The pregnancy-specific hypertensive disorder preeclampsia is triggered by a placental “toxin”, and trophoblast debris that is shed from the syncytiotrophoblast into the maternal blood, may be one toxin. The largest fragment of trophoblast debris is multinucleated syncytial nuclear aggregates (SNAs). SNAs are extruded from the placenta to become trapped in the maternal lungs. The clearance of SNAs is most likely affected by pulmonary endothelial cells and changes in SNAs may alter endothelial cell responses to them. Antiphospholipid autoantibodies (aPL) increase a woman’s risk of preeclampsia 9-fold and affect the extrusion of trophoblast debris. This study was undertaken determine whether aPL induce changes in the proteome of SNAs.
Placental explants (138) from 10 first trimester placentae were cultured with the murine monoclonal antiphospholipid antibody ID2 or an isotype-matched control (50µg/mL) for 24 hours in Netwells. Individual SNAs (1117±120 SNAs/treatment) were isolated using a micromanipulator. SNAs from each of the treatments were lysed, labelled with iTRAQ reagents and analysed by LC-tandem mass spectrometry. Data was analysed using the one sample t-test and corrected for multiple testing using the Benjamini-Hochberg method.
The aPL increased the numbers of SNA extruded from placental explants by 57% (p<0.05). 190 proteins were differentially expressed between the SNAs from aPL-treated and control explants of which 29 were associated with apoptosis (p<0.05, Gene Ontology GO: 0042981). Immunohistochemical validation experiments confirmed annexin A5 expression was significantly reduced (p<0.05) in SNAs and calreticulin expression was increased in the syncytiotrophoblast of placentae treated with aPL.
Antiphospholipid antibodies caused a major change in the proteome of SNAs. Many of the differentially expressed proteins were involved in the regulation of syncytiotrophoblast cell death. This proteomic investigation suggests that aPL may contribute to the pathogenesis of preeclampsia by altering the normal cell death process that occurs in the syncytiotrophoblast, leading to the extrusion of SNAs that are more likely to cause maternal endothelial dysfunction.