Occurrence of phosphatidyl-D-serine in the rat cerebrum

Phosphatidylserine in the brain: metabolism and function

Phosphatidylserine (PS) is the major anionic phospholipid class particularly enriched in the inner leaflet of the plasma membrane in neural tissues. PS is synthesized from phosphatidylcholine or phosphatidylethanolamine by exchanging the base head group with serine, and this reaction is catalyzed by phosphatidylserine synthase 1 and phosphatidylserine synthase 2 located in the endoplasmic reticulum. Activation of Akt, Raf-1 and protein kinase C signaling, which supports neuronal survival and differentiation, requires interaction of these proteins with PS localized in the cytoplasmic leaflet of the plasma membrane. Furthermore, neurotransmitter release by exocytosis and a number of synaptic receptors and proteins are modulated by PS present in the neuronal membranes. Brain is highly enriched with docosahexaenoic acid (DHA), and brain PS has a high DHA content. By promoting PS synthesis, DHA can uniquely expand the PS pool in neuronal membranes and thereby influence PS-dependent signaling and protein function. Ethanol decreases DHA-promoted PS synthesis and accumulation in neurons, which may contribute to the deleterious effects of ethanol intake. Improvement of some memory functions has been observed in cognitively impaired subjects as a result of PS supplementation, but the mechanism is unclear.

Identification of novel mammalian phospholipids containing threonine, aspartate, and glutamate as the base moiety

In this study, we showed the occurrence of phosphatidyl-L-threonine (PThr), phosphatidyl-L-aspartate (PAsp), and phosphatidyl-L-glutamate (PGlu) in rat brain. Analyses using an HPLC-ESI-MS and an amino acid analyzer showed the presence of L-threonine, L-aspartate, and L-glutamate in the acid-hydrolysates of phospholipids from porcine cerebrum, rat cerebrum, and rat liver. Results of ESI-MS/MS analyses with neutral loss scanning and product ion scanning suggest the presence of PThr-(18:0, 18:1), PThr-(18:0, 22:6), PAsp-(18:0, 18:1), PAsp-(18:0, 22:6), PGlu-(18:0, 18:1), and PGlu-(18:0, 22:6) in rat brain. This is the first study to identify 2 novel phospholipids, PAsp and PGlu, with a carboxylate-phosphate anhydride bond, in living organisms.

The distribution of phosphatidyl-D-serine in the rat

Phosphatidylserine plays an important role in cell membranes. We have reported the occurrence of phosphatidyl-D-serine (D-PS) in the rat cerebrum. Here, we describe the tissue distribution of D-PS in the rat. The D/D+L ratio of D-PS in the cerebrum was 0.9%, while no detectable amount of D-PS was detected in the cerebellum. D-PS was also found in the heart, spleen, lung, testis, liver, and kidney in a range of 0.05-0.7% (the D/D+L ratio). Thus, D-PS, even in small amounts, is localized to the cerebrum in the brain and is distributed to various tissues other than the brain in the rat.