HIV-1 Tat-Induced Changes in Synaptically-Driven Network Activity Adapt During Prolonged Exposure
Kelly A. Krogh,
Matthew V. Green,
Stanley A. Thayer.
HIV-associated neurocognitive disorders (HAND) afflict approximately half of HIVinfected
patients. The HIV-1 transactivator of transcription (Tat) protein is released by infected
cells and contributes to the pathogenesis of HAND, but many of the underlying mechanisms
remain poorly understood. Here we used fura-2-based Ca2+ imaging and whole-cell patch-clamp
recording to study the effects of Tat on the spontaneous synaptic activity that occurs in networked
rat hippocampal neurons in culture. Tat triggered aberrant network activity that exhibited a
decrease in the frequency of spontaneous action potential bursts and Ca2+ spikes with a
simultaneous increase in burst duration and Ca2+ spike amplitude. These network changes were
apparent after 4 h treatment with Tat and required the low-density lipoprotein receptor-related
protein (LRP). Interestingly, Tat-induced changes in network activity adapted during 24 h
exposure. The activity returned to control levels in the maintained presence of Tat for 24 h. These
observations indicate that Tat causes aberrant network activity, which is dependent on LRP, and adapts following
prolonged exposure. Changes in network excitability may contribute to Tat-induced neurotoxicity in vitro and seizure
disorders in vivo. Adaptation of neural networks may be a neuroprotective response to the sustained presence of the
neurotoxic protein Tat and could underlie the behavioral and electrophysiological changes observed in HAND.
Keywords: Adaptation, Ca2+ signaling, excitotoxicity, fura-2, hippocampal culture, HIV associated neurocognitive disorders
(HAND), lipoprotein receptor, synaptic network.
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