Human trophoblast invasion and migration are mediated by the YAP1-CCN1 pathway: defective signaling in trophoblasts during early-onset severe preeclampsia

The transcription coactivator YAP1 mediates the major effects of the Hippo signaling pathway. The CCN family is a small group of glycoproteins known to be downstream effectors of YAP1 in diverse tissues. However, whether CCN family members mediate the effects of YAP1 in human trophoblasts is unknown. In this study, placental expression of both YAP1 and CCN1 was found to be impaired in pregnancies complicated by early-onset severe preeclampsia (sPE). CCN1 was expressed not only in cytotrophoblasts, trophoblast columns and mesenchymal cells, similar to active YAP1, but also in syncytiotrophoblasts of normal first-trimester placental villi; moreover, decidual staining of active YAP1 and CCN1 was found in both interstitial and endovascular extravillous trophoblasts. In cultured immortalized human trophoblastic HTR-8/SVneo cells, knockdown of YAP1 decreased CCN1 mRNA and protein expression and led to impaired cell invasion and migration. Also, CCN1 knockdown negatively affected HTR-8/SVneo cell invasion and migration but not viability. YAP1 knockdown was further found to impair HTR-8/SVneo cell viability via G0/G1 cell cycle arrest and apoptosis, while CCN1 knockdown had minimal effect on cell cycle arrest and no effect on apoptosis. Accordingly, treatment with recombinant CCN1 partially reversed the YAP1 knockdown-induced impairment in trophoblast invasion and migration but not in viability. Thus, CCN1 mediates the effects of YAP1 on human trophoblast invasion and migration but not apoptosis, and decreased placental expression of YAP1 and CCN1 in pregnancies complicated by early-onset sPE might contribute to the pathogenesis of this disease.