HIV induces synaptic hyperexcitation via cGMP-dependent protein kinase II activation in the FIV infection model

Abstract

Over half of individuals infected with human immunodeficiency virus (HIV) suffer from HIV-associated neurocognitive disorders (HANDs), yet the molecular mechanisms leading to neuronal dysfunction are poorly understood. Feline immunodeficiency virus (FIV) naturally infects cats and shares its structure, cell tropism, and pathology with HIV, including wide-ranging neurological deficits. We employ FIV as a model to elucidate the molecular pathways underlying HIV-induced neuronal dysfunction, in particular, synaptic alteration. Among HIV-induced neuron-damaging products, HIV envelope glycoprotein gp120 triggers elevation of intracellular Ca2+ activity in neurons, stimulating various pathways to damage synaptic functions. We quantify neuronal Ca2+ activity using intracellular Ca2+ imaging in cultured hippocampal neurons and confirm that FIV envelope glycoprotein gp95 also elevates neuronal Ca2+ activity. In addition, we reveal that gp95 interacts with the chemokine receptor, CXCR4, and facilitates the release of intracellular Ca2+ by the activation of the endoplasmic reticulum (ER)-associated Ca2+ channels, inositol triphosphate receptors (IP3Rs), and synaptic NMDA receptors (NMDARs), similar to HIV gp120. This suggests that HIV gp120 and FIV gp95 share a core pathological process in neurons. Significantly, gp95’s stimulation of NMDARs activates cGMP-dependent protein kinase II (cGKII) through the activation of the neuronal nitric oxide synthase (nNOS)-cGMP pathway, which increases Ca2+ release from the ER and promotes surface expression of AMPA receptors, leading to an increase in synaptic activity. Moreover, we culture feline hippocampal neurons and confirm that gp95-induced neuronal Ca2+ overactivation is mediated by CXCR4 and cGKII. Finally, cGKII activation is also required for HIV gp120-induced Ca2+ hyperactivation. These results thus provide a novel neurobiological mechanism of cGKII-mediated synaptic hyperexcitation in HAND.

Selective co-activation of α7- and α4β2-nicotinic acetylcholine receptors reverses beta-amyloid-induced synaptic dysfunction

“…We thus examined whether the interaction of Aβ 1-42 (Aβ42) with nAChRs is important for neuronal hyperactivity by using the Aβcore peptide (42,43). As neuronal Ca 2+ indicates neuronal activity (46), we measured Ca 2+ activity in cultured 12-14 days in vitro (DIV) mouse hippocampal pyramidal neurons transfected with GCaMP6f (a genetically encoded Ca 2+ indicator) as described previously (32,47). We treated neurons with soluble Aβ42 oligomers (oAβ42) and determined Ca 2+ activity in hippocampal neurons immediately after treatment.…”

“…GCaMP Ca 2+ imaging was carried out by the previously reported method (32,47). DIV 4 neurons were transfected with pGP-CMV-GCaMP6f (a gift from Douglas Kim, Addgene plasmid # 40755; http://n2t.net/addgene:40755 ; RRID:Addgene_40755) (87) for imaging hippocampal pyramidal cells or pAAV-mDlx-GCaMP6f-Fishell-2 (a gift from Gordon Fishell, Addgene plasmid # 83899; http://n2t.net/addgene:83899; RRID:Addgene_83899) (88) for imaging interneurons by using Lipofectamine 2000 (Life Technologies) according to the manufacturer’s protocol.…”

“…Mouse hippocampal neuron cultures were prepared as described previously (32,47,(84)(85)(86). Hippocampi were isolated from postnatal day 0 (P0) CD-1 (Charles River) mouse brain tissues and digested with 10U/mL papain (Worthington Biochemical Corp. Lakewood, NJ).…”

“…Surface biotinylation was performed according to the previous studies (32,47,(84)(85)(86). Cells were washed with ice-cold PBS containing 1mM CaCl2 and 0.5mM MgCl2 and incubated with 1mg/ml Sulfo-NHS-SS-biotin (Thermo Scientific) for 15 min on ice.…”

HIV Associated Neurodegenerative Disorders: A New Perspective on the Role of Lipid Rafts in Gp120-Mediated Neurotoxicity

“…Feline immunodeficiency virus (FIV) represents an animal model of immunodeficiency with similarities in pathogenesis to HIV infection in humans, including subsequent FIV infection of the CNS in domestic cats that results in neurological symptoms comparable to those observed in HAND [76]. A recently published study investigating the role of FIV envelope glycoprotein gp95-mediated synaptic dysfunction found gp95 signaling through neuronal CXCR4 facilitates an elevation in intracellular Ca 2+ and subsequent increase in synaptic activity [75].…”