Role of neural barriers in the pathogenesis and outcome of Streptococcus pneumoniae meningitis

The Effects of Appropriate Perioperative Exercise on Perioperative Neurocognitive Disorders: a Narrative Review

Perioperative neurocognitive disorders (PNDs) are now considered the most common neurological complication in older adult patients undergoing surgical procedures. A significant increase exists in the incidence of post-operative disability and mortality in patients with PNDs. However, no specific treatment is still available for PNDs. Recent studies have shown that exercise may improve cognitive dysfunction-related disorders, including PNDs. Neuroinflammation is a key mechanism underlying exercise-induced neuroprotection in PNDs; others include the regulation of gut microbiota and mitochondrial and synaptic function. Maintaining optimal skeletal muscle mass through preoperative exercise is important to prevent the occurrence of PNDs. This review summarizes current clinical and preclinical evidence and proposes potential molecular mechanisms by which perioperative exercise improves PNDs, providing a new direction for exploring exercise-mediated neuroprotective effects on PNDs. In addition, it intends to provide new strategies for the prevention and treatment of PNDs.

Metabolic insights and background from naturally affected pigs during Streptococcus suis outbreaks

Streptococcus suis (S. suis) is an endemic zoonotic pathogen still lacking adequate prevention in pigs. The present case study looked back to the occurrence and consequences of S. suis outbreaks in our swine research facilities in search of new metabolic and physiological insight. From a series of outbreaks, a dataset was created including 56 pigs sampled during disease detection based on clinical signs. Pigs suspected with S. suis infection were defined as diseased (n = 28) and included pigs defined as neurologically diseased (n = 20) when severe neurological signs (central nervous system dysfunctions, i.e., opisthotonos, ataxia, and generalized tremor) were observed. Another set of 28 pigs included respective pen mates from each case and were defined as control. Representative deaths were confirmed to be caused by S. suis. Tonsillar swabs were collected and analyzed by quantitative polymerase chain reaction (qPCR) for total bacteria, total S. suis, and S. suis serotypes (SS) 2 (and/or 1/2) and 9. Blood and sera were analyzed to quantify blood gases, minerals, and S. suis reactive immunoglobulins against current isolates. Data collected included litter sibling associations, birth and weaning body weight (BW), and average daily gain (ADG) 7 d after the disease detection. In general, the disease increased pH, sO2 and the incidence of alkalosis, but reduced pCO2, glucose, Ca, P, Mg, K, and Na in blood/serum compared to control. The SS2 (and/or SS1/2) prevalence was significantly (P < 0.05) increased in neurologically diseased pigs and its relative abundance tended (P < 0.10) to increase in tonsils. In contrast, the relative abundance of total S. suis was lower (P > 0.05) in diseased pigs than control pigs. Levels of S. suis reactive IgG2 were lower, but IgM were higher (P < 0.03) in neurologically affected pigs compared to control. Furthermore, there was an increased proportion of sibling pigs that were diseased compared to control. In conclusion, our results evidence that naturally affected pigs were associated to average performing pigs without any predisease trait to highlight but a sow/litter effect. Besides, neurologically affected pigs had increased S. suis (SS2 and/or 1/2) prevalence and relative abundance, a respiratory alkalosis profile, and mineral loss.

Immune Activation and Inflammatory Response Mediated by the NOD/Toll-like Receptor Signaling Pathway-The Potential Mechanism of Bullfrog (Lithobates catesbeiana) Meningitis Caused by Elizabethkingia miricola

Elizabethkingia miricola is an emerging opportunistic pathogen that is highly pathogenic in both immunocompromised humans and animals. Once the disease occurs, treatment can be very difficult. Therefore, a deep understanding of the pathological mechanism of Elizabethkingia miricola is the key to the prevention and control of the disease. In this study, we isolated the pathogenic bacteria from bullfrogs with dark skin color, weak limbs, wryneck, and cataracts. Via subsequent morphological observations and a 16S rRNA gene sequence analysis, the pathogen was identified as Elizabethkingia miricola. The histopathological and transmission electron microscopy analysis revealed that the brain was the main target organ. Therefore, brain samples from diseased and healthy bullfrogs were used for the RNA-Seq analysis. The comparative transcriptome analysis revealed that the diseased bullfrog brain was characterized by the immune activation and inflammatory response, which were mediated by the "NOD-like receptor signaling pathway" and the "Toll-like receptor signaling pathway". We also performed qRT-PCR to examine the expression profile of inflammation-related genes, which further verified the reliability of our transcriptome data. Based on the above results, it was concluded that the NOD/Toll-like receptor-related networks that dominate the immune activation and inflammatory response were activated in the brain of Elizabethkingia miricola-infected bullfrogs. This study contributes to the search for therapeutic targets for bullfrog meningitis and provides basic information for establishing effective measures to prevent and control bullfrog meningitis.

Oral GSH Exerts a Therapeutic Effect on Experimental Salmonella Meningitis by Protecting BBB Integrity and Inhibiting Salmonella-induced Apoptosis

Bacterial meningitis (BM) is the main cause of the central nervous system (CNS) infection and continues to be an important cause of mortality and morbidity. Glutathione (GSH), an endogenous tripeptide antioxidant, has been proved to exert crucial role in reducing superoxide radicals, hydroxyl radicals and peroxynitrites. The purpose of this study is to expand the application scope of GSH via exploring its therapeutic effect on BM caused by Salmonella typhimurium SL1344 and then provide a novel approach for the treatment of BM. The results suggested that intragastric administration of GSH could significantly increase median survival and improve experimental autoimmune encephalomyelitis score of BM model mice. However, exogenous GSH did not affect the adhesion, invasion and cytotoxicity of SL1344 to C6, BV2 and primary microglia. Due to the contradiction between the therapeutic and bactericidal effects of GSH, the effect of GSH on blood-brain barrier (BBB) was investigated to explore its action target for the treatment of meningitis. GSH was found to repair the damage of BBB and then prevent the leakage of SL1344 from the brain to the blood circulation. The repaired BBB could also effectively reduce the entry of macrophages and neutrophils into the brain, and significantly reverse the microglia activation induced by SL1344. More importantly, exogenous GSH was proved to reduce mouse brain cell apoptosis by inhibiting the activation of caspase-8 followed by caspase-3, and reversing the up-regulation of ICAD and PARP-1 caused by SL1344.

Immunological defense of CNS barriers against infections

Neuroanatomical barriers with physical, chemical, and immunological properties play an essential role in preventing the spread of peripheral infections into the CNS. A failure to contain pathogens within these barriers can result in very serious CNS diseases. CNS barriers are inhabited by an elaborate conglomerate of innate and adaptive immune cells that are highly responsive to environmental challenges. The CNS and its barriers can also be protected by memory T and B cells elicited by prior infection or vaccination. Here, we discuss the different CNS barriers from a developmental, anatomical, and immunological standpoint and summarize our current understanding of how memory cells protect the CNS compartment. We then discuss a contemporary challenge to CNS-barrier system (SARS-CoV-2 infection) and highlight approaches to promote immunological protection of the CNS via vaccination.

Gut microbiota mediates cognitive impairment in young mice after multiple neonatal exposures to sevoflurane

Multiple exposures to anesthesia may increase the risk of cognitive impairment in young children. However, the mechanisms underlying this neurodevelopmental disorder remain elusive. In this study, we investigated alteration of the gut microbiota after multiple neonatal exposures to the anesthetic sevoflurane and the potential role of microbiota alteration on cognitive impairment using a young mice model. Multiple neonatal sevoflurane exposures resulted in obvious cognitive impairment symptoms and altered gut microbiota composition. Fecal transplantation experiments confirmed that alteration of the microbiota was responsible for the cognitive disorders in young mice. Microbiota profiling analysis identified microbial taxa that showed consistent differential abundance before and after fecal microbiota transplantation. Several of the differentially abundant taxa are associated with memory and/or health of the host, such as species of Streptococcus, Lachnospiraceae, and Pseudoflavonifractor. The results reveal that abnormal composition of the gut microbiota is a risk factor for cognitive impairment in young mice after multiple neonatal exposures to sevoflurane and provide insight into a potential therapeutic strategy for sevoflurane-related neurotoxicity.

STIM1 Regulates Endothelial Calcium Overload and Cytokine Upregulation During Sepsis

BACKGROUND

Stromal interaction molecule 1 (STIM1)-mediated store-operated Ca²⁺ entry (SOCE) is now recognized as the main mechanism of the majority of nonexcitable cell calcium influx. Calcium overload is a primary mechanism of endothelial cell injury during systemic inflammatory response and sepsis. Whether STIM1-mediated SOCE plays a role in calcium overload in vascular endothelial cell injury remains unclear.

MATERIALS AND METHODS

To explore the role of STIM1-gated SOCE in vascular endothelial cell calcium overload and inflammation, we established a human septic serum or lipopolysaccharide (LPS)-induced human umbilical vein endothelial cell (HUVEC) experimental system and derived ribonucleic acid interference (RNAi)-mediated STIM1, ORAI1 (orai gene [HGNC: 25896 Entrez Gene: 84876] coding protein, ORAI Calcium Release-Activated Calcium Modulator 1), and transient receptor potential channel 1 (TRPC1) (core components of store-operated Ca²⁺[SOC]) downregulated HUVECs, as well as STIM1 overinduced HUVECs.

RESULTS

Our results show that sepsis serum or LPS stimulation increased STIM1 in HUVECs and increased all cytokines except for VEGF and the inflammatory mediators tumor necrosis factor, intercellular cell adhesion molecule-1, and endothelin-1 in a time-dependent manner. RNAi-mediated knockdown of STIM1 significantly inhibited serum or LPS-induced inflammatory cytokine expression, and STIM1 overexpression in HUVECs promoted LPS-mediated induction of these cytokines. Meanwhile, similar to the blocking effect of the specific SOC inhibitors Gd³⁺ and La³⁺ on LPS-induced calcium influx, RNAi-mediated depletion of STIM1 or the SOC proteins TRPC1 and ORAI1 could significantly inhibit serum or LPS-induced extracellular calcium influx, as well as the expression of the inflammatory cytokines tumor necrosis factor, intercellular cell adhesion molecule-1, and endothelin-1. Simultaneous downregulation of the SOCE core units TRPC1 and ORAI1 inhibited LPS-induced calcium influx and cytokine expression, which could not be restored by inducing STIM1. Forced expression of nuclear factor-κB (NF-κB) in HUVECs significantly induced STIM1 expression, whereas RNAi-mediated depletion of NF-κB significantly inhibited STIM1 mRNA levels and significantly reduced the thapsigargin-mediated SOCE calcium influx, which was similar to results with the NF-κB inhibitor wogonin.

CONCLUSIONS

Septic serum stimulates the expression of STIM1, cytokines, and inflammatory mediators in HUVECs. STIM1-mediated SOCE is required for Ca²⁺ influx induced by LPS or septic serum and contributes cytokines and inflammatory mediators in septic serum-stimulated HUVECs. In addition, STIM1-mediated SOCE on Ca²⁺ influx by septic serum or LPS involves NF-κB signaling.

CSF Levels of Elongation Factor Tu Is Associated With Increased Mortality in Malawian Adults With Streptococcus pneumoniae Meningitis

Background

Mortality from bacterial meningitis, predominately caused by Streptococcus pneumoniae, exceeds 50% in sub-Saharan African countries with high HIV prevalence. Underlying causes of high mortality are poorly understood. We examined the host and pathogen proteome in the CSF of adults with proven pneumococcal meningitis (PM), testing if there was an association between differentially expressed proteins and outcome.

Materials/Methods

CSF proteomes were analyzed by quantitative Mass-Spectrometry. Spectra were identified using the Swissprot human and TIGR4 pneumococcal protein libraries. Proteins were quantitated and analyzed against mortality. Unique proteins in PM were identified against published normal CSF proteome. Random-Forest models were used to test for protein signatures discriminating outcome. Proteins of interest were tested for their effects on growth and neutrophil opsonophagocytic killing of S. pneumoniae.

Results

CSF proteomes were available for 57 Adults with PM (median age 32 years, 60% male, 70% HIV-1 co-infected, mortality 63%). Three hundred sixty individual human and 23 pneumococcal proteins were identified. Of the human protein hits, 30% were not expressed in normal CSF, and these were strongly associated with inflammation and primarily related to neutrophil activity. No human protein signature predicted outcome. However, expression of the essential S. pneumoniae protein Elongation Factor Tu (EF-Tu) was significantly increased in CSF of non-survivors [False Discovery Rate (q) <0.001]. Expression of EF-Tu was negatively co-correlated against expression of Neutrophil defensin (r 0.4 p p < 0.002), but not against complement proteins C3 or Factor H. In vitro, addition of EF-Tu protein impaired S. pneumoniae neutrophil killing in CSF.

Conclusions

Excessive S. pneumoniae EF-Tu protein in CSF was associated with reduced survival in meningitis in a high HIV prevalence population. We show EF-Tu may inhibit neutrophil mediated killing of S. pneumoniae in CSF. Further mechanistic work is required to better understand how S. pneumoniae avoids essential innate immune responses during PM through production of excess EF-Tu.

Receptor Blockade: A Novel Approach to Protect the Brain From Pneumococcal Invasion

Background

Pneumococci are the major cause of bacterial meningitis globally. To cause meningitis pneumococci interact with the 2 endothelial receptors, polymeric immunoglobulin receptor (pIgR) and platelet endothelial cell adhesion molecule (PECAM-1), to penetrate the blood-brain barrier (BBB) and invade the brain.

Methods

C57BL/6 mice were infected intravenously with bioluminescent pneumococci, and treated with ceftriaxone (1 hour postinfection) and anti-pIgR and PECAM-1 antibodies (1 or 5 hours postinfection), then monitored for 5 and 10 days. Bacterial brain invasion was analyzed using IVIS imaging and bacterial counts.

Results

Ceftriaxone, given early after pneumococcal challenge, cleared pneumococci from the blood but not from the brain. After combining ceftriaxone with receptor blockade, using anti-pIgR and PECAM-1 antibodies, we found 100% survival after 5 and 10 days of infection, in contrast to 60% for ceftriaxone alone. Combined antibiotic and antibody treatment resulted in no or few viable bacteria in the brain and no microglia activation. Antibodies remained bound to the receptors during the study period. Receptor blockade did not interfere with antibiotic permeability through the BBB.

Conclusions

We suggest that adjunct treatment with pIgR and PECAM-1 antibodies to antibiotics may prevent pneumococcal meningitis development and associated brain damages. However, further evaluations are required.

Streptococcus pneumoniae Cell Wall-Localized Trigger Factor Elicits a Protective Immune Response and Contributes to Bacterial Adhesion to the Host

Trigger factor (TF) has a known cytoplasmic function as a chaperone. In a previous study we showed that pneumococcal TF is also cell-wall localized and this finding combined with the immunogenic characteristic of TF, has led us to determine the vaccine potential of TF and decipher its involvement in pneumococcal pathogenesis. Bioinformatic analysis revealed that TF is conserved among pneumococci and has no human homologue. Immunization of mice with recombinant (r)TF elicited a protective immune response against a pneumococcal challenge, suggesting that TF contributes to pneumococcal pathogenesis. Indeed, rTF and an anti-rTF antiserum inhibited bacterial adhesion to human lung derived epithelial cells, indicating that TF contributes to the bacterial adhesion to the host. Moreover, bacteria lacking TF demonstrated reduced adhesion, in vitro, to lung-derived epithelial cells, neural cells and glial cells. The reduced adhesion could be restored by chromosomal complementation. Furthermore, bacteria lacking TF demonstrated significantly reduced virulence in a mouse model. Taken together, the ability of rTF to elicit a protective immune response, involvement of TF in bacterial adhesion, conservation of the protein among pneumococcal strains and the lack of human homologue, all suggest that rTF can be considered as a future candidate vaccine with a much broader coverage as compared to the currently available pneumococcal vaccines.

Group A Streptococcus Subcutaneous Infection-Induced Central Nervous System Inflammation Is Attenuated by Blocking Peripheral TNF

Group A streptococcus (GAS) infection causes a strong inflammatory response associated with cytokine storms, leading to multiorgan failure, which is characterized as streptococcal toxic shock syndrome. However, little is known about GAS subcutaneous infection-mediated brain inflammation. Therefore, we used a bioluminescent GAS strain and reporter mice carrying firefly luciferase under transcriptional control of the nuclear factor-kappa B (NF-κB) promoter to concurrently monitor the host immune response and bacterial burden in a single mouse. Notably, in addition to the subcutaneous inoculation locus at the back of mice, we detected strong luminescence signals from NF-κB activation and increased inflammatory cytokine production in the brain, implying the existence of central nervous system inflammation after GAS subcutaneous infection. The inflamed brain exhibited an increased expression of glial fibrillary acidic protein and nicotinamide adenine dinucleotide phosphate oxidase components and greater microglial activation and blood–brain barrier (BBB) disruption. Furthermore, Fluoro-Jade C positive cells increased in the brain, indicating that neurons underwent degeneration. Peripheral tumor necrosis factor (TNF), which contributes to pathology in brain injury, was elevated in the circulation, and the expression of its receptor was also increased in the inflamed brain. Blockage of peripheral TNF effectively reduced brain inflammation and injury, thereby preventing BBB disruption and improving survival. Our study provides new insights into GAS-induced central nervous system inflammation, such as encephalopathy, which can be attenuated by circulating TNF blockage.