Human Immunodeficiency Virus Protein Tat Induces Synapse Loss via a Reversible Process That Is Distinct from Cell Death

• Published in: The Journal of neuroscience 2008-11, Vol.28 (48), p.12604-12613
• Main Authors: Kim, Hee Jung, Martemyanov, Kirill A, Thayer, Stanley A
• Format: Article
• Language: English
• Subjects: AIDS Dementia Complex - pathology; AIDS Dementia Complex - physiopathology; Animals; Biological Assay - methods; Brain - pathology; Brain - physiopathology; Brain - virology; Calcium Signaling - physiology; Cells, Cultured; Disks Large Homolog 4 Protein; Down-Regulation - physiology; Green Fluorescent Proteins - analysis; Green Fluorescent Proteins - genetics; Green Fluorescent Proteins - metabolism; Hippocampus - pathology; Hippocampus - physiopathology; Hippocampus - virology; HIV - metabolism; Humans; Intracellular Signaling Peptides and Proteins - analysis; Intracellular Signaling Peptides and Proteins - genetics; Intracellular Signaling Peptides and Proteins - metabolism; LDL-Receptor Related Protein-Associated Protein - metabolism; LDL-Receptor Related Protein-Associated Protein - pharmacology; Membrane Proteins - analysis; Membrane Proteins - genetics; Membrane Proteins - metabolism; Nerve Degeneration - pathology; Nerve Degeneration - physiopathology; Nerve Degeneration - virology; Neurons - pathology; Neurons - virology; Rats; Receptors, LDL - metabolism; Receptors, N-Methyl-D-Aspartate - metabolism; Synapses - metabolism; Synapses - pathology; Synaptic Membranes - metabolism; Synaptic Membranes - pathology; tat Gene Products, Human Immunodeficiency Virus - metabolism; tat Gene Products, Human Immunodeficiency Virus - toxicity; Tumor Suppressor Proteins - metabolism; Ubiquitination
• ISSN: 0270-6474; 1529-2401
• DOI: 10.1523/JNEUROSCI.2958-08.2008

Human immunodeficiency virus (HIV)-1 infection of the CNS produces changes in dendritic morphology that correlate with cognitive decline in patients with HIV-1 associated dementia (HAD). Here, we investigated the effects of HIV-1 transactivator of transcription (Tat), a protein released by virus-infected cells, on synapses between hippocampal neurons using an imaging-based assay that quantified clusters of the scaffolding protein postsynaptic density 95 fused to green fluorescent protein (PSD95-GFP). Tat (24 h) decreased the number of PSD95-GFP puncta by 50 +/- 7%. The decrease was concentration-dependent (EC(50) = 6 +/- 2 ng/ml) and preceded cell death. Tat acted via the low-density lipoprotein receptor-related protein (LRP) because the specific LRP blocker, receptor associated protein (RAP), prevented the Tat-induced decrease in the number of PSD95-GFP puncta. Ca(2+) influx through the NMDA receptor was necessary for Tat-induced synapse loss. Expression of an ubiquitin ligase inhibitor protected synapses, implicating the ubiquitin-proteasome pathway. In contrast to synapse loss, Tat induced cell death (48 h) required activation of nitric oxide synthase. The ubiquitin ligase-inhibitor nutlin-3 prevented synapse loss but not cell death induced by Tat. Thus, the pathways diverged, consistent with the hypothesis that synapse loss is a mechanism to reduce excess excitatory input rather than a symptom of the neuron's demise. Furthermore, application of RAP to cultures treated with Tat for 16 h reversed synapse loss. These results suggest that the impaired network function and decreased neuronal survival produced by Tat involve distinct mechanisms and that pharmacologic targets, such as LRP, might prove useful in restoring function in HAD patients.