Author ORCID Identifier

https://orcid.org/0000-0003-1985-6602

Date of Award

12-16-2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Dr. Didier Merlin

Second Advisor

Dr. Pallavi Garg

Third Advisor

Dr. Andrew Gewirtz

Abstract

Ulcerative colitis (UC) is an inflammatory bowel disease (IBD) that causes chronic inflammation and ulcers affecting the innermost layer of the colon. Almost 1 million people suffer from UC in the United States. UC patients have an increased risk of colitis associated cancer (CAC). It is driven by continuous exposure to inflammation and progresses through “dysplasia-carcinoma axis”. Notch1 signaling is a conserved intracellular signaling pathway. It regulates cell fate, proliferation, differentiation, and death. However, Notch1 acts as a mediator or suppressor depending on the cellular context and disease stage. Aim of this study is to understand the mechanistic role of Notch1 in acute colitis and CAC. We used WT mice (control group) and crossed them with villin-cre mice to generate NCre, which cannot express Notch1 in colon epithelium. Acute colitis was induced with dextran sodium sulfate (DSS) for five days and in recovery period, mice were given water after the completion of DSS cycle. CAC was induced by intraperitoneal injection of azoxymethane and two cycles of DSS. Enteroids were isolated from six weeks old NCre and WT mice to study proliferation and differentiation. Inhibition of Notch1 compromised epithelial crypt architecture, led to higher number of goblet cells, and compromised intestinal barrier function at the basal level. Notch1 mediated inflammation in DSS- induced acute colitis by increasing inflammatory cytokine levels and activating NF-kB pathway. In the acute colitis model following a recovery period, Notch1 promoted wound healing. In CAC, NCre mice showed higher susceptibility to inflammation as indicated by histology, higher number of polyps, and defective barrier function compared to WT mice. Western blot data showed increased p53 and cleaved caspase-3 expressions while decreased expressions of γ-H2AX and MLH1. Notch1 mediates acute colitis by cross-talking with NF-kB pathway and promoting abnormal proliferation. However, during the recovery period after acute colitis, Notch1 promotes wound healing. Inhibition of Notch1exarcebates CAC condition due to lower levels of non-mutated p53 expression. Therefore, this study suggests that Notch1 inhibitors might be a better option as therapeutics only for acute colitis patients and induction of Nocth1 signaling as a therapy, can protect against chronic colitis/CAC.

DOI

https://doi.org/10.57709/15850964

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