Effect of dietary cholesterol and alloxan-diabetes on tissue cholesterol and apolipoprotein E mRNA levels in the rabbit

Alloxan-diabetic rabbits develop hypercholesterolemia and hypertriglyceridemia in response to cholesterol feeding. To determine whether alterations in apolipoprotein composition of plasma lipoproteins were due to changes in apolipoprotein gene expression, we measured the steady state apoE mRNA levels in several tissues from both control and diabetic rabbits. Control rabbits were fed either chow or chow plus 1.5% cholesterol (chow-fed or cholesterol-fed groups) and diabetic rabbits were fed either chow or chow plus 0.5% cholesterol for dietary periods of 5, 21, and 42 days. The tissues examined were liver, small intestine, brain, adrenals, and aorta. ApoE mRNA levels were measured by Northern and dot blot analysis with a human apoE cDNA probe. In control rabbits fed either chow or cholesterol diets for up to 42 days, the steady state apoE mRNA levels remained relatively constant in all of the tissues examined. In contrast, in alloxan-diabetic rabbits fed a 0.5% cholesterol diet, apoE mRNA was reduced in liver, brain, and adrenals (46 +/- 19%, 56 +/- 5%, and 39 +/- 18% of chow-fed control, respectively), but showed little change in the aorta (91 +/- 22% of chow-fed control). Despite a similar increase in plasma cholesterol, the cholesterol content of the liver and adrenals of cholesterol-fed diabetic rabbits were 20% and 50%, respectively, of that of the liver and adrenals in cholesterol-fed control rabbits. The result that apoE mRNA levels and tissue cholesterol content are altered in the diabetic cholesterol-fed rabbit suggests that insulin deficiency in the rabbit may influence apoE gene expression and tissue cholesterol homeostasis.