Date of Award

11-19-2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Colin K. Combs

Abstract

Multiple cytokines are secreted in the brain during inflammatory conditions and likely affect neuronal survival. Previous studies demonstrated that glutamate and tumor necrosis factor alpha (TNFα) kill neurons via activation of the NMDA and TNFα receptors, respectively. Nevertheless the mechanisms of neuronal death are not completely elucidated. The goal of this study was to characterize the signaling cross-talk pathway initiated during this inflammation-related mechanism of cell death. Stimulation of mouse cortical neuron cultures with TNFα resulted in a transient increase in NMDA receptor-dependent calcium influx that is additive with NMDA stimulation and inhibited by pretreatment with the NMDA receptor antagonist. Combined TNFα and NMDA stimulation resulted in a transient increase in activation of ERK and JNK. Specific inhibition of ERK but not JNK was protective against TNFα and NMDA receptor-dependent death. Death was mediated via the low affinity TNFα receptor, TNFRII, as observed by stimulation of NMDA receptor-dependent calcium influx. These data demonstrated how microglial proinflammatory secretions including TNFα can acutely facilitate glutamate-dependent neuronal death. The previous studies were performed with mouse cortical neurons relatively resistant to NMDA receptor-dependent toxicity. Using immature and mature murine cortical neuron cultures, we further demonstrated a detrimental role of TNFα through its TNFRII via modulation of NMDA receptor activity and cell-surface localization. NMDA receptor-dependent toxicity of both immature and mature neuron cultures was enhanced by co-stimulation of TNFRII but not TNFRI involving elevated NMDA receptor-mediated calcium influx. However, stimulation of TNFRII alone was sufficient to induce neuronal death only in mature cultures. Furthermore, we found that TNFRII stimulation in mature neuron cultures led to increased NR1 subunit cell surface localization in both synaptic and extrasynaptic compartments. The TNFRII-stimulated change in NR1 localization was mediated by PKC activation. Also, we provide evidence that preconditioning with oligomeric Aβ reduced TNFRII stimulated death and changes in NR1 localization. These data suggests that TNFα-stimulated effects on neuron phenotype and viability are age specific and mechanistically diverse even in the same neuron population. Understanding the contribution of TNFα to health and disease in the CNS must involve paradigm specific elucidation.

Download

Share

COinS