Activation of nuclear factor κB in colonic mucosa from patients with collagenous and ulcerative colitis

Background and aims: Expression of inducible nitric oxide synthase (iNOS) is greatly upregulated in the colonic mucosa of patients with collagenous and ulcerative colitis. As the transcription factor nuclear factor kappa B (NF kappa B) is a major inducer of iNOS gene expression, we compared activation and transcriptional activity of NF kappa B in colonic mucosal biopsies from these patients. Patients: Eight patients with collagenous colitis, six with relapsing ulcerative colitis, and eight with uninflamed bowel were studied. Methods: NF kappa B DNA binding activity was assessed by electrophoretic mobility shift assay and inhibitor of NF kappa B (I kappa B) kinase (IKK) activity by immunocomplex kinase assay. In vivo recruitment of NF kappa B to the iNOS promoter was determined by chromatin immunoprecipitation analysis and transcriptional activity by NF kappa B gene expression profiling arrays. Cells showing NF kappa B activation were identified by immunohistochemistry. Results: In collagenous and ulcerative colitis, as opposed to uninflamed bowel, IKK beta activity and strong NF kappa B DNA binding gave rise to activation of identical NF kappa B subunits and recruitment of transcriptionally active p65 to the iNOS promoter. In collagenous colitis, activated NF kappa B was observed only in epithelial cells while up to 10% of lamina propria macrophages showed activation in ulcerative colitis. Conclusions: In collagenous and ulcerative colitis, colonic mucosal NF kappa B is activated and recruited to the iNOS promoter in vivo via an IKK beta mediated pathway. As collagenous colitis is not associated with tissue injury, these data challenge the prevailing view that activation of NF kappa B per se mediates tissue injury. Our results suggest that downstream inflammatory reactions leading to tissue damage originate in lamina propria immune cells, as increased NF kappa B activity in collagenous colitis was localised solely in epithelial cells, but present also in macrophages in ulcerative colitis.