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Macrophages modify beta-VLDL by proteolysis and enhance subsequent lipid accumulation in arterial smooth muscle cells
1Pathology Department, University of Cambridge, U.K.
Abstract:
Murine resident peritoneal macrophages (MRPM), incubated with beta-very low density lipoprotein (beta-VLDL), modify the beta-VLDL, producing an increase in the mobility of the lipoprotein. The modification does not result in an increase of thiobarbituric acid-reactive substances (TBARS) in the lipoprotein, and is not inhibited by butylated hydroxyanisole (BHA), EDTA, removal of copper and iron from the medium, or by diphenyliodonium (DPI), suggesting that the mechanism of modification is independent of oxidation. Macrophage conditioned medium performed the modification in the absence of cells, and phenylmethylsulphonyl fluoride (PMSF) inhibited beta-VLDL modification, whereas other protease inhibitors did not, suggesting that a secreted neutral serine protease may possibly be involved in the mechanism. The modified beta-VLDL enhanced the accumulation of cholesterol esters by smooth muscle cells (SMC).
Insights
Murine resident peritoneal macrophages modify beta-very low density lipoprotein (beta-VLDL) via a protease, not oxidation. This modified beta-VLDL enhances cholesterol ester accumulation in smooth muscle cells.
Area of Science:
- Cell Biology
- Biochemistry
- Lipid Metabolism
Background:
- Macrophages play a role in lipoprotein metabolism.
- Beta-very low density lipoprotein (beta-VLDL) is implicated in atherosclerosis.
- Understanding lipoprotein modification is crucial for cardiovascular research.
Purpose of the Study:
- To investigate the mechanism by which murine resident peritoneal macrophages (MRPM) modify beta-VLDL.
- To determine the effect of modified beta-VLDL on smooth muscle cells (SMC).
Main Methods:
- Incubation of MRPM with beta-VLDL.
- Analysis of beta-VLDL modification using thiobarbituric acid-reactive substances (TBARS) assay.
- Testing the effect of various inhibitors (BHA, EDTA, PMSF) and conditions (metal ion removal, cell-free medium).
- Assessing cholesterol ester accumulation in SMC exposed to modified beta-VLDL.
Main Results:
- MRPM modify beta-VLDL, increasing its mobility.
- The modification is independent of oxidation, as indicated by lack of TBARS increase and inhibition resistance.
- Phenylmethylsulphonyl fluoride (PMSF) inhibited the modification, suggesting a serine protease involvement.
- Modified beta-VLDL promoted cholesterol ester accumulation in SMC.
Conclusions:
- Macrophage-mediated beta-VLDL modification appears to be a non-oxidative process involving a secreted neutral serine protease.
- This modification enhances the atherogenic potential of beta-VLDL by promoting cholesterol ester accumulation in SMC.