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A soluble factor produced by macrophages mediates the neurotoxic effects of HIV-1 Tat in vitro
C Brana1, T E Biggs, C H Barton
1Department of Clinical Neurological Sciences, University of Southampton, Southampton General Hospital, UK.
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).
Insights
HIV-1 Tat protein induces neurotoxicity indirectly. Macrophages exposed to Tat release soluble factors that damage neurons and glial cells in brain slices, suggesting a key indirect mechanism in HIV-associated neurodegeneration.
Area of Science:
- Neuroscience
- Immunology
- Virology
Background:
- HIV-1 neurotoxicity is thought to be indirect, involving infected mononuclear cells damaging neurons.
- Understanding the precise mechanisms is crucial for developing effective treatments.
Purpose of the Study:
- To investigate the neurotoxic potential of HIV-1 Tat protein using a murine macrophage cell line.
- To determine if HIV-1 Tat can induce neurotoxic effects in a more physiologically relevant model.
Main Methods:
- Developed a co-culture model using rat organotypic hippocampal slices and RAW264.7 murine macrophages.
- Assessed neurotoxicity by measuring cell death (propidium iodide) and visualizing astrocytic (GFAP) and neuronal (MAP2) markers.
Main Results:
- RAW264.7 cells expressing or exposed to HIV-1 Tat produced a soluble factor.
- This factor caused significant degeneration of both glial cells and neurons in hippocampal slice cultures.
- HIV-1 Tat alone, without macrophages, did not exhibit neurotoxicity in this model.
Conclusions:
- HIV-1 Tat-induced neurotoxicity is likely mediated by soluble factors released from macrophages.
- This study highlights the critical role of macrophage-derived factors in HIV-1 neuropathogenesis.