GBS is the most common bacterium causing neonatal meningitis, and neonatal GBS meningitis continues to be an important cause of mortality and morbidity. However, the microbe-host interactions involved in GBS invasion of the blood-brain barrier and penetration into the brain remain incompletely understood (18
). Previous studies have identified several microbial factors promoting GBS invasion of HBMEC and/or penetration into the brain, including fibrinogen adhesion protein FbsA, laminin-binding protein Lmb, hemolysin-cytolysin, pilus, lipoteichoic acid-anchoring protein IagA, the serine-rich repeat 1 glycoprotein, and the hypervirulent GBS adhesin (HvgA) (26
), but relevant host factors involved in GBS invasion of the blood-brain barrier have not been determined.
The findings reported here using pharmacological inhibition and gene deletion demonstrate for the first time that host cPLA2
α contributes to type III GBS invasion of the HBMEC monolayer and penetration into the brain, the key step required for the development of meningitis (18
). Deletion of a functional cPLA2
α has been shown to attenuate the development of arthritis, bone resorption, and pulmonary fibrosis (11
), but the role of host cPLA2
α in GBS penetration into the brain has not previously been reported. We showed that type III GBS penetration into the brain of cPLA2
mice was significantly less compared to that of wild-type mice, but the magnitudes of bacteremia were similar between cPLA2
and wild-type mice. Therefore, the significantly decreased penetration of type III GBS into the brains of cPLA2
mice was not the result of decreased levels of bacteremia. cPLA2
α deletion, however, did not affect type III GBS penetration into the nonbrain organs, such as kidneys and spleens, as shown by similar numbers of bacterial counts recovered from cPLA2
and wild-type mice. The basis for this selective role of host cPLA2
α in type III GBS penetration into the brain but not into nonbrain organs remains unclear.
α selectively liberates arachidonic acid from membrane phospholipids (9
), suggesting that the contribution of cPLA2
α to type III GBS invasion of HBMEC is likely to be related to metabolites of arachidonic acid. 5-LO and FLAP oxygenate arachidonic acid to LTs, and LTB4
and cysteinyl LTs represent terminal LTs, interacting with their respective GPCRs, BLT-1 and CysLT1, respectively () (33
). We showed that the CysLT1 antagonists (MK571 and montelukast) inhibited type III GBS invasion of HBMEC, while the BLT-1 antagonist failed to affect type III GBS invasion of HBMEC. Taken together, these findings demonstrate that host cPLA2
α contributes to type III GBS invasion of HBMEC, most likely involving lipoxygenated metabolites of arachidonic acid, cysteinyl LTs.
Another novel finding of our study is the demonstration that the contribution of host cPLA2
α and cysteinyl LTs to type III GBS invasion of HBMEC involves PKCα. These findings differ from those of other investigators who showed that PKCα contributes to cPLA2
α phosphorylation in immortalized rat brain endothelial cells (1
) but are similar to those of our earlier studies with E. coli
invasion of HBMEC, where PKCα is shown to be downstream of cPLA2
α and cysteinyl LTs in E. coli
K1 invasion of HBMEC (41
). These findings suggest that cPLA2
α-cysteinyl LT-PKCα pathways are likely to be involved in neonatal meningitis-causing bacteria (e.g., type III GBS and E. coli
K1) for their penetration of the blood-brain barrier, and additional studies are needed to elucidate how the pathways involving cPLA2
α, cysteinyl LTs, and PKCα contribute to neonatal meningitis.
Clinical isolates of type III GBS contain a limited number of clonal complexes, defined by multilocus sequence typing. ST-17 is strongly associated with neonatal meningitis and was designated the hypervirulent clone (16
). A recent study identified that an ST-17-specific surface-expressed GBS protein, HvgA, is linked to the hypervirulence of the ST-17 GBS clone in type III GBS crossing of the blood-brain barrier (39
). In our study, the contribution of host cPLA2
α to GBS invasion of the blood-brain barrier was demonstrated for type III isolates of both ST-17 and ST-23 clones. It is therefore likely that the host-microbe interactions involved in host cPLA2
α-mediated invasion of the blood-brain barrier differ from those involved in HvgA-mediated GBS invasion of host cells. The determination and characterization of the GBS-host interactions involved in cPLA2
α-mediated invasion of the blood-brain barrier are therefore likely to elucidate the mechanisms for selective penetration of GBS into the brain, and studies are in progress to investigate this issue.
In summary, our findings demonstrate for the first time that type III GBS strains exploit host cPLA2α and 5-LO-derived cysteinyl LTs for their invasion of the blood-brain barrier and penetration into the brain, and host cPLA2α and cysteinyl LTs contribute to type III GBS invasion of the blood-brain barrier, involving PKCα.