Nod1 Activation by Bacterial iE-DAP Induces Maternal–Fetal Inflammation and Preterm Labor

Abstract

There is a strong association between infection and prematurity; however, the underlying mechanisms remain largely unknown. Nod1 and Nod2 are intracellular pattern recognition receptors that are activated by bacterial peptides and mediate innate immunity. We previously demonstrated that human first-trimester trophoblasts express Nod1 and Nod2, which trigger inflammation upon stimulation. This study sought to determine the expression and function of Nod1 and Nod2 in third-trimester trophoblasts, and to characterize the in vivo effects of Nod1 activation on pregnancy outcome. Human term placental tissues and isolated term trophoblast expressed Nod1, but not Nod2. Activation of Nod1 by its agonist, bacterial γ-D-glutamyl-meso-diaminopimelic acid (iE-DAP), in term trophoblast cultures induced a proinflammatory cytokine profile, characterized by elevated levels of secreted IL-6, GRO-α, and MCP-1, when compared with the control. However, these cytokines were not upregulated in response to Nod2 stimulation with bacterial MDP. Administration of high-dose bacterial iE-DAP to pregnant C57BL/6J mice on embryonic day 14.5 triggered preterm delivery within 24 h. iE-DAP at a lower dose that did not induce prematurity, reduced fetal weight, altered the cytokine profile at the maternal–fetal interface, and induced fetal inflammation. Thus, functional Nod1 is expressed by trophoblast cells across gestation and may have a role in mediating infection-associated inflammation and prematurity. This study demonstrates that pattern recognition receptors, other than the TLRs, may be implicated or involved in infection-associated preterm labor.

Activation of Nod1 Signaling Induces Fetal Growth Restriction and Death through Fetal and Maternal Vasculopathy

“…A recent study demonstrated that administration of iE-DAP to pregnant mice caused preterm birth, reduced fetal weight, and induced proinflammatory responses at the maternal-fetal interface (21), which was in part consistent with our study. We found new evidence that among the various fetal tissues, including the placenta and yolk sac, the production of CCL2 and IL-6 after the stimulation with FK565 was observed predominantly in the vascular tissue, wherein Nod1 was expressed at high levels in a physiological condition.…”

“…Other groups also reported that stimulation of Nod1 directly activated blood vessels and induced the inflammatory response via activation of NF-kB and MAPK pathways, which eventually caused experimental shock in vivo (26,27). However, there was no evidence of cellular infiltration in the arteries of the placentae or fetuses in the current study, which is similar to a previous study using another Nod1 ligand (iE-DAP) (21). When a higher dose of FK565 was injected into pregnant mice, vascular inflammation was induced only in the pregnant mice, but not in the fetal and maternal vessels of the placentae or fetuses (Supplemental Fig.…”

“…1C, 1D). Notably, a previous report showed that maternal injection of iE-DAP, another Nod1 agonist, induced preterm delivery (21). However, FK565 did not induce preterm delivery at 1 mg (0%, n = 29), 10 mg (0%, n = 11) or 500 mg (0%, n = 18) in our study (Fig.…”

Cytokines and the Innate Immune Response at the Materno-Fetal Interface

“…The NOD1 ligand, iEDAP, can induce preterm delivery in a murine model. When lower doses that did not induce preterm delivery were used there was heightened inflammation at the materno-fetal interface and in the fetus itself (Cardenas, Mulla et al 2011). Immunohistochemical studies have shown that the CLR DC-SIGN is expressed by fetal macrophages (Hofbauer cells) within the chorionic villi of the term placenta (Geijtenbeek, van Vliet et al 2001).…”

“…In contrast only NOD1 is expressed in term trophoblast cells. This corresponds to the functional outputs of first versus third trimester trophoblast cells; first trimester cells respond to both MDP and iE-DAP, and third trimester cells only respond to iE-DAP (Abrahams 2011;Cardenas, Mulla et al 2011). The NOD1 ligand, iEDAP, can induce preterm delivery in a murine model.…”