Nod2 in normal and abnormal intestinal immune function

The NOD2 single nucleotide polymorphisms rs2066843 and rs2076756 are novel and common Crohn's disease susceptibility gene variants

Background

The aims were to analyze two novel NOD2 variants (rs2066843 and rs2076756) in a large cohort of patients with inflammatory bowel disease and to elucidate phenotypic consequences.

Methodology/Principal Findings

Genomic DNA from 2700 Caucasians including 812 patients with Crohn's disease (CD), 442 patients with ulcerative colitis (UC), and 1446 healthy controls was analyzed for the NOD2 SNPs rs2066843 and rs2076756 and the three main CD-associated NOD2 variants p.Arg702Trp (rs2066844), p.Gly908Arg (rs2066847), and p.Leu1007fsX1008 (rs2066847). Haplotype and genotype-phenotype analyses were performed. The SNPs rs2066843 (p = 3.01×10⁻⁵, OR 1.48, [95% CI 1.23-1.78]) and rs2076756 (p = 4.01×10⁻⁶; OR 1.54, [95% CI 1.28-1.86]) were significantly associated with CD but not with UC susceptibility. Haplotype analysis revealed a number of significant associations with CD susceptibility with omnibus p values <10⁻¹⁰. The SNPs rs2066843 and rs2076756 were in linkage disequilibrium with each other and with the three main CD-associated NOD2 mutations (D'>0.9). However, in CD, SNPs rs2066843 and rs2076756 were more frequently observed than the other three common NOD2 mutations (minor allele frequencies for rs2066843 and rs2076756: 0.390 and 0.380, respectively). In CD patients homozygous for these novel NOD2 variants, genotype-phenotype analysis revealed higher rates of a penetrating phenotype (rs2076756: p = 0.015) and fistulas (rs2076756: p = 0.015) and significant associations with CD-related surgery (rs2076756: p = 0.003; rs2066843: p = 0.015). However, in multivariate analysis only disease localization (p<2×10⁻¹⁶) and behaviour (p = 0.02) were significantly associated with the need for surgery.

Conclusion/Significance

The NOD2 variants rs2066843 and rs2076756 are novel and common CD susceptibility gene variants.

Interactions of the intestinal epithelium with the pathogen and the indigenous microbiota: a three-way crosstalk

The mucosal surfaces of the gastrointestinal tract harbor a vast number of commensal microbiota that have coevolved with the host, and in addition display one of the most complex relationships with the host. This relationship affects several important aspects of the biology of the host including the synthesis of nutrients, protection against infection, and the development of the immune system. On the other hand, despite the existence of several lines of mucosal defense mechanisms, pathogenic organisms such as Shigella and Salmonella have evolved sophisticated virulence strategies for breaching these barriers. The constant challenge from these pathogens and the attempts by the host to counter them set up a dynamic equilibrium of cellular and molecular crosstalk. Even slight perturbations in this equilibrium may be detrimental to the host leading to severe bacterial infection or even autoimmune diseases like inflammatory bowel disease. Several experimental model systems, including germ-free mice and antibiotic-treated mice, have been used by various researchers to study this complex relationship. Although it is only the beginning, it promises to be an exciting era in the study of these host-microbe relationships.

The expanding universe of inflammatory bowel disease genetics

PURPOSE OF REVIEW

Genetic factors play an important role in the pathogenesis of inflammatory bowel disease. In this review, we will provide an update on the rapid advances in the discovery of inflammatory bowel disease, primarily Crohn's disease, associated genes.

RECENT FINDINGS

Seven recently published Crohn's disease genome-wide association studies have confirmed prior findings related to the nucleotide-binding oligomerization domain 2 (NOD2) gene and the IBD5 locus. In addition, 10 novel loci have been identified and well replicated.

SUMMARY

Several promising associations between Crohn's disease and gene variants have been identified and replicated, the two most widely replicated being variants in the IL23R and ATG16L1 genes. These findings highlight and further support the importance of the immune system and its interactions with the intestinal microflora in the pathogenesis of inflammatory bowel disease.

The ATG16L1 gene variants rs2241879 and rs2241880 (T300A) are strongly associated with susceptibility to Crohn's disease in the German population

OBJECTIVES

We analyzed ATG16L1, a recently identified Crohn's disease (CD) susceptibility gene, in a large cohort with inflammatory bowel disease (IBD) including potential interactions with other IBD genes as well as factors regulating its gene expression.

METHODS

Genomic DNA from 2,890 Caucasians including 768 patients with CD, 507 patients with ulcerative colitis (UC), and 1,615 healthy controls was analyzed for 9 different ATG16L1 single nucleotide polymorphisms (SNPs). Genotyping included CARD15/NOD2 variants p.Arg702Trp, p.Gly908Arg, and p.Leu1007fsX1008 and polymorphisms in SLC22A4/OCTN1 (1672 C-->T) and SLC22A5/OCTN2 (-207 G-->C) as well as 10 CD-associated IL23R variants. The transcriptional regulation of ATG16L1 was studied in intestinal epithelial cells following stimulation with Toll-like receptor (TLR) ligands and proinflammatory cytokines and in a murine ileitis model and CD biopsies.

RESULTS

All nine ATG16L1 gene variants analyzed displayed highly significant associations with CD demonstrating a CD-protective effect for the minor allele. The strongest associations were found for rs2241879 and the coding SNP rs2241880 (T300A); P= 3.6 x 10(-6) and 3.7 x 10(-6), respectively (OR 0.74, 95% CI 0.65-0.84 for both variants). The genotype-phenotype analysis revealed no significant associations. In UC, only rs6431660 was weakly disease-associated. There was no evidence for epistasis between the ATG16L1 gene and other susceptibility genes (IL23R, CARD15, SLC22A4/5). ATG16L1 mRNA expression was not upregulated in CD and murine ileitis, and was less than threefold increased in cells stimulated with proinflammatory cytokines and TLR ligands.

CONCLUSION

ATG16L1 is a CD susceptibility gene without epistatic interaction with other CD susceptibility genes and is not upregulated in intestinal inflammation.

IL23R and ATG16L1 SNPs in IBD: alphabet soup or something more?

The results of recently completed genome-wide association studies have rapidly advanced knowledge of inflammatory bowel disease (IBD) genetics. Several promising associations between IBD and gene variants have been identified with the two best replicated so far being variants in the IL23R and ATG16L1 genes. These findings highlight the importance of the immune system and interactions with intestinal microflora in the pathogenesis of IBD.

Crohn's disease: a review of current treatment with a focus on biologics

Crohn's disease is a debilitating and expensive disease that is growing in incidence in both developing and developed countries. While conventional therapies, such as corticosteroids and immunosuppressants, continue to play a vital role in treating this condition, it is evident that many affected individuals do not respond to therapy or develop intolerable adverse effects. The addition of modern biological therapies to the Crohn's disease armamentarium is providing a change in expectations for disease outcome. Infliximab and adalimumab are currently the only biological agents approved for induction and maintenance treatment in adults (infliximab and adalimumab) and children (infliximab) with Crohn's disease. Furthermore, infliximab has a beneficial effect on perianal fistulas. Other tumour necrosis factor (TNF)-alpha inhibitors, such as certolizumab pegol, also demonstrate promising results in adults with moderate to severe active disease. In addition, adalimumab and certolizumab pegol have shown clinical efficacy in patients who are intolerant to or lose response to infliximab, suggesting that switching between agents may allow response to be maintained over time. The primary safety concerns with TNFalpha inhibitors include increased risk of serious infection (including reactivation of tuberculosis), malignancy (particularly lymphoma) and demyelinating disease. Other agents in development include recombinant human anti-inflammatory cytokines, agents that target pro-inflammatory cytokines and granulocyte-macrophage colony-stimulating factors. Further prospective studies will provide interesting insight into different mechanisms by which factors involved in the pathophysiology of Crohn's disease can be modulated.

The effects of NOD2/CARD15 mutations on the function of the intestinal barrier

NOD2 variants have been identified to be a susceptibility factor for Crohn's disease. The NOD2 protein is an intracellular sensor of the bacterial wall product muramyl dipeptide (MDP) and activates the transcription factor NF-kappaB upon MDP-binding. NOD2 variants are associated with reduced NF-kappaB activation and reduced production of epithelial derived antibacterial peptides such as defensins. A reduced expression of defensins is described and found in patients with Crohn's disease and ulcerative colitis especially when NOD2 variants are present. Furthermore recent evidence from mouse models suggests that the ability of intestinal epithelial cells to activate NF-kappaB upon bacterial stimulation protects from mucosal inflammation. Taken together these data indicate that NOD2 mediated NF-kappaB activation, subsequent induction of anti-microbial peptides such as defensins and induction of cytokine expression are essential for the function of the intestinal barrier and for the prevention of bacterial translocation. The data indicate why a defect in the induction of this acute defense response is associated with chronic inflammation. Invading bacteria that cannot be readily detected and eliminated may start a backup mechanism of inflammation finally resulting in chronic inflammatory reaction followed by further impairment of the mucosal barrier.

NOD2/CARD15 gene polymorphisms are not associated with collagenous colitis

BACKGROUND

Collagenous colitis is a chronic inflammatory bowel disease of unknown origin. In some cases of collagenous colitis, histomorphological features are comparable to other inflammatory bowel diseases.

AIM

To assess functional NOD2/CARD15 polymorphisms for the susceptibility to collagenous colitis in a case-control study.

MATERIALS AND METHODS

Seventy-five patients with symptomatic collagenous colitis and 534 healthy blood donors were genotyped for SNP 8, 12, and 13 of the NOD2/CARD15 gene using TaqMan technology. Susceptibility to collagenous colitis was tested using Chi(2)-test comparing the carrier status of the rare allele.

RESULTS

The carrier frequency of the rare allele in SNP 8, 12, and 13 was 9.5, 1.3, and 8.1% in patients with collagenous colitis and 8.9, 1.1, and 8.4% in healthy blood donors, respectively. There were no significant differences in allele-, genotype, and carrier frequency (p>0.05).

CONCLUSION

Our data suggest that functional polymorphisms in the NOD2/CARD15 gene might not be involved in the susceptibility to collagenous colitis.