A soluble factor produced by macrophages mediates the neurotoxic effects of HIV-1 Tat in vitro

Objectives: There is now a strong consensus that the neurotoxic properties of HIV-1 are likely to be mediated by an indirect mechanism in which neuron es are damaged by infected mononuclear cells. The aim of this study was to determine the ability of HIV-1 Tat to induce neurotoxic properties in a mur ine macrophage cell line RAW264.7. Design: Simple culture systems using dissociated neurones may not provide t he appropriate microenvironment in which to observe the complex cell-cell i nteractions that occur in the brain. We have therefore developed a more phy siological model in which rat organotypic hippocampal slices are co-culture d with the murine macrophage cell line RAW264.7. Effects of Tat were studie d by using a stable Tat expressing RAW264.7 cell line or by addition of rec ombinant Tat protein to co-cultures. Methods: Organotypic hippocampal slices prepared from 8-10 day rat pups wer e grown on membrane inserts that were placed into six-well plates on which RAW264.7 cells were growing as an adherent monolayer. Cell death in the sli ces was assessed using propidium iodide. Specific astrocytic (glial Fibrill ary acidophilic protein; GFAP) and neuronal (microtubule-associated protein ; MAP2) markers were visualized by immunocytochemistry. Results: RAW264.7 cells that either expressed or were exposed to HIV-1 Tat protein,produced a soluble factor that caused profound degeneration in brai n slice cultures involving loss of both glial cells and neurones. By contra st treatment of slice cultures with Tat in the absence of RAW264.7 cells wa s not neurotoxic. Conclusions: The neurotoxic properties previously attributed to HIV-1 Tat a re likely to be mediated via induction of macrophage derived soluble factor (s). (C) 1999 Lippincott Williams & Wilkins.