Neisseria meningitidis Induces Brain Microvascular Endothelial Cell Detachment from the Matrix and Cleavage of Occludin: A Role for MMP-8

Abstract

Disruption of the blood-brain barrier (BBB) is a hallmark event in the pathophysiology of bacterial meningitis. Several inflammatory mediators, such as tumor necrosis factor alpha (TNF-α), nitric oxide and matrix metalloproteinases (MMPs), contribute to this disruption. Here we show that infection of human brain microvascular endothelial cells (HBMEC) with Neisseria meningitidis induced an increase of permeability at prolonged time of infection. This was paralleled by an increase in MMP-8 activity in supernatants collected from infected cells. A detailed analysis revealed that MMP-8 was involved in the proteolytic cleavage of the tight junction protein occludin, resulting in its disappearance from the cell periphery and cleavage to a lower-sized 50-kDa protein in infected HBMEC. Abrogation of MMP-8 activity by specific inhibitors as well as transfection with MMP-8 siRNA abolished production of the cleavage fragment and occludin remained attached to the cell periphery. In addition, MMP-8 affected cell adherence to the underlying matrix. A similar temporal relationship was observed for MMP activity and cell detachment. Injury of the HBMEC monolayer suggested the requirement of direct cell contact because no detachment was observed when bacteria were placed above a transwell membrane or when bacterial supernatant was directly added to cells. Inhibition of MMP-8 partially prevented detachment of infected HBMEC and restored BBB permeability. Together, we established that MMP-8 activity plays a crucial role in disassembly of cell junction components and cell adhesion during meningococcal infection.

Matrix Metalloprotease 8-Dependent Extracellular Matrix Cleavage at the Blood-CSF Barrier Contributes to Lethality during Systemic Inflammatory Diseases

“…MMP8 was recently implicated in disruption of the BBB by proteolytic cleavage of the brain endothelial tight junction (TJ) junction protein occludin (Schubert-Unkmeir et al, 2010). However, we did not observe fluorescence leakage from the vasculature into the brain tissue 8 h after challenge in MMP8 ϩ/ϩ mice (data not shown).…”

“…This indicates that the observed brain dysfunction in SIRS is not a consequence of the different inflammation states of MMP8 ϩ/ϩ and MMP8 Ϫ/Ϫ mice. Recently, MMP8 was shown to proteolytically degrade the TJ protein occludin in an in vitro model of bacterial meningitis, which resulted in the disruption of the BBB (Schubert-Unkmeir et al, 2010). Consequently, we speculated that MMP8 might also induce disruption of the BCSFB by cleavage of occludin, but EM analysis of the CP did not reveal disruption of TJs (data not shown).…”

“…Our in vivo data show that SIRS, in contrast to bacterial meningitis, is associated with rapid MMP8-dependent loss of the BCSFB, caused by leakage of the epithelial cell layer of the CP, whereas the BBB is unaffected. Based on the meningitis data (Schubert-Unkmeir et al, 2010), it is tempting to speculate that MMP8 might also induce disruption of the BCSFB by cleaving occludin. However, electron microscopic (EM) analysis of the CP did not reveal severe disruption of TJs (data not shown).…”

Dynamic regulation of plasma matrix metalloproteinases in human diabetic ketoacidosis

“…The primary substrates for MMP-8 are the fibrillary collagens, I, II, III, as well as other extracellular matrix components (8). Vascular leukocyte trafficking and blood-brain barrier disruption are mediated by MMP-8 and may involve cleavage of the endothelial cell tight junction proteins (17,18). Our results raise the possibility that the DKA-induced elevations in MMP-8 may contribute to cerebrovascular endothelial perturbations.…”

Matrix Metalloproteinase-8 Plays a Pivotal Role in Neuroinflammation by Modulating TNF-α Activation

“…Considering neurologic disorders, the role of MMP-8 has been studied in bacterial meningitis and experimental autoimmune encephalomyelitis (EAE), an animal model of human MS. In bacterial meningitis, MMP-8 degrades occludin, a component of the BBB, and induces neuroinflammation (12). In EAE, MMP-8 modulates Th1/Th2 polarization, causing inflammation and demyelination (13), and knockout of MMP-8 or administration of an MMP-8 inhibitor attenuates BBB breakdown and EAE progression.…”