Sepsis-induced selective loss of NMDA receptors modulates hippocampal neuropathology in surviving septic mice

Protective effects of the saltinduced kinase inhibitor HG99101 on sepsisassociated cognitive dysfunction in mice and the underlying mechanisms

OBJECTIVES

Sepsis-associated cognitive dysfunction is a common complication in patients with sepsis and lack of effective treatment. Its pathological mechanisms remain unclear. Salt-induced kinase (SIK) is an important molecule in the regulation of metabolism, immunity, and inflammatory response. It is associated with the development of many neurological diseases. This study aims to investigate the expression of SIK in the hippocampus of septic mice, and to evaluate the role and mechanism of the SIK inhibitor HG-9-91-01 in sepsis-associated cognitive dysfunction.

METHODS

Firstly, C57BL/6 mice were randomly divided into a control group (Con group) and a sepsis model group [lipopolysaccharide (LPS) group]. The model group was injected intraperitoneally with LPS at a dose of 8 mg/kg and the Con group was injected with an equal volume of normal saline. Hippocampal tissues were harvested at 1, 3, and 6 days after injection and the expressions of SIK1, SIK2, and SIK3 were detected by real-time fluorescence quantitative PCR (qPCR) and Western blotting. Secondly, C57BL/6 mice were randomly divided into a Con group, a LPS group, and a SIK inhibitor group (HG group). The LPS and HG groups were injected with LPS to establish a sepsis model; in the HG group, HG-9-91-01 (10 mg/kg) was injected intraperitoneally at 3-6 days after LPS injection, and the LPS group was injected with the same volume of vehicle. Cognitive function was assessed at 7-11 days after LPS injection using the Morris water maze (MWM). Hippocampal tissues were harvested after the behavioral tests, and the mRNA levels of inflammatory factors and microglial markers were assessed by qPCR. The protein levels of inducible nitric oxide synthase (iNOS), CD68, ionized calcium binding adaptor molecule 1 (Iba-1), N-methyl-D-aspartate (NMDA) receptor (NR) subunit, cAMP response element-binding protein (CREB)-regulated transcription coactivator 1 (CRTC1), and insulin-like growth factor 1 (IGF-1) were detected by Western blotting. Immunohistochemistry (IHC) was used to detect the expression of Iba-1 positive cells in the CA1, CA3 and dentate gyrus (DG) of the hippocampus, followed by Sholl analysis.

RESULTS

Compared with the Con group, the mRNA and protein levels of SIK1, SIK2, and SIK3 in the hippocampus were increased in the LPS group (all P<0.05). Compared with the Con group, mice in the LPS group had a significantly longer escape latency, a lower percentage of target quadrant dwell time and a reduced locomotor speed (all P<0.05); the HG group had a decreased escape latency and an increased percentage of time spent in the target quadrant in comparison with the LPS group (both P<0.05). The mRNA levels of inflammatory factors [tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6)], and the M1-type microglial markers iNOS and CD68 in the hippocampus of the LPS group were increased in comparison with the Con group, while the M2-type microglial markers CD206 and arginase-1 (Arg-1) were decreased. Compared with the LPS group, the mRNA levels of TNF-α, IL-1β, IL-6, and iNOS were downregulated, while the levels of CD206 and Arg-1 were upregulated in the HG group (all P<0.05). The protein levels of iNOS, CD68, and Iba-1 in the hippocampus of the LPS group were increased in comparison with the Con group, but they were downregulated in the HG group in comparison with the LPS group (all P<0.05). The number of Iba-1 positive cells in CA1, CA3, and DG of the hippocampus was increased in the LPS group in comparison with the Con group, but they were decreased in the HG group in comparison with the LPS group (all P<0.05). Sholl analysis showed that the number of intersections at all radii between 8-38 µm from the microglial soma was decreased in the LPS group in comparison with the Con group (all P<0.05). Compared with the LPS group, the number of intersections at all radii between 14-20 µm was significantly increased in the HG group (all P<0.05). The protein levels of NR subunit NR1, NR2A, NR2B, and IGF-1 were downregulated in the hippocampus of the LPS group in comparison with the Con group, while the expression of phosphorylated CRTC1 (p-CRTC1) was increased. Compared with the LPS group, the levels of NR1, NR2A, NR2B, and IGF-1 were upregulated, while p-CRTC1 was downregulated in the HG group (all P<0.05).

CONCLUSIONS

SIK expression is upregulated in the hippocampus of septic mice. The SIK inhibitor HG-9-91-01 ameliorates sepsis-associated cognitive dysfunction in mice, and the mechanism may involve in the activation of the CRTC1/IGF-1 pathway, inhibition of neuroinflammation, and enhancement of synaptic plasticity.

Inhaled molecular hydrogen reduces hippocampal neuroinflammation, glial reactivity and ameliorates memory impairment during systemic inflammation

Sepsis is associated with numerous physiological and biochemical abnormalities that result in a life-threatening condition. The involvement of the Central Nervous System (CNS) during sepsis has received considerable attention, especially the hippocampus which plays a key role in the learning and memory processes. The increased interest in this limbic region during systemic inflammation (SI) is related to the number of sepsis survivor patients who have cognitive impairments. A single injection of lipopolysaccharide (LPS)-induced systemic inflammation is the most commonly used murine endotoxemia model because it replicates several pathophysiological changes observed in severe sepsis. Molecular hydrogen (H₂) has been used as an anti-inflammatory therapeutic strategy to prevent neuroinflammation. However, the mechanisms by which inhaled H₂ mitigate memory loss during SI remains unknown. To understand how H₂ acts in the hippocampus, the current study focused on specific mechanisms that may be involved in reducing neuroinflammation in rats during SI. We hypothesized that inhaled H₂ decreases LPS-induced hippocampal pro-inflammatory cytokines surges and this effect is associated with reduced memory loss. Using different and integrative approaches, i.e., from hippocampal cells electrophysiology to animal behavior, we report that inhaled H₂ decreased LPS-induced peripheral and hippocampal inflammation, decreased microglial and astrocytic activation, lessen memory loss without affecting long-term potentiation (LTP). To our knowledge, this is the first evidence showing that inhaled H₂ reduces hippocampal microglial and glial cells inflammation, which may be associated with a reduced memory impairment induced by SI.

Effect of Systemic Inflammation in the CNS: A Silent History of Neuronal Damage

Central nervous system (CNS) infections including meningitis and encephalitis, resulting from the blood-borne spread of specific microorganisms, provoke nervous tissue damage due to the inflammatory process. Moreover, different pathologies such as sepsis can generate systemic inflammation. Bacterial lipopolysaccharide (LPS) induces the release of inflammatory mediators and damage molecules, which are then released into the bloodstream and can interact with structures such as the CNS, thus modifying the blood-brain barrier's (BBB´s) and blood-cerebrospinal fluid barrier´s (BCSFB´s) function and inducing aseptic neuroinflammation. During neuroinflammation, the participation of glial cells (astrocytes, microglia, and oligodendrocytes) plays an important role. They release cytokines, chemokines, reactive oxygen species, nitrogen species, peptides, and even excitatory amino acids that lead to neuronal damage. The neurons undergo morphological and functional changes that could initiate functional alterations to neurodegenerative processes. The present work aims to explain these processes and the pathophysiological interactions involved in CNS damage in the absence of microbes or inflammatory cells.

The Impact of Persistent Noise Exposure under Inflammatory Conditions

The aim of this study was to investigate the impact of noise exposure in an intensive care unit (ICU) environment on the development of postoperative delirium in a mouse model that mimics the ICU environment. Additionally, we aimed to identify the underlying mechanisms contributing to delirium and provide evidence for reducing the risk of delirium. In this study, to mimic an ICU environment, lipopolysaccharide (LPS)-injected sepsis mouse models were exposed to a 75 dB noise condition. Furthermore, we assessed neurobehavioral function and observed the level of neuroinflammatory response and blood-brain barrier (BBB) integrity in the hippocampal region. The LPS-injected sepsis mouse model exposed to noise exhibited increased anxiety-like behavior and cognitive impairment. Moreover, severe neuroinflammation and BBB disruption were detected in the hippocampal region. This study provides insights suggesting that persistent noise exposure under systemic inflammatory conditions may cause cognitive dysfunction and anxiety- like behavior via the mediation of BBB disruption and neuroinflammation. As a result, we suggest that the detailed regulation of noise exposure may be required to prevent the development of postoperative delirium.

Munc18-1 Contributes to Hippocampal Injury in Septic Rats Through Regulation of Syntanxin1A and Synaptophysin and Glutamate Levels

Sepsis-associated encephalopathy (SAE) is a diffuse brain dysfunction closely associated with mortality in the acute phase of sepsis. Abnormal neurotransmitters release, such as glutamate, plays a crucial role in the pathological mechanism of SAE. Munc18-1 is a key protein regulating neurotransmission. However, whether Munc18-1 plays a role in SAE by regulating glutamate transmission is still unclear. In this study, a septic rat model was established by the cecal ligation and perforation. We found an increase in the content of glutamate in the hippocampus of septic rat, the number of synaptic vesicles in the synaptic active area and the expression of the glutamate receptor NMDAR1. Meanwhile, it was found that the expressions of Munc18-1, Syntaxin1A and Synaptophysin increased, which are involved in neurotransmission. The expression levels of Syntaxin1A and Synaptophysin in hippocampus of septic rats decreased after interference using Munc18-1siRNA. We observed a decrease in the content of glutamate in the hippocampus of septic rats, the number of synaptic vesicles in the synaptic activity area and the expression of NMDAR1. Interestingly, it was also found that the down-regulation of Munc18-1 improved the vital signs of septic rats. This study shows that CLP induced the increased levels of glutamate in rat hippocampus, and Munc18-1 may participate in the process of hippocampal injury in septic rats by affecting the levels of glutamate via regulating Syntaxin1A and Synaptophysin. Munc18-1 may serve as a potential target for SAE therapy.

Maternal Hyperhomocysteinemia Produces Memory Deficits Associated with Impairment of Long-Term Synaptic Plasticity in Young Rats

Maternal hyperhomocysteinemia (HCY) is a common pregnancy complication caused by high levels of the homocysteine in maternal and fetal blood, which leads to the alterations of the cognitive functions, including learning and memory. In the present study, we investigated the mechanisms of these alterations in a rat model of maternal HCY. The behavioral tests confirmed the memory impairments in young and adult rats following the prenatal HCY exposure. Field potential recordings in hippocampal slices demonstrated that the long-term potentiation (LTP) was significantly reduced in HCY rats. The whole-cell patch-clamp recordings in hippocampal slices demonstrated that the magnitude of NMDA receptor-mediated currents did not change while their desensitization decreased in HCY rats. No significant alterations of glutamate receptor subunit expression except GluN1 were detected in the hippocampus of HCY rats using the quantitative real-time PCR and Western blot methods. The immunofluorescence microscopy revealed that the number of synaptopodin-positive spines is reduced, while the analysis of the ultrastructure of hippocampus using the electron microscopy revealed the indications of delayed hippocampal maturation in young HCY rats. Thus, the obtained results suggest that maternal HCY disturbs the maturation of hippocampus during the first month of life, which disrupts LTP formation and causes memory impairments.

The biological alterations of synapse/synapse formation in sepsis-associated encephalopathy

Sepsis-associated encephalopathy (SAE) is a common complication caused by sepsis, and is responsible for increased mortality and poor outcomes in septic patients. Neurological dysfunction is one of the main manifestations of SAE patients. Patients may still have long-term cognitive impairment after hospital discharge, and the underlying mechanism is still unclear. Here, we first outline the pathophysiological changes of SAE, including neuroinflammation, glial activation, and blood-brain barrier (BBB) breakdown. Synapse dysfunction is one of the main contributors leading to neurological impairment. Therefore, we summarized SAE-induced synaptic dysfunction, such as synaptic plasticity inhibition, neurotransmitter imbalance, and synapses loss. Finally, we discuss the alterations in the synapse, synapse formation, and mediators associated with synapse formation during SAE. In this review, we focus on the changes in synapse/synapse formation caused by SAE, which can further understand the synaptic dysfunction associated with neurological impairment in SAE and provide important insights for exploring appropriate therapeutic targets of SAE.

Peripheral Transplantation of Mesenchymal Stem Cells at Sepsis Convalescence Improves Cognitive Function of Sepsis Surviving Mice

Objective

To investigate the effects of peripheral transplantation of mesenchymal stem cells (MSCs) at sepsis convalescence on post-sepsis cognitive function and underlying mechanisms in mice.

Methods

Sepsis was induced by cecal ligation and puncture (CLP) in mice. Bone marrow-derived MSCs from mice were cultured and injected via tail vein on the 8^th day after CLP. Cognitive function was detected in open field, novel object recognition task, and delayed matching-to-place water maze task during 10-26 days after CLP. Neuroinflammation, neurogenesis, and peripheral inflammation were detected on the 12^th and 31^th days after CLP. MSCs tracing was detected during 8-10 days after CLP.

Results

Transplanted MSCs were located at peripheral organs (lung, spleen, liver) and had no obvious effects on survival and weight of sepsis mice. Transplanted MSCs mitigated cognitive impairments and hippocampal microglial activation, improved hippocampal neurogenesis of sepsis surviving mice, and had no obvious effect on the leukocyte amount, the neutrophil percentage, and the inflammatory factors of peripheral blood, and the hippocampal inflammatory factors.

Conclusions

Our data indicated that MSCs transplantation via peripheral vein at later phase of sepsis can improve post-sepsis cognitive impairment and hippocampal neurogenesis of sepsis surviving mice.

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

Background

Perioperative neurocognitive disorders (PNDs) are considered the most common postoperative complication in geriatric patients. However, its pathogenesis is not fully understood. Surgery-triggered neuroinflammation is a major contributor to the development of PNDs. Neuroinflammation can influence N-methyl-D-aspartate receptor (NMDAR) expression or function which is closely associated with cognition. We, therefore, hypothesized that the persistent changes in NMDAR expression or function induced by transient neuroinflammation after surgery were involved in the development of PNDs.

Methods

Eighteen-month-old male Sprague–Dawley rats were subjected to abdominal surgery with sevoflurane anesthesia to establish the PNDs animal model. Then, we determined the transient neuroinflammation by detecting the protein levels of proinflammatory cytokines and microglia activation using ELISA, western blot, immunohistochemistry, and microglial morphological analysis from postoperative days 1–20. Persistent changes in NMDAR expression were determined by detecting the protein levels of NMDAR subunits from postoperative days 1–59. Subsequently, the dysfunction of synaptic NMDAR was evaluated by detecting the structural plasticity of dendritic spine using Golgi staining. Pull-down assay and western blot were used to detect the protein levels of Rac1-GTP, phosphor-cofilin, and Arp3, which contribute to the regulation of the structural plasticity of dendritic spine. Finally, glycyrrhizin, an anti-inflammatory agent, was administered to further explore the role of synaptic NMDAR dysfunction induced by transient neuroinflammation in the neuropathogenesis of PNDs.

Results

We showed that transient neuroinflammation induced by surgery caused sustained downregulation of synaptic NR2A and NR2B subunits in the dorsal hippocampus and led to a selective long-term spatial memory deficit. Meanwhile, the detrimental effect of neuroinflammation on the function of synaptic NMDARs was shown by the impaired structural plasticity of dendritic spines and decreased activity of the Rac1 signaling pathways during learning. Furthermore, anti-inflammatory treatment reversed the downregulation and hypofunction of synaptic NR2A and NR2B and subsequently rescued the long-term spatial memory deficit.

Conclusions

Our results identify sustained synaptic NR2A and NR2B downregulation and hypofunction induced by transient neuroinflammation following surgery as important contributors to the development of PNDs in elderly rats.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02528-5.

Cerebral dysfunctions caused by sepsis during ageing

Systemic inflammation elicited by sepsis can induce an acute cerebral dysfunction known as sepsis-associated encephalopathy (SAE). Recent evidence suggests that SAE is common but shows a dynamic trajectory over time. Half of all patients with sepsis develop SAE in the intensive care unit, and some survivors present with sustained cognitive impairments for several years after initial sepsis onset. It is not clear why some, but not all, patients develop SAE and also the factors that determine the persistence of SAE. Here, we first summarize the chronic pathology and the dynamic changes in cognitive functions seen after the onset of sepsis. We then outline the cerebral effects of sepsis, such as neuroinflammation, alterations in neuronal synapses and neurovascular changes. We discuss the key factors that might contribute to the development and persistence of SAE in older patients, including premorbid neurodegenerative pathology, side effects of sedatives, renal dysfunction and latent virus reactivation. Finally, we postulate that some of the mechanisms that underpin neuropathology in SAE may also be relevant to delirium and persisting cognitive impairments that are seen in patients with severe COVID-19.

In this Review, Manabe and Heneka examine how the systemic inflammation associated with sepsis can lead to acute cerebral dysfunction known as sepsis-associated encephalopathy (SAE). Moreover, they suggest that some of the mechanisms involved in SAE may be relevant for understanding the cognitive impairments that develop in some patients with COVID-19.

Kynurenic Acid and Its Synthetic Derivatives Protect Against Sepsis-Associated Neutrophil Activation and Brain Mitochondrial Dysfunction in Rats

Background and Aims

The systemic host response in sepsis is frequently accompanied by central nervous system (CNS) dysfunction. Evidence suggests that excessive formation of neutrophil extracellular traps (NETs) can increase the permeability of the blood–brain barrier (BBB) and that the evolving mitochondrial damage may contribute to the pathogenesis of sepsis-associated encephalopathy. Kynurenic acid (KYNA), a metabolite of tryptophan catabolism, exerts pleiotropic cell-protective effects under pro-inflammatory conditions. Our aim was to investigate whether exogenous KYNA or its synthetic analogues SZR-72 and SZR-104 affect BBB permeability secondary to NET formation and influence cerebral mitochondrial disturbances in a clinically relevant rodent model of intraabdominal sepsis.

Methods

Sprague–Dawley rats were subjected to fecal peritonitis (0.6 g kg^-1 ip) or a sham operation. Septic animals were treated with saline or KYNA, SZR-72 or SZR-104 (160 µmol kg^-1 each ip) 16h and 22h after induction. Invasive monitoring was performed on anesthetized animals to evaluate respiratory, cardiovascular, renal, hepatic and metabolic parameters to calculate rat organ failure assessment (ROFA) scores. NET components (citrullinated histone H3 (CitH3); myeloperoxidase (MPO)) and the NET inducer IL-1β, as well as IL-6 and a brain injury marker (S100B) were detected from plasma samples. After 24h, leukocyte infiltration (tissue MPO) and mitochondrial complex I- and II-linked (CI–CII) oxidative phosphorylation (OXPHOS) were evaluated. In a separate series, Evans Blue extravasation and the edema index were used to assess BBB permeability in the same regions.

Results

Sepsis was characterized by significantly elevated ROFA scores, while the increased BBB permeability and plasma S100B levels demonstrated brain damage. Plasma levels of CitH3, MPO and IL-1β were elevated in sepsis but were ameliorated by KYNA and its synthetic analogues. The sepsis-induced deterioration in tissue CI–CII-linked OXPHOS and BBB parameters as well as the increase in tissue MPO content were positively affected by KYNA/KYNA analogues.

Conclusion

This study is the first to report that KYNA and KYNA analogues are potential neuroprotective agents in experimental sepsis. The proposed mechanistic steps involve reduced peripheral NET formation, lowered BBB permeability changes and alleviation of mitochondrial dysfunction in the CNS.

Systemic inflammation induced the delayed reduction of excitatory synapses in the CA3 during ageing

Sepsis-associated encephalopathy (SAE) represents diverse cerebral dysfunctions in response to pathogen-induced systemic inflammation. Peripheral exposure to lipopolysaccharide (LPS), a component of the gram-negative bacterial cell wall, has been extensively used to model systemic inflammation. Our previous studies suggested that LPS led to hippocampal neuron death and synaptic destruction in vivo. However, the underlying roles of activated microglia in these neuronal changes remained unclear. Here, LPS from two different bacterial strains (Salmonella enterica or E. coli) were compared and injected in 14- to 16-month-old mice and evaluated for neuroinflammation and neuronal integrity in the hippocampus at 7 or 63 days post-injection (dpi). LPS injection resulted in persistent neuroinflammation lasting for seven days and a subsequent normalisation by 63 dpi. Of note, increases in proinflammatory cytokines, microglial morphology and microglial mean lysosome volume were more pronounced after E. coli LPS injection than Salmonella LPS at 7 dpi. While inhibitory synaptic puncta density remained normal, excitatory synaptic puncta were locally reduced in the CA3 region of the hippocampus at 63 dpi. Finally, we provide evidence that excitatory synapses coated with complement factor 3 (C3) decreased between 7 dpi and 63 dpi. Although we did not find an increase of synaptic pruning by microglia, it is plausible that microglia recognised and eliminated these C3-tagged synapses between the two time-points of investigation. Since a region-specific decline of CA3 synapses has previously been reported during normal ageing, we postulate that systemic inflammation may have accelerated or worsened the CA3 synaptic changes in the ageing brain.

Injection of Anti-proBDNF Attenuates Hippocampal-Dependent Learning and Memory Dysfunction in Mice With Sepsis-Associated Encephalopathy

Sepsis-associated encephalopathy (SAE) is a risk factor for cognitive and memory dysfunction; however, the mechanism remains unclear. Brain-derived neurotrophic factor (BDNF) was reported to have a positive effect on cognition and emotion regulation, but the study of its precursor, proBDNF, has been limited. This study aimed to elucidate the effects and associated mechanisms of hippocampal proBDNF in a lipopolysaccharide (LPS)-induced SAE mouse model. In this study, we found that the mice exhibited cognitive dysfunction on day 7 after LPS injection. The expression of proBDNF and its receptor, p75^NTR, was also increased in the hippocampus, while the levels of BDNF and its receptor, TrkB, were decreased. A co-localization study showed that proBDNF and p75^NTR were mainly co-localized with neurons. Furthermore, LPS treatment reduced the expression of NeuN, Nissl bodies, GluR4, NR1, NR2A, and NR2B in the hippocampus of SAE mice. Furthermore, an intrahippocampal or intraperitoneal injection of anti-proBDNF antibody was able to ameliorate LPS-induced cognitive dysfunction and restore the expression of NeuN, Nissl bodies, GluR4, NR1, NR2A, NR2B, and PSD95. These results indicated that treatment with brain delivery by an intrahippocampal and systemic injection of mAb-proBDNF may represent a potential therapeutic strategy for treating patients with SAE.

NU9056, a KAT 5 Inhibitor, Treatment Alleviates Brain Dysfunction by Inhibiting NLRP3 Inflammasome Activation, Affecting Gut Microbiota, and Derived Metabolites in LPS-Treated Mice

Background: The pathogenesis of sepsis-associated encephalopathy (SAE) is complicated, while the efficacy of current treatment technologies is poor. Therefore, the discovery of related targets and the development of new drugs are essential.

Methods: A mouse model of SAE was constructed by intraperitoneal injection of lipopolysaccharide (LPS). LPS treatment of microglia was used to build an in vitro model of inflammation. Nine-day survival rates, behavioral testing, transmission electron microscopy (TEM), immunohistochemical (IHC), immunofluorescence (IF), and ELISA were performed. The expression levels of Occludin, Claudin 5, NLRP3, caspase-1, and ASC genes and proteins were detected by RT-qPCR or Western blot. Caspase-1 P10 (Casp-1 P10) protein expression was detected. 16S rDNA sequencing and gas chromatography-mass spectrometer (GC-MS) were used to analyze the gut microbiota and metabolism. Flow cytometric experiment and Cell Counting Kit-8 (CCK8) assay were performed.

Results: NU9056 improved the survival rate of mice and alleviated LPS-induced cognitive impairment, anxiety, and depression in vivo. The tight junctions were thickened via NU9056 treatment. Further, the mRNAs and proteins expression levels of Occludin and Claudin 5 were up-regulated by NU9056. NU9056 increased the expression level of DCX. The expression levels of Iba-1, NLRP3, IL-1β, ASC, and Casp-1 P10 were down-regulated by NU9056. The composition of the gut microbiota changed. Kyoto Encyclopedia of Genes and Genomes data predicted that the effects of NU9056 might be related to apoptosis and tight junction pathways. NU9056 up-regulated the concentration of acetate, propionate, and butyrate. NU9056 significantly reduced LPS-induced apoptosis of microglia, the average fluorescence intensity of ROS, and the release of IL-1β and IL-18, while improving cell viability in vitro.

Conclusions: NU9056 might effectively alleviate LPS-induced cognitive impairment and emotional disorder in experimental mice by inhibiting the NLRP3 inflammasome. The therapeutic effects may be related to gut microbiota and derived metabolites. NU9056 might be a potential drug of SAE prevention.

Alterations in mRNA and Protein Expression of Glutamate Receptor Subunits Following Pentylenetetrazole-induced Acute Seizures in Young Rats

Acute seizures can severely affect brain function and development. However, the underlying pathophysiological mechanisms are still poorly understood. Disturbances of the glutamatergic system are considered one of the critical mechanisms of neurological abnormalities. In the present study, we analyzed changes in the expression of NMDA and AMPA receptor subunits in the different brain regions (dorsal hippocampus, amygdala, and the medial prefrontal, temporal, and entorhinal cortex) using a pentylenetetrazole (PTZ) model of seizures in 3-week-old rats. A distinctive feature of this model is that the administration of PTZ causes severe acute seizures, which are not followed by the development of spontaneous recurrent seizures later on. Subunit expression was analyzed using qRT-PCR and Western blotting during the first week after seizures. The most pronounced alterations of mRNA and protein levels were observed in the dorsal hippocampus. We found decreased expression of the GluA2 mRNA 7 days after seizures (PSE7), as well as reduced GluN2a protein levels on PSE7. Significant alterations in the expression of different receptor subunits in the mRNA but not protein levels were observed in the entorhinal cortex and amygdala. In contrast, in the medial prefrontal and temporal cortex, we found almost no changes in the expression of the studied genes. The identified changes deepen our understanding of post-seizure disturbances in the developing brain and confirm that although various brain structures are involved in seizures, the hippocampus is the most vulnerable.

The Surviving Sepsis Campaign: Basic/Translational Science Research Priorities

Objectives:

Expound upon priorities for basic/translational science identified in a recent paper by a group of experts assigned by the Society of Critical Care Medicine and the European Society of Intensive Care Medicine.

Data Sources:

Original paper, search of the literature.

Study Selection:

By several members of the original task force with specific expertise in basic/translational science.

Data Extraction:

None.

Data Synthesis:

None.

Conclusions:

In the first of a series of follow-up reports to the original paper, several members of the original task force with specific expertise provided a more in-depth analysis of the five identified priorities directly related to basic/translational science. This analysis expounds on what is known about the question and what was identified as priorities for ongoing research. It is hoped that this analysis will aid the development of future research initiatives.

Elamipretide (SS-31) Improves Functional Connectivity in Hippocampus and Other Related Regions Following Prolonged Neuroinflammation Induced by Lipopolysaccharide in Aged Rats

Neuroinflammation has been recognized as a major cause for neurocognitive diseases. Although the hippocampus has been considered an important region for cognitive dysfunction, the influence of hippocampal neuroinflammation on brain functional connectivity (FC) has been rarely studied. In this study, lipopolysaccharide (LPS) was used to induce systemic inflammation and neuroinflammation in the aged rat brain, while elamipretide (SS-31) was used for treatment. Systemic and hippocampal inflammation were determined using ELISA, while astrocyte responses during hippocampal neuroinflammation were determined by interleukin 1 beta (IL-1β)/tumor necrosis factor alpha (TNFα) double staining immunofluorescence. Oxidative stress was determined by reactive oxidative species (ROS), electron transport chain (ETC) complex, and superoxide dismutase (SOD). Short- (<7 days) and long-term (>30 days) learning and spatial working memory were tested by the Morris water maze (MWM). Resting-state functional magnetic resonance imaging (rs-fMRI) was used to analyze the brain FC by placing seed voxels on the left and right hippocampus. Compared with the vehicle group, rats with the LPS exposure showed an impaired MWM performance, higher oxidative stress, higher levels of inflammatory cytokines, and astrocyte activation in the hippocampus. The neuroimaging examination showed decreased FC on the right orbital cortex, right olfactory bulb, and left hippocampus on day 3, 7, and 31, respectively, after treatment. In contrast, rats with SS-31 treatment showed lower levels of inflammatory cytokines, less astrocyte activation in the hippocampus, and improved MWM performance. Neuroimaging examination showed increased FC on the left-parietal association cortex (L-PAC), left sensory cortex, and left motor cortex on day 7 with the right flocculonodular lobe on day 31 as compared with those without SS-31 treatment. Our study demonstrated that inhibiting neuroinflammation in the hippocampus not only reduces inflammatory responses in the hippocampus but also improves the brain FC in regions related to the hippocampus. Furthermore, early anti-inflammatory treatment with SS-31 has a long-lasting effect on reducing the impact of LPS-induced neuroinflammation.

Persistent inflammatory states and their implications in brain disease

PURPOSE OF REVIEW

Apart from mental, motor and sensory functions, the human central nervous system (CNS) regulates a plethora of homeostatic (autonomic and hormonal) bodily functions. These functions are dependent on specialized neuronal networks. To ensure connectivity of these networks, they are continuously refined and supported by glial cells that outnumber neurons by, according to some accounts, an order of magnitude. Among glial cells, microglia - the brain resident macrophages - plays a crucial role in maintaining neuronal networks. However, in their concomitant role as brain immune cells microglia also engage in inflammatory signaling that may disrupt neuronal networks. Here, we review novel insights for molecular pathways involved in the protective functions of microglia and other immune cells in response to systemic signals and stimuli.

RECENT FINDINGS

Recent evidence suggests that aging and systemic disease push individual microglia toward proinflammatory phenotypes compromising the connectivity of neuronal networks, resulting in neuropsychiatric disease. Furthermore, cells (self as well as the microbiome) outside the CNS have been shown to affect neuronal function.

SUMMARY

These recent findings have critical implications for mental health, particularly of an aging population, in particular for the development of novel immunomodulatory therapies for brain disease.

pSynGAP1 disturbance-mediated hippocampal oscillation network impairment might contribute to long-term neurobehavioral abnormities in sepsis survivors

Although more patients survive sepsis and are increasingly discharged from the hospital, they often experience long-term cognitive and psychological impairment with significant socioeconomic impact. However, the pathophysiological mechanisms have not been fully elucidated. In the present study, we showed that LPS induced long-term neurobehavioral abnormities, as reflected by significantly decreased freezing time to context and sucrose preference. Using a high-throughput quantitative proteomic screen, we showed that phosphorylation of synaptic GTPase-activating protein 1 (pSynGAP1) was identified as the hub of synaptic plasticity and was significantly decreased following LPS exposure. This decreased pSynGAP was associated with significantly lower theta and gamma oscillations in the CA1 of the hippocampus. Notably, restoration of pSynGAP1 by roscovitine was able to reverse most of these abnormities. Taken together, our study suggested that pSynGAP1 disturbance-mediated hippocampal oscillation network impairment might play a critical role in long-term neurobehavioral abnormities of sepsis survivors.

Aging influences in the blood-brain barrier permeability and cerebral oxidative stress in sepsis

Sepsis is a set of serious manifestations throughout the body produced by an infection, leading to changes that compromise cellular homeostasis and can result in dysfunction of the central nervous system. The elderly have a higher risk of developing sepsis than younger peoples. Under the influence of inflammatory mediators and oxidizing agents released in the periphery as a result of the infectious stimulus, changes occur in the blood-brain barrier (BBB) permeability, with neutrophil infiltration, the passage of toxic compounds, activation of microglia and production of reactive species that results in potentiation of neuroimmune response, with the progression of neuronal damage and neuroinflammation. The objective of this study is to compare BBB permeability and the development of oxidative stress in the hippocampus and prefrontal cortex of young and old rats submitted to polymicrobial sepsis induction. Male Wistar rats grouped into sham (60d), sham (210d), cecal ligation and perforation (CLP) (60d) and CLP (210d) with n = 16 per experimental group were evaluated using the CLP technique to induce sepsis. The brain regions were collected at 24 h after sepsis induction to determine BBB permeability, myeloperoxidase (MPO) activity as marker of neutrophil activation, nitrite/nitrate (N/N) levels as marker of reactive nitrogen species, thiobarbituric acid reactive substances as marker of lipid peroxidation, protein carbonylation as marker of protein oxidation, and activity of antioxidant enzyme catalase (CAT). There was an increase in the BBB permeability in the CLP groups, and this was enhanced with aging in both brain region. MPO activity in the brain regions increased in the CLP groups, along with a hippocampal increase in the CLP 210d group compared to the 60d group. The concentration of N/N in the brain region was increased in the CLP groups. The damage to lipids and proteins in the two structures was enhanced in the CLP groups, while only lipid peroxidation was higher in the prefrontal cortex of the CLP 210d group compared to the 60d. CAT activity in the hippocampus was decreased in both CLP groups, and this was also influenced by age, whereas in the prefrontal cortex there was only a decrease in CAT in the CLP 60d group compared to the sham 60d. These findings indicate that aging potentiated BBB permeability in sepsis, which possibly triggered an increase in neutrophil infiltration and, consequently, an increase in oxidative stress.

S100A9 Upregulation Contributes to Learning and Memory Impairments by Promoting Microglia M1 Polarization in Sepsis Survivor Mice

Sepsis-associated encephalopathy (SAE) is a clinical syndrome of brain dysfunction secondary to sepsis, which is characterized by long-term neurocognitive deficits such as memory, attention, and executive dysfunction. However, the mechanisms underlying SAE remain unclear. By using transcriptome sequencing approach, we showed that hippocampal S100A9 was significantly increased in sepsis induced by cecal ligation and puncture (CLP) or lipopolysaccharide (LPS) challenge. Thus, we used S100A9 inhibitor Paquinimod to study the role of S100A9 in cognitive impairments in CLP-induced and LPS-induced mice models of SAE. Sepsis survivor mice underwent behavioral tests or the hippocampal tissues subjected to Western blotting, real-time quantitative PCR, and immunohistochemistry. Our results showed that CLP-induced and LPS-induced memory impairments were accompanied with increased expressions of hippocampal microglia Iba1 and CD86 (M1 markers), but reduced expression of Arg1 (M2 marker). Notably, S100A9 inhibition significantly improved the survival rate and learning and memory impairments in sepsis survivors, with a shift from M1 to M2 phenotype. Taken together, our study suggests that S100A9 upregulation might contribute to learning and memory impairments by promoting microglia M1 polarization in sepsis survivors, whereas S100A9 inhibition might provide a potential therapeutic target for SAE.

Exposure to elevated embryonic kynurenine in rats: Sex-dependent learning and memory impairments in adult offspring

Distinct abnormalities in kynurenine pathway (KP) metabolism have been reported in various psychiatric disorders, including schizophrenia (SZ). Kynurenic acid (KYNA), a neuroactive metabolite of the KP, is elevated in individuals diagnosed with SZ and has been linked to cognitive impairments seen in the disorder. To further understand the role of KYNA in SZ etiology, we developed a prenatal insult model where kynurenine (100 mg/day) is fed to pregnant Wistar rats from embryonic day (ED) 15 to ED 22. As sex differences in the prevalence and severity of SZ have been observed, we presently investigated the impact of prenatal kynurenine exposure on KP metabolism and spatial learning and memory in male and female offspring. Specifically, brain tissue and plasma from offspring (control: ECon; kynurenine-treated: EKyn) in prepuberty (postnatal day (PD) 21), adolescence (PD 32-35), and adulthood (PD 56-85) were collected. Separate cohorts of adult offspring were tested in the Barnes maze to assess hippocampus- and prefrontal cortex-mediated learning and memory. Plasma tryptophan, kynurenine, and KYNA were unchanged between ECon and EKyn offspring across all three ages. Hippocampal and frontal cortex KYNA were elevated in male EKyn offspring only in adulthood, compared to ECon, while brain KYNA levels were unchanged in adult females. Male EKyn offspring were significantly impaired during acquisition of the Barnes maze and during reversal learning in the task. In female EKyn offspring, learning and memory remained relatively intact. Taken together, our data demonstrate that exposure to elevated kynurenine during the last week of gestation results in intriguing sex differences and further support the EKyn model as an attractive tool to study the pathophysiology of schizophrenia.

The surviving sepsis campaign: basic/translational science research priorities

Objectives

Expound upon priorities for basic/translational science identified in a recent paper by a group of experts assigned by the Society of Critical Care Medicine and the European Society of Intensive Care Medicine.

Data sources

Original paper, search of the literature.

Study selection

This study is selected by several members of the original task force with specific expertise in basic/translational science. Data extraction and data synthesis are not available.

Conclusions

In the first of a series of follow-up reports to the original paper, several members of the original task force with specific expertise provided a more in-depth analysis of the five identified priorities directly related to basic/translational science. This analysis expounds on what is known about the question and what was identified as priorities for ongoing research. It is hoped that this analysis will aid the development of future research initiatives.

Differential Effect of Repeated Lipopolysaccharide Treatment and Aging on Hippocampal Function and Biomarkers of Hippocampal Senescence

Markers of brain aging and cognitive decline are thought to be influenced by peripheral inflammation. This study compared the effects of repeated lipopolysaccharide (LPS) treatment in young rats to age-related changes in hippocampal-dependent cognition and transcription. Young Fischer 344 X Brown Norway hybrid rats were given intraperitoneal injections once a week for 7 weeks with either LPS or vehicle. Older rats received a similar injection schedule of vehicle. Old vehicle and young LPS rats exhibited a delay-dependent impairment in spatial memory. Further, LPS treatment reduced the hippocampal CA3-CA1 synaptic response. RNA sequencing, performed on CA1, indicated an increase in genes linked to neuroinflammation in old vehicle and young LPS animals. In contrast to an age-related decrease in transcription of synaptic genes, young LPS animals exhibited increased expression of genes that support the growth and maintenance of synapses. We suggest that the increased expression of genes for growth and maintenance of synapses in young animals represents neuronal resilience/recovery in response to acute systemic inflammation. Thus, the results indicate that repeated LPS treatment does not completely recapitulate the aging phenotype for synaptic function, possibly due to the chronic nature of systemic inflammation in aging and resilience of young animals to acute treatments.

Subcutaneous administration of β-hydroxybutyrate improves learning and memory of sepsis surviving mice

Post-sepsis cognitive impairment is one of the major sequelae in sepsis survivors. Its prevention remains clinically challenging. Here we tested the effects and underlying mechanisms of exogenous β-hydroxybutyrate (BHB) on post-sepsis cognitive impairment. We found that subcutaneous administration of BHB increased survival and body weight recovery of sepsis mice and improved learning and memory of sepsis surviving mice in a cecal ligation and perforation-induced sepsis model. Additionally, the improvement of learning and memory of sepsis surviving mice was still detected even if BHB was administrated at the late stage of sepsis. In contrast, glucose solution did not show similar effects. Mechanistically, subcutaneous administration of BHB increased the BHB level of hippocampus, and limited neuroinflammation and neuroplasticity damage in sepsis mice. Intracerebroventricular administration of BHB also alleviated neuroinflammation and cognitive impairment of sepsis surviving mice. In the coculture of neurons, astrocytes, and BV2 cells (a microglial cell line), knocking down the expression of microglial HCA2 (BHB receptor) via a specific shRNA reduced the protection of BHB to lipopolysaccharide-induced inflammatory response and neuron damage more significantly than knocking down neuronal MCT2 (BHB transporter). These data showed that (1) BHB was a potential pharmacological adjunct treatment for prevention of post-sepsis cognitive impairment and (2) inhibiting neuroinflammation via HCA2 was an important mechanism.

Administration of Bacterial Lipopolysaccharide during Early Postnatal Ontogenesis Induces Transient Impairment of Long-Term Synaptic Plasticity Associated with Behavioral Abnormalities in Young Rats

Infectious diseases in early postnatal ontogenesis often result in cognitive impairments, particularly learning and memory. The essential foundation of learning and memory is long-term synaptic plasticity, which depends on N-methyl-D-aspartate (NMDA) receptors. In the present study, bacterial infection was modeled by treating rat pups with bacterial lipopolysaccharide (LPS, 25 µg/kg) three times, during either the first or the third week of life. These time points are critical for the maturation of NMDA receptors. We assessed the effects of LPS treatments on the properties of long-term potentiation (LTP) in the CA1 hippocampus of young (21–23 days) and adolescent (51–55 days) rats. LTP magnitude was found to be significantly reduced in both groups of young rats, which also exhibited investigative and motor behavior disturbances in the open field test. No changes were observed in the main characteristics of synaptic transmission, although the LTP induction mechanism was disturbed. In rats treated with LPS during the third week, the NMDA-dependent form of LTP was completely suppressed, and LTP switched to the Type 1 metabotropic glutamate receptor (mGluR1)-dependent form. These impairments of synaptic plasticity and behavior were temporary. In adolescent rats, no difference was observed in LTP properties between the control and experimental groups. Lastly, the investigative and motor behavior parameters in both groups of adult rats were similar.

Microglial Ultrastructure in the Hippocampus of a Lipopolysaccharide-Induced Sickness Mouse Model

Sickness behavior is a set of behavioral changes induced by infections and mediated by pro-inflammatory cytokines. It is characterized by fatigue, decreased appetite and weight loss, changes in sleep patterns, cognitive functions, and lost interest in social activity. It can expedite recovery by conserving energy to mount an immune response involving innate immunity. To provide insights into microglial implication in sickness behavior with special focus on cognitive and social impairment, we investigated changes in their ultrastructure and interactions with synapses using a toxemia mouse model. Adult mice were injected with 1 mg/kg lipopolysaccharide (LPS) or saline, and assayed for signs of sickness behavior. LPS treated mice displayed reduced activity in open-field tests 24 h post-injection, while social avoidance and weight gain/loss were not significantly different between treatment groups. Microglia were investigated using electron microscopy to describe changes in their structure and function at nanoscale resolution. Microglial cell bodies and processes were investigated in the hippocampus CA1, a region responsible for learning and memory that is often impacted after peripheral LPS administration. Microglia in LPS treated animals displayed larger cell bodies as well as less complex processes at the time point examined. Strikingly, microglial processes in LPS injected animals were also more likely to contact excitatory synapses and contained more phagocytic material compared with saline injected controls. We have identified at the ultrastructural level significant changes in microglia-synapse interactions shortly after LPS administration, which draws attention to studying the roles of microglia in synaptic rewiring after inflammatory stimuli.

Gold nanoparticles potentiates N-acetylcysteine effects on neurochemicals alterations in rats after polymicrobial sepsis

Herein, we report the effect of gold nanoparticles (AuNP) and n-acetylcysteine (NAC) isolated or in association as important anti-inflammatory and antioxidant compounds on brain dysfunction in septic rats. Male Wistar rats after sham operation or caecal ligation and perforation (CLP) were treated with subcutaneously injection of AuNP (50 mg/kg) and/or NAC (20 mg/kg) or saline immediately and 12 h after surgery. Twenty-four hours after CLP, hippocampus and prefrontal cortex were obtained and assayed for myeloperoxidase (MPO) activity, cytokines, lipid peroxidation, protein carbonyls formation, mitochondrial respiratory chain, and CK activity. AuNP + NAC association decreased MPO activity and pro-inflammatory cytokines production, being more effective than NAC or AuNP isolated treatment. AuNP + NAC association and NAC isolated treatment decreased oxidative stress to lipids in both brain structures, while protein oxidation decreased only in the hippocampus of AuNP + NAC association-treated animals. Complex I activity was increased with AuNP + NAC association and NAC isolated in the hippocampus. Regarding CK activity, AuNP and AuNP + NAC association increased this marker in both brain structures after CLP. Our data provide the first experimental demonstration that AuNP and NAC association was able to reduce sepsis-induced brain dysfunction in rats by decreasing neuroinflammation, oxidative stress parameters, mitochondrial dysfunction and CK activity.

NMDA receptor modulation of glutamate release in activated neutrophils

Background

Neutrophil depletion improves neurologic outcomes in experimental sepsis/brain injury. We hypothesized that neutrophils may exacerbate neuronal injury through the release of neurotoxic quantities of the neurotransmitter glutamate.

Methods

Real-time glutamate release by primary human neutrophils was determined using enzymatic biosensors. Bacterial and direct protein-kinase C (Phorbol 12-myristate 13-acetate; PMA) activation of neutrophils in human whole blood, isolated neutrophils or human cell lines were compared in the presence/absence of N-Methyl-d-aspartic acid receptor (NMDAR) antagonists. Bacterial and direct activation of neutrophils from wild-type and transgenic murine neutrophils deficient in NMDAR-scaffolding proteins were compared using flow cytometry (phagocytosis, reactive oxygen species (ROS) generation) and real-time respirometry (oxygen consumption).

Findings

Both glutamate and the NMDAR co-agonist d-serine are rapidly released by neutrophils in response to bacterial and PMA-induced activation. Pharmacological NMDAR blockade reduced both the autocrine release of glutamate, d-serine and the respiratory burst by activated primary human neutrophils. A highly specific small-molecule inhibitor ZL006 that limits NMDAR-mediated neuronal injury also reduced ROS by activated neutrophils in a murine model of peritonitis, via uncoupling of the NMDAR GluN2B subunit from its' scaffolding protein, postsynaptic density protein-95 (PSD-95). Genetic ablation of PSD-95 reduced ROS production by activated murine neutrophils. Pharmacological blockade of the NMDAR GluN2B subunit reduced primary human neutrophil activation induced by Pseudomonas fluorescens, a glutamate-secreting Gram-negative bacillus closely related to pathogens that cause hospital-acquired infections.

Interpretation

These data suggest that release of glutamate by activated neutrophils augments ROS production in an autocrine manner via actions on NMDAR expressed by these cells.

Fund

GLA: Academy Medical Sciences/Health Foundation Clinician Scientist. AVG is a Wellcome Trust Senior Research Fellow.

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Neutrophil depletion improves neurologic outcome after injury and infection.

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Pharmacologic NMDAR blockade reduces rapid autocrine release of glutamate/d-serine from activated neutrophils.

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Genetic ablation/small-molecule inhibition of PSD-95 reduces neutrophil ROS.

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NMDAR blockade reduces human neutrophil activated by glutamate-secreting bacteria.

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Activated neutrophils may exacerbate neuronal injury in various forms of critical illness through the release of glutamate.

Activation of β2-Adrenoceptor Attenuates Sepsis-Induced Hippocampus-Dependent Cognitive Impairments by Reversing Neuroinflammation and Synaptic Abnormalities

Sepsis-associated encephalopathy induces cognitive dysfunction via mechanisms that commonly involve neuroinflammation and synaptic plasticity impairment of the hippocampus. The β2-adrenoceptor (β2-AR) is a G-protein coupled receptor that regulates immune response and synaptic plasticity, whereas its dysfunction has been implicated in various neurodegenerative diseases. Thus, we hypothesized abnormal β2-AR signaling is involved in sepsis-induced cognitive impairment. In the present study, C57BL/6 mice were subjected to cecal ligation and puncture (CLP) to mimic the clinical human sepsis-associated encephalopathy. The levels of hippocampal β2-AR, proinflammatory cytokines tumor necrosis factor (TNF-α), interleukin-1β (IL-1β), IL-6, cAMP-response element binding protein (CREB), brain derived neurotrophic factor (BDNF), post-synaptic density protein 95 (PSD95), and NMDA receptor 2 B subtypes (GluN2B) were determined at 6, 12, 24 h and 7 and 16 days after CLP. For the interventional study, mice were treated with β2-AR agonist clenbuterol in two ways: early treatment (immediately following CLP) and delayed treatment (on the 8th day following CLP). Neurobehavioral performances were assessed by open field and fear conditioning tests. Here, we found that hippocampal β2-AR expression was significantly decreased starting from 12 h and persisted until 16 days following CLP. Besides, sepsis mice also exhibited increasing neuroinflammation, down-regulated CREB/BDNF, decreasing PSD95 and GluN2B expression, and displayed hippocampus-dependent cognitive impairments. Notably, early clenbuterol treatment alleviated sepsis-induced cognitive deficits by polarizing microglia toward an anti-inflammatory phenotype, reducing proinflammatory cytokines including IL-1β, TNF-α, and up-regulating CREB/BDNF, PSD95, and GluN2B. Intriguingly, delayed clenbuterol treatment also improved cognitive impairments by normalization of hippocampal CREB/BDNF, PSD95, and GluN2B. In summary, our results support the beneficial effects of both early and delayed clenbuterol treatment, which suggests that activation of β2-AR has a translational value in sepsis-associated organ dysfunction including cognitive impairments.

Inhibiting RIP1 Improves Chronic Stress-Induced Cognitive Impairments in D-Galactose-Induced Aging Mice

Mounting evidence shows that chronic stress can affect both the structure and function of the brain resulting in decreased synaptic plasticity and cognitive dysfunction. Although several studies have indicated that aged brains are more vulnerable to chronic stress, it remains unknown how to prevent stress-induced memory deficits in aged animals. Neuroinflammation plays an important role in the pathogenesis of chronic stress-related brain dysfunction. Receptor-interacting protein 1 (RIP1) is a key molecule that can modulate inflammation, apoptosis, and necroptosis. Here, we investigated whether inhibiting RIP1 using necrostatin-1 during chronic stress could improve chronic stress-related brain dysfunction in D-galactose-induced aging mice. The stressed mice underwent restraint stress for 14 days. Necrostatin-1 (6.25 mg/kg) or vehicle was administered intraperitoneally once every 3 days during the stress period. Locomotor activity was tested using the open field test and cognitive function was assessed using the novel object recognition and Barnes maze tests. The hippocampus was collected to assess neuroinflammation (Iba1, IL-1α, IL-1β, TNF-α, and C1q), necroptosis [RIP1, RIP3, mixed lineage kinase domain-like (MLKL), and NF-κB], neuroplasticity (doublecortin, NR1, NR2A, NR2B, GluA1, and GluA2), and the expression of glucocorticoid and mineralocorticoid receptors. Blood samples were collected to quantify the levels of corticosterone. We found that chronic stress induced obvious memory impairment and neuroinflammation, decreased neurogenesis and GluA2 expression, and increased the expression of RIP1 and NF-κB. Inhibiting RIP1 by necrostatin-1 during chronic stress rescued the memory impairment and alleviated the pathological changes induced by stress. These suggest that inhibiting RIP1 using necrostatin-1 improves chronic stress-related brain dysfunction in D-galactose-induced aging mice. The potential mechanisms include limitation of neuroinflammation and the rescue of neurogenesis and GluA2 expression.

Inhibiting RIPK1 Limits Neuroinflammation and Alleviates Postoperative Cognitive Impairments in D-Galactose-Induced Aged Mice

Neuroinflammation plays a critical role in the pathogenesis of postoperative cognitive dysfunction (POCD) of the elderly patients. Receptor-interacting protein kinase1 (RIPK1) is a key molecular switch modulating inflammation, apoptosis and necroptosis. Here, we investigated whether inhibiting RIPK1 by necrostatin-1 (Nec-1) could limit neuroinflammation and attenuate POCD in D-Galactose (D-Gal)-induced aged mice. The mice were subjected to anesthesia and partial hepatectomy, and necrostatin-1 was administered intraperitoneally 1 h prior to anesthesia and surgery. Cognitive function and movement were tested 24 h after surgery by open field, Barnes maze and puzzle box. The hippocampal tissues were collected to detect the following: neuroinflammation (Iba-1, IL-1α, IL-1β, TNF-α), Necroptosis (Propidium Iodide (PI) labeling, RIPK1, nuclear transcription factor kappa B (NF-κB) and neuroplasticity (doublecortin (DCX), NR2B, GluA1, GluA2). We found that anesthesia and surgery induced a significant deficit in spatial memory acquisition and impairment of executive function and memory to simple task in D-Galactose-induced aged mice. Inhibiting RIPK1 by necrostatin-1 strikingly mitigated cognitive impairment and alleviated postoperative amplified neuroinflammation, necroptosis and GluA1 loss in hippocampus. These suggest that targeting RIPK1 by necrostatin-1 may serve as a promising therapeutics for prevention of POCD in elderly patients.

Long-Term Cognitive Outcomes After Sepsis: a Translational Systematic Review

Sepsis is systemic inflammatory response syndrome with a life-threatening organ dysfunction that is caused by an unbalanced host immune response in an attempt to eliminate invasive microorganisms. We posed questions, "Does sepsis survivor patients have increased risk of neuropsychiatric manifestations?" and "What is the mechanism by which sepsis induces long-term neurological sequelae, particularly substantial cognitive function decline in survivor patients and in pre-clinical sepsis models?" The studies were identified by searching PubMed/MEDLINE (National Library of Medicine), PsycINFO, EMBASE (Ovid), LILACS (Latin American and Caribbean Health Sciences Literature), IBECS (Bibliographical Index in Spanish in Health Sciences), and Web of Science databases for peer-reviewed journals that were published until January 2018. A total of 3555 papers were included in the primary screening. After that, 130 articles were selected for the study. A number of pre-clinical studies have shown an auto amplification of pro-inflammatory cytokines such as tumor necrosis factor alpha (TNF-α), interleukin (IL)-1β, and IL-6 in the first few hours after sepsis induction, also increased blood-brain barrier permeability, elevated levels of matrix metalloproteinases, increased levels of damage-associated molecular patterns were demonstrated. In addition, the rodents presented long-term cognitive impairment in different behavioral tasks that were prevented by blocking the mechanism of action of these inflammatory mediators. Clinical studies have showed that sepsis survivors presented increased bodily symptoms such as fatigue, pain, visual disturbances, gastrointestinal problems, and neuropsychiatric problems compared to before sepsis. Sepsis leaves the survivors with an aftermath of physiological, neuropsychiatric, and functional impairment. Systematic review registration: CRD42017071755.