Perturbation of Plasma Membrane Physical Properties by Endogenous and Exogenous Mediators Affects Cell Function

Abstract

In mammalian plasma membranes (PM), ordered, lipid-driven lateral domains - known as lipid rafts - have been implicated as central regulators of a broad range of cell functions and pathophysiological processes. Recent observations suggest these domains comprise a major fraction of mammalian plasma membranes, so rather than isolated islands of distinct composition, they may be fundamental to PM structure and function. However, direct demonstrations of lipid raft involvement in specific cell functions remain elusive because of artifact-prone, indirect, and poorly characterized experimental paradigms for raft perturbation. Giant Plasma Membrane Vesicles (GPMVs) are isolated PMs that separate into coexisting raft and non-raft phases in a temperature dependent manner, with the miscibility transition temperature providing a quantitative estimate of the stability of raft domains in live cells. We have evaluated a number of endogenous and exogenous mediators of the plasma membrane phenotype - defined as the fluidity of PM and the stability of lipid raft domains - and measured the effects of these perturbations on cell function. Cell autonomously, we find that differentiation of Mesenchymal Stem Cells (MSC) causes rapid divergence of both aspects of the PM phenotype. Inversely, perturbation of PM physical properties by ω-3 poly-unsaturated fatty acids (PUFAs) affects MSC differentiation, promoting the osteogenic over the adipogenic phenotype. Extending these studies to other cell functions, we have discovered a variety of exogenous mediators of the PM phenotype (in addition to ω-3 PUFAs) and find that any deviation from optimal raft stability has a suppressive effect on antigen-mediated mast cell activation. These observations provide a quantitative framework to measure the PM phenotype, identify exogenous fatty acids as potential mediators of this phenotype, and demonstrate the effect of perturbations of PM physical properties on cell function.