Interleukin‐15 Regulates Decidual Osteopontin Expression in Rats

Abstract

Introduction Placenta accreta (PA) is a potentially life-threatening pregnancy complication in which the placenta invades too deeply into the uterus. The underlying causes of PA remain unknown, but abnormal function of uterine natural killer (uNK) cells may be involved. uNK cells are the most prevalent immune cells within the uterus during early pregnancy. They secrete cytokines and growth factors that are thought to control the depth of placental invasion, yet the function of uNK cells remains poorly characterized. We recently generated rats devoid of uNK cells using targeted genomic editing of the Interleukin-15 (IL15) locus. Il15 encodes a cytokine needed for uNK cell survival. During pregnancy, Il15-deficient dams do not have uNK cells, and they exhibit an over invasive placenta. We therefore hypothesize that uNK cells produce factors during early pregnancy that control the depth of placental invasion. Objective: The goal of this study isto profile gene expression differences in the decidua between wild-type (WT) and IL15-deficient (IL15Δ/Δ) rats during early pregnancy, in order to deduce which genes are expressed by rat uNK cells. Methods: Pregnant IL-15Δ/Δ and WT Sprague-Dawley Holtzman rats (n=3 dams/group) were sacrificed on gestational day (GD) 9.5, conceptuses dissected, mRNA isolated, and global transcriptional changes assessed using Clariom S gene expression array (n=3 conceptuses/dam). Expression of select transcripts was determined in a separate cohort of conceptuses (n=13) using quantitative RT-PCR. To determine localization of perforin (PRF) and osteopontin (OPN), GD 7.5, 9.5, and 11.5 conceptuses were sectioned, and immunohistochemistry (IHC) was performed. Data was analyzed using Student's t-test or Analysis of Variance and P≤0.05 was considered statistically significant, unless indicated otherwise. Results: On GD 9.5, 230 genes were differentially expressed between WT and IL-15Δ/Δ rats (P≤0.01). Gene ontology analysis revealed pathways associated with immune responses, cell migration, and cell adhesion to be significantly altered in IL-15Δ/Δ conceptuses. Notably, we detected a pronounced decrease in Prf, a uNK cell marker (p≤0.0001), and Spp1 (p=0.0031), which encodes OPN. IHC staining of GD 9.5 conceptuses showed intracellular OPN staining in the uterine glands, decidua, and primitive placenta of WT, but not IL-15Δ/Δ rats. OPN and PRF staining was co-localized, suggesting that OPN is produced by uNK cells. Conclusion: IL-15Δ/Δ rats exhibited impaired immune responses and cellular adhesion and migration pathways in the decidua during early pregnancy. OPN expression was significantly decreased in IL-15Δ/Δ rats at mRNA and protein levels. We believe that reduced OPN in the decidua of IL-15Δ/Δ rats may contribute to the increased placental invasion that is apparent in these rats. Significance: This study provides new insights into factors produced by uNK cells that may contribute to the regulation of placental invasion during pregnancy. We are currently determining whether OPN is directly involved in controlling the extent of placental cell adhesion and invasion. Our research will lead to a better understanding of the early events controlling decidualization and placentation, and may provide insight into the mechanisms of serious placental diseases like PA.