HIV-1 Tat Protein Increases Microglial Outward K+ Current and Resultant Neurotoxic Activity

Jianuo Liu,Han Liu,Cory Collins,Peng Xu,James P Keblesh,Jingdong Zhang,Huangui Xiong,Michelle L Block

doi:10.1371/journal.pone.0064904

Abstract

Microglia plays a crucial role in the pathogenesis of HIV-1-associated neurocognitive disorders. Increasing evidence indicates the voltage-gated potassium (Kv) channels are involved in the regulation of microglia function, prompting us to hypothesize Kv channels may also be involved in microglia-mediated neurotoxic activity in HIV-1-infected brain. To test this hypothesis, we investigated the involvement of Kv channels in the response of microglia to HIV-1 Tat protein. Treatment of rat microglia with HIV-1 Tat protein (200 ng/ml) resulted in pro-inflammatory microglial activation, as indicated by increases in TNF-α, IL-1β, reactive oxygen species, and nitric oxide, which were accompanied by enhanced outward K+ current and Kv1.3 channel expression. Suppression of microglial Kv1.3 channel activity, either with Kv1.3 channel blockers Margatoxin, 5-(4-Phenoxybutoxy)psoralen, or broad-spectrum K+ channel blocker 4-Aminopyridine, or by knockdown of Kv1.3 expression via transfection of microglia with Kv1.3 siRNA, was found to abrogate the neurotoxic activity of microglia resulting from HIV-1 Tat exposure. Furthermore, HIV-1 Tat-induced neuronal apoptosis was attenuated with the application of supernatant collected from K+ channel blocker-treated microglia. Lastly, the intracellular signaling pathways associated with Kv1.3 were investigated and enhancement of microglial Kv1.3 was found to correspond with an increase in Erk1/2 mitogen-activated protein kinase activation. These data suggest targeting microglial Kv1.3 channels may be a potential new avenue of therapy for inflammation-mediated neurological disorders.

Highlights

Individuals infected with human immunodeficiency virus type 1 (HIV-1) often suffer from neurocognitive impairments which are referred to as HIV-1-associated neurocognitive disorders (HAND) [1,2]
Our results demonstrated that HIV-1 Tat1-72 protein (Tat) increases microglia production of neurotoxins and resultant neurotoxicity through enhancements of Kv1.3 protein expression and outward K+ currents, which can be blocked by pretreatment of microglia with specific Kv channel blockers Margatoxin (MgTx) or 5-(4-Phenoxybutoxy)psoralen (PAP), or by transfection of microglia with Kv1.3 siRNA, suggesting an involvement of Kv1.3 in microglia-mediated neurotoxic activity
To determine whether the Tat-induced Iout currents were conducted via Kv1.3 channels, Tat-treated microglia were perfused with artificial cerebrospinal fluid (ACSF) contained specific Kv1.3 blockers PAP (10 nM), MgTx (5 nM), or a broad spectrum Kv channel blocker 4-AP (1 mM), and the Iout was significantly reduced by 52.1614.72% (n = 8), 87.2667.79% (n = 8) or 89.8163.09% (n = 7) (Fig. 1D & 1E)

Summary

Introduction

Individuals infected with human immunodeficiency virus type 1 (HIV-1) often suffer from neurocognitive impairments which are referred to as HIV-1-associated neurocognitive disorders (HAND) [1,2]. The severity of HAND varies, ranging from asymptomatic neurocognitive impairment to its severest form: HIV-1-associated dementia [2]. The persistence of HAND is multifactorial, the paucity of effective therapeutic modalities in the control of brain macrophage and microglia activation and resultant production of neurotoxins, a striking pathological feature in HIV-1infected brain, plays an important role as pathogenesis and severity of HAND is highly correlated with activated brain macrophages and microglia but not the presence and amount of virus in the brain [6,7]. It is well known that the activated microglia secrete a number of neurotoxins including, but not limited to, pro-inflammatory cytokines, and excitatory amino acids, reactive oxygen species (ROS), nitric oxygen (NO), which can result in neuronal injury and consequent neurocognitive impairments [8,9,10]. Studies on elucidation of the mechanisms by which HIV-1 triggers microglial neurotoxicity and identification of specific target(s) to control microglia activation are imperative

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Conclusion