Docosahexaenoic Acid Modifies the Clustering and Size of Lipid Rafts and the Lateral Organization and Surface Expression of MHC Class I of EL4 Cells

Abstract

An emerging molecular mechanism by which docosahexaenoic acid (DHA) exerts its effects is modification of lipid raft organization. The biophysical model, based on studies with liposomes, shows that DHA avoids lipid rafts because of steric incompatibility between DHA and cholesterol. The model predicts that DHA does not directly modify rafts; rather, it incorporates into nonrafts to modify the lateral organization and/or conformation of membrane proteins, such as the major histocompatibility complex (MHC) class I. Here, we tested predictions of the model at a cellular level by incorporating oleic acid, eicosapentaenoic acid (EPA), and DHA, compared with a bovine serum albumin (BSA) control, into the membranes of EL4 cells. Quantitative microscopy showed that DHA, but not EPA, treatment, relative to the BSA control diminished lipid raft clustering and increased their size. Approximately 30% of DHA was incorporated directly into rafts without changing the distribution of cholesterol between rafts and nonrafts. Quantification of fluorescence colocalization images showed that DHA selectively altered MHC class I lateral organization by increasing the fraction of the nonraft protein into rafts compared with BSA. Both DHA and EPA treatments increased antibody binding to MHC class I compared with BSA. Antibody titration showed that DHA and EPA did not change MHC I conformation but increased total surface levels relative to BSA. Taken together, our findings are not in agreement with the biophysical model. Therefore, we propose a model that reconciles contradictory viewpoints from biophysical and cellular studies to explain how DHA modifies lipid rafts on several length scales. Our study supports the notion that rafts are an important target of DHA's mode of action.

Severe Alterations in Lipid Composition of Frontal Cortex Lipid Rafts from Parkinson’s Disease and Incidental Parkinson’s Disease

“…However, the poor affinity of DHA, and perhaps other LCPUFAs for cholesterol, provides a lipid-driven mechanism for lateralphase separation of cholesterol-and sphingolipid-rich lipid microdomains from the surrounding l d phase in model membranes altering the size, physical order, elastic compressibility, lateral segregation and clustering of cell surface lipid microdomains (42)(43)(44). Furthermore, it has been proposed that PUFA impoverishment in microdomains may have profound consequences on the dynamic partitioning of acylated proteins, membrane fusion, rapid flip-flop, receptor binding and resident protein function, thereby altering signal transduction and neurotransmission (27,42,44).…”

n-3 PUFA improves fatty acid composition, prevents palmitate-induced apoptosis, and differentially modifies B cell cytokine secretion in vitro and ex vivo

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“…Antibodies for fl ow cytometry were conjugated to FITC, Cy3 or Cy5 fl uorophores (GE Healthcare) using kits as previously described ( 18 ). Median fl uorescence intensity (MFI) values from fl ow cytometry experiments were normalized to the control.…”

Fish oil increases raft size and membrane order of B cells accompanied by differential effects on function

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