Sphingosine-1-Phosphate Is a Key Signaling Molecule in Normal Conditions and in Multiple Sclerosis

Sphingosine-1-phosphate (S1P) is one of the most extensively studied bioactive signaling molecules of sphingolipid metabolism, which plays a pivotal role in regulating numerous processes in the central nervous system and immune system. Acting as an extracellular ligand for five subtypes of G-protein-coupled receptors (S1PR₁-S1PR₅) as well as an intracellular metabolic mediator, S1P controls lymphocyte migration, blood-brain barrier permeability, survival and differentiation of oligodendrocytes, reactivity of astrocytes and microglia, and balance between inflammation, neurodegeneration, and neuroprotection. In pathogenesis of the demyelinative diseases, particularly multiple sclerosis, disruption of the "sphingolipid rheostat" is observed - a shift toward predominance of pro-apoptotic ceramides and relative decrease in the S1P levels, which promotes prevalence of the neuroinflammatory and neurodegenerative processes over remyelination. This review summarizes current data on the structure, metabolism, and intra- and extracellular signaling pathways of S1P, its dual role under physiological conditions and in multiple sclerosis, and analyzes approaches to pharmacological modulation of S1P signaling pathways, highlighting the prospects of selective targeted therapy aimed at immunomodulation, neuroprotection, and stimulation of remyelination.