N-3 polyunsaturated Fatty Acids Disrupt Micron and Nanometer Scale Non-Raft Organization by Increasing Cell Size and Minimizing Molecular Interactions with Surrounding Rafts

Abstract

N-3 polyunsaturated fatty acids (PUFAs), due to their unique molecular structure, modify plasma membrane organization; however, very few mechanistic details are known. Here we tested the hypothesis that n-3 PUFAs, in comparison to other fatty acids, can specifically disrupt the organization of non-rafts on several length scales using quantitative imaging. On a micron scale, EL4 cells treated with eicosapentaenoic (EPA) and docosahexaenoic (DHA) acid robustly increased accumulation of the non-raft probe FAST DiI. The increase in FAST DiI accumulation was dependent on the total cellular levels of EPA and DHA, as revealed by linear regression analysis across differing cell types treated with n-3 PUFAs in vitro and in vivo. Unexpectedly, in vivo studies also revealed n-3 PUFAs disrupted rafts by increasing their size. On a nanometer scale, FRET imaging showed EPA and DHA increased the distance between non-raft molecules of EL4 cells. The increase in distance between non-raft molecules was due to an increase in cell size, driven by EPA and DHA's ability to promote cellular proliferation. Finally, we used model membranes to determine how EPA and DHA disrupted nonraft organization at a molecular level. NMR spectroscopy and quantitative microscopy revealed EPA and DHA acyl chains increased the nano- and micrometer size of non-raft domains by minimizing molecular interactions with surrounding rafts. Taken together, the data suggest a unifying model in which EPA and DHA target and disorder the organization of not only rafts but also non-rafts, which could serve as key intermediates to disrupt membrane architecture and cellular function.