Chemical Imaging of Lipid Organization in the Plasma Membranes of Intact Cells with High Lateral Resolution

Abstract

Compartmentalization of the plasma membrane into domains of differing composition is required for proper cell function, but the extent and origins of this organization is poorly understood. The non-random distributions of specific membrane proteins has been established through the use of functionalized immunolabels and genetically encoded fluorescent protein constructs. Cholesterol- and sphingolipid-enriched microdomains, which are sometimes called lipid rafts, are also postulated to be present in the plasma membrane and mediate cell signaling, virus budding, and many other disease-related cellular processes. Advanced high-resolution fluorescence microscopy techniques have revealed the presence of biophysically distinct microdomains and cholesterol-dependent nanoclusters within the plasma membranes of living cells. However a chemically specific and spatially well-resolved imaging technique is required to unambiguously establish how specific lipid species are organized within the plasma membrane. Imaging mass spectrometry is a promising approach for visualizing lipid distribution within membranes with chemical specificity and submicron lateral resolution. Previously, the distributions of two isotopically labeled lipids within phase-separated model lipid membranes were successfully imaged with 100-nm-lateral resolution by using high-resolution secondary ion mass spectrometry (SIMS). Here we extend this approach to actual cells and chemically image the distributions of specific lipids within the plasma membrane with better than 100 nm lateral resolution.