Inhibition of tumour necrosis factor‐α (TNFα)‐induced NF‐κB p52 converts the metabolic effects of microglial‐derived TNFα on mouse cerebellar neurones to neurotoxicity

Abstract

Activated microglia are implicated in the injury of neurones and macroglia both in vitro and in vivo. Here, we demonstrate that media conditioned by interferon-γ treated microglia initially impair the metabolism of mouse cerebellar neurones grown in serum-free conditions without inducing cell death. Metabolic effects include inhibition of the ability of mitochondria to reduce 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) and cytochrome oxidase activity. These effects are blocked by antibodies to tumour necrosis factor-α (TNFα), a cytokine produced by microglial activation, and they are not reproduced by media conditioned by resting microglia. The metabolic effects are evident for up to 24 h in vitro. More prolonged exposure, up to 48 h, results in TNFα dependent neuronal death as previously observed. Between 2 and 48 h TNFα present in media conditioned by interferon-γ treated but not resting microglia is associated with nuclear factor kappa B (NF-κB) consensus sequence binding in paired mouse cerebellar neuronal cultures without affecting activation of the signal transducer and activator of transcription (STAT) transcription factor. Neuronal death can be accelerated by peptide blockade of the nuclear transport of NF-κB p52 subunit during exposure of cerebellar neurones to medium from interferon-γ treated microglia. This toxicity is blocked by anti-TNFα antibody. Soluble factors released by activated microglia therefore contribute to neuronal dysfunction that is initially reversible but may culminate in neurotoxicity. Characterizing and manipulating these events in vivo theoretically provides an opportunity for neuroprotection in selected diseases affecting the central nervous system.