NF-κB activation by oxidative stress and inflammation suppresses contractility in colonic circular smooth muscle cells

Background & Aims: Transcription factor nuclear factor κB (NF-κB) plays a critical role in transcriptional changes in several diseases, including inflammation. The aim of this study was to investigate whether NF-κB is activated by inflammation and oxidative stress in colonic circular smooth muscle cells and whether that leads to suppression of their contractility. Methods: The experiments were performed on freshly dissociated single cells using electrophoretic mobility shift assay, Western immunoblotting, and immunofluorescence imaging. Results: The NF-κB DNA binding was ∼6-fold greater in cells from the inflamed colon vs. those from the normal colon. Supershift assay indicated that the antibodies to p65, p50, and c-Rel, but not that to p52, shifted the NF-κB band. Western immunoblotting and immunofluorescence imaging also demonstrated the presence of p65, p50, and c-Rel proteins in the cytoplasm and their translocation to the nucleus by H₂O₂-induced oxidative stress. H₂O₂ treatment degraded IκB_β, but not IκB_α to translocate NF-κB to the nucleus. Hydrogen peroxide concentration and time dependently activated NF-κB DNA binding and suppressed cell contraction to acetylcholine. NF-κB inhibitors significantly inhibited these effects. Inhibition of NF-κB prior to and during inflammation in intact dogs also reversed the suppression of contractility. Conclusions: Transcription factor NF-κB is activated in colonic circular muscle cells by inflammation and oxidative stress. This activation of NF-κB mediates the suppression of cell contractility.