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Regulation of macrophage lipoprotein lipase secretion by the scavenger receptor
Y Murata1, S R Behr, F B Kraemer
1Division of Endocrinology, Stanford University School of Medicine, CA 94305.
Abstract:
The effects of ligand binding to the scavenger receptor on the secretion of lipoprotein lipase by murine macrophages were examined. Inflammatory macrophages exposed to acetylated low-density lipoprotein (AcLDL) exhibited a dose-dependent, 40-80% increase in lipoprotein lipase secretion. This stimulation appeared to be unrelated to intracellular cholesterol and triacylglycerol levels and to phagocytosis in general. Resident and inflammatory macrophages treated with maleylated bovine serum albumin (Mal-BSA) showed a 3-fold increase in lipoprotein lipase secretion in a dose-dependent and time-dependent fashion. In contrast, dextran sulfate, which is another ligand recognized by the scavenger receptor, caused a dose-dependent decrease in lipoprotein lipase secretion. Casein, a ligand recognized by the Mal-BSA receptor, did not affect lipoprotein lipase secretion nor the ability of Mal-BSA to stimulate the enzyme, while dextran sulfate abolished the stimulatory effects of Mal-BSA. Since ethylamine, an inhibitor of receptor-mediated endocytosis, attenuated the increase in lipoprotein lipase secretion induced by AcLDL and Mal-BSA, but did not affect the inhibition induced by dextran sulfate, it is suggested that receptor-mediated endocytosis of ligands via the scavenger receptor might play a key role in the stimulation of lipoprotein lipase secretion in macrophages. This study reveals another mechanism for regulation of macrophage lipoprotein lipase secretion.
Insights
Scavenger receptor ligand binding influences lipoprotein lipase secretion in macrophages. Receptor-mediated endocytosis of acetylated low-density lipoprotein (AcLDL) and maleylated bovine serum albumin (Mal-BSA) stimulates secretion, while dextran sulfate inhibits it.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Macrophages play a crucial role in lipid metabolism.
- Lipoprotein lipase (LPL) secretion by macrophages is a key factor in regulating lipid levels.
- Scavenger receptors (SRs) are involved in various cellular processes, including lipid uptake and immune responses.
Purpose of the Study:
- To investigate the effect of scavenger receptor ligand binding on lipoprotein lipase secretion in murine macrophages.
- To elucidate the role of receptor-mediated endocytosis in regulating LPL secretion.
- To understand the differential effects of various SR ligands on LPL secretion.
Main Methods:
- Murine macrophages (resident and inflammatory) were treated with different scavenger receptor ligands: acetylated low-density lipoprotein (AcLDL), maleylated bovine serum albumin (Mal-BSA), and dextran sulfate.
- Lipoprotein lipase secretion levels were measured.
- The role of receptor-mediated endocytosis was assessed using ethylamine, an inhibitor.
Main Results:
- AcLDL and Mal-BSA induced a dose-dependent increase in LPL secretion (40-80% and 3-fold, respectively).
- Dextran sulfate caused a dose-dependent decrease in LPL secretion.
- Ethylamine attenuated the stimulatory effects of AcLDL and Mal-BSA, suggesting a role for endocytosis.
Conclusions:
- Scavenger receptor ligand binding differentially regulates macrophage LPL secretion.
- Receptor-mediated endocytosis of specific ligands (AcLDL, Mal-BSA) stimulates LPL secretion.
- This study reveals a novel mechanism for regulating macrophage LPL secretion via scavenger receptors.