Cholesterol synthesis inhibitor U18666A and the role of sterol metabolism and trafficking in numerous pathophysiological processes.
ABSTRACT The multiple actions of U18666A have enabled major discoveries in lipid research and contributed to understanding the pathophysiology of multiple diseases. This review describes these advances and the utility of U18666A as a tool in lipid research. Harry Rudney's recognition that U18666A inhibited oxidosqualene cyclase led him to discover a pathway for formation of polar sterols that he proved to be important regulators of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase. Laura Liscum's recognition that U18666A inhibited the egress of cholesterol from late endosomes and lysosomes led to greatly improved perspective on the major pathways of intracellular cholesterol trafficking. The inhibition of cholesterol trafficking by U18666A mimicked the loss of functional Niemann-Pick type C protein responsible for NPC disease and thus provided a model for this disorder. U18666A subsequently became a tool for assessing the importance of molecular trafficking through the lysosomal pathway in other conditions such as atherosclerosis, Alzheimer's disease, and prion infections. U18666A also provided animal models for two important disorders: petite mal (absence) epilepsy and cataracts. This was the first chronic model of absence epilepsy. U18666A is also being used to address the role of oxidative stress in apoptosis. How can one molecule have so many effects? Perhaps because of its structure as an amphipathic cationic amine it can interact and inhibit diverse proteins. Restricting the availability of cholesterol for membrane formation through inhibition of cholesterol synthesis and intracellular trafficking could also be a mechanism for broadly affecting many processes. Another possibility is that through intercalation into membrane U18666A can alter membrane order and therefore the function of resident proteins. The similarity of the effects of natural and enantiomeric U18666A on cells and the capacity of intercalated U18666A to increase membrane order are arguments in favor of this possibility.
SourceAvailable from: Edward Bryan Neufeld[Show abstract] [Hide abstract]
ABSTRACT: We have developed a suitable heterologous cell expression system to study the localization, trafficking, and site(s) of function of the human ABCG1 transporter. Increased plasma membrane (PM) and late endosomal (LE) cholesterol generated by ABCG1 was removed by lipoproteins and liposomes, but not apoA-I. Delivery of ABCG1 to the PM and LE was required for ABCG1-mediated cellular cholesterol efflux. ABCG1 LEs frequently contacted the PM, providing a collisional mechanism for transfer of ABCG1-mobilized cholesterol, similar to ABCG1-mediated PM cholesterol efflux to lipoproteins. ABCG1-mobilized LE cholesterol also trafficked to the PM by a non-vesicular pathway. Transfer of ABCG1-mobilized cholesterol from the cytoplasmic face of LEs to the PM and concomitant removal of cholesterol from the outer leaflet of the PM bilayer by extracellular acceptors suggests that ABCG1 mobilizes cholesterol on both sides of the lipid bilayer for removal by acceptors. ABCG1 increased uptake of HDL into LEs, consistent with a potential ABCG1-mediated cholesterol efflux pathway involving HDL resecretion. Thus, ABCG1 at the PM mobilizes PM cholesterol and ABCG1 in LE/LYS generates mobile pools of cholesterol that can traffic by both vesicular and non-vesicular pathways to the PM where it can also be transferred to extracellular acceptors with a lipid surface.Biology 12/2014; 3(4):781-800. DOI:10.3390/biology3040781
[Show abstract] [Hide abstract]
ABSTRACT: It is suspected that excess of brain cholesterol plays a role in Alzheimer's disease (AD). Membrane-associated cholesterol was shown to be increased in the brain of individuals with sporadic AD and to correlate with the severity of the disease. We hypothesized that an increase of membrane cholesterol could trigger sporadic AD early phenotypes. We thus acutely loaded the plasma membrane of cultured neurons with cholesterol to reach the 30% increase observed in AD brains. We found changes in gene expression profiles that are reminiscent of early AD stages. We also observed early AD cellular phenotypes. Indeed we found enlarged and aggregated early endosomes using confocal and electron microscopy after immunocytochemistry. In addition amyloid precursor protein vesicular transport was inhibited in neuronal processes, as seen by live-imaging. Finally transient membrane cholesterol loading lead to significantly increased amyloid-beta42 secretion. Membrane cholesterol increase in cultured neurons reproduces most early AD changes and could thus be a relevant model for deciphering AD mechanisms and identifying new therapeutic targets.Molecular Neurodegeneration 12/2014; 9(1):60. DOI:10.1186/1750-1326-9-60 · 5.29 Impact Factor
[Show abstract] [Hide abstract]
ABSTRACT: Picornaviruses are a family of positive-strand RNA viruses that represent important human and animal pathogens. Upon infection, picornaviruses induce an extensive remodeling of host cell membranes into replication organelles, which is critical for replication. Membrane lipids and lipid remodeling processes are at the base of RO formation, yet their involvement remains largely obscure. Recently, phosphatidylinositol-4-phosphate (PI4P) was the first lipid discovered to be important for the replication of a number of picornaviruses. Here, we investigate the role of the lipid cholesterol in picornavirus replication. We show that two picornaviruses from distinct genera that rely on different host factors for replication, namely the enterovirus coxsackievirus B3 (CVB3) and the cardiovirus encephalomyocarditis virus (EMCV), both recruited cholesterol to their ROs. Although CVB3 and EMCV both required cholesterol for efficient genome replication, the viruses appeared to rely on different cellular cholesterol pools. Treatments that altered the distribution of endosomal cholesterol inhibited replication of both CVB3 and EMCV, showing the importance of endosomal cholesterol shuttling for the replication of these viruses. Summarizing, we here demonstrate the importance of cholesterol homeostasis for efficient replication of CVB3 and EMCV.Cellular Microbiology 01/2015; DOI:10.1111/cmi.12425 · 4.82 Impact Factor