Endocytosed beta-VLDL and LDL are delivered to different intracellular vesicles in mouse peritoneal macrophages.

Tabas, Ira; Lim, Sungtae; Xu, Xiang Xi; Maxfield, Frederick R.

doi:10.1083/jcb.111.3.929

Cited by 117 publications

(94 citation statements)

References 36 publications

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“…Second, the staining pattern of SMase in the cellular regions of both the normal aorta (ie, the endothelium) and lesions (ie, the intima) was not typical of 1 that was solely lysosomal, which usually appears as a perinuclear vesicular pattern. 65 Rather, some of the stain appeared on the outer edges of cells or bound to the pericellular matrix. In fact, even though our data suggest that the media of lesions is rather devoid of S-SMase, it is notable that this region showed poor staining of intracellular lysosomal SMase, which is an enzyme presence in all cells, including SMCs.…”

Section: Discussionmentioning

confidence: 99%

Sphingomyelinase, an Enzyme Implicated in Atherogenesis, Is Present in Atherosclerotic Lesions and Binds to Specific Components of the Subendothelial Extracellular Matrix

Marathe¹,

Kuriakose²,

Williams³

et al. 1999

ATVB

113

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Abstract-Atherosclerotic lesions contain an extracellular sphingomyelinase (SMase) activity that hydrolyzes the sphingomyelin of subendothelial low density lipoprotein (LDL). This SMase activity may promote atherosclerosis by enhancing subendothelial LDL retention and aggregation, foam cell formation, and possibly other atherogenic processes.The results of recent cell-culture studies have led to the hypothesis that a specific molecule called secretory SMase (S-SMase) is responsible for the SMase activity known to be in lesions, although its presence in atheromata had not been examined directly. Herein we provide immunohistochemical and biochemical support for this hypothesis. First, 2 different antibodies against S-SMase detected extracellular immunoreactive protein in the intima of mouse, rabbit, and human atherosclerotic lesions. Much of this material in lesions appeared in association with the subendothelial matrix. Second, binding studies in vitro demonstrated that 125 I-S-SMase adheres to the extracellular matrix of cultured aortic smooth muscle and endothelial cells, specifically to the laminin and collagen components. Third, in its bound state, S-SMase retains substantial enzymatic activity against lipoprotein substrates. Overall, these data support the hypothesis that S-SMase is an extracellular arterial wall SMase that contributes to the hydrolysis of the sphingomyelin of subendothelial LDL. S-SMase may therefore be an important participant in atherogenesis through local enzymatic effects that stimulate subendothelial retention and aggregation of atherogenic lipoproteins. (Arterioscler Thromb Vasc

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Section: Discussionmentioning

confidence: 99%

Sphingomyelinase, an Enzyme Implicated in Atherogenesis, Is Present in Atherosclerotic Lesions and Binds to Specific Components of the Subendothelial Extracellular Matrix

Marathe¹,

Kuriakose²,

Williams³

et al. 1999

ATVB

113

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“…Several studies from our (16,25,26) and other (27) laboratories have shown that foam cell-inducing lipoproteins undergo prolonged contact with the surface of macrophages, an event that may be important in the stimulation of the cholesterol esterification pathway (28). In this report, we examined the relationship in location between one such lipoprotein, ␤-VLDL, and ACAT.…”

Section: Figmentioning

confidence: 90%

“…Rhodamine-conjugated anti-rabbit and anti-chicken IgG were from Jackson ImmunoResearch Laboratories, Inc. (West Grove, PA), and Oregon green-conjugated antirabbit IgG was from Molecular Probes, Inc. (Eugene, OR). ␤-VLDL was prepared from the sera of rabbits fed a high fat, high cholesterol diet (2% cholesterol and 10% soy bean oil) as described previously (16) and conjugated to Texas Red (Molecular Probes, Inc.) according to the manufacturer's instructions. All other reagents were purchased from Sigma.…”

Section: Methodsmentioning

confidence: 99%

Immunolocalization of Acyl-Coenzyme A:CholesterolO-Acyltransferase in Macrophages

Khelef¹,

Buton²,

Beatini³

et al. 1998

Journal of Biological Chemistry

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Macrophages in atherosclerotic lesions accumulate large amounts of cholesteryl-fatty acyl esters ("foam cell" formation) through the intracellular esterification of cholesterol by acyl-coenzyme A:cholesterol O-acyltransferase (ACAT). In this study, we sought to determine the subcellular localization of ACAT in macrophages. Using mouse peritoneal macrophages and immunofluorescence microscopy, we found that a major portion of ACAT was in a dense reticular cytoplasmic network and in the nuclear membrane that colocalized with the luminal endoplasmic reticulum marker protein-disulfide isomerase (PDI) and that was in a similar distribution as the membrane-bound endoplasmic reticulum marker ribophorin. Remarkably, another portion of the macrophage ACAT pattern did not overlap with PDI or ribophorin, but was found in as yet unidentified cytoplasmic structures that were juxtaposed to the nucleus. Compartments containing labeled ␤-very low density lipoprotein, an atherogenic lipoprotein, did not overlap with the ACAT label, but rather were embedded in the dense reticular network of ACAT. Furthermore, cell-surface biotinylation experiments revealed that freshly harvested, non-attached macrophages, but not those attached to tissue culture dishes, contained ϳ10 -15% of ACAT on the cell surface. In summary, ACAT was found in several sites in macrophages: a cytoplasmic reticular/nuclear membrane site that overlaps with PDI and ribophorin and has the characteristics of the endoplasmic reticulum, a perinuclear cytoplasmic site that does not overlap with PDI or ribophorin and may be another cytoplasmic structure or possibly a unique subcompartment of the endoplasmic reticulum, and a cellsurface site in non-attached macrophages. Understanding possible physiological differences of ACAT in these locations may reveal an important component of ACAT regulation and macrophage foam cell formation.Macrophages enter atherosclerotic lesions at an early stage and are found at all stages of lesion development thereafter (1). Several studies have provided evidence that macrophages play an important role in both lesion initiation and late lesion complications (2, 3). A major property of lesional macrophages is their tendency to become massively loaded with cholesteryl ester, a process known as foam cell formation because the numerous cholesteryl ester droplets give the cells a foamy appearance (1). The pathway by which macrophages accumulate cholesteryl ester is complex and not completely understood. Data from several laboratories suggest that macrophages internalize cholesterol through the uptake of certain "atherogenic" lipoproteins or by direct uptake of lipoprotein cholesterol. When the cellular cholesterol content increases to a certain threshold level, mixed pools of lipoprotein-derived and cellular cholesterol gain access to an integral membrane enzyme called ACAT, 1 which then catalyzes the esterification of the cholesterol to fatty acid via a fatty acyl-CoA intermediate (4).Given the importance of macrophage foam cells in atheroscleros...

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“…In contrast to the lysosomal degradation of LDL-derived apoB (14), ␤-VLDL-derived apoE was identified in widely distributed vesicles and showed a slow protein degradation in mouse macrophages (15,16). However, in the same cells, ␤-VLDLderived lipids were delivered to perinuclear, lysosomal compartments (17).…”

mentioning

confidence: 98%

Recycling of Apolipoprotein E and Lipoprotein Lipase through Endosomal Compartments in Vivo

Heeren¹,

Grewal²,

Jäckle

et al. 2001

Journal of Biological Chemistry

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We have recently described a novel recycling pathway of triglyceride-rich lipoprotein (TRL)-associated apolipoprotein (apo) E in human hepatoma cells. We now demonstrate that not only TRL-derived apoE but also lipoprotein lipase (LPL) is efficiently recycled in vitro and in vivo. Similar recycling kinetics of apoE and LPL in normal and low density lipoprotein receptor-negative human fibroblasts also indicate that the low density lipoprotein receptor-related protein seems to be involved. Intracellular sorting mechanisms are responsible for reduced lysosomal degradation of both ligands after receptor-mediated internalization. Immediately after internalization in rat liver, TRLs are disintegrated, and apoE and LPL are found in endosomal compartments, whereas TRL-derived phospholipids accumulate in the perinuclear region of hepatocytes. Subsequently, substantial amounts of both proteins can be found in purified recycling endosomes, indicating a potential resecretion of these TRL components. Pulse-chase experiments of perfused rat livers with radiolabeled TRLs demonstrated a serum-induced release of internalized apoE and LPL into the perfusate. Analysis of the secreted proteins identified ϳ80% of the recycled TRLderived proteins in the high density lipoprotein fractions. These results provide the first evidence that recycling of TRL-derived apoE and LPL could play an important role in the modulation of lipoproteins in vivo.Triglycerides are transported mainly by two distinct classes of triglyceride-rich lipoproteins (TRLs), 1 the chylomicrons and the very low density lipoproteins (VLDLs). After assembly in the intestine, chylomicrons are transported via lymph into the bloodstream, where they are converted at the endothelial surface to remnant lipoproteins through the catalytic action of lipoprotein lipase (LPL) (for review, see Refs. 1 and 2). After lipolysis, LPL remains associated with the chylomicron remnants and, in concert with apolipoprotein (apo) E (3-5), facilitates their clearance into hepatocytes (6) via LDL receptor (LDLR) and the LDLR-related protein (LRP) (7-10). The essential role for both receptors in TRL removal in vivo has been demonstrated in gene knockout and gene transfer experiments (Refs. 11 and 12; for a recent review, see Ref. 13).Several studies have used different "model particles" to investigate the intracellular processing of TRL constituents. In contrast to the lysosomal degradation of LDL-derived apoB (14), ␤-VLDL-derived apoE was identified in widely distributed vesicles and showed a slow protein degradation in mouse macrophages (15, 16). However, in the same cells, ␤-VLDLderived lipids were delivered to perinuclear, lysosomal compartments (17). Delayed transport and degradation of TRL proteins were also observed in hepatoma cells (18,19). In recent studies, we have been able to demonstrate that the altered transport and retarded degradation of internalized TRLs is due to intracellular disintegration and sorting of TRL components in a peripheral cellular compartment. Whereas lipids are ...

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Endocytosed beta-VLDL and LDL are delivered to different intracellular vesicles in mouse peritoneal macrophages.

Cited by 117 publications

References 36 publications

Sphingomyelinase, an Enzyme Implicated in Atherogenesis, Is Present in Atherosclerotic Lesions and Binds to Specific Components of the Subendothelial Extracellular Matrix

Sphingomyelinase, an Enzyme Implicated in Atherogenesis, Is Present in Atherosclerotic Lesions and Binds to Specific Components of the Subendothelial Extracellular Matrix

Immunolocalization of Acyl-Coenzyme A:CholesterolO-Acyltransferase in Macrophages

Recycling of Apolipoprotein E and Lipoprotein Lipase through Endosomal Compartments in Vivo

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