A streptococcal Fic domain-containing protein disrupts blood-brain barrier integrity by activating moesin in endothelial cells.

Zhe Ma,Huixing Lin,Hongjie Fan,Joseph S Park,Bin Xu,Jie Peng,Chengping Lu,Dandan Yu,Matthew K Waldor,Mathieu Coureuil

doi:10.1371/journal.ppat.1007737

Abstract

Streptococcus equi subsp. zooepidemicus (SEZ) is a zoonotic pathogen capable of causing meningitis in humans. The mechanisms that enable pathogens to traverse the blood-brain barrier (BBB) are incompletely understood. Here, we investigated the role of a newly identified Fic domain-containing protein, BifA, in SEZ virulence. BifA was required for SEZ to cross the BBB and to cause meningitis in mice. BifA also enhanced SEZ translocation across human Brain Microvascular Endothelial Cell (hBMEC) monolayers. Purified BifA or its Fic domain-containing C-terminus alone were able to enter into hBMECs, leading to disruption of monolayer barrier integrity. A SILAC-based proteomic screen revealed that BifA binds moesin. BifA’s Fic domain was required for its binding to this regulator of host cell cytoskeletal processes. BifA treatment of hBMECs led to moesin phosphorylation and downstream RhoA activation. Inhibition of moesin activation or moesin depletion in hBMEC monolayers abrogated BifA-mediated increases in barrier permeability and SEZ’s capacity to translocate across monolayers. Thus, BifA activation of moesin appears to constitute a key mechanism by which SEZ disrupts endothelial monolayer integrity to penetrate the BBB.

Highlights

Streptococcus equi subsp. zooepidemicus (SEZ) is a Lancefield Group C opportunistic pathogen capable of infecting a broad range of animal species, including humans [1]
Little is known about how this Group C streptococcal species penetrates the blood-brain barrier (BBB)
We identified bifA, a gene that is critical for SEZ to cause meningitis in mice and to penetrate a human brain endothelial monolayer in a tissue culture model

Summary

Introduction

Streptococcus equi subsp. zooepidemicus (SEZ) is a Lancefield Group C opportunistic pathogen capable of infecting a broad range of animal species, including humans [1]. Zooepidemicus (SEZ) is a Lancefield Group C opportunistic pathogen capable of infecting a broad range of animal species, including humans [1]. SEZ, like most streptococci, is an extracellular pathogen [2] and to cause meningitis, these organisms must penetrate the blood-brain barrier (BBB), a functional barrier established in part by the endothelial cells lining the brain microvasculature. This highly selective barrier between the brain and the circulatory system acts as an important protective mechanism, excluding blood-borne pathogens and toxins from the central nervous system [5]. Diverse factors facilitating pathogen adhesion to brain capillary endothelial cells have been identified and both transcellular and paracellular routes for pathogens to cross the BBB have been reported [6, 7]

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Conclusion