Association of a functional variant in the Wnt co-receptor LRP6 with early onset ileal Crohn's disease.

Ileal Crohn's Disease (CD), a chronic small intestinal inflammatory disorder, is characterized by reduced levels of the antimicrobial peptides DEFA5 (HD-5) and DEFA6 (HD-6). Both of these α-defensins are exclusively produced in Paneth cells (PCs) at small intestinal crypt bases. Different ileal CD-associated genes including NOD2, ATG16L1, and recently the ß-catenin-dependant Wnt transcription factor TCF7L2 have been linked to impaired PC antimicrobial function. The Wnt pathway influences gut mucosal homeostasis and PC maturation, besides directly controlling HD-5/6 gene expression. The herein reported candidate gene study focuses on another crucial Wnt factor, the co-receptor low density lipoprotein receptor-related protein 6 (LRP6). We analysed exonic single nucleotide polymorphisms (SNPs) in a large cohort (Oxford: n = 1,893) and prospectively tested 2 additional European sample sets (Leuven: n = 688, Vienna: n = 1,628). We revealed an association of a non-synonymous SNP (rs2302685; Ile1062Val) with early onset ileal CD (OR 1.8; p = 0.00034; for homozygous carriers: OR 4.1; p = 0.00004) and additionally with penetrating ileal CD behaviour (OR 1.3; p = 0.00917). In contrast, it was not linked to adult onset ileal CD, colonic CD, or ulcerative colitis. Since the rare variant is known to impair LRP6 activity, we investigated its role in patient mucosa. Overall, LRP6 mRNA was diminished in patients independently from the genotype. Analysing the mRNA levels of PC product in biopsies from genotyped individuals (15 controls, 32 ileal, and 12 exclusively colonic CD), we found particularly low defensin levels in ileal CD patients who were carrying the variant. In addition, we confirmed a direct relationship between LRP6 activity and the transcriptional expression of HD-5 using transient transfection. Taken together, we identified LRP6 as a new candidate gene in ileal CD. Impairments in Wnt signalling and Paneth cell biology seem to represent pathophysiological hallmarks in small intestinal inflammation and should therefore be considered as interesting targets for new therapeutic approaches.

Differences in goblet cell differentiation between Crohn's disease and ulcerative colitis.

Goblet cells are mucin-secreting intestinal cells forming the mucus layer that protects the mucosal surface. Ulcerative colitis (UC) has been associated with a defective colonic mucus layer and a reduced number of goblet cells. In experimental animals, colonic goblet cell differentiation is regulated by interacting transcription factors Hath1, KLF4 and the Notch, as well as Wnt pathways, whereas data in humans are limited. We investigated goblet cell differentiation factors and mucins in controls and in inflammatory bowel diseases (IBDs). We performed real-time PCR for Hath1, KLF4, several ligands, receptors and target genes of the Notch and Wnt pathways, as well as several mucins in biopsies from the sigmoid colon of controls (n=21), Crohn's disease (CD, n=48) and UC (n=40). In addition, Hath1 protein was quantitated with Western blot and localized with immunohistochemistry. Notably, the degree of inflammation as measured by IL-8 and histology was similar in both disease entities. The proportion of goblet cells was lowered in both IBDs, but specifically diminished in the upper third of the crypt in UC. Comparable levels of inflammation induced both Hath1 (2.0-fold, p<0.001) and KLF4 (1.8-fold for KLF4, p=0.031) mRNA expression in CD but not in UC (0.8-0.9-fold, ns). The differential induction was confirmed for Hath1 protein using Western blot. Hath1 immunostaining was found mostly in the lower half of the colonic crypts. Hath1, KLF4 and the Notch target gene Hes1 were significantly (p<0.001) and positively correlated. Moreover, both Hath1 and KLF4 were correlated (p<0.001) with MUC1, MUC2 as well as MUC4 in all control and IBD cohorts. The results indicate that both transcription factors are key regulators of goblet cell differentiation and mucin formation in the human colon. Conspicuously, inflammation is associated with an enhanced goblet cell differentiation in CD but not in UC, a defect possibly of pathogenic importance.

Genetic variants of Wnt transcription factor TCF-4 (TCF7L2) putative promoter region are associated with small intestinal Crohn's disease.

Reduced expression of Paneth cell antimicrobial alpha-defensins, human defensin (HD)-5 and -6, characterizes Crohn's disease (CD) of the ileum. TCF-4 (also named TCF7L2), a Wnt signalling pathway transcription factor, orchestrates Paneth cell differentiation, directly regulates the expression of HD-5 and -6, and was previously associated with the decrease of these antimicrobial peptides in a subset of ileal CD. To investigate a potential genetic association of TCF-4 with ileal CD, we sequenced 2.1 kb of the 5' flanking region of TCF-4 in a small group of ileal CD patients and controls (n = 10 each). We identified eight single nucleotide polymorphisms (SNPs), of which three (rs3814570, rs10885394, rs10885395) were in linkage disequilibrium and found more frequently in patients; one (rs3814570) was thereby located in a predicted regulatory region. We carried out high-throughput analysis of this SNP in three cohorts of inflammatory bowel disease (IBD) patients and controls. Overall 1399 healthy individuals, 785 ulcerative colitis (UC) patients, 225 CD patients with colonic disease only and 784 CD patients with ileal involvement were used to determine frequency distributions. We found an association of rs3814570 with ileal CD but neither with colonic CD or UC, in a combined analysis (allele positivity: OR 1.27, 95% CI 1.07 to 1.52, p = 0.00737), which was the strongest in ileal CD patients with stricturing behaviour (allele frequency: OR 1.32, 95% CI 1.08 to1.62, p = 0.00686) or an additional involvement of the upper GIT (allele frequency: OR 1.38, 95% CI 1.03 to1.84, p = 0.02882). The newly identified genetic association of TCF-4 with ileal CD provides evidence that the decrease in Paneth cell alpha-defensins is a primary factor in disease pathogenesis.

The Paneth cell alpha-defensin deficiency of ileal Crohn's disease is linked to Wnt/Tcf-4.

Ileal Crohn's disease (CD), a chronic mucosal inflammation, is characterized by two pertinent features: a specific decrease of Paneth cell-produced antimicrobial alpha-defensins and the presence of mucosal-adherent bacteria. A mutation in NOD2, the muramyl dipeptide recognition receptor, is found in some patients, which leads to an even more pronounced alpha-defensin decrease. However, the underlying mechanism remains unclear for the majority of patients. In this study, we report a reduced expression in ileal CD of the Wnt-signaling pathway transcription factor Tcf-4, a known regulator of Paneth cell differentiation and alpha-defensin expression. Within specimens, the levels of Tcf-4 mRNA showed a high degree of correlation with both HD5 and HD6 mRNA. The levels of Tcf-4 mRNA were decreased in patients with ileal disease irrespective of degree of inflammation, but were not decreased in colonic CD or ulcerative colitis. As a functional indicator of Tcf-4 protein, quantitative binding analysis with nuclear extracts from small intestine biopsies to a Tcf-4 high-affinity binding site in the HD-5 and HD-6 promoters showed significantly reduced activity in ileal CD. Furthermore, a causal link was shown in a murine Tcf-4 knockout model, where the comparably reduced expression of Tcf-4 in heterozygous (+/-) mice was sufficient to cause a significant decrease of both Paneth cell alpha-defensin levels and bacterial killing activity. Finally, the association between Paneth cell alpha-defensins and Tcf-4 was found to be independent of the NOD2 genotype. This new link established between a human inflammatory bowel disease and the Wnt pathway/Tcf-4 provides a novel mechanism for pathogenesis in patients with ileal CD.