GM‐CSF and M‐CSF modulate β‐chemokine and HIV‐1 expression in microglia

Abstract

Significant numbers of patients with acquired immunodeficiency syndrome (AIDS) develop CNS infection primarily in macrophages and microglial cells. Therefore, the regulation of human immunodeficiency virus type 1 (HIV-1) infection and activation of the brain mononuclear phagocytes subsequent to infection are important areas of investigation. In the current report, we studied the role of granulocyte-macrophage colony-stimulating factor (GM-CSF) and macrophage-CSF (M-CSF) in the expression of antiviral beta-chemokines and HIV-1 p24 in cultures of primary human fetal microglia. We found that stimulation with GM-CSF or M-CSF induced macrophage inflammatory proteins (MIP-1alpha and MIP-1beta) and augmented RANTES expression, after HIV-1 infection of microglia. This was not due to the effect of GM-CSF on viral expression because GM-CSF was neither necessary nor stimulatory for viral infection, nor did GM-CSF enhance the expression of env-pseudotyped reporter viruses. Blocking GM-CSF-induced microglial proliferation by nocodazole had no effect on beta-chemokine or p24 expression. The functional significance of the GM-CSF-induced beta-chemokines was suggested by the finding that, in the presence of GM-CSF, exogenous beta-chemokines lost their anti-HIV-1 effects. We further show that although HIV-1-infected microglia produced M-CSF, they failed to produce GM-CSF. In vivo, GM-CSF expression was localized to activated astrocytes and some inflammatory cells in HIV-1 encephalitis, suggesting paracrine activation of microglia through GM-CSF. Our results demonstrate a complex interplay between CSFs, chemokines, and virus in microglial cells and may have bearing on the interpretation of data derived in vivo and in vitro.

Increased In Vivo Activation of Microglia and Astrocytes in the Brains of Mice Transgenic for an Infectious R5 Human Immunodeficiency Virus Type 1 Provirus and for CD4-Specific Expression of Human Cyclin T1 in Response to Stimulation by Lipopolysaccharides

“…We previously demonstrated that the CD4 promoter-regulated expression of hu-cycT1 was associated with a marked increase in granulocyte-macrophage colony-stimulating factor (GM-CSF)-induced HIV-1 production by JR-CSF mouse monocytes (69). Inflammatory factors such as LPS induce activated astrocytes to produce GM-CSF, and increased GM-CSF production may play a contributory role in the development of HAD (67). We investigated if the support of Tat responsiveness by the expression of hu-cycT1 also increased HIV production induced by GM-CSF in mouse brains carrying an integrated HIV provirus.…”

“…Activated astrocytes produce GM-CSF in response to inflammatory signals that would activate microglia, stimulate them to proliferate, and trigger the CNS inflammatory response (41). HIVE is associated with increased GM-CSF production in brains that localized predominantly to astrocytes (15,67), and the AIDS dementia complex is associated with elevated levels of GM-CSF in the cerebrospinal fluid (53). Systemic GM-CSF was reported to induce a 10-fold increase in the HIV load in the spinal fluid of a treated patient (38), and GM-CSF has been reported to increase HIV-1 replication in brain tissue explants (32) and primary monocyte/macrophages and monocyte cell lines (19,37,47,60).…”

Role of Microglia in Central Nervous System Infections

“…IL-4 and IL-10 enhance the entry and replication of HIV-1 in microglia through up-regulation of CD4 and CCR5 expression, respectively (368). The chemokines CCL5/RANTES, CCL3/MIP-1␣, CCL4/MIP-1␤, all of which bind to CCR5, are inhibitory to HIV-1 replication in microglial cells, apparently by their ability to block viral entry (177,327). GM-CSF and macrophage-colony stimulating factor (M-CSF) stimulate the production of these ␤-chemokines but actually inhibit the antiviral properties of these chemokines when added to microglial cell cultures (327).…”

15-Deoxy-Δ12,14-Prostaglandin J2 Inhibits IFN-Inducible Protein 10/CXC Chemokine Ligand 10 Expression in Human Microglia: Mechanisms and Implications

“…Human fetal CNS cell cultures were prepared from human fetal abortuses as previously described (20,22,26,27). All procedures were approved by the Albert Einstein College of Medicine institutional review board.…”

“…HIV-1 isolates were obtained from the AIDS Repository and propagated in PBMC as previously described (27). Mock infection consisted of exposure to PBMC supernatants without HIV-1.…”