Type III hyperlipoproteinemia and spontaneous atherosclerosis in mice resulting from gene replacement of mouse Apoe with human Apoe*2.

To study isoform-specific effects of apolipoprotein E (apoE) in vivo, we generated mice with a human APOE*2 allele in place of the mouse Apoe gene via targeted gene replacement in embryonic stem cells. Mice expressing human apoE2 (2/2) have virtually all the characteristics of type III hyperlipoproteinemia. Their plasma cholesterol and triglyceride levels are both twice to three times those in (normolipidemic) mice that are expressing human apoE3 (3/3) made in an identical manner. The 2/2 mice are markedly defective in clearing beta-migrating VLDL particles, and spontaneously develop atherosclerotic plaques, even on a regular diet. An atherogenic diet, high in fat and cholesterol, exacerbates development of atherosclerosis and xanthomas in the 2/2 mice. Thus, comparisons between the 2/2 and 3/3 mice unequivocally demonstrate that a single amino acid difference (Arg158 Cys) in the apoE protein is sufficient to cause type III HLP and spontaneous atherosclerosis in mice

Type III hyperlipoproteinemia and spontaneous atherosclerosis in mice resulting from gene replacement of mouse Apoe with human Apoe*2.

To study isoform-specific effects of apolipoprotein E (apoE) in vivo, we generated mice with a human APOE*2 allele in place of the mouse Apoe gene via targeted gene replacement in embryonic stem cells. Mice expressing human apoE2 (2/2) have virtually all the characteristics of type III hyperlipoproteinemia. Their plasma cholesterol and triglyceride levels are both twice to three times those in (normolipidemic) mice that are expressing human apoE3 (3/3) made in an identical manner. The 2/2 mice are markedly defective in clearing beta-migrating VLDL particles, and spontaneously develop atherosclerotic plaques, even on a regular diet. An atherogenic diet, high in fat and cholesterol, exacerbates development of atherosclerosis and xanthomas in the 2/2 mice. Thus, comparisons between the 2/2 and 3/3 mice unequivocally demonstrate that a single amino acid difference (Arg158 Cys) in the apoE protein is sufficient to cause type III HLP and spontaneous atherosclerosis in mice

Paradoxical enhancement of atherosclerosis by probucol treatment in apolipoprotein E-deficient mice.

Dietary administration of probucol (0.5%, wt/wt) efficiently reduced total plasma cholesterol levels in apolipoprotein E-deficient mice (apoE-/-) by 40%, with decreases in high density lipoprotein (HDL) and apoAI by 70 and 50%, respectively. Paradoxically, however, aortic atherosclerotic plaques in the probucol-treated apoE-/- mice formed more rapidly than in the untreated apoE-/- mice, and the lesions were two to four times larger and more mature regardless of sex, age, and genetic background (P < 10(-)6). Histologically, lesions in probucol-treated mice contained increased fibrous materials and cells other than foam cells, and were commonly associated with focal inflammation and aneurysmal dilatation. Probucol treatment also accelerated lesion development in apoE+/- mice fed an atherogenic diet, indicating that the adverse effect is not dependent on the complete absence of apoE. Furthermore, mice lacking apoE and apoAI have plasma lipoprotein profiles very similar to the probucol-treated apoE-/- mice, but do not have accelerated plaque development. Thus, the enhanced atherosclerosis in the probucol-treated animals is unlikely to be caused by the reduction of HDL and apoAI levels. Our data indicate that a reduction in plasma cholesterol caused by probucol does not necessarily lead to an antiatherogenic effect