Transient neuroinflammation following surgery contributes to long-lasting cognitive decline in elderly rats via dysfunction of synaptic NMDA receptor

Interleukin-33 ameliorates perioperative neurocognitive disorders by modulating microglial state

Perioperative neurocognitive disorders (PND) are cognitive dysfunctions that usually occur in elderly patients after anesthesia and surgery. Microglial overactivation is a key underlying mechanism. Interleukin-33 (IL-33) is a member of the IL-1 family that orchestrates microglial function. In the present study, we explored how IL-33, which regulates microglia, contributes to cognitive improvement in a male mouse model of PND. An exploratory laparotomy was performed to establish a PND model. The expression levels of IL-33 and its receptor ST2 were evaluated using Western blot. IL-33/ST2 secretion, microglial density, morphology, phagocytosis of synapse, and proliferation, and dystrophic microglia were assessed using immunofluorescence. Synaptic plasticity was measured using Golgi staining and long-term potentiation. The Morris water maze and open field test were used to evaluate cognitive function and anxiety. Hippocampal expression of IL-33 and ST2 were elevated on postoperative day 3. We confirmed that IL-33 was secreted by astrocytes and neurons, whereas ST2 mainly colocalized with microglia. IL-33 treatment induced microgliosis after anesthesia and surgery. These microglia had larger soma sizes and shorter and fragmented branches. Compared to the Surgery group, IL-33 treatment reduced the synaptic phagocytosis of microglia and increased microglial proliferation and dystrophic microglia. IL-33 treatment also reversed the impaired synaptic plasticity and cognitive function caused by anesthesia and surgery. In conclusion, these results indicate that IL-33 plays a key role in regulating microglial state and synaptic phagocytosis in a PND mouse model. IL-33 treatment has a therapeutic potential for improving cognitive dysfunction in PND.

Low-frequency repetitive transcranial magnetic stimulation alleviates abnormal behavior in valproic acid rat model of autism through rescuing synaptic plasticity and inhibiting neuroinflammation

Autism is a complex neurodevelopmental disorder with no effective treatment available currently. Repetitive transcranial magnetic stimulation (rTMS) is emerging as a promising neuromodulation technique to treat autism. However, the mechanism how rTMS works remains unclear, which restrict the clinical application of magnetic stimulation in the autism treatment. In this study, we investigated the effect of low-frequency rTMS on the autistic-like symptoms and explored if this neuroprotective effect was associated with synaptic plasticity and neuroinflammation in the hippocampus. A rat model of autism was established by intraperitoneal injection of valproic acid (VPA) in pregnant rats and male offspring were treated with 1 Hz rTMS daily for two weeks continuously. Behavior tests were performed to identify behavioral abnormality. Synaptic plasticity was measured by in vivo electrophysiological recording and Golgi-Cox staining. Synapse and inflammation associated proteins were detected by immunofluorescence and Western blot analyses. Results showed prenatal VPA-exposed rats exhibited autistic-like and anxiety-like behaviors, and cognitive impairment. Synaptic plasticity deficits and the abnormality expression of synapse-associated proteins were found in the hippocampus of prenatal VPA-exposed rats. Prenatal VPA exposure increased the level of inflammation cytokines and promoted the excessive activation of microglia. rTMS significantly alleviated the prenatal VPA-induced abnormalities including behavioral and synaptic plasticity deficits, and excessive neuroinflammation. TMS maybe a potential strategy for autism therapy via rescuing synaptic plasticity and inhibiting neuroinflammation.

Acute exposure of microwave impairs attention process by activating microglial inflammation

BACKGROUND

Attention provides the foundation for cognitions, which was shown to be affected by microwave (MW) radiation. With the ubiquitous of microwaves, public concerns regarding the impact of MW radiation on attention has hence been increased. Our study aims to investigate the potential effect and mechanism of acute microwave exposure on attention.

RESULTS

We identified obvious impairment of attention in mice by the five-choice serial reaction time (5-CSRT) task. Proteomic analysis of the cerebrospinal fluid (CSF) revealed neuroinflammation and microglial activation potentially due to acute MW exposure. Moreover, biochemical analysis further confirmed microglial activation in the prefrontal cortex (PFC) of mice subjected to acute MW exposure. Finally, minocycline, a commercially available anti-inflammatory compound, attenuated neuroinflammation, inhibited the upregulation of N-methyl-D-aspartic acid receptor (NMDAR) including NR2A and NR2B, and also accelerated the attentional recovery after MW exposure.

CONCLUSIONS

We believe that microglial activation and NMDAR upregulation likely contribute to inattention induced by acute MW exposure, and we found that minocycline may be effective in preventing such process.

Dexmedetomidine mitigates neuroinflammation in an Alzheimer's disease mouse model via the miR-204-3p/FBXL7 signaling axis

Alzheimer's disease (AD) is a prevalent neurodegenerative disorder characterized by neuroinflammation. Dexmedetomidine (Dex) is known for its neuroprotective properties in clinical settings. In this study, we investigated the potential of Dex in protecting against neuroinflammation in an AD mouse model induced by amyloid-beta (Aβ) injection. First, in the AD mouse model, Aβ injection were administered, and the model was confirmed through behavioral tests, including the Morris water maze and Y-maze. Neuroinflammatory states in Aβ-injected mice were assessed using hematoxylin and eosin staining and enzyme-linked immunosorbent assay. Expression levels of microRNA (miR)-204-3p and F-box/LRR-repeat protein 7 (FBXL7) in mouse tissues were determined through real-time quantitative polymerase chain reaction and Western blot. The binding interaction between miR-204-3p and FBXL7 was elucidated using dual-luciferase analysis. Aβ-injected mice exhibited cognitive impairment, neuroinflammation, and downregulated miR-204-3p. Upregulation of miR-204-3p reduced inflammatory infiltration and mitigated neuroinflammation in Aβ-injected mice. Dex treatment reduced inflammation in hippocampal tissues of Aβ-injected mice. Dex treatment upregulated miR-204-3p, leading to suppressed FBXL7 expression in tissues. Inhibition of miR-204-3p or overexpression of FBXL7 reversed the alleviating effect of Dex on neuroinflammation in Aβ-injected mice. Overall, Dex increased miR-204-3p expression, resulting in the inhibition of FBXL7, and subsequently alleviated neuroinflammation in Aβ-injected mice.

The role of N-methyl-D-aspartate glutamate receptors in Alzheimer's disease: From pathophysiology to therapeutic approaches

N-Methyl-D-aspartate glutamate receptors (NMDARs) are involved in multiple physiopathological processes, including synaptic plasticity, neuronal network activities, excitotoxic events, and cognitive impairment. Abnormalities in NMDARs can initiate a cascade of pathological events, notably in Alzheimer's disease (AD) and even other neuropsychiatric disorders. The subunit composition of NMDARs is plastic, giving rise to a diverse array of receptor subtypes. While they are primarily found in neurons, NMDAR complexes, comprising both traditional and atypical subunits, are also present in non-neuronal cells, influencing the functions of various peripheral tissues. Furthermore, protein-protein interactions within NMDAR complexes has been linked with Aβ accumulation, tau phosphorylation, neuroinflammation, and mitochondrial dysfunction, all of which potentially served as an obligatory relay of cognitive impairment. Nonetheless, the precise mechanistic link remains to be fully elucidated. In this review, we provided an in-depth analysis of the structure and function of NMDAR, investigated their interactions with various pathogenic proteins, discussed the current landscape of NMDAR-based therapeutics, and highlighted the remaining challenges during drug development.

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.

Levodopa-induced dyskinesia: interplay between the N-methyl-D-aspartic acid receptor and neuroinflammation

Parkinson's disease (PD) is a common neurodegenerative disorder of middle-aged and elderly people, clinically characterized by resting tremor, myotonia, reduced movement, and impaired postural balance. Clinically, patients with PD are often administered levodopa (L-DOPA) to improve their symptoms. However, after years of L-DOPA treatment, most patients experience complications of varying severity, including the "on-off phenomenon", decreased efficacy, and levodopa-induced dyskinesia (LID). The development of LID can seriously affect the quality of life of patients, but its pathogenesis is unclear and effective treatments are lacking. Glutamic acid (Glu)-mediated changes in synaptic plasticity play a major role in LID. The N-methyl-D-aspartic acid receptor (NMDAR), an ionotropic glutamate receptor, is closely associated with synaptic plasticity, and neuroinflammation can modulate NMDAR activation or expression; in addition, neuroinflammation may be involved in the development of LID. However, it is not clear whether NMDA receptors are co-regulated with neuroinflammation during LID formation. Here we review how neuroinflammation mediates the development of LID through the regulation of NMDA receptors, and assess whether common anti-inflammatory drugs and NMDA receptor antagonists may be able to mitigate the development of LID through the regulation of central neuroinflammation, thereby providing a new theoretical basis for finding new therapeutic targets for LID.

Young plasma reverses anesthesia and surgery-induced cognitive impairment in aged rats by modulating hippocampal synaptic plasticity

We investigated the protective effect of young plasma on anesthesia- and surgery-induced cognitive impairment and the potential underlying mechanism using bioinformatics, functional enrichment analysis, gene set enrichment analysis, Golgi-Cox staining, dendritic spine analysis, immunofluorescence assay, western blot analysis, and transmission electron microscopy. Furthermore, we performed behavioral assessments using the open field test, the novel object recognition test, and the Morris water maze test. We identified 1969 differentially expressed genes induced by young plasma treatment, including 800 upregulated genes and 1169 downregulated genes, highlighting several enriched biological processes (signal release from synapse, postsynaptic density and neuron to neuron synapse). Anesthesia- and surgery-induced cognitive impairment in aged rats was comparatively less severe following young plasma preinfusion. In addition, the decreased levels of synapse-related and tyrosine kinase B/extracellular signal-regulated protein kinase/cyclic adenosine monophosphate response element-binding protein (TrkB/ERK/CREB) signaling pathway-related proteins, dendritic and spine deficits, and ultrastructural changes were ameliorated in aged mice following young plasma preinfusion. Together, these findings suggest that young plasma reverses anesthesia- and surgery-induced cognitive impairment in aged rats and that the mechanism is associated with the activation of the TrkB/ERK/CREB signaling pathway and improvement in hippocampal synaptic plasticity.

Vitamin D3 Supplementation Attenuates Surgery-Induced Neuroinflammation and Cognitive Impairment by Regulating NLRP3 Inflammasome in Mice

Neuroinflammation plays a dominant role in the progression of postoperative cognitive dysfunction (POCD). Vitamin D has been known to have important regulatory functions in inflammation and immune response. The NOD-like receptor protein 3 (NLRP3) is an essential inflammasome in the inflammatory response and could be activated by anesthesia and surgery. In this study, male C57BL/6 mice aged 14-16 months were given VD3 for 14 days straight before having an open tibial fracture surgery. The animals were either sacrificed to obtain the hippocampus or tested in a Morris water maze test. Western blot was employed to estimate the levels of NLRP3, ASC, and caspase-1, immunohistochemistry was used to identify microglial activation, and an enzyme-linked immunosorbent assay was used to measure the expression of IL-18 and IL-1β, while using the corresponding assay kits to assess ROS and MDA levels to reflect the oxidative stress status. We showed that VD3 pretreatment significantly improved surgery-induced memory and cognitive dysfunctions in aged mice, which was linked to the inactivation of the NLRP3 inflammasome and the inhibition of neuroinflammation. This finding provided a novel preventative strategy for clinically reducing postoperative cognitive impairment in elderly surgical patients. This study has some limitations. Gender differences in the effects of VD3 were not considered, and only male mice were used. Additionally, VD3 was given as a preventative measure; however, it is unknown whether it has any therapeutic benefits for POCD mice. This trial is registered with ChiCTR-ROC-17010610.