Understanding the Role of Selenium and Selenoproteins during Gut Inflammation

Restricted (Penn State Only)
- Author:
- Nettleford, Shaneice Kimarie
- Graduate Program:
- Pathobiology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 13, 2022
- Committee Members:
- Connie Rogers, Outside Unit & Field Member
Girish Kirimanjeswara, Major Field Member
Margherita Cantorna, Major Field Member
Kumble Prabhu, Chair & Dissertation Advisor
Kumble Prabhu, Program Head/Chair - Keywords:
- Selenium
Selenoproteins
Inflammatory Bowel Disease
Enteric Infections
Selenoprotein W
Yap1
Egfr
15-PGDH
15d-PGJ2
Gut Inflammation - Abstract:
- Inflammatory bowel disease (IBD) and enteric pathogens such as enteropathogenic Escherichia coli (EPEC) are concerning due to the debilitating symptoms and associated mortalities. It is believed that factors such as genetics, diet, and an uncontrolled immune response to commensal bacteria are involved in the pathogenesis of IBD. As there are no cures for IBD, treatment of the disease is mostly focused on the suppression of the immune system. On the other hand, a recurrence of enteric infections can give rise to IBD. Understanding the mechanism to combat such infections is important as repeated and/or sustained inflammation is a key etiological factor. Nutritional status often dictates disease outcomes. The micronutrient, selenium (Se), has been shown to inhibit and promote the resolution of inflammation. In fact, Se has been shown to promote resolution through the class switching of the metabolites of the arachidonic acid from the production of pro-inflammatory mediators such as prostaglandin E2 (PGE2), towards the production of anti-inflammatory mediators such as PGD2 and its downstream metabolites such as 15-deoxy-∆12,14 - prostaglandin J2 (15d-PGJ2). As the therapies for IBD and enteric infections have detrimental side effects, there is a need for better understanding of the role of nutritional status, specifically Se status, which will aid in the generation of alternate therapies. The murine pathogen, Citrobacter rodentium (C. rodentium), was used as a model of EPEC. In the current studies, a higher percentage of Se deficient (Se-Def; <0.01ppm Se) mice succumbed to the infection when compared to Se adequate (Se-Ade; 0.08ppm Se) and Se supplemented (Se-Supp; 0.4ppm Se) mice. The Se-Def mice also had a lower percentage of type 3 innate lymphoid (ILC3s) cells and T helper 17 (Th17 cells) at the peak of infection. Consequently, a decrease in the enzyme that breaks down PGE2, 15-prostaglandin dehydrogenase (15-PGDH), was observed in colonic lysates as a result of deficiency, in comparison to adequate and supplemented levels of Se in the diets of these mice. Furthermore, the administration of CAY10397, which inhibits the activity of 15-PGDH, diminished the protection afforded by addition of Se to the diet. The CAY10397 treated mice had a higher bacterial burden, accompanied by decreased percentages of ILC3s and Th17 cells at the peak of infection. Surprisingly, treatment with CAY10397 decreased the expression of the tight junction protein zonula occludens 1 (Zo-1) and disrupted the intestinal epithelial barrier. The opposite was observed when Se-Def mice were administered 15d-PGJ2. Even though on deficient diet, when Se-Def mice were administered15d-PGJ2, these mice had a higher percentage of ILC3s and Th17 cells, in conjunction with an increase in Zo-1 expression, mimicking the Se-Supp mice. Mice that lacked the selenoprotein making machinery in macrophages (Trspfl/fl LysMCre) also succumbed to injury following infection with C. rodentium. These studies suggested that Se and selenoproteins are integral part of combatting an enteric infection and associated inflammation as it promotes resolution of the inflammation through modulation of immune responses and the intestinal epithelial barrier function. To further pinpoint the role of specific selenoproteins in gastrointestinal inflammation and based on the recent research showing increased expression of Selenoprotein W (Selenow) in inflamed macrophages, dextran sodium sulfate (DSS) was administered to Selenow knock out (Selenow KO) mice. DSS is a colitinogen used as a model of IBD, specifically colitis. Induction of colitis in Selenow KO mice resulted in a worsened disease outcome, where Selenow KO mice had increased weight loss and decreased colon lengths, in comparison to wild type (WT) mice. Along with an increase in Tnf alpha producing macrophages, Selenow KO mice also displayed a disrupted epithelial barrier characterized by decreased Zo-1 expression. To understand the mechanism behind the disrupted barrier, the expression of proteins, including epidermal growth factor receptor (Egfr) and Yes-associated protein 1 (Yap1), involved in intestinal repair were investigated. Selenow KO mice had reduced expression of both Yap1 and Egfr in colonic lysates. Interestingly, there was a greater interaction between pYap1 and 14-3-3 and increased tyrosine phosphorylation of MOB kinase activator 1A and 1B (Mob1A/B), suggesting a Selenow mediated link between Egr and Yap1. These studies imply that Selenow aids in the resolution of inflammation and promotes efficient repair of the intestinal epithelium following injury. In summary, this dissertation demonstrates the importance of the supplementation of Se during an enteric infection and IBD. The fact that Se is crucial for mounting the appropriate immune responses to infection further advocates for more studies in human subjects to address the prospect of adjuvant therapy. Importantly, the studies demonstrated for the first time, the involvement of Selenow in intestinal repair via Egfr and Yap1 signaling in epithelial cells, further corroborating with the data that increased Selenow expression via Se supplementation could potentially serve as an adjunct therapy via multiple mechanisms.