Hepatic low-density lipoprotein receptor–related protein deficiency in mice increases atherosclerosis independent of plasma cholesterol

Abstract

The low-density lipoprotein (LDL) receptor–related protein (LRP) has a well-established role in the hepatic removal of atherogenic apolipoprotein E (APOE)–rich remnant lipoproteins from plasma. In addition, LRP recognizes multiple distinct pro- and antiatherogenic ligands in vitro. Here, we investigated the role of hepatic LRP in atherogenesis independent of its role in removal of APOE-rich remnant lipoproteins. Mice that allow inducible inactivation of hepatic LRP were combined with LDL receptor and APOE double-deficient mice (MX1Cre+LRPflox/floxLDLR–/–APOE–/–). On an LDLR–/–APOE–/– background, hepatic LRP deficiency resulted in decreased plasma cholesterol and triglycerides (cholesterol: 17.1 ± 5.2 vs 23.4 ± 6.3 mM, P = .025; triglycerides: 1.1 ± 0.5 vs 2.2 ± 0.8 mM, P = .002, for MX1Cre+LRPflox/flox-LDLR–/–APOE–/– and control LRPflox/flox-LDLR–/–APOE–/– mice, respectively). Lower plasma cholesterol in MX1Cre+LRPflox/flox-LDLR–/–APOE–/– mice coincided with increased plasma lipoprotein lipase (71.2 ± 7.5 vs 19.1 ± 2.4 ng/ml, P = .002), coagulation factor VIII (4.4 ± 1.1 vs 1.9 ± 0.5 U/mL, P = .001), von Willebrand factor (2.8 ± 0.6 vs 1.4 ± 0.3 U/mL, P = .001), and tissue-type plasminogen activator (1.7 ± 0.7 vs 0.9 ± 0.5 ng/ml, P = .008) compared with controls. Strikingly, MX1Cre+LRPflox/floxLDLR–/–APOE–/– mice showed a 2-fold higher atherosclerotic lesion area compared with controls (408.5 ± 115.1 vs 219.1 ± 86.0 103μm2, P = .003). Our data indicate that hepatic LRP plays a clear protective role in atherogenesis independent of plasma cholesterol, possibly due to maintaining low levels of its proatherogenic ligands.