Sfingomyelin

Sphingomyelin, sometimes spelled sfingomyelin, is a type of sphingolipid found in animal cell membranes, especially in the myelin sheath that surrounds nerve fibers. It consists of a ceramide backbone linked to a phosphocholine headgroup, making it a phosphosphingolipid. In humans and other mammals, sphingomyelin is abundant in plasma membranes and is particularly enriched in myelin.

Biosynthesis occurs in the Golgi apparatus, where sphingomyelin synthase transfers a phosphocholine group from phosphatidylcholine to ceramide. It can also arise from salvage pathways. Sphingomyelin contributes to membrane lipid rafts and helps regulate membrane curvature and permeability. It is distributed throughout many tissues, with high concentrations in nervous tissue and myelin.

Metabolically, sphingomyelin can be hydrolyzed by sphingomyelinase to yield ceramide and phosphorylcholine. Ceramide is a bioactive lipid involved in signaling pathways that influence cell growth, differentiation, and apoptosis. Thus sphingomyelin serves not only a structural role but also participates in intracellular signaling when hydrolyzed.

Clinical relevance: impaired metabolism of sphingomyelin is a hallmark of Niemann-Pick disease types A and B, caused by deficiency of acid sphingomyelinase, leading to lysosomal accumulation of sphingomyelin. Other lysosomal storage disorders and disruptions of sphingomyelin metabolism have been studied for their roles in neurodegenerative diseases and inflammation.

Analytical approaches include lipidomics using mass spectrometry, chromatography, and enzymatic assays. Because sphingomyelin is a major component of myelin, it is of interest in studies of demyelinating diseases and nerve function. Dietary sphingomyelin is present in animal products, and its digestion yields ceramide and sphingosine, which may have signaling roles in the gut.