Investigating the Wnt/MYC axis in the pathogenesis of Crohn's disease
Open Access
- Author:
- Matthews, Stephen
- Graduate Program:
- Biomedical Sciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 02, 2021
- Committee Members:
- David Degraff, Major Field Member
Vladimir Spiegelman, Outside Unit & Field Member
Gregory Yochum, Chair & Dissertation Advisor
Walter Koltun, Major Field Member
Ralph Keil, Program Head/Chair - Keywords:
- Wnt
rs6651252
MYC
IBD
Crohn's Disease
WRE
Enhancer - Abstract:
- A single layer of intestinal epithelial cells (IECs) protects underlying tissues from contents of the intestinal lumen and is composed of differentiated cells at the luminal surface, and non-differentiated, crypt structures embedded in the submucosa. Due to the harsh environment of the intestinal lumen, differentiated IECs are routinely lost through damage or controlled cell death. To maintain barrier integrity, IECs must be rapidly replaced by proliferating cells within the crypts. The primary driver for this proliferation is the Wnt/beta-catenin signaling pathway. Beta-catenin is a transcriptional co-activator that activates gene expression through interaction with the TCF/LEF family of sequence specific transcription factors. Crohn’s disease (CD) is one subtype of inflammatory bowel disease (IBD), a recrudescent and chronic inflammatory disease of the gastrointestinal (GI) tract. Through genome-wide association studies (GWAS), over 200 single nucleotide polymorphisms (SNPs) have been linked with predisposition for developing IBD. As the vast majority of these SNPs are intergenic, how these variants are associated with disease predisposition, and the relevant target genes impacted, represent significant gaps in knowledge in the IBD research community. We investigated one such CD-associated SNP, rs6651252, which maps to a gene desert on chromosome 8. Work presented within this dissertation demonstrate that rs6651252 resides within a novel Wnt responsive DNA enhancer element (WRE), and that the disease associated allele enhances binding of the TCF7L2 transcription factor to this region of DNA. Using CRISPR- mediated genomic editing and epigenetic modulation, we found that the rs6651252-enhancer regulates expression of the c-MYC proto-oncogene (MYC). Furthermore, in patient-derived intestinal tissue, we saw a positive correlation between MYC transcript levels and the presence of rs6651252 disease-associated allele. These results suggest one mechanism by which Wnt/MYC signaling contributes to CD pathogenesis. Furthermore, our findings suggest patients with the disease-associated allele may benefit from therapies that target MYC, or its downstream target genes.