Sphingolipid Domains in the Plasma Membranes of Fibroblasts Are Not Enriched with Cholesterol

The plasma membranes of mammalian cells are widely expected to contain domains that are enriched with cholesterol and sphingolipids. In this work, we have used high-resolution secondary ion mass spectrometry to directly map the distributions of isotope-labeled cholesterol and sphingolipids in the plasma membranes of intact fibroblast cells. Although acute cholesterol depletion reduced sphingolipid domain abundance, cholesterol was evenly distributed throughout the plasma membrane and was not enriched within the sphingolipid domains. Thus, we rule out favorable cholesterol-sphingolipid interactions as dictating plasma membrane organization in fibroblast cells. Because the sphingolipid domains are disrupted by drugs that depolymerize the cells actin cytoskeleton, cholesterol must instead affect the sphingolipid organization via an indirect mechanism that involves the cytoskeleton. Background: Although cholesterol abundance affects cell function, its distribution within the plasma membrane is not established. Results: Cholesterol is uniformly distributed throughout the plasma membrane and is not enriched within sphingolipid domains. Conclusion: Sphingolipid organization in the plasma membrane is not dictated by direct cholesterol-sphingolipid interactions. Significance: Cholesterol abundance affects sphingolipid organization in the plasma membrane via an indirect mechanism.