title: Human placenta secretes apolipoprotein B-100-containing lipoproteins.
abstract: Supply of lipids from the mother is essential for fetal growth and development. In mice, disruption of yolk sac cell secretion of apolipoprotein (apo) B-containing lipoproteins results in embryonic lethality. In humans, the yolk sac is vestigial. Nutritional functions are instead established very early during pregnancy in the placenta. To examine whether the human placenta produces lipoproteins, we examined apoB and microsomal triglyceride transfer protein (MTP) mRNA expression in placental biopsies. ApoB and MTP are mandatory for assembly and secretion of apoB-containing lipoproteins. Both genes were expressed in placenta and microsomal extracts from human placenta contained triglyceride transfer activity, indicating expression of bioactive MTP. To detect lipoprotein secretion, biopsies from term placentas were placed in medium with [(35)S]methionine and [(35)S]cysteine for 3-24 h. Upon sucrose gradient ultracentrifugation of the labeled medium, fractions were analyzed by apoB-immunoprecipitation. (35)S-labeled apoB-100 was recovered in d approximately 1.02-1.04 g/ml particles (i.e. similar to the density of plasma low density lipoproteins). Electron microscopy of negatively stained lipoproteins secreted from placental tissue showed spherical particles with a diameter of 47 +/- 10 nm. These results demonstrate that human placenta expresses both apoB and MTP and consequently synthesize and secrete apoB-100-containing lipoproteins. Placental lipoprotein formation constitutes a novel pathway of lipid transfer from the mother to the developing fetus.
authors.affiliation: Department of Clinical Biochemistry, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, DK-2100 Copenhagen, Denmark.
authors.forename: Eva M
authors.initials: EM
authors.lastname: Madsen
authors.forename: Marie L S
authors.initials: ML
authors.lastname: Lindegaard
authors.forename: Claus B
authors.initials: CB
authors.lastname: Andersen
authors.forename: Peter
authors.initials: P
authors.lastname: Damm
authors.forename: Lars B
authors.initials: LB
authors.lastname: Nielsen
mesh_terms: D000818:Animals; D053299:Apolipoprotein B-100; D001055:Apolipoproteins B / Q000378:metabolism*; D001706:Biopsy; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D002499:Centrifugation, Density Gradient; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D006868:Hydrolysis; D047468:Immunoprecipitation; D050356:Lipid Metabolism; D008074:Lipoproteins / Q000737:chemistry / Q000378:metabolism*; D008077:Lipoproteins, LDL / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008854:Microscopy, Electron; D010920:Placenta / Q000378:metabolism* / Q000648:ultrastructure; D012333:RNA, Messenger / Q000378:metabolism; D013395:Sucrose / Q000494:pharmacology; D014280:Triglycerides / Q000378:metabolism
chemical_list: D053299:Apolipoprotein B-100; D001055:Apolipoproteins B; D002352:Carrier Proteins; D018076:DNA, Complementary; D008074:Lipoproteins; D008077:Lipoproteins, LDL; D012333:RNA, Messenger; D014280:Triglycerides; C106092:microsomal triglyceride transfer protein; D013395:Sucrose