Role of nuclear factor kappa B in central nervous system regeneration

Activation of nuclear factor kappa B (NF-KB) is a hallmark of various central nervous system (CNS) pathologies. Neuron-specific inhibition of its transcriptional activator subunit RelA, also referred to as p65, promotes neuronal survival under a range of conditions, i.e., for ischemic or excitotoxic insults. In macro- and microglial cells, post-lesional activation of NF-KB triggers a growth-permissive program which contributes to neural tissue inflammation, scar formation, and the expression of axonal growth inhibitors. Intriguingly, inhibition of such inducible NF-KB in the neuro-glial compartment, i.e., by genetic ablation of RelA or overexpression of a trans-dominant negative mutant of its upstream regulator IKB alpha, significantly enhances functional recovery and promotes axonal regeneration in the mature CNS. By contrast, depletion of the NF-KB subunit p50, which lacks transcriptional activator function and acts as a transcriptional repressor on its own, causes precocious neuronal loss and exacerbates axonal degeneration in the lesioned brain. Collectively, the data imply that NF-KB orchestrates a multicellular program in which KB-dependent gene expression establishes a growth-repulsive terrain within the post-lesioned brain that limits structural regeneration of neuronal circuits. Considering these subunit-specific functions, interference with the NF-KB pathway might hold clinical potentials to improve functional restoration following traumatic CNS injury.