Characterization of Colonic Apoptosis Following DSS Induced Colitis in the Absence of Lrig3
Research in the Powell lab focuses on the epithelium of the small intestine and colon during homeostasis and disease. Homeostasis within the gut requires intricate control of stem cell proliferation, differentiation, migration and controlled cell death. Previous research in the Powell lab has shown the transmembrane protein and intestinal stem cell marker Lrig1, may play both a protective and restorative role in the colon of injury induced mice. Another member of the family, Lrig3, is also expressed in the intestines and localized to the stem cell compartment. In my project, I examine how a structurally similar protein, Lrig3, may play a role in the protection of the colonic epithelium of injury induced mice. My experiments examined the intestinal pathology of ulcerative colitis, that is characterized by inflammation of the colon, by using Dextran Sulfate Sodium (DSS) to induce colitis in an Lrig3 transgenic mouse model. Apoptosis in the cells of the colonic epithelium is a normal result of DDS-induced ulcerative colitis. Understanding if the loss of the Lrig3 affects cell death in the presence of an inflammatory response, is an important step towards potential recovery and/or protective methods for colitis and other inflammatory bowel conditions. Thus, we wanted to investigate if the loss of Lrig3 prior to induced injury would influence this response. To accomplish this, I used a transgenic mouse model with a tamoxifen inducible cre-lox recombination system controlled by an Lrig1 promoter, to allow for specific spatial and temporal excision of Lrig3, only in Lrig1 expressing cells. The experimental cohort was injected with tamoxifen for 3 days and then treated with 3% DSS for 7 days, allowing us to examine molecular and morphological changes in the absence of Lrig3 during DSS-induced colitis. The tissue was co-stained with a TUNEL assay and Beta-catenin antibody to visualize apoptotic cells and adheren junctions, respectively, in the colonic epithelium. The amount of apoptosis present in the colonic epithelium of mice with and without Lrig3 was quantified and analyzed. Although a two tailed t-test revealed no biological statistical significance, we did observe a slight decrease (p=0.0655) in the number of apoptotic cells per mm of colon analyzed in the Lrig3 mutants when compared to the DSS treated control animals. From these results, we will next analyze changes in proliferation, inflammation, and morphology to determine if Lrig3 participates in the protection or recovery of the colonic epithelium following induced injury.