Constitutive activation of epithelial TLR4 augments inflammatory responses to mucosal injury and drives colitis-associated tumorigenesis.

BACKGROUND: Chronic intestinal inflammation culminates in cancer and a link to Toll-like receptor-4 (TLR4) has been suggested by our observation that TLR4 deficiency prevents colitis-associated neoplasia. In the current study we address the effect of the aberrant activation of epithelial TLR4 on induction of colitis and colitis-associated tumor development. We take a translational approach to address the consequences of increased TLR signaling in the intestinal mucosa.
METHODS: Mice transgenic for a constitutively active TLR4 under the intestine-specific villin promoter (villin-TLR4 mice) were treated with dextran sodium sulfate (DSS) for acute colitis and azoxymethane (AOM)-DSS TLR4 expression was analyzed by immunohistochemistry in colonic tissue from patients with ulcerative colitis (UC) and UC-associated cancer. The effect of an antagonist TLR4 antibody (Ab) was tested in prevention of colitis-associated neoplasia in the AOM-DSS model.
RESULTS: Villin-TLR4 mice were highly susceptible to both acute colitis and colitis-associated neoplasia. Villin-TLR4 mice had increased epithelial expression of COX-2 and mucosal PGE₂ production at baseline. Increased severity of colitis in villin-TLR4 mice was characterized by enhanced expression of inflammatory mediators and increased neutrophilic infiltration. In human UC samples, TLR4 expression was upregulated in almost all colitis-associated cancer and progressively increased with grade of dysplasia. As a proof of principle, a TLR4/MD-2 antagonist antibody inhibited colitis-associated neoplasia in the mouse model.
CONCLUSIONS: Our results show that regulation of TLRs can affect the outcome of both acute colitis and its consequences, cancer. Targeting TLR4 and other TLRs may ultimately play a role in prevention or treatment of colitis-associated cancer.