1. ¹Molecular Neuroscience and Vascular Biology Laboratory, Department of Surgery, University of Kentucky Medical Center, Kentucky, USA
2. ²College of Agriculture, University of Kentucky, Lexington, Kentucky, USA

Correspondence: Dr M Toborek, Molecular Neuroscience and Vascular Biology Laboratory, Department of Surgery/Neurosurgery, University of Kentucky Medical Center, 593 Wethington Bldg., 900 S Limestone, Lexington, KY 40536, USA. E-mail: mjtobo00@uky.edu

Received 4 December 2004; Revised 26 December 2004; Accepted 28 January 2005; Published online 13 April 2005.

Abstract

HIV-1 Tat protein plays an important role in inducing monocyte infiltration into the brain and may alter the structure and functions of the blood–brain barrier (BBB). The BBB serves as a frontline defense system, protecting the central nervous system from infected monocytes entering the brain. Therefore, the aim of the present study was to examine the mechanisms of Tat effect on the integrity of the BBB in the mouse brain. Tat was injected into the right hippocampi of C57BL/6 mice and expression of tight junction protein zonula occludens-1 (ZO-1) was determined in control and treated mice. Tat administration resulted in decreased mRNA levels of ZO-1 and marked disruption of ZO-1 continuity. These changes were associated with accumulation of inflammatory cells in brain tissue of Tat-treated mice. Further experiments indicated that Tat-mediated alterations of redox-related signaling may be responsible for decreased ZO-1 expression. Specifically, injections with Tat resulted in activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and pretreatment with U0126, a specific inhibitor of ERK kinase, effectively ameliorated the Tat-induced diminished ZO-1 levels. In addition, administration of N-acetylcysteine (NAC), a precursor of glutathione and a potent antioxidant, attenuated both Tat-induced ERK1/2 activation and alterations in ZO-1 expression. These results indicate that Tat-induced oxidative stress can play an important role in affecting the integrity of the BBB through the ERK1/2 pathway.