ABSTRACT
The role of lipids, such as phosphatidylinositides, diacylglycerides (DG), and phosphatidic acid (PA) species in both intracellular homeostatic and inflammatory signaling has been well established for over a decade, although initial evidence for the significance of PA-related signaling can be found in research from the period 1950–1955. PA is an anionic phospholipid present in eukaryotic cells at concentrations ranging from 0.5 to 3% of total phospholipid mass. PA, along with DG, is a fun damental precursor of the storage lipid triacylglyceride and of all phospholipids, and hence both its de novo and phospholipid-based syntheses are tightly regulated and its normal biological half-life is short. Endogenous PA levels have pronounced effects upon known intracellular signaling proteins over and above their effects on cellular calcium currents. A noteworthy effect of PA on membrane properties is its induction of increased fusogenicity. Mechanisms by which bacterial lipid A moieties alter the functional properties of cells remain incompletely understood.
