[11] Isolation and characterization of apolipoprotein B-100

Fisher, Waldo R.; Schumaker, Verne N.

doi:10.1016/0076-6879(86)28071-4

Cited by 36 publications

(11 citation statements)

References 37 publications

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“…Intraocular mRNA transcripts for apoB were first detected for combined RPE/choroid (19) and then localized, with apoB protein, to native RPE (8). ApoB was detected in drusen by immunofluorescence (8) but not by proteomics (56), likely because the chloroform-methanol extraction used in that investigation removed core lipids and precipitated the amphipathic apoB peptide (57). In our report, ARPE-19 extracts contained a small but readily detectable high molecular mass band at the same position as in HepG2 extracts.…”

Section: Discussionmentioning

confidence: 99%

Retina expresses microsomal triglyceride transfer protein: implications for age-related maculopathy

Presley

Zhang

et al. 2005

Journal of Lipid Research

105

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The principal extracellular lesions of age-related maculopathy (ARM), the leading cause of vision loss in the elderly, involve Bruch's membrane (BrM), a thin vascular intima between the retinal pigment epithelium (RPE) and its blood supply. With age, 80-100 nm solid particles containing esterified cholesterol (EC) accumulate in normal BrM, and apolipoprotein B (apoB) immunoreactivity is detectable in BrM-and ARM-associated lesions. Yet little evidence indicates that increased plasma cholesterol is a risk factor for ARM. To determine if RPE is capable of assembling its own apoB-containing lipoprotein, we examined RPE for the expression of microsomal triglyceride transfer protein (MTP), which is required for this process. Embryologically part of the central nervous system, the retina ( Fig. 1A ) converts light energy to electrochemical signals for transmission to the brain. The photoreceptors are supported by the retinal pigment epithelium (RPE), a monolayer with diverse functions including daily phagocytosis of the distal tips of photoreceptor outer segments (OS), and the choroid, a vascular bed with the body's highest blood flow. The choriocapillaris is a dense capillary plexus in the innermost choroid, and Bruch's membrane (BrM) is a thin vascular intima between the RPE and the choriocapillaris (Fig. 1B, arrowheads). In human retina, the macula subserves high-acuity vision and is vulnerable to age-related maculopathy (ARM), the major cause of vision loss among the elderly of industrialized societies. The most prominent histopathologic and clinical signs of ARM are extracellular lesions [drusen (Fig. 1E, F) and basal linear deposits (not shown)] in the RPE/BrM complex that ultimately impact vision by the photoreceptors (1, 2). Choroidal neovascularization, an invasion of choriocapillaries across BrM and lateral spread within the plane of drusen and basal linear deposit (see 3), is the principal sight-threatening complication of ARM's obscure underlying degeneration.Recent findings highlight a role for lipids and lipoproteins in this degeneration. These include a protective effect of the apolipoprotein E4 (apoE4) genotype in populations and the presence of apoB and apoE and histochemically identified lipids in aging-and ARM-associated drusen and deposits in human tissues (4-8) (Fig. 1E, F). The best established risk factor for early ARM is advanced age (9). A Abbreviations: ABL, abetalipoproteinemia; apoB, apolipoprotein B; apoBEC-1, apolipoprotein B-editing complex-1; ARM, age-related maculopathy; BrM, Bruch's membrane; EC, esterified cholesterol; ESI/MS, electrospray ionization mass spectrometry; INL, inner nuclear layer; MCT3, monocarboxylate transporter 3; MTP, microsomal triglyceride transfer protein; OS, outer segments of photoreceptors; RGC, retinal ganglion cell; RPE, retinal pigment epithelium; TC, total cholesterol; TG, triglyceride; UC, unesterified cholesterol.

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Section: Discussionmentioning

confidence: 99%

Retina expresses microsomal triglyceride transfer protein: implications for age-related maculopathy

Presley

Zhang

et al. 2005

Journal of Lipid Research

105

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“…Isolation, Labeling, and Oxidation of Lipoproteins-LDL (d ϭ 1.019 -1.05 g/ml) and HDL (d ϭ 1.063-1.21 g/ml) were isolated from fresh human plasma by density gradient ultracentrifugation as described previously (21,22). The HDL 3 subfraction (d ϭ 1.13-1.18 g/ml) was isolated from other HDL subfractions using a density gradient fractionator (ISCO).…”

Section: Methodsmentioning

confidence: 99%

Oxidized Low Density Lipoprotein Displaces Endothelial Nitric-oxide Synthase (eNOS) from Plasmalemmal Caveolae and Impairs eNOS Activation

Blair

Shaul

Yuhanna

et al. 1999

Journal of Biological Chemistry

326

261

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Hypercholesterolemia-induced vascular disease and atherosclerosis are characterized by a decrease in the bioavailability of endothelium-derived nitric oxide. Endothelial nitric-oxide synthase (eNOS) associates with caveolae and is directly regulated by the caveola protein, caveolin. In the present study, we examined the effects of oxidized low density lipoprotein (oxLDL) on the subcellular location of eNOS, on eNOS activation, and on caveola cholesterol in endothelial cells. We found that treatment with 10 g/ml oxLDL for 60 min caused greater than 90% of eNOS and caveolin to leave caveolae. Treatment with oxLDL also inhibited acetylcholine-induced activation of eNOS but not prostacyclin production. oxLDL did not affect total cellular eNOS abundance. Oxidized LDL also did not affect the palmitoylation, myristoylation or phosphorylation of eNOS. Oxidized LDL, but not native LDL, or HDL depleted caveolae of cholesterol by serving as an acceptor for cholesterol. Cyclodextrin also depleted caveolae of cholesterol and caused eNOS and caveolin to translocate from caveolae. Furthermore, removal of oxLDL allowed eNOS and caveolin to return to caveolae. We conclude that oxLDL-induced depletion of caveola cholesterol causes eNOS to leave caveolae and inhibits acetylcholine-induced activation of the enzyme. This process may be an important mechanism in the early pathogenesis of atherosclerosis.Studies in animal models and in humans have shown that hypercholesterolemia-induced vascular disease and atherosclerosis are characterized by an early, selective impairment of endothelium-derived relaxation. This impairment is due to a decrease in bioavailable endothelium-derived nitric oxide (NO) 1 (1). In the initial phase of the disease process, there is impaired responsiveness to receptor-dependent stimuli, such as acetylcholine, whereas responsiveness to receptor-independent stimuli such as the calcium ionophore A23187 is not altered. As such, the early pathogenesis involves attenuated endothelial NO production in response to extracellular stimuli, but the capacity for maximal enzyme activation and the breakdown of NO are not affected. As the disease progresses, there is nonspecific inhibition of NO bioavailability. Although this later inhibition is most likely multifactorial in origin, it is at least partly due to enhanced inactivation of NO by superoxide anions (2-4). These processes result in increased neutrophil adherence to the endothelium, thereby promoting a key step in the pathogenesis of atherosclerosis (5). The chronic inhibition of NO synthesis in rabbit models of hypercholesterolemia accelerates the development of vascular dysfunction and intimal lesions, providing additional evidence that the impairment of NO synthesis promotes atherogenesis (6). In vitro investigations have further shown that oxidized LDL (oxLDL) inhibits NO-mediated responses. Antioxidants reduce both the formation of free radicals and the oxidative modification of LDL that lead to impaired NO-related responses (7). Thus, NO is critically involved ...

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“…Isolation, Labeling, and Oxidation of Lipoproteins-LDL (d ϭ 1.019 -1.05 g/ml) and HDL (d ϭ 1.063-1.21 g/ml) were isolated from fresh human plasma by density gradient ultracentrifugation as described previously (28,29). The HDL 3 subfraction (d ϭ 1.13-1.18 g/ml) was isolated from other HDL subfractions using a density gradient fractionator (Isco).…”

Section: Methodsmentioning

confidence: 99%

High Density Lipoprotein Prevents Oxidized Low Density Lipoprotein-induced Inhibition of Endothelial Nitric-oxide Synthase Localization and Activation in Caveolae

Uittenbogaard

Shaul

Yuhanna

et al. 2000

Journal of Biological Chemistry

294

199

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Oxidized LDL (oxLDL) depletes caveolae of cholesterol, resulting in the displacement of endothelial nitric-oxide synthase (eNOS) from caveolae and impaired eNOS activation. In the present study, we determined if the class B scavenger receptors, CD36 and SR-BI, are involved in regulating nitric-oxide synthase localization and function. We demonstrate that CD36 and SR-BI are expressed in endothelial cells, co-fractionate with caveolae, and co-immunoprecipitate with caveolin-1. Co-incubation of cells with 10 g/ml high density lipoprotein (HDL) prevented oxLDLinduced translocation of eNOS from caveolae and restored acetylcholine-induced nitric-oxide synthase stimulation. Acetylcholine caused eNOS activation in cells incubated with 10 g/ml oxLDL (10-15 thiobarbituric acid-reactive substances) and blocking antibodies to CD36, whereas cells treated with only oxLDL were unresponsive. Furthermore, CD36-blocking antibodies prevented oxLDL-induced redistribution of eNOS. SR-BI-blocking antibodies were used to demonstrate that the effects of HDL are mediate by SR-BI. HDL binding to SR-BI maintained the concentration of caveola-associated cholesterol by promoting the uptake of cholesterol esters, thereby preventing oxLDL-induced depletion of caveola cholesterol. We conclude that CD36 mediates the effects of oxLDL on caveola composition and eNOS activation. Furthermore, HDL prevents oxLDL from decreasing the capacity for eNOS activation by preserving the cholesterol concentration in caveolae and, thereby maintaining the subcellular location of eNOS.Hypercholesterolemia-induced vascular disease and atherosclerosis are characterized by an early, selective decrease in the bioavailability of endothelium-derived nitric oxide (NO) (1). Responsiveness to receptor-dependent stimuli, such as acetylcholine, is decreased in the initial phase of the disease process, whereas responsiveness to receptor-independent stimuli such as the calcium ionophore A23187 is not altered. Therefore, the early pathogenesis is characterized by attenuated endothelial NO production in response to extracellular stimuli, even though the capacity for maximal enzyme activation and the breakdown of NO are not affected. As the disease progresses, nonspecific inhibition of NO bioavailability occurs, which is at least partly due to enhanced inactivation of NO by superoxide anions (2-4). The chronic inhibition of NO synthesis in rabbit models of hypercholesterolemia accelerates the development of vascular dysfunction and intimal lesions, providing additional evidence that the impairment of NO synthesis promotes atherogenesis (5). In vitro investigations have further shown that oxLDL 1 inhibits NO-mediated responses (6). Numerous studies have demonstrated that the endothelial isoform of NO synthase (eNOS) is localized in plasmalemmal caveolae and that caveolin is a negative regulator of eNOS enzymatic activity (7). Caveolae are lipid domains that typically represent about 1-4% of the total plasma membrane surface area (8). The structure and function of caveolae is dep...

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[11] Isolation and characterization of apolipoprotein B-100

Cited by 36 publications

References 37 publications

Retina expresses microsomal triglyceride transfer protein: implications for age-related maculopathy

Retina expresses microsomal triglyceride transfer protein: implications for age-related maculopathy

Oxidized Low Density Lipoprotein Displaces Endothelial Nitric-oxide Synthase (eNOS) from Plasmalemmal Caveolae and Impairs eNOS Activation

High Density Lipoprotein Prevents Oxidized Low Density Lipoprotein-induced Inhibition of Endothelial Nitric-oxide Synthase Localization and Activation in Caveolae

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