The Mechanism of HIV Entry Inhibition by 25-Hydroxycholesterol

Abstract

Among the known biological activities of 25-hydroxycholesterol (25HC) are its potential immunological functions. A recent work demonstrated that 25HC blocks HIV-1 entry, preventing the release of the viral content into the host cell, which suggests an action at the membrane level.The aim of this work is to clarify 25HC antiviral mechanism, studying its effects on membrane properties and on the viral fusion process, using lipids and HIV-fusion peptide (HIV-FP). Different biophysical studies, with small unilamellar vesicles (SUVs) and lipid monolayers, were performed to understand the differences that occur at the membrane level when cholesterol is substituted by 25HC. The effect of binary lipid mixtures, with 25HC or cholesterol, on HIV-FP structure was evaluated by Fourier transform infrared spectroscopy (FTIR).HIV-FP-induced lipid mixing assays were performed to calculate fusion efficiency. When cholesterol is substituted by 25HC, membrane fusion efficiency is reduced by 50%, demonstrating that 25HC can directly block membrane. Fusion fluorescence anisotropy, dipole potential and surface pressure assays show that the conversion of cholesterol in 25HC leads to a loss of the cholesterol modulating effect on membrane properties. On the contrary, FTIR reveals a similar HIV-FP structure in the presence of both sterols.Overall, our data show that 25HC can directly block HIV entry through the inhibition of HIV-FP-induced membrane fusion. The mechanism supporting this activity is not based on effects at the level of HIV-FP structure, but in changes of membrane biophysical properties, associated with the broad-spectrum activity against different enveloped viruses.