Invasion Of Human Brain Microvascular Endothelial Cells Research Articles

Role of Ibea Gene in Hbmecs Invasion and Biofilm Formation Induced By Neonatal Meningitis Escherichia coli

Background: Bacterial meningitis is a severe infectious disease that affects the central nervous system and can result in high mortality rates and neurological complications. In neonates, meningitis is mainly caused by neonatal meningitis Escherichia coli (NMEC), which invades the intestine, leading to hematogenous spreadand potential bacterial meningitis through blood-brain barrier. Previous studies indicated that the ability of NMEC to adhere and invade is associated with biofilm formation and a deficiency in ibeA may result in decreased virulence and biofilm-forming ability of avian pathogenic Escherichia coli (APEC). Furthermore, the ibeA gene is positioned downstream of ibeR. Our previous studies have shown that ibeR and ibeA genes can both regulate the virulence and relevant phenotypes in E. coli K1. However, the effects of ibeR and ibeA on the biofilm formation and invasion of K1 strain remain to be further studied. Recent studies suggest that indole may act as a signaling molecule to regulate the expression of adhesion and biofilm-promoting factors in E. coli. However, the mechanism by which indole affects biofilms is still unclear. This study aimed to investigate the mechanism of ibeA inhibition of indole-induced NMEC invasion and biofilm formation. Methods: The viability and growth of the wild strain E44 and ibeA-deletion mutant strain ZD1 were assessed by MTT cell proliferation assay kit (Coolaber). The absorbance values were measured at 490 nm and 540 nm by ELISA. The invasion activities and the biofilm formation ability of E44 and ZD1 were detected in vitro studies. We conducted a cell invasion test using the Human Brain Microvascular Endothelial Cells (HBMEC) model. The ability to form a biofilm was measured at 600 nm using a specific biofilm formation index. Biofilm phenotypic was observed by an confocal laser-scanning microscope(Olympus FV-1000, Japan). Then, we used indole as a regulatory agency to compare its biofilm inhibitory efficacy between E44 and ibeR-deletion mutant strain BR2. The experimental data were analyzed using the SPSS 19.0 statistical package. A statistically significant difference was indicated by P<0.05. Results: No difference was found in bacterial growth between the E. coli strains E44 and ZD1. The biofilm formation and HBMECs invasion of ZD1 was significantly lower than that of E44. After treatment with 0.5mM indole, the biofilm formation ability and the ibeA protein expressions of E44 were significantly inhibited. However, indole at different concentrations had no obvious inhibition on BR2 biofilm formation and the ibeA protein expressions. Conclusion: In summary, the study found that ibeA had a significant regulatory effect on HBMECs invasion and biofilm formation of NMEC, which may inhibit by indole via regulating ibeA through ibeR. ( Acknowledgements: Grant from School of Public Health of Southern Medical University, Guangzhou, China, No. GW202329; J.Z., Q.L. and L.W. contributed equally to this work; Corresponding author: Hong Cao, gzhcao@smu.edu.cn)

YbdO Promotes the Pathogenicity of Escherichia coli K1 by Regulating Capsule Synthesis.

Escherichia coli K1 is the most popular neonatal meningitis-causing Gram-negative bacterium. As a key virulence determinant, the K1 capsule enhances the survival of E. coli K1 in human brain microvascular endothelial cells (HBMECs) upon crossing the blood–brain barrier; however, the regulatory mechanisms of capsule synthesis during E. coli K1 invasion of HBMECs remain unclear. Here, we identified YbdO as a transcriptional regulator that promotes E. coli K1 invasion of HBMECs by directly activating K1 capsule gene expression to increase K1 capsule synthesis. We found that ybdO deletion significantly reduced HBMEC invasion by E. coli K1 and meningitis occurrence in mice. Additionally, electrophoretic mobility shift assay and chromatin immunoprecipitation–quantitative polymerase chain reaction analysis indicated that YbdO directly activates kpsMT and neuDBACES expression, which encode products involved in K1 capsule transport and synthesis by directly binding to the kpsM promoter. Furthermore, ybdO transcription was directly repressed by histone-like nucleoid structuring protein (H-NS), and we observed that acidic pH similar to that of early and late endosomes relieves this transcriptional repression. These findings demonstrated the regulatory mechanism of YbdO on K1 capsule synthesis, providing further insights into the evolution of E. coli K1 pathogenesis and host–pathogen interaction.

Regulation of Toll-like receptor 2 interaction with Ecgp96 controlsEscherichia coli K1 invasion of brain endothelial cells

The interaction of outer membrane protein A (OmpA) with its receptor, Ecgp96 (a homologue of Hsp90β), is critical for the pathogenesis of Escherichia coli K1 meningitis. Since Hsp90 chaperones Toll-like receptors (TLRs), we examined the role of TLRs in E. coli K1 infection. Herein, we show that newborn TLR2(-/-) mice are resistant to E. coli K1 meningitis, while TLR4(-/-) mice succumb to infection sooner. In vitro, OmpA+ E. coli infection selectively upregulates Ecgp96 and TLR2 in human brain microvascular endothelial cells (HBMEC), whereas OmpA- E. coli upregulates TLR4 in these cells. Furthermore, infection with OmpA+ E. coli causes Ecgp96 and TLR2 translocate to the plasma membrane of HBMEC as a complex. Immunoprecipitation studies of the plasma membrane fractions from infected HBMEC reveal that the C termini of Ecgp96 and TLR2 are critical for OmpA+ E. coli invasion. Knockdown of TLR2 using siRNA results in inefficient membrane translocation of Ecgp96 and significantly reduces invasion. In addition, the interaction of Ecgp96 andTLR2 induces a bipartite signal, one from Ecgp96 through PKC-α while the other from TLR2 through MyD88, ERK1/2 and NF-κB. This bipartite signal ultimately culminates in the efficient production of NO, which in turn promotes E. coli K1 invasion of HBMEC.

Cryptococcus neoformans Activates RhoGTPase Proteins Followed by Protein Kinase C, Focal Adhesion Kinase, and Ezrin to Promote Traversal across the Blood-Brain Barrier

Cryptococcus neoformans is an opportunistic fungal pathogen that causes meningoencephalitis. Previous studies have demonstrated that Cryptococcus binding and invasion of human brain microvascular endothelial cells (HBMEC) is a prerequisite for transmigration across the blood-brain barrier. However, the molecular mechanism involved in the cryptococcal blood-brain barrier traversal is poorly understood. In this study we examined the signaling events in HBMEC during interaction with C. neoformans. Analysis with inhibitors revealed that cryptococcal association, invasion, and transmigration require host actin cytoskeleton rearrangement. Rho pulldown assays revealed that Cryptococcus induces activation of three members of RhoGTPases, e.g. RhoA, Rac1, and Cdc42, and their activations are required for cryptococcal transmigration across the HBMEC monolayer. Western blot analysis showed that Cryptococcus also induces phosphorylation of focal adhesion kinase (FAK), ezrin, and protein kinase C α (PKCα), all of which are involved in the rearrangement of host actin cytoskeleton. Down-regulation of FAK, ezrin, or PKCα by shRNA knockdown, dominant-negative transfection, or inhibitors significantly reduces cryptococcal ability to traverse the HBMEC monolayer, indicating their positive role in cryptococcal transmigration. In addition, activation of RhoGTPases is the upstream event for phosphorylation of FAK, ezrin, and PKCα during C. neoformans-HBMEC interaction. Taken together, our findings demonstrate that C. neoformans activates RhoGTPases and subsequently FAK, ezrin, and PKCα to promote their traversal across the HBMEC monolayer, which is the critical step for cryptococcal brain infection and development of meningitis.

Cell Invasion by Neisseria meningitidis Requires a Functional Interplay between the Focal Adhesion Kinase, Src and Cortactin

Entry of Neisseria meningitidis (the meningococcus) into human brain microvascular endothelial cells (HBMEC) is mediated by fibronectin or vitronectin bound to the surface protein Opc forming a bridge to the respective integrins. This interaction leads to cytoskeletal rearrangement and uptake of meningococci. In this study, we determined that the focal adhesion kinase (FAK), which directly associates with integrins, is involved in integrin-mediated internalization of N. meningitidis in HBMEC. Inhibition of FAK activity by the specific FAK inhibitor PF 573882 reduced Opc-mediated invasion of HBMEC more than 90%. Moreover, overexpression of FAK mutants that were either impaired in the kinase activity or were not capable of autophosphorylation or overexpression of the dominant-negative version of FAK (FRNK) blocked integrin-mediated internalization of N. meningitidis. Importantly, FAK-deficient fibroblasts were significantly less invaded by N. meningitidis. Furthermore, N. meningitidis induced tyrosine phosphorylation of several host proteins including the FAK/Src complex substrate cortactin. Inhibition of cortactin expression by siRNA silencing and mutation of critical amino acid residues within cortactin, that encompass Arp2/3 association and dynamin binding, significantly reduced meningococcal invasion into eukaryotic cells suggesting that both domains are critical for efficient uptake of N. meningitidis into eukaryotic cells. Together, these results indicate that N. meningitidis exploits the integrin signal pathway for its entry and that FAK mediates the transfer of signals from activated integrins to the cytoskeleton. A cooperative interplay between FAK, Src and cortactin then enables endocytosis of N. meningitidis into host cells.

IQGAP1 mediates the disruption of adherens junctions to promoteEscherichia coliK1 invasion of brain endothelial cells

The transcellular entry of Escherichia coli K1 through human brain microvascular endothelial cells (HBMEC) is responsible for tight junction disruption, leading to brain oedema in neonatal meningitis. Previous studies demonstrated that outer membrane protein A (OmpA) of E. coli K1 interacts with its receptor, Ecgp96, to induce PKC-α phosphorylation, adherens junction (AJ) disassembly (by dislodging β-catenin from VE-cadherin), and remodelling of actin in HBMEC. We report here that IQGAP1 mediates β-catenin dissociation from AJs to promote actin polymerization required for E. coli K1 invasion of HBMEC. Overexpression of C-terminal truncated IQGAP1 (IQΔC) that cannot bind β-catenin prevents both AJ disruption and E. coli K1 entry. Of note, phospho-PKC-α interacts with the C-terminal portion of Ecgp96 as well as with VE-cadherin after IQGAP1-mediated AJ disassembly. HBMEC overexpressing either C-terminal truncated Ecgp96 (Ecgp96Δ200) or IQΔC upon infection with E. coli showed no interaction of phospho-PKC-α with Ecgp96. These data indicate that the binding of OmpA to Ecgp96 induces PKC-α phosphorylation and association of phospho-PKC-α with Ecgp96, and then signals IQGAP1 to detach β-catenin from AJs. Subsequently, IQGAP1/β-catenin bound actin translocates to the site of E. coli K1 attachment to promote invasion.

IbeA and OmpA of Escherichia coli K1 Exploit Rac1 Activation for Invasion of Human Brain Microvascular Endothelial Cells

Meningitis-causing Escherichia coli K1 internalization of the blood-brain barrier is required for penetration into the brain, but the host-microbial interactions involved in E. coli entry of the blood-brain barrier remain incompletely understood. We show here that a meningitis-causing E. coli K1 strain RS218 activates Rac1 (GTP-Rac1) of human brain microvascular endothelial cells (HBMEC) in a time-dependent manner. Both activation and bacterial invasion were significantly inhibited in the presence of a Rac1 inhibitor. We further showed that the guanine nucleotide exchange factor Vav2, not β-Pix, was involved in E. coli K1-mediated Rac1 activation. Since activated STAT3 is known to bind GTP-Rac1, the relationship between STAT3 and Rac1 was examined in E. coli K1 invasion of HBMEC. Downregulation of STAT3 resulted in significantly decreased E. coli invasion compared to control HBMEC, as well as a corresponding decrease in GTP-Rac1, suggesting that Rac1 activation in response to E. coli is under the control of STAT3. More importantly, two E. coli determinants contributing to HBMEC invasion, IbeA and OmpA, were shown to affect both Rac1 activation and their association with STAT3. These findings demonstrate for the first time that specific E. coli determinants regulate a novel mechanism of STAT3 cross talk with Rac1 in E. coli K1 invasion of HBMEC.

P54nrb, a PSF Protein Partner, Contributes to Meningitic <i>Escherichia coli</i> K1-Mediated Pathogenicities

IbeA is an important invasion determinant contributing to Escherichia coli K1 entry into brain microvascular endothelial cells (BMEC) that is a key step in the pathogenesis of E. coli meningitis. Our previous studies have shown that IbeA-induced signaling and E. coli K1 invasion is mediated by two IbeA-binding proteins, vimentin, which is constitutively present in the surface of human BMECs (HBMECs), and PSF, which is inducibly expressed in both mesenchymal (endothelium) and non-mesenchymal (epithelium) cells. However, it is unknown whether p54nrb, a PSF partner protein, could contribute to the pathogenesis of E. coli K1 meningitis. Here, we reported that a 54-kDa protein was identified by copurification with PSF through IbeA-affinity chromatography as an IbeA-binding protein, which is identical to p54nrb. Both p54nrb and PSF are RNA-binding proteins and share significant sequence homology. The specific interaction between IbeA and p54nrb was confirmed by Western blot and ligand overlay assays. Recombinant p54nrb blocked E. coli K1 invasion of human BMEC very effectively. Overexpressed p54nrb as a GFP fusion protein in the transfected 293T cells significantly enhanced E. coli K1 invasion. Furthermore, higher levels of surface p54nrb in the transfected 293T cells were detected by flow cytometry. These results suggest that the IbeA invasion protein of E. coli K1 interacts with p54nrb for bacterial invasion of human BMEC.

Hcp Family Proteins Secreted via the Type VI Secretion System Coordinately Regulate Escherichia coli K1 Interaction with Human Brain Microvascular Endothelial Cells

Type VI secretion systems (T6SSs) are involved in the pathogenicity of several gram-negative bacteria. Based on sequence analysis, we found that a cluster of Escherichia coli virulence factors (EVF) encoding a putative T6SS exists in the genome of the meningitis-causing E. coli K1 strain RS218. The T6SS-associated deletion mutants exhibited significant defects in binding to and invasion of human brain microvascular endothelial cells (HBMEC) compared with the parent strain. Hcp family proteins (the hallmark of T6SS), including Hcp1 and Hcp2, were localized in the bacterial outer membrane, but the involvements of Hcp1 and Hcp2 have been shown to differ in E. coli-HBMEC interaction. The deletion mutant of hcp2 showed defects in the bacterial binding to and invasion of HBMEC, while Hcp1 was secreted in a T6SS-dependent manner and induced actin cytoskeleton rearrangement, apoptosis, and the release of interleukin-6 (IL-6) and IL-8 in HBMEC. These findings demonstrate that the T6SS is functional in E. coli K1, and two Hcp family proteins participate in different steps of E. coli interaction with HBMEC in a coordinate manner, e.g., binding to and invasion of HBMEC, the cytokine and chemokine release followed by cytoskeleton rearrangement, and apoptosis in HBMEC. This is the first demonstration of the role of T6SS in meningitis-causing E. coli K1, and T6SS-associated Hcp family proteins are likely to contribute to the pathogenesis of E. coli meningitis.

YgfZ contributes to secretion of cytotoxic necrotizing factor 1 into outer-membrane vesicles in Escherichia coli

Cytotoxic necrotizing factor 1 (CNF1), a Rho GTPase-activating bacterial toxin, has been shown to contribute to invasion by meningitis-causing Escherichia coli K1 of human brain microvascular endothelial cells (HBMEC), which constitute the blood-brain barrier. However, CNF1 is a cytosolic protein and it remains unclear how its secretion occurs, contributing to E. coli invasion of HBMEC. To investigate the genetic requirement for CNF1 secretion in E. coli K1 strain RS218, we performed mini-Tn5 in vitro mutagenesis and constructed a transposon mutant library of strain NBC, in which β-lactamase was fused to the C-terminus of CNF1 in the chromosome of strain RS218. We identified a transposon mutant (NBC-1E6) that exhibited reduced β-lactamase activity in its culture supernatant and had the transposon inserted into the ygfZ gene. When ygfZ was deleted from the genome of strain RS218 (ΔygfZ), the translocation of CNF1 into HBMEC was impaired. Subcellular localization analysis of CNF1 demonstrated that YgfZ, a periplasmic protein, contributes to secretion of CNF1 into outer-membrane vesicles (OMVs). The ΔygfZ mutant was significantly defective in invasion of HBMEC compared to the parent E. coli K1 strain. The defects of the ΔygfZ mutant in CNF1 secretion into OMVs and translocation into HBMEC as well as invasion of HBMEC were abrogated by complementation with ygfZ. Taken together, our findings demonstrate that YgfZ contributes to CNF1 secretion into OMVs in meningitis-causing E. coli K1.

Invasion of Cryptococcus neoformans into Human Brain Microvascular Endothelial Cells Is Mediated through the Lipid Rafts-Endocytic Pathway via the Dual Specificity Tyrosine Phosphorylation-regulated Kinase 3 (DYRK3)

Cryptococcus neoformans is a neurotropic fungal pathogen, which provokes the onset of devastating meningoencephalitis. We used human brain microvascular endothelial cells (HBMEC) as the in vitro model to investigate how C. neoformans traverses across the blood-brain barrier. In this study, we present several lines of evidence indicating that C. neoformans invasion is mediated through the endocytic pathway via lipid rafts. Human CD44 molecules from lipid rafts can directly interact with hyaluronic acid, the C. neoformans ligand. Bikunin, which perturbs CD44 function in the lipid raft, can block C. neoformans adhesion and invasion of HBMEC. The lipid raft marker, ganglioside GM1, co-localizes with CD44 on the plasma membrane, and C. neoformans cells can adhere to the host cell in areas where GM1 is enriched. These findings suggest that C. neoformans entry takes place on the lipid rafts. Upon C. neoformans engagement, GM1 is internalized through vesicular structures to the nuclear membrane. This endocytic redistribution process is abolished by cytochalasin D, nocodazole, or anti-DYRK3 (dual specificity tyrosine-phosphorylation-regulated kinase 3) siRNA. Concomitantly, the knockdown of DYRK3 significantly reduces C. neoformans invasion across the HBMEC monolayer in vitro. Our data demonstrate that the lipid raft-dependent endocytosis process mediates C. neoformans internalization into HBMEC and that the CD44 protein of the hosts, cytoskeleton, and intracellular kinase-DYRK3 are involved in this process.

Host Cytosolic Phospholipase A 2 α Contributes to Group B Streptococcus Penetration of the Blood-Brain Barrier

Group B Streptococcus (GBS) is the most common bacterium causing neonatal meningitis, and neonatal GBS meningitis continues to be an important cause of mortality and morbidity. Here we provide the first direct evidence that host cytosolic phospholipase A₂α (cPLA₂α) contributes to type III GBS invasion of human brain microvascular endothelial cells (HBMEC), which constitute the blood-brain barrier and penetration into the brain, the key step required for the development of GBS meningitis. This was shown by our demonstration that pharmacological inhibition and gene deletion of cPLA₂α significantly decreased GBS invasion of the HBMEC monolayer and penetration into the brain. cPLA₂α releases arachidonic acid from membrane phospholipids, and we showed that the contribution of cPLA₂α to GBS invasion of HBMEC involved lipoxygenated metabolites of arachidonic acid, cysteinyl leukotrienes (LTs). In addition, type III GBS invasion of the HBMEC monolayer involves protein kinase Cα (PKCα), as shown by time-dependent PKCα activation in response to GBS as well as decreased GBS invasion in HBMEC expressing dominant-negative PKCα. PKCα activation in response to GBS, however, was abolished by inhibition of cPLA₂α and cysteinyl LTs, suggesting that cPLA₂α and cysteinyl LTs contribute to type III GBS invasion of the HBMEC monolayer via PKCα. These findings demonstrate that specific host factors involving cPLA₂α and cysteinyl LTs contribute to type III GBS penetration of the blood-brain barrier and their contribution involves PKCα.

Recruitment of α7 Nicotinic Acetylcholine Receptor to Caveolin-1-Enriched Lipid Rafts is Required for Nicotine-Enhanced Escherichia Coli K1 Entry into Brain Endothelial Cells

We investigate how the α7 nicotinic acetylcholine receptor (α7 nAChR), an essential regulator of inflammation, contributes to the α7 agonist nicotine-enhanced Escherichia coli K1 invasion of human brain microvascular endothelial cells (HBMECs) through lipid rafts/caveolae-mediated signaling. α7 nAChR-mediated signaling and bacterial invasion were defined by lipid raft fractionation, immunofluorescence microscopy and siRNA knockdown. Nicotine-enhanced bacterial invasion was dose-dependently inhibited by two raft-disrupting agents, nystatin and filipin. Significant accumulation of the lipid raft marker GM3 was observed in HBMEC induced by E. coli K1 and nicotine. The recruitment of α7 nAChR and related signaling molecules, including vimentin, and Erk1/2, to caveolin-1 enriched lipid rafts was increased upon treatment with E44 or E44 plus nicotine. Erk1/2 activation (phosphorylation), which is required for α7 nAChR-mediated signaling and E44 invasion, was associated with lipid rafts and nicotine-enhanced bacterial infection. Furthermore, E44 invasion, E44/nicotine-induced activation of Erk1/2 and clustering of α7 nAChR and caveolin-1 was specifically blocked by both siRNAs. α7 nAChR-mediated signaling through lipid rafts/caveolae is required for nicotine-enhanced E. coli K1 invasion of HBMEC.

Glycosaminoglycan Binding Facilitates Entry of a Bacterial Pathogen into Central Nervous Systems

Certain microbes invade brain microvascular endothelial cells (BMECs) to breach the blood-brain barrier (BBB) and establish central nervous system (CNS) infection. Here we use the leading meningitis pathogen group B Streptococcus (GBS) together with insect and mammalian infection models to probe a potential role of glycosaminoglycan (GAG) interactions in the pathogenesis of CNS entry. Site-directed mutagenesis of a GAG-binding domain of the surface GBS alpha C protein impeded GBS penetration of the Drosophila BBB in vivo and diminished GBS adherence to and invasion of human BMECs in vitro. Conversely, genetic impairment of GAG expression in flies or mice reduced GBS dissemination into the brain. These complementary approaches identify a role for bacterial-GAG interactions in the pathogenesis of CNS infection. Our results also highlight how the simpler yet genetically conserved Drosophila GAG pathways can provide a model organism to screen candidate molecules that can interrupt pathogen-GAG interactions for future therapeutic applications.

PI3K-dependent host cell actin rearrangements are required for Cronobacter sakazakii invasion of human brain microvascular endothelial cells

Cronobacter sakazakii (C. sakazakii) is an opportunistic pathogen that can cause neonatal sepsis and meningitis. The mechanism involved in the pathogenesis of C. sakazakii meningitis remains largely unknown. Previous studies indicated that bacterial invasion of brain microvascular endothelial cells is required for penetration into the central nervous system. In this study, we found that C. sakazakii invasion of human brain microvascular endothelial cells (HBMEC) was significantly inhibited by cytochalasin D, a disrupting agent of actin microfilaments. Disassembly of actin stress fibers and cortical actin fibers was observed in HBMEC infected with C. sakazakii. C. sakazakii infection leads to increased Akt phosphorylation in HBMEC, which was blocked by treatment with PI3K inhibitors. Meanwhile, PI3K and Akt inhibitors significantly inhibited C. sakazakii invasion of HBMEC. Our further results illustrated that the C. sakazakii-induced Akt activation and C. sakazakii invasion were attenuated in HBMEC transfected with dominant-negative PI3K (Δp110). More importantly, the actin filaments rearrangements in HBMEC induced by C. sakazakii were effectively blocked by PI3K inhibitors treatment and transfection with Δp110. Taken together, our findings demonstrated that PI3K-mediated actin rearrangements are required for C. sakazakii invasion of HBMEC.

Vascular Endothelial Growth Factor Receptor 1 Contributes toEscherichia coliK1 Invasion of Human Brain Microvascular Endothelial Cells through the Phosphatidylinositol 3-Kinase/Akt Signaling Pathway

Escherichia coli is the most common Gram-negative organism causing neonatal meningitis. Previous studies demonstrated that E. coli K1 invasion of brain microvascular endothelial cells (BMEC) is required for penetration into the central nervous system, but the microbe-host interactions that are involved in this process remain incompletely understood. Here we report the involvement of vascular endothelial growth factor receptor 1 (VEGFR1) expressed on human brain microvascular endothelial cells (HBMEC) in E. coli K1 invasion of HBMEC. Our results showed that treatment of confluent HBMEC with pan-VEGFR inhibitors significantly inhibited E. coli K1 invasion of HBMEC. Immunofluorescence results indicated the colocalization of VEGFR1 with E. coli K1 during bacterial invasion of HBMEC. The E. coli-induced actin cytoskeleton rearrangements in HBMEC were blocked by VEGFR inhibitors but not by VEGFR2-specific inhibitors. The small interfering RNA (siRNA) knockdown of VEGFR1 in HBMEC significantly attenuated E. coli invasion and the concomitant actin filament rearrangement. Furthermore, we found an increased association of VEGFR1 with the p85 subunit of phosphatidylinositol 3-kinase (PI3K) in HBMEC infected with E. coli K1 and that E. coli K1-triggered Akt activation in HBMEC was blocked by VEGFR1 siRNA and VEGFR inhibitors. Taken together, our results demonstrate that VEGFR1 contributes to E. coli K1 invasion of HBMEC via recruitment of the PI3K/Akt signaling pathway.

Arachidonic acid metabolism regulates Escherichia coli penetration of the blood-brain barrier.

Escherichia coli K1 meningitis occurs following penetration of the blood-brain barrier, but the underlying mechanisms involved in E. coli penetration of the blood-brain barrier remain incompletely understood. We have previously shown that host cytosolic phospholipase A(2)α (cPLA(2)α) contributes to E. coli invasion of human brain microvascular endothelial cells (HBMEC), which constitute the blood-brain barrier, but the underlying mechanisms remain unclear. cPLA(2)α selectively liberates arachidonic acid from membrane phospholipids. Here, we provide the first direct evidence that host 5-lipoxygenase and lipoxygenase products of arachidonic acid, cysteinyl leukotrienes (LTs), contribute to E. coli K1 invasion of HBMEC and penetration into the brain, and their contributions involve protein kinase C alpha (PKCα). These findings demonstrate that arachidonic acid metabolism regulates E. coli penetration of the blood-brain barrier, and studies are needed to further elucidate the mechanisms involved with metabolic products of arachidonic acid for their contribution to E. coli invasion of the blood-brain barrier.

Prevention of Escherichia coli K1 penetration of the blood-brain barrier by counteracting the host cell receptor and signaling molecule involved in E. coli invasion of human brain microvascular endothelial cells.

Escherichia coli meningitis is an important cause of mortality and morbidity, and a key contributing factor is our incomplete understanding of the pathogenesis of E. coli meningitis. We have shown that E. coli penetration into the brain requires E. coli invasion of human brain microvascular endothelial cells (HBMEC), which constitute the blood-brain barrier. E. coli invasion of HBMEC involves its interaction with HBMEC receptors, such as E. coli cytotoxic necrotizing factor 1 (CNF1) interaction with its receptor, the 67-kDa laminin receptor (67LR), and host signaling molecules including cytosolic phospholipase A(2)alpha (cPLA(2)alpha). In the present study, we showed that treatment with etoposide resulted in decreased expression of 67LR on HBMEC and inhibited E. coli invasion of HBMEC. Pharmacological inhibition of cysteinyl leukotrienes, lipoxygenated products of arachidonic acid released by cPLA(2)alpha, using montelukast (an antagonist of the type 1 cysteinyl leukotriene receptor) also inhibited E. coli invasion of HBMEC. E. coli penetration into the brain was significantly decreased by etoposide as well as by montelukast, and a combination of etoposide and montelukast was significantly more effective in inhibiting E. coli K1 invasion of HBMEC than single agents alone. These findings demonstrate for the first time that counteracting the HBMEC receptor and signaling molecule involved in E. coli invasion of HBMEC provides a novel approach for prevention of E. coli penetration into the brain, the essential step required for development of E. coli meningitis.

NlpI Contributes to Escherichia coli K1 Strain RS218 Interaction with Human Brain Microvascular Endothelial Cells

Escherichia coli K1 is the most common Gram-negative bacillary organism causing neonatal meningitis. E. coli K1 binding to and invasion of human brain microvascular endothelial cells (HBMECs) is a prerequisite for its traversal of the blood-brain barrier (BBB) and penetration into the brain. In the present study, we identified NlpI as a novel bacterial determinant contributing to E. coli K1 interaction with HBMECs. The deletion of nlpI did not affect the expression of the known bacterial determinants involved in E. coli K1-HBMEC interaction, such as type 1 fimbriae, flagella, and OmpA, and the contribution of NlpI to HBMECs binding and invasion was independent of those bacterial determinants. Previous reports have shown that the nlpI mutant of E. coli K-12 exhibits growth defect at 42 degrees C at low osmolarity, and its thermosensitive phenotype can be suppressed by a mutation on the spr gene. The nlpI mutant of strain RS218 exhibited similar thermosensitive phenotype, but additional spr mutation did not restore the ability of the nlpI mutant to interact with HBMECs. These findings suggest the decreased ability of the nlpI mutant to interact with HBMECs is not associated with the thermosensitive phenotype. NlpI was determined as an outer membrane-anchored protein in E. coli, and the nlpI mutant was defective in cytosolic phospholipase A(2)alpha (cPLA(2)alpha) phosphorylation compared to the parent strain. These findings illustrate the first demonstration of NlpI's contribution to E. coli K1 binding to and invasion of HBMECs, and its contribution is likely to involve cPLA(2)alpha.

Vimentin-mediated signalling is required for IbeA+ E. coli K1 invasion of human brain microvascular endothelial cells

IbeA in meningitic Escherichia coli K1 strains has been described previously for its role in invasion of BMECs (brain microvascular endothelial cells). Vimentin was identified as an IbeA-binding protein on the surface of HBMECs (human BMECs). In the present study, we demonstrated that vimentin is a primary receptor required for IbeA+ E. coli K1-induced signalling and invasion of HBMECs, on the basis of the following observations. First, E44 (IbeA+ E. coli K1 strain) invasion was blocked by vimentin inhibitors (withaferin A and acrylamide), a recombinant protein containing the vimentin head domain and an antibody against the head domain respectively. Secondly, overexpression of GFP (green fluorescent protein)-vimentin and GFP-VDM (vimentin head domain deletion mutant) significantly increased and decreased bacterial invasion respectively. Thirdly, bacterial invasion was positively correlated with phosphorylation of vimentin at Ser82 by CaMKII (Ca2+/calmodulin-dependent protein kinase II) and IbeA+ E. coli-induced phosphorylation of ERK (extracellular-signal-regulated kinase). Blockage of CaMKII by KN93 and inhibition of ERK1/2 phosphorylation by PD098059 resulted in reduced IbeA+ E. coli invasion. Fourthly, IbeA+ E. coli and IbeA-coated beads induced the clustering of vimentin that was correlated with increased entry of bacteria and beads. Lastly, IbeA+ E. coli K1 invasion was inhibited by lipid-raft-disrupting agents (filipin and nystatin) and caveolin-1 siRNA (small interfering RNA), suggesting that caveolae/lipid rafts are signalling platforms for inducing IbeA-vimentin-mediated E. coli invasion of HBMECs. Taken together, the present studies suggest that a dynamic and function-related interaction between IbeA and its primary receptor vimentin at HBMEC membrane rafts leads to vimentin phosphorylation and ERK-mediated signalling, which modulate meningitic E. coli K1 invasion.