Abstract
Cholesterol plays a crucial role in cell membrane organization, dynamics and function. Depletion of cholesterol represents a popular approach to explore cholesterol-sensitivity of membrane proteins. An emerging body of literature shows that the consequence of membrane cholesterol depletion often depends on the actual process (acute or chronic), although the molecular mechanism underlying the difference is not clear. Acute depletion, using cyclodextrin-type carriers, is faster relative to chronic depletion, in which inhibitors of cholesterol biosynthesis are used. With the overall goal of addressing molecular differences underlying these processes, we monitored membrane dipole potential under conditions of acute and chronic cholesterol depletion in CHO-K1 cells, using a voltage-sensitive fluorescent dye in dual wavelength ratiometric mode. Our results show that the observed membrane dipole potential exhibits difference under acute and chronic cholesterol depletion conditions, even when cholesterol content was identical. To the best of our knowledge, these results provide, for the first time, molecular insight highlighting differences in dipolar reorganization in these processes. A comprehensive understanding of processes in which membrane cholesterol gets modulated would provide novel insight in its interaction with membrane proteins and receptors, thereby allowing us to understand the role of cholesterol in cellular physiology associated with health and disease.
Highlights
Dipole potential is an important electrostatic property of organized molecular assemblies
We have previously shown that membrane cholesterol is required for the organization and function of the serotonin1A receptor, an important member of the G protein-coupled receptor family (GPCR)[32, 33]
While it has been previously reported that increasing membrane cholesterol results in higher membrane dipole potential[25, 29, 30], our present work shows that membrane dipole potential could depend on the actual process used to deplete cholesterol, and not on absolute cholesterol content in the membrane
Summary
Dipole potential is an important electrostatic property of organized molecular assemblies (such as membranes and micelles). Membrane cholesterol has been shown to increase dipole potential in model and natural membranes[25, 29, 30] in a stereo-specific manner[31]. In spite of these important structural correlates, the molecular mechanism underlying the modulation of membrane cholesterol is not clear, with reference to the manner in which depletion is carried out (acute vs chronic). By measurement of membrane dipole potential, that dipolar reorganization could be very different in acute and chronic cholesterol depletion, even when the extent of cholesterol depletion is identical
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