Lipids Serve as Signaling Molecules

This type of signaling can be roughly categorized into four areas as follows  

SIP may be involved in cell survival, cell migration, and inflammation [48], The involvement of S IP in these cellular processes is largely through interactions with the G-protein-coupled receptors, known as SIP receptors [48], Inside the cell, SIP can induce calcium release, which is independent of the S1P receptors, the mechanism of which remains unknown. Other sphingolipids such as GluCer and gangliosides are also involved in cellular signaling processes [36,49], 

The third category of signaling lipids are those serving as activators of G-protein-coupled receptors, including lysoGPLs (lysoPA in particular), SIP, platelet-activating factor (PAF), endocannabinoids, eicosanoids, fatty acid-hydroxy fatty acids, and retinol derivatives. Increased mass levels of these lipids may lead to the activation of the corresponding G-protein-coupled receptor(s). 

Finally, steroid hormones, retinoic acid, eicosanoids, some NEFA, etc., can bind to nuclear receptors to activate transcription factors. For instance, retinoic acid can activate retinoic acid receptor to control differentiation and proliferation of many types of cells during development [53]. 

Overall, many lipids serve as signaling molecules. Any significant changes of these kinds of lipid species should consider their role in this direction and interpreted accordingly. Further cellular and molecular determination of their downstream changes such as kinase activation, transcription factor upregulation, and cell growth or apoptosis could confirm this type of cellular functions of the lipids. 

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