title: Fractalkine/CX3CL1 protects striatal neurons from synergistic morphine and HIV-1 Tat-induced dendritic losses and death.
abstract: BACKGROUND
  Fractalkine/CX3CL1 and its cognate receptor CX3CR1 are abundantly expressed in the CNS. Fractalkine is an unusual C-X3-C motif chemokine that is important in neuron-microglial communication, a co-receptor for HIV infection, and can be neuroprotective. To assess the effects of fractalkine on opiate-HIV interactive neurotoxicity, wild-type murine striatal neurons were co-cultured with mixed glia from the striata of wild-type or Cx3cr1 knockout mice ± HIV-1 Tat and/or morphine. Time-lapse digital images were continuously recorded at 20 min intervals for up to 72 h using computer-aided microscopy to track the same cells repeatedly.
  
  
  RESULTS
  Co-exposure to Tat and morphine caused synergistic increases in neuron death, dendritic pruning, and microglial motility as previously reported. Exogenous fractalkine prevented synergistic Tat and morphine-induced dendritic losses and neuron death even though the inflammatory mediator TNF-α remained significantly elevated. Antibody blockade of CX3CR1 mimicked the toxic effects of morphine plus Tat, but did not add to their toxicity; while fractalkine failed to protect wild-type neurons co-cultured with Cx3cr1-/--null glia against morphine and Tat toxicity. Exogenous fractalkine also normalized microglial motility, which is elevated by Tat and morphine co-exposure, presumably limiting microglial surveillance that may lead to toxic effects on neurons. Fractalkine immunofluorescence was expressed in neurons and to a lesser extent by other cell types, whereas CX3CR1 immunoreactivity or GFP fluorescence in cells cultured from the striatum of Cx3cr1-/- (Cx3cr1GFP/GFP) mice were associated with microglia. Immunoblotting shows that fractalkine levels were unchanged following Tat and/or morphine exposure and there was no increase in released fractalkine as determined by ELISA. By contrast, CX3CR1 protein levels were markedly downregulated.
  
  
  CONCLUSIONS
  The results suggest that deficits in fractalkine-CX3CR1 signaling contribute to the synergistic neurotoxic effects of opioids and Tat. Importantly, exogenous fractalkine can selectively protect neurons from the injurious effects of chronic opioid-HIV-1 Tat co-exposure, and this suggests a potential therapeutic course for neuroAIDS. Although the cellular mechanisms underlying neuroprotection are not certain, findings that exogenous fractalkine reduces microglial motility and fails to protect neurons co-cultured with Cx3cr1-/- mixed glia suggest that fractalkine may act by interfering with toxic microglial-neuron interactions.
authors.affiliation: Department of Pharmacology and Toxicology, Virginia Commonwealth University School of Medicine, Richmond, VA 23298-0613, USA.
authors.forename: Masami
authors.initials: M
authors.lastname: Suzuki
authors.forename: Nazira
authors.initials: N
authors.lastname: El-Hage
authors.forename: Shiping
authors.initials: S
authors.lastname: Zou
authors.forename: Yun-Kyung
authors.initials: YK
authors.lastname: Hahn
authors.forename: Mary E
authors.initials: ME
authors.lastname: Sorrell
authors.forename: Jamie L
authors.initials: JL
authors.lastname: Sturgill
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Conrad
authors.forename: Pamela E
authors.initials: PE
authors.lastname: Knapp
authors.forename: Kurt F
authors.initials: KF
authors.lastname: Hauser
mesh_terms: D000818:Animals; D016923:Cell Death / Q000187:drug effects; D002465:Cell Movement / Q000502:physiology; D002478:Cells, Cultured; D054428:Chemokine CX3CL1 / Q000172:deficiency / Q000378:metabolism*; D018920:Coculture Techniques; D003342:Corpus Striatum / Q000187:drug effects / Q000378:metabolism*; D003712:Dendrites / Q000187:drug effects / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D015497:HIV-1; D051379:Mice; D018345:Mice, Knockout; D017628:Microglia / Q000378:metabolism; D009020:Morphine / Q000008:administration & dosage / Q000633:toxicity*; D009294:Narcotics / Q000633:toxicity*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D054322:tat Gene Products, Human Immunodeficiency Virus / Q000633:toxicity*
chemical_list: D054428:Chemokine CX3CL1; C515539:Cx3cl1 protein, mouse; D009294:Narcotics; D054322:tat Gene Products, Human Immunodeficiency Virus; D009020:Morphine
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