Pregnancies in women with the antiphospholipid syndrome (APS) are frequently complicated by fetal loss and intrauterine growth restriction (IUGR). How circulating antiphospholipid antibodies (aPL) cause pregnancy complications in APS is poorly understood. We sought to determine whether the low-density lipoprotein receptor family member apolipoprotein E receptor 2 (ApoER2) mediates trophoblast dysfunction and pregnancy complications induced by aPL.
Placental and trophoblast ApoER2 expression was evaluated by immunohistochemistry and immunoblotting. Normal human IgG and aPL were purified from healthy individuals and APS patients, respectively. The role of ApoER2 in aPL-induced changes in trophoblast proliferation and migration and in kinase activation was assessed using RNA interference in HTR-8/SVneo cells. The participation of ApoER2 in aPL-induced pregnancy loss and IUGR was evaluated in pregnant ApoER2(+/+) and ApoER2(-/-) mice injected with aPL or normal human IgG.
We found that ApoER2 is abundant in human and mouse placental trophoblasts and in multiple trophoblast-derived cell lines, including HTR-8/SVneo cells. ApoER2 and its interaction with the cell surface protein β2 -glycoprotein I were required for aPL-induced inhibition of cultured trophoblast proliferation and migration. In parallel, aPL antagonism of Akt kinase activation by epidermal growth factor in trophoblasts was mediated by ApoER2. Furthermore, in a murine passive-transfer model of pregnancy complications of APS, ApoER2(-/-) mice were protected from both aPL-induced fetal loss and aPL-induced IUGR.
ApoER2 plays a major role in the attenuation of trophoblast function by aPL, and the receptor mediates aPL-induced pregnancy complications in vivo in mice. ApoER2-directed interventions can now potentially be developed to combat the pregnancy complications associated with APS.