Name of Student:
Natasha Ryz
Research Supervisor: Drs. Bruce Vallance & Kevan Jacobson
Title of Presentation: Active Vitamin D Increases Susceptibility of Mice to Citrobacter rodentium
Induced Colitis
Abstract
Background: Inflammatory bowel disease (IBD) is characterized by chronic gastrointestinal inflammation and mucosal damage resulting from a complex interplay among genetic, immunologic, microbial and environmental factors. Interestingly, IBD is most prevalent in northern climates where sunlight
exposure is limited, suggesting a link to vitamin D. Indeed, low serum metabolites of vitamin D are
common in patients with IBD and are associated with longer disease duration and higher disease activity, while supplementation is protective. The active form of vitamin D (1,25(OH)2D3 or calcitriol) signals through the vitamin D receptor (VDR), a nuclear receptor that is expressed by almost all nucleated
cells in the body, including immune cells and colonic epithelial cells. Calcitriol regulates directly or
indirectly >200 different genes through the VDR and is involved in a variety of cellular functions including cell proliferation, differentiation, apoptosis and immune modulation. In mice, treatment with
calcitriol and its analogues has been shown to ameliorate spontaneous (IL-10-/- mice) as well as chemically induced colitis (TNBS and DSS). I have also verified that calcitriol can protect against DSSinduced damage in wild-type (WT) mice in our facility. Using a similar protocol, I sought to determine
if calcitriol could also protect mice against an infectious colitis induced by the murine specific pathogen Citrobacter rodentium. It has previously been shown that calcitriol treatment had no effect on various infections in mice, including Listeria monocytogenes, Shistosoma mansoni or Candida albicans.
However, it has been shown that mice lacking the VDR, and thus having no functional calcitriol signaling, are more susceptible to the enteric pathogen Salmonella typhimurium, as evident by increased bacterial burdens and mortality. Furthermore, Salmonella infection increased the amount and altered the
location of VDR in the colons of WT mice, indicating that epithelial responses to bacteria may be determined in part through vitamin D signaling.
Hypothesis: Calcitriol will protect mice against C. rodentium induced colitis.
Methods: 6-8-week-old male C57Bl/6 mice were administered either vehicle or 10 ng calcitriol via
intraperitoneal injection 1 day prior to infection with C. rodentium, and then everyday thereafter until
sacrifice at day 10 post infection. Intestinal tissues were assessed for damage by macroscopic and histological analysis. Bacterial loads were determined by plating tissues, while Tir staining assessed bacterial location. Immunofluorescence staining assessed cellular proliferation and inflammatory cells. Cytokines were analyzed by qPCR.
Results: Surprisingly, calcitriol treated mice had shortened colons (15% shorter) and developed macroscopic erosions in the mid/distal colon in 75% of the mice. Histologically, the distal and mid colon of
calcitriol treated mice appeared most damaged, with increased edema and more infiltrating lymphocytes. In addition, calcitriol treated mice had 10 fold higher bacterial burdens in the colon and cecum,
as well as increased Tir staining, indicating greater colonization of C. rodentium throughout the entire
colon. In the distal colon, calcitriol treated mice had reduced expression of Th1 (IFN-) and Th17 (IL17a and IL-6) related cytokines, compared to PBS-treated mice.
Conclusion: Calcitriol treated mice are more susceptible to C. rodentium induced colitis. The immunosuppressive actions of calcitriol could potentially impair host defense, since Th1/Th17 responses are
also critical for the clearance of many bacterial infections.