HIV-1 Tat-Mediated Effects on Focal Adhesion Assembly and Permeability in Brain Microvascular Endothelial Cells

Abstract

The blood-brain barrier (BBB) is a network formed mainly by brain microvascular endothelial cells (BMECs). The integrity of the BBB is critical for brain function. Breakdown of the BBB is commonly seen in AIDS patients with HIV-1-associated dementia despite the lack of productive HIV infection of the brain endothelium. The processes by which HIV causes these pathological conditions are not well understood. In this study we characterized the molecular mechanisms by which Tat mediates its pathogenic effects in vitro on primary human BMECs (HBMECs). Tat treatment of HBMECs stimulated cytoskeletal organization and increased focal adhesion sites compared with control cells or cells treated with heat-inactivated Tat. Pretreatment with Tat Abs or with the specific inhibitor SU-1498, which interferes with vascular endothelial growth factor receptor type 2 (Flk-1/KDR) phosphorylation, blocked the ability of Tat to stimulate focal adhesion assembly and the migration of HBMECs. Focal adhesion kinase (FAK) was tyrosine-phosphorylated by Tat and was found to be an important component of focal adhesion sites. Inhibition of FAK by the dominant interfering mutant form, FAK-related nonkinase, significantly blocked HBMEC migration and disrupted focal adhesions upon Tat activation. Furthermore, HIV-Tat induced permeability changes in HBMECs in a time-dependent manner. Tat also impaired BBB permeability, as observed in HIV-1 Tat transgenic mice. These studies define a mechanism for HIV-1 Tat in focal adhesion complex assembly in HBMECs via activation of FAK, leading to cytoskeletal reorganization and permeability changes.

Enhanced Pulmonary Arteriopathy in Simian Immunodeficiency Virus–infected Macaques Exposed to Morphine

“…Recently, findings from our laboratory (40) and by Lund and colleagues (41) demonstrate the development of a pulmonary arteriopathy under the influence of HIV-1 proteins alone, leading to pulmonary hypertension in a noninfectious HIVtransgenic rat model. Tat can promote growth and migration of endothelial cells through production of various growth factors as well as the induction of apoptosis of microvascular endothelial cells via caspase activation (24,(42)(43)(44)(45). Like Tat, morphine has also been shown to have a dual action on both proapoptotic and prosurvival signals (15,17).…”

HIV-TAT Protein Upregulates Expression of Multidrug Resistance Protein 1 in the Blood–Brain Barrier

“…Tat is believed to be one of the potent viral neurotoxins in the pathogenesis of neuronal dysfunction in HIV-infected patients (Nath and Geiger, 1998). In addition, Tat can induce profound vascular changes by its influence on brain endothelial cells (Toborek et al, 2003;Price et al, 2005;Avraham et al, 2004;Wu et al, 2000). For example, exposure to Tat can induce inflammatory responses in BMEC and alter the expression of tight-junction proteins through the vascular endothelial growth factor receptor type 2 (VEGFR-2) and mitogen-activated protein kinase (MAPK) signaling pathways Pu et al, 2005).…”

HIV-1 Tat Activates Dual Nox Pathways Leading to Independent Activation of ERK and JNK MAP Kinases

“…Like other angiogenic factors, Tat also stimulates cytoskeletal rearrangements leading to junctional separation and increased motility (12,18). Previously, we found that Tat caused dramatic actin rearrangements through activation of the Ste20 kinase p21/cdc42/Rac1-activated kinase1 (PAK1) and downstream phosphorylation of p47 phox , the adapter for the Nox2 oxidase (9).…”