Listeria Monocytogenes Induces The Activation Of NLRP3Inflammasome In Trophoblast Cells

Listeria monocytogenes is a Gram-positive intracellular bacterium whichubiquitously exsits. Although the incidence of listeriosis is lower, Listeriamonocytogenes pose a great threat to human health and agriculture because of thesevere effects. Listeria monocytogenes especially infect immunosuppressedindividuals, such as the elder, the neonatus and pregnant women and inducepregnancy complications, such as miscarry, preterm labor, fetal developmentaldisability.Innate immune system act as the primary defense against invading pathogenicmicrobes. As a part of innate immune system, inflammasome is a large cytoplasmiccomplexes which consist of PRRs, pro-caspase-1and the adaptor ASC. With theformation of inflammasome, it catalyses the auto-proteolytic activation ofpro-caspase-1which results in IL-1β/IL-18maturation and cell death termed“pyrotosis”, a type of programmed cell death depending on the activation ofcaspase-1. Pathogenic microbes or its components, such as Listeria monocytogene,nigericin, microbial DNA can trigger inflammasome’s activation which plays a rolein the battle adainst invading microbes. Up to now, it have not been reported thatListeria monocytigenens active trophoblastic inflammasome in the maternal-fetalinterface.Not only is the placenta a bridge linking mother and fetus, but also a placewhere they can exchange mutual matter and energe. Trophoblast cells are part ofplacental barrier which prevent pathogens crossing over. Moreover, trophoblast cellsexhibit intense phagocytic activity and express many PRRs, which make trophoblastcells respond to invading pathogen. Therefore,wo hypothesize that functionalinflammasomes could exist in trophoblast cells and probably play a role in the defence against microbes.This research was conducted to primarily detect the activation of inflammasomein Listeria-infected placenta. The results showed that bioactive caspase-1and IL-1βwere elevated and the secretion of IL-1β was increased, which gave an evidence tosupport the activation of inflammasome in placenta.Trophoblast cells are part of placental barrier and are very important forplacental barrier. In order to confirm the activation of inflammasome in placenta isdue to the trophoblast cells, we explore the expression of NLRP3inflammasome andAIM2inflammasome associated genes in human placental villi and varioustrophoblast cell lines by PCR, Western Blot and immunohistochemical. And wefound that human placental villi and3trophoblast cell lines: HTR-8/SV40, JAR,JEG3, all of them constitutively expressed inflammasome associated genes such asNLRP3, AIM2, ASC, caspase-1. This implied trophoblast cells could functionallyactive inflammasome. Then we analyzed the activation of HTR-8/SV40infectedwith Listeria monocytogenes in the presence of LPS or not. We found that bioactiveIL-1β was increased, proteolytic activitity of caspase-1was enhanced and thesecretion of IL-1βrose. These results were consistant with that in vivo and weensured the activation of inflammasome in trophoblast cells contributed to that inListeria-infected placenta. Furthermore, we observed an increased NLRP3whichindicated the activation of NLRP3inflammasome. Subsequently, wo isolatedprimary trophoblast cells derived from C57BL/6J and NLRP3-/-, following by theinfection with Listeria monocytogenes. The results showed an attenuated secretion ofIL-1β and confirmed our assumption.Finally, we infected pregnant C57BL/6J and NLRP3-/-mice with Listeriamonocytogenes respectively. The results showed an more detrimental pregnancyoutcome in NLRP3-/-mice and an increased fetal loss rate in comparison withC57BL/6J mice.In conclusion, this research revealed an function role of trophoblast cells whichcould prevent Listeria-induced abortion via NLRP3inflammasome and provided an insight into the molecular mechanism of the role of trophoblast cells in thedefence against microbes.