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


METHODS
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).
Brana
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C
Department of Clinical Neurological Sciences, University of Southampton, Southampton General Hospital, UK.
Biggs
T E
TE
Barton
C H
CH
Sundstrom
L E
LE
Mann
D A
DA
D000818:Animals; D002460:Cell Line; D018920:Coculture Techniques; D017077:Culture Media, Conditioned; D015696:Gene Products, tat / Q000378:metabolism / Q000633:toxicity*; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D015497:HIV-1 / Q000502:physiology*; D006624:Hippocampus; D007150:Immunohistochemistry; D008264:Macrophages / Q000378:metabolism* / Q000821:virology*; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D009498:Neurotoxins / Q000378:metabolism*; D009924:Organ Culture Techniques; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D054322:tat Gene Products, Human Immunodeficiency Virus
D017077:Culture Media, Conditioned; D015696:Gene Products, tat; D005904:Glial Fibrillary Acidic Protein; D008869:Microtubule-Associated Proteins; D009498:Neurotoxins; D011994:Recombinant Proteins; D054322:tat Gene Products, Human Immunodeficiency Virus