Biochemical and genetic studies of the apoprotein E secreted by mouse macrophages and human monocytes

S. K. Basu, Y. K. Ho, M. S. Brown, D. W. Bilheimer, R. G. Anderson, J. L. Goldstein

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Abstract

Monolayers of mouse peritoneal macrophages secrete large amounts of apoliprotein E (apo-E) after the cells have been loaded with cholesterol by incubation with modified lipoproteins. In the current studies, we characterize some of the biochemical morphological, and functional properties of macrophage-secreted apo-E, and we also show that a similar protein is secreted by human blood monocytes. Apo-E was secreted by mouse macrophages in the form of lipoprotein particles with a mean density of 1.075 g/ml. By electron microscopy, these lipoproteins appeared as lamellar discs. The 35S-labeled apo-E secreted by macrophages was able to bind to low density lipoprotein receptors on human fibroblasts and was taken up and degraded with high affinity. The 35S-labeled apo-E secreted by human monocytes was examined by two-dimensional isoelectric focusing-sodium dodecyl sulfate polyacrylamide gel electrophoresis. The secreted protein was more acidic than the apo-E of plasma very low density lipoprotein from the same individual. Treatment with neuramidase converted the monocyte-produced apo-E to a form that resembled plasma apo-E, suggesting that the secreted product had more sialic acid residues than the circulating form. Monocytes from individuals with different alleles at the genetic locus specifying apo-E secreted a form of 35S-labeled apo-E that was electrophoretically similar to their plasma apo-E after neuraminidase treatment, suggesting that the monocyte-secreted apo-E and the plasma apo-E are products of the same gene. The finding that cholesterol-loaded macrophages and monocytes synthesize and secrete apo-E is discussed in relation to the in vivo process of 'reverse cholesterol transport.'

Original languageEnglish (US)
Pages (from-to)9788-9795
Number of pages8
JournalJournal of Biological Chemistry
Volume257
Issue number16
StatePublished - 1982

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Macrophages
Apolipoproteins E
Molecular Biology
Monocytes
Lipoproteins
Plasmas
Cholesterol
VLDL Lipoproteins
LDL Receptors
Neuraminidase
N-Acetylneuraminic Acid
Fibroblasts
Electrophoresis
Genetic Loci
Sodium Dodecyl Sulfate
Electron microscopy
Peritoneal Macrophages
Isoelectric Focusing
Monolayers
Proteins

ASJC Scopus subject areas

  • Biochemistry

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Biochemical and genetic studies of the apoprotein E secreted by mouse macrophages and human monocytes. / Basu, S. K.; Ho, Y. K.; Brown, M. S.; Bilheimer, D. W.; Anderson, R. G.; Goldstein, J. L.

In: Journal of Biological Chemistry, Vol. 257, No. 16, 1982, p. 9788-9795.

Research output: Contribution to journalArticle

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