Biphasic NF-kappaB activation in the excitotoxic hippocampus

Area of Science:

• Neuroscience
• Molecular Biology
• Cellular Biology

Background:

• Excitotoxic stimulation of NMDA receptors triggers neuronal responses.
• The inducible transcription factor NF-kappaB plays a role in these excitotoxic responses.

Purpose of the Study:

• To investigate the temporal profile of NF-kappaB activation in hippocampal slices following NMDA exposure.
• To elucidate the role of IkappaB inhibitors in the biphasic NF-kappaB activation.
• To examine the distinct gene regulation events associated with each phase of NF-kappaB activity.

Main Methods:

• NMDA exposure in hippocampal slices.
• Analysis of NF-kappaB activation patterns over time.
• Examination of IkappaBalpha, IkappaBbeta, and p105 degradation.
• Assessment of bcl-2 and bax gene expression.
• Use of NMDA receptor antagonist AP5.

Main Results:

• NF-kappaB activation occurred in a biphasic manner: an early phase (0.5-1 h) and a delayed phase (10-24 h).
• IKappaBbeta degradation correlated with both phases of NF-kappaB activation; IkappaBalpha and p105 levels remained unchanged.
• Both phases were sensitive to AP5 but differed in complex composition and response to culture conditions.
• Early NF-kappaB activity was linked to bcl-2 up-regulation, while delayed activity correlated with increased bax expression.

Conclusions:

• Excitotoxic insults induce distinct biphasic NF-kappaB activation in the hippocampus.
• These phases are mediated by differential IkappaBbeta degradation and are associated with distinct gene expression profiles.
• The biphasic NF-kappaB activation may orchestrate opposing cellular responses to excitotoxicity.