Endotoxin-mediated regulation of nuclear factor-kappaB nuclear translocation and activation in the hippocampus of the central nervous system: modulation by intracerebroventricular treatment with thymulin and the immunomodulatory role of the IkappaB-alpha/pIkappaB-alpha pathway.

The transcription factor nuclear factor kappaB (NF-kappaB) is one member of a ubiquitously expressed family of Rel-related transcription factors that serve as critical regulators of many proinflammatory genes and immunomodulators. Nevertheless, the immunomodulatory potential of thymulin and its effect on NF-kappaB in vivo, and particularly in the central nervous system (CNS), is not well characterized. In this study, the role of endotoxin (ET/LPS) in regulating NF-kappaB was deciphered in various compartments of the CNS. Stereotaxic localization reverberated specific intracerebroventricular (ICV) injection of ET into the CNS, with or without pretreatment with ICV thymulin. Treatment with ET (1 microg for 45 min; ICV) upregulated the expression and nuclear localization of NF-kappaB(1) (p50), NF-kappaB(2) (p52), RelA (p65), RelB (p68) and c-Rel (p75) in the hippocampus (HC), an effect abrogated, in a dose-dependent manner, by ICV pretreatment (30 min) with thymulin. Thymulin modulated the phosphorylation of IkappaB-alpha in the HC by upregulating the cytosolic accumulation of IkappaB-alpha and downregulating its phosphorylation (pIkappaB-alpha). Further analysis of the DNA-binding activity revealed an upregulated activity in the HC relative to saline-constitutive expression of the RelA (p65) subunit, the specificity of which was determined by a mutant oligonucleotide of RelA and a cold, non-specific competitor. ET did not induce the DNA-binding activity of NF-kappaB in the diencephalon (DE) or substantia nigra (SN) at various time points, when compared with baseline levels of expression. Intraperitoneal (IP) injections of ET (25 microg for 15 min) in vivo upregulated the expression of NF-kappaB subunits in the liver and reduced the cytosolic accumulation of IkappaB-alpha by inducing pIkappaB-alpha. Furthermore, IP pretreatment with thymulin followed by ICV injection of ET attenuated and reduced the DNA-binding activity of NF-kappaB in the HC. These results indicate that ICV injection of ET regulates the nuclear translocation and activation of NF-kappaB subunits within specific compartments in the brain, an effect particularly localized to the hippocampus. Additionally, thymulin attenuated the ET-induced response, with particular involvement of the transduction pathway implicating IkappaB-alpha, the major cytosolic inhibitor of NF-kappaB. The in vivo molecular regulation of thymulin via the NF-kappaB pathway is critical to understanding the alleviating anti-inflammatory role of this nonapeptide and paving the way to unraveling pathways associated with neuroimmune interactions mediating proinflammatory signals in the CNS.