The surface-anchored NanA protein promotes pneumococcal brain endothelial cell invasion

Abstract

In humans, Streptococcus pneumoniae (SPN) is the leading cause of bacterial meningitis, a disease with high attributable mortality and frequent permanent neurological sequelae. The molecular mechanisms underlying the central nervous system tropism of SPN are incompletely understood, but include a primary interaction of the pathogen with the blood–brain barrier (BBB) endothelium. All SPN strains possess a gene encoding the surface-anchored sialidase (neuraminidase) NanA, which cleaves sialic acid on host cells and proteins. Here, we use an isogenic SPN NanA-deficient mutant and heterologous expression of the protein to show that NanA is both necessary and sufficient to promote SPN adherence to and invasion of human brain microvascular endothelial cells (hBMECs). NanA-mediated hBMEC invasion depends only partially on sialidase activity, whereas the N-terminal lectinlike domain of the protein plays a critical role. NanA promotes SPN–BBB interaction in a murine infection model, identifying the protein as proximal mediator of CNS entry by the pathogen.

Concepts and Mechanisms: Crossing Host Barriers

“…Significant progress has been made in understanding the molecular interactions between the BBB and microbial pathogens with the availability of in vitro tissue culture models of human BMEC (hBMEC) (Stins et al 1994;Weksler et al 2005) and in vivo animal models (Smith et al 1973;Doran et al 2002;Wickham et al 2007;Uchiyama et al 2009;Sheen et al 2010). Microbial interactions with the BBB may involve crossing of BMEC in a vacuole (transcytosis), through the intercellular junctional spaces ( paracytosis), or while inside a host cell (e.g., infected phagocyte) using it as a vehicle to cross the barrier (Trojan horse) (Kim 2008(Kim , 2010 (Fig.…”

“…Many studies have focused on the identification of bacterial and host components involved in microbial interactions with the BBB (Kim 2008). Critical bacterial components have been discovered by screening random mutant libraries (Badger et al 2000;Doran et al 2005), analyzing bacterial transcription profiles during infection (Dietrich et al 2003;Teng et al 2005), and using bioinformatic approaches for whole genome comparisons (Uchiyama et al 2009;van Sorge et al 2009;Tazi et al 2010). Bacterial pili, or fimbriae, have emerged as a common class of adhesins used by many meningeal pathogens, such as E. coli K1 (Teng et al 2005), GBS (Maisey et al 2007;van Sorge et al 2009), and N. meningitides (Kirchner and Meyer 2005) to initiate attachment to brain endothelium.…”

Competence-induced protein Ccs4 facilitates pneumococcal invasion into brain tissue and virulence in meningitis

“…CbpA binds to the cerebral endothelial laminin receptor and platelet-activating factor receptor [5,6], and those interactions induce pneumococcal invasion into the host brain. NanA, which localizes on bacterial cell surfaces by its cell-wall anchoring motif, activates hBMECs via its lectin-like domain and increases pneumococcal invasion into hBMECs [7,8]. Therefore, it was considered important to assess pneumococcal cbpA and nanA expressions of the Δ ccs4 strain.…”

“…Pneumococcal penetration of the BBB and invasion into the brain via the bloodstream is also critical for development of meningitis. In S. pneumoniae , choline binding protein A (CbpA) [5,6], pneumococcal neuraminidase (NanA) [7–9], and pneumococcal pilus-1 (RrgA) [10,11] each contribute to pneumococcal penetration across the BBB. On the other hand, we reported findings indicating that zinc metalloproteinase ZmpC may have evolved to suppress excess pneumococcal virulence by inhibiting bacterial invasion into central nervous system [12].…”

Assessing the function of pneumococcal neuraminidases NanA, NanB and NanC inin vitroandin vivolung infection models using monoclonal antibodies

“…Additional roles of NanA during persistance in the chinchilla middle ear infection model were shown [41–43]. NanA is required for adherence and invasion of brain endothelial cells, indicating its involvement in the development of meningitis [44]. The role of NanA during sepsis is more controversial, with reports ranging from greatly attenuated virulence of S. pneumoniae nanA gene deletion strains to no effect [40,45].…”