HIV-1 infected individuals who are injecting opioid drugs show increased cognitive defects and undergo an accelerated rate of progression to AIDS. Accumulating evidence suggests that opioid drug abuse intrinsically exacerbates the pathogenesis of HIV-1. We have found that neuronal death is preceded by a prolonged period of synaptic culling, functional losses, and dendritic pathology that are presumed reversible. Importantly, opioid abuse potentiates the neuropathogenesis of HIV-1 by synergistically increasing dendritic pathology (varicosity formation, beading, fragmentation, pruning), while promoting additive dendritic spine losses (plasticity). This has been verified in medium spiny neurons (MSN) of the striatum and synaptic pruning has been confirmed electron microscopically. Moreover, behavioral defects in locomotor activity are accompanied by synaptic losses and dendritic pathology in the absence of demonstrable neuron death, suggesting that sublethal neuronal injury and reduced synaptic connectivity underlie the ability of opioids to aggravate HIV-1-associated neurological disorders (HAND). While death per se is significant, the interruption of events preceding neuron death may be more strategic therapeutically. This grant will focus on the functional level of MSN by investigating the underlying physiological mechanisms of opioid +/- HIV-induced excitotoxicity. It is hypothesized that Tat induces changes in the cellular homeostasis and excitability of MSN that are exacerbated by opioid drugs through a complex sequence of events involving OR-mediated pathways. In vitro approaches are being proposed by assessing the effects of opioid drug and HIV-1 Tat-induced neurotoxicity in dissociated cortical-striatal cell cultures. Whole-cell patch-clamp recordings wil be conducted in voltage- and current-clamp mode by assessing action potentials as well as sodium, potassium, AMPA, NMDA, and calcium (Ca2+) currents. The role of OR will be elucidated by applying pharmacological (OR antagonists), genetic (OR knockout mice) and silencing (silencing NMDAR) strategies to identify mechanisms underlying opioid + HIV protein interaction. To sort out whether opioids exacerbate the excitotoxic effects of Tat in the striatum via OR on MSN we will conduct experiments in vivo using two types of Cre-lox mice. Conditionally deleting OR at key sites will define the targets and associated mechanisms by which opioids exacerbate neuronal excitability (action potentials, ion channel activity, ion imaging, mitochondrial membrane potential), injury (including dendritic pathology and spine density), and behavioral defects (locomotor activity) in the striatum.
Opioids can exacerbate the excitotoxic effects of HIV-1 products by activating opioid receptor (OR)-mediated pathways in striatal neurons. Excitotoxicity involves overactivation of NMDA and AMPA receptors, a loss in cellular homeostasis, and calcium overload, which can result in a loss of synaptic spines, sublethal dendritic injury, and behavioral deficits. Finding treatments for preventing or reversing sublethal neuronal injury that precedes permanent neuronal losses will determine best therapeutic strategies for limiting neurocognitive deficits seen in HIV-1 positive drug abusers.
|Marks, William D; Paris, Jason J; Schier, Christina J et al. (2016) HIV-1 Tat causes cognitive deficits and selective loss of parvalbumin, somatostatin, and neuronal nitric oxide synthase expressing hippocampal CA1 interneuron subpopulations. J Neurovirol 22:747-762|
|Fitting, Sylvia; Stevens, David L; Khan, Fayez A et al. (2016) Morphine Tolerance and Physical Dependence Are Altered in Conditional HIV-1 Tat Transgenic Mice. J Pharmacol Exp Ther 356:96-105|
|Fitting, Sylvia; Booze, Rosemarie M; Mactutus, Charles F (2015) HIV-1 proteins, Tat and gp120, target the developing dopamine system. Curr HIV Res 13:21-42|
|Fitting, S; Ngwainmbi, J; Kang, M et al. (2015) Sensitization of enteric neurons to morphine by HIV-1 Tat protein. Neurogastroenterol Motil 27:468-80|
|Ellis, Kelstan; Marlin, Jerry W; Taylor, Tracey A H et al. (2015) The effects of human immunodeficiency virus infection on the expression of the drug efflux proteins P-glycoprotein and breast cancer resistance protein in a human intestine model. J Pharm Pharmacol 67:178-88|
|Zou, Shiping; Fuss, Babette; Fitting, Sylvia et al. (2015) Oligodendrocytes Are Targets of HIV-1 Tat: NMDA and AMPA Receptor-Mediated Effects on Survival and Development. J Neurosci 35:11384-98|
|Fitting, Sylvia; Knapp, Pamela E; Zou, Shiping et al. (2014) Interactive HIV-1 Tat and morphine-induced synaptodendritic injury is triggered through focal disruptions in Na? influx, mitochondrial instability, and Ca²? overload. J Neurosci 34:12850-64|
|Fitting, Sylvia; Zou, Shiping; El-Hage, Nazira et al. (2014) Opiate addiction therapies and HIV-1 Tat: interactive effects on glial [Ca²?]i, oxyradical and neuroinflammatory chemokine production and correlative neurotoxicity. Curr HIV Res 12:424-34|
|Ngwainmbi, Joy; De, Dipanjana D; Smith, Tricia H et al. (2014) Effects of HIV-1 Tat on enteric neuropathogenesis. J Neurosci 34:14243-51|