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Lipid-protein particles secreted from activated platelets reduce macrophage uptake of low density lipoprotein

B Fuhrman1, G J Brook, M Aviram

  • 1Lipid Research Unit, Rambam Medical Center, Haifa, Israel.

Atherosclerosis
|August 1, 1991
PubMed

Insights

Activated platelets release a particle that reduces low-density lipoprotein (LDL) uptake by macrophages. This process involves the scavenger receptor and inhibits cholesterol accumulation, suggesting a role for platelet-derived lipids in macrophage cholesterol regulation.

Area of Science:

  • Biochemistry
  • Cell Biology
  • Immunology

Background:

  • Low-density lipoprotein (LDL) uptake by macrophages is crucial for cholesterol homeostasis.
  • Platelets play a role in various physiological and pathological processes, including inflammation and lipid metabolism.

Purpose of the Study:

  • To investigate the effect of activated platelet conditioned medium (PCM) on macrophage LDL uptake.
  • To identify the component in PCM responsible for inhibiting LDL uptake and cholesterol accumulation.

Main Methods:

  • Macrophages were preincubated with PCM from activated platelets.
  • LDL-mediated cholesterol accumulation and esterification were measured.
  • LDL receptor activity was assessed.
  • PCM was fractionated and delipidated to identify the active component.
  • Experiments were conducted using U937 macrophages lacking scavenger receptors.

Main Results:

  • PCM reduced cellular LDL uptake by 30-40% and inhibited LDL-mediated cholesterol accumulation and esterification in macrophages.
  • The inhibitory effect was dose-dependent and linked to a reduction in LDL receptor number (apparent Vmax decreased by 35%).
  • The active component was a lipid fraction of PCM (molecular weight >25,000 Da) that was taken up via the scavenger receptor, essential for reducing LDL receptor activity.

Conclusions:

  • Activated platelets secrete a lipoprotein-like particle recognized by macrophage scavenger receptors.
  • This interaction leads to reduced cellular LDL uptake, primarily due to the lipid constituents of the particle.
  • Platelet-derived lipids may influence macrophage cholesterol metabolism through scavenger receptor-mediated pathways.

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