Cell-specific Activation of the Nrf2 Antioxidant Pathway Increases Mucosal Inflammation in Acute but Not in Chronic Colitis.

Background And Aims: The transcription factor Nrf2 is a major modulator of the cellular antioxidant response. Oxidative burst of infiltrating macrophages leads to a massive production of reactive oxygen species in inflamed tissue of inflammatory bowel disease patients. This oxidative burst contributes to tissue destruction and epithelial permeability, but it is also an essential part of the antibacterial defence. We therefore investigated the impact of the Nrf2 orchestrated antioxidant response in both acute and chronic intestinal inflammation.

Methods: To study the role of Nrf2 overexpression in mucosal inflammation, we used transgenic mice conditionally expressing a constitutively active form of Nrf2 [caNrf2] either in epithelial cells or in the myeloid cell lineage. Acute colitis was induced by dextran sulphate sodium [DSS] in transgenic and control animals, and changes in gene expression were evaluated by genome-wide expression studies. Long-term effects of Nrf2 activation were studied in mice with an IL-10-/- background.

Results: Expression of caNrf2 either in epithelial cells or myeloid cells resulted in aggravation of DSS-induced acute colitis. Aggravation of inflammation by caNrf2 was not observed in the IL-10-/- model of spontaneous chronic colitis, where even a trend towards reduced prolapse rate was observed.

Conclusions: Our findings show that a well-balanced redox homeostasis is as important in epithelial cells as in myeloid cells during induction of colitis. Aggravation of acute DSS colitis in response to constitutive Nrf2 expression emphasises the importance of tight regulation of Nrf2 during the onset of intestinal inflammation.