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

Abstract

Abstract-Exposure of the LpA1-containing particles present in HDL 3 and plasma to a minimal degree of proteolysis by the neutral protease chymase from exocytosed rat mast cell granules (granule remnants) leads to a reduction in the high-affinity component of cholesterol efflux from macrophage foam cells. In this study, we demonstrate for the first time, a role for mast cell chymase in the depletion of the lipid-poor minor components of HDL that are specifically involved in reverse cholesterol transport as initial acceptors of cellular cholesterol. Thus, addition of proteolytically active granule remnants or human skin chymase to cholesterol-loaded macrophages of mouse or human origin incubated with human apoA1, ie, a system in which pre␤ 1 LpA1 is generated, resulted in a sharp reduction in the high-affinity cholesterol efflux promoted by apoA1. As determined by nondenaturing 2-dimensional polyacrylamide gradient gel electrophoresis, the granule remnants effectively depleted the pre␤ 1 LpA1, but not the ␣LpA1, in HDL 3 and in plasma during incubation at 37°C for Ͻ1 hour. Incubation of plasma with granule remnants for 1 hour also led to near disappearance of the LpA4 -1 and LpA4 -2 particles, but did not affect the distribution of the apoA2-containing lipoproteins present in the plasma. We conclude that the reduced ability of granule remnant-treated HDL 3 and granule remnant-treated plasma to induce cholesterol efflux from macrophage foam cells is caused by selective depletion by mast cell chymase of quantitatively minor A1-and A4-containing subpopulations of HDL. Because these particles, ie, pre␤ 1 LpA1 and LpA4, are efficient acceptors of cholesterol from cell surfaces, their depletion by mast cells may block the initiation of reverse cholesterol transport in vivo and thereby favor foam cell formation in the arterial intima, the site of atherogenesis.

Concentrations of Electrophoretic and Size Subclasses of Apolipoprotein A-I–Containing Particles in Human Peripheral Lymph

“…Theoretically, these might include catabolism by cells, although tissue culture studies have indicated that this is unlikely to be quantitatively significant. 39 Because pre-␤ HDLs are more susceptible to proteolysis than are other HDLs, 40 they might be degraded by enzymes released into tissue fluid, 41,42 although no apoA-I fragments were detected in our HP-SEC fractions of lymph. A third possibility is that some small pre-␤ HDLs are converted in tissue fluid into larger discoidal species that are incompletely resolved by our laboratory procedures, as a consequence of uptake of cell-derived PL and UC.…”

Association of cholesteryl ester transfer protein with HDL particles reduces its proteolytic inactivation by mast cell chymase

“…Furthermore, studies in vitro have demonstrated that chymase specifically depletes preb-HDL particles (26), thus blocking cholesterol efflux mediated by the ABCA1 pathway (27). In contrast, limited proteolysis of HDL 3 particles by chymase does not impair their ability to activate LCAT (28) or to act as phospholipid acceptors in PLTP-mediated phospholipid transfer reactions (29).…”

Association of Coronary Heart Disease with Pre-β-HDL Concentrations in Japanese Men

“…Efflux of UC from cells to pre-␤ 0 -HDLs in tissue fluids exceeds its esterification, leading to accumulation of UC-rich discoidal HDLs in lymph (16,17 ). For this pathway of RCT, which presumably applies to arterial smooth muscle and macrophages, ABCA1 transporter function (4,18,19 ) and pre-␤-HDL concentration (20,21 ) appear to play critical roles in regulating UC efflux.…”