Microglia enhance β-amyloid peptide-induced toxicity in cortical and mesencephalic neurons by producing reactive oxygen species

Authors

  • Liya Qin,

    1. Neuropharmacology Section, Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA
    Search for more papers by this author
    • 1

      Liya Qin is a winner of the National Institutes of Health Fellow's Award for Research Excellence of the year 2001.

  • Yuxin Liu,

    1. Neuropharmacology Section, Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA
    Search for more papers by this author
  • Cynthia Cooper,

    1. Division of Science, Truman State University, Kirksville, Missouri, USA
    Search for more papers by this author
  • Bin Liu,

    1. Neuropharmacology Section, Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA
    Search for more papers by this author
  • Belinda Wilson,

    1. Neuropharmacology Section, Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA
    Search for more papers by this author
  • Jau-Shyong Hong

    1. Neuropharmacology Section, Laboratory of Pharmacology and Chemistry, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA
    Search for more papers by this author

Address correspondence and reprint requests to Liya Qin, PhD, MD F1-01 NIEHS, PO Box 12233, Research Triangle Park, NC 27709, USA. E-mail: qin1@niehs.nih.gov

Abstract

The purpose of this study was to assess and compare the toxicity of β-amyloid (Aβ) on primary cortical and mesencephalic neurons cultured with and without microglia in order to determine the mechanism underlying microglia-mediated Aβ-induced neurotoxicity. Incubation of cortical or mesencephalic neuron-enriched and mixed neuron–glia cultures with Aβ(1–42) over the concentration range 0.1–6.0 μm caused concentration-dependent neurotoxicity. High concentrations of Aβ (6.0 μm for cortex and 1.5–2.0 μm for mesencephalon) directly injured neurons in neuron-enriched cultures. In contrast, lower concentrations of Aβ (1.0–3.0 μm for cortex and 0.25–1.0 μm for mesencephalon) caused significant neurotoxicity in mixed neuron–glia cultures, but not in neuron- enriched cultures. Several lines of evidence indicated that microglia mediated the potentiated neurotoxicity of Aβ, including the observations that low concentrations of Aβ activated microglia morphologically in neuron–glia cultures and that addition of microglia to cortical neuron–glia cultures enhanced Aβ-induced neurotoxicity. To search for the mechanism underlying the microglia-mediated effects, several proinflammatory factors were examined in neuron–glia cultures. Low doses of Aβ significantly increased the production of superoxide anions, but not of tumor necrosis factor-α, interleukin-1β or nitric oxide. Catalase and superoxide dismutase significantly protected neurons from Aβ toxicity in the presence of microglia. Inhibition of NADPH oxidase activity by diphenyleneiodonium also prevented Aβ-induced neurotoxicity in neuron–glia mixed cultures. The role of NADPH oxidase-generated superoxide in mediating Aβ-induced neurotoxicity was further substantiated by a study which showed that Aβ caused less of a decrease in dopamine uptake in mesencephalic neuron–glia cultures from NADPH oxidase-deficient mutant mice than in that from wild-type controls. This study demonstrates that one of the mechanisms by which microglia can enhance the neurotoxicity of Aβ is via the production of reactive oxygen species.

Ancillary