Nod1 acts as an intracellular receptor to stimulate chemokine production and neutrophil recruitment in vivo

Abstract

Nod1 is a member of family of intracellular proteins that mediate host recognition of bacterial peptidoglycan. To characterize immune responses mediated by Nod1, synthetic ligand compounds possessing enhanced ability to stimulate Nod1 were developed to study the function of Nod1. Stimulation of epithelial cells with Nod1 stimulatory molecules induced chemokines and other proinflammatory molecules that are important for innate immune responses and recruitment of acute inflammatory cells. Administration of Nod1 ligands into mice induced chemokines and recruitment of acute inflammatory cells, an activity that was abolished in Nod1-null mice. Microarray analysis revealed that Nod1 stimulation induces a restricted number of genes in intestinal epithelial cells compared with that induced by tumor necrosis factor (TNF) α. Nod1 stimulation did not induce TNFα, interleukin 12, and interferon γ, suggesting that the primary role of Nod1 is to induce the recruitment of immune cells. These results indicate that Nod1 functions as a pathogen recognition molecule to induce expression of molecules involved in the early stages of the innate immune response.

A Role of Lipophilic Peptidoglycan-related Molecules in Induction of Nod1-mediated Immune Responses

“…pCMV-SPORT6-hNod1, pMX2-HA-Nod2, pcDNA3-MD2-FLAG, and pcDNA3-TLR4-FLAG have been described (18). Human MonoMac6 cells and human embryonic kidney (HEK) 293T were cultured in RPMI 1640 and Dulbecco's modified Eagle's medium, respectively, containing 10% heat-inactivated fetal calf serum and 100 units/ml penicillin and 100 g/ml streptomycin (all culture reagents from Invitrogen) as described (22).…”

“…Therefore, Nod1 and Nod2 might be involved in the recognition of lipophilic stimulatory molecules on host membranes. Although Nod2 is expressed by several phagocytic cells including monocytes, granulocytes, and dendritic cells (28,29), Nod1 is mainly expressed by non-phagocytotic epithelial cells (22,30). Because the polypronoyl residue of lipids I and II is too large to undergo spontaneous flip-flap translocation, the primary site of interaction between Nod1 and lipophilic stimulatory molecules produced by bacteria is unclear and needs to be determined.…”

“…However, it was possible that the enhanced ability of these acyl compounds is due to stimulation of other host immune regulators or to enhance TLR4 signaling in MonoMac6 cells. To eliminate this possibility, we tested the ability of these acyl compounds to induce immune responses of mouse primary mesothelial cells, which secrete MCP-1 in a Nod1-dependent manner even in the absence of LPS (18,22). All N-acyl iE-DAP compounds that possess enhanced ability to induce NF-B activation in Nod1-expressing HEK293T cells and to enhance LPS-induced cytokine secretion in MonMac6 showed higher induction of chemokine secretion from mesothelial cells isolated from wild-type mice (Fig.…”

The Kinase Activity of Rip2 Determines Its Stability and Consequently Nod1- and Nod2-mediated Immune Responses

“…In particular, stimulation with a synthetic Nod1 ligand has been shown to induce chemokines such as KC (also known as CXCL1) in vitro and in vivo (30,31). Our aim was to determine whether Rip2 kinase activity was involved in chemokine production upon NLR stimulation.…”

Identification of Pathogenic Cardiac CD11c + Macrophages in Nod1-Mediated Acute Coronary Arteritis

“…Recently, the role of Nod1 in nonhematopoietic cells has been demonstrated in numerous in vivo models. [35][36][37] Thus, Nod1 seems to be a principal pattern recognition receptor that shapes nonhematopoietic environments for the function of hematopoietic cells in various physiological and pathological settings.…”