Molecular Mechanisms of Cytokine-Induced Neuroprotection: NFκB and Neuroplasticity

Abstract

Since the first attempts to understand the mechanisms of learning, memory, development, and other instances of neuroplasticity, gene expression has been an attractive explanation for the persistence of such processes. It has been hypothesized that changes in the levels of expression of a gene, or a coordinated set of genes, would be necessary for dramatic structural changes like the growth of new neurites. And more subtle biochemical changes at existing synapses might also result from an alteration in the array of gene products being manufactured in the relevant cells. However, a great deal of what is classified as neuroplasticity is dependent on primary changes in electrophysiological activity or other conditions at synapses. Therefore, a seminal question to those interested in the molecular underpinnings of neuroplasticity is that of signal transduction: How do changes in synaptic activity get communicated to the nucleus? To many who learn about the regulation of the transcription factor NFkappaB with this question in mind, its utility seems clear. Furthermore, NFkappaB is an important signaling factor for cytokines that appear to participate in several pathological conditions (e.g., Parkinson's disease, multiple sclerosis, and depression), so understanding its mechanisms of action and its relationship to other elements of cytokine signaling may be fundamental to determining the role of the inflammatory system in psychiatric and neurodegenerative conditions. For these reasons, NFkappaB has garnered considerable attention in various aspects of neuroplasticity, from long-term potentiation to the most dramatic forms of plasticity: cell birth and death. In a few cases, elegant experimental design has resulted in convincing evidence for the involvement of NFkappaB in specific phenomena. However, the complexity of this transcription factor-including confusion over what exactly is meant by "NFkappaB"-has led to some misleading conclusions, as well. This chapter highlights some of the potential red herrings to be encountered in the study of NFkappaB and will summarize the data and interpretations in which some degree of confidence can be placed. The final answers will depend on the application of models and tools only now in development.

Differential Transcriptional Control of the Superoxide Dismutase-2 κB Element in Neurons and Astrocytes

“…The influence of p65 was completely blocked by IB␣ co-transfection, consistent with our previous observation (32). Application of Sp1 decoy oligonucleotides and IB␣ to primary astrocytes yielded results very different from those observed in neurons (Fig.…”

“…The situation in CNS neurons appears to be an extreme example. Evidence indicates that DNA-binding activity from bona fide NFB is severely restricted in CNS neurons (17,19,20,32) (Fig. 3B), making the role of Sp-factors in these cells much more critical.…”

“…1732 641, Roche Applied Science) and cloned in-frame into pEFGP-N1 (p65) or pDsRed2-N1 (IB␣) (BD BiosciencesClontech, Mountain View CA), creating p65-EGFP and IBDsRed2 fusion proteins. Clones were verified by sequencing, and p65-EGFP proteins were located in nuclei while IB␣ cotransfection retained all p65-EGFP in cytosol (32). The pRL-CMV (Promega) plasmid expressing Renilla luciferase constitutively was used as a control for transfection efficiency and viability.…”

Cautionary notes on the use of NF-κB p65 and p50 antibodies for CNS studies

“…The lack of neuronal NF-κB response observed with the authentic p65 antibodies is a finding consistent with studies employing in situ hybridization histochemistry showing non-neuronal localization of induced IκBα mRNA expression in injury, infection, and pain models [20,54-56] and of known NF-κB-regulated genes in similar models [57-61]. Future studies with validated monoclonal antibodies and molecular tools such as a knock-in p65-GFP fusion protein [62] (but note the caveats associated with this approach [63]) will provide the proper means to address the cellular localization of NF-κB activation in the brain.…”

The cellular response in neuroinflammation: The role of leukocytes, microglia and astrocytes in neuronal death and survival

“…Recent data clearly refutes this view. For example, NF-κB is an inducible transcription factor that initiates the subsequent expression of several inflammatory molecules [12,13]. Several studies now indicate that neuronal expression of NF-κB is induced by a variety of insults, including TNF and mechanical injury and that this neuronal induction is associated with subsequent neuronal expression of inducible nitric oxide synthase (INOS) and superoxide dismutase (SOD) [14][15][16][17].…”