Meningitic Escherichia coli K1 penetration and neutrophil transmigration across the blood-brain barrier are modulated by alpha7 nicotinic receptor

Neuroprotective effects of ulinastatin on Escherichia coli meningitis rats through inhibiting PKCα phosphorylation and reducing zonula occludens-1 degradation

Ulinastatin, a broad-spectrum inflammatory inhibitor widely employed in the management of severe pancreatitis and sepsis, has not been extensively investigated for its therapeutic potential in bacterial meningitis. This study aims to assess the neuroprotective effects of ulinastatin on bacterial meningitis and elucidate its underlying mechanism. The rat model of bacterial meningitis was established by intracerebral injection of Escherichia coli. 3-week-old SD rats were randomly divided into 5 groups with 8 rats in each group, including control group, E.coli group, E.coli + UTI group (ulinastatin 50000IU/kg), E.coli + UTI + PMA group (ulinastatin 50000IU/kg + PMA 200 ug/kg), and E.coli + PMA group(PMA 200 ug/kg). Behavioral changes were assessed by Loeffler neurobehavioral score. Histomorphologic changes and apoptosis were assessed by hematoxylin and eosin staining, Nissl staining and TUNEL staining. Immunohistochemistry and immunofluorescence and western blotting were used to detect the expression levels of zonula occludens-1 (ZO-1) and phosphorylation protein kinase C (PKCα).It was found that ulinastatin treatment in Escherichia coli meningitis rats improved neurological function, alleviated meningeal inflammatory infiltration, reduced neuronal death, promoted the integrity of the blood-brain barrier structure. Moreover, phorbol myristate acetate (PMA, a protein kinase C activator), blocked the effective action of ulinastatin. These findings suggest that ulinastatin had neuroprotective effects on bacterial meningitis by inhibiting PKCα phosphorylation and reducing ZO-1 degradation, demonstrating that ulinastatin may be a promising strategy in the treatment of bacterial meningitis.

KYNA Ameliorates Glutamate Toxicity of HAND by Enhancing Glutamate Uptake in A2 Astrocytes

Reactive astrocytes are key players in HIV-associated neurocognitive disorders (HAND), and different types of reactive astrocytes play opposing roles in the neuropathologic progression of HAND. A recent study by our group found that gp120 mediates A1 astrocytes (neurotoxicity), which secrete proinflammatory factors and promote HAND disease progression. Here, by comparing the expression of A2 astrocyte (neuroprotective) markers in the brains of gp120 tgm mice and gp120+/α7nAChR-/- mice, we found that inhibition of alpha 7 nicotinic acetylcholine receptor (α7nAChR) promotes A2 astrocyte generation. Notably, kynurenine acid (KYNA) is an antagonist of α7nAChR, and is able to promote the formation of A2 astrocytes, the secretion of neurotrophic factors, and the enhancement of glutamate uptake through blocking the activation of α7nAChR/NF-κB signaling. In addition, learning, memory and mood disorders were significantly improved in gp120 tgm mice by intraperitoneal injection of kynurenine (KYN) and probenecid (PROB). Meanwhile, the number of A2 astrocytes in the mouse brain was significantly increased and glutamate toxicity was reduced. Taken together, KYNA was able to promote A2 astrocyte production and neurotrophic factor secretion, reduce glutamate toxicity, and ameliorate gp120-induced neuropathological deficits. These findings contribute to our understanding of the role that reactive astrocytes play in the development of HAND pathology and provide new evidence for the treatment of HAND via the tryptophan pathway.

Alpha-Lipoic Acid Ameliorates Doxorubicin-Induced Cognitive Impairments by Modulating Neuroinflammation and Oxidative Stress via NRF-2/HO-1 Signaling Pathway in the Rat Hippocampus

Chemotherapy-induced cognitive impairment (CICI) is a common complication associated with the use of chemotherapeutics. Doxorubicin (DOX) is a reactive oxygen species (ROS) producing anticancer agent capable of causing potential neurotoxic effects via cytokine-induced oxidative and nitrosative damage to brain tissues. On the other hand, alpha-lipoic acid (ALA), a nutritional supplement, is reputable for its excellent antioxidant, anti-inflammatory, and anti-apoptotic activities. Consequently, the objective of the current investigation was to examine any potential neuroprotective and memory-improving benefits of ALA against DOX-induced behavioral and neurological anomalies. DOX (2 mg/kg/week, i.p.) was administrated for 4 weeks to Sprague-Dawley rats. ALA (50, 100, and 200 mg/kg) was administered for 4 weeks. The Morris water maze (MWM) and novel objective recognition task (NORT) tests were used to assess memory function. Biochemical assays with UV-visible spectrophotometry were used to analyze oxidative stress markers [malondialdehyde (MDA), protein carbonylation (PCO)], endogenous antioxidants [reduced glutathione (GSH), catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px)] and acetylcholinesterase (AChE) activity in hippocampal tissue. Inflammatory markers [tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and nuclear factor kappa B (NF-κB)], nuclear factor erythroid 2-related factor-2 (NRF-2) and hemeoxygenase-1 (HO-1) levels were estimated using enzyme-linked immunosorbent assay (ELISA). In addition, reactive oxygen species (ROS) levels were measured in hippocampus tissue using 2-7-dichlorofluorescein-diacetate (DCFH-DA) assay with fluorimetry. ALA treatment significantly protected against DOX-induced memory impairment. Furthermore, ALA restored hippocampal antioxidants, halted DOX-induced oxidative and inflammatory insults via upregulation of NRF-2/HO-1 levels, and alleviated the increase in NF-κB expression. These results indicate that ALA offers neuroprotection against DOX-induced cognitive impairment, which could be attributed to its antioxidant potential via the NRF-2/HO-1 signaling pathway.

Melatonin Is Neuroprotective in Escherichia coli Meningitis Depending on Intestinal Microbiota

Avian meningitis Escherichia coli (E. coli) can cause acute bacterial meningitis which threatens poultry health, causes great economic losses in the poultry industry, and has recently been speculated as a potential zoonotic pathogen. Melatonin can counteract bacterial meningitis-induced disruption of the blood-brain barrier (BBB), neuroinflammation, and reduce mortality. There are increasing data showing that melatonin's beneficial effects on bacterial meningitis are associated with intestinal microbiota. In this study, our data showed that melatonin alleviated neurological symptoms, enhanced survival rate, protected the integrity of the BBB, reduced the bacterial load in various tissues and blood, and inhibited inflammation and neutrophil infiltration of brain tissue in an APEC TW-XM-meningitis mice model. The results of 16S rRNA showed that melatonin pretreatment significantly maintained the composition of intestinal microbiota in APEC-meningitis mice. The abundance and diversity of intestinal microbiota were disturbed in APEC TW-XM-meningitis mice, with a decreased ratio of Firmicutes to Bacteroides and an increased the abundance of Proteobacteria. Melatonin pretreatment could significantly improve the composition and abundance of harmful bacteria and alleviate the decreased abundance of beneficial bacteria. Importantly, melatonin failed to affect the meningitis neurologic symptoms caused by APEC TW-XM infection in antibiotic-pretreated mice. In conclusion, the results suggest that melatonin can effectively prevent meningitis induced by APEC TW-XM infection in mice, depending on the intestinal microbiota. This finding is helpful to further explore the specific target mechanism of melatonin-mediated intestinal microbiota in the prevention of and protection against Escherichia coli meningitis.

Alpha7 Nicotinic Acetylcholine Receptor Antagonists Prevent Meningitic Escherichia coli-Induced Blood–Brain Barrier Disruptions by Targeting the CISH/JAK2/STAT5b Axis

Despite the availability of antibiotics over the last several decades, excessive antibiotic treatments for bacterial sepsis and meningitis (BSM) in children may result in several adverse outcomes. Hematogenous pathogens may directly induce permeability increases in human brain microvascular endothelial cells (HBMECs) and blood–brain barrier (BBB) dysfunctions. Our preliminary studies demonstrated that the alpha7 nicotinic acetylcholine receptor (α7nAChR) played an important role in the pathogenesis of BSM, accompanied by increasing cytokine-inducible SH2-containing protein (CISH) at the transcriptome level, but it has remained unclear how α7nAChR-CISH works mechanistically. The study aims to explore the underlying mechanism of α7nAChR and CISH during E. coli-induced BSM in vitro (HBMECs) and in vivo (α7nAChR-KO mouse). We found that in the stage of E. coli K1-induced BBB disruptions, α7nAChR functioned as the key regulator that affects the integrity of HBMECs by activating the JAK2–STAT5 signaling pathway, while CISH inhibited JAK2–STAT5 activation and exhibited protective effects against E. coli infection. Notably, we first validated that the expression of CISH could be regulated by α7nAChR in HBMECs. In addition, we determined the protective effects of MLA (methyllycaconitine citrate) and MEM (memantine hydrochloride) (functioning as α7nAChR antagonists) on infected HBMECs and suggested that the α7nAChR–CISH axis could explain the protective effects of the two small-molecule compounds on E. coli-induced HBMECs injuries and BBB disruptions. In conclusion, we dissected the α7nAChR/CISH/JAK2/STAT5 axis as critical for the pathogenesis of E. coli-induced brain microvascular leakage and BBB disruptions and provided novel evidence for the development of α7nAChR antagonists in the prevention of pediatric E. coli BSM.

Endogenous α7 nAChR Agonist SLURP1 Facilitates Escherichia coli K1 Crossing the Blood-Brain Barrier

Alpha 7 nicotinic acetylcholine receptor (α7 nAChR) is critical for the pathogenesis of Escherichia coli (E. coli) K1 meningitis, a severe central nervous system infection of the neonates. However, little is known about how E. coli K1 manipulates α7 nAChR signaling. Here, through employing immortalized cell lines, animal models, and human transcriptional analysis, we showed that E. coli K1 infection triggers releasing of secreted Ly6/Plaur domain containing 1 (SLURP1), an endogenous α7 nAChR ligand. Exogenous supplement of SLURP1, combined with SLURP1 knockdown or overexpression cell lines, showed that SLURP1 is required for E. coli K1 invasion and neutrophils migrating across the blood-brain barrier (BBB). Furthermore, we found that SLURP1 is required for E. coli K1-induced α7 nAChR activation. Finally, the promoting effects of SLURP1 on the pathogenesis of E. coli K1 meningitis was significantly abolished in the α7 nAChR knockout mice. These results reveal that E. coli K1 exploits SLURP1 to activate α7 nAChR and facilitate its pathogenesis, and blocking SLURP1-α7 nAChR interaction might represent a novel therapeutic strategy for E. coli K1 meningitis.

The Amino Acid-mTORC1 Pathway Mediates APEC TW-XM-Induced Inflammation in bEnd.3 Cells

The blood-brain barrier (BBB) is key to establishing and maintaining homeostasis in the central nervous system (CNS); meningitis bacterial infection can disrupt the integrity of BBB by inducing an inflammatory response. The changes in the cerebral uptake of amino acids may contribute to inflammatory response during infection and were accompanied by high expression of amino acid transporters leading to increased amino acid uptake. However, it is unclear whether amino acid uptake is changed and how to affect inflammatory responses in mouse brain microvascular endothelial (bEnd.3) cells in response to Avian Pathogenic Escherichia coli TW-XM (APEC XM) infection. Here, we firstly found that APEC XM infection could induce serine (Ser) and glutamate (Glu) transport from extracellular into intracellular in bEnd.3 cells. Meanwhile, we also shown that the expression sodium-dependent neutral amino acid transporter 2 (SNAT2) for Ser and excitatory amino acid transporter 4 (EAAT4) for Glu was also significantly elevated during infection. Then, in amino acid deficiency or supplementation medium, we found that Ser or Glu transport were involving in increasing SNAT2 or EAAT4 expression, mTORC1 (mechanistic target of rapamycin complex 1) activation and inflammation, respectively. Of note, Ser or Glu transport were inhibited after SNAT2 silencing or EAAT4 silencing, resulting in inhibition of mTORC1 pathway activation, and inflammation compared with the APEC XM infection group. Moreover, pEGFP-SNAT2 overexpression and pEGFP-EAAT4 overexpression in bEnd.3 cells all could promote amino acid uptake, activation of the mTORC1 pathway and inflammation during infection. We further found mTORC1 silencing could inhibit inflammation, the expression of SNAT2 and EAAT4, and amino acid uptake. Taken together, our results demonstrated that APEC TW-XM infection can induce Ser or Glu uptake depending on amino acid transporters transportation, and then activate amino acid-mTORC1 pathway to induce inflammation in bEnd.3 cells.

Nicotine Reduces Human Brain Microvascular Endothelial Cell Response to Escherichia coli K1 Infection by Inhibiting Autophagy

Studies have shown that exposure to environmental tobacco smoke can increase the risk of bacterial meningitis, and nicotine is the core component of environmental tobacco smoke. Autophagy is an important way for host cells to eliminate invasive pathogens and resist infection. Escherichia coli K1 strain (E. coli K1) is the most common Gram-negative bacterial pathogen that causes neonatal meningitis. The mechanism of nicotine promoting E. coli K1 to invade human brain microvascular endothelial cells (HBMECs), the main component of the blood–brain barrier, is not clear yet. Our study found that the increase of HBMEC autophagy level during E. coli K1 infection could decrease the survival of intracellular bacteria, while nicotine exposure could inhibit the HBMEC autophagic response of E. coli K1 infection by activating the NF-kappa B and PI3K/Akt/mTOR pathway. We concluded that nicotine could inhibit HBMEC autophagy upon E. coli K1 infection and decrease the scavenging effect on E. coli K1, thus promoting the occurrence and development of neonatal meningitis.

Polymorphonuclear Leukocyte Transendothelial Migration Proceeds at Blood-Brain Barrier in Neonatal Meningitis

Neonatal bacterial meningitis remains a life-threatening and causative sequelae disease in newborns, despite the effective usage of antibiotics and improved critical medical care. Polymorphonuclear leukocyte (PMN) transendothelial migration across the blood-brain barrier, one of the three hallmarks of bacterial meningitis, now is considered as a “double-edge sword”. When participating in host immune system defending against virulent pathogens, it results in tissue inflammation and following severe damage of central nervous system at the same time, which contributes to a disastrous consequence. Recently, several researches have focused on this multi-step process and the mechanism of how the virulent factors of different pathogens influence PMN migration. The great progression they made has enlightened a new research hotspot and a novel therapeutic strategy. This mini review outlines the determinants and progression of PMN transmigration in neonatal meningitis caused by different predominant pathogens.

Memantine Displays Antimicrobial Activity by Enhancing Escherichia coli Pathogen-Induced Formation of Neutrophil Extracellular Traps

Bacterial infection remains one of the leading causes of death worldwide due to the continuous rise of multiple antibiotic-resistant bacteria. Focusing solely on bacteria as the drug targets is a major limitation inherent in the conventional antibiotic therapy. Recently, host-directed therapies have become such an innovative approach to modulate the host defense system and the interplay of innate and adaptive immunity. Our previous studies showed that memantine (MEM), an α7 nAChR antagonist, could efficiently block multi-drug resistant Escherichia coli-caused bacteremia and meningitis in a mouse model. However, the underlying mechanisms that govern the antibacterial effects of MEM are still unknown. In this study, we demonstrated that MEM is able to significantly suppress E. coli infection by enhancing E. coli-induced formation and release of NETs in vitro and in vivo. MEM could promote the trapping and bactericidal activities of the polymorphonuclear neutrophils (PMNs) in a manner dependent on α7 nAChR, since knockdown of this receptor noticeably reduces the survival ability of bacteria in PMNs while MEM no longer affects the survival of bacteria in PMNs. Our results also showed that when the expression of S100A9, an antiseptic protein, is inhibited, pathogen survival rates in PMNs increase significantly. MEM reverses this effect in a concentration-dependent manner. MEM stimulates the production of MPO, S100A9, and DNA in PMNs and accelerates the release of depolymerized chromatin fibers into the extracellular space, suggesting the formation of NETs. Taken together, our data suggest that MEM effectively blocks bacterial infection through the promotion of the antibacterial function of NETs induced by E. coli.

The Group B Streptococcal surface antigen I/II protein, BspC, interacts with host vimentin to promote adherence to brain endothelium and inflammation during the pathogenesis of meningitis

Streptococcus agalactiae (Group B Streptococcus, GBS) normally colonizes healthy adults but can cause invasive disease, such as meningitis, in the newborn. To gain access to the central nervous system, GBS must interact with and penetrate brain or meningeal blood vessels; however, the exact mechanisms are still being elucidated. Here, we investigate the contribution of BspC, an antigen I/II family adhesin, to the pathogenesis of GBS meningitis. Disruption of the bspC gene reduced GBS adherence to human cerebral microvascular endothelial cells (hCMEC), while heterologous expression of BspC in non-adherent Lactococcus lactis conferred bacterial attachment. In a murine model of hematogenous meningitis, mice infected with ΔbspC mutants exhibited lower mortality as well as decreased brain bacterial counts and inflammatory infiltrate compared to mice infected with WT GBS strains. Further, BspC was both necessary and sufficient to induce neutrophil chemokine expression. We determined that BspC interacts with the host cytoskeleton component vimentin and confirmed this interaction using a bacterial two-hybrid assay, microscale thermophoresis, immunofluorescent staining, and imaging flow cytometry. Vimentin null mice were protected from WT GBS infection and also exhibited less inflammatory cytokine production in brain tissue. These results suggest that BspC and the vimentin interaction is critical for the pathogenesis of GBS meningitis.

Group B Streptococcus (GBS) typically colonizes healthy adults but can cause severe disease in immune-compromised individuals, including newborns. Despite wide-spread intrapartum antibiotic prophylaxis given to pregnant women, GBS remains a leading cause of neonatal meningitis. To cause meningitis, GBS must interact with and penetrate the blood-brain barrier (BBB), which separates bacteria and immune cells in the blood from the brain. In order to develop targeted therapies to treat GBS meningitis, it is important to understand the mechanisms of BBB crossing. Here, we describe the role of the GBS surface factor, BspC, in promoting meningitis and discover the host ligand for BspC, vimentin, which is an intermediate filament protein that is constitutively expressed by endothelial cells. We determined that BspC interacts with the C-terminal domain of cell-surface vimentin to promote bacterial attachment to brain endothelial cells and that purified BspC protein can induce immune signaling pathways. In a mouse model of hematogenous meningitis, we observed that a GBS mutant lacking BspC was less virulent compared to WT GBS and resulted in less inflammatory disease. We also observed that mice lacking vimentin were protected from GBS infection. These results reveal the importance of the BspC-vimentin interaction in the progression of GBS meningitis disease.

CD48 and α7 Nicotinic Acetylcholine Receptor Synergistically Regulate FimH-Mediated Escherichia coli K1 Penetration and Neutrophil Transmigration Across Human Brain Microvascular Endothelial Cells

FimH-mediated bacterial invasion and polymorphonuclear neutrophil (PMN) transmigration across human brain microvascular endothelial cells (HBMECs) are required for the pathogenesis of Escherichia coli meningitis. However, the underlying mechanism remains unclear. This study demonstrated that the TnphoA mutant (22A33) and FimH-knockout mutant (ΔFimH) of E coli strain E44, which resulted in inactivation of FimH, were less invasive and less effective in promoting PMN transmigration than their wild-type strain. FimH protein induced PMN transmigration, whereas calmodulin inhibitor significantly blocked this effect. Moreover, immunofluorescence and co-immunoprecipitation analysis indicated that colocalized CD48 and α7 nAChR formed a complex on the surface of HBMECs that is associated with increased cofilin dephosphorylation, which could be remarkably enhanced by FimH+ E44. Our study concluded that FimH-induced E coli K1 invasion and PMN migration across HBMECs may be mediated by the CD48-α7nAChR complex in lipid rafts of HBMEC via Ca2+ signaling and cofilin dephosphorylation.

Characterization of a Two-Component System Transcriptional Regulator, LtdR, That Impacts Group B Streptococcal Colonization and Disease

Streptococcus agalactiae (group B Streptococcus [GBS]) is often a commensal bacterium that colonizes healthy adults asymptomatically and is a frequent inhabitant of the vaginal tract in women. However, in immunocompromised individuals, particularly the newborn, GBS may transition to an invasive pathogen and cause serious disease. Despite the use of the currently recommended intrapartum antibiotic prophylaxis for GBS-positive mothers, GBS remains a leading cause of neonatal septicemia and meningitis. To adapt to the various host environments encountered during its disease cycle, GBS possesses multiple two-component regulatory systems (TCSs). Here we investigated the contribution of a transcriptional regulator containing a LytTR domain, LtdR, to GBS pathogenesis. Disruption of the ltdR gene in the GBS chromosome resulted in a significant increase in bacterial invasion into human cerebral microvascular endothelial cells (hCMEC) in vitro as well as the greater penetration of the blood-brain barrier (BBB) and the development of meningitis in vivo Correspondingly, infection of hCMEC with the ΔltdR mutant resulted in increased secretion of the proinflammatory cytokines interleukin-8 (IL-8), CXCL-1, and IL-6. Further, using a mouse model of GBS vaginal colonization, we observed that the ΔltdR mutant was cleared more readily from the vaginal tract and also that infection with the ΔltdR mutant resulted in increased cytokine production from human vaginal epithelial cells. RNA sequencing revealed global transcriptional differences between the ΔltdR mutant and the parental wild-type GBS strain. These results suggest that LtdR regulates many bacterial processes that can influence GBS-host interactions to promote both bacterial persistence and disease progression.

Alpha7 nicotinic acetylcholine receptor is required for amyloid pathology in brain endothelial cells induced by Glycoprotein 120, methamphetamine and nicotine

One of the most challenging issues in HIV-associated neurocognitive disorders (HAND) caused by HIV-1 virotoxins and drug abuse is the lack of understanding the underlying mechanisms that are commonly associated with disorders of the blood-brain barrier (BBB), which mainly consists of brain microvascular endothelial cells (BMEC). Here, we hypothesized that Glycoprotein 120 (gp120), methamphetamine (METH) and nicotine (NT) can enhance amyloid-beta (Aβ) accumulation in BMEC through Alpha7 nicotinic acetylcholine receptor (α7 nAChR). Both in vitro (human BMEC) (HBMEC) and in vivo (mice) models of BBB were used to dissect the role of α7 nAChR in up-regulation of Aβ induced by gp120, METH and NT. Aβ release from and transport across HBMEC were significantly increased by these factors. Methyllycaconitine (MLA), an antagonist of α7 nAChR, could efficiently block these pathogenic effects. Furthermore, our animal data showed that these factors could significantly increase the levels of Aβ, Tau and Ubiquitin C-Terminal Hydrolase L1 (UCHL1) in mouse cerebrospinal fluid (CSF) and Aβ in the mouse brains. These pathogenicities were significantly reduced by MLA, suggesting that α7 nAChR may play an important role in neuropathology caused by gp120, METH and NT, which are the major pathogenic factors contributing to the pathogenesis of HAND.

Vimentin, a Novel NF-κB Regulator, Is Required for Meningitic Escherichia coli K1-Induced Pathogen Invasion and PMN Transmigration across the Blood-Brain Barrier

BACKGROUND

NF-κB activation, pathogen invasion, polymorphonuclear leukocytes (PMN) transmigration (PMNT) across the blood-brain barrier (BBB) are the pathogenic triad hallmark features of bacterial meningitis, but the mechanisms underlying these events remain largely unknown. Vimentin, which is a novel NF-κB regulator, is the primary receptor for the major Escherichia coli K1 virulence factor IbeA that contributes to the pathogenesis of neonatal bacterial sepsis and meningitis (NSM). We have previously shown that IbeA-induced NF-κB signaling through its primary receptor vimentin as well as its co-receptor PTB-associated splicing factor (PSF) is required for pathogen penetration and leukocyte transmigration across the BBB. This is the first in vivo study to demonstrate how vimentin and related factors contributed to the pathogenic triad of bacterial meningitis.

METHODOLOGY/PRINCIPAL FINDINGS

The role of vimentin in IbeA+ E. coli K1-induced NF-κB activation, pathogen invasion, leukocyte transmigration across the BBB has now been demonstrated by using vimentin knockout (KO) mice. In the in vivo studies presented here, IbeA-induced NF-κB activation, E. coli K1 invasion and polymorphonuclear neutrophil (PMN) transmigration across the BBB were significantly reduced in Vim-/- mice. Decreased neuronal injury in the hippocampal dentate gyrus was observed in Vim-/- mice with meningitis. The major inflammatory regulator α7 nAChR and several signaling molecules contributing to NF-κB activation (p65 and p-CamKII) were significantly reduced in the brain tissues of the Vim-/- mice with E. coli meningitis. Furthermore, Vim KO resulted in significant reduction in neuronal injury and in α7 nAChR-mediated calcium signaling.

CONCLUSION/SIGNIFICANCE

Vimentin, a novel NF-κB regulator, plays a detrimental role in the host defense against meningitic infection by modulating the NF-κB signaling pathway to increase pathogen invasion, PMN recruitment, BBB permeability and neuronal inflammation. Our findings provide the first evidence for Vim-dependent mechanisms underlying the pathogenic triad of bacterial meningitis.

CD44-mediated monocyte transmigration across Cryptococcus neoformans-infected brain microvascular endothelial cells is enhanced by HIV-1 gp41-I90 ectodomain

Background

Cryptococcus neoformans (Cn) is an important opportunistic pathogen in the immunocompromised people, including AIDS patients, which leads to fatal cryptococcal meningitis with high mortality rate. Previous researches have shown that HIV-1 gp41-I90 ectodomain can enhance Cn adhesion to and invasion of brain microvascular endothelial cell (BMEC), which constitutes the blood brain barrier (BBB). However, little is known about the role of HIV-1 gp41-I90 in the monocyte transmigration across Cn-infected BBB. In the present study, we provide evidence that HIV-1 gp41-I90 and Cn synergistically enhance monocytes transmigration across the BBB in vitro and in vivo. The underlying mechanisms for this phenomenon require further study.

Methods

In this study, the enhancing role of HIV-1 gp41-I90 in monocyte transmigration across Cn-infected BBB was demonstrated by performed transmigration assays in vitro and in vivo.

Results

Our results showed that the transmigration rate of monocytes are positively associated with Cn and/or HIV-1 gp41-I90, the co-exposure (HIV-1 gp41-I90 + Cn) group showed a higher THP-1 transmigration rate (P < 0.01). Using CD44 knock-down HBMEC or CD44 inhibitor Bikunin in the assay, the facilitation of transmigration rates of monocyte enhanced by HIV-1 gp41-I90 was significantly suppressed. Western blotting analysis and biotin/avidin enzyme-linked immunosorbent assays (BA-ELISAs) showed that Cn and HIV-1 gp41-I90 could increase the expression of CD44 and ICAM-1 on the HBMEC. Moreover, Cn and/or HIV-1 gp41-I90 could also induce CD44 redistribution to the membrane lipid rafts. By establishing the mouse cryptococcal meningitis model, we found that HIV-1 gp41-I90 and Cn could synergistically enhance the monocytes transmigration, increase the BBB permeability and injury in vivo.

Conclusions

Collectively, our findings suggested that HIV-1 gp41-I90 ectodomain can enhance the transmigration of THP-1 through Cn-infected BBB, which may be mediated by CD44. This novel study enlightens the future prospects to elaborate the inflammatory responses induced by HIV-1 gp41-I90 ectodomain and to effectively eliminate the opportunistic infections in AIDS patients.

Pathogenic Triad in Bacterial Meningitis: Pathogen Invasion, NF-κB Activation, and Leukocyte Transmigration that Occur at the Blood-Brain Barrier

Bacterial meningitis remains the leading cause of disabilities worldwide. This life-threatening disease has a high mortality rate despite the availability of antibiotics and improved critical care. The interactions between bacterial surface components and host defense systems that initiate bacterial meningitis have been studied in molecular and cellular detail over the past several decades. Bacterial meningitis commonly exhibits triad hallmark features (THFs): pathogen penetration, nuclear factor-kappaB (NF-κB) activation in coordination with type 1 interferon (IFN) signaling and leukocyte transmigration that occur at the blood-brain barrier (BBB), which consists mainly of brain microvascular endothelial cells (BMEC). This review outlines the progression of these early inter-correlated events contributing to the central nervous system (CNS) inflammation and injury during the pathogenesis of bacterial meningitis. A better understanding of these issues is not only imperative to elucidating the pathogenic mechanism of bacterial meningitis, but may also provide the in-depth insight into the development of novel therapeutic interventions against this disease.

Alpha7 nicotinic acetylcholine receptor is required for blood-brain barrier injury-related CNS disorders caused by Cryptococcus neoformans and HIV-1 associated comorbidity factors

Background

Cryptococcal meningitis is the most common fungal infection of the central nervous system (CNS) in HIV/AIDS. HIV-1 virotoxins (e.g., gp41) are able to induce disorders of the blood-brain barrier (BBB), which mainly consists of BMEC. Our recent study suggests that α7 nAChR is an essential regulator of inflammation, which contributes to regulation of NF-κB signaling, neuroinflammation and BBB disorders caused by microbial (e.g., HIV-1 gp120) and non-microbial [e.g., methamphetamine (METH)] factors. However, the underlying mechanisms for multiple comorbidities are unclear.

Methods

In this report, an aggravating role of α7 nAChR in host defense against CNS disorders caused by these comorbidities was demonstrated by chemical [inhibitor: methyllycaconitine (MLA)] and genetic (α7^−/− mice) blockages of α7 nAChR.

Results

As shown in our in vivo studies, BBB injury was significantly reduced in α7^−/− mice infected with C. neoformans. Stimulation by the gp41 ectodomain peptide (gp41-I90) and METH was abolished in the α7^−/− animals. C. neoformans and gp41-I90 could activate NF-κB. Gp41-I90- and METH-induced monocyte transmigration and senescence were significantly inhibited by MLA and CAPE (caffeic acid phenethyl ester, an NF-κB inhibitor).

Conclusions

Collectively, our data suggest that α7 nAChR plays a detrimental role in the host defense against C. neoformans- and HIV-1 associated comorbidity factors-induced BBB injury and CNS disorders.

Olfactory and gustatory dysfunction in Myasthenia gravis: A study in Turkish patients

OBJECTIVE

Myasthenia gravis (MG) is commonly viewed as a muscle disorder. Less is known about neurosensory function and dysfunction in MG. We aim to evaluate olfactory and gustatory behavior in Turkish patients with MG, and compare these results with age and sex-matched healthy controls.

MATERIAL/METHODS

30 individuals with MG, and 30 healthy volunteers were studied. Olfactory function was studied with the Sniffin' sticks test. Taste strip test was used for studying taste function. The t-test was used for analyzing continuous variables, and the chi-square test for categorical data. Clinical staging and medication status were included in a model analyzed using analysis of variances.

RESULTS

MG patients showed significantly lower olfactory (p<0.001) and gustatory scores (p<0.001) than the healthy controls. In addition, olfactory loss correlated with the severity of the disease. Medications for MG did not influence these results.

CONCLUSION

This study replicates the olfactory dysfunction found elsewhere in MG. Further, gustatory dysfunction, an activity unrelated to muscle strength, was also unveiled. Medications used for treating MG must not be blamed for the chemosensory dysfunction found in this neurological disorder.

Endothelial actin-binding proteins and actin dynamics in leukocyte transendothelial migration

The endothelium is the first barrier that leukocytes have to overcome during recruitment to sites of inflamed tissues. The leukocyte extravasation cascade is a complex multistep process that requires the activation of various adhesion molecules and signaling pathways, as well as actin remodeling, in both leukocytes and endothelial cells. Endothelial adhesion molecules, such as E-selectin or ICAM-1, are connected to the actin cytoskeleton via actin-binding proteins (ABPs). Although the contribution of receptor-ligand interactions to leukocyte extravasation has been studied extensively, the contribution of endothelial ABPs to the regulation of leukocyte adhesion and transendothelial migration remains poorly understood. This review focuses on recently published evidence that endothelial ABPs, such as cortactin, myosin, or α-actinin, regulate leukocyte extravasation by controlling actin dynamics, biomechanical properties of endothelia, and signaling pathways, such as GTPase activation, during inflammation. Thus, ABPs may serve as targets for novel treatment strategies for disorders characterized by excessive leukocyte recruitment.

Repositioning of Memantine as a Potential Novel Therapeutic Agent against Meningitic E. coli-Induced Pathogenicities through Disease-Associated Alpha7 Cholinergic Pathway and RNA Sequencing-Based Transcriptome Analysis of Host Inflammatory Responses

Neonatal sepsis and meningitis (NSM) remains a leading cause worldwide of mortality and morbidity in newborn infants despite the availability of antibiotics over the last several decades. E. coli is the most common gram-negative pathogen causing NSM. Our previous studies show that α7 nicotinic receptor (α7 nAChR), an essential regulator of inflammation, plays a detrimental role in the host defense against NSM. Despite notable successes, there still exists an unmet need for new effective therapeutic approaches to treat this disease. Using the in vitro/in vivo models of the blood-brain barrier (BBB) and RNA-seq, we undertook a drug repositioning study to identify unknown antimicrobial activities for known drugs. We have demonstrated for the first time that memantine (MEM), a FDA-approved drug for treatment of Alzheimer’s disease, could very efficiently block E. coli-caused bacteremia and meningitis in a mouse model of NSM in a manner dependent on α7 nAChR. MEM was able to synergistically enhance the antibacterial activity of ampicillin in HBMEC infected with E. coli K1 (E44) and in neonatal mice with E44-caused bacteremia and meningitis. Differential gene expression analysis of RNA-Seq data from mouse BMEC infected with E. coli K1 showed that several E44-increased inflammatory factors, including IL33, IL18rap, MMP10 and Irs1, were significantly reduced by MEM compared to the infected cells without drug treatment. MEM could also significantly up-regulate anti-inflammatory factors, including Tnfaip3, CISH, Ptgds and Zfp36. Most interestingly, these factors may positively and negatively contribute to regulation of NF-κB, which is a hallmark feature of bacterial meningitis. Furthermore, we have demonstrated that circulating BMEC (cBMEC) are the potential novel biomarkers for NSM. MEM could significantly reduce E44-increased blood level of cBMEC in mice. Taken together, our data suggest that memantine can efficiently block host inflammatory responses to bacterial infection through modulation of both inflammatory and anti-inflammatory pathways.

Pathogens penetrating the central nervous system: infection pathways and the cellular and molecular mechanisms of invasion

The brain is well protected against microbial invasion by cellular barriers, such as the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCSFB). In addition, cells within the central nervous system (CNS) are capable of producing an immune response against invading pathogens. Nonetheless, a range of pathogenic microbes make their way to the CNS, and the resulting infections can cause significant morbidity and mortality. Bacteria, amoebae, fungi, and viruses are capable of CNS invasion, with the latter using axonal transport as a common route of infection. In this review, we compare the mechanisms by which bacterial pathogens reach the CNS and infect the brain. In particular, we focus on recent data regarding mechanisms of bacterial translocation from the nasal mucosa to the brain, which represents a little explored pathway of bacterial invasion but has been proposed as being particularly important in explaining how infection with Burkholderia pseudomallei can result in melioidosis encephalomyelitis.

Circulating brain microvascular endothelial cells (cBMECs) as potential biomarkers of the blood-brain barrier disorders caused by microbial and non-microbial factors

Despite aggressive research, central nervous system (CNS) disorders, including blood-brain barrier (BBB) injury caused by microbial infection, stroke, abused drugs [e.g., methamphetamine (METH) and nicotine], and other pathogenic insults, remain the world's leading cause of disabilities. In our previous work, we found that dysfunction of brain microvascular endothelial cells (BMECs), which are a major component of the BBB, could be caused by nicotine, meningitic pathogens and microbial factors, including HIV-1 virulence factors gp41 and gp120. One of the most challenging issues in this area is that there are no available cell-based biomarkers in peripheral blood for BBB disorders caused by microbial and non-microbial insults. To identify such cellular biomarkers for BBB injuries, our studies have shown that mice treated with nicotine, METH and gp120 resulted in increased blood levels of CD146+(endothelial marker)/S100B+ (brain marker) circulating BMECs (cBMECs) and CD133+[progenitor cell (PC) marker]/CD146+ endothelial PCs (EPCs), along with enhanced Evans blue and albumin extravasation into the brain. Nicotine and gp120 were able to significantly increase the serum levels of ubiquitin C-terminal hydrolase 1 (UCHL1) (a new BBB marker) as well as S100B in mice, which are correlated with the changes in cBMECs and EPCs. Nicotine- and meningitic E. coli K1-induced enhancement of cBMEC levels, leukocyte migration across the BBB and albumin extravasation into the brain were significantly reduced in alpha7 nAChR knockout mice, suggesting that this inflammatory regulator plays an important role in CNS inflammation and BBB disorders caused by microbial and non-microbial factors. These results demonstrated that cBMECs as well as EPCs may be used as potential cell-based biomarkers for indexing of BBB injury.

Profound olfactory dysfunction in myasthenia gravis

In this study we demonstrate that myasthenia gravis, an autoimmune disease strongly identified with deficient acetylcholine receptor transmission at the post-synaptic neuromuscular junction, is accompanied by a profound loss of olfactory function. Twenty-seven MG patients, 27 matched healthy controls, and 11 patients with polymiositis, a disease with peripheral neuromuscular symptoms analogous to myasthenia gravis with no known central nervous system involvement, were tested. All were administered the University of Pennsylvania Smell Identification Test (UPSIT) and the Picture Identification Test (PIT), a test analogous in content and form to the UPSIT designed to control for non-olfactory cognitive confounds. The UPSIT scores of the myasthenia gravis patients were markedly lower than those of the age- and sex-matched normal controls [respective means (SDs) = 20.15 (6.40) & 35.67 (4.95); p<0.0001], as well as those of the polymiositis patients who scored slightly below the normal range [33.30 (1.42); p<0.0001]. The latter finding, along with direct monitoring of the inhalation of the patients during testing, implies that the MG-related olfactory deficit is unlikely due to difficulties sniffing, per se. All PIT scores were within or near the normal range, although subtle deficits were apparent in both the MG and PM patients, conceivably reflecting influences of mild cognitive impairment. No relationships between performance on the UPSIT and thymectomy, time since diagnosis, type of treatment regimen, or the presence or absence of serum anti-nicotinic or muscarinic antibodies were apparent. Our findings suggest that MG influences olfactory function to the same degree as observed in a number of neurodegenerative diseases in which central nervous system cholinergic dysfunction has been documented.

Polyphosphate kinase 1 is required for the pathogenesis process of meningitic Escherichia coli K1 (RS218)

Aim: Polyphosphate kinase 1 (PPK1), encoded by the ppk1 gene, is one of the major enzymes to reversibly catalyze the synthesis of polyphosphate (poly P) from the terminal phosphate of ATP. Poly P confers resistance to stress in a number of bacterial species but its role in the virulence of meningitic bacterial pathogens is unknown. The aim of this study was to determine the role of PPK1 in the pathogenesis of Escherichia coli meningitis. Materials & methods: An isogenic in-frame ppk1 deletion mutant (PD44) of E. coli K1 strain E44 was constructed and characterized. Human brain microvascular endothelial cells and neonatal rats were used as the in vitro and in vivo models, respectively, to evaluate bacterial adhesion/invasion and the abilities of bacteria crossing the blood–brain barrier (BBB) to cause meningitis. The survival of PD44 and E44 under osmotic and acid stress conditions were also examined. Results: Poly P levels in E44 were clearly higher than those in PD44, especially at the stationary phase (SP). The ppk1 deletion mutant PD44 also showed poor survival rates during osmotic shock and acidic challenge, which the bacteria would face during pathogenesis. In vitro and in vivo assays revealed that PD44 was defective in bacterial adhesion and translocation across the BBB. By using the Evans blue method, we found that E44-induced permeability of the BBB in neonatal rats was significantly higher than that of the animals infected with PD44. Cytokine ELISA results showed that the TNF-α and IL-1β levels in the serum and brain tissues of the neonatal rats infected with PD44 were lower than that of the E44 group. A more obvious meningeal inflammation could be observed in the brain tissues of the rats infected with E44 when compared with that of the PD44 group by histopathological examination. Furthermore, the mRNA expression of IbeR, which is an RpoS-like regulator contributing to the SP regulation in E44, was found to be decreased in PD44 when compared with the parent strain. PD44 was also deficient in mRNA expression of the invasin IbeA, the adhesin FimH and the outer member protein A, which contributes to E44 penetration across BBB and resistance to the stimulations of low pH and high osmolarity. Conclusion: These results indicate that ppk1 plays an important role in stress adaption and virulence in meningitic E. coli K1 strain E44, and controls the relevant phenotypes by modulating the expression of the SP regulatory gene ibeR and the virulence genes ibeA, fimH and ompA.