Acetylated low density lipoprotein endocytosis by human syncytiotrophoblast in culture.

Low density lipoproteins (LDL) were chemically modified (acetyl LDL) and then conjugated to colloïdal gold (gold acetyl LDL), firstly, to visualize the acetyl LDL binding sites, and secondly, to demonstrate a possible internalization by human syncytiotrophoblast in culture. Cells were obtained by a trypsin DNase method followed by a Percoll gradient centrifugation. After 3 days of culture the syncytiotrophoblast characterization was performed by using ultramicroscopy, immunohistochemistry, and by studying the secretion of gestational hormones during culture. Binding experiments showed gold acetyl LDL attached to the membrane with random distribution. After incubation at 37 degrees C, gold acetyl LDL was internalized by the syncytiotrophoblast following the classical receptor mediated endocytosis process and a non-specific internalization process. These results suggest the existence in the placenta of a 'scavenger pathway' concomittant of the classical LDL internalization. This phenomenon may be related to the high amount of cholesterol required by the human placenta for its cellular growth and intensive progesterone synthesis.