Detection of Fetal DNA and RNA in Placenta-Derived Syncytiotrophoblast Microparticles Generated in Vitro

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Abstract
Fetal DNA and RNA can be readily detected in maternal plasma samples (1)(2)(3)(4). Most of this material appears to be of placental origin (5), and it appears to be in a predominantly cell-free form (2), whereas circulatory mRNA is membrane-encapsulated (6). Pregnancy is associated with the release of microparticles by the syncytiotrophoblast membrane into the maternal circulation (7). These particles, frequently termed STBM, are released by turnover of the syncytiotrophoblast monolayer covering the entire villous tree (8)(9)(10)(11). This process of normal physiologic syncytiotrophoblast turnover involves the release of apoptotic material into the maternal circulation by the extrusion of syncytial knots and the associated release of STBM (8)(9)(10)(11). The amount of material that is released by apoptotic shedding of syncytial knots (and STBM) is several grams per day (9), and the circulating concentrations are increased significantly in preeclampsia (11). STBM particles have been suggested to evoke the mild maternal inflammatory response accompanying normal pregnancies (12), and increased release has been proposed to play a role in the etiology of preeclampsia by triggering maternal endothelial cell damage (13)(14). As these particles are difficult to detect and prepare from maternal blood samples, use is frequently made of in vitro-prepared particles to study their physiologic activity (13). In this context, we have recently extensively examined three different modes of STBM preparation: mechanical dissection of fresh placental villous tissues; in vitro cultures of villous explants; and perfusion of single placental cotyledons (15). All three preparations lead to the production of STBM as confirmed by the presence of the syncytiotrophoblast-specific protein placental alkaline phosphatase, physiologic activity on human endothelial cell cultures, and their morphology, as seen by scanning electron microscopy (15). …