Side-Chain Oxysterols Modulate Cholesterol Accessibility through Membrane Remodeling

Abstract

Side-chain oxysterols, such as 25-hydroxycholesterol (25-HC), are key regulators of cholesterol homeostasis. New evidence suggests that the alteration of membrane structure by 25-HC contributes to its regulatory effects. We have examined the role of oxysterol membrane effects on cholesterol accessibility within the membrane using perfringolysin O (PFO), a cholesterol-dependent cytolysin that selectively binds accessible cholesterol, as a sensor of membrane cholesterol accessibility. We show that 25-HC increases cholesterol accessibility in a manner dependent on the membrane lipid composition. Structural analysis of molecular dynamics simulations reveals that increased cholesterol accessibility is associated with membrane thinning, and that the effects of 25-HC on cholesterol accessibility are driven by these changes in membrane thickness. Further, we find that the 25-HC antagonist LY295427 (agisterol) abrogates the membrane effects of 25-HC in a nonenantioselective manner, suggesting that agisterol antagonizes the cholesterol-homeostatic effects of 25-HC indirectly through its membrane interactions. These studies demonstrate that oxysterols regulate cholesterol accessibility, and thus the availability of cholesterol to be sensed and transported throughout the cell, by modulating the membrane environment. This work provides new insights into how alterations in membrane structure can be used to relay cholesterol regulatory signals.

Synthesis and characterization of diazirine alkyne probes for the study of intracellular cholesterol trafficking

“…Esterification of the LKM38 probe was more robust than for d7-cholesterol. Increased esterification of LKM38 could be an indication of increased delivery to the ER compartment or increased ACAT activity, possibly due to increased membrane availability (28,29). Trafficking of LKM38 to the plasma membrane was essentially identical to native cholesterol trafficking to this compartment at early time points.…”

New insights into the regulation of cholesterol efflux from the sperm membrane

“…In other cell types, the formation of trace amounts of oxysterols is reported to facilitate RCT by regulating cholesterol availability in the membrane environment: 89 90 91 92 for model see Figure 4 . It is possible that bicarbonate induction of the oxysterol formation facilitates cholesterol efflux from sperm by one of these means.…”

A novel intrinsically fluorescent probe for study of uptake and trafficking of 25-hydroxycholesterol

“…At 24 h, cells were treated with 5 M 25-HC, or In addition to transcriptional regulation, 25-HC also regulates cholesterol homeostasis by modulating cholesterol accessibility in membranes ( 14,15 ). While the exact mechanism is not known, 25-HC has been shown to have membrane-disordering effects and thins the bilayer, which increases cholesterol accessibility ( 16,17 ) and results in enhanced fl ux of plasma membrane cholesterol to the ER (18)(19)(20). Studies with the enantiomer of 25-HC have implicated direct interactions with membranes for inhibition of SREBP-2 processing as well as degradation of HMG-CoA reductase (HMGR) ( 14,15 ), sterol homeostatic responses that likely are modulated by ER cholesterol accessibility ( 21 ).…”