sphingomyeliini

Sphingomyelin, known as sphingomyeliini in Finnish, is a phosphosphingolipid widely present in animal cell membranes, and it is especially abundant in the myelin sheath that surrounds nerve fibers. It consists of a ceramide backbone linked to a phosphocholine headgroup, with the ceramide formed from a fatty acid attached to a long-chain sphingoid base such as sphingosine. As a major component of the outer leaflet of the plasma membrane, sphingomyelin contributes to membrane rigidity and to the formation of lipid raft domains that organize membrane proteins and signaling molecules.

Biosynthesis occurs in the Golgi apparatus, where sphingomyelin synthase transfers the phosphocholine headgroup from phosphatidylcholine to ceramide, producing sphingomyelin and diacylglycerol. Degradation is carried out mainly by sphingomyelinases in lysosomes and at the plasma membrane, yielding ceramide and phosphocholine. Ceramide, in turn, acts as a bioactive lipid involved in various signaling pathways related to cell growth, differentiation, and stress responses.

Functionally, sphingomyelin supports the structural integrity of cellular membranes and plays a role in myelin formation, which is essential for efficient nerve conduction. It also participates in membrane trafficking and the organization of signaling platforms known as lipid rafts. Metabolites of sphingomyelin participate in intracellular signaling processes that influence cell fate decisions.

Clinical relevance includes Niemann-Pick disease types A and B, caused by inherited deficiencies of acid sphingomyelinase and resulting in lysosomal accumulation of sphingomyelin with organomegaly and, in type A, neurodegeneration. Altered sphingomyelin metabolism has been associated with various metabolic and neurodegenerative disorders, and sphingomyelin levels are studied in research and some clinical contexts.