In vivo evidence of inflammasome activation during spontaneous labor at term

Abstract

Objective: Upon inflammasome activation, the adaptor protein of the inflammasome ASC (apoptosis-associated speck-like protein containing a CARD) forms intracellular specks, which can be released into the extracellular space. The objectives of this study were to investigate whether (1) extracellular ASC is present in the amniotic fluid of women who delivered at term; (2) amniotic fluid ASC concentrations are greater in women who underwent spontaneous labor at term than in those who delivered at term in the absence of labor; and (3) amniotic epithelial and mesenchymal cells can form intracellular ASC specks in vitro.

Methods: This retrospective cross-sectional study included amniotic fluid samples from 41 women who delivered at term in the absence of labor (n = 24) or underwent spontaneous labor at term (n = 17). Amniotic epithelial and mesenchymal cells were also isolated from the chorioamniotic membranes obtained from a separate group of women who delivered at term (n = 3), in which ASC speck formation was assessed by confocal microscopy. Monocytes from healthy individuals were used as positive controls for ASC speck formation (n = 3).

Results: (1) The adaptor protein of the inflammasome ASC is detectable in the amniotic fluid of women who delivered at term; (2) amniotic fluid ASC concentration was higher in women who underwent spontaneous labor at term than in those who delivered at term without labor; and (3) amniotic epithelial and mesenchymal cells are capable of forming ASC specks and/or filaments in vitro.

Conclusion: Amniotic fluid ASC concentrations are increased in women who undergo spontaneous labor at term. Amniotic epithelial and mesenchymal cells are capable of forming ASC specks, suggesting that these cells are a source of extracellular ASC in the amniotic fluid. These findings provide in vivo evidence that there is inflammasome activation in the amniotic cavity during the physiological process of labor at term.

Keywords:

• Amnion
• apoptosis-associated speck-like protein containing a CARD (ASC)
• ASC speck
• caspase-1
• chorioamniotic membranes
• chorion
• cytokine
• interleukin-18
• interleukin-1beta
• intra-amniotic inflammation
• pregnancy
• parturition
• pattern recognition receptor (PRR)
• amniotic fluid
• PYD and CARD Domain-Containing Protein (Pycard)
• sterile inflammation

Acknowledgements

This research was supported, in part, by the Perinatology Research Branch (PRB), Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, U. S. Department of Health and Human Services (NICHD/NIH/DHHS), and, in part, with federal funds from the NICHD/NIH/DHHS under Contract No. HHSN275201300006C. This research was also supported by the Wayne State University Perinatal Initiative in Maternal, Perinatal and Child Health. We gratefully acknowledge the PRB Translational Research Laboratory for their contributions to the execution of this study. The authors thank the physicians and nurses from the Center for Advanced Obstetrical Care and Research and the Intrapartum Unit for their help in collecting human samples. The authors also thank staff members of the PRB Clinical Laboratory and the PRB Histology/Pathology Unit for the processing and examination of the pathological sections.

Disclosure statement

The authors report no conflicts of interest.

Additional information

Funding

This research was supported, in part, by the Perinatology Research Branch (PRB), Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, U. S. Department of Health and Human Services (NICHD/NIH/DHHS), and, in part, with federal funds from the NICHD/NIH/DHHS under Contract No. HHSN275201300006C. This research was also supported by the Wayne State University Perinatal Initiative in Maternal, Perinatal and Child Health.