Controlling Membrane Cholesterol Content. A Role for Polyunsaturated (Docosahexaenoate) Phospholipids

Abstract

The molecular organization of cholesterol in 1,2-didocosahexaenoylphosphatidylcholine (22:6-22:6PC) and 1-stearoyl-2-docosahexaenoylphosphatidylcholine (18:0-22:6PC) bilayers was investigated. Using low- and wide-angle X-ray diffraction (XRD), we determined that the solubility of the sterol at 20 degrees C was 11 +/- 3 mol % in 22:6-22:6PC vs 55 +/- 3 mol % in 18:0-22:6PC bilayers. Solubility in the dipolyunsaturated membrane rose to 17 +/- 3 mol % at 40 degrees C, while in the saturated-polyunsaturated membrane there was no change within experimental uncertainty. We compared the molecular orientation of [3alpha-(2)H(1)]cholesterol incorporated into 22:6-22:6PC bilayers to its solubility limit and into 18:0-22:6PC bilayers to a comparable concentration (10 mol %) in solid-state (2)H NMR experiments. The sterol possessed a tilt angle alpha(0) = 24 degrees +/- 1 degrees in 22:6-22:6PC that was independent of temperature over a range from 20 to 40 degrees C. In contrast, the value was alpha(0) = 21 degrees +/- 1 degrees in 18:0-22:6 bilayers at 20 degrees C and increased to alpha(0) = 24 degrees +/- 1 degrees at 40 degrees C. We attribute the low solubility of cholesterol in 22:6-22:6PC membranes to steric incompatibility between the rigid steroid moiety and the highly disordered docosahexaenoic acid (DHA) chain, which has the potential to promote lateral heterogeneity within DHA-rich membranes. Considering 22:6-22:6PC to be the most unsaturated phospholipid found in vivo, this model membrane study provides a point of reference for elucidating the role of sterol-lipid interactions in controlling local compositional organization. Our results form the basis for a model that is consistent with cholesterol's ability to modulate the activity of certain neural transmembrane proteins.

Structural insights on biologically relevant cationic membranes by ESR spectroscopy

“…Cholesterol-rich domains could be either inside or outside the bilayer. This contrasts with the high solubility of cholesterol in phosphatidylcholine bilayers (Huang et al 1999), but is in agreement with the poor mixing of cholesterol in anionic charged bilayers (Bach and Wachtel 2003) and in membranes composed of polyunsaturated acyl chains (Brzustowicz et al 2002;Marquardt et al 2016). While the latter effect can be understood from the irregular contour of the polyunsaturated chains that do not pack well with the flat surface of cholesterol, the first can be a consequence of the contrast between the more hydrophilic charged group and the hydrophobic nature of cholesterol (Benatti et al 2008).…”

Docosahexaenoic acid affects cell signaling by altering lipid rafts

“…In companion 2 H NMR experiments we measured the most probable orientation (tilt angle) for [3a-2 H 1 ]cholesterol in bilayers composed of various PCs and PEs [113][114][115]118]. We discovered that, irrespective of the degree of sn-2 chain unsaturation, the tilt angle (α 0 = 16°) was the same for all the hetero-acid phospholipids studied with a saturated sn-1 chain.…”

“…Recently we have directly tested this hypothesis using a combination of solid state 2 H NMR spectroscopy and XRD (X-ray diffraction) [113][114][115][116]. The NMR technique identifies a narrow spectral component due to cholesterol incorporation into the membrane superimposed upon a broad component from solid crystalline monohydrate cholesterol form outside the membrane.…”

Chemical–Physical Changes in Cell Membrane Microdomains of Breast Cancer Cells After Omega-3 PUFA Incorporation

“…The plasma membrane is involved in almost all aspects of cell biology, including morphogenesis, proliferation, migration, invasion, transformation, differentiation, secretion and apoptosis. Numerous experimental data indicate that the presence of PUFA in the membrane bilayer might determine dramatic changes in physicalchemical properties [4][5], a significant lowering of cholesterol solubility [6], and changes in the activity of transmembrane proteins such as the G-protein coupled membrane receptors [7][8]. In fact the structure and dynamics of these polyunsaturated chains at the molecular level are profoundly different from their saturated counterpart, with very short reorientational correlation times and extremely low chain order.…”

“…This could in principle alter the size, stability and distribution of cell surface lipid microdomains such as rafts. Indeed, evidences obtained from model membrane suggest that the energetically less favourable interaction between cholesterol and PUFA, especially DHA, promotes lateral phase segregation into sterol-poor/ PUFA-rich and sterolrich/saturated fatty acid-rich microdomains [60][61][62].…”