Regulation of murine hepatocyte apolipoprotein secretion by cytokines

R. Zhan, Dennis Black

Research output: Contribution to journalArticle

Abstract

Conditions associated with reticuloendothelial system activation result in disordered lipoprotein metabolism, associated with reduced circulating apolipoprotein (apo) A-I and E levels. Purpose: To test the hypothesis that cytokines, specifically tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1) and interleukin-6 (IL-6), produced by activated hepatic Kupffer cells, modulate secretion of hepatocyte apo A-I and E. Methods: Cultured murine hepatocytes were incubated with 100 ng/ml of each cytokine for 48 hrs. Culture medium apoLp secretion was determined by ELISA using rabbit anti-rat apo E and anti-mouse apo A-I antibodies. Secretion was measured as μg apoLp secreted/well during the final 4 hrs of cytokine treatment, expressed as % of control There were no differences in viable cell density per well among the experimental groups at the end of the incubation as determined by vital dye staining and cell counting. Apo A-I and E synthesis was measured by 35S-methionine radiolabeling during the final 4 hrs of cytokine treatment followed by culture medium and cell homogenate immunoprecipitation, SDS PAGE, and scintillation counting. Results: TNF-α, IL-1, and IL-6 treatment resulted in apo A-I secretion rates of 33±8% (mean ± SEM) (p=0.001), 119±13% (pNS), and 88±18% (pNS), respectively, of control cultures. For apo E, secretion rates were 60±15% (p=0.02), 59±10% (p=0.001), and 59±10% (p=0.001), respectively, of control cultures. Secretion of radiolabeled apo A-I and E paralleled secretion of apoLp mass. ApoLp synthesis (cell apoLp DPM as % of cell total protein DPM) was unchanged by any cytokine for apo A-I and reduced only by TNF-α for apo E. Conclusions: TNF-α, but not IL-1 or IL-6, reduces apo A-I secretion by cultured murine hepatocytes. All three cytokines reduce apo E secretion. Dissociation of synthesis and secretion can occur in some instances suggesting post-translational regulation. Regulation of hepatocyte apoLp secretion by cytokines produced locally by activated Kupffer cells may contribute to the abnormal lipoprotein metabolism in conditions with reticuloendothelial activation.

Original languageEnglish (US)
JournalJournal of Investigative Medicine
Volume44
Issue number1
StatePublished - Jan 1 1996
Externally publishedYes

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Apolipoproteins
Apolipoprotein A-I
Apolipoproteins E
Hepatocytes
Cytokines
Tumor Necrosis Factor-alpha
Interleukin-1
Interleukin-6
Kupffer Cells
Metabolism
Lipoproteins
Culture Media
Chemical activation
Scintillation Counting
Mononuclear Phagocyte System
Scintillation
Immunoprecipitation
Methionine
Rats
Polyacrylamide Gel Electrophoresis

All Science Journal Classification (ASJC) codes

  • Medicine(all)
  • Biochemistry, Genetics and Molecular Biology(all)

Cite this

Regulation of murine hepatocyte apolipoprotein secretion by cytokines. / Zhan, R.; Black, Dennis.

In: Journal of Investigative Medicine, Vol. 44, No. 1, 01.01.1996.

Research output: Contribution to journalArticle

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title = "Regulation of murine hepatocyte apolipoprotein secretion by cytokines",
abstract = "Conditions associated with reticuloendothelial system activation result in disordered lipoprotein metabolism, associated with reduced circulating apolipoprotein (apo) A-I and E levels. Purpose: To test the hypothesis that cytokines, specifically tumor necrosis factor-α (TNF-α), interleukin-1 (IL-1) and interleukin-6 (IL-6), produced by activated hepatic Kupffer cells, modulate secretion of hepatocyte apo A-I and E. Methods: Cultured murine hepatocytes were incubated with 100 ng/ml of each cytokine for 48 hrs. Culture medium apoLp secretion was determined by ELISA using rabbit anti-rat apo E and anti-mouse apo A-I antibodies. Secretion was measured as μg apoLp secreted/well during the final 4 hrs of cytokine treatment, expressed as {\%} of control There were no differences in viable cell density per well among the experimental groups at the end of the incubation as determined by vital dye staining and cell counting. Apo A-I and E synthesis was measured by 35S-methionine radiolabeling during the final 4 hrs of cytokine treatment followed by culture medium and cell homogenate immunoprecipitation, SDS PAGE, and scintillation counting. Results: TNF-α, IL-1, and IL-6 treatment resulted in apo A-I secretion rates of 33±8{\%} (mean ± SEM) (p=0.001), 119±13{\%} (pNS), and 88±18{\%} (pNS), respectively, of control cultures. For apo E, secretion rates were 60±15{\%} (p=0.02), 59±10{\%} (p=0.001), and 59±10{\%} (p=0.001), respectively, of control cultures. Secretion of radiolabeled apo A-I and E paralleled secretion of apoLp mass. ApoLp synthesis (cell apoLp DPM as {\%} of cell total protein DPM) was unchanged by any cytokine for apo A-I and reduced only by TNF-α for apo E. Conclusions: TNF-α, but not IL-1 or IL-6, reduces apo A-I secretion by cultured murine hepatocytes. All three cytokines reduce apo E secretion. Dissociation of synthesis and secretion can occur in some instances suggesting post-translational regulation. Regulation of hepatocyte apoLp secretion by cytokines produced locally by activated Kupffer cells may contribute to the abnormal lipoprotein metabolism in conditions with reticuloendothelial activation.",
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AU - Black, Dennis

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