Loss of epithelial RelA results in deregulated intestinal proliferative/apoptotic homeostasis and susceptibility to inflammation.

NF-kappaB plays a central, proinflammatory role in chronic intestinal inflammation, yet recent work suggests a predominantly protective function for this transcription factor group in some cell types of the intestine. We herein describe the conditional deletion of the NF-kappaB RelA gene in murine intestinal epithelia and determine its function in homeostatic control of enterocyte proliferation/apoptosis and susceptibility to colonic inflammation. Mice lacking RelA in ileal and colonic enterocytes were born in expected Mendelian ratios, and RelA-null epithelia differentiated normally. Spontaneous intestinal disease and death occurred with low penetrance in neonates lacking epithelial RelA. IkappaBalpha and IkappaBbeta were significantly diminished in RelA-null epithelia, and endotoxin challenge revealed elevated p50 and c-Rel DNA binding activity as compared with controls. Deletion of RelA resulted in diminished expression of antimicrobial (defensin-related cryptdin 4, defensin-related cryptdin 5, RegIIIgamma) and antiapoptotic, prorestitution genes (Bcl-x(L), RegIV, IL-11, IL-18), and basal rates of epithelial apoptosis and proliferation were elevated. Mice lacking colonic RelA were sensitive to dextran sodium sulfate-induced colitis. Although experimental colitis enhanced proliferation in cells lacking RelA, sustained epithelial cell apoptosis precluded mucosal healing and decreased animal survival. We conclude that activation of RelA is required for homeostatic regulation of cell death and division in intestinal epithelia, as well as for protection from development of severe, acute inflammation of the intestine.