Antiphospholipid antibodies (aPL) are autoantibodies that cause pregnancy complications including stillbirth, recurrent miscarriage, and preeclampsia by a poorly defined mechanism. These maternal autoantibodies are internalised by the placental syncytiotrophoblast where they induce intracellular changes as well as changes in the extracellular vesicles (EVs) this cell produces. We have previously identified changes in individual proteins in EVs from aPL (eg HMGB-1) that may trigger adverse reactions in the placenta or maternal physiology. Here we took an unbiased approach to quantifying the total changes in the proteome of EVs from aPL-treated placentae.
Placental explants were cultured with monoclonal aPL (n=5) or an isotype-matched control antibody (n=5). Nano-vesicles were harvested by differential centrifugation and further enriched using qEV size-exclusion chromatography. The proteomes of the enriched vesicles were quantified by SWATH. The String Network software was used to analyse the list of proteins obtained from SWATH analysis.
A total of 2583 proteins were quantified in the nano-vesicles of which 28 were more than twice as abundant in the EVs from aPL-treated placentae. These proteins were involved in pathways regulating the rate of production of proteins within cells. In particular, proteins that are a part of the large ribosomal subunit, the proteasome core and spliceosome subunits were more abundant in EVs from aPL-treated placentae. Proteins involved in the transfer of particles between the nucleus and cytoplasm were also more abundant in EVs from aPL-treated placentae.
Antiphospholipid antibodies either significantly upregulated the expression or increased the packaging of these proteins into nano-vesicles. This suggests aPL may affect syncytiotrophoblast cellular function through upregulation of subcellular components involved in the rate of protein synthesis. The increase in proteins that facilitate nuclear to cytoplasmic transfer is also consistent with our previous findings of increases in cytoplasmic and vesicular HMBG-1 which is typically a nuclear protein.