Occurrence of an unusual phospholipid, phosphatidyl-L-threonine, in cultured hippocampal neurons. Exogenous L-serine is required for the synthesis of neuronal phosphatidyl-L-serine and sphingolipids.
We have recently reported that L-serine released from astroglial cells supports the survival and neuritogenesis of hippocampal neurons under a serum- and glia-free culture condition (Mitoma, J., Furuya, S., and Hirabayashi, Y. (1998) Neurosci. Res. 30, 195-199). In this study, we show that exogenous L-serine is required for the synthesis of phosphatidyl-L-serine (PS) and sphingolipids in hippocampal neurons. When hippocampal neurons were maintained under an astroglial cell-free condition, the levels of sphingolipids and phosphatidyl-L-serine in the neurons were greatly reduced in the absence of external L-serine or glycine. Instead, a novel phospholipid appeared just ahead of PS on TLC. This novel lipid was determined to be phosphatidyl-L-threonine by TLC blotting/negative secondary ion mass spectrometry and amino acid analysis. Biochemical studies on rat brain microsomes have indicated that phosphatidyl-L-threonine is synthesized by the base exchange enzyme that is involved in PS synthesis with much lower affinity, that is, approximately (1)/(150) of L-serine. Addition of L-serine or glycine to the culture medium restored the synthesis of PS and sphingolipids in the neurons. These observations show that hippocampal neurons require exogenous L-serine for the synthesis of PS and sphingolipids in the absence of astroglial cells and suggested that astroglial cells contribute to neuronal lipid synthesis through the supply of L-serine.
Laboratory for Cellular Glycobiology, Frontier Research Program, The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-0198, Japan.
J
J
Mitoma
T
T
Kasama
S
S
Furuya
Y
Y
Hirabayashi
D000818:Animals; D001253:Astrocytes / Q000737:chemistry*; D002478:Cells, Cultured; D002855:Chromatography, Thin Layer; D005732:Gangliosides / Q000737:chemistry; D020404:Glycerophospholipids; D006624:Hippocampus / Q000737:chemistry*; D007700:Kinetics; D013058:Mass Spectrometry; D008861:Microsomes / Q000201:enzymology; D010712:Phosphatidic Acids / Q000737:chemistry*; D010718:Phosphatidylserines / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D012694:Serine / Q000378:metabolism; D013107:Sphingolipids / Q000032:analysis; D013912:Threonine / Q000031:analogs & derivatives* / Q000737:chemistry
D005732:Gangliosides; D020404:Glycerophospholipids; D010712:Phosphatidic Acids; D010718:Phosphatidylserines; D013107:Sphingolipids; C017629:phosphatidylthreonine; D013912:Threonine; D012694:Serine