Synthesis of phospholipids in human placenta

Placental phospholipid synthesis is critical for the expansion of the placental exchange surface area and for production of signaling molecules. Despite their importance, it is not yet established which enzymes involved in the de novo synthesis and remodeling of placental phospholipids are expressed and active in the human placenta.

We identified phospholipid synthesis enzymes by immunoblotting in placental homogenates and immunofluorescence in placenta tissue sections. Primary human trophoblast (PHT) cells from term healthy placentas (n = 10) were cultured and exposed to ¹³C labeled fatty acids (16:0, 18:1 and 18:2 n-6, 22:6 n-3) for 2 and 24 h. Three phospholipid classes; phosphatidic acid, phosphatidylcholine, and lysophosphatidylcholine containing ¹³C fatty acids were quantified by Liquid Chromatography with tandem mass spectrometry (LC/MS-MS).

Acyl transferase and phospholipase enzymes were detected in human placenta homogenate and primarily expressed in the syncytiotrophoblast. Three representative ¹³C fatty acids (16:0, 18:1 and 18:2 n-6) were incorporated rapidly into phosphatidic acid in trophoblasts, but ¹³C labeled docosahexaenoic acid (DHA; 22:6 n-3) incorporation was not detected. ¹³C DHA was incorporated into phosphatidylcholine. Lysophosphatidylcholine containing all four ¹³C labeled fatty acids were found in high abundance.

Phospholipid synthesis and remodeling enzymes are present in the syncytiotrophoblast. ¹³C labeled fatty acids were rapidly incorporated into cellular phospholipids. ¹³C DHA was incorporated into phospholipids through the remodeling pathway rather than by de novo synthesis. These understudied pathways are highly active and critical for structure and function of the placenta.