Chymase in exocytosed rat mast cell granules effectively proteolyzes apolipoprotein AI-containing lipoproteins, so reducing the cholesterol efflux-inducing ability of serum and aortic intimal fluid.

Abstract

Degranulated mast cells are present in human fatty streaks. Chymase in granules released from degranulated rat serosal mast cells, i.e., in granule remnants, proteolyzes human high density lipoprotein 3 (HDL 3 ), and so reduces its ability to induce cholesterol efflux from macrophage foam cells in vitro. In this study we found that remnant chymase, by proteolyzing human serum and human aortic intimal fluid, prevents these two physiologic fluids from effectively inducing cholesterol efflux from cultured macrophage foam cells. Inhibition was strongest when remnants were added to apolipoprotein AI (apoAI)-containing lipoproteins; the remnants had no effect on the weaker efflux produced by apoAI-deficient serum. Western blot analysis showed that granule remnants degrade apoAI in serum and in intimal fluid. When released from remnants, chymase lost its ability to proteolyze HDL 3 in the presence of serum. Thus, remnant chymase (but not isolated chymase) was able to resist the natu-

Matrix Metalloproteinases-3, -7, and -12, but Not -9, Reduce High Density Lipoprotein-induced Cholesterol Efflux from Human Macrophage Foam Cells by Truncation of the Carboxyl Terminus of Apolipoprotein A-I

“…2). This accords with our previous findings that exposure of the LpA-I-containing particles present in HDL 3 and in plasma to a minimal degree of proteolysis by the neutral protease chymase from exocytosed rat mast cell granules or from human skin results in reduced high affinity efflux of cholesterol from macrophage foam cells (15,16). Interestingly, Mendez and Oram (49) have shown that mild trypsin treatment, by proteolyzing a minor trypsin-labile fraction of HDL, almost completely abolished apolipoprotein-mediated cholesterol removal.…”

“…Cells-Human monocytes were separated from buffy coat cells, allowed to differentiate to macrophages, and loaded with cholesterol, as described before (15).…”

“…Proteolysis was stopped by adding EDTA to give a final concentration of 15 mM. Aliquots of the incubation mixtures were added to macrophage foam cells, and other aliquots of the remainders were delipidated (28) (10 g of total cholesterol/ml; each corresponding to 25 g of protein in control HDL 3 /ml) were incubated for 6 h in dishes containing [ 3 H]cholesterol-loaded human monocyte-derived macrophage foam cells, as described previously (15). Under these conditions, the efflux of [ 3 H]cholesterol was linear.…”

Depletion of Preβ 1 LpA1 and LpA4 Particles by Mast Cell Chymase Reduces Cholesterol Efflux From Macrophage Foam Cells Induced by Plasma

“…31 The present study was directed toward understanding the mechanisms underlying the blocking effect of chymase on the cholesterol efflux promoted by HDL 3 as previously described. 13,32 For this purpose, we investigated the effect of mast cell granule remnants on the small subpopulations of HDL containing apoAs (pre␤ 1 LpA1, LpA4 -1, and LpA4 -2), which play a role as early cholesterol acceptors from cells. Specifically, we determined whether proteolysis of pre␤ 1 LpA1 would be responsible for the previously observed inhibitory effect of mast cell chymase on the high affinity component of cholesterol efflux from macrophage foam cells.…”

“…Specifically, we determined whether proteolysis of pre␤ 1 LpA1 would be responsible for the previously observed inhibitory effect of mast cell chymase on the high affinity component of cholesterol efflux from macrophage foam cells. 32 …”