Background: Dysfunction in mononuclear phagocyte (MP; brain macrophage and microglia) immune function plays a prominent role in the pathogenesis of HIV-1-associated dementia (HAD). In particular, pro-inflammatory factors produced by MP, as a consequence of immune activation and viral infection, can induce neuronal injury. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is a type II integral membrane protein which interacts with at least 4 receptors expressed on multiple cell types including neurons. As this ligand is up-regulated by immune stimuli, we examined whether HIV-1-infected and immune-activated MP can mediate neurotoxic activities through TRAIL.
Potential Links between Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) and Macrophage-Mediated Neuronal Injury in the Pathogenesis of HIV-1-Associated Dementia|
L. A. Ryan*, A. L. Lopez, A. Ghorpade, H. E. Gendelman, and J. Zheng
Univ. of Nebraska Med. Ctr., Omaha
Methods: The expression of TRAIL and its receptors on human monocytes, monocyte-derived macrophages (MDM), and neurons was demonstrated by Western blot, immunohistochemical assays, and fluorescence-activated flow cytometry (FACS). mRNA regulation was monitored by RT-PCR. Chemokines secreted by MDM activated with recombinant human TRAIL (rhTRAIL) were detected by ELISA. TRAIL induced neuronal apoptosis was measured by cytochrome c release assays and DNA fragmentation ELISA.
Results: TRAIL mRNA and cell surface protein levels were increased in MDM after HIV-1 infection and/or lipopolysaccharide, tumor necrosis factor-alpha and interferon-gamma mediated activation. rhTRAIL activated MDM to secrete MIP-1alpha and IL-8. A dose-dependent effect of TRAIL, 0.5 - 50 ng/mL, on neuronal apoptosis was observed. Neuronal apoptosis was enhanced by HIV-1 protein gp120 (1 nM, p<0.01). Further, rhTRAIL-mediated neuronal apoptosis was blocked by TRAIL neutralizing antibody as well as inhibitors of caspases 3, 8 and 9.
Conclusions: These results support both direct and indirect roles for TRAIL in MP-mediated neurotoxicity during HAD.