Adenovirus-Mediated Gene Transfer of Human Lipoprotein Lipase Ameliorates the Hyperlipidemias Associated with Apolipoprotein E and LDL Receptor Deficiencies in Mice

Abstract

Lipoprotein lipase (LPL) is the rate-limiting enzyme for the hydrolysis of triglyceride-rich lipoproteins. We tested the efficacy of adenovirus-mediated gene transfer of LPL as treatment of experimental hyperlipidemias associated with apolipoprotein (apoE) deficiency (apoE–/–) and low-density lipoprotein receptor (LDLr) deficiency (LDLr–/–) in mice. Replication-defective adenovirus containing the human LPL cDNA driven by a cytomegalovirus promoter (Ad.hLPL) efficiently transduced CHO-ldlA7 cells in vitro, inducing in these cells the production of bioactive LPL (73 mU/ml). Intravenous injection of Ad.hLPL (2 × 10⁹ pfu) led to high-level expression of hLPL mRNA and LPL activity in the liver (88.3 mU/ml) and in post-heparin plasma (116.1 mU/ml). Overexpression of LPL resulted in marked reductions in total plasma cholesterol (TC; 48%, 43%, 25%) and triglycerides (TTg; 63%, 40%, 70%, p < 0.01) in apoE–/–, LDLr–/–, and wild-type (WT) mice, respectively. Fast protein liquid chromatography (FPLC) fractionation of plasma lipoproteins showed a marked decrease in very-low-density lipoprotein (VLDL)/chylomicron remnant cholesterol (V/CR-C) in apoE–/– (83%), LDLr–/– (84%), and WT mice (58%, p < 0.01). VLDL/chylomicron remnant triglycerides (V/CR-Tg) were virtually eliminated in apoE–/– (92%), LDLr–/– (86%), and WT mice (84%, p < 0.05). No significant changes were detected in LPL activities, plasma lipids, or lipoproteins of mice injected with a control virus, Ad.Luc, containing the luciferase instead of the LPL cDNA. In summary, infusion of Ad.hLPL leads to increased liver and post-heparin plasma LPL activities, significantly reduced TC, TTg, V/CR-C, and V/CR-Tg in WT mice, as well as in mice with apoE and LDLr deficiencies. Adenovirus-mediated LPL gene transfer to the liver is an effective means of reversing many of the lipoprotein abnormalities in apoE- and LDLr-deficient mice.

Overview summary

It is well known that hypercholesterolemia is an important risk factor for atherosclerosis. Recent clinical studies have also implicated hypertriglyceridemia as another predisposing factor for the development of atherosclerosis. Triglyceride molecules transported in the circulation in association with plasma lipoproteins are hydrolyzed at the endothelial surface by lipoprotein lipase (LPL). In the present study, hepatic overexpression of LPL by adenovirus-mediated gene transfer led to high levels of LPL activity and significant reduction in triglyceride-rich lipoproteins (very-low-density lipoprotein and chylomicron remnants) in wild-type mice. Furthermore, high levels of LPL expression also markedly lowered the total plasma cholesterol and ameliorated the atherogenic plasma lipoprotein profiles of apoE-deficient and LDLr-deficient mice, two genetic mouse models of hyperlipidemias that are associated with accelerated atherosclerosis. The results of this study suggest a promising role for LPL in gene therapy interventions aimed to correct genetic dyslipoproteinemias and to prevent atherosclerosis.