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

Miriam Lee-Rueckert,Riikka Vikstedt,Jari Metso,Matti Jauhiainen,Petri T Kovanen

doi:10.1194/jlr.m700392-jlr200

Abstract

Human atherosclerotic intima contains mast cells that secrete the neutral protease chymase into the intimal fluid, which also contains HDL-modifying proteins, such as cholesteryl ester transfer protein (CETP), in addition to abundant amounts of nascent discoidal HDL particles. Here, we studied chymase-dependent degradation of a) CETP isolated from human plasma and b) CETP-HDL complexes as well as the functional consequences of such degradations. Incubation with chymase caused a rapid cleavage of CETP, yielding a specific proteolytic pattern with a concomitant reduction in its cholesteryl ester transfer activity. These chymase-dependent effects were attenuated after CETP was complexed with HDL. This attenuation was more effective when CETP was complexed with HDL(3) and HDL(2) than with discoidal reconstituted high density lipoprotein (rHDL). Conversely, rHDL, but not spherical HDLs, was protected in such CETP complexes against functional inactivation by chymase. Thus, in contrast to the complexes of CETP with spherical HDLs, the ability of the CETP-rHDL complexes to promote cholesterol efflux from macrophage foam cells remained unchanged, despite treatment with chymase. In summary, complexation of CETP and HDL modifies their resistance to proteolytic inactivation: spherical HDLs protect CETP, and CETP protects discoidal HDL. These results suggest that in inflamed atherosclerotic intima, CETP, via its complexation with HDL, has a novel protective role in early steps of reverse cholesterol transport.

Highlights

Human atherosclerotic intima contains mast cells that secrete the neutral protease chymase into the intimal fluid, which contains HDL-modifying proteins, such as cholesteryl ester transfer protein (CETP), in addition to abundant amounts of nascent discoidal HDL particles
The extracellular fluid of the arterial intima is a filtrate of plasma components [51] that contains, in addition to HDL particles, other proteins that participate in reverse cholesterol transport, such as CETP [10] and phospholipid transfer protein (PLTP) [14]
CETP can enter the intimal fluid from the plasma compartment in association with HDL particles and can be expressed and secreted locally by cholesterol-loaded macrophages [13]

Summary

Introduction

Human atherosclerotic intima contains mast cells that secrete the neutral protease chymase into the intimal fluid, which contains HDL-modifying proteins, such as cholesteryl ester transfer protein (CETP), in addition to abundant amounts of nascent discoidal HDL particles. Incubation with chymase caused a rapid cleavage of CETP, yielding a specific proteolytic pattern with a concomitant reduction in its cholesteryl ester transfer activity These chymase-dependent effects were attenuated after CETP was complexed with HDL. In contrast to the complexes of CETP with spherical HDLs, the ability of the CETP-rHDL complexes to promote cholesterol efflux from macrophage foam cells remained unchanged, despite treatment with chymase. The two plasma lipid transfer proteins, cholesteryl ester transfer protein (CETP) and phospholipid transfer protein (PLTP), in turn remodel HDL, with ensuing generation of preb-HDL particles [3] Both preb-HDL and a-HDL particles promote the efflux of cholesterol from macrophage foam cells via the ATP binding cassette transporters ABCA1 and ABCG1 [4]. This article is available online at http://www.jlr.org

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