Ablation of Gly96/immediate early gene-X1 (gly96/iex-1) aggravates DSS-induced colitis in mice: Role for gly96/iex-1 in the regulation of NF-kB

Background: Inflammatory bowel diseases (IBDs) result from environmental and genetic factors and are characterized by an imbalanced immune response in the gut and deregulated activation of the transcription factor NF-kB. Addressing the potential role of gly96/iex-1 in the regulation of NF-kB in IBD, we used the dextran sodium sulfate (DSS) colitis model in mice in which the gly96/iex-1 gene had been deleted. Methods: C57BL/6 mice of gly96/iex-1^-/- or gly96/iex-1^+/+ genotype were treated continuously with 4% DSS (5 days) and repeatedly with 2% DSS (28 days) for inducing acute and chronic colitis, respectively. In addition to clinical and histological exploration, colon organ culture and bone marrow-derived cells (BMCs) were analyzed for chemo/cytokine expression and NF-kB activation. Results: Compared to wildtype littermates, gly96/iex-1^-/- mice exhibited an aggravated phenotype of both acute and chronic colitis, along with a greater loss of body weight and colon length. Colonic endoscopy revealed a higher degree of hyperemia, edema, and bleeding in gly96/iex-1^-/- mice, and immunohistochemistry detected massive mucosal infiltration of leukocytes and marked histological changes. The expression of proinflammatory chemoand cytokines was higher in the colon of DSS-treated gly96/iex-1^-/- mice, and the NF-jB activation was enhanced particularly in the distal colon. In cultured BMCs from gly96/iex-1^-/- mice, Pam3Cys4 treatment induced expression of proinflammatory mediators to a higher degree than in gly96/iex-1^+/+ BMCs, along with greater NF-kB activation. Conclusions: Based on the observation that genetic ablation of gly96/iex-1 triggers intestinal inflammation in mice, we demonstrate for the first time that gly96/iex-1 exerts strong antiinflammatory activity via its NF-kB-counterregulatory effect.