A role for TLR7 activation by miR-146a-3p in antiphospholipid antibody-induced trophoblast IL-8 and inflammasome-mediated IL-1β production

Women with antiphospholipid antibodies (aPL) are at high risk for pregnancy complications. In obstetric antiphospholipid syndrome (APS), aPL specific for beta₂ glycoprotein I (β₂GPI), target the placental trophoblast leading to inflammation. Studies from our group have shown that aPL trigger trophoblast cells to produce elevated inflammatory IL-1β and IL-8 via activation of Toll-like receptor (TLR) 4, and that downstream, IL-1β is mediated by uric acid-induced NLRP3 inflammasome activation, and IL-8 is mediated by a novel TLR8-activating microRNA (miR), miR-146a-3p. The objective of this study was to further explore the role of TLR7- and TLR8-activating miRs in the aPL-driven trophoblast chemokine and inflammasome response. Using the human first trimester trophoblast cell line, Sw.71, we found that aPL elevated miR-146a-3p expression but had no effect on levels of miR-21a, miR-29a or Let-7b. aPL-induced trophoblast IL-8 secretion was reduced by the TLR7 inhibitor, IRS661, and by the TLR8 inhibitor, CU-CPT9a, while aPL-induced uric acid, caspase-1 activity, and IL-1β secretion was reduced only by the TLR7 inhibitor. Over expression of miR-146a-3p using a specific miR mimic induced trophoblast IL-8 secretion in a TLR7- and TLR8-dependent manner, while miR-146a-3p induced trophoblast IL-1β secretion only via TLR7. This study highlights a role for TLR7/TLR8-activating miR-146a-3p as an intermediate signal that contributes to and modulates upstream TLR-driven trophoblast inflammatory responses, and adds to our knowledge of the molecular and innate immune mechanisms that underpin the pathogenesis of obstetric APS.