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

Abstract

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.

Dual roles of astrocytes in plasticity and reconstruction after traumatic brain injury

“…While endothelial tight junctions are formed by proteins such as claudin, occludin and zonula occluden (ZO), the basal lamina forms the basement membrane of ECM and includes laminin, collagen, and fibronectin [177,178]. Astrocyte-derived factors including angiopoietin-1 (ANG-1) [179][180][181], sonic hedgehog (SHH) [182][183][184][185], glial-derived neurotrophic factor (GDNF) [186][187][188], retinoic acid (RA) [189][190][191], and IGF-1 [192,193] have been demonstrated to promote recovery of the BBB by protecting endothelial cells and/or enhancing tight junction reassembly, via signaling mediated by their receptors, tie-2, patched-1, GDNF receptor alpha-1 and alpha-2, nuclear RA receptor, and IGF-1 receptor, respectively [78,79] (Table. 1).…”

Heavy Metal-Induced Cerebral Small Vessel Disease: Insights into Molecular Mechanisms and Possible Reversal Strategies

“…Vascular pruning requires post-hypoxia activation of MMP-9, which induces fragmentation of vascular laminin and claudin-5 (tight junction protein) [236]. The claudin-5 expression is regulated in glia by Sonic hedgehog signaling mediated transcription controlled byGli-1 [237]. Early expression of vascular endothelial growth factor may after ischemia, which then promotes further activation of MMPs [238] ( Figure 4).…”

Excretory/secretory products of Angiostrongylus cantonensis fifth-stage larvae induce endoplasmic reticulum stress via the Sonic hedgehog pathway in mouse astrocytes

“…Finally, some studies have shown that the Shh pathway has a protective effect on the BBB. Astrocyte-derived Shh proteins can upregulate BBB formation through the stimulation of tight junction protein expression and inhibit proinflammatory cell entry [70][71][72]. Moreover, Shh signalling protects neurons by inhibiting cell apoptosis in oxidative stress and brain injury.…”