Sunny H. Zhang, Ph.D.

Dissertation research performed under the guidence of Dr. Nobuyo N. Maeda

ABSTRACT
    Atherosclerosis is a complex disease that is multifactorial in nature. An animal model produces a great advantage in the study of lipid metabolic disorders and the pathogenesis of atherosclerosis. Apolipoprotein E (apo E) is a ligand for receptors that clear remnants of chylomicrons and very low density lipoproteins (VLDL). Lack of apo E is, therefore, expected to cause accumulation in plasma of cholesterol-rich remnants whose prolonged circulation should be atherogenic. Using gene targeting technique, we successfully disrupted the apo E gene in mouse ES cells and generated mice that lack apo E protein in their plasma. These mice look and behave like normal animals, and are fertile. On a low fat, low cholesterol diet, these mutant mice have 5-times normal plasma cholesterol, and develop foam cell lesions in the aorta by 3 months age. These spontaneous arterial lesions progress with time as indicated by their increase in size and complexity and by their broader distribution. By 5 months of age, foam cell deposits, free cholesterol and admixed smooth muscle cells comprise the atherosclerotic lesions. After 8-9 months of age, the arterial lesions show increased complexity and the formation of fibrous caps as well as calcifications. Involvement of coronary and pulmonary arteries is usually present at this time. When apo E-deficient mice are stressed by an atherogenic diet, high in fat and cholesterol, dramatic acceleration of the development of arterial lesions occurs. Extensive lipid deposition is also found outside the cardiovascular system. Mice heterozygous for the disrupted apo E gene are more susceptible to atherosclerosis than the normal mice, as shown by the induction of substantially larger atherosclerotic lesions by an atherogenic diet as compared to the normal mice. The cholesterol-lowering drug, lovastatin paradoxically doubled cholesterol levels in the apo E-deficient mice. Although probucol halved cholesterol levels, it increased the atheroma lesion size 4-fold. Vitamin C, vitamin E, and b-carotene cocktail retarded the lesion size progression by 40%, although the cholesterol levels in the apo E-deficient mice increased slightly. Our data show the apo E-deficient mice are of great value for investigating genetic and environmental factors that modify the atherogenic process.