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Primary macrophages infected by human immunodeficiency virus trigger CD95-mediated apoptosis of uninfected astrocytes
S Aquaro1, S Panti, M C Caroleo
1Department of Experimental Medicine, University of Rome Tor Vergata, Italy. aquaro@uniroma2.it
Abstract:
Infection of macrophages (M/M) by human immunodeficiency virus (HIV) is a main pathogenetic event leading to neuronal dysfunction and death in patients with AIDS dementia complex. Alteration of viability of neurons and astrocytes occurs in vivo even without their infection, thus it is conceivable that HIV-infected M/M may affect viability of such cells even without direct infection. To assess this hypothesis, we studied the effects of HIV-infected M/M on an astrocytic cell-line lacking CD4-receptor expression. Exposure to supernatants of HIV-infected M/M triggers complete disruption and apoptotic death of astrocytic cells. This effect is not related to HIV transmission from infected M/M, because HIV-DNA and p24 production in astrocytic cells remained negative. Apoptotic death of astrocytes is mainly mediated by Fas ligand released in supernatants of HIV-infected M/M (as demonstrated by complete reversal of such phenomenon by adding neutralizing antibodies against CD95 receptor). Treatment of astrocytic cells with recombinant (biologically active) Tat induces < 10% apoptosis, and gp120 was totally ineffective. Treatment of HIV-infected M/M with AZT completely reverses the proapoptotic effect of their supernatants on astrocytes, thus demonstrating that productive virus replication within M/M is required for the induction of astrocytic cell death. Taken together, data suggest that homeostasis of astrocytes may be affected by HIV-infected M/M in the absence of productive infection of target cells. This phenomenon may help to explain the cellular damage found in HIV-infected patients also in areas of the brain not strictly adjacent to HIV-infected M/M.
Insights
Human immunodeficiency virus (HIV)-infected macrophages induce astrocyte death via Fas ligand, independent of direct viral infection. Productive HIV replication in macrophages is essential for this pro-apoptotic effect on astrocytes.
Area of Science:
- Neurovirology
- Cell Biology
- Immunology
Background:
- Human immunodeficiency virus (HIV) infection of macrophages is central to AIDS dementia complex, causing neuronal damage.
- Astrocytes and neurons can be affected by HIV even without direct infection, suggesting indirect mechanisms.
- HIV-infected macrophages may influence the viability of surrounding non-infected cells.
Purpose of the Study:
- To investigate the effect of HIV-infected macrophages on astrocyte viability.
- To determine the mechanism by which HIV-infected macrophages induce astrocyte death.
- To assess the role of productive viral replication in this process.
Main Methods:
- Exposure of an astrocytic cell line to supernatants from HIV-infected macrophages.
- Detection of HIV-DNA and p24 antigen in astrocytes to rule out viral transmission.
- Use of neutralizing antibodies against CD95 (Fas receptor) to identify the mediator of apoptosis.
- Treatment of astrocytes with recombinant Tat and gp120.
- Treatment of HIV-infected macrophages with AZT to inhibit viral replication.
Main Results:
- Supernatants from HIV-infected macrophages caused complete disruption and apoptotic death of astrocytes.
- Astrocytes did not show signs of HIV infection (negative for HIV-DNA and p24).
- Apoptotic death was mediated primarily by Fas ligand, with complete reversal by anti-CD95 antibodies.
- Recombinant Tat induced minimal apoptosis (<10%), while gp120 was ineffective.
- AZT treatment of HIV-infected macrophages abolished the pro-apoptotic effect of their supernatants on astrocytes.
Conclusions:
- HIV-infected macrophages can induce astrocyte death through secreted factors, notably Fas ligand.
- Productive viral replication within macrophages is necessary for inducing this pro-apoptotic effect.
- This mechanism highlights how HIV-infected macrophages can contribute to brain pathology in AIDS dementia complex without direct infection of target cells.