Activation of NOD2-mediated intestinal pathway in a pediatric population with Crohn's disease.

BACKGROUND: NOD2 is an intracellular protein involved in host recognition of specific bacterial molecules and is genetically associated with several inflammatory diseases, including Crohn's disease (CD). NOD2 stimulation activates the transcription factor, NF-kappaB, through RIP2, a caspase-recruitment domain-containing kinase. NOD2/RIP2 signaling also mediates the activation of antimicrobial peptides such as human alpha-defensin 5 (HD-5) and human alpha-defensin 6 (HD-6), both produced by Paneth cells. The present study is aimed at describing the downstream events triggered specifically by NOD2 induction in order to demonstrate that the protein, other than overexpressed, is also physiologically associated with RIP2 and Erbin in the bioptic intestinal inflamed specimens of children affected by CD.

METHODS: Fifteen children with CD and 10 children used as controls were entered in the study. Mucosal biopsy specimens were taken during endoscopy and mRNA and protein expressions were detected by using real-time polymerase chain reaction and Western blot.

RESULTS: NOD2 is able to form an immunocomplex with the kinase RIP2. As compared to controls, in the inflamed mucosa of patients both mRNA and protein expression levels of RIP2 are increased, and its active phosphorylated form is overexpressed.

CONCLUSIONS: In this study we provide for the first time ex vivo evidence of physiologically relevant protein interactions with NOD2, which are able to trigger the innate immune response in intestinal mucosal specimens of children with CD.