ABSTRACT: NLRX1 is a mitochondrial-associated NOD-like receptor that modulates antiviral immunity, cellular stress, autophagy, and reactive oxygen species (ROS) production. The role of NLRX1 in inflammatory bowel disease (IBD) remains largely unknown. This study aimed to characterize NLRX1-mediated mechanisms of protection from IBD. We investigated the ability of NLRX1 to modulate global colonic gene expression, gut pathology, inflammation and immunity by using loss-of-function approaches in dextran sodiu sulfate (DSS) and CD4+CD45RBhigh transfer colitis models. Colons, spleens, and mesenteric lymph nodes (MLN) were excised for characterizing immune cell subsets, histological analyses, cytokine, RNA sequencing analyses, and autophagy expression, NF-κB activity, and ROS production. The loss of NLRX1 increased severity of disease and colonic histopathology in both models of IBD. Colons of NLRX1-/- mice had significantly increased epithelial ulceration and leukocyte infiltration mostly in the form of neutrophils, lymphocytes, and macrophages in the DSS model, while recipients of NLRX1-/- CD4+ T cells had increased leukocytic infiltration, proliferation, fibrosis, and crypt abscessation in both colon and ileum. The loss of NLRX1 increased numbers of effector T helper (Th1), Th17, and regulatory T cells (Treg) cells in the colonic mucosa and spleen, increased colonic NF-κB activity, upregulation of IL-17, IFNγ and TNF-α production, and increased ROS production. Global transcriptomic analyses demonstrates that NLRX1 regulates immunity and lipid metabolism pathways. NLRX1 ameliorates intestinal pathology during IBD by acting as an internal thermostat that modulates the balance of effector versus regulatory CD4+ T cell responses, and suppressing colonic NF-κB activity, inflammatory cytokine expression, lipid metabolism gene expression, ROS production and autophagy.
