Lipids Signaling, broadly defined, refers to any biological signaling event involving a lipid messenger that binds a protein target, such as a receptor, kinase or phosphatase, which in turn mediate the effects of these lipids on specific cellular responses.
Normal cellular membranes have roughly equal amounts of protein and lipid. Lipid signaling is normally a response to some inner/outer stimulus leading to the release of lipids moyeties.
The cell membrane is described in detail here
The most important lipidic messengers are:
- DAG, or diacylglycerol, is a molecule consisting of two fatty acid and linked to a glycerol through ester bonds. It derives, like IP3, or inositol triphosphate, from the hydrolisis of a molecule of phosphatidylinositol-4,5-diphosphate by phospholipase C. DAG leads to the activation of Protein Kinase C (PKC) while IP3http://flipper.diff.org/app/pathways/info/438 membrane lipids promotes a release of Ca++ into the cytosol (Ca++ is necessary to properly activate PKC).
- Ceramides (wiki) are composed of sphingosine and a fatty acid and derive from the hydrolisis of sphingolipids. Sphingolipids have an important structural role in cell membrane but, when hydrolized by sphingomyelinase (wiki), they release ceramides in the cytosol that can act as second messengers, promoting differentiation, proliferation and apoptosis.
- PAF, or platelet activating factor (wiki), derives from the acetilation on the second carbon of lyso PAF, that derives from the hydrolisis of a alkylacylglycerophosphocoline by phospholipase A2. PAF is released by neutrophils, basophils, platelets, and some other cells, to induce platelets aggregation, inflammation and anaphylaxis.
- Arachidonic Acid is a carboxylic acid with 20-carbon chain and 4 cis double bonds in position 5,8,11,14. It derives from the hydrolisis of phospholipids (like phosphatidylethanolamine, phosphatidylcholine, phosphatidylinositides) by phospholipase A2. Arachidonic acid is the substrate for the synthesis of prostaglandins, thromboxanes and leukotrienes.