Background: NOD2 single nucleotide polymorphisms have been associated with increased risk of ileal Crohn's disease (CD). This exploratory study was conducted to compare ileal mucosal gene expression in CD patients with and without NOD2 risk alleles.
Methods: Ileal samples were prospectively collected from 18 nonsmoking CD patients not treated with anti-TNF-α biologics and 9 nonsmoking control patients without inflammatory bowel disease undergoing initial resection and genotyped for the 3 major NOD2 risk alleles (Arg702Trp, Gly908Arg, Leu1007fs). Microarray analysis was performed in samples from 4 NOD2(R) (at least 1 risk allele) CD patients, 4 NOD2(NR) (no risk alleles) CD patients, and 4 NOD2(NR) controls. Candidate genes selected by significance analysis of microarrays (SAM) were confirmed by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) assays of all the samples.
Results: SAM detected upregulation of 18 genes in affected ileum in NOD2(R) compared to NOD2(NR) CD patients, including genes related to lymphocyte activation. SAM also detected altered ileal gene expression in unaffected NOD2(NR) ileal mucosal CD samples compared to NOD2(NR) control samples. qRT-PCR conducted on all the samples confirmed that increased CD3D expression in affected samples was associated with NOD2(R) status, and that increased MUC1, DUOX2, DMBT1 and decreased C4orf7 expression in unaffected samples was associated with CD, independent of NOD2 status.
Conclusions: The results support the concept that NOD2 risk alleles contribute to impaired regulation of inflammation in the ileum. Furthermore, altered ileal gene expression, independent of NOD2 status, is detected in the unaffected proximal margin of resected ileum from CD patients.