Abstract
NF-κB signaling pathways are dysregulated in both the central nervous system (CNS) and peripheral blood cells in multiple sclerosis (MS), but the cause of this is unknown. We have recently reported that peripheral blood mononuclear cells (PBMC) of patients with MS have increased constitutive activation and translocation of the transcription factor NF-κB to the nucleus compared to healthy subjects. NF-κB can be activated through either canonical or non-canonical pathways. In the canonical pathway, activation of NF-κB is normally negatively regulated by the inhibitor IκB. We therefore hypothesized that the increased activation of NF-κB could be caused by reduced IκB-α in the cells of patients with MS, possibly due to increased activity of the IκB kinase (IKK) complex, which regulates IκB-α. Alternatively, changes to the activity of key molecules in the non-canonical pathway, such as IKKα, could also lead to increased NF-κB activation. We therefore used Western blotting to detect IκB-α levels and ELISA to investigate NF-κB DNA binding activity and phosphorylation of IKKα and IKKβ in samples from PBMC of MS patients and controls. The level of full-length IκB-α protein in the cytosolic fraction of PBMC of MS patients was significantly reduced compared to healthy subjects, with significantly more evidence of multiple low molecular weight putative degradation products of IκB-α present in MS patients compared to healthy subjects. Conversely, the level of NF-κB DNA binding activity was increased in whole cell lysates from MS patients. Both IKKα and IKKβ showed increased overall activity in MS compared to healthy subjects, although not all of the MS patients showed increased activity compared to the healthy subjects, suggesting that there may be several different mechanisms underlying the constitutive activation of NF-κB in MS. Taken together, these findings suggest that there may be multiple points at which the NF-κB pathway is dysregulated in MS and that decreased levels of the full-length IκB-α protein are a major component in this.