Human immunodeficiency virus type 1 Tat-mediated cytotoxicity of human brain microvascular endothelial cells

Human immunodeficiency virus (HIV)-1 infection is often complicated with neurologic disorders, but the pathogenesis of HIV-1 encephalopathy is incompletely understood. Tat (HIV-1 transactivator protein) is released from HIV-1-infected cells and has been detected in the sera and cerebrospinal fluid of HIV-1-infected patients. Tat, along with increased inflammatory cytokines such as interferon-gamma (IFN-gamma), have been implicated in the pathogenesis of HIV-1-associated blood-brain barrier dysfunction. The present study examined the effects of Tat and IFN-gamma on human brain microvascular endothelial cells (HBMECs), which constitute the blood-brain barrier. Tat produced cytotoxicity of HBMECs, but required IFN-gamma. IFN-gamma treatment of HBMECs up-regulates vascular endothelial growth factor receptor-2 (VEGFR2/KDR), which is known to be the receptor for Tat. Tat activated KDR in the presence of IFN-gamma, and Tat-mediated cytopathic changes involve its interaction with KDR and phosphatidylinositol 3-kinase (PI3K). Further understanding and characterization of Tat-HBMEC interactions should help us understand HIV-1 neuropathogenesis and develop strategies to prevent HIV-1 encephalopathy.