Molecular and Epigenetic Insights into RASSF1A Regulated Pathways in Inflammatory Bowel Disease

• Author / Creator

  Salla, Mohamed

• Inflammatory Bowel Disease (IBD) is an idiopathic non-curable disease characterized by pain, chronic diarrhea, rectal bleeding with weight loss and erosion of the colon in severe cases. In many cases, IBD is a chronic relapsing inflammatory disorder of the gastrointestinal tract that usually onsets in late childhood or early adulthood leaving the patient with decades of chronic inflammation to deal with. IBD has two main sub-types, ulcerative colitis (UC) and Cohn’s disease (CD). Additionally, it is a common inflammatory disorder that is associated with a greater risk of CRC. The unpredictable nature of IBD exerts a burden on both the patients and governments with hospitalization, surgery, poor economic productivity and less social involvement.
  The advancement in diagnostic tools as well as the emergence of the concept of personalized medicine rationalizes the importance of understanding the disease in a more specific fashion, at the level of the individual. Our current understanding of IBD outlines genetic factors including > 200 genes linked to IBD. This is in synergy with external environmental variables as well as internal micro-environment conditions, mainly the microbiome of the gut. In this thesis, several genes were explored as potential drivers of disease pathogenesis of IBD that may influence different aspects of the pathogenesis of IBD. Our first molecular focus was on the tumor suppressor gene, Ras association domain family 1A (RASSF1A). This gene has been reported to be epigenetically silenced by promoter specific hypermethylation in IBD and in IBD related colorectal cancer (CRC). Prior to the start of my thesis project, our group demonstrated that the loss of RASSF1A resulted in excessive intestinal inflammation and injury. RASSF1A was found to restrict signaling of the pathogen recognition receptors (PRRs) following receptor engagement and subsequent restriction of the activation of nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB), a key molecular driver of inflammation. Rassf1a-/- mice were highly susceptible to chemical induction of colitis in a murine model to suggest that RASSF1A controlled pathways are dysregulated in IBD and significantly modulate disease pathogenesis. Our research group also demonstrated that RASSF1A physically interacts with the Toll-like receptor (TLR) family of innate immunity PPRs and with the nucleotide-containing oligomerization domain protein (NOD2) family of intracellular PRRs. The modulation of NOD2 results in the failure to activate its obligate kinase, receptor interacting protein kinase 2 (RIPK2), the second molecular focus of my thesis. We thus hypothesized that epigenetic loss of RASSF1A would result in hyperactivation of RIPK2 to drive NFkB-directed inflammation. Connected to both epigenetic modifications and elevated inflammation in IBD patients and in our mouse models of IBD, is a metabolic disorder syndrome that results in modulation of AMP-activated kinase (AMPK), the third molecular focus of this thesis. Acute inflammation in IBD patients resulted in the loss of AMPK activity and metabolic disorder. Thus to effectively treat IBD, we need to prevent epigenetic loss of RASSF1A (or regain expression of RASSF1A), restore the activation levels of AMPK and inhibit RIPK2 to prevent further inflammatory damage.
  The objectives of this thesis were:
  
  (1) Exploring RASSF1A promoter methylation in IBD;
  (2) Exploring therapeutics to targeting NFκB dysregulated pathways including the abnormal NOD2/RIPK2 pathway;
  (3) Identification of molecular biomarkers for both diagnostic and prognostic purposes in IBD.
  We believe that our observations will aid in better understanding the key players that control inflammation in IBD and possibly progress in IBD related CRC. The identification of these novel biomarkers will allow rational design of specific or multi-specific therapeutics to reduce inflammation and better manage IBD.

• Subjects / Keywords

  • RIPK2
  • RASSF1A
  • AMPK
  • IBD

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3794195H

• License

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