Modulation of Arteriosclerosis by Gene-Therapy

Abstract

Abnormalities in plasma lipoprotein metabolism are mostly based upon specific gene defects. Gene therapy forms the ultimate treatment of these disorders. The present data, focused upon the treatment of apolipoprotein E (ApoE) and LDL-receptor deficiency are the first examples of and analysis of gene-replacement on the development atherosclerotic lesions.Inactivation of the apoE gene in mice leads to a prominent increase in serum cholesterol and triglyceride levels and the development of premature atherosclerosis. The role of monocyte/macrophage-derived apoE in atherogenesis was assessed by bone marrow transplantation in apoE-deficient mice, using donor bone marrow of wild-type mice. Quantitation of atherosclerotic lesions in the aortic root, after 4 months of “Western-type” diet, revealed that the mean lesion area was approximately 10-fold smaller in mice tranplanted with bone marrow from wild-type donors as compared to control apoE-deficient mice.The influence of apoE gene-dosage on serum lipid concentrations was determined by transplantation with homozygous apoE-deficient heterozygous apoE-deficient and wild-type bone marrow. The concentration of apoE, detected in serum, was found to be gene-dosage dependent, being 3.52 ± 0.74%, 1.87 ± 74% and 0% of normal in transplanted mice receiving either wild-type, heterozygote apoE-deficient, or homozygous apoE-deficient bone marrow, respectively. These low concentrations of apoE nevertheless reduced serum cholesterol levels dramatically due to a reduction of VLDL, and to a lesser extent, of LDL, while HDl levels were slightly raised.The relative importance of the LDLR on macrophages for lipoprotein metabolism and atherogenesis was assessed by transplantation of LDLR knockout (-/-) mice with bone marrow of normal C57BI mice. The transplantation resulted in a decrease can almost completely be attributed to a decrease in LDL-cholesterol. The specific lowering of LDL-cholesterol was more pronounced 4 weeks after transplantation than 12 weeks after transplantation.Quantitation of atherosclerotic lesions of mice fed a 1% cholesterol diet for 6 months, revealed that there were no differences in mean lesion area between mice transplanted with wild-type bone marrow or LDLR-/- bone marrow. We anticipate that in the LDLR-/- mice transplanted with wild-type bone marrow, the LDLR is down-regulated by the relatively high concentrations of circulating cholesterol. In vitro incubations of peritoneal microphages with 125I-LDL indicated that the LDLR of these cells could be downregulated by 25-OH cholesterol. PEritoneal macrophages isolated from LDLR-/- mice tranplanted with wild-type bone marrow, in contrast to those tranplanted woth LDLR-/- bone marrow, were able to degrade 125I-LDL, indicating that the capaity to express functional LDLR was achieved. In conclusion, introduction of the LDLR in LDLR-/- mice via bone marrow transplantation resulted in a relatively modest decrease of LDL-cholesterol levels in apoE-deficient mice. Atherosclerotic lesions in apoE deficient mice were 10-fold smaller in mice transplanted with bone marrow from wild-type donor, establishing the anti-atherogenic role of macrophage-associated apoE production.