Matrix metalloproteinase-9 activity and a downregulated Hedgehog pathway impair blood-brain barrier function in an in vitro model of CNS tuberculosis

• Published in: Scientific reports Vol. 7; no. 1; pp. 16031 - 15
• Main Authors: Brilha, Sara, Ong, Catherine W. M., Weksler, Babette, Romero, Nacho, Couraud, Pierre-Olivier, Friedland, Jon S.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 22.11.2017; Nature Publishing Group
• Subjects: 13/106; 13/31; 14/19; 38/77; 631/250/255/1856; 631/250/262; Astrocytes; Blood-brain barrier; Blood-Brain Barrier - metabolism; Cell culture; Cell Line; Cells, Cultured; Central nervous system; Collagen (type IV); Culture Media, Conditioned; Endothelial cells; Enzyme-Linked Immunosorbent Assay; Gelatinase B; Hedgehog protein; Hedgehog Proteins - genetics; Hedgehog Proteins - metabolism; Humanities and Social Sciences; Humans; Matrix metalloproteinase; Matrix Metalloproteinase 9 - genetics; Matrix Metalloproteinase 9 - metabolism; Membrane permeability; Metalloproteinase; Morbidity; multidisciplinary; Mycobacterium tuberculosis - pathogenicity; Permeability; Science; Science (multidisciplinary); Secretion; Signal Transduction - physiology; Tight Junctions - metabolism; Tuberculosis; Tuberculosis, Central Nervous System - metabolism; Brain Microvascular Endothelial Cells; Tight Junction Proteins (TJP); Leukocyte Transmigration; Hedgehog Pathway; Central Nervous System Tuberculosis
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-017-16250-3

Central nervous system tuberculosis (CNS TB) has a high mortality and morbidity associated with severe inflammation. The blood-brain barrier (BBB) protects the brain from inflammation but the mechanisms causing BBB damage in CNS TB are uncharacterized. We demonstrate that Mycobacterium tuberculosis (Mtb) causes breakdown of type IV collagen and decreases tight junction protein (TJP) expression in a co-culture model of the BBB. This increases permeability, surface expression of endothelial adhesion molecules and leukocyte transmigration. TJP breakdown was driven by Mtb-dependent secretion of matrix metalloproteinase (MMP)-9. TJP expression is regulated by Sonic hedgehog (Shh) through transcription factor Gli-1. In our model, the hedgehog pathway was downregulated by Mtb-stimulation, but Shh levels in astrocytes were unchanged. However, Scube2, a glycoprotein regulating astrocyte Shh release was decreased, inhibiting Shh delivery to brain endothelial cells. Activation of the hedgehog pathway by addition of a Smoothened agonist or by addition of exogenous Shh, or neutralizing MMP-9 activity, decreased permeability and increased TJP expression in the Mtb-stimulated BBB co-cultures. In summary, the BBB is disrupted by downregulation of the Shh pathway and breakdown of TJPs, secondary to increased MMP-9 activity which suggests that these pathways are potential novel targets for host directed therapy in CNS TB.