Tail-Oxidized Cholesterol Enhances Membrane Permeability for Small Solutes

Area of Science:

• Biochemistry
• Biophysics
• Cell Biology

Background:

• Cholesterol compacts cell membranes, regulating permeability to water and water-soluble molecules.
• Small structural modifications in cholesterol can significantly alter membrane properties.
• Oxysterols, oxidized forms of cholesterol, are implicated in various biological processes.

Purpose of the Study:

• To investigate how cholesterol oxidation affects the permeability barrier function of cell membranes.
• To compare the effects of ring-oxidized (7β-hydroxycholesterol) and tail-oxidized (27-hydroxycholesterol) sterols.

Main Methods:

• Fluorescence quenching spectroscopy and microscopy to study membrane permeability.
• Atomistic molecular dynamics simulations to characterize membrane structure and dynamics.
• Utilized NBD-lipid probes and dithionite for permeability assays.

Main Results:

• 27-hydroxycholesterol (tail-oxidized) significantly increases membrane permeability to dithionite anions.
• Molecular dynamics simulations confirm that 27-hydroxycholesterol facilitates water transport across the membrane.
• The 'bobbing' motion of 27-hydroxycholesterol across the membrane is linked to increased permeability.
• 7β-hydroxycholesterol (ring-oxidized) did not show significant effects on membrane permeability.

Conclusions:

• Oxysterol bobbing, particularly of tail-oxidized forms like 27-hydroxycholesterol, perturbs the membrane's hydrophobic core.
• These perturbations enhance the permeation of water and small molecules, impairing the membrane's barrier function.
• The findings suggest that subtle cholesterol structural changes can have substantial physiological consequences for eukaryotic organisms.