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J Biol Chem. 2014 Dec 26;289(52):35711-23. doi: 10.1074/jbc.M114.588657. Epub 2014 Nov 4.

The role of autophagy during group B Streptococcus infection of blood-brain barrier endothelium.

Author information

1
From the Department of Biology and.
2
Division of Biological Sciences and San Diego Center for Systems Biology, University of California, San Diego, La Jolla, California 92093-0322, Stem Cell Pathologies Group, Life and Brain Center, University of Bonn, D-53127 Bonn, Germany, and.
3
Division of Biological Sciences and San Diego Center for Systems Biology, University of California, San Diego, La Jolla, California 92093-0322.
4
Donald P. Shiley BioScience Center, San Diego State University, San Diego, California 92182.
5
From the Department of Biology and Department of Pediatrics, University of California San Diego School of Medicine, La Jolla, California 92093 kdoran@mail.sdsu.edu.

Abstract

Bacterial meningitis occurs when bloodborne pathogens invade and penetrate the blood-brain barrier (BBB), provoking inflammation and disease. Group B Streptococcus (GBS), the leading cause of neonatal meningitis, can enter human brain microvascular endothelial cells (hBMECs), but the host response to intracellular GBS has not been characterized. Here we sought to determine whether antibacterial autophagy, which involves selective recognition of intracellular organisms and their targeting to autophagosomes for degradation, is activated in BBB endothelium during bacterial infection. GBS infection resulted in increased punctate distribution of GFP-microtubule-associated protein 1 light chain 3 (LC3) and increased levels of endogenous LC3-II and p62 turnover, two hallmark indicators of active autophagic flux. Infection with GBS mutants revealed that bacterial invasion and the GBS pore-forming β-hemolysin/cytolysin (β-h/c) trigger autophagic activation. Cell-free bacterial extracts containing β-h/c activity induced LC3-II conversion, identifying this toxin as a principal provocative factor for autophagy activation. These results were confirmed in vivo using a mouse model of GBS meningitis as infection with WT GBS induced autophagy in brain tissue more frequently than a β-h/c-deficient mutant. Elimination of autophagy using Atg5-deficient fibroblasts or siRNA-mediated impairment of autophagy in hBMECs led to increased recovery of intracellular GBS. However, electron microscopy revealed that GBS was rarely found within double membrane autophagic structures even though we observed GBS-LC3 co-localization. These results suggest that although autophagy may act as a BBB cellular defense mechanism in response to invading and toxin-producing bacteria, GBS may actively thwart the autophagic pathway.

KEYWORDS:

Autophagy; Bacterial Meningitis; Bacterial Toxin; Endothelium; Host Defense; Host-Pathogen Interaction; Infectious Disease; Molecular Cell Biology; Streptococcus

PMID:
25371213
PMCID:
PMC4276841
DOI:
10.1074/jbc.M114.588657
[Indexed for MEDLINE]
Free PMC Article

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