HIF-1α is involved in blood-brain barrier dysfunction and paracellular migration of bacteria in pneumococcal
Gayatri Devraj1, Sylvaine Guérit2, Jana Seele3,4
1Institute for Medical Microbiology and Infection Control, Goethe University, Frankfurt am Main, Germany.
Abstract:
Bacterial meningitis is a deadly disease most commonly caused by Streptococcus pneumoniae, leading to severe neurological sequelae including cerebral edema, seizures, stroke, and mortality when untreated. Meningitis is initiated by the transfer of S. pneumoniae from 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-1α) in bacterial infections, we hypothesized that HIF-1α, via induction of vascular endothelial growth factor (VEGF) is involved in transmigration of pathogens across the BBB. In human, murine meningitis brain samples, HIF-1α activation was observed by immunohistochemistry. S. pneumoniae infection in brain endothelial cells (EC) resulted in in vitro upregulation of HIF-1α/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. pneumoniae deposition in the brain, along with upregulation of genes in the HIF-1α/VEGF pathway (RNA sequencing of brain microvessels). Inhibition of HIF-1α with echinomycin, siRNA in bEnd5 cells or using primary brain ECs from HIF-1α knock-out mice revealed reduced endothelial permeability and transmigration of S. pneumoniae. Therapeutic rescue using the HIF-1α inhibitor echinomycin resulted in increased survival and improvement of BBB function in S. pneumoniae-infected mice. We thus demonstrate paracellular migration of bacteria across BBB and a critical role for HIF-1α/VEGF therein and hence propose targeting this pathway to prevent BBB dysfunction and ensuing brain damage in infections.
Insights
Hypoxia-inducible factor-1α (HIF-1α) drives Streptococcus pneumoniae entry into the brain by increasing blood-brain barrier (BBB) permeability. Targeting HIF-1α with echinomycin improves survival and BBB function in meningitis models.
Area of Science:
- Neuroscience
- Infectious Diseases
- Molecular Biology
Background:
- Bacterial meningitis, primarily caused by Streptococcus pneumoniae, leads to severe neurological damage and mortality.
- Current treatments like dexamethasone have inconclusive efficacy for managing cerebral edema, a key complication.
- The mechanisms of pathogen transmigration across the blood-brain barrier (BBB) remain poorly understood.
Purpose of the Study:
- To investigate the role of hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) in Streptococcus pneumoniae transmigration across the BBB.
- To evaluate the therapeutic potential of inhibiting the HIF-1α pathway in bacterial meningitis.
Main Methods:
- Immunohistochemistry on human and murine meningitis brain samples to detect HIF-1α activation.
- In vitro studies using brain endothelial cells (EC) to assess HIF-1α/VEGF upregulation and paracellular permeability.
- In vivo studies in infected mice, including RNA sequencing of brain microvessels and treatment with HIF-1α inhibitors.
Main Results:
- HIF-1α activation and increased HIF-1α/VEGF signaling were observed in infected brain ECs and human/murine meningitis samples.
- Inhibition of HIF-1α significantly reduced endothelial permeability and Streptococcus pneumoniae transmigration.
- Therapeutic administration of the HIF-1α inhibitor echinomycin improved survival and restored BBB function in infected mice.
Conclusions:
- Streptococcus pneumoniae utilizes a paracellular migration route across the BBB.
- The HIF-1α/VEGF pathway plays a critical role in mediating BBB dysfunction during bacterial meningitis.
- Targeting the HIF-1α pathway represents a promising therapeutic strategy to prevent brain damage in meningitis.
