Neuropathological abnormalities in AIDS patients have been associated with perivascular HIV-infected macrophages, gliosis and a focal breakdown of the blood-brain-barrier (BBB). The processes by which HIV causes these pathological conditions are not well understood. The HIV-derived regulatory protein, tat, has been demonstrated in the serum of HIV infected patients and functions as an extracellular growth factor, as well as a regulatory factor for HIV transcription. This laboratory has shown that: (l) HIV-infected macrophages are present in the central nervous system (CNS); (2) these macrophages produce tumor necrosis factor-alpha (TNF); and (3) prominent gliosis is apparent. The hypothesis of this study is that tat protein released by HIV-infected macrnphages, alone or together with TNF or IL-1 induces the pathological changes observed in CNS AIDS. Preliminary data presented here demonstrates that (l) tat is present in the CNS of HIV positive brain specimens using immunocytochemistry; (2) tat activates CNS-derived endothelial cells (CNS-EC) to upregulate the adhesion molecule ELAM-1; (3) tat upregulates cytokine production in CNS-EC, and (4) tat downregulates protein kinase C, and increases activity of cAMP- dependent protein kinase A in glioinas and CNS-EC. Based on this and previous findings, the aims of this proposal are to determine: (l) whether tat can alter the function of CNS-EC and astrocytes; (2) whether tat acts in concert with TNF or IL-1; and (3) what is the molecular mechanism of tat activation. Using CNS-EC established in this laboratory, primary cultured astrocytes and astrocytoma cells lines, we will examine upregulation of adhesion molecules expression (eg. ELAM-1), cytokine production (eg. IL-1, IL-6, GM-CSF and TNF), for CNS-EC and glial cells, and proliferation for astrocytes in the presence of tat protein alone, and in conjunction with TNF and IL-1. We will explore the molecular mechanisms by which tat activates these CNS cells by determining and identifying the tat binding sites, and analyzing the signal transduction pathways used by tat for cell activation. To further identify the specific region of the tat protein responsible for tat binding and/or activation, different length tat constructs will be synthesized and tested in these systems. These data will provide direct information about the role of tat and cytokines in the activation of CNS-EC and glial cells, and their subsequent effects on the dissemination of HIV into the brain and the gliosis typically observed in CNS AIDS.
| Hofman, F M; Chen, P; Incardona, F et al. (1999) HIV-1 tat protein induces the production of interleukin-8 by human brain-derived endothelial cells. J Neuroimmunol 94:28-39 |
| Zidovetzki, R; Wang, J L; Chen, P et al. (1998) Human immunodeficiency virus Tat protein induces interleukin 6 mRNA expression in human brain endothelial cells via protein kinase C- and cAMP-dependent protein kinase pathways. AIDS Res Hum Retroviruses 14:825-33 |
