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MEDIATORS OF INFLAMMATION IN ACUTE NEUROTOXICITY
[Thesis]. Manchester, UK: The University of Manchester; 2013.
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Abstract
Neuroinflammation is a major feature of most neurodegenerative conditions, and can leadto the exacerbation of neuronal injury. Inflammatory challenges in the central nervoussystem (CNS) have been shown to activate peripheral immune cells, which subsequentlyinfiltrate into the brain. Concurrently, resident inflammatory cells in the CNS, such asmicroglia, become activated and release inflammatory mediators, including cytokines.The pro-inflammatory cytokine interleukin-1 (IL-1) is a key mediator of neuronal injury.Although two IL-1 agonists exist, IL-1α and IL-1β, the majority of research has focussedon the contribution of IL-1β to neuronal injury. Excitotoxic cell death in the rat brain,induced by striatal injection of the glutamate agonist AMPA, is exacerbated by coadministrationof recombinant IL-1β. To identify possible mediators which facilitate theexacerbation of neuronal injury by IL-1 this study investigated the early peripheral andcentral mediators of inflammation in response to AMPA + IL-1β.Neutrophil infiltration and increased neuronal activity were found to be present at 4h post-AMPA + IL-1β injection, which lead to the induction of microglial IL-1α in the ipsilateralcortex, in the absence of any IL-1β expression. To target the peripheral neutrophil responsean intervention study was performed to inhibit peripheral TNFα, which is thought tomobilise neutrophils. No significant effect of pre-treatment with etanercept, a TNFαinhibitor, was observed on neuronal injury produced in response to AMPA + IL-1β, thougha slight trend for protection was seen. To target the central IL-1α response after AMPA +IL-1β treatment an anti-IL-1α antibody was injected directly into the cerebral cortex, butthis had no effect on AMPA + IL-1β induced cell death. Therefore, using a reductionist invitro approach in organotypic slice cultures haemin, an inducer of endogenous IL-1α, wasused to investigate IL-1α mediated cell death. Haemin induced cell death was shown to beIL-1 dependent and preliminary studies using IL-1αKO mice indicated that IL-1α maypartially mediate this effect. This suggests that in the AMPA + IL-1β paradigm IL-1α is thedominant IL-1 isoform early after AMPA + IL-1β treatment, which can trigger subsequentneuronal cell death, as a result of the additive effects of neutrophil infiltration and highneuronal activity in the cortex. This study highlights the potential therapeutic value ofinhibiting IL-1α expression early following acute neuronal injury.