Impairment of a NIK-SIX Feedback Axis Results in Dysregulation of Intestinal Immune Homeostasis and Promotes Early-onset Fatal Spontaneous Colitis.

Abstract

The negative feedback circuit NIK-SIN could inhibit the systemic inflammation and protect mouse from endotoxic shock. However, the physiological significance of NIK-SIX feedback circuit in the maintenance of intestinal immune homeostasis and prevention of early-onset spontaneous colitis is not known. To explore the role of NIK-SIX axis in the maintenance of intestinal immune homeostasis. The conditional knockout of NIK encoding gene, Map3k14, in the Cd11c+ dendritic cells were generated by crossing Map3k14-flox mice with Cd11c-Cre mice. DSS was used for colitis models. The expression of cytokines in the intestinal immune cells, isolated from Map3k14-cKO mice were detected by qPCR. The siRNA molecules were used for the silencing of SIN-proteins. Then luciferase assays and chromatin immunoprecipitation combined with qPCR were applied for mechanism investigations. The expression of SIX1 and SIX2 protein in BMDMs from WT were significantly lower than in the Map3k14-cKO mice. In vitro, the NIK-/- human-derived circulating monocytes also failed to express SIX-proteins under the stimulation of non-canonical NF-κB agonists. The expression of cytokines was significantly decreased in human circulating monocytes with overexpression SIN-proteins. The expression of cytokines in macrophages, DCs and T cells isolated from Map3k14-cKO mice were significantly increased in the DSS-induced models. Higher expression of cytokines was observed in the SIN1-/- and SIN2-/- cells including human circulating monocytes, mouse-derived BMDMs, intestinal macrophages and DCs. SIN-proteins directly bound the promoter region of inflammatory genes. NIK-SIX axis down-regulated inflammatory gene expression and plays a pivotal role in the maintenance of intestinal immune homeostasis.