INFLAMMATORY BOWEL DISEASE Activation of nuclear factor kB 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 kB (NFkB) is a major inducer of iNOS gene expression, we compared activation and transcriptional activity of NFkB 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: NFkB DNA binding activity was assessed by electrophoretic mobility shift assay and inhibitor of NFkB (IkB) kinase (IKK) activity by immunocomplex kinase assay. In vivo recruitment of NFkB to the iNOS promoter was determined by chromatin immunoprecipitation analysis and transcriptional activity by NFkB gene expression profiling arrays. Cells showing NFkB activation were identified by immunohistochemistry. Results: In collagenous and ulcerative colitis, as opposed to uninflamed bowel, IKKb activity and strong NFkB DNA binding gave rise to activation of identical NFkB subunits and recruitment of transcriptionally active p65 to the iNOS promoter. In collagenous colitis, activated NFkB 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 NFkB is activated and recruited to the iNOS promoter in vivo via an IKKb mediated pathway. As collagenous colitis is not associated with tissue injury, these data challenge the prevailing view that activation of NFkB per se mediates tissue injury. Our results suggest that downstream inflammatory reactions leading to tissue damage originate in lamina propria immune cells, as increased NFkB activity in collagenous colitis was localised solely in epithelial cells, but present also in macrophages in ulcerative colitis.