Cholesterol Precursors Stabilize Ordinary and Ceramide-rich Ordered Lipid Domains (Lipid Rafts) to Different Degrees

Abstract

Genetic disorders of cholesterol biosynthesis result in accumulation of cholesterol precursors and cause severe disease. We examined whether cholesterol precursors alter the stability and properties of ordered lipid domains (rafts). Tempo quenching of a raft-binding fluorophore was used to measure raft stability in vesicles containing sterol, dioleoylphosphatidylcholine, and one of the following ordered domain-forming lipids/lipid mixtures: dipalmitoylphosphatidylcholine (DPPC), sphingomyelin (SM), a SM/cerebroside mixture or a SM/ceramide (cer) mixture. Relative to cholesterol, early cholesterol precursors containing an 8 -9 double bond (lanosterol, dihydrolanosterol, zymosterol, and zymostenol) only weakly stabilized raft formation by SM or DPPC. Desmosterol, a late precursor containing the same 5-6 double bond as cholesterol, but with an additional 24 -25 double bond, also stabilized domain formation weakly. In contrast, two late precursors containing 7-8 double bonds (lathosterol and 7-dehydrocholesterol) were better raft stabilizers than cholesterol. For vesicles containing SM/cerebroside and SM/cer mixtures the effect of precursor upon raft stability was small, although the relative effects of different precursors were the same. Using both detergent resistance and a novel assay involving fluorescence quenching induced by certain sterols we found cholesterol precursors were displaced from cer-rich rafts, and could displace cer from rafts. Precursor displacement by cer was inversely correlated to precursor raft-stabilizing abilities, whereas precursor displacement of cer was greatest for the most highly raft-stabilizing precursors. These observations support the hypothesis that sterols and cer compete for raft-association

Cholesterol homeostasis and the escape tendency (activity) of plasma membrane cholesterol

“…They show that, compared to cholesterol, androstenolone, coprostanol, cholestane and cholestenone have weak or even negative effects on domain formation [26,49,50,88]. The same is true for lanosterol and succeeding sterol intermediates: dihydrolanosterol, desmosterol, zymosterol, and zymostenol [89]. That lanosterol in particular is inferior to cholesterol in many respects has been carefully documented [87].…”

“…While the studies just mentioned document the particular ability of cholesterol to promote the formation of condensed liquid-ordered phases, these publications also provide evidence that various sterols (biosynthetic intermediates and otherwise) are as good as and sometimes better than cholesterol at building rafts [26,49,50,88,89,91]. In this set are ergosterol, 25-hydroxycholesterol, lathosterol, epicholesterol, 7-dehydrocholesterol and dihydrocholesterol.…”

Autonomic Denervation of Lymphoid Organs Leads to Epigenetic Immune Atrophy in a Mouse Model of Krabbe Disease

“…For instance, the clustering of GalCer within rafts facilitates bacterial and viruses such as HIV-1 initial cell adhesion Harouse et al, 1991;Fantini et al, 2000). Sphingolipids also displace cholesterol from rafts (Megha and London, 2004;Yu et al, 2005;Megha et al, 2006) altering signaling through the membrane. Thus, abnormal sphingolipid catabolism or accumulation in lipid microdomains might result in a cell autonomous defect accounting for GLD hematopoietic stem cells compromised functionality (i.e., proliferation, migration, and maturation).…”

Enzymatic generation of ceramide induces membrane restructuring: Correlated AFM and fluorescence imaging of supported bilayers

“…This work has demonstrated that ceramide leads to increased membrane heterogeneity and that its effects depend on the membrane composition. Ceramide has also been shown to displace cholesterol from raft domains in model and cellular membranes (Ali et al, 2006;Chiantia et al, 2006;Megha and London, 2004;Megha et al, 2006;Yu et al, 2005b). Several recent studies have concluded that the ability of ceramide to modulate the properties of liquid-ordered domains and form ceramide-enriched gel domains is affected by the chain length and that short-chain ceramides (<C 12 ) are not good models for studies of the biological activity of ceramide (Chiantia et al, 2007;Megha et al, 2007).…”