Downregulation of miR-33a/b and miR-181a contributes to recurrent pregnancy loss by upregulating S1PR1 and repressing regulatory T cell differentiation.

INTRODUCTION: Successful pregnancy in humans requires adequate maternal-fetal immune tolerance. During regulatory T (Treg) cells play a key role. Sphingosine-1-phosphate (S1P) and S1P receptor (S1PR) signaling represses Treg cell differentiation, but whether this relates to the process of recurrent pregnancy loss is still unclear.

METHODS: Treg cells in the placenta were examined using flow cytometry. The expression of sphingosine kinase-1 and -2(SPHK1 and SPHK2), two key kinases controlling S1P production, was detected in placenta samples from 36 patients with recurrent pregnancy loss (RPL) and 40 control participants using immunoblotting. The level of sphingosine-1-phosphate receptor-1 (S1PR1) in placental T cells was examined using RT-qPCR and immunoblotting. Cell surface S1PR1 levels were detected using flow cytometry. The interactions between miRNAs and S1PR1 mRNA were predicted using bioinformatics tools and were confirmed by dual luciferase assay and immunoblotting.

RESULTS: RPL patients had fewer Treg cells (p = 0.034) in the placenta, especially TIM3+ Treg cells (p = 0.0076). S1PR1 protein levels were significantly increased in placental T cells of patients with RPL (p = 0.0065). MiR-33a, miR-33b, and miR-181a were reduced in the placenta from patients with RPL, which were identified to repress S1PR1 expression by targeting the 3'UTR. Knockdown of miR-33a, miR-33b and miR-181a in human naïve T cells inhibits Treg cell differentiation by upregulating S1PR1 in vitro.

DISCUSSION: This study, for the first time, successfully constructed the correlation between dysregulated miRNAs in placenta and RPL, which partially unveiled the etiology of RPL and provided a therapeutic potential for RPL treatment.