Phosphatidylserine

Phosphatidylserine (PS) is the major acidic phospholipid in human membranes 60 and constitutes 2% to 20% of the total phospholipid mass of adult human plasma and intracellular membranes. Within the healthy human brain, myelin is enriched in phosphatidylserine and the phosphatidylserine content of grey matter doubles from birth to age 80 years. Throughout the human body, phosphatidylserine is a structural component of endoplasmic reticulum, nuclear envelopes, Golgi apparati, inner (cytosolic) leaflets of plasma membranes, outer mitochondrial membranes, and myelin.
In the synapses, phosphatidylserine plays an important role in exocytosis by influencing Ca2+ dependent membrane fusion between synaptic vesicles and the target plasma membrane. This is mediated by synaptotagmin and soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex.
Cell surface expression of phosphatidylserine has been found with aging erythrocytes, activated platelets, activated macrophages, endothelial cells of tumor blood vessels, apoptotic cells, apoptotic bodies and cell-derived microparticles. It is generally believed that phagocytes in healthy tissues rapidly and efficiently remove phosphatidylserine expressing cells and cell remnants. Diseased tissues, on the other hand, have a sustained presence of cell surface expressed phosphatidylserine as a result of an imbalance in appearance and clearance of phosphatidylserine expressing cells and cell remnants. Cell surface-expressed phosphatidylserine is a useful target for Molecular Imaging and Targeted Drug Delivery strategies