Defective inflammasome signalling in trophoblasts: implications for aberrant trophoblast innate and immune responses in preeclampsia.

Objectives: Pre-eclampsia (PE) is a multi-systemic disorder that manifests primarily with hypertension and proteinuria, presents in the second half of pregnancy and affects between 3% to 5% of pregnancies worldwide. PE originates in the placenta, although the molecular basis of the placental dysfunction associated with PE is largely unknown. The human placenta is immunologically functional with trophoblasts able to generate specific and diverse innate and immune responses through the expression of multimeric self-assembling protein complexes, termed inflammasomes. However, the expression of the components of the placental inflammasomes in PE is incompletely understood. We hypothesised that the expression of the components of the inflammasomes will be increased in PE.

Methods: Human placentae from PE (n=20) and gestation-matched control pregnancies (n=20, 28-40 weeks of gestation) were collected to determine the expression of the components of the inflammasomes using a Fluidigm Biomark™ array and independently validated by real-time PCR. Candidate inflammasome expression was further investigated in human placental organoids (6-9 weeks of gestation, n=6) with PE-like insults in vitro following pre-treatment for inflammation (low-dose lipopolysaccharide, 1ng/mL) or oxidative stress ((2.3mM xanthine and 0.0015 units xanthine oxidase) or hypoxia (1% O2) over 72h in culture.

Results: Placental mRNA expression of inflammasome components including NLRP3, NLRC5, CASP1, NFκB1, IFNγ, IL-1β and IL-6, relative to 18S rRNA were significantly increased (p<0.001), while the anti-inflammatory cytokine, IL-10 mRNA expression was significantly decreased, in PE compared with controls (all p<0.001). NLRP3 expression and secretion was similarly increased in the in vitro human placental organoid model established.

Conclusion: Enhanced expression of components of the inflammasomes was observed in both the in vitro model of placental organoids and PE-associated intact human placentae. Inflammasome expression was also associated with increased pro-inflammatory cytokine expression in PE. Further functional analysis in placental cells may identify inflammasomes as potential biomarkers of pregnancies at risk of developing PE.