Polar invasion and translocation of Neisseria meningitidis and Streptococcus suis in a novel human model of the blood-cerebrospinal fluid barrier

In vitro models of the choroid plexus and the blood-cerebrospinal fluid barrier: advances, applications, and perspectives

The choroid plexus (CP), a highly vascularized endothelial-epithelial convolute, is placed in the ventricular system of the brain and produces a large part of the cerebrospinal fluid (CSF). Additionally, the CP is the location of a blood-CSF barrier (BCSFB) that separates the CSF from the blood stream in the CP endothelium. In vitro models of the CP and the BCSFB are of high importance to investigate the biological functions of the CP and the BCSFB. Since the CP is involved in several serious diseases, these in vitro models promise help in researching the processes contributing to the diseases and during the development of treatment options. In this review, we provide an overview on the available models and the advances that have been made toward more sophisticated and "in vivo near" systems as organoids and microfluidic lab-on-a-chip approaches. We go into the applications and research objectives for which the various modeling systems can be used and discuss the possible future prospects and perspectives.

The hypervirulent Group B Streptococcus HvgA adhesin promotes central nervous system invasion through transcellular crossing of the choroid plexus

BACKGROUND

Group B Streptococcus (GBS) is the leading cause of neonatal meningitis responsible for a substantial cause of death and disability worldwide. The vast majority of GBS neonatal meningitis cases are due to the CC17 hypervirulent clone. However, the cellular and molecular pathways involved in brain invasion by GBS CC17 isolates remain largely elusive. Here, we studied the specific interaction of the CC17 clone with the choroid plexus, the main component of the blood-cerebrospinal fluid (CSF) barrier.

METHODS

The interaction of GBS CC17 or non-CC17 strains with choroid plexus cells was studied using an in vivo mouse model of meningitis and in vitro models of primary and transformed rodent choroid plexus epithelial cells (CPEC and Z310). In vivo interaction of GBS with the choroid plexus was assessed by microscopy. Bacterial invasion and cell barrier penetration were examined in vitro, as well as chemokines and cytokines in response to infection.

RESULTS

GBS CC17 was found associated with the choroid plexus of the lateral, 3rd and 4th ventricles. Infection of choroid plexus epithelial cells revealed an efficient internalization of the bacteria into the cells with GBS CC17 displaying a greater ability to invade these cells than a non-CC17 strain. Internalization of the GBS CC17 strain involved the CC17-specific HvgA adhesin and occurred via a clathrin-dependent mechanism leading to transcellular transcytosis across the choroid plexus epithelial monolayer. CPEC infection resulted in the secretion of several chemokines, including CCL2, CCL3, CCL20, CX3CL1, and the matrix metalloproteinase MMP3, as well as immune cell infiltration.

CONCLUSION

Our findings reveal a GBS strain-specific ability to infect the blood-CSF barrier, which appears to be an important site of bacterial entry and an active site of immune cell trafficking in response to infection.

Enrichment of infection-associated bacteria in the low biomass brain bacteriota of Alzheimer's disease patients

Alzheimer's disease (AD) is a neurodegenerative disease accompanied by neuroimmune inflammation in the frontal cortex and hippocampus. Recently, the presence of bacteria in AD-affected brains has been documented, prompting speculation about their potential role in AD-associated neuroinflammation. However, the characterization of bacteriota in human brains affected by AD remains inconclusive. This study aimed to investigate potential associations between specific bacteria and AD pathology by examining brain tissues from AD-associated neurodegenerative regions (frontal cortex and hippocampus) and the non-AD-associated hypothalamus. Employing 16S rRNA gene sequencing, 30 postmortem brain tissue samples from four individuals with normal brain histology (N) and four AD patients were analyzed, along with three blank controls. A remarkably low biomass characterized the brain bacteriota, with their overall structures delineated primarily by brain regions rather than the presence of AD. While most analyzed parameters exhibited no significant distinction in the brain bacteriota between the N and AD groups, the unique detection of Cloacibacterium normanense in the AD-associated neurodegenerative regions stood out. Additionally, infection-associated bacteria, as opposed to periodontal pathogens, were notably enriched in AD brains. This study's findings provide valuable insights into potential link between bacterial infection and neuroinflammation in AD.

Current progress and challenges in the development of brain tissue models: How to grow up the changeable brain in vitro?

In vitro modeling of brain tissue is a promising but not yet resolved problem in modern neurobiology and neuropharmacology. Complexity of the brain structure and diversity of cell-to-cell communication in (patho)physiological conditions make this task almost unachievable. However, establishment of novel in vitro brain models would ultimately lead to better understanding of development-associated or experience-driven brain plasticity, designing efficient approaches to restore aberrant brain functioning. The main goal of this review is to summarize the available data on methodological approaches that are currently in use, and to identify the most prospective trends in development of neurovascular unit, blood-brain barrier, blood-cerebrospinal fluid barrier, and neurogenic niche in vitro models. The manuscript focuses on the regulation of adult neurogenesis, cerebral microcirculation and fluids dynamics that should be reproduced in the in vitro 4D models to mimic brain development and its alterations in brain pathology. We discuss approaches that are critical for studying brain plasticity, deciphering the individual person-specific trajectory of brain development and aging, and testing new drug candidates in the in vitro models.

Inhibition of serum- and glucocorticoid-induced kinase 1 ameliorates hydrocephalus in preclinical models

BACKGROUND

Hydrocephalus is a pathological accumulation of cerebrospinal fluid (CSF), leading to ventriculomegaly. Hydrocephalus may be primary or secondary to traumatic brain injury, infection, or intracranial hemorrhage. Regardless of cause, current treatment involves surgery to drain the excess CSF. Importantly, there are no long-term, effective pharmaceutical treatments and this represents a clinically unmet need. Many forms of hydrocephalus involve dysregulation in water and electrolyte homeostasis, making this an attractive, druggable target.

METHODS

In vitro, a combination of electrophysiological and fluid flux assays was used to elucidate secretory transepithelial electrolyte and fluid flux in a human cell culture model of the choroid plexus epithelium and to determine the involvement of serum-, glucocorticoid-induced kinase 1 (SGK1). In vivo, MRI studies were performed in a genetic rat model of hydrocephalus to determine effects of inhibition of SGK1 with a novel inhibitor, SI113.

RESULTS

In the cultured cell line, SI113 reduced secretory transepithelial electrolyte and fluid flux. In vivo, SI113 blocks the development of hydrocephalus with no effect on ventricular size of wild-type animals and no overt toxic effects. Mechanistically, the development of hydrocephalus in the rat model involves an increase in activated, phosphorylated SGK1 with no change in the total amount of SGK1. SI113 inhibits phosphorylation with no changes in total SGK1 levels in the choroid plexus epithelium.

CONCLUSION

These data provide a strong preclinical basis for the use of SGK1 inhibitors in the treatment of hydrocephalus.

Circadian rhythmicity of amyloid-beta-related molecules is disrupted in the choroid plexus of a female Alzheimer's disease mouse model

The choroid plexus (CP) is part of the blood-cerebrospinal fluid barrier (BCSFB) and was recently described as an important component of the circadian clock system. It is the principal source of cerebrospinal fluid (CSF) and responsible for the synthesis and secretion of various neuroprotective peptides including those involved in amyloid-β (Aβ) transport/degradation, contributing to Aβ homeostasis. Inadequate Aβ metabolic clearance and transport across the BCSFB have been associated with circadian dysfunctions in Alzheimer's disease (AD) patients. To investigate whether AD pathology influences Aβ scavengers circadian expression, we collected CP at different time points from an AD mouse model (APP/PS1) (female and male animals, aged 6- and 12-months-old) and analyzed their mRNA expression by Real-time RT-PCR. Only angiotensin-converting enzyme (Ace) expression in 6-month-old female wild-type mice and transthyretin (Ttr) expression in 12-month-old female wild-type mice presented significant rhythmicity. The circadian rhythmicity of Ace and Ttr, prompt us to analyze the involvement of circadian rhythm in Aβ uptake. A human CP papilloma (HIBCPP) cell line was incubated with Aβ-488 and uptake was evaluated at different time points using flow cytometry. Aβ uptake displayed circadian rhythmicity. Our results suggest that AD might affect Aβ scavengers rhythmicity and that Aβ clearance is a rhythmic process possibly regulated by the rhythmic expression of Aβ scavengers.

Role of Metabolic Adaptation of Streptococcus suis to Host Niches in Bacterial Fitness and Virulence

Streptococcus suis, both a common colonizer of the porcine upper respiratory tract and an invasive pig pathogen, successfully adapts to different host environments encountered during infection. Whereas the initial infection mainly occurs via the respiratory tract, in a second step, the pathogen can breach the epithelial barrier and disseminate within the whole body. Thereby, the pathogen reaches other organs such as the heart, the joints, or the brain. In this review, we focus on the role of S. suis metabolism for adaptation to these different in vivo host niches to encounter changes in nutrient availability, host defense mechanisms and competing microbiota. Furthermore, we highlight the close link between S. suis metabolism and virulence. Mutants deficient in metabolic regulators often show an attenuation in infection experiments possibly due to downregulation of virulence factors, reduced resistance to nutritive or oxidative stress and to phagocytic activity. Finally, metabolic pathways as potential targets for new therapeutic strategies are discussed. As antimicrobial resistance in S. suis isolates has increased over the last years, the development of new antibiotics is of utmost importance to successfully fight infections in the future.

The phosphoproteome of choroid plexus epithelial cells following infection with Neisseria meningitidis

The Gram-negative bacterium Neisseria meningitidis, which causes meningitis in humans, has been demonstrated to manipulate or alter host signalling pathways during infection of the central nervous system (CNS). However, these complex signalling networks are not completely understood. We investigate the phosphoproteome of an in vitro model of the blood-cerebrospinal fluid barrier (BCSFB) based on human epithelial choroid plexus (CP) papilloma (HIBCPP) cells during infection with the N. meningitidis serogroup B strain MC58 in presence and absence of the bacterial capsule. Interestingly, our data demonstrates a stronger impact on the phosphoproteome of the cells by the capsule-deficient mutant of MC58. Using enrichment analyses, potential pathways, molecular processes, biological processes, cellular components and kinases were determined to be regulated as a consequence of N. meningitidis infection of the BCSFB. Our data highlight a variety of protein regulations that are altered during infection of CP epithelial cells with N. meningitidis, with the regulation of several pathways and molecular events only being detected after infection with the capsule-deficient mutant. Mass spectrometry proteomics data are available via ProteomeXchange with identifier PXD038560.

Characterization of TRPV4-mediated signaling pathways in an optimized human choroid plexus epithelial cell line

The objectives of these studies were twofold: 1) to characterize the human choroid plexus papilloma (HIBCPP) cell line as a model of the blood-cerebrospinal fluid barrier (BCSFB) via morphology, tightness, and polarization of transporters in choroid plexus epithelia (CPe), and 2) to utilize Ussing-style electrophysiology to elucidate signaling pathways associated with the activation of the transient receptor potential vanilloid 4 (TRPV4) channel involved in cerebrospinal fluid (CSF) secretion. RT-PCR was implemented to determine gene expression of cell fate markers, junctional complex proteins, and transporters of interest. Scanning electron microscopy and confocal three-dimensional renderings of cultures grown on permeable supports were utilized to delineate the morphology of the brush border, junctional complexes, and polarization of key transporters. Electrophysiology was used to understand and explore TRPV4-mediated signaling in the HIBCPP cell line, considering both short-circuit current (Isc) and conductance responses. HIBCPP cells grown under optimized culture conditions exhibited minimal multilayering, developed an intermediate resistance monolayer, retained differentiation properties, and expressed, and correctly localized, junctional proteins and native transporters. We found that activation of TRPV4 resulted in a robust, multiphasic change in electrogenic ion flux and increase in conductance accompanied by substantial fluid secretion. This response appears to be modulated by a number of different effectors, implicating phospholipase C (PLC), protein kinase C (PKC), and phosphoinositide 3-kinase (PI3K) in TRPV4-mediated ion flux. The HIBCPP cell line is a representative model of the human BCSFB, which can be utilized for studies of transporter function, intracellular signaling, and regulation of CSF production.

Modeling infectious diseases of the central nervous system with human brain organoids

Bacteria, fungi, viruses, and protozoa are known to infect and induce diseases in the human central nervous system (CNS). Modeling the mechanisms of interaction between pathogens and the CNS microenvironment is essential to understand their pathophysiology and develop new treatments. Recent advancements in stem cell technologies have allowed for the creation of human brain organoids, which more closely resembles the human CNS microenvironment when compared to classical 2-dimensional (2D) cultures. Now researchers can utilize these systems to investigate and reinvestigate questions related to CNS infection in a human-derived brain organoid system. Here in this review, we highlight several infectious diseases which have been tested in human brain organoids and compare similarities in response to these pathogens across different investigations. We also provide a brief overview of some recent advancements which can further enrich this model to develop new and better therapies to treat brain infections.

Different Involvement of Vimentin during Invasion by Listeria monocytogenes at the Blood–Brain and the Blood–Cerebrospinal Fluid Barriers In Vitro

The human central nervous system (CNS) is separated from the blood by distinct cellular barriers, including the blood–brain barrier (BBB) and the blood–cerebrospinal fluid (CFS) barrier (BCSFB). Whereas at the center of the BBB are the endothelial cells of the brain capillaries, the BCSFB is formed by the epithelium of the choroid plexus. Invasion of cells of either the BBB or the BCSFB is a potential first step during CNS entry by the Gram-positive bacterium Listeria monocytogenes (Lm). Lm possesses several virulence factors mediating host cell entry, such as the internalin protein family—including internalin (InlA), which binds E-cadherin (Ecad) on the surface of target cells, and internalin B (InlB)—interacting with the host cell receptor tyrosine kinase Met. A further family member is internalin (InlF), which targets the intermediate filament protein vimentin. Whereas InlF has been shown to play a role during brain invasion at the BBB, its function during infection at the BCSFB is not known. We use human brain microvascular endothelial cells (HBMEC) and human choroid plexus epithelial papilloma (HIBCPP) cells to investigate the roles of InlF and vimentin during CNS invasion by Lm. Whereas HBMEC present intracellular and surface vimentin (besides Met), HIBCPP cells do not express vimentin (except Met and Ecad). Treatment with the surface vimentin modulator withaferin A (WitA) inhibited invasion of Lm into HBMEC, but not HIBCPP cells. Invasion of Lm into HBMEC and HIBCPP cells is, however, independent of InlF, since a deletion mutant of Lm lacking InlF did not display reduced invasion rates.

Following Ussing's legacy: from amphibian models to mammalian kidney and brain

Professor Hans H. Ussing (1911-2000) was one of the founding members of the field of epithelial cell biology. He is most famous for the electrophysiological technique that he developed to measure electrogenic ion flux across epithelial tissues. Ussing-style electrophysiology has been applied to multiple tissues and has informed fields as diverse as amphibian biology and medicine. In the latter, this technique has contributed to a basic understanding of maladies such as hypertension, polycystic kidney disease, cystic fibrosis, and diarrheal diseases to mention but a few. In addition to this valuable contribution to biological methods, Prof. Ussing also provided strong evidence for the concept of active transport several years before the elucidation of Na+K+ATPase. In addition, he provided cell biologists with the important concept of polarized epithelia with specific and different transporters found in the apical and basolateral membranes, thus providing these cells with the ability to conduct directional, active and passive transepithelial transport. My studies have used Ussing chamber electrophysiology to study the toad urinary bladder, an amphibian cell line, renal cell lines, and, most recently, choroid plexus cell lines. This technique has formed the basis of our in vitro mechanistic studies that are used in an iterative manner with animal models to better understand disease progress and treatment. I was honored to be invited to deliver the 2022 Hans Ussing Lecture sponsored by the Epithelial Transport Group of the American Physiological Society. This manuscript is a version of the material presented in that lecture.

Protocol to analyze the transmigration efficiency of T. brucei using an in vitro model of the blood-cerebrospinal fluid barrier

At present, the only approach to investigate the transmigration of Trypanosoma brucei, the causative agent of human African trypanosomiasis, from blood to cerebrospinal fluid is through animal experiments. This protocol details how to analyze the transmigration efficiency using an in vitro model of the blood-cerebrospinal fluid (blood-CSF) barrier. We describe how to grow human choroid plexus epithelial cells on cell culture filter inserts to form the barrier, followed by isolating and quantifying genomic DNA of transmigrated parasites by qPCR. For complete details on the use and execution of this protocol, please refer to Speidel et al. (2022).

Immortalized human choroid plexus endothelial cells enable an advanced endothelial-epithelial two-cell type in vitro model of the choroid plexus

The choroid plexus (CP) is a highly vascularized structure containing endothelial and epithelial cells located in the ventricular system of the central nervous system (CNS). The role of the fenestrated CP endothelium is under-researched and requires the generation of an immortalized CP endothelial cell line with preserved features. Transduction of primary human CP endothelial cells (HCPEnC) with the human telomerase reverse transcriptase (hTERT) resulted in immortalized HCPEnC (iHCPEnC), which grew as monolayer with contact inhibition, formed capillary-like tubes in Matrigel, and showed no colony growth in soft agar. iHCPEnC expressed pan-endothelial markers and presented characteristic plasmalemma vesicle-associated protein-containing structures. Cultivation of iHCPEnC and human epithelial CP papilloma (HIBCPP) cells on opposite sides of cell culture filter inserts generated an in vitro model with a consistently enhanced barrier function specifically by iHCPEnC. Overall, iHCPEnC present a tool that will contribute to the understanding of CP organ functions, especially endothelial-epithelial interplay.

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Generation of an immortalized human choroid plexus endothelial cell line (iHCPEnC)

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iHCPEnC immortalized by telomerase maintain essential endothelial properties

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The mRNA expression profile distinguishes iHCPEnC from other endothelial cell types

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iHCPEnC enhance the barrier function of a choroid plexus epithelium in coculture

Transmigration of Trypanosoma brucei across an in vitro blood-cerebrospinal fluid barrier

Trypanosoma brucei is the causative agent of human African trypanosomiasis. The parasite transmigrates from blood vessels across the choroid plexus epithelium to enter the central nervous system, a process that leads to the manifestation of second stage sleeping sickness. Using an in vitro model of the blood-cerebrospinal fluid barrier, we investigated the mechanism of the transmigration process. For this, a monolayer of human choroid plexus papilloma cells was cultivated on a permeable membrane that mimics the basal lamina underlying the choroid plexus epithelial cells. Plexus cells polarize and interconnect forming tight junctions. Deploying different T. brucei brucei strains, we observed that geometry and motility are important for tissue invasion. Using fluorescent microscopy, the parasite's moving was visualized between plexus epithelial cells. The presented model provides a simple tool to screen trypanosome libraries for their ability to infect cerebrospinal fluid or to test the impact of chemical substances on transmigration.

The Daily Expression of ABCC4 at the BCSFB Affects the Transport of Its Substrate Methotrexate

The choroid plexuses (CPs), located in the brain ventricles, form an interface between the blood and the cerebrospinal fluid named the blood-cerebrospinal barrier, which, by the presence of tight junctions, detoxification enzymes, and membrane transporters, limits the traffic of molecules into the central nervous system. It has already been shown that sex hormones regulate several CP functions, including the oscillations of its clock genes. However, it is less explored how the circadian rhythm regulates CP functions. This study aimed to evaluate the impact of sex hormones and circadian rhythms on the function of CP membrane transporters. The 24 h transcription profiles of the membrane transporters rAbca1, rAbcb1, rAbcc1, rAbcc4, rAbcg2, rAbcg4, and rOat3 were characterized in the CPs of intact male, intact female, sham-operated female, and gonadectomized rats. We found that rAbcc1 is expressed in a circadian way in the CPs of intact male rats, rAbcg2 in the CPs of intact female rats, and both rAbcc4 and rOat3 mRNA levels were expressed in a circadian way in the CPs of intact male and female rats. Next, using an in vitro model of the human blood–cerebrospinal fluid barrier, we also found that methotrexate (MTX) is transported in a circadian way across this barrier. The circadian pattern of Abcc4 found in the human CP epithelial papilloma cells might be partially responsible for MTX circadian transport across the basal membrane of CP epithelial cells.

Central Nervous System Stimulants Limit Caffeine Transport at the Blood-Cerebrospinal Fluid Barrier

Caffeine, a common ingredient in energy drinks, crosses the blood-brain barrier easily, but the kinetics of caffeine across the blood-cerebrospinal fluid barrier (BCSFB) has not been investigated. Therefore, 127 autopsy cases (Group A, 30 patients, stimulant-detected group; and Group B, 97 patients, no stimulant detected group) were examined. In addition, a BCSFB model was constructed using human vascular endothelial cells and human choroid plexus epithelial cells separated by a filter, and the kinetics of caffeine in the BCSFB and the effects of 4-aminopyridine (4-AP), a neuroexcitatory agent, were studied. Caffeine concentrations in right heart blood (Rs) and cerebrospinal fluid (CSF) were compared in the autopsy cases: caffeine concentrations were higher in Rs than CSF in Group A compared to Group B. In the BCSFB model, caffeine and 4-AP were added to the upper layer, and the concentration in the lower layer of choroid plexus epithelial cells was measured. The CSF caffeine concentration was suppressed, depending on the 4-AP concentration. Histomorphological examination suggested that choroid plexus epithelial cells were involved in inhibiting the efflux of caffeine to the CSF. Thus, the simultaneous presence of stimulants and caffeine inhibits caffeine transfer across the BCSFB.

Characterization of Oxygen Levels in an Uninfected and Infected Human Blood-Cerebrospinal-Fluid-Barrier Model

The host–pathogen interaction during meningitis can be investigated with blood-cerebrospinal-fluid-barrier (BCSFB) cell culture models. They are commonly handled under atmospheric oxygen conditions (19–21% O₂), although the physiological oxygen conditions are significantly lower in cerebrospinal fluid (CSF) (7–8% O₂). We aimed to characterize oxygen levels in a Streptococcus (S.) suis-infected BCSFB model with transmigrating neutrophils. A BCSFB model with human choroid plexus epithelial cells growing on transwell-filters was used. The upper “blood”-compartment was infected and blood-derived neutrophils were added. S. suis and neutrophils transmigrated through the BCSFB into the “CSF”-compartment. Here, oxygen and pH values were determined with the non-invasive SensorDish^® reader. Slight orbital shaking improved the luminescence-based measurement technique for detecting free oxygen. In the non-infected BCSFB model, an oxygen value of 7% O₂ was determined. However, with S. suis and transmigrating neutrophils, the oxygen value significantly decreased to 2% O₂. The pH level decreased slightly in all groups. In conclusion, we characterized oxygen levels in the BCSFB model and demonstrated the oxygen consumption by cells and bacteria. Oxygen values in the non-infected BCSFB model are comparable to in vivo values determined in pigs in the CSF. Infection and transmigrating neutrophils decrease the oxygen value to lower values.

Capsule-dependent impact of MAPK signalling on host cell invasion and immune response during infection of the choroid plexus epithelium by Neisseria meningitidis

Background

The Gram-negative bacterium Neisseria meningitidis (Nm) can cause meningitis in humans, but the host signalling pathways manipulated by Nm during central nervous system (CNS) entry are not completely understood.

Methods

We investigate the role of the mitogen-activated protein kinases (MAPK) Erk1/2 and p38 in an in vitro model of the blood-cerebrospinal fluid barrier (BCSFB) based on human epithelial choroid plexus (CP) papilloma (HIBCPP) cells during infection with Nm serogroup B (NmB) and serogroup C (NmC) strains. A transcriptome analysis of HIBCPP cells following infection with Nm by massive analysis of cDNA ends (MACE) was done to further characterize the cellular response to infection of the barrier.

Results

Interestingly, whereas NmB and NmC wild type strains required active Erk1/2 and p38 pathways for infection, invasion by capsule-deficient mutants was independent of Erk1/2 and, in case of the NmB strain, of p38 activity. The transcriptome analysis of HIBCPP cells following infection with Nm demonstrated specific regulation of genes involved in the immune response dependent on Erk1/2 signalling. Gene ontology (GO) analysis confirmed loss of MAPK signalling after Erk1/2 inhibition and revealed an additional reduction of cellular responses including NFκB and JAK-STAT signalling. Interestingly, GO terms related to TNF signalling and production of IL6 were lost specifically following Erk1/2 inhibition during infection with wild type Nm, which correlated with the reduced infection rates by the wild type in absence of Erk1/2 signalling.

Conclusion

Our data point towards a role of MAPK signalling during infection of the CP epithelium by Nm, which is strongly influenced by capsule expression, and affects infection rates as well as the host cell response.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-021-00288-7.

Identification of Streptococcus suis putative zoonotic virulence factors: A systematic review and genomic meta-analysis

Streptococcus suis is an emerging zoonotic pathogen. Over 100 putative virulence factors have been described, but it is unclear to what extent these virulence factors could contribute to zoonotic potential of S. suis. We identified all S. suis virulence factors studied in experimental models of human origin in a systematic review and assessed their contribution to zoonotic potential in a subsequent genomic meta-analysis. PubMed and Scopus were searched for English-language articles that studied S. suis virulence published until 31 March 2021. Articles that analyzed a virulence factor by knockout mutation, purified protein, and/or recombinant protein in a model of human origin, were included. Data on virulence factor, strain characteristics, used human models and experimental outcomes were extracted. All publicly available S. suis genomes with available metadata on host, disease status and country of origin, were included in a genomic meta-analysis. We calculated the ratio of the prevalence of each virulence factor in human and pig isolates. We included 130 articles and 1703 S. suis genomes in the analysis. We identified 53 putative virulence factors that were encoded by genes which are part of the S. suis core genome and 26 factors that were at least twice as prevalent in human isolates as in pig isolates. Hhly3 and NisK/R were particularly enriched in human isolates, after stratification by genetic lineage and country of isolation. This systematic review and genomic meta-analysis have identified virulence factors that are likely to contribute to the zoonotic potential of S. suis.

The type II histidine triad protein HtpsC facilitates invasion of epithelial cells by highly virulent Streptococcus suis serotype 2

Streptococcus suis serotype 2 (S. suis 2) is an important zoonotic pathogen that presents a significant threat both to pigs and to workers in the pork industry. The initial steps of S. suis 2 pathogenesis are unclear. In this study, we found that the type II histidine triad protein HtpsC from the highly virulent Chinese isolate 05ZYH33 is structurally similar to internalin A (InlA) from Listeria monocytogenes, which plays an important role in mediating listerial invasion of epithelial cells. To determine if HtpsC and InlA function similarly, an isogenic htpsC mutant (ΔhtpsC) was generated in S. suis by homologous recombination. The htpsC deletion strain exhibited a diminished ability to adhere to and invade epithelial cells from different sources. Double immunofluorescence microscopy also revealed reduced survival of the ΔhtpsC mutant after co-cultivation with epithelium. Adhesion to epithelium and invasion by the wild type strain was inhibited by a monoclonal antibody against E-cadherin. In contrast, the htpsC-deficient mutant was unaffected by the same treatment, suggesting that E-cadherin is the host-cell receptor that interacts with HtpsC and facilitates bacterial internalization. Based on these results, we propose that HtpsC is involved in the process by which S. suis 2 penetrates host epithelial cells, and that this protein is an important virulence factor associated with cell adhesion and invasion.

Invasion of the choroid plexus epithelium by Neisseria meningitidis is differently mediated by Arp2/3 signaling and possibly by dynamin dependent on the presence of the capsule

Neisseria meningitis (Nm) is a human-specific bacterial pathogen that can cause sepsis and meningitis. To cause meningitis Nm must enter the central nervous system (CNS) across one of the barriers between the blood and the brain. We have previously shown that a capsule-depleted Serogroup B strain of Nm displays enhanced invasion into human choroid plexus (CP) epithelial papilloma (HIBCPP) cells, which represent an in vitro model of the blood-cerebrospinal fluid barrier (BCSFB). Still, the processes involved during CNS invasion by Nm, especially the role of host cell actin cytoskeleton remodeling, are not investigated in detail. Here, we demonstrate that invasion into CP epithelial cells by encapsulated and capsule-depleted Nm is mediated by distinct host cell pathways. Whereas a Serogroup B wild-type strain enters HIBCPP cells by a possibly dynamin-independent, but actin related protein 2/3 (Arp2/3)-dependent mechanism, invasion by a capsule-depleted mutant is reduced by the dynamin inhibitor dynasore and Arp2/3-independent. Both wild-type and mutant bacteria require Src kinase activity for entry into HIBCPP cells. Our data show that Nm can employ different mechanisms for invasion into the CP epithelium dependent on the presence of a capsule.

Genomic diversity contributes to the neuroinvasiveness of the Yellow fever French neurotropic vaccine

Mass vaccination with the live attenuated vaccine YF-17D is the current way to prevent infection with Yellow fever virus (YFV). However, 0.000012-0.00002% of vaccinated patients develop post-vaccination neurological syndrome (YEL-AND). Understanding the factors responsible for neuroinvasion, neurotropism, and neurovirulence of the vaccine is critical for improving its biosafety. The YF-FNV vaccine strain, known to be associated with a higher frequency of YEL-AND (0.3-0.4%) than YF-17D, is an excellent model to study vaccine neuroinvasiveness. We determined that neuroinvasiveness of YF-FNV occured both via infection and passage through human brain endothelial cells. Plaque purification and next generation sequencing (NGS) identified several neuroinvasive variants. Their neuroinvasiveness was not higher than that of YF-FNV. However, rebuilding the YF-FNV population diversity from a set of isolated YF-FNV-N variants restored the original neuroinvasive phenotype of YF-FNV. Therefore, we conclude that viral population diversity is a critical factor for YFV vaccine neuroinvasiveness.

A Comparative Transcriptome Analysis of Human and Porcine Choroid Plexus Cells in Response to Streptococcus suis Serotype 2 Infection Points to a Role of Hypoxia

Streptococcus suis (S. suis) is an important opportunistic pathogen, which can cause septicemia and meningitis in pigs and humans. Previous in vivo observations in S. suis-infected pigs revealed lesions at the choroid plexus (CP). In vitro experiments with primary porcine CP epithelial cells (PCPEC) and human CP epithelial papilloma (HIBCPP) cells demonstrated that S. suis can invade and traverse the CP epithelium, and that the CP contributes to the inflammatory response via cytokine expression. Here, next generation sequencing (RNA-seq) was used to compare global transcriptome profiles of PCPEC and HIBCPP cells challenged with S. suis serotype (ST) 2 infected in vitro, and of pigs infected in vivo. Identified differentially expressed genes (DEGs) were, amongst others, involved in inflammatory responses and hypoxia. The RNA-seq data were validated via quantitative PCR of selected DEGs. Employing Gene Set Enrichment Analysis (GSEA), 18, 28, and 21 enriched hallmark gene sets (GSs) were identified for infected HIBCPP cells, PCPEC, and in the CP of pigs suffering from S. suis ST2 meningitis, respectively, of which eight GSs overlapped between the three different sample sets. The majority of these GSs are involved in cellular signaling and pathways, immune response, and development, including inflammatory response and hypoxia. In contrast, suppressed GSs observed during in vitro and in vivo S. suis ST2 infections included those, which were involved in cellular proliferation and metabolic processes. This study suggests that similar cellular processes occur in infected human and porcine CP epithelial cells, especially in terms of inflammatory response.

The Choroid Plexus Is Permissive for a Preactivated Antigen-Experienced Memory B-Cell Subset in Multiple Sclerosis

The role of B cells in multiple sclerosis (MS) is increasingly recognized. B cells undergo compartmentalized redistribution in blood and cerebrospinal fluid (CSF) during active MS, whereby memory B cells accumulate in the CSF. While B-cell trafficking across the blood-brain barrier has been intensely investigated, cellular diapedesis through the blood-CSF barrier (BCSFB) is incompletely understood. To investigate how B cells interact with the choroid plexus to transmigrate into the CSF we isolated circulating B cells from healthy donors (HC) and MS patients, utilized an inverted cell culture filter system of human choroid plexus papilloma (HIBCPP) cells to determine transmigration rates of B-cell subsets, immunofluorescence, and electron microscopy to analyze migration routes, and qRT-PCR to determine cytokines/chemokines mediating B-cell diapedesis. We also screened the transcriptome of intrathecal B cells from MS patients. We found, that spontaneous transmigration of HC- and MS-derived B cells was scant, yet increased significantly in response to B-cell specific chemokines CXCL-12/CXCL-13, was further boosted upon pre-activation and occurred via paracellular and transcellular pathways. Migrating cells exhibited upregulation of several genes involved in B-cell activation/migration and enhanced expression of chemokine receptors CXCR4/CXCR5, and were predominantly of isotype class switched memory phenotype. This antigen-experienced migratory subset displayed more pronounced chemotactic activities in MS than in HC and was retrieved in intrathecal B cells from patients with active MS. Trafficking of class-switched memory B cells was downscaled in a small cohort of natalizumab-exposed MS patients and the proportions of these phenotypes were reduced in peripheral blood yet were enriched intrathecally in patients who experienced recurrence of disease activity after withdrawal of natalizumab. Our findings highlight the relevance of the BCSFB as important gate for the entry of potentially harmful activated B cells into the CSF.

Host transcriptome response to Borrelia burgdorferi sensu lato

The host immune response to infection is a well-coordinated system of innate and adaptive immune cells working in concert to prevent the colonization and dissemination of a pathogen. While this typically leads to a beneficial outcome and the suppression of disease pathogenesis, the Lyme borreliosis bacterium, Borrelia burgdorferi sensu lato, can elicit an immune profile that leads to a deleterious state. As B. burgdorferi s.l. produces no known toxins, it is suggested that the immune and inflammatory response of the host are responsible for the manifestation of symptoms, including flu-like symptoms, musculoskeletal pain, and cognitive disorders. The past several years has seen a substantial increase in the use of microarray and sequencing technologies to investigate the transcriptome response induced by B. burgdorferi s.l., thus enabling researchers to identify key factors and pathways underlying the pathophysiology of Lyme borreliosis. In this review we present the major host transcriptional outcomes induced by the bacterium across several studies and discuss the overarching theme of the host inflammatory and immune response, and how it influences the pathology of Lyme borreliosis.

Interactions and Signal Transduction Pathways Involved during Central Nervous System Entry by Neisseria meningitidis across the Blood-Brain Barriers

The Gram-negative diplococcus Neisseria meningitidis, also called meningococcus, exclusively infects humans and can cause meningitis, a severe disease that can lead to the death of the afflicted individuals. To cause meningitis, the bacteria have to enter the central nervous system (CNS) by crossing one of the barriers protecting the CNS from entry by pathogens. These barriers are represented by the blood–brain barrier separating the blood from the brain parenchyma and the blood–cerebrospinal fluid (CSF) barriers at the choroid plexus and the meninges. During the course of meningococcal disease resulting in meningitis, the bacteria undergo several interactions with host cells, including the pharyngeal epithelium and the cells constituting the barriers between the blood and the CSF. These interactions are required to initiate signal transduction pathways that are involved during the crossing of the meningococci into the blood stream and CNS entry, as well as in the host cell response to infection. In this review we summarize the interactions and pathways involved in these processes, whose understanding could help to better understand the pathogenesis of meningococcal meningitis.

Targeting the Choroid Plexuses for Protein Drug Delivery

Delivery of therapeutic agents to the central nervous system is challenged by the barriers in place to regulate brain homeostasis. This is especially true for protein therapeutics. Targeting the barrier formed by the choroid plexuses at the interfaces of the systemic circulation and ventricular system may be a surrogate brain delivery strategy to circumvent the blood-brain barrier. Heterogenous cell populations located at the choroid plexuses provide diverse functions in regulating the exchange of material within the ventricular space. Receptor-mediated transcytosis may be a promising mechanism to deliver protein therapeutics across the tight junctions formed by choroid plexus epithelial cells. However, cerebrospinal fluid flow and other barriers formed by ependymal cells and perivascular spaces should also be considered for evaluation of protein therapeutic disposition. Various preclinical methods have been applied to delineate protein transport across the choroid plexuses, including imaging strategies, ventriculocisternal perfusions, and primary choroid plexus epithelial cell models. When used in combination with simultaneous measures of cerebrospinal fluid dynamics, they can yield important insight into pharmacokinetic properties within the brain. This review aims to provide an overview of the choroid plexuses and ventricular system to address their function as a barrier to pharmaceutical interventions and relevance for central nervous system drug delivery of protein therapeutics. Protein therapeutics targeting the ventricular system may provide new approaches in treating central nervous system diseases.

Polar Infection of Echovirus-30 Causes Differential Barrier Affection and Gene Regulation at the Blood-Cerebrospinal Fluid Barrier

Echovirus-30 (E-30) is responsible for the extensive global outbreaks of meningitis in children. To gain access to the central nervous system, E-30 first has to cross the epithelial blood-cerebrospinal fluid barrier. Several meningitis causing bacteria preferentially infect human choroid plexus papilloma (HIBCPP) cells in a polar fashion from the basolateral cell side. Here, we investigated the polar infection of HIBCPP cells with E-30. Both apical and basolateral infections caused a significant decrease in the transepithelial electrical resistance of HIBCPP cells. However, to reach the same impact on the barrier properties, the multiplicity of infection of the apical side had to be higher than that of the basolateral infection. Furthermore, the number of infected cells at respective time-points after basolateral infection was significantly higher compared to apical infection. Cytotoxic effects of E-30 on HIBCPP cells during basolateral infection were observed following prolonged infection and appeared more drastically compared to the apical infection. Gene expression profiles determined by massive analysis of cDNA ends revealed distinct regulation of specific genes depending on the side of HIBCPP cells' infection. Altogether, our data highlights the polar effects of E-30 infection in a human in vitro model of the blood-cerebrospinal fluid barrier leading to central nervous system inflammation.

Cadaverine and Spermine Elicit Ca2+ Uptake in Human CP Cells via a Trace Amine-Associated Receptor 1 Dependent Pathway

The choroid plexus (CP) constitutes a barrier between the blood and the cerebrospinal fluid (CSF) which regulates the exchange of substances between these two fluids through mechanisms that are not completely understood. Polyamines as spermine, spermidine and putrescine are produced by all cells and are present in the CSF. Interestingly, their levels are altered in some neuronal disorders as Alzheimer's and Parkinson's diseases, thus increasing the interest in their signalling in the central nervous system (CNS). Cadaverine, on the other hand, is synthetized by the intestinal microbiome, suggesting that the presence of this bacterial metabolite in the CSF requires that it is up taken to the CNS across brain barriers. We knew that polyamines are detected by the olfactory signalling cascade operating at the CP, but the receptor involved had not been identified. The zebrafish TAAR13c was the only receptor known to bind a polyamine-cadaverine. Thus, we searched for a human receptor with homology to TAAR13c and found that some human TAARs including TAAR1 showed great homology. Then, we confirmed the expression of TAAR1 mRNA and protein in a human cell line of the CP, and in human CP samples. Calcium imaging assays after TAAR1 knockdown in these cells with a specific siRNA against TAAR1 showed a consistent reduction in the responses of these cells to cadaverine and spermidine, but not to spermine, suggesting that TAAR1 is activated by cadaverine and spermidine, but not spermine.

Non-Typeable Haemophilus influenzae Invade Choroid Plexus Epithelial Cells in a Polar Fashion

Non-typeable Haemophilus influenzae (NTHI) is a pathogen of the human respiratory tract causing the majority of invasive H. influenzae infections. Severe invasive infections such as septicemia and meningitis occur rarely, but the lack of a protecting vaccine and the increasing antibiotic resistance of NTHI impede treatment and emphasize its relevance as a potential meningitis causing pathogen. Meningitis results from pathogens crossing blood-brain barriers and invading the immune privileged central nervous system (CNS). In this study, we addressed the potential of NTHI to enter the brain by invading cells of the choroid plexus (CP) prior to meningeal inflammation to enlighten NTHI pathophysiological mechanisms. A cell culture model of human CP epithelial cells, which form the blood-cerebrospinal fluid barrier (BCSFB) in vivo, was used to analyze adhesion and invasion by immunofluorescence and electron microscopy. NTHI invade CP cells in vitro in a polar fashion from the blood-facing side. Furthermore, NTHI invasion rates are increased compared to encapsulated HiB and HiF strains. Fimbriae occurrence attenuated adhesion and invasion. Thus, our findings underline the role of the BCSFB as a potential entry port for NTHI into the brain and provide strong evidence for a function of the CP during NTHI invasion into the CNS during the course of meningitis.

The Lyme disease bacterium, Borrelia burgdorferi, stimulates an inflammatory response in human choroid plexus epithelial cells

The main functions of the choroid plexus (CP) are the production of cerebral spinal fluid (CSF), the formation of the blood-CSF barrier, and regulation of immune response. This barrier allows for the exchange of specific nutrients, waste, and peripheral immune cells between the blood stream and CSF. Borrelia burgdorferi (Bb), the causative bacteria of Lyme disease, is associated with neurological complications including meningitis-indeed, Bb has been isolated from the CSF of patients. While it is accepted that B. burgdorferi can enter the central nervous system (CNS) of patients, it is unknown how the bacteria crosses this barrier and how the pathogenesis of the disease leads to the observed symptoms in patients. We hypothesize that during infection Borrelia burgdorferi will induce an immune response conducive to the chemotaxis of immune cells and subsequently lead to a pro-inflammatory state with the CNS parenchyma. Primary human choroid plexus epithelial cells were grown in culture and infected with B. burgdorferi strain B31 MI-16 for 48 hours. RNA was isolated and used for RNA sequencing and RT-qPCR validation. Secreted proteins in the supernatant were analyzed via ELISA. Transcriptome analysis based on RNA sequencing determined a total of 160 upregulated genes and 98 downregulated genes. Pathway and biological process analysis determined a significant upregulation in immune and inflammatory genes specifically in chemokine and interferon related pathways. Further analysis revealed downregulation in genes related to cell to cell junctions including tight and adherens junctions. These results were validated via RT-qPCR. Protein analysis of secreted factors showed an increase in inflammatory chemokines, corresponding to our transcriptome analysis. These data further demonstrate the role of the CP in the modulation of the immune response in a disease state and give insight into the mechanisms by which Borrelia burgdorferi may disseminate into, and act upon, the CNS. Future experiments aim to detail the impact of B. burgdorferi on the blood-CSF-barrier (BCSFB) integrity and inflammatory response within animal models.

Choroid plexus and the blood-cerebrospinal fluid barrier in disease

The choroid plexus (CP) forming the blood-cerebrospinal fluid (B-CSF) barrier is among the least studied structures of the central nervous system (CNS) despite its clinical importance. The CP is an epithelio-endothelial convolute comprising a highly vascularized stroma with fenestrated capillaries and a continuous lining of epithelial cells joined by apical tight junctions (TJs) that are crucial in forming the B-CSF barrier. Integrity of the CP is critical for maintaining brain homeostasis and B-CSF barrier permeability. Recent experimental and clinical research has uncovered the significance of the CP in the pathophysiology of various diseases affecting the CNS. The CP is involved in penetration of various pathogens into the CNS, as well as the development of neurodegenerative (e.g., Alzheimer´s disease) and autoimmune diseases (e.g., multiple sclerosis). Moreover, the CP was shown to be important for restoring brain homeostasis following stroke and trauma. In addition, new diagnostic methods and treatment of CP papilloma and carcinoma have recently been developed. This review describes and summarizes the current state of knowledge with regard to the roles of the CP and B-CSF barrier in the pathophysiology of various types of CNS diseases and sets up the foundation for further avenues of research.

The bitter taste receptor TAS2R14 regulates resveratrol transport across the human blood-cerebrospinal fluid barrier

The regulation of transport mechanisms at brain barriers must be thoroughly understood, so that novel strategies for improving drug delivery to the brain can be designed. The blood-cerebrospinal fluid barrier (BCSFB) established by the choroid plexus (CP) epithelial cells has been poorly studied in this regard despite its relevance for the protection of the central nervous system (CNS). This study assessed the role of bitter taste receptors (TAS2Rs), TAS2R14 and TAS2R39, in the transport of resveratrol across CP epithelial cells using an in vitro model of the human BCSFB. Both receptors are expressed in human CP cells and known to bind resveratrol. First, Ca²⁺ imaging assays demonstrated that resveratrol specifically activates the TAS2R14 receptor, but not TAS2R39, in these human CP epithelial cells. Then, we proceeded with permeation studies that showed resveratrol can cross the human BCSFB, from the blood to the CSF side and that TAS2R14 knockdown decreased the transport of resveratrol across these cells. Conversely, inhibition of efflux transporters ABCC1, ABCC4 or ABCG2 also restrained the transport of resveratrol across these cells. Interestingly, resveratrol upregulated the expression of ABCG2 located at the apical membrane of the cells via TAS2R14, whereas ABCC1 and ABCC4 at the basolateral membrane of the cells were not affected. Altogether, our study demonstrates that the BCSFB is a gateway for resveratrol entrance into the CNS and that the receptor TAS2R14 regulates its transport by regulating the action of efflux transporters at CP epithelial cells.

Bitter taste receptors profiling in the human blood-cerebrospinal fluid-barrier

The choroid plexus (CP) epithelial cells establish an important blood-brain interface, the blood-cerebrospinal fluid barrier (BCSFB), which constitutes a complementary gateway to the blood-brain-barrier for the entrance of several molecules into the central nervous system (CNS). However, the mechanisms that operate at the BCSFB to regulate the molecular traffic are still poorly understood. The taste signalling machinery, present in many extra-oral tissues, is involved in the chemical sensing of the composition of body fluids. We have identified this pathway in rat CP and hypothesised that it could also be present in the human BCSFB. In this study, we characterised the bitter taste receptors (TAS2Rs) expression profiling in human CP by combining data retrieved from available databases of the human CP transcriptome with its expression analysis in a human CP cell line and immunohistochemistry of human CP sections from men and women. TAS2R4, 5, 14 and 39 expression was confirmed in human CP tissue by immunohistochemistry and in HIBCPP cells by RT-PCR, immunofluorescence and Western blot. Moreover, the presence of downstream effector proteins GNAT3, PLCβ2 and TRPM5 was also detected in HIBCPP cells. Then, we demonstrated that HIBCPP cells respond to chloramphenicol via TAS2R39 and to quercetin via TAS2R14. Our findings support an active role of TAS2Rs at the human BCSFB, as surveyors of the bloodstream and CSF compositions. These findings open new avenues for studies on the uptake of relevant compounds for targeted therapies of the CNS.

Mechanisms of Pathogen Invasion into the Central Nervous System

CNS infections continue to rise in incidence in conjunction with increases in immunocompromised populations or conditions that contribute to the emergence of pathogens, such as global travel, climate change, and human encroachment on animal territories. The severity and complexity of these diseases is impacted by the diversity of etiologic agents and their routes of neuroinvasion. In this review, we present historical, clinical, and molecular concepts regarding the mechanisms of pathogen invasion of the CNS. We also discuss the structural components of CNS compartments that influence pathogen entry and recent discoveries of the pathways exploited by pathogens to facilitate CNS infections. Advances in our understanding of the CNS invasion mechanisms of different neurotropic pathogens may enable the development of strategies to control their entry and deliver drugs to mitigate established infections.

Cortisol levels after cold exposure are independent of adrenocorticotropic hormone stimulation

We previously showed that postmortem serum levels of adrenocorticotropic hormone (ACTH) were significantly higher in cases of hypothermia (cold exposure) than other causes of death. This study examined how the human hypothalamic-pituitary-adrenal axis, and specifically cortisol, responds to hypothermia. Human samples: Autopsies on 205 subjects (147 men and 58 women; age 15-98 years, median 60 years) were performed within 3 days of death. Cause of death was classified as either hypothermia (cold exposure, n = 14) or non-cold exposure (controls; n = 191). Cortisol levels were determined in blood samples obtained from the left and right cardiac chambers and common iliac veins using a chemiluminescent enzyme immunoassay. Adrenal gland tissues samples were stained for cortisol using a rabbit anti-human polyclonal antibody. Cell culture: AtT20, a mouse ACTH secretory cell line, and Y-1, a corticosterone secretory cell line derived from a mouse adrenal tumor, were analyzed in mono-and co-culture, and times courses of ACTH (in AtT20) and corticosterone (in Y-1) secretion were assessed after low temperature exposure mimicking hypothermia and compared with data for samples collected postmortem for other cases of death. However, no correlation between ACTH concentration and cortisol levels was observed in hypothermia cases. Immunohistologic analyses of samples from hypothermia cases showed that cortisol staining was localized primarily to the nucleus rather than the cytoplasm of cells in the zona fasciculata of the adrenal gland. During both mono-culture and co-culture, AtT20 cells secreted high levels of ACTH after 10-15 minutes of cold exposure, whereas corticosterone secretion by Y-1 cells increased slowly during the first 15-20 minutes of cold exposure. Similar to autopsy results, no correlation was detected between ACTH levels and corticosterone secretion, either in mono-culture or co-culture experiments. These results suggested that ACTH-independent cortisol secretion may function as a stress response during cold exposure.

Human CD4+ T cell subsets differ in their abilities to cross endothelial and epithelial brain barriers in vitro

Background

The brain barriers establish compartments in the central nervous system (CNS) that significantly differ in their communication with the peripheral immune system. In this function they strictly control T-cell entry into the CNS. T cells can reach the CNS by either crossing the endothelial blood–brain barrier (BBB) or the epithelial blood-cerebrospinal fluid barrier (BCSFB) of the choroid plexus (ChP).

Objective

Analysis of the cellular and molecular mechanisms involved in the migration of different human CD4⁺ T-cell subsets across the BBB versus the BCSFB.

Methods

Human in vitro models of the BBB and BCSFB were employed to study the migration of circulating and CNS-entry experienced CD4⁺ T helper cell subsets (Th1, Th1*, Th2, Th17) across the BBB and BCSFB under inflammatory and non-inflammatory conditions in vitro.

Results

While under non-inflammatory conditions Th1* and Th1 cells preferentially crossed the BBB, under inflammatory conditions the migration rate of all Th subsets across the BBB was comparable. The migration of all Th subsets across the BCSFB from the same donor was 10- to 20-fold lower when compared to their migration across the BBB. Interestingly, Th17 cells preferentially crossed the BCSFB under both, non-inflamed and inflamed conditions. Barrier-crossing experienced Th cells sorted from CSF of MS patients showed migratory characteristics indistinguishable from those of circulating Th cells of healthy donors. All Th cell subsets could additionally cross the BCSFB from the CSF to ChP stroma side. T-cell migration across the BCSFB involved epithelial ICAM-1 irrespective of the direction of migration.

Conclusions

Our observations underscore that different Th subsets may use different anatomical routes to enter the CNS during immune surveillance versus neuroinflammation with the BCSFB establishing a tighter barrier for T-cell entry into the CNS compared to the BBB. In addition, CNS-entry experienced Th cell subsets isolated from the CSF of MS patients do not show an increased ability to cross the brain barriers when compared to circulating Th cell subsets from healthy donors underscoring the active role of the brain barriers in controlling T-cell entry into the CNS. Also we identify ICAM-1 to mediate T cell migration across the BCSFB.

Distinct migratory pattern of naive and effector T cells through the blood-CSF barrier following Echovirus 30 infection

Background

Echovirus 30 (E-30) is one of the most frequently isolated pathogens in aseptic meningitis worldwide. To gain access to the central nervous system (CNS), E-30 and immune cells have to cross one of the two main barriers of the CNS, the epithelial blood–cerebrospinal fluid barrier (BCSFB) or the endothelial blood–brain barrier (BBB). In an in vitro model of the BCSFB, it has been shown that E-30 can infect human immortalized brain choroid plexus papilloma (HIBCPP) cells.

Methods

In this study we investigated the migration of different T cell subpopulations, naive and effector T cells, through HIBCPP cells during E-30 infection. Effects of E-30 infection and the migration process were evaluated via immunofluorescence and flow cytometry analysis, as well as transepithelial resistance and dextran flux measurement.

Results

Th1 effector cells and enterovirus-specific effector T cells migrated through HIBCPP cells more efficiently than naive CD4⁺ T cells following E-30 infection of HIBCPP cells. Among the different naive T cell populations, CD8⁺ T cells crossed the E-30-infected HIBCPP cell layer in a significantly higher number than CD4⁺ T cells. A large amount of effector T cells also remained attached to the basolateral side of the HIBCPP cells compared with naive T cells. Analysis of HIBCPP barrier function showed significant alteration after E-30 infection and trans- as well as paracellular migration of T cells independent of the respective subpopulation. Morphologic analysis of migrating T cells revealed that a polarized phenotype was induced by the chemokine CXCL12, but reversed to a round phenotype after E-30 infection. Further characterization of migrating Th1 effector cells revealed a downregulation of surface adhesion proteins such as LFA-1 PSGL-1, CD44, and CD49d.

Conclusion

Taken together these results suggest that naive CD8⁺ and Th1 effector cells are highly efficient to migrate through the BCSFB in an inflammatory environment. The T cell phenotype is modified during the migration process through HIBCPP cells.

Virulence Factors of Meningitis-Causing Bacteria: Enabling Brain Entry across the Blood-Brain Barrier

Infections of the central nervous system (CNS) are still a major cause of morbidity and mortality worldwide. Traversal of the barriers protecting the brain by pathogens is a prerequisite for the development of meningitis. Bacteria have developed a variety of different strategies to cross these barriers and reach the CNS. To this end, they use a variety of different virulence factors that enable them to attach to and traverse these barriers. These virulence factors mediate adhesion to and invasion into host cells, intracellular survival, induction of host cell signaling and inflammatory response, and affect barrier function. While some of these mechanisms differ, others are shared by multiple pathogens. Further understanding of these processes, with special emphasis on the difference between the blood-brain barrier and the blood-cerebrospinal fluid barrier, as well as virulence factors used by the pathogens, is still needed.

Review of functional in vitro models of the blood-cerebrospinal fluid barrier in leukaemia research

Acute lymphoblastic leukaemia represents the most common paediatric malignancy. Although survival rates approach up to 90% in children, investigation of leukaemic infiltration into the central nervous system (CNS) is essential due to the presence of ongoing fatal complications. Recent in vitro studies mostly employed models of the blood-brain barrier (BBB), as endothelial cells of the microvasculature represent the largest surface between the blood stream and the brain parenchyma. However, crossing the blood-cerebrospinal fluid barrier (BCSFB) within the choroid plexus (CP) has been shown to be a general capability of leukaemic blasts. Hence, in vitro models of the BCSFB to study leukaemic transmigration may be of major importance to understand the development of CNS leukaemia. This review will summarise available in vitro models of the BCSFB employed to study the cellular interactions with leukaemic blasts during cancer cell transmigration into the brain compartment across primary or immortal/immortalised BCSFB cells. It will also provide an outlook on prospective improvements in BCSFB in vitro models by developing barrier-on-a-chip models and brain organoids.

Virulence factor-dependent basolateral invasion of choroid plexus epithelial cells by pathogenic Escherichia coli in vitro

Escherichia coli is the most common Gram-negative causative agent of neonatal meningitis and E. coli meningitis is associated with high morbidity and mortality. Previous research has been carried out with regard to the blood-brain barrier and thereby unveiled an assortment of virulence factors involved in E. coli meningitis. Little, however, is known about the role of the blood-cerebrospinal fluid (CSF) barrier (BCSFB), in spite of several studies suggesting that the choroid plexus (CP) is a possible entry point for E. coli into the CSF spaces. Here, we used a human CP papilloma (HIBCPP) cell line that was previously established as valid model for the study of the BCSFB. We show that E. coli invades HIBCPP cells in a polar fashion preferentially from the physiologically relevant basolateral side. Moreover, we demonstrate that deletion of outer membrane protein A, ibeA or neuDB genes results in decreased cell infection, while absence of fimH enhances invasion, although causing reduced adhesion to the apical side of HIBCPP cells. Our findings suggest that the BCSFB might constitute an entry point for E. coli into the central nervous system, and HIBCPP cells are a valuable tool for investigating E. coli entry of the BCSFB.

Optimized cultivation of porcine choroid plexus epithelial cells, a blood-cerebrospinal fluid barrier model, for studying granulocyte transmigration

The blood-cerebrospinal fluid barrier (BCSFB) plays important roles during the transport of substances into the brain, the pathogenesis of central nervous system (CNS) diseases, and neuro-immunological processes. Along these lines, transmigration of granulocytes across the blood-cerebrospinal fluid (CSF) barrier (BCSFB) is a hallmark of inflammatory events in the CNS. Choroid plexus (CP) epithelial cells are an important tool to generate in vitro models of the BCSFB. A porcine CP epithelial cell line (PCP-R) has been shown to present properties of the BCSFB, including a strong barrier function, when cultivated on cell culture filter inserts containing a membrane with 0.4 µm pore size. For optimal analysis of pathogen and host immune cell interactions with the basolateral side of the CP epithelium, which presents the physiologically relevant "blood side", the CP epithelial cells need to be grown on the lower face of the filter in an inverted cell culture insert model, with the supporting membrane possessing a pore size of at least 3.0 µm. Here, we demonstrate that PCP-R cells cultivated in the inverted model on filter support membranes with a pore size of 3.0 µm following a "conventional" protocol grow through the pores and cross the membrane, forming a second layer on the upper face. Therefore, we developed a cell cultivation protocol, which strongly reduces crossing of the membrane by the cells. Under these conditions, PCP-R cells retain important properties of a BCSFB model, as was observed by the formation of continuous tight junctions and a strong barrier function demonstrated by a high transepithelial electrical resistance and a low permeability for macromolecules. Importantly, compared with the conventional cultivation conditions, our optimized model allows improved investigations of porcine granulocyte transmigration across the PCP-R cell layer.

Capsule and fimbriae modulate the invasion of Haemophilus influenzae in a human blood-cerebrospinal fluid barrier model

The Gram-negative bacterium Haemophilus influenzae (H. influenzae) can commensally colonize the upper respiratory tract, but also cause life threatening disease including epiglottitis, sepsis and meningitis. The H. influenzae capsule protects the bacteria against both phagocytosis and opsonization. Encapsulated H. influenzae strains are classified into serotypes ranging from a to f dependent on their distinct polysaccharide capsule. Due to the implementation of vaccination the incidence of invasive H. influenzae type b (Hib) infections has strongly decreased and infections with other capsulated types, including H. influenzae type f (Hif), are emerging. The pathogenesis of H. influenzae meningitis is not clarified. To enter the central nervous system (CNS) the bacteria generally have to cross either the blood-brain barrier (BBB) or the blood-cerebrospinal fluid barrier (BSCFB). Using a cell culture model of the BCSFB based on human choroid plexus papilloma (HIBCPP) cells and different H. influenzae strains we investigated whether Hib and Hif invade the cells, and if invasion differs between encapsulated vs. capsular-deficient and fimbriated vs. non-fimbriated variants. We find that Hib can adhere to and invade into HIBCPP cells. Invasion occurs in a strongly polar fashion, since the bacteria enter the cells preferentially from the basolateral "blood "side. Fimbriae and capsule attenuate invasion into choroid plexus (CP) epithelial cells, and capsulation can influence the bacterial distribution pattern. Finally, analysis of clinical Hib and Hif isolates confirms the detected invasive properties of H. influenzae. Our data point to roles of capsule and fimbriae during invasion of CP epithelial cells.

Interactions of antisera to different Chlamydia and Chlamydophila species with the ribosomal protein RPS27a correlate with impaired protein synthesis in a human choroid plexus papilloma cell line

Chlamydia trachomatis (CT) and the Chlamydophila species (CS) Chlamydophila pneumoniae (CPn), and Chlamydophila psittaci (CPs) are suggested to induce autoantibodies causative of several human autoimmune disorders like rheumatoid arthritis and systemic lupus erythematosus (SLE). The aim of the present study was therefore to identify cellular protein interaction partners with antisera to CT (α-CT) or CS (α-CS) and to identify functional consequences of such interaction in vitro. As detected with a commercial first trimester human prenatal brain multiprotein array (hEXselect, Engine, Germany), the most frequent interaction partner with both α-CT and α-CS was the ribosomal small subunit protein RPS27a. This could be confirmed by Western blot analysis with a recombinant RPS27a sample. In addition, immunocytochemistry with both antisera in the human choroid plexus papilloma cell line HIBCPP revealed a granular cytoplasmic staining, and Western blot analysis with whole-cell protein samples of HIBCPP cells revealed both antisera to label protein bands of different molecular weights and intensity. By 2D Western blot analysis and mass spectrometry, one of the protein spots interacting with α-CT could be identified as the RPS27a. Finally, two different methods for the detection of protein synthesis activity, the SUnSET technique and an HPG fluorescence assay revealed both antisera to cause reduced translational activity in HIBCPP cells. Together with previous findings of RPS27a as an autoimmune target in a mouse model of systemic lupus erythematosus (SLE), these results suggest that infections with CT and/or CS could induce SLE-associated immune modifications. However, direct evidence for a pathogenic role of these interactions for SLE demands further investigations.

Prolactin selectively transported to cerebrospinal fluid from blood under hypoxic/ischemic conditions

Aim

The aim of this study was to determine and to verify the correlation between the amount of prolactin (PRL) levels in the blood and in the cerebrospinal fluid (CSF) by various causes of death as an indicator for acute hypoxia in autopsy cases. It is to confirm the cause of the change in prolactin level in CSF by in vitro system.

Materials and methods

In autopsy materials, the PRL levels in blood from the right heart ventricle and in the CSF were measured by chemiluminescent enzyme immunoassay, and changes in the percentage of PRL-positive cells in the pituitary gland were examined using an immunohistochemical method. Furthermore, an inverted culture method was used as an in vitro model of the blood-CSF barrier using epithelial cells of the human choroid plexus (HIBCPP cell line) and SDR-P-1D5 or MSH-P3 (PRL-secreting cell line derived from miniature swine hypophysis) under normoxic or hypoxic (5% oxygen) conditions, and as an index of cell activity, we used Vascular Endothelial Growth Factor (VEGF).

Results and discussion

Serum PRL levels were not significantly different between hypoxia/ischemia cases and other causes of death. However, PRL levels in CSF were three times higher in cases of hypoxia/ischemia than in those of the other causes of death. In the cultured cell under the hypoxia condition, PRL and VEGF showed a high concentration at 10 min. We established a brain-CSF barrier model to clarify the mechanism of PRL transport to CSF from blood, the PRL concentrations from blood to CSF increased under hypoxic conditions from 5 min. These results suggested that PRL moves in CSF through choroidal epithelium from blood within a short time. PRL is hypothesized to protect the hypoxic/ischemic brain, and this may be because of the increased transportation of the choroid plexus epithelial cells.

Activation of TRPV4 stimulates transepithelial ion flux in a porcine choroid plexus cell line

The choroid plexus (CP) epithelium plays a major role in the production of cerebrospinal fluid (CSF). A polarized cell line, the porcine CP-Riems (PCP-R) line, which exhibits many of the characteristics of the native epithelium, was used to study the effect of activation of the transient receptor potential vanilloid 4 (TRPV4) cation channel found in the PCP-R cells as well as in the native epithelium. Ussing-style electrophysiological experiments showed that activation of TRPV4 with a specific agonist, GSK1016790A, resulted in an immediate increase in both transepithelial ion flux and conductance. These changes were inhibited by either of two distinct antagonists, HC067047 or RN1734. The change in conductance was reversible and did not involve disruption of epithelial junctional complexes. Activation of TRPV4 results in Ca²⁺ influx, therefore, we examined whether the electrophysiological changes were the result of secondary activation of Ca²⁺-sensitive channels. PCP-R cells contain two Ca²⁺-activated K⁺ channels, the small conductance 2 (SK2) and the intermediate conductance (IK) channels. Based on inhibitor studies, the former is not involved in the TRPV4-mediated electrophysiological changes whereas one of the three isoforms of the IK channel (KCNN4c) may play a role in the apical secretion of K⁺. Blocking the activity of this IK isoform with TRAM34 inhibited the TRPV4-mediated change in net transepithelial ion flux and the increased conductance. These studies implicate TRPV4 as a hub protein in the control of CSF production through stimulation by multiple effectors resulting in transepithelial ion and subsequent water movement.

Loss of Mpdz impairs ependymal cell integrity leading to perinatal-onset hydrocephalus in mice

Hydrocephalus is a common congenital anomaly. LCAM1 and MPDZ (MUPP1) are the only known human gene loci associated with non‐syndromic hydrocephalus. To investigate functions of the tight junction‐associated protein Mpdz, we generated mouse models. Global Mpdz gene deletion or conditional inactivation in Nestin‐positive cells led to formation of supratentorial hydrocephalus in the early postnatal period. Blood vessels, epithelial cells of the choroid plexus, and cilia on ependymal cells, which line the ventricular system, remained morphologically intact in Mpdz‐deficient brains. However, flow of cerebrospinal fluid through the cerebral aqueduct was blocked from postnatal day 3 onward. Silencing of Mpdz expression in cultured epithelial cells impaired barrier integrity, and loss of Mpdz in astrocytes increased RhoA activity. In Mpdz‐deficient mice, ependymal cells had morphologically normal tight junctions, but expression of the interacting planar cell polarity protein Pals1 was diminished and barrier integrity got progressively lost. Ependymal denudation was accompanied by reactive astrogliosis leading to aqueductal stenosis. This work provides a relevant hydrocephalus mouse model and demonstrates that Mpdz is essential to maintain integrity of the ependyma.