Excessive placental inflammation is associated with several pathological conditions, including stillbirth and fetal growth restriction (FGR). While infection is a known cause of inflammation, a significant proportion of pregnancies have evidence of inflammation without any detectable infection. Inflammation can also be triggered by endogenous mediators, called damage associated molecular pattern (DAMPs) or alarmins. One of these DAMPs, uric acid is increased in the maternal circulation in pathological pregnancies and is a known agonist of the Nlrp3 inflammasome and inducer of inflammation. However its effects within the placenta and on pregnancy outcome remain largely unknown. We found that uric acid crystals (monosodium urate, MSU, crystals) induces a pro-inflammatory profile in isolated human term cytotrophoblast cells, with a predominant secretion of IL-1β and IL-6, a result confirmed in human term placental explants. Pro-inflammatory effects of MSU crystals were shown to be IL-1-dependent using a caspase-1 inhibitor (inhibits IL-1 maturation) and IL-1Ra (inhibits IL-1 signaling). The pro-inflammatory effect of MSU crystals was accompanied by trophoblast apoptosis and decreased syncytialisation. Correspondingly, administration of MSU crystals to rats during late gestation induced placental inflammation and was associated with fetal growth restriction. These results make a strong case for an active pro-inflammatory role of MSU crystals at the maternal-fetal interface in pathological pregnancies, and highlight a key mediating role of IL-1. Furthermore, our study describes a novel in vivo animal model of non-infectious inflammation during pregnancy, which is triggered by MSU crystals and leads to reduced fetal growth.

No abstract

This protocol describes how villous cytotrophoblast cells are isolated from placentas at term by successive enzymatic digestions, followed by density centrifugation, media gradient isolation and immunomagnetic purification. As observed in vivo, mononucleated villous cytotrophoblast cells in primary culture differentiate into multinucleated syncytiotrophoblast cells after 72 hr. Compared to normoxia (8% O2), villous cytotrophoblast cells that undergo hypoxia/reoxygenation (0.5% / 8% O2) undergo increased oxidative stress and intrinsic apoptosis, similar to that observed in vivo in pregnancy complications such as preeclampsia, preterm birth, and intrauterine growth restriction. In this context, primary villous trophoblasts cultured under hypoxia/reoxygenation conditions represent a unique experimental system to better understand the mechanisms and signalling pathways that are altered in human placenta and facilitate the search for effective drugs that protect against certain pregnancy disorders. Human villous trophoblasts produce melatonin and express its synthesizing enzymes and receptors. Melatonin has been suggested as a treatment for preeclampsia and intrauterine growth restriction because of its protective antioxidant effects. In the primary villous cytotrophoblast cell model described in this paper, melatonin has no effect on trophoblast cells in normoxic state but restores the redox balance of syncytiotrophoblast cells disrupted by hypoxia/reoxygenation. Thus, human villous trophoblast cells in primary culture are an excellent approach to study the mechanisms behind the protective effects of melatonin on placental function during hypoxia/reoxygenation.

No abstract