This article describes a method to induce colitis in a murine model using dextran sulfate sodium (DSS). The process involves monitoring the mouse for signs of gastrointestinal disorders and performing surgical isolation of the colon for further analysis.
To induce colitis — an inflammatory bowel disease — in a murine model, take a mouse housed in a cage.
Replace the drinking water with a solution of dextran sulfate sodium, DSS, a colitis-inducing polysaccharide. Allow the mouse to consume the solution to develop colitis.
Upon consumption, DSS enters the lumen of the mouse's colon. The colon contains a thick mucus layer, providing a physical barrier between the commensal microbes and the underlying epithelial cell monolayer.
DSS penetrates the mucus layer, entering the epithelial cells. Inside the cells, DSS alters the expression of tight-junction proteins and induces apoptosis, resulting in the disruption of the epithelial layer and mucosal barrier. This allows the entry of luminal microbes into the lamina propria — the underlying tissue with resident dendritic cells and macrophages.
The immune cells recognize the microbes, activating downstream signaling to secrete pro-inflammatory cytokines. Cytokines cause the infiltration of a large number of T cells which mount an exaggerated immune response, resulting in inflammation.
Monitor the treated mouse for gastrointestinal disorders and weight loss, indicating the onset of colitis.
Euthanize the mouse; surgically isolate the entire colon. Divide the colon into proximal, middle, and distal sections and add a fixative for tissue preservation.
The tissue is ready for downstream assays to evaluate colitis.
To induce dextran sulfate sodium, or DSS colitis, replace the regular drinking water with 3% DSS solution ad libitum for seven days, measuring each mouse's body weight, DSS solution consumption, and stool production daily. At the end of the seven-day treatment, place the mouse in the supine position, and use small scissors to make a three-centimeter-long midline incision in the abdomen.
Then, use forceps to lift the colon to allow it to be separated from the surrounding mesentery, and extract the whole colon until the cecum and rectum are visible. Transect the tissue at the colonocecal margin and deep within the pelvis, to free the proximal and distal colon respectively.
Measure and record the length of the isolated colon, and use a 10-milliliter syringe equipped with a gavage needle to flush the colon with 10 milliliters of ice-cold PBS to remove the feces and blood until the eluate runs clear. For histological identification, divide the tissue samples into equally-sized proximal, middle, and distal sections, and fix the tissues in 4% paraformaldehyde overnight at four degrees Celsius.
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