HIF-1α is involved in blood-brain barrier dysfunction and paracellular migration of bacteria in pneumococcal meningitis

Bacterial meningitis is a deadly disease most commonly caused byStreptococcus pneumoniae, leading to severe neurological sequelae including cerebral edema, seizures, stroke, and mortality when untreated. Meningitis is initiated by the transfer ofS. pneumoniaefrom blood to the brain across the blood-cerebrospinal fluid barrier or the blood-brain barrier (BBB). The underlying mechanisms are still poorly understood. Current treatment strategies include adjuvant dexamethasone for inflammation and cerebral edema, followed by antibiotics. The success of dexamethasone is however inconclusive, necessitating new therapies for controlling edema, the primary reason for neurological complications. Since we have previously shown a general activation of hypoxia inducible factor (HIF-1 alpha) in bacterial infections, we hypothesized that HIF-1 alpha, via induction of vascular endothelial growth factor (VEGF) is involved in transmigration of pathogens across the BBB. In human, murine meningitis brain samples, HIF-1 alpha activation was observed by immunohistochemistry.S. pneumoniaeinfection in brain endothelial cells (EC) resulted in in vitro upregulation of HIF-1 alpha/VEGF (Western blotting/qRT-PCR) associated with increased paracellular permeability (fluorometry, impedance measurements). This was supported by bacterial localization at cell-cell junctions in vitro and in vivo in brain ECs from mouse and humans (confocal, super-resolution, electron microscopy, live-cell imaging). Hematogenously infected mice showed increased permeability,S. pneumoniaedeposition in the brain, along with upregulation of genes in the HIF-1 alpha/VEGF pathway (RNA sequencing of brain microvessels). Inhibition of HIF-1 alpha with echinomycin,siRNA in bEnd5 cells or using primary brain ECs from HIF-1 alpha knock-out mice revealed reduced endothelial permeability and transmigration ofS. pneumoniae. Therapeutic rescue using the HIF-1 alpha inhibitor echinomycin resulted in increased survival and improvement of BBB function inS. pneumoniae-infected mice. We thus demonstrate paracellular migration of bacteria across BBB and a critical role for HIF-1 alpha/VEGF therein and hence propose targeting this pathway to prevent BBB dysfunction and ensuing brain damage in infections.