Reelin Increases the Sphingomyelin Content of the Plasma Membrane and Affects the Surface Expression of <scp>GPI</scp> ‐Anchored Proteins in Hippocampal Neurons

Sphingomyelin (SM) is primarily located in the outer leaflet of the plasma membrane. It plays a crucial role in intercellular communication and the morphology of neuronal cells by influencing the localization and function of various proteins. However, the mechanisms regulating the SM content in the neuronal plasma membrane remain largely elusive. In this study, we discovered that Reelin, an important secreted signaling protein in the central nervous system, increases the SM content of the plasma membrane of cultured hippocampal neurons by promoting SM synthesis using a SM specific probe and a fluorescently labeled SM precursor molecule. This increase in SM was associated with increased surface expression of glycosylphosphatidylinositol (GPI)-anchored proteins analyzed by immunohistochemistry or using phosphatidylinositol-specific phospholipase C, suggesting a functional link between SM levels and membrane protein trafficking. Furthermore, comparative lipidomic analysis of the postsynaptic density fraction by LC-MS/MS revealed distinct alterations in SM-related lipid species between wild-type and Reelin-deficient mice. These findings suggest that Reelin regulates the SM content in the neuronal plasma membrane, which, in turn, affects the function and morphology of the neuron by affecting the surface levels of GPI-anchored proteins. These findings identify a novel role for Reelin in modulating neuronal membrane lipid composition, which may underlie its diverse functions in neuronal development and synaptic plasticity in both the developing and adult brain.