In Vitro Models for Studying the Interaction of Neisseria meningitidis with Human Brain Endothelial Cells

Human-Induced Pluripotent Stem Cell-Based Model of the Blood-Brain at 10 Years: A Retrospective on Past and Current Disease Models

The initial discovery and derivation of induced pluripotent stem cells (iPSCs) by Yamanaka and colleagues in 2006 revolutionized the field of personalized medicine, as it opened the possibility to model diseases using patient-derived stem cells. A decade of adoption of iPSCs within the community of the blood-brain barrier (BBB) significantly opened the door for modeling diseases at the BBB, a task until then considered challenging, if not impossible.In this book chapter, we provided an extensive review of the literature on the use of iPSC-based models of the human BBB to model neurological diseases including infectious diseases (COVID-19, Streptococcus, Neisseria) neurodevelopmental diseases (adrenoleukodystrophy, Allan-Herndon-Dudley Syndrome, Batten's disease, GLUT1 deficiency syndrome), and neurodegenerative diseases (Alzheimer's disease, the current findings and observations, but also the challenges and limitations inherent to the use of iPSC-based models in reproducing the human BBB during health and diseases in a Petri dish.

Development of a multicellular in vitro model of the meningeal blood-CSF barrier to study Neisseria meningitidis infection

Background

Bacterial meningitis is a life-threatening disease that occurs when pathogens such as Neisseria meningitidis cross the meningeal blood cerebrospinal fluid barrier (mBCSFB) and infect the meninges. Due to the human-specific nature of N. meningitidis, previous research investigating this complex host–pathogen interaction has mostly been done in vitro using immortalized brain endothelial cells (BECs) alone, which often do not retain relevant barrier properties in culture. Here, we developed physiologically relevant mBCSFB models using BECs in co-culture with leptomeningeal cells (LMCs) to examine N. meningitidis interaction.

Methods

We used BEC-like cells derived from induced pluripotent stem cells (iBECs) or hCMEC/D3 cells in co-culture with LMCs derived from tumor biopsies. We employed TEM and structured illumination microscopy to characterize the models as well as bacterial interaction. We measured TEER and sodium fluorescein (NaF) permeability to determine barrier tightness and integrity. We then analyzed bacterial adherence and penetration of the cell barrier and examined changes in host gene expression of tight junctions as well as chemokines and cytokines in response to infection.

Results

Both cell types remained distinct in co-culture and iBECs showed characteristic expression of BEC markers including tight junction proteins and endothelial markers. iBEC barrier function as determined by TEER and NaF permeability was improved by LMC co-culture and remained stable for seven days. BEC response to N. meningitidis infection was not affected by LMC co-culture. We detected considerable amounts of BEC-adherent meningococci and a relatively small number of intracellular bacteria. Interestingly, we discovered bacteria traversing the BEC-LMC barrier within the first 24 h post-infection, when barrier integrity was still high, suggesting a transcellular route for N. meningitidis into the CNS. Finally, we observed deterioration of barrier properties including loss of TEER and reduced expression of cell-junction components at late time points of infection.

Conclusions

Here, we report, for the first time, on co-culture of human iPSC derived BECs or hCMEC/D3 with meningioma derived LMCs and find that LMC co-culture improves barrier properties of iBECs. These novel models allow for a better understanding of N. meningitidis interaction at the mBCSFB in a physiologically relevant setting.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12987-022-00379-z.

Induced Pluripotent Stem Cell (iPSC)-Derived Endothelial Cells to Study Bacterial-Brain Endothelial Cell Interactions

Bacterial meningitis is a serious infection of the central nervous system (CNS) that occurs when blood-borne bacteria are able to exit the cerebral vasculature and cause inflammation. The blood-brain barrier (BBB) and the meningeal blood-CSF barrier (mBCSFB) are composed of highly specialized brain endothelial cells (BECs) that possess unique phenotypes when compared to their peripheral endothelial counterparts. To cause meningitis, bacterial pathogens must be able to interact and penetrate these specialized BECs to gain access to the CNS. In vitro models have been employed to study bacterial-BEC interactions; however, many lack BEC phenotypes. Induced pluripotent stem cell (iPSC) technologies have enabled the derivation of brain endothelial-like cells that phenocopy BECs in culture. Recently, these iPSC-BECs have been employed to examine the host-pathogen interaction at the endothelial brain barriers. Using two clinically relevant human meningeal pathogens, this chapter describes the use of iPSC-BECs to study various aspects of BEC-bacterial interaction.

The blood-brain barrier is dysregulated in COVID-19 and serves as a CNS entry route for SARS-CoV-2

Neurological complications are common in COVID-19. Although SARS-CoV-2 has been detected in patients’ brain tissues, its entry routes and resulting consequences are not well understood. Here, we show a pronounced upregulation of interferon signaling pathways of the neurovascular unit in fatal COVID-19. By investigating the susceptibility of human induced pluripotent stem cell (hiPSC)-derived brain capillary endothelial-like cells (BCECs) to SARS-CoV-2 infection, we found that BCECs were infected and recapitulated transcriptional changes detected in vivo. While BCECs were not compromised in their paracellular tightness, we found SARS-CoV-2 in the basolateral compartment in transwell assays after apical infection, suggesting active replication and transcellular transport of virus across the blood-brain barrier (BBB) in vitro. Moreover, entry of SARS-CoV-2 into BCECs could be reduced by anti-spike-, anti-angiotensin-converting enzyme 2 (ACE2)-, and anti-neuropilin-1 (NRP1)-specific antibodies or the transmembrane protease serine subtype 2 (TMPRSS2) inhibitor nafamostat. Together, our data provide strong support for SARS-CoV-2 brain entry across the BBB resulting in increased interferon signaling.

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IFNγ signaling is upregulated in COVID-19 human neurovascular unit

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SARS-CoV-2-infected hiPS-BCECs display similar upregulation of IFNγ signaling

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SARS-CoV-2 replicates in hiPS-BCECs and is released while barrier remains intact

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SARS-CoV-2 infection of hiPS-BCECs is decreased by antibodies and protease inhibitors

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.

Induced Pluripotent Stem Cell-Derived Brain Endothelial Cells as a Cellular Model to Study Neisseria meningitidis Infection

Meningococcal meningitis is a severe central nervous system infection that occurs when Neisseria meningitidis (Nm) penetrates brain endothelial cells (BECs) of the meningeal blood-cerebrospinal fluid barrier. As a human-specific pathogen, in vivo models are greatly limited and pose a significant challenge. In vitro cell models have been developed, however, most lack critical BEC phenotypes limiting their usefulness. Human BECs generated from induced pluripotent stem cells (iPSCs) retain BEC properties and offer the prospect of modeling the human-specific Nm interaction with BECs. Here, we exploit iPSC-BECs as a novel cellular model to study Nm host-pathogen interactions, and provide an overview of host responses to Nm infection. Using iPSC-BECs, we first confirmed that multiple Nm strains and mutants follow similar phenotypes to previously described models. The recruitment of the recently published pilus adhesin receptor CD147 underneath meningococcal microcolonies could be verified in iPSC-BECs. Nm was also observed to significantly increase the expression of pro-inflammatory and neutrophil-specific chemokines IL6, CXCL1, CXCL2, CXCL8, and CCL20, and the secretion of IFN-γ and RANTES. For the first time, we directly observe that Nm disrupts the three tight junction proteins ZO-1, Occludin, and Claudin-5, which become frayed and/or discontinuous in BECs upon Nm challenge. In accordance with tight junction loss, a sharp loss in trans-endothelial electrical resistance, and an increase in sodium fluorescein permeability and in bacterial transmigration, was observed. Finally, we established RNA-Seq of sorted, infected iPSC-BECs, providing expression data of Nm-responsive host genes. Altogether, this model provides novel insights into Nm pathogenesis, including an impact of Nm on barrier properties and tight junction complexes, and suggests that the paracellular route may contribute to Nm traversal of BECs.