Phorbol ester induced short- and long-term permeabilization of the blood-CSF barrier in vitro

Interconnected by tight junctions, the epithelial cells of the choroid plexus form a barrier separating the cerebrospinal fluid (CSF) from blood. Using an in vitro model based on porcine choroid plexus epithelial cells (PCPEC), we investigated the influence of PKC activating phorbol 12-myristate 13-acetate (PMA) on barrier properties and analyzed mechanisms involved in the regulation of barrier tightness. Applied in concentrations of 5-25 nM, PMA induced a fast and lasting decrease of the transepithelial electrical resistance (TER), which could be blocked by rottlerin, indicating the involvement of PKCdelta in signal transduction. The immediate impairment of barrier integrity was accompanied by dephosphorylation of occludin and formation of actin bundles. Moreover, in the presence of at least 25 nM PMA, changes of cell shape as well as discontinuities of tight junction strands were observed, suggesting the disruption of cell-cell contacts. Exposure to PMA for 1-2 days additionally induced down-regulation of claudin-2 and up-regulation of barrier modulating matrix metalloproteinase (MMP)-9, respectively. The results show that different interconnected mechanisms directly and indirectly targeting at the tight junctions are released by PMA contributing to the short-term and long-term decrease of TER and opening of the blood-CSF barrier in vitro.