Lipolytic and ligand-binding functions of hepatic lipase protect against atherosclerosis in LDL receptor-deficient mice

Lita Freeman,Marcelo J.A Amar,Robert Shamburek,Beverly Paigen,H Bryan Brewer,Silvia Santamarina-Fojo,Herminia González-Navarro

doi:10.1194/jlr.m600321-jlr200

Abstract

To elucidate the separate contributions of the lipolytic versus ligand-binding functions of hepatic lipase (HL) to lipoprotein metabolism and atherosclerosis, and to investigate the role of the low density lipoprotein receptor (LDLr) in these processes, we compared mice expressing catalytically active HL (HL-WT) with mice expressing inactive HL (HL-S145G) in a background lacking endogenous HL and the LDLr (LDLr-KOxHL-KO). HL-WT and HL-S145G reduced (P < 0.05 for all) cholesterol (55% vs. 20%), non-HDL-cholesterol (63% vs. 22%), and apolipoprotein B (apoB; 34% vs. 16%) by enhancing the catabolism of autologous (125)I-apoB-intermediate density lipoprotein (IDL)/LDL (fractional catabolic rate in day(-1): 6.07 +/- 0.25, LDLr-KOxHL-WT; 4.76 +/- 0.30, LDLr-KOxHL-S145G; 3.70 +/- 0.13, LDLr-KOxHL-KO); HL-WT had a greater impact on the concentration, composition, particle size, and catabolism of apoB-containing lipoproteins (apoB-Lps) and HDL. Importantly, consistent with the changes in apoB-Lps, atherosclerosis in LDLr-KOxHL-KO mice fed a regular chow diet (RCD) was reduced by both HL-WT and HL-S145G (by 71% and 51% in cross-sectional analysis, and by 85% and 67% in en face analysis; P < 0.05 for all). These data identify physiologically relevant but distinct roles for the lipolytic versus ligand-binding functions of HL in apoB-Lp metabolism and atherosclerosis and demonstrate that their differential effects on these processes are mediated by changes in catabolism via non-LDLr pathways. These changes, evident even in the presence of apoE, establish an antiatherogenic role of the ligand-binding function of HL in LDLr-deficient mice.

Highlights

To elucidate the separate contributions of the lipolytic versus ligand-binding functions of hepatic lipase (HL) to lipoprotein metabolism and atherosclerosis, and to investigate the role of the low density lipoprotein receptor (LDLr) in these processes, we compared mice expressing catalytically active HL (HL -WT) with mice expressing inactive HL (HL -S145G) in a background lacking endogenous HL and the LDLr (LDLr-KO3HL-KO)
Northern analysis of RNA isolated from livers of LDLrKO3HL-WT and LDLr-KO3HL-S145G mice demonstrated that HL-WT and HL-S145G were expressed at similar levels
Expression of HL-WT and HL-S145G in low density lipoprotein receptor knockout (LDLr-KO) mice lacking endogenous mouse HL decreased plasma lipids relative to those in control LDLr-KO3HL-KO mice (Fig. 1A); the lipolytic activity of HL-WT was more effective at decreasing plasma lipids than HL-S145G (Fig. 1A)

Summary

Introduction

To elucidate the separate contributions of the lipolytic versus ligand-binding functions of hepatic lipase (HL) to lipoprotein metabolism and atherosclerosis, and to investigate the role of the low density lipoprotein receptor (LDLr) in these processes, we compared mice expressing catalytically active HL (HL -WT) with mice expressing inactive HL (HL -S145G) in a background lacking endogenous HL and the LDLr (LDLr-KO3HL-KO). Consistent with the changes in apoB-Lps, atherosclerosis in LDLr-KO3HL-KO mice fed a regular chow diet (RCD) was reduced by both HL-WT and HLS145G (by 71% and 51% in cross-sectional analysis, and by 85% and 67% in en face analysis; P , 0.05 for all) These data identify physiologically relevant but distinct roles for the lipolytic versus ligand-binding functions of HL in apoBLp metabolism and atherosclerosis and demonstrate that their differential effects on these processes are mediated by changes in catabolism via non-LDLr pathways. Initial adenoviral and transgenic overexpression of catalytically active and inactive HL in apolipoprotein E knockout (apoEKO) versus low density lipoprotein receptor knockout (LDLr-KO) mice [5,6,7,8, 21] established a role for the ligandbinding function of HL in decreasing plasma levels of the proatherogenic apoB-Lps independent of lipolysis These studies, limited by the confounding effects of the fully active, endogenous mouse HL or by the transient, nonsteady-state expression of catalytically active HL (HL-WT). This article is available online at http://www.jlr.org or inactive HL (HL-S145G), suggested different effects for the lipolytic versus ligand-binding functions of HL in apoB-Lp and HDL metabolism

Methods

Results

Conclusion