Maternal peripheral blood natural killer cells incorporate placenta-associated microRNAs during pregnancy

Although recent studies have demonstrated that microRNAs (miRNAs or miRs) regulate fundamental natural killer (NK) cellular processes, including cytotoxicity and cytokine production, little is known about the miRNAgene regulatory relationships in maternal peripheral blood NK (pNK) cells during pregnancy. In the present study, to determine the roles of miRNAs within gene regulatory networks of maternal pNK cells, we performed comprehensive miRNA and gene expression profiling of maternal pNK cells using a combination of reverse transcription quantitative PCR (RTqPCR)based miRNA array and DNA microarray analyses and analyzed the differential expression levels between first and thirdtrimester pNK cells. Furthermore, we constructed regulatory networks for miRNAmediated gene expression in pNK cells during pregnancy by Ingenuity Pathway Analysis (IPA). PCRbased array analysis revealed that the placentaderived miRNAs [chromosome 19 miRNA cluster (C19MC) miRNAs] were detected in pNK cells during pregnancy. Twentyfive miRNAs, including six C19MC miRNAs, were significantly upregulated in the third compared to firsttrimester pNK cells. The rapid clearance of C19MC miRNAs also occurred in the pNK cells following delivery. Nine miRNAs, including eight C19MC miRNAs, were significantly downregulated in the postdelivery pNK cells compared to those of the thirdtrimester. DNA microarray analysis identified 69 NK cell functionrelated genes that were differentially expressed between the first and thirdtrimester pNK cells. On pathway and network analysis, the observed gene expression changes of pNK cells likely contribute to the increase in the cytotoxicity, as well as the cell cycle progression of third compared to firsttrimester pNK cells. Thirteen of the 69 NK cell functionrelated genes were significantly downregulated between the first and thirdtrimester pNK cells. Nine of the 13 downregulated NKfunctionassociated genes were in silico target candidates of 12 upregulated miRNAs, including C19MC miRNA miR5123p. The results of this study suggest that the transfer of placental C19MC miRNAs into maternal pNK cells occurs during pregnancy. The present study provides new insight into maternal NK cell functions.