CXCR5 Knockdown Attenuates Hippocampal Neurogenesis Deficits and Cognitive Impairment in a Mouse Model of Sepsis-associated Encephalopathy

Down-regulating nuclear factor of activated T cells 1 alleviates cognitive deficits in a mouse model of sepsis-associated encephalopathy, possibly by stimulating hippocampal neurogenesis

Sepsis-associated encephalopathy (SAE) is a common complication of sepsis, and has been associated with increased morbidity and mortality. Nuclear factor of activated T cells (NFATs) 1, a transcriptional factor that regulates T cell development, activation and differentiation, has been implicated in neuronal plasticity. Here we examined the potential role of NFAT1 in sepsis-associated encephalopathy in mice. Adult male C57BL/6J mice received intracerebroventricular injections of short interfering RNA against NFAT1 or sex-determining region Y-box 2 (SOX2), or a scrambled control siRNA prior to cecal ligation and perforation (CLP). A group of mice receiving sham surgery were included as an additional control. CLP increased escape latency and decreased the number of crossings into, and total time spent within, the target quadrant in the Morris water maze test. CLP also decreased the freezing time in context-dependent, but not context-independent, fear conditioning test. Knockdown of either NFAT1 or SOX2 attenuated these behavioral deficits. NFAT1 knockdown also attenuated CLP-induced upregulation of SOX2, increased the numbers of nestin-positive cells and newborn astrocytes, reduced the number of immature newborn neurons, and promoted the G1 to S transition of neural stem cells in hippocampus. These findings suggest that NFAT1 may contribute to sepsis-induced behavioral deficits, possibly by promoting SOX2 signaling and neurogenesis.

Mechanism of IRF5-regulated CXCL13/CXCR5 Signaling Axis in CCI-induced Neuropathic Pain in Rats

BACKGROUND

Neuropathic pain is chronic and affects the patient's life. Studies have shown that IRF5 and CXCL13/CXCR5 are involved in neuropathic pain; however, their interactions are unknown.

OBJECTIVE

In this study, a rat neuropathic pain model was constructed by inducing chronic compression injury (CCI). IRF5 recombinant lentiviral vector and CXCL13 neutralizing antibody were administered to investigate their action mechanisms in neuropathic pain. Consequently, the new strategies for disease treatment could be evolved.

METHODS

The CCI rats were intrathecally injected with recombinant lentivirus plasmid LV-IRF5 (overexpression), LV-SH-IRF5 (silencing), and CXCL13 neutralizing antibody. Mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were measured. The tumor necrosis factor (TNF)-alpha, interleukin (IL)-1β, and IL-6 levels were recorded via the enzyme-linked immunosorbent assay (ELISA). The spinal cord was stained using hematoxylin-eosin (HE). The binding of IRF5 to CXCL13 was analyzed by chromatin immunoprecipitation (ChIP) and dual luciferase reporter assay. The IRF5, neuronal nuclei (NeuN), CXCL13, and CXCR5 expressions were detected through quantitative real-time polymerase chain reaction and Western blot.

RESULTS

The MWT and TWL values in the CCI group were lower than in the Sham group. The expressions of CXCL13, CXCR5, and IRF5 in CCI rats were gradually increased with the modeling time. IRF5 silencing suppressed the expression of NeuN and lumbar enlargement in CCI rats and promoted MWT and TWL. Moreover, IRF5 silencing inhibited the expressions of CXCR5 and CXCL13 genes and down-regulated the expression levels of inflammatory factors. IRF5 was directly and specifically bound with the endogenous CXCL13 promoter and thus regulated it. IRF5 overexpression exacerbated the disease phenotype of CCI-induced neuropathic pain in rats. Administration of CXCL13 neutralizing antibodies reversed the IRF5 overexpression effects.

CONCLUSION

The IRF5 silencing alleviated neuropathic pain in CCI rats by downregulating the pain threshold, inflammatory cytokine levels, and CXCL13/CXCR5 signaling. IRF5 overexpression exacerbated the disease parameters of CCI-induced neuropathic pain in rats; however, they were reversed by neutralizing antibodies against CXCL13.

Memantine Attenuates Cognitive and Emotional Dysfunction in Mice with Sepsis-Associated Encephalopathy

Sepsis-associated encephalopathy (SAE) is the most common complication of sepsis, with increased morbidity and mortality. To date, there has still been no established pharmacological therapy. Memantine, as an NMDA (N-methyl-d-aspartate) receptor antagonist, exhibited neuroprotective effects against cognitive and emotional dysfunction in many disorders. We performed cecal ligation and puncture (CLP) inducing sepsis as the ideal animal model of SAE. CLP-induced septic mice were given a memantine treatment through intragastric administration. The novel object recognition test indicated that memantine significantly improved cognitive dysfunction in septic mice. The open field test revealed that the anxiety-like behaviors and locomotion ability of septic mice were relieved by memantine. The pole test further confirmed the protective effects of memantine against immobility. Memantine significantly inhibited the excessive glutamate production and improved impaired neurogenesis on first and seventh day after sepsis, accompanying with reducing proinflammatory cytokines production (tumor necrosis factor alpha (TNF-α), interleukin (IL)-1beta (IL-1β), and IL-10) and microglia activation in the brain of SAE. In addition, memantine treatment also reducing sepsis-induced brain blood barrier disruption via inhibiting the expression of metalloproteinase-9 (MMP-9). In conclusion, memantine exerted neuro-protective effects against cognitive and emotional defects, which might be considered as a promising therapy for SAE.

Acute and long-term cognitive impairment following sepsis: mechanism and prevention

INTRODUCTION

Sepsis is a severe host response to infection, which induces both acute and long-term cognitive impairment. Despite its high incidence following sepsis, the underlying mechanisms remain elusive and effective treatments are not available clinically.

AREA COVERED

This review focuses on elucidating the pathological mechanisms underlying cognitive impairment following sepsis. Specifically, the authors discuss the role of systemic inflammation response, blood-brain barrier disruption, neuroinflammation, mitochondrial dysfunction, neuronal dysfunction, and Aβ accumulation and tau phosphorylation in cognitive impairment after sepsis. Additionally, they review current strategies to ameliorate cognitive impairment.

EXPERT OPINION

Potential interventions to reduce cognitive impairment after sepsis include earlier diagnosis and effective infection control, hemodynamic homeostasis, and adequate brain perfusion. Furthermore, interventions to reduce inflammatory response, reactive oxygen species, blood-brain barrier disruption, mitochondrial dysfunction, neuronal injury or death could be beneficial. Implementing strategies to minimize delirium, sleep disturbance, stress factors, and immobility are also recommended. Furthermore, avoiding neurotoxins and implementing early rehabilitation may also be important for preventing cognitive impairment after sepsis.

Resveratrol glycoside mediates microglial endoplasmic reticulum stress to mitigate LPS-induced sepsis-associated cognitive dysfunction

BACKGROUND

As a common complication of sepsis, sepsis-associated encephalopathy (SAE) is characterized by diffuse brain dysfunction and neurological damage and closely associated with long-term cognitive dysfunction. The dysregulated host response triggered by neurotoxicity of microglia is an important cause of diffuse brain dysfunction in SAE. Resveratrol glycoside has anti-inflammatory and antioxidant effects. However, there is no evidence whether resveratrol glycoside could alleviate SAE.

METHODS

LPS administration was used to induce SAE in mice. Step-down test (SDT) and Morris water maze test (MWM) were performed to evaluate the cognitive function of mice with SAE. Western blot and immunofluorescence were used to reveal the endoplasmic reticulum stress (ERS) regulation. Microglia cell line BV-2 was used to validate the effect of resveratrol glycoside on LPS-stimulated ERS in vitro.

RESULTS

Compared with the control group, LPS-stimulated mice had decreased cognitive function, but this phenomenon was well reversed by resveratrol glycoside administration, in which the SDT assay showed longer retention time, both in short-term memory (STM) and long-term memory (LTM). Western blot indicated that the expression of ER stress-related protein PERK/CHOP in LPS-stimulated mice were significantly increased, while that in the resveratrol glycoside-treated group were relieved. Furthermore, Immunofluorescence revealed resveratrol glycoside mainly worked on microglia in mediating the ER stress, in which the expression of PERK/CHOP were significantly inhibited in resveratrol glycoside group mice. In vitro, BV2 showed consistent results with the aforementioned.

CONCLUSION

Resveratrol glycoside could alleviate the cognitive dysfunction caused by LPS-induced SAE, mainly by inhibiting the ER stress and maintaining the homeostasis of ER function of microglia.

Disrupted metabolic and spontaneous neuronal activity of hippocampus in sepsis associated encephalopathy rats: A study combining magnetic resonance spectroscopy and resting-state functional magnetic resonance imaging

BACKGROUND

The diagnosis of sepsis associated encephalopathy (SAE) remains challenging in clinical settings because of a lack of specific biomarkers. Functional magnetic resonance imaging (fMRI) and proton magnetic resonance spectroscopy (1H-MRS) can be used to aid in the diagnosis of cognition related diseases. This study investigated changes in functional activities and brain metabolites in the hippocampus in SAE rats by fMRI and 1H-MRS.

MATERIALS AND METHODS

Sepsis associated encephalopathy rats underwent cecal ligation and perforation (CLP) surgery. The Morris water maze (MWM) test was then used to evaluate cognitive function. Resting state-fMRI and 1H-MRS scanning were performed 7 and 14 days after CLP surgery to reveal spontaneous neuronal activity and metabolite changes in the hippocampus. The amplitude of low-frequency fluctuation (ALFF) was used to evaluate spontaneous neuronal activity in the hippocampus. Creatine (Cr), Myo-inositol (mI), and glutamine/glutamate (Glx) levels were measured with 1H-MRS scanning. Immunofluorescence and levels of interleukin (IL)-1β, interleukin (IL)-6, and C-reactive protein (CRP) in the hippocampus were additionally detected to evaluate microglial mediated inflammatory responses. Statistical analysis was performed to evaluate correlations between hippocampal metabolism and behavioral findings.

RESULTS

Cecal ligation and perforation treated rats exhibited impaired learning and memory function in the MWM test at days 7 and 14. Elevation of IL-1β in the hippocampus, as well as immunofluorescence results, confirmed severe neuro inflammation in the hippocampus in SAE rats. Compared with the sham group, the ALFF of the right CA-1 area of the hippocampus was higher at day 7after CLP surgery. The Glx/Cr and mI/Cr ratios were enhanced at day 7 after CLP surgery and slightly lower at day 14 after CLP surgery. The ALFF value, and Glx/Cr and mI/Cr ratios were negatively correlated with time spent in the target quadrant in the MWM test.

CONCLUSION

Spontaneous neuronal activity and metabolites showed significant alterations in SAE rats. The elevated ALFF value, Glx/Cr ratio, and mI/Cr ratio in the hippocampus were positively associated with cognitive deficits. Changes in ALFF and metabolites in hippocampus may serve as potential neuroimaging biomarkers of cognitive disorders in patients with SAE.

Short Chain Fatty Acids Protect the Cognitive Function of Sepsis Associated Encephalopathy Mice via GPR43

Objective

This study aims to analyze the changes of fecal short chain fatty acids (SCFAs) content and gut microbiota composition in sepsis associated encephalopathy (SAE) mice, further evaluating the effect of SCFAs on cognitive function and the underlying mechanism in SAE mice.

Methods

A total of 55 male adult C57BL/6 mice (2–3 months of age, 20–25 g) were divided into four groups randomly: sham group (n = 10), cecal ligation and puncture group (CLP group, n = 15), CLP+SCFAs group (n = 15), and CLP+SCFAs+GLPG0974 group (n = 15). Seven days after surgery, fecal samples were collected for microbiota composition and SCFA analysis from 6 mice in each group randomly. Behavioral test was applied to assess cognitive impairment at the same time. After that, mice were sacrificed and brain tissue was harvested for inflammatory cytokines analysis.

Results

The levels of acetic acid (.57 ± 0.09 vs 2.00 ± 0.24, p < 0.001) and propionic acid (.32 ± 0.06 vs .66 ± 0.12, p = 0.002) were significantly decreased in the CLP group compared with the sham group. The administration of SCFAs significantly increased the levels of acetic acid (1.51 ± 0.12 vs. 0.57 ± 0.09, p < 0.001) and propionic acid (0.54 ± 0.03 vs. 0.32 ± 0.06, p = 0.033) in CLP+SCFAs group compared with CLP group. Relative abundance of SCFAs-producing bacteria, including Allobaculum (0.16 ± 0.14 vs. 15.21 ± 8.12, p = 0.037), Bacteroides (1.82 ± 0.38 vs. 15.21 ± 5.95, p = 0.002) and Bifidobacterium (0.16 ± 0.06 vs. 2.24 ± 0.48, p = 0.002), significantly decreased in the CLP group compared with the sham group. The behavioral tests suggested that cognitive function was impaired in SAE mice, which could be alleviated by SCFAs pretreatment. ELISA tests indicated that the levels of IL-1β, IL-6, and TNF-α were elevated in SAE mice and SCFAs could lower them. However, the GPR43 antagonist, GLPG0974, could reverse the cognitive protective effect and anti-neuroinflammation effect of SCFAs.

Conclusion

Our study suggested that in SAE, the levels of acetate and propionate decreased significantly, accompanied by gut microbiota dysbiosis, particularly a decrease in SCFAs-producing bacteria. GPR43 was essential for the anti-neuroinflammation and cognitive protective effect of SCFAs in SAE.

Inflammatory mediators of cytokines and chemokines in sepsis: From bench to bedside

Background: Sepsis is a serious clinical condition characterized by damage to the immune system as a result of an uncontrolled response to infection. Septic patients show complications such as fever, cardiovascular shock, and/or systemic organ failure. Acute organ failure formed in sepsis mostly affects the respiratory and cardiovascular systems. In sepsis, responses including pro-inflammatory and anti-inflammatory processes in addition to the Toll-Like Receptor 4 (TLR4) signals leading to the release of inflammatory mediators have been suggested to be fundamental pathways in the pathophysiology of sepsis. Purpose: In this context, unregulated levels of sepsis-associated inflammatory mediators may increase the risk of mortality. In sepsis, infection-induced pathogens lead to a systemic inflammatory response. These systemic responses may contribute to septic shock and organ dysfunction. In the unfavorable clinical course of sepsis, an uncontrolled inflammatory response is observed. Accordingly, the mechanism of inflammatory mediators such as cytokines and chemokines in sepsis might increase. Neurotransmitters and gene regulators affect inflammatory mediators and control the inflammatory response. In this review, we aimed to show the new therapeutic targets in sepsis treatment with current studies. New clinical implications targeting inflammatory mediators in high mortality affected by the uncontrolled inflammatory response in sepsis can contribute to the understanding of the symptoms.

CXCR5 down-regulation alleviates cognitive dysfunction in a mouse model of sepsis-associated encephalopathy: potential role of microglial autophagy and the p38MAPK/NF-κB/STAT3 signaling pathway

Background

Cognitive deficits are common in patients with sepsis. Previous studies in sepsis-associated encephalopathy (SAE) implicated the C-X-C chemokine receptor type (CXCR) 5. The present study used a mouse model of SAE to examine whether CXCR5 down-regulation could attenuate cognitive deficits.

Methods

Sepsis was induced in adult male C57BL/6 J and CXCR5^−/− mice by cecal ligation and puncture (CLP). At 14–18 days after surgery, animals were tested in a Morris water maze, followed by a fear conditioning test. Transmission electron microscopy of hippocampal sections was used to assess levels of autophagy. Primary microglial cultures challenged with lipopolysaccharide (LPS) were used to examine the effects of short interfering RNA targeting CXCR5, and to investigate the possible involvement of the p38MAPK/NF-κB/STAT3 signaling pathway.

Results

CLP impaired learning and memory and up-regulated CXCR5 in hippocampal microglia. CLP activated hippocampal autophagy, as reflected by increases in numbers of autophagic vacuoles, conversion of microtubule-associated protein 1 light chain 3 (LC3) from form I to form II, accumulation of beclin-1 and autophagy-related gene-5, and a decrease in p62 expression. CLP also shifted microglial polarization to the M1 phenotype, and increased levels of IL-1β, IL-6 and phosphorylated p38MAPK. CXCR5 knockout further enhanced autophagy but partially reversed all the other CLP-induced effects, including cognitive deficits. Similar effects on autophagy and cytokine expression were observed after knocking down CXCR5 in LPS-challenged primary microglial cultures; this knockdown also partially reversed LPS-induced up-regulation of phosphorylated NF-κB and STAT3. The p38MAPK agonist P79350 partially reversed the effects of CXCR5 knockdown in microglial cultures.

Conclusions

CXCR5 may act via p38MAPK/NF-κB/STAT3 signaling to inhibit hippocampal autophagy during sepsis and thereby contribute to cognitive dysfunction. Down-regulating CXCR5 can restore autophagy and mitigate the proinflammatory microenvironment in the hippocampus.

Chemokine CXCL13 acts via CXCR5-ERK signaling in hippocampus to induce perioperative neurocognitive disorders in surgically treated mice

Background

Perioperative neurocognitive disorders (PNDs) occur frequently after surgery and worsen patient outcome. How C-X-C motif chemokine (CXCL) 13 and its sole receptor CXCR5 contribute to PNDs remains poorly understood.

Methods

A PND model was created in adult male C57BL/6J and CXCR5^−/− mice by exploratory laparotomy. Mice were pretreated via intracerebroventricular injection with recombinant CXCL13, short hairpin RNA against CXCL13 or a scrambled control RNA, or ERK inhibitor PD98059. Then surgery was performed to induce PNDs, and animals were assessed in the Barnes maze trial followed by a fear-conditioning test. Expression of CXCL13, CXCR5, and ERK in hippocampus was examined using Western blot, quantitative PCR, and immunohistochemistry. Levels of interleukin-1 beta (IL-1β) and tumor necrosis factor alpha (TNF-α) in hippocampus were assessed by Western blot.

Results

Surgery impaired learning and memory, and it increased expression of CXCL13 and CXCR5 in the hippocampus. CXCL13 knockdown partially reversed the effects of surgery on CXCR5 and cognitive dysfunction. CXCR5 knockout led to similar cognitive outcomes as CXCL13 knockdown, and it repressed surgery-induced activation of ERK and production of IL-1β and TNF-α in hippocampus. Recombinant CXCL13 induced cognitive deficits and increased the expression of phospho-ERK as well as IL-1β and TNF-α in hippocampus of wild-type mice, but not CXCR5^−/− mice. PD98059 partially blocked CXCL13-induced cognitive dysfunction as well as production of IL-1β and TNF-α.

Conclusions

CXCL13-induced activation of CXCR5 may contribute to PNDs by triggering ERK-mediated production of pro-inflammatory cytokines in hippocampus.

Sepsis-associated encephalopathy and septic encephalitis: an update

INTRODUCTION

Sepsis-associated encephalopathy (SAE) and septic encephalitis (SE) are associated with increased mortality, long-term cognitive impairment, and focal neurological deficits.

AREAS COVERED

The PUBMED database was searched 2016-2020. The clinical manifestation of SAE is delirium, SE additionally is characterized by focal neurological symptoms. SAE is caused by inflammation with endothelial/microglial activation, increase of permeability of the blood-brain-barrier, hypoxia, imbalance of neurotransmitters, glial activation, axonal, and neuronal loss. Septic-embolic (SEE) and septic-metastatic encephalitis (SME) are characterized by focal ischemia (SEE) and small abscesses (SME). The continuum between SAE, SME, and SEE is documented by imaging techniques and autopsies. The backbone of treatment is rapid optimum antibiotic therapy. Experimental approaches focus on modulation of inflammation, stabilization of the blood-brain barrier, and restoration of membrane/mitochondrial function.

EXPERT OPINION

The most promising diagnostic approaches are new imaging techniques. The most important measure to fight delirium remains establishment of daily structure and adequate sensory stimuli. Dexmedetomidine and melatonin appear to reduce the frequency of delirium, their efficacy in SAE and SE remains to be established. Drugs already licensed for other indications or available as food supplements which may be effective in SAE are statins, L-DOPA/benserazide, β-hydroxybutyrate, palmitoylethanolamide, and tetracyclines or other bactericidal non-lytic antibiotics.