Amount Of Membrane Cholesterol Research Articles

Exploring in vivo cholesterol-mediated interactions between activated EGF receptors in plasma membrane with single-molecule optical tracking.

BackgroundThe first step in many cellular signaling processes occurs at various types of receptors in the plasma membrane. Membrane cholesterol can alter these signaling pathways of living cells. However, the process in which the interaction of activated receptors is modulated by cholesterol remains unclear.MethodsIn this study, we measured single-molecule optical trajectories of epidermal growth factor receptors moving in the plasma membranes of two cancerous cell lines and one normal endothelial cell line. A stochastic model was developed and applied to identify critical information from single-molecule trajectories.ResultsWe discovered that unliganded epidermal growth factor receptors may reside nearby cholesterol-riched regions of the plasma membrane and can move into these lipid domains when subjected to ligand binding. The amount of membrane cholesterol considerably affects the stability of correlated motion of activated epidermal growth factor receptors.ConclusionsOur results provide single-molecule evidence of membrane cholesterol in regulating signaling receptors. Because the three cell lines used for this study are quite diverse, our results may be useful to shed light on the mechanism of cholesterol-mediated interaction between activated receptors in live cells.

Unraveling the mechanism of cholesterol-mediated regulation of receptor dimerization in plasma membranes in vivo

Membrane cholesterol can alter the signaling pathways of living cells. However, the process that modulates the interaction of receptor proteins is still unclear. We performed single-molecule optical tracking of ligand-induced dimerization of epidermal growth factor receptors (EGFRs) in two cancerous cell lines (HeLa and A431) and one normal endothelial cell line (MCF12A). We discovered that unliganded EGFRs typically reside in non-raft regions of the plasma membrane and can move into raft domains upon ligand binding. This ligand-induced motion could be a common behavior in live cells. We found that the amount of membrane cholesterol significantly affects the stability of EGFR dimers by manipulating the total amount of membrane cholesterol with methyl-β-cyclodextrin and the local concentration of cholesterol with nystatin. The EGFR dimers in the plasma membrane of normal cells are more sensitive to changes in the local concentration of cholesterol compared with the cancer cells. Our methodology can yield useful information for understanding cholesterol-mediated protein-protein interactions in live cells.

Hormonal modulation of cholesterol: experimental evidence and possible translational impact

Alzheimer's disease (AD) is still an incurable condition. There is in vitro evidence that estrogens exert neuroprotective effects; however, their role in the treatment of AD is still controversial. Approximately 10 years ago, a new gene, named seladin-1 (for selective AD indicator-1), was identified and found to be downregulated in brain regions affected by AD. Seladin-1 has neuroprotective properties, which have been associated, at least in part, with its anti-apoptotic activity. Estrogens stimulate the expression of the seladin-1 gene. Seladin-1 also has enzymatic activity (3-β-hydroxysterol Δ-24-reductase), which is involved in the synthesis of cholesterol from desmosterol. The amount of membrane cholesterol appears to play an important role in conferring protection to brain cells. This review focuses on the relationship between estrogens (and IGF-1, another hormone with neuroprotective properties), cholesterol and seladin-1.

High Membrane Cholesterol in CLL B-Cells and Differential Expression of Cholesterol Synthesis Genes in IG GENE-Unmutated vs Mutated Cells

Objectives: Chronic lymphocytic leukaemia (CLL) is associated with abnormalities of the B-Cell Receptor (BCR) signalling, including low responsiveness to antigenic stimulation and constitutive phosphorylation of several components of the signalling pathway. In Bcells, BCR-mediated signalling is regulated in part by the amount of membrane cholesterol. It was observed that Statins, pharmacological inhibitors of cholesterol synthesis, induce apoptosis of CLL cells in vitro and in vivo . Having previously reported that ectopic expression of CD5 in a B-cell line stimulated the transcription of genes involved in the synthesis of cholesterol, we investigated the expression and synthesis of cholesterol in CLL B-cells. Study Design & Methodology: Plasma membrane cholesterol in CLL cells was evaluated by staining with Filipin and Flow cytometry in 26 patients. CLL cells were cultured with Lovastatin and subG1 cells and Gumprecht’s shadows counted thereafter; surface expression of IgM, CD19 and CD5 was analysed. The expression of cholesterol synthesis genes was investigated in transcriptomic data from the MILE project (150 CLL and 110 controls). Research Article

K252a, an Indrocarbazole Derivative, Causes the Membrane of Myoblasts to Enter a Fusion-Capable State

K252a, an indrocarbazole derivative and protein kinase inhibitor, is reported to promote myogenic differentiation in C2 mouse myoblasts. We examined the effects of K252a on QM-RSV cells, quail myoblasts transformed with a temperature-sensitive mutant of Rous sarcoma virus. K252a promoted myotube formation of QM-RSV cells. Presumptive QM-RSV cells also formed multinucleated cells when exposed to K252a. However, the expression of myogenin, a muscle regulatory factor, was not stimulated in the presence of the drug, suggesting that it promotes membrane fusion but not myogenic differentiation. To confirm the promotion of membrane fusion by K252a, presumptive C2 cells, which are strongly resistant to HVJ-mediated cell fusion, were fused by HVJ (Sendai virus) after K252a treatment. Presumptive C2 cells treated with K252a fused with HVJ, demonstrating that K252a causes the cells to enter a fusion-capable state. The amount of membrane cholesterol, a factor that decreases membrane fluidity, fell in K252a-treated C2 cells. The results suggest that a decrease of membrane cholesterol is a cause of the change that renders myoblast membrane susceptible to fusion in the presence of K252a.

Amyloid β-peptide1-40 increases neuronal membrane fluidity: role of cholesterol and brain region

There is increasing evidence of an interaction between cholesterol dynamics and Alzheimer's disease (AD), and amyloid β-peptide may play an important role in this interaction. Aβ destabilizes brain membranes and this action of Aβ may be dependent on the amount of membrane cholesterol. We tested this hypothesis by examining effects of Aβ1-40 on the annular fluidity (i.e., lipid environment adjacent to proteins) and bulk fluidity of rat synaptic plasma membranes (SPM) of the cerebral cortex, cerebellum, and hippocampus using the fluorescent probe pyrene and energy transfer. Amounts of cholesterol and phospholipid of SPM from each brain region were determined. SPM of the cerebellum were significantly more fluid as compared with SPM of the cerebral cortex and hippocampus. Aβ significantly increased (P ≤ 0.01) annular and bulk fluidity in SPM of cerebral cortex and hippocampus. In contrast, Aβ had no effect on annular fluidity and bulk fluidity of SPM of cerebellum. The amounts of cholesterol in SPM of cerebral cortex and hippocampus were significantly higher (P ≤ 0.05) than amount of cholesterol in SPM of cerebellum. There was significantly less (P ≤ 0.05) total phospholipid in cerebellar SPM as compared with SPM of cerebral cortex. Neuronal membranes enriched in cholesterol may promote accumulation of Aβ by hydrophobic interaction, and such an interpretation is consistent with recent studies showing that soluble Aβ can act as a seed for fibrillogenesis in the presence of cholesterol. —Chochina, S. V., N. A. Avdulov, U. Igbavboa, J. P. Cleary, E. O. O'Hare, and W. G. Wood. Amyloid β-peptide1-40 increases neuronal membrane fluidity: role of cholesterol and brain region.

Ultrastructural characterization of cholesterol distribution in toad bladder using filipin.

The polyene antibiotic filipin was used to characterize the cholesterol distribution in the membranes of the toad bladder epithelium in freeze-fracture replicas. The apical membranes of granular and mitochondria-rich cells incorporate moderate amounts of filipin while the basolateral membranes of both cell types incorporate substantially greater amounts. Intracellular membranes, in general, take up very little filipin. The major exception to this is the granule membrane, which appears to be rich in cholesterol. An inverse correlation was found between the density of filipin-sterol complexes in the apical membrane and the incidence of granules in the cytoplasm. This suggests that fusion of granules with the apical membrane may be responsible for variation in the concentration of cholesterol in the apical membrane. Thirty minutes following vasopressin exposure, there is no consistent change in the cholesterol content of the apical membrane of granular cells as measured by the incidence of filipin-sterol complexes. The lack of change in the amount of membrane cholesterol indicates that the vasopressin-induced increase in transepithelial water permeability is not mediated by a change in cholesterol content of the apical membrane.

The Effect of Intravenous Hyperalimentation on Erythrocyte Lipids

SummaryLipid analyses of erythrocytes from patients undergoing intravenous hyperalimentation therapy are presented herein. The amount of membrane cholesterol and phospholipid remained normal during the 4-month therapy and so did individual phospholipids. Phospholipid fatty acids, however, showed variations with a tendency toward increased percentages of palmitic and oleic acids and decreased percentages of linoleic and arachidonic acids. 5,8,11-Eicosatrienoic acid, characteristic of essential fatty-acid deficiency, increased markedly as the therapy progressed. Similar changes were observed in plasma fatty-acid phospholipids. The results suggested that during intravenous hyperalimentation, cell-membrane phospholipids became responsive to altered plasmalipid concentrations. The exchange of phospholipids between red blood cells and lipoproteins in man is less selective in essential fatty-acid deficiency resulting from intravenous hyperalimentation than from other causes.The authors are very much indebted to ...