TNF Induces Choroid Plexus Epithelial Cell Barrier Alterations by Apoptotic and Nonapoptotic Mechanisms

Christian Schwerk,Marie-Louise Mölleken,Annette Seibt,Tobias Tenenbaum,Frank Essmann,Horst Schroten,Patrick Zeni,Kasia Rybarczyk

doi:10.1155/2010/307231

Abstract

The choroid plexus epithelium constitutes the structural basis of the blood-cerebrospinal fluid barrier. Since the cytokine TNFα is markedly increased during inflammatory diseases in the blood and the central nervous system, we investigated by which mechanisms TNFα induces barrier alteration in porcine choroid plexus epithelial cells. We found a dose-dependent decrease of transepithelial electrical resistance, increase of paracellular inulin-flux, and induction of histone-associated DNA fragmentation and caspase-3 activation after TNFα stimulation. This response was strongly aggravated by the addition of cycloheximide and could partially be inhibited by the NF-κB inhibitor CAPE, but most effectively by the pan-caspase-inhibitor zVAD-fmk and not by the JNK inhibitor SP600125. Partial loss of cell viability could also be attenuated by CAPE. Immunostaining showed cell condensation and nuclear binding of high-mobility group box 1 protein as a sign of apoptosis after TNFα stimulation. Taken together our findings indicate that TNFα compromises PCPEC barrier function by caspase and NF-κB dependent mechanisms.

Highlights

In the mammalian brain the cerebrospinal fluid (CSF) is produced by the choroid plexus (CP), which regulates homeostasis in the central nervous system (CNS), and participates in neurohumoral brain modulation as well as neuroimmune interaction [1, 2]
Employing an in vitro model of the blood-CSF barrier we have previously shown that cell death by apoptosis and necrosis participates in barrier loss of porcine choroid plexus epithelial cells (PCPEC) after infection with Streptococcus suis [13]
To investigate the influence of TNFα on PCPEC barrier function we treated PCPEC monolayers grown on Transwell filters with TNFα for 24 hours and measured the transepithelial electrical resistance (TEER)

Summary

Introduction

In the mammalian brain the cerebrospinal fluid (CSF) is produced by the choroid plexus (CP), which regulates homeostasis in the central nervous system (CNS), and participates in neurohumoral brain modulation as well as neuroimmune interaction [1, 2]. Signalling through TNFR ligation can initiate (i) programmed cell death (apoptosis), (ii) antiapoptotic and proinflammatory responses through NF-κB, and (iii) activation of the mitogen activated protein kinase (MAPK) JNK signalling pathway [11]. These signal transduction mechanisms are tightly interconnected with each other through a complex network and their modulation allows to shifting the cellular state either towards survival or cell death [11, 12]. Employing an in vitro model of the blood-CSF barrier we have previously shown that cell death by apoptosis and necrosis participates in barrier loss of porcine choroid plexus epithelial cells (PCPEC) after infection with Streptococcus suis [13].

Materials and Methods

Results

Discussion