Structural and functional changes in mitochondria associated with trophoblast differentiation: Methods to isolate enriched preparations of syncytiotrophoblast mitochondria

The syncytiotrophoblast of the human placenta is derived from the fusion of cytotrophoblast cells. The syncytiotrophoblast and cytotrophoblast cells have different functional properties. Here, we document that syncytiotrophoblast mitochondria have a distinct phenotype that differs from that of the mitochondria of cytotrophoblast cells. Syncytiotrophoblast mitochondria are small and have a dense matrix and vesicular cristae. They contain the machinery to convert cholesterol into pregnenolone. The larger cytotrophoblast mitochondria have lamellar cristae and do not have detectable P450(scc). These observations imply that trophoblast mitochondria undergo morphological and functional changes as cytotrophoblast cells differentiate into syncytiotrophoblast. Structural changes in mitochondria and accumulation of P450(scc) were induced in a clonal line of BeWo choriocarcinoma cells by treatment with 8-Br-cAMP, which promotes formation of syncytial structures in these cultures. We conclude that the terminal differentiation program of trophoblast cells includes major changes in the architecture and function of mitochondria. Based on the unique features of syncytiotrophoblast mitochondria, we developed a method to prepare highly enriched syncytiotrophoblast mitochondria from term placenta using differential centrifugation and density gradient centrifugation.