The overall objective of this proposal is to determine if there is a functional interaction between apolipo-protein (apo)E, hepatic lipase, and apoC-III in the metabolism and clearance of chylomicrons and high density lipoproteins (HDL). We will determine which of these individual proteins is rate-limiting in lipoprotein clearance and whether modulation of their interactions affects the development of atherosclerosis. The rabbit is used as the experimental model because of its sensitivity to apoE levels, its deficiency in hepatic lipase, and its exaggerated response to dietary cholesterol. Transgenic rabbits that overexpress human apoE, hepatic lipase, and apoC-III will be prepared using vectors that express these sequences at high levels in the liver or macrophage, or that permit induction in the small intestine in response to a high-fat cholesterol- supplemented atherogenic diet. The plasma lipoprotein distribution and metabolism in chow-fed and cholesterol-fed rabbits, as well as the formation of atherosclerotic lesions, will be examined. Cross-breeding experiments will allow us to determine if apoC-III can inhibit the interaction or activity of hepatic lipase, apoE, or other factors that regulate lipoprotein clearance. These experiments will test the hypothesis that apoE and hepatic lipase are rate limiting in chylomicron remnant and HDL metabolism and clearance, that apoC-III modulates apoE and hepatic lipase function, and that variations in the availability of these proteins mediate the dietary response to cholesterol, altering lipoprotein metabolism and leading to the development of atherosclerosis. These transgenic rabbits are expected to be important new models for elucidating molecular mechanisms that contribute to atherosclerosis.
