Loss of Epithelial RelA Results in Deregulated Intestinal Proliferative/Apoptotic Homeostasis and Susceptibility to Inflammation

Abstract

NF-κB 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-κB 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. IκBα and IκBβ 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, RegIIIγ) and antiapoptotic, prorestitution genes (Bcl-xL, 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.

Prohibitin Inhibits Tumor Necrosis Factor alpha–induced Nuclear Factor-kappa B Nuclear Translocation via the Novel Mechanism of Decreasing Importin α3 Expression

“…n ϭ 7 for normal; n ϭ 8 for Crohn's disease; *p Ͻ 0.05 vs. normal. decreased animal survival (Steinbrecher et al, 2008). Unlike this animal model in which NF-B signaling is abolished in the intestinal epithelium, we show that PHB overexpression in epithelial cells reduces the magnitude and duration of NF-B activation by the proinflammatory cytokine TNF-␣ via decreasing expression of importin ␣3.…”

“…A major signaling pathway activated by TNF-␣ is the nuclear factor-kappa B (NF-B) pathway, which plays a central role in inflammatory responses and also regulates transcription of multiple cytokines including interleukin (IL)-2, IL-6, IL-8, TNF-␣, and ICAM-1 (Ali and Mann, 2004), and is required for regulation of apoptosis and proliferation of intestinal epithelia (Steinbrecher et al, 2008). In most cells, the predominant form of NF-B is comprised of a heterodimer of p50 (NF-B1) and p65 (Rel-A) that is sequestered in the cytosol complexed to inhibitory I B proteins, preferentially I B-␣.…”

NF-κB in the regulation of epithelial homeostasis and inflammation

“…Since lack of only one of the IKKs or the NF-κB subunits does not completely abrogate NF-κB activation due to compensatory effects of the remaining subunits, it appears that low thresholds of NF-κB activation in IECs are sufficient to maintain intestinal immune homeostasis under basal conditions. However, both IKK2 IEC-KO and RelA IEC-KO mice are hypersensitive to colitis induced by DSS [22,38,39], suggesting that the intestinal epithelium needs to be capable of raising NF-κB activity in order to cope with tissue damage. Interestingly, Zaph et al [40] found that IKK2 IEC-KO mice showed deregulated immune responses to infection with the intestinal parasite Trichuris muris, and suggested that epithelial NF-κB orchestrates mucosal immune responses by regulating the production of essential immunomodulatory cytokines such as TSLP by IECs.…”

“…Therefore, NEMO-dependent IKK signaling in epithelial cells controls intestinal immune homeostasis in both mice and humans. In contrast to NEMO IEC-KO and TAK1 IEC-KO mice, RelA IEC-KO as well as IKK2 IEC-KO and IKK1 IEC-KO mice did not develop spontaneous intestinal inflammation [31,38,39]. Since lack of only one of the IKKs or the NF-κB subunits does not completely abrogate NF-κB activation due to compensatory effects of the remaining subunits, it appears that low thresholds of NF-κB activation in IECs are sufficient to maintain intestinal immune homeostasis under basal conditions.…”

Commensal microbes drive intestinal inflammation by IL-17–producing CD4 + T cells through ICOSL and OX40L costimulation in the absence of B7-1 and B7-2

“…Staining with PE-conjugated I-A b :2W1S 52-68 tetramer and enrichment using anti-PE beads were performed as described (32). For cytokine production, cells were stimulated with phorbol myristate acetate/ionomycin in media supplemented with GolgiPlug (BD Biosciences) for 5 h. For histology, each tissue was fixed with paraformaldehyde and embedded in paraffin, cut to 5-μM sections, and stained with H&E. Tissue inflammation scoring was performed in a blinded fashion using previously reported parameters (29,(45)(46)(47), which are more fully described in SI Appendix.…”