant with reduced levels of the neuroinflammatory cytokines IL-1ß and IL-6, as well as suppressed activation of microglia and astrocytes in the hippocampus. Similarly, OI treatment inhibited the expression of IL-1ß and IL-6 in LPS and isoflurane-induced primary microglia in vitro. Intraperitoneal administration of OI led to alterations in the gut microbiota and promoted the production of microbiota-derived metabolites associated with neurogenesis. We further confirmed that OI promoted endogenous neurogenesis and inhibited neuronal apoptosis in the hippocampal dentate gyrus of aged mice. Mechanistically, we observed a decrease in Nrf2 expression in hippocampal neurons both in vitro and in vivo, which was reversed by OI treatment. We found that Nrf2 was required for OI treatment to inhibit neuroinflammation in POCD. The enhanced POCD recovery and promotion of neurogenesis triggered by OI exposure were, at least partially, mediated by the activation of the Nrf2/ERK signaling pathway. CONCLUSIONS: Our findings demonstrate that OI can attenuate anesthesia/surgery-induced cognitive impairment by stabilizing the gut microbiota and activating Nrf2 signaling to restrict neuroinflammation and promote neurogenesis. Boosting endogenous itaconate or supplementation with exogenous itaconate derivatives may represent novel strategies for the treatment of POCD.

Post-operative cognitive dysfunction is exacerbated by high-fat diet via TLR4 and prevented by dietary DHA supplementation.

Post-operative cognitive dysfunction (POCD) is an abrupt decline in neurocognitive function arising shortly after surgery and persisting for weeks to months, increasing the risk of dementia diagnosis. Advanced age, obesity, and comorbidities linked to high-fat diet (HFD) consumption such as diabetes and hypertension have been identified as risk factors for POCD, although underlying mechanisms remain unclear. We have previously shown that surgery alone, or 3-days of HFD can each evoke sufficient neuroinflammation to cause memory deficits in aged, but not young rats. The aim of the present study was to determine if HFD consumption before surgery would potentiate and prolong the subsequent neuroinflammatory response and memory deficits, and if so, to determine the extent to which these effects depend on activation of the innate immune receptor TLR4, which both insults are known to stimulate. Young-adult (3mo) & aged (24mo) male F344xBN F1 rats were fed standard chow or HFD for 3-days immediately before sham surgery or laparotomy. In aged rats, the combination of HFD and surgery caused persistent deficits in contextual memory and cued-fear memory, though it was determined that HFD alone was sufficient to cause the long-lasting cued-fear memory deficits. In young adult rats, HFD + surgery caused only cued-fear memory deficits. Elevated proinflammatory gene expression in the hippocampus of both young and aged rats that received HFD + surgery persisted for at least 3-weeks after surgery. In a separate experiment, rats were administered the TLR4-specific antagonist, LPS-RS, immediately before HFD onset, which ameliorated the HFD + surgery-associated neuroinflammation and memory deficits. Similarly, dietary DHA supplementation for 4 weeks prior to HFD onset blunted the neuroinflammatory response to surgery and prevented development of persistent memory deficits. These results suggest that HFD 1) increases risk of persistent POCD-associated memory impairments following surgery in male rats in 2) a TLR4-dependent manner, which 3) can be targeted by DHA supplementation to mitigate development of persistent POCD.

SS-31 inhibits mtDNA-cGAS-STING signaling to improve POCD by activating mitophagy in aged mice.

BACKGROUND: Neuroinflammation is crucial in the development of postoperative cognitive dysfunction (POCD), and microglial activation is an active participant in this process. SS-31, a mitochondrion-targeted antioxidant, is widely regarded as a potential drug for neurodegenerative diseases and inflammatory diseases. In this study, we sought to explore whether SS-31 plays a neuroprotective role and the underlying mechanism. METHODS: Internal fixation of tibial fracture was performed in 18-month-old mice to induce surgery-associated neurocognitive dysfunction. LPS was administrated to BV2 cells to induce neuroinflammation. Neurobehavioral deficits, hippocampal injury, protein expression, mitophagy level and cell state were evaluated after treatment with SS-31, PHB2 siRNA and an STING agonist. RESULTS: Our study revealed that SS-31 interacted with PHB2 to activate mitophagy and improve neural damage in surgically aged mice, which was attributed to the reduced cGAS-STING pathway and M1 microglial polarization by decreased release of mitochondrial DNA (mtDNA) but not nuclear DNA (nDNA). In vitro, knockdown of PHB2 and an STING agonist abolished the protective effect of SS-31. CONCLUSIONS: SS-31 conferred neuroprotection against POCD by promoting PHB2-mediated mitophagy activation to inhibit mtDNA release, which in turn suppressed the cGAS-STING pathway and M1 microglial polarization.

C8-ceramide modulates microglia BDNF expression to alleviate postoperative cognition dysfunction via PKCδ/NF-κB signaling pathway.

Postoperative cognitive dysfunction (POCD) is a kind of serious postoperative complication in surgery with general anesthesia and it may affect patients' normal lives. Activated microglia are thought to be one of the key factors in the regulation of POCD process. Once activated, resident microglia change their phenotype and secrete kinds of cytokines to regulate inflammatory response in tissues. Among these secretory factors, brain-derived neurotrophic factor (BDNF) is considered to be able to inhibit inflammation response and protect nervous system. Therefore, the enhancement of BDNF expression derived from resident microglia is suggested to be potential treatment for POCD. In our study, we focused on the role of C8-ceramide (a kind of interventional drug) and assessed its regulatory effect on improving the expression of BDNF secreted from microglia to treat POCD. According to the results of our study, we observed that C8-ceramide stimulated primary microglia to up-regulate the expression of BDNF mRNA after being treated with lipopolysaccharide (LPS) in vitro. We proved that C8-ceramide had ability to effectively improve POCD of mice after being accepted carotid artery exposure and their abnormal behavior recovered better than that of mice from the surgery group. Furthermore, we also demonstrated that C8-ceramide enhanced the cognitive function of mice via the PKCδ/NF-κB signaling pathway. In general, our study has confirmed a potential molecular mechanism that led to the occurrence of POCD caused by surgery and provided a new clinical strategy to treat POCD.

Impaired synaptic plasticity and decreased glutamatergic neuron excitability induced by SIRT1/BDNF downregulation in the hippocampal CA1 region are involved in postoperative cognitive dysfunction.

BACKGROUND: Postoperative cognitive dysfunction (POCD) is a common complication after anesthesia/surgery, especially among elderly patients, and poses a significant threat to their postoperative quality of life and overall well-being. While it is widely accepted that elderly patients may experience POCD following anesthesia/surgery, the exact mechanism behind this phenomenon remains unclear. Several studies have indicated that the interaction between silent mating type information regulation 2 homologue 1 (SIRT1) and brain-derived neurotrophic factor (BDNF) is crucial in controlling cognitive function and is strongly linked to neurodegenerative disorders. Hence, this research aims to explore how SIRT1/BDNF impacts cognitive decline caused by anesthesia/surgery in aged mice. METHODS: Open field test (OFT) was used to determine whether anesthesia/surgery affected the motor ability of mice, while the postoperative cognitive function of 18 months old mice was evaluated with Novel object recognition test (NORT), Object location test (OLT) and Fear condition test (FC). The expressions of SIRT1 and other molecules were analyzed by western blot and immunofluorescence staining. The hippocampal synaptic plasticity was detected by Golgi staining and Long-term potentiation (LTP). The effects of SIRT1 and BDNF overexpression as well as chemogenetic activation of glutamatergic neurons in hippocampal CA1 region of 18 months old vesicular glutamate transporter 1 (VGLUT1) mice on POCD were further investigated. RESULTS: The research results revealed that older mice exhibited cognitive impairment following intramedullary fixation of tibial fracture. Additionally, a notable decrease in the expression of SIRT1/BDNF and neuronal excitability in hippocampal CA1 glutamatergic neurons was observed. By increasing levels of SIRT1/BDNF or enhancing glutamatergic neuron excitability in the CA1 region, it was possible to effectively mitigate synaptic plasticity impairment and ameliorate postoperative cognitive dysfunction. CONCLUSIONS: The decline in SIRT1/BDNF levels leading to changes in synaptic plasticity and neuronal excitability in older mice could be a significant factor contributing to cognitive impairment after anesthesia/surgery.

Smad7 in the hippocampus contributes to memory impairment in aged mice after anesthesia and surgery.

BACKGROUND: Postoperative cognitive dysfunction (POCD) is a common neurological complication following anesthesia and surgery. Increasing evidence has demonstrated that neuroinflammation caused by systemic inflammatory responses during the perioperative period is a key factor in the occurrence of POCD. In addition, SMAD family member 7 (Smad7) has been confirmed to play vital roles in the pathogenesis and treatment of inflammatory diseases, such as inflammatory bowel disease. However, whether Smad7 participates in the regulatory process of neuroinflammation and apoptosis in the development of POCD is still unknown. METHODS: In this study, a POCD mouse model was constructed by unilateral nephrectomy under anesthesia, and cognitive function was assessed using the fear conditioning test and open field test. The expression of Smad7 at the mRNA and protein levels in the hippocampus 3 days after surgery was examined by qRT-PCR, western blot and immunofluorescence assays. Furthermore, to identify whether the elevation of Smad7 in the hippocampus after unilateral nephrectomy contributes to cognitive impairment, the expression of Smad7 in the hippocampal CA1 region was downregulated by crossing Smad7fl/fl conditional mutant mice and CaMKIIα-Cre line T29-1 transgenic mice or stereotaxic injection of shRNA-Smad7. Inflammation and apoptosis in the hippocampus were assessed by measuring the mRNA levels of typical inflammatory cytokines, including TNF-α, IL-1ß, IL-6, CCL2, CXCL1, and CXCL2, and the protein levels of apoptotic proteins, including Bax and Bcl2. In addition, apoptosis in the hippocampus postoperation was investigated by a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining assay. Finally, western blotting was used to explore how Smad7 mediates inflammation and apoptosis postoperation. RESULTS: The results unequivocally revealed that elevated Smad7 in the hippocampal CA1 region significantly inhibited TGF-ß signal transduction by blocking Smad2/3 phosphorylation, which enhanced neuroinflammation and apoptosis in the hippocampus and further led to learning and memory impairment after surgery. CONCLUSIONS: Our results revealed that Smad7 contributes to cognitive impairment after surgery by enhancing neuroinflammation and apoptosis in the hippocampus and might serve as a promising therapeutic target for the treatment of memory impairment after anesthesia surgery.

Tregs dysfunction aggravates postoperative cognitive impairment in aged mice.

OBJECTIVES: Enhanced neuroinflammation is an important mechanism underlying perioperative neurocognitive disorders. Regulatory T cells (Tregs) play a crucial role in regulating systemic immune responses. The present study was aimed to investigate the participation of Tregs in the development of postoperative cognitive dysfunction (POCD). METHODS: Surgery-associated neurocognitive disorder was induced in 18-month-old mice subjected to internal fixation of tibial fracture. Morris water maze was used to examine mice cognitive function. Splenic Tregs were collected for RNA sequencing and flow cytometry. Levels of inflammatory factors in the circulation and hippocampus were measured by enzyme-linked immunosorbent assay. Protein presences of tight junction proteins were detected by immunofluorescence. RESULTS: Surgery of internal fixation of tibial fracture induced cognitive impairment in aged mice, accompanied by elevated plasma levels of inflammatory factors and increased circulating Tregs. Transfusion of Tregs from young mice partially restored the structure of the blood-brain barrier and alleviated POCD in aged mice. Compared with young Tregs, differentially expressed genes in aged Tregs were enriched in tumor necrosis factor (TNF) signaling pathway and cytokine-cytokine receptor interaction. Flow cytometry revealed that aged Tregs had blunted functions under basal and stimulated conditions. Blockade of the CD25 epitope protected the blood-brain barrier structure, reduced TNF-α levels in the hippocampus, and improved surgery-associated cognition in aged mice. CONCLUSIONS: Blocking peripheral regulatory T cells improves surgery-induced cognitive function in aged mice. Therefore, aged Tregs play an essential role in the occurrence of POCD.

Neuronal-specific TNFAIP1 ablation attenuates postoperative cognitive dysfunction via targeting SNAP25 for K48-linked ubiquitination.

BACKGROUND: Synaptosomal-associated protein 25 (SNAP25) exerts protective effects against postoperative cognitive dysfunction (POCD) by promoting PTEN-induced kinase 1 (PINK1)/Parkin-mediated mitophagy and repressing caspase-3/gasdermin E (GSDME)-mediated pyroptosis. However, the regulatory mechanisms of SNAP25 protein remain unclear. METHODS: We employed recombinant adeno-associated virus 9 (AAV9)-hSyn to knockdown tumor necrosis factor α-induced protein 1 (TNFAIP1) or SNAP25 and investigate the role of TNFAIP1 in POCD. Cognitive performance, hippocampal injury, mitophagy, and pyroptosis were assessed. Co-immunoprecipitation (co-IP) and ubiquitination assays were conducted to elucidate the mechanisms by which TNFAIP1 stabilizes SNAP25. RESULTS: Our results demonstrated that the ubiquitin ligase TNFAIP1 was upregulated in the hippocampus of mice following isoflurane (Iso) anesthesia and laparotomy. The N-terminal region (residues 1-96) of TNFAIP1 formed a conjugate with SNAP25, leading to lysine (K) 48-linked polyubiquitination of SNAP25 at K69. Silencing TNFAIP1 enhanced SH-SY5Y cell viability and conferred antioxidant, pro-mitophagy, and anti-pyroptosis properties in response to Iso and lipopolysaccharide (LPS) challenges. Conversely, TNFAIP1 overexpression reduced HT22 cell viability, increased reactive oxygen species (ROS) accumulation, impaired PINK1/Parkin-dependent mitophagy, and induced caspase-3/GSDME-dependent pyroptosis by suppressing SNAP25 expression. Neuron-specific knockdown of TNFAIP1 ameliorated POCD, restored mitophagy, and reduced pyroptosis, which was reversed by SNAP25 depletion. CONCLUSIONS: In summary, our findings demonstrated that inhibiting TNFAIP1-mediated degradation of SNAP25 might be a promising therapeutic approach for mitigating postoperative cognitive decline. Video Abstract.

TAK1 Reduces Surgery-induced Overactivation of RIPK1 to Relieve Neuroinflammation and Cognitive Dysfunction in Aged Rats.

BACKGROUND: Postoperative cognitive dysfunction (POCD) is a common clinical complication in elderly patients, but its underlying mechanism remains unclear. Receptor-interacting protein kinase 1 (RIPK1), a key molecule mediating necroptosis and regulated by transforming growth factor ß-activated kinase 1 (TAK1), was reported to be associated with cognitive impairment in several neurodegenerative diseases. This study was conducted to investigate the possible role of TAK1/RIPK1 signalling in POCD development following surgery in rats. METHODS: Young (2-month-old) and old (24-month-old) Sprague-Dawley rats were subjected to splenectomy under isoflurane anaesthesia. The young rats were treated with the TAK1 inhibitor takinib or the RIPK1 inhibitor necrostatin-1 (Nec-1) before surgery, and old rats received adeno-associated virus (AAV)-TAK1 before surgery. The open field test and contextual fear conditioning test were conducted on postoperative day 3. The changes in TNF-α, pro-IL-1ß, AP-1, NF-κB p65, pRIPK1, pTAK1 and TAK1 expression and astrocyte and microglia activation in the hippocampus were assessed. RESULTS: Old rats had low TAK1 expression and were more susceptible to surgery-induced POCD and neuroinflammation than young rats. TAK1 inhibition exacerbated surgery-induced pRIPK1 expression, neuroinflammation and cognitive dysfunction in young rats, and this effect was reversed by a RIPK1 inhibitor. Conversely, genetic TAK1 overexpression attenuated surgery-induced pRIPK1 expression, neuroinflammation and cognitive dysfunction in old rats. CONCLUSION: Ageing-related decreases in TAK1 expression may contribute to surgery-induced RIPK1 overactivation, resulting in neuroinflammation and cognitive impairment in old rats.

The m6A Reader YTHDF1 Improves Sevoflurane-Induced Neuronal Pyroptosis and Cognitive Dysfunction Through Augmenting CREB-BDNF Signaling.

Sevoflurane is one of the most widely used anesthetics in surgery which is the main cause of postoperative cognitive dysfunction (POCD). Previous reports confirmed that YTHDF1 is differently expressed in sevoflurane-induced POCD, while the roles and mechanistic details remain unclear. The molecular expressions were assessed using qRT-PCR, western blot, immunofluorescence and immunohistochemistry. Pathological change in the hippocampus tissues was analyzed using HE staining. Cognitive ability in rats was measured using MWM test. Hippocampal neuronal viability and apoptosis were measured by MTT assay and flow cytometry, respectively. The levels of pro-inflammatory cytokines were assessed using ELISA. The interaction between YTHDF1 and CREB was analyzed by RNA immunoprecipitation assay. YTHDF1 was significantly decreased in hippocampus tissues by sevoflurane exposure, and its overexpression could improve sevoflurane-induced neuron damage and cognitive dysfunction. Meanwhile, YTHDF1 upregulation repressed sevoflurane-induced activation of NLRP3 inflammation and pyroptosis in hippocampus tissues. Subsequently, YTHDF1 directly interacted to CREB mRNA to augment its stability and translation via a m6A-dependent manner, thus activating CREB/BDNF pathway. In addition, the inactivation of CREB/BDNF pathway could reverse the protective effects of YTHDF1 overexpression on sevoflurane-mediated neuronal damage and pyroptosis. These findings revealed that YTHDF1 improved sevoflurane-induced neuronal pyroptosis and cognitive dysfunction through activating CREB-BDNF signaling.

taVNS Alleviates Sevoflurane-Induced Cognitive Dysfunction in Aged Rats Via Activating Basal Forebrain Cholinergic Neurons.

Postoperative cognitive dysfunction (POCD) is a common complication of central nervous system after anesthesia or surgery. Sevoflurane, an inhalation anesthetic, may inhibit cholinergic pathway that induce neuronal death and neuroinflammation, ultimately leading to POCD. Transauricular vagus nerve stimulation (taVNS) has neuroprotective effects in POCD rats, but the mechanisms related to cholinergic system have not been revealed. Sprague-Dawley rats were anesthetized with sevoflurane to construct the POCD model. The immunotoxin 192-IgG-saporin (192-sap) selectively lesioned cholinergic neurons in the basal forebrain, which is the major source of cholinergic projections to hippocampus. After lesion, rats received 5 days of taVNS treatment (30 min per day) starting 24 h before anesthesia. Open field test and Morris water maze were used to test the cognitive function. In this study, rats exposed to sevoflurane exhibited cognitive impairment that was attenuated by taVNS. In addition, taVNS treatment activated cholinergic system in the basal forebrain and hippocampus, and downregulated the expression of apoptosis- and necroptosis-related proteins, such as cleaved Caspase-3 and p-MLKL, in the hippocampus. Meanwhile, the activation of Iba1+ microglial by sevoflurane was reduced by taVNS. 192-sap blocked the cholinergic system activation in the basal forebrain and hippocampus and inhibited taVNS-mediated neuroprotection and anti-inflammation effects in the hippocampus. Generally, our study indicated that taVNS might alleviate sevoflurane-induced hippocampal neuronal apoptosis, necroptosis and microglial activation though activating cholinergic system in the basal forebrain.

Fluoxetine alleviates postoperative cognitive dysfunction by attenuating TLR4/MyD88/NF-κB signaling pathway activation in aged mice.

OBJECTIVE AND DESIGN: Postoperative cognitive dysfunction (POCD) is a common complication following surgery among elderly patients. Emerging evidence demonstrates that neuroinflammation plays a pivotal role in the pathogenesis of POCD. This study tested the hypothesis that fluoxetine can protect against POCD by suppressing hippocampal neuroinflammation through attenuating TLR4/MyD88/NF-κB signaling pathway activation. SUBJECTS: Aged C57BL/6 J male mice (18 months old) were studied. TREATMENT: Aged mice were intraperitoneally injected with fluoxetine (10 mg/kg) or saline for seven days before splenectomy. In addition, aged mice received an intracerebroventricular injection of a TLR4 agonist or saline seven days before splenectomy in the rescue experiment. METHODS: On postoperative days 1, 3, and 7, we assessed hippocampus-dependent memory, microglial activation status, proinflammatory cytokine levels, protein levels related to the TLR4/MyD88/NF-κB signaling pathway, and hippocampal neural apoptosis in our aged mouse model. RESULTS: Splenectomy induced a decline in spatial cognition, paralleled by parameters indicating exacerbation of hippocampal neuroinflammation. Fluoxetine pretreatment partially restored the deteriorated cognitive function, downregulated proinflammatory cytokine levels, restrained microglial activation, alleviated neural apoptosis, and suppressed the increase in TLR4, MyD88, and p-NF-κB p65 in microglia. Intracerebroventricular injection of LPS (1 µg, 0.5 µg/µL) before surgery weakened the effect of fluoxetine. CONCLUSION: Fluoxetine pretreatment suppressed hippocampal neuroinflammation and mitigated POCD by inhibiting microglial TLR4/MyD88/NF-κB pathway activation in aged mice.

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 ß 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.

Hepcidin regulates neuronal ferroptosis: A mechanism for postoperative cognitive dysfunction.

Toll-like receptor 4 (TLR4) is a signaling molecule responsible for the expression of hepcidin (Hepc), while myeloid differentiation protein 2 (MD2) is one major accessory protein of TLR4. This study focuses on exploring the neurocyte ferroptosis mediated through the regulation of Hepc expression by MD2, which is also one of the mechanisms for postoperative cognitive dysfunction (POCD). An experimental study was carried out using aged wild-type (Wt) and MD2 transgenic (Tg) mice. The neurocyte ferroptosis and POCD in the mice were assessed following splenectomy. Morris water maze was utilized to assess the neurocognitive abilities, hematoxylin and eosin (H&E) assay was performed to examine histopathology, and Nissl staining was used to evaluate the neurocyte damage. The Fe2+ , superoxide dismutase(SOD), malondialdehyde (MDA), glutathione(GSH), and glutathione peroxidase 4 (GPX4) levels were determined with kits. The expressions of transferrin receptor (TFR), Hepc, and MD2 were measured by Western blotting, while the expressions of TFR and GPX4 were measured by immunohistochemical staining. In Tg mice, we observed neurocyte ferroptosis and POCD following treatment with an MD2 inhibitor. PC12 cells were used as a neurocyte model. Ferroptosis was induced after treatment with an MD2 inhibitor, and the cell viability was assayed by Cell Counting Kit-8. Immunofluorescent staining was used to measure the TFR and GPX4 expressions. Meanwhile, the intracellular levels of Fe2+ , SOD, MDA, GSH, GPX4, and Hepc were also measured. POCD occurred among aged Wt and Tg mice. The Tg-POCD mice had more apparent POCD than the Wt-POCD mice. Nissl and H&E staining revealed neurocyte damage in brain tissues. Besides this, the Fe2+ and MDA expressions were upregulated, while the SOD, GSH, and GPX4 expressions were downregulated. Elevations in tissue levels of TFR, Hepc, and MD2 were observed, which were higher than those of Wt-POCD mice. After treatment with an MD2 inhibitor, the POCD could be prominently ameliorated in Tg-POCD mice, the Fe2+ and MDA levels could be reduced, while the SOD, GSH, and GPX4 levels could be elevated. In the PC12 model, ferroptosis could be suppressed by inhibiting the expression of MD2. MD2 is capable of regulating neurocyte ferroptosis by promoting Hepc expression, which has great potential as a novel target for POCD therapy.

Exogenous insulin-like growth factor 1 attenuates sevoflurane anesthesia-induced cognitive dysfunction in aged rats.

Sevoflurane anesthesia is correlated with the generation of postoperative cognitive dysfunction. Insulin-like growth factor 1 (IGF-1) has important function in the nervous system development. Intravenously injected IGF-1 is reported to successfully pass the blood-brain barrier and perform neuroprotection effect in the brain. Memory and learning abilities were analyzed through Morris water maze task. Relative levels of protein were examined through Western blot and enzyme-linked immunosorbent assay (ELISA). Relative mRNA levels were shown through quantitative real-time polymerase chain reaction (qRT-PCR). IGF-1 expression in the plasma and hippocampus was downregulated in sevoflurane anesthesia-induced rats and rescued by intravenous IGF-1 injection. In aged rats, intravenous injection of IGF-1 alleviated sevoflurane-caused cognitive injuries and elevated TNF-α, IL-1ß, and IL-6 levels in the plasma and hippocampus and rescued sevoflurane-depressed Akt phosphorylation. In conclusion, the administration of IGF-1 through intravenous injection alleviates sevoflurane anesthesia-mediated neuroinflammation and cognitive impairment in rats. The effects of IGF-1 in this process may depend on its function in regulating the PI3K/Akt signaling pathway.NEW & NOTEWORTHY IGF-1 expression was downregulated by sevoflurane anesthesia in rats and could be rescued by intravenous IGF-1 injection, which alleviated sevoflurane-caused cognitive injuries and enhanced inflammatory responses in aged rats. Intravenous injection of IGF-1 rescued sevoflurane-depressed Akt phosphorylation in aged rats.

Orthopedic surgery-induced cognitive dysfunction is mediated by CX3CL1/R1 signaling.

BACKGROUND: Postoperative pain is a common phenomenon after surgery and is closely associated with the development of postoperative cognitive dysfunction (POCD). Persistent pain and systemic inflammation caused by surgery have been suggested as key factors for the development of POCD. Fractalkine (CX3CL1) and its receptor, the CX3C chemokine receptor 1 (CX3CR1), are known to play a key role in pain and inflammation signaling pathways. Recent studies have shown that the regulation of CX3CR1/L1 signaling influences the development of various diseases including neuronal diseases. We determined whether CX3CR1/L1 signaling is a putative therapeutic target for POCD in a mouse model. METHODS: Adult (9-11 weeks) male mice were treated with neutralizing antibody to block CX3CR1/L1 signaling both before and after surgery. Inflammatory and behavioral responses including pain were assessed postoperatively. Also, CX3CR1 mRNA level was assessed. Hippocampal astrocyte activation, Mao B expression, and GABA expression were assessed at 2 days after surgery following neutralizing antibody administration. RESULTS: The behavioral response indicated cognitive dysfunction and development of pain in the surgery group compared with the control group. Also, increased levels of pro-inflammatory cytokines and CX3CR1 mRNA were observed in the surgery group. In addition, increased levels of GABA and increased Mao B expression were observed in reactive astrocytes in the surgery group; these responses were attenuated by neutralizing antibody administration. CONCLUSIONS: Increased CX3CR1 after surgery is both necessary and sufficient to induce cognitive dysfunction. CX3CR1 could be an important target for therapeutic strategies to prevent the development of POCD.

Sirtuin 3 protects against anesthesia/surgery-induced cognitive decline in aged mice by suppressing hippocampal neuroinflammation.

BACKGROUND: Postoperative cognitive dysfunction (POCD) is a very common complication that might increase the morbidity and mortality of elderly patients after surgery. However, the mechanism of POCD remains largely unknown. The NAD-dependent deacetylase protein Sirtuin 3 (SIRT3) is located in the mitochondria and regulates mitochondrial function. SIRT3 is the only sirtuin that specifically plays a role in extending lifespan in humans and is associated with neurodegenerative diseases. Therefore, the aim of this study was to evaluate the effect of SIRT3 on anesthesia/surgery-induced cognitive impairment in aged mice. METHODS: SIRT3 expression levels were decreased after surgery. For the interventional study, an adeno-associated virus (AAV)-SIRT3 vector or an empty vector was microinjected into hippocampal CA1 region before anesthesia/surgery. Western blotting, immunofluorescence staining, and enzyme-linked immune-sorbent assay (ELISA) were used to measure the oxidative stress response and downstream microglial activation and proinflammatory cytokines, and Golgi staining and long-term potentiation (LTP) recording were applied to evaluate synaptic plasticity. RESULTS: Overexpression of SIRT3 in the CA1 region attenuated anesthesia/surgery-induced learning and memory dysfunction as well as synaptic plasticity dysfunction and the oxidative stress response (superoxide dismutase [SOD] and malondialdehyde [MDA]) in aged mice with POCD. In addition, microglia activation (ionized calcium binding adapter molecule 1 [Iba1]) and neuroinflammatory cytokine levels (tumor necrosis factor-alpha [TNF-α], interleukin [IL]-1ß and IL-6) were regulated after anesthesia/surgery in a SIRT3-dependent manner. CONCLUSION: The results of the current study demonstrate that SIRT3 has a critical effect in the mechanism of POCD in aged mice by suppressing hippocampal neuroinflammation and reveal that SIRT3 may be a promising therapeutic and diagnostic target for POCD.

Acute pre-operative ibuprofen improves cognition in a rat model for postoperative cognitive dysfunction.

BACKGROUND: Inflammation is considered a key factor in the development of postoperative cognitive dysfunction (POCD). Therefore, we hypothesized that pre-operative anti-inflammatory treatment with ibuprofen would inhibit POCD in our rat-model. METHODS: Male Wistar rats of 3 or 23 months old received a single injection of ibuprofen (15 mg/kg i.p.) or were control handled before abdominal surgery. Timed blood and fecal samples were collected for analyses of inflammation markers and gut microbiome changes. Behavioral testing was performed from 9 to 14 days after surgery, in the open field, novel object- and novel location-recognition tests and Morris water maze. Neuroinflammation and neurogenesis were assessed by immune histochemistry after sacrifice on postoperative day 14. RESULTS: Ibuprofen improved short-term spatial memory in the novel location recognition test, and increased hippocampal neurogenesis. However, these effects were associated with increased hippocampal microglia activity. Whereas plasma cytokine levels (IL1-ß, IL6, IL10, and TNFα) were not significantly affected, VEGF levels increased and IFABP levels decreased after ibuprofen. Long-term memory in the Morris water maze was not significantly improved by ibuprofen. The gut microbiome was neither significantly affected by surgery nor by ibuprofen treatment. In general, effects in aged rats appeared similar to those in young rats, though less pronounced. CONCLUSION: A single injection of ibuprofen before surgery improved hippocampus-associated short-term memory after surgery and increased neurogenesis. However, this favorable outcome seemed not attributable to inhibition of (neuro)inflammation. Potential contributions of intestinal and blood-brain barrier integrity need further investigation. Although less pronounced compared to young rats, effects in aged rats indicate that even elderly individuals could benefit from ibuprofen treatment.

Dexmedetomidine Ameliorates Postoperative Cognitive Dysfunction in Aged Mice.

Neuroinflammation and oxidative stress coexist and interact in the progression of postoperative cognitive dysfunction (POCD) and other neurodegenerative disease. Mounting studies reveal that Dexmedetomidine (Dex) possesses anti-inflammatory and antioxidant properties. Nevertheless, whether Dex exerts neuroprotective effect on the cognitive sequelae of oxidative stress and inflammatory process remains unclear. A mouse model of abdominal exploratory laparotomy-induced cognitive dysfunction was employed to explore the underlying mechanism of neuroprotective effects exerted by Dex in POCD. Aged mice were treated with Dex (20 µg/kg) 20 min prior to surgery. Open field test (OFT) and Morris water maze (MWM) were employed to examine the cognitive function on postoperative day 3 (POD 3) or POD 7. In the present study, mice underwent surgery exhibited cognitive impairment without altering spontaneous locomotor activity, while the surgery-induced cognitive impairment could be alleviated by Dex pretreatment. Dex inhibited surgery-induced pro-inflammatory cytokines accumulation and microglial activation in the hippocampi of mice. Furthermore, Dex decreased MDA levels, enhanced SOD activity, modulated CDK5 activity and increased BDNF expression in the hippocampus. In addition, Dex remarkably reduced the surgery-induced increased ratio of Bax/Bcl-2 and apoptotic neurons in the hippocampi of aged mice. Collectively, our study provides evidence that Dex may exert neuroprotective effects against surgery-induced cognitive impairment through mechanisms involving its anti-inflammatory and antioxidant properties, as well as the suppression on the mitochondrial permeability transition pore and apoptosis-related pathway.