The Uptake, Storage, and Intracellular Hydrolysis of Carbohydrates by Macrophages

Cohn, Zanvil A.; Ehrenreich, Barbara A.

doi:10.1084/jem.129.1.201

Cited by 184 publications

(86 citation statements)

References 13 publications

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“…Similarly, exocytosis or reverse pinocytosis cannot account for the export of cholesterol. This conclusion is based upon experiments in which high molecular weight, nondegradable, intralysosomal markers are quantitatively retained within the macrophage for many days (61)(62)(63). It therefore appears that cholesterol molecules are exchanged in the absence of membrane translocations and independent of their membrane "carriers."…”

Section: Discussionmentioning

confidence: 99%

Cholesterol Metabolism in the Macrophage

Werb

Cohn

1971

The Journal of Experimental Medicine

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Cholesterol is a constituent of all mammalian cells and serves as a structural unit of membranes. Cytomembranes of the "thick" variety (80-100 A) which have potential access to the extracellular milieu are rich in cholesterol and include plasma membrane, lysosomal membrane, and secretion granules (1-10). In contrast, "thin" membranes (40-70 A) such as endoplasmic reticulum, mitochondria, and nuclear envelope are poor in cholesterol, whereas Golgi membranes are intermediate in size and cholesterol content (5,11,12).Although there is an extensive literature on cholesterol metabolism of the whole organism (13-16), our knowledge of the cellular level is fragmentary. Exceptions are the well-documented studies first described by Hagerman and Gould (17) demonstrating cholesterol exchange from plasma lipoproteins to the membrane of erythrocytes. No net change in cholesterol content of red cell takes place and cholesterol ester (CE) 1 exchange is very limited. Recently, the de novo biosynthesis of cholesterol by cultured eukaryotic cells has been shown (18-20) although its conversion to metabolites other than its esters has not been demonstrated (19,21,22).We have chosen to examine the metabolism of cholesterol in homogeneous populations of macrophages. This was prompted by the physiological role of this cell in the processing of chylomicrons and effete erythrocytes (23)(24)(25) and its association with a number of pathological events in which lipid storage takes place (26)(27)(28)(29)(30). In addition, macrophages exhibit striking endocytic activity in which the flow and turnover of cholesterol-rich membranes might be examined.In this article we will describe the content and subcellular distribution of macrophage cholesterol, the factors controlling exchange, and its biosynthesis under defined cultural conditions.

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Section: Discussionmentioning

confidence: 99%

Cholesterol Metabolism in the Macrophage

Werb

Cohn

1971

The Journal of Experimental Medicine

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“…To maintain the size and content of these structures, nondigestible materials of either soluble or particulate nature may be employed. In this study we use nondegradable disaccharities and polysaccharides as well as polystyrene beads to interiorize plasma membrane and enrich the intracytoplasmic pool of secondary lysosomes (20,21).…”

Section: Resultsmentioning

confidence: 99%

“…Exchange takes place in the absence of membrane flow from plasma membrane to lysosomal membrane, and reverse membrane flow is extremely unlikely (16,17,20). Since membrane-membrane interactions analogous to soluble lipoproteins-membrane interactions are also unlikely by morphological criteria, an intracellular carrier may exist.…”

Section: Morphological Identification Of the Slowly Exchanging Cholesmentioning

confidence: 99%

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Cholesterol Metabolism in the Macrophage

Werb

Cohn

1971

The Journal of Experimental Medicine

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Macrophage membrane cholesterol is present in two subcellular cholesterol pools, a rapidly exchanging compartment comprising about two-thirds of the total cholesterol, and a slowly exchanging compartment comprising one-third of the total. The morphological identification of the kinetically distinguishable pools proceeded by alteration of each compartment. Trypsin treatment markedly decreased the rate of cholesterol exchange without removing cholesterol from the membrane. Recovery of normal exchange rates took more than 7 hr and required protein synthesis. This suggested that a plasma membrane receptor is involved in positioning of lipoproteins for exchange, and is consistent with the plasma membrane localization of the rapidly exchanging compartment. Extensive pinocytosis by nondegradable dextran, dextran sulfate, or sucrose resulted in the accumulation of many secondary lysosomes, thus increasing the relative proportion of intracellular membranes. The measurable granule membrane area, cholesterol content, phospholipid content, and the relative size of the slowly exchanging cholesterol compartment all increased. The amount of intracellular membrane altered by extensive phagocytosis of latex particles also increased the size of the slowly exchanging cholesterol compartment. This suggested that the slowly exchanging pool of cholesterol represented the intracellular membranes primarily of lysosomal origin. Rabbit alveolar macrophages and thioglycollate-stimulated peritoneal macrophages contain many secondary lysosomes as a result of multiple bouts of in vivo phagocytosis and pinocytosis. In both of these cells the fast and slow pools are equal in size. The increased cholesterol content was attributable to the increase in the relative size of the slowly exchanging compartment. L-cells and melanoma cells also exchange their cholesterol with that of serum lipoproteins. Both cells contain few cholesterol-rich intracellular membranes, and had lower cellular cholesterol contents. In these cells the slowly exchanging pool was a minor contribution to cell cholesterol. Studies with these cells provided further evidence for the lysosomal membrane and plasma membrane localization of the slowly and rapidly exchanging cholesterol compartments.

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“…Pinocytosis of fluid and solutes would therefore seem redundant. When macromolecular solutes are interiorized, they too are digested to small molecular weight components in the lysosomal space (8,15,16,17,40). It is likely that the electrolyte composition of vesicle fluid, being a sample of the extracellular fluid, contains high concentrations of the very ions the cell is actively (i.e., spending metabolic energy) trying to exclude, such as sodium and calcium.…”

Section: Steinman Brodie A~d Cohn Membrane Flow During Pinocytosis 681mentioning

confidence: 99%

Membrane flow during pinocytosis. A stereologic analysis.

Steinman¹,

Brodie²,

Cohn³

1976

The Journal of Cell Biology

615

346

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HRP has been used as a cytochemical marker for a stereologic analysis of pinocytic vesicles and secondary lysosomes in cultivated macrophages and L cells. Evidence is presented that the diaminobenzidine technique (a) detects all vacuoles containing enzyme and (b) distinguishes between incoming pinocytic vesicles and those which have fused with pre-existing lysosomes to form secondary lysosomes.The HRP reactive pinocytic vesicle space fills completely within 5 min after exposure to enzyme, while the secondary lysosome compartment is saturated in 45-60 min. The size distribution of sectioned (profile) vacuole diameters was measured at equilibrium and converted to actual (spherical) dimensions using a technique modified from Dr. S. D. Wicksell.The most important findings in this study have to do with the rate at which pinocytosed fluid and surface membrane move into the cell and on their subsequent fate. Each minute macrophages form at least 125 pinocytic vesicles having a fractional vol of 0.43% of the cell's volume and a fractional area of 3.1% of the cell's surface area. The fractional volume and surface area influx rates for L cells were 0.05% and 0.8% per minute respectively. Macrophages and L cells thus interiorize the equivalent of their cell surface area every 33 and 125 min.During a 3-h period, the size of the secondary lysosome compartment remains constant and represents 2.5% of the cell volume and 18% of the surface area. Each hour, therefore, the volume and surface area of incoming vesicles is 10 times greater than the dimensions of the secondary lysosomes in both macrophages and L cells. This implies a rapid reduction in vesicle size during the formation of the secondary lysosome and the egress of pinocytosed fluid from the vacuole and the cell. In addition, we postulate that membrane components of the vacuole are subsequently recycled back to the cell surface.Pinocytosis involves the formation of a membranebound vesicle from the cell surface, trapping within it fluid and solutes from the extracellular environment. In most cells, these incoming pinocytic vesicles fuse with acid-hydrolase-containing granules or lysosomes. These events have been studied largely in relation to macromolecular and small particulate markers occupying the content of the incoming vesicle (e.g., 9, 15, 40, 41). In these instances, interiorized materials undergo digestion and/or sequestration within the lysosomal apparatus. Very little else is known about pinocytic vesicles. We lack quantitative information on their surface areas and volumes, especially in relation to

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The Uptake, Storage, and Intracellular Hydrolysis of Carbohydrates by Macrophages

Cited by 184 publications

References 13 publications

Cholesterol Metabolism in the Macrophage

Cholesterol Metabolism in the Macrophage

Cholesterol Metabolism in the Macrophage

Membrane flow during pinocytosis. A stereologic analysis.

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