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 neurones 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 murine macrophage cell line RAW264.7.
Design: Simple culture systems using dissociated neurones may not provide the appropriate microenvironment in which to observe the complex cell-cell interactions that occur in the brain. We have therefore developed a more physiological model in which rat organotypic hippocampal slices are co-cultured with the murine macrophage cell line RAW264.7. Effects of Tat were studied by using a stable Tat expressing RAW264.7 cell line or by addition of recombinant Tat protein to co-cultures.
Methods: Organotypic hippocampal slices prepared from 8-10 day rat pups were 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 slices was assessed using propidium iodide. Specific astrocytic (glial fibrillary 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 brain slice cultures involving loss of both glial cells and neurones. By contrast treatment of slice cultures with Tat in the absence of RAW264.7 cells was not neurotoxic.
Conclusions: The neurotoxic properties previously attributed to HIV-1 Tat are likely to be mediated via induction of macrophage derived soluble factor(s).
From the Department of Clinical Neurological Sciences, the aDepartment of Medicine, University of Southampton, Southampton General Hospital and the bBiochemistry Department, School of Biological Sciences, University of Southampton, Southampton, UK.
Sponsorship: Supported by grants from Wessex Medical Trust (L.S. and D.M.) and the MRC. T.B was supported under the BBSRC research studentship scheme.
Requests for reprints to: D.A. Mann, Department of Medicine, Level D, South Academic Block, University of Southampton, Southampton General Hospital, Tremona Rd, Southampton, SO16 6YD, UK.
Received: 15 December 1998; revised: 5 May 1999; accepted: 11 May 1999.