The Role of Astrocytes in Blood‐Brain Barrier Function During Bacterial Infection
Authors: Hancoock Bryan M , Weston Thomas A , Renken Christian W , Doran Kelly S 
Published: November 2023

Bacterial meningitis is the most common serious infection of the central nervous system (CNS) and a major cause of death and disability worldwide, especially in children. Although antibiotic therapy has changed bacterial meningitis from a uniformly fatal disease to an often curable one, mortality remains at 5 to 10% with permanent neurologic sequelae occurring in up to 40% of survivors, including cerebral ischemia, brain edema, hydrocephalus, increased intracranial pressure, seizure activity, and arterial and venous cerebral vascular insults. To produce meningitis, blood‐borne bacteria must typically penetrate the blood‐brain barrier (BBB), which is primarily composed of a layer of specialized brain microvascular endothelial cells (BMEC), and together with astrocytes, pericytes, neurons and the extracellular matrix, constitute the neurovascular unit (NVU). The BBB functions to protect the brain from toxins and microbes that may be present in the blood by maintaining specialized intracellular tight junctions and strict regulation of endocytosis. To study bacterial‐BBB interactions we used a well‐characterized human BMEC cell line (hBMEC) and the model organism Streptococcus agalactiae, also known as Group B Streptococcus (GBS), which has emerged as the leading cause of bacterial meningitis in the neonatal period. To assess hBMEC integrity and barrier function we monitored changes in trans‐endothelial electrical resistance (TEER) in real time using the electrical cell impedance sensing (ECIS) system from Applied Biophysics. At various seeding densities we observed an increase in TEER that reached 1000 ohms over 24 hours. However following GBS infection TEER values were greatly reduced. As part of the NVU, astrocytes have previously been shown to help maintain BBB function, however, little is known about the interaction and response of astrocytes to bacterial infection and the subsequent impact on BBB function during the progression of meningitis. Using the human astrocyte cell line, SVG‐A, we have shown previously that GBS adheres to and invades astrocytes. Here we examined the response of astrocytes to GBS infection using RT‐qPCR and found that infection resulted in the induction of several pro‐inflammatory cytokines such as interleukin (IL)‐1β, IL‐6, IL‐8, and IL‐36 as well as factors that promote cell motility and BBB breakdown such as VEGF, and two key members of the matrix metalloproteinase family, MMP‐2 and MMP‐9. Thus we hypothesize that GBS activation of astrocytes may impact neuroinflammation and BBB breakdown. To investigate the contribution of astrocytes to BBB barrier integrity we have co‐cultured astrocytes and hBMEC on opposing sides of trans‐well inserts to develop a more robust in vitro BBB model. Future studies will use the ECIS system to measure TEER during GBS infection to determine how astrocytic response impacts BBB function. Understanding the role of astrocytes during bacterial infection will provide important information in the modulation of BBB disruption during the development of meningitis.

Support or Funding Information

R01 NS051247‐05

ARCS Foundation

Sharp Reese Steely/SDSU Heart Institute Special thanks to Applied BioPhysics for their support.