Novel Mechanisms Of Trophoblast Responses To Antiphospholipid Antibodies And Therapeutics In Obstetric Antiphospholipid Syndrome

Obstetric antiphospholipid syndrome (APS) is a systemic autoimmune disorder characterized by circulating antiphospholipid antibodies (aPL) and an increased risk of recurrent pregnancy loss and preeclampsia. Current treatments, such as low molecular weight heparin (LMWH) may maintain pregnancy but do not reduce the risk of these late gestational complications. aPL trigger placental inflammation by activating trophoblast Toll-like receptor 4 (TLR4), leading to cytokine production. Since some microRNAs (miRs) regulate TLR responses, this study sought to determine the functional role of aPL-induced miR expression in regulating trophoblast inflammation. Since vitamin D deficiency is common in APS patients, the effect of vitamin D on trophoblast function in the setting of aPL and LMWH was also evaluated. Thus, the human first trimester trophoblast cell line (HTR8) and primary trophoblast cultures were incubated with or without aPL in the presence or absence of vitamin D and/or LMWH. miR expression was profiled using RT-qPCR, and cytokine secretion was measured by ELISA. miR function was assessed by transfection of specific miR mimics or inhibitors. Indeed, treatment of trophoblast cells with aPL significantly upregulated expression of miR-146a-5p, miR146a-3p, miR-155, and miR-210 when compared to controls. Furthermore, miR-146a-5p and miR-146a-3p upregulation by aPL was TLR4 dependent. Functional studies demonstrated that miR-146a-3p directly promoted trophoblast IL-8 secretion by activating the RNA sensing receptor, TLR8. Vitamin D reduced aPL-induced miR-146a5p, IL-8 and LMWH-induced sFlt-1 release, but did not reduce aPL-induced miR-146a3p. These findings suggest that aPL induce trophoblast IL-8 production through upregulation of miR-146a-3p and subsequent activation of TLR8. Our findings also suggest that that vitamin D can dampen this inflammatory response downstream of miR146a-3p. Thus, further study of trophoblast miR function in the context of aPL and the therapeutic potential of vitamin D for obstetric APS is warranted.