Differential expression of hepatic sterol carrier proteins in the streptozotocin-treated diabetic rat.

Sterol carrier protein-2 (SCP2) is a 13.2-kilodalton protein that has been implicated in intracellular cholesterol transport, whereas a related sterol carrier protein, sterol carrier protein-X (SCPx; 58 kilodaltons) has been suggested to function also in the beta-oxidation of fatty acids. Although diabetes-related hyperlipidemia and altered cholesterol metabolism have been extensively studied, the intracellular cholesterol transport capacity during hyperglycemic states has not been examined. The fact that beta-oxidation is increased in diabetes whereas hepatic cholesterol metabolism is reduced suggests that differential expression of these sterol carrier proteins may accompany diabetic dyslipidemia. In this study, SCP2 protein levels were reduced by 60% in mildly hypercholesterolemic (cholesterol, > 130 and < 150 mg/dl; P < 0.01) diabetic rats and by 90% in severely hypercholesterolemic (cholesterol, > 150 mg/dl; P < 0.002) diabetic animals. In contrast, hepatic SCPx protein expression increased (3.5-fold) after diabetes induction with streptozotocin (STZ). The decline in SCP2 was inversely related to serum cholesterol levels. Hepatic SCP messenger RNA levels examined by ribonuclease protection assay demonstrated that hepatic SCP messenger RNA was increased 2-fold in diabetic animals. Northern blot analysis indicated that both the 0.8-kilobase SCP2-specific and the 2.1-kilobase SCPx-specific transcripts increased after STZ injection. SCPx protein induction preceded the decline in SCP2 by 4-5 days. Insulin treatment reversed the increase in SCPx and prevented the decline in SCP2. We conclude that SCP2 and SCPx are differentially expressed in the STZ-diabetic rat and suggest that this change in SCP expression should be considered a potential contributing mechanism through which cholesterol metabolism may be altered in diabetes.