Endocytic Trafficking of HIV gp120 is Mediated by Dynamin and Plays a Role in gp120 Neurotoxicity

Abstract

Neurons that endocytose the human immunodeficiency virus-1 (HIV) protein gp120 exhibit neurite retraction and activation of caspase-3, suggesting that the endocytic process may be crucial for gp120-mediated neuronal injury. The goal of this study is to demonstrate that internalization and accumulation of gp120 play a role in its neurotoxic effects. In mammalian cells, endocytosis is primarily a dynamin-dependent process. To establish whether gp120 is endocytosed in a dynamin-dependent manner, we used fibroblasts in which deletion of dynamins was induced by tamoxifen. We observed a robust reduction of intracellular gp120 immunoreactivity in tamoxifen-treated cells. To examine whether endocytosis of gp120 is crucial for its neurotoxic effect, we blocked gp120 internalization into primary rat cortical neurons by dynasore, an inhibitor of the dynamin GTPase activity. We found that dynasore blocks both gp120 internalization and neurotoxicity. We then utilized gp120-loaded mesoporous silica nanoparticles to deliver gp120 intracellularly. We established that once internalized, gp120 is neurotoxic regardless of chemokine receptor activation. Our data suggest that dynamin-dependent endocytosis of gp120 is critical for its neurotoxicity.

HIV gp120 upregulates tonic inhibition through α5-containing GABAARs

“…6), in which microglia release of IL-1β that acts on neurons, is the most parsimonious pathway consistent with the results of this study. This model is consistent with prior studies from our laboratory and others showing that the highly potent (picomolar) effects that result from prolonged exposure to gp120 are indirect (Kim et al, 2011;Meucci and Miller, 1996;Viviani et al, 2006;Yang et al, 2013), whereas higher concentrations will elicit direct actions on neurons (Hesselgesser et al, 1998;Teodorof et al, 2014;Wenzel et al, 2017). IL-1β alone increased tonic inhibition, as previously reported (Wang et al, 2012), effectively mimicking the actions of gp120.…”

Human Immunodeficiency Virus Type 1 gp120 and Tat Induce Mitochondrial Fragmentation and Incomplete Mitophagy in Human Neurons

“…Our first set of experiments were designed to examine the localization of gp120 and Tat following internalization into HPNs. HPNs were treated with 100 ng/ml of gp120, Tat, or both proteins for 24 h. Heat-inactivated HIV gp120, which does not internalize, and 0.5 M dextran sulfate, which blocks the binding and uptake of Tat, were used to demonstrate the specificity of HIV gp120 and Tat protein internalization (22)(23)(24). Protein internalization in microtubuleassociated protein 2 (MAP2)-positive neurons was observed by immunostaining with antibodies against the neuronal somatodendritic marker MAP2 and antibodies against gp120 and Tat and examining stained cells by confocal microscopy.…”

“…HIV gp120 binds the chemokine receptors CXCR4 and CCR5, resulting in its internalization (39,40). It then forms a vesicular complex with mannose-binding lectin (MBL) (41), binds microtubules (42), and undergoes anterograde or retrograde axonal trafficking (22,23,41,43). Thus, internalized HIV gp120 impairs mitochondrial transport and dynamics (42), which negatively impacts synaptic energy distribution.…”

Aging and Apolipoprotein E in HIV Infection

“…Macrophages, together with microglia and to some extent astrocytes, constitute the principal population of cells supporting HIV replication in the brain (Liu et al 2004 ; Thompson et al 2011 ) and drive the neuropathogenesis of neurological disease. Potential mechanisms of neuropathogenesis include direct neurotoxicity by the HIV proteins Tat (Buscemi et al 2007 ; Fan and He 2016 ; Fields et al 2015 ; Rahimian and He 2016 ; Sabatier et al 1991 ) and gp120 (Bachis et al 2006 ; Bachis et al 2012 ; Mocchetti et al 2012 ; Nosheny et al 2006 ; Reddy et al 2012 ; Wenzel et al 2017 ; Zhou et al 2017 ), and the pro-inflammatory milieu generated by factors released by infected and/or immune-activated microglia and astrocytes (Faissner et al 2014 ; Wu et al 2015 ; Zenon et al 2015 ). HIV replication in the central nervous system (CNS) is clinically associated with a spectrum of neurological abnormalities collectively known as HAND (HIV-associated neurological disorders) and subdivided into asymptomatic neurocognitive impairment (ANI), minor neurocognitive disorder (MND), and HIV-associated dementia (HAD) (reviewed by Wendelken and Valcour 2012 ).…”