The receptor for the low density lipoproteins (LDL) is expressed on the surface of cells and is critical for the removal of cholesterol from the blood. Mutations in the LDL receptor gene lead to defective removal of atherogenic lipoprotein particles from the circulation, and this leads to premature coronary artery atherosclerosis. Mutations in the LDL receptor gene lead to the disease familial hypercholesterolemia in man. A model system for this disease has been developed in the rabbit in which a partial deletion of a portion of the LDL receptor binding domain leads to both profound hyperlipidemia and atherosclerosis. This strain of rabbit, termed the Watanabe Heritable Hyperlipoproteinemic (WHHL) rabbit, provides a means to test a variety of hypotheses relevant to lipoprotein metabolism and atherosclerosis. We have initiated the development of a transgenic rabbit program to systematically investigate the impact of genes relevant to HDL metabolism, reverse cholesterol transport, and atherosclerosis. This basic science project was initiated by the cloning of genomic apolipoprotein A-I and the generation of a variety of constructs anticipated to induce overexpression of the linearized genomic construct. Superovulation strategies, mating techniques, rabbit nursery protocols, and DNA and specific protein assays have all been developed over the past 2 years. We have evaluated the endocrinologic basis for infertility in WHHL rabbits and have characterized aberrant corpus luteal steroidogenesis in WHHL rabbits. After refining our superovulation strategies, we have successfully generated 6 transgenic rabbits, 3 of which express apolipoprotein A-I. As little as 2 mg/dl of expression of human apolipoprotein A-I in the plasma of these rabbits have led to a 2-3 fold increase in the concentration of HDL cholesterol. We are currently characterizing the impact of overexpression of apolipoprotein A-I on both lipoprotein metabolism and on the ability of HDL to prevent atherosclerotic cardiovascular disease. The establishment of a transgenic rabbit program permits the direct testing of a central concept in cardiovascular research, the reverse cholesterol transport hypothesis.
