ALTERED OVARIAN STEROL CARRIER PROTEIN EXPRESSION IN THE PREGNANT STREPTOZOTOCIN-TREATED DIABETIC RAT

Reproductive dysfunction in the diabetic female rat is associated with impaired folliculogenesis, reduced corpus luteum progesterone output, and spontaneous abortion. The underlying mechanism for reduced steroi d production remains unresolved. In this study we examined whether or not diabetes alters levels of P450 side-chain cleavage enzyme (P450(sc c)), 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), or the choleste rol transport proteins, steroidogenic acute regulatory (StAR) protein and sterol carrier protein-2 (SCP2), leading to lower progesterone lev els and pregnancy loss. Rats (Day 3 pregnant) received an injection of streptozotocin (STZ, 60 mg/kg; i.v.) to induce a diabetic state; P450 (scc), 3 beta-HSD, and SCP2 were examined by Western and Northern blot analysis in ovarian tissue 12 days after injection of STZ (diabetic r ats, n = 12) or vehicle (nondiabetic mts, n = 12). Serum progesterone, triglyceride, and beta-hydroxybutyrate (beta-H8A) levels were also ex amined. Results indicate that diabetic rats that aborted (diabetic -fe tus [Ft], n = 6) had significantly lower progesterone levels (7.04 +/- 2.6 ng/ml; p < 0.003) than nondiabetic animals (108.6 +/- 5.15 ng/ml) and diabetic +Ft animals (74.3 +/- 8.9 ng/ml, n = 6). Western blot an alysis of ovarian P450(scc) and 3 beta-HSD in the nondiabetic rats and the diabetic rats with fetuses indicated no significant difference. I n contrast, ovaries from diabetic animals without fetuses had signific antly lower SCP2 levels (p < 0.017) compared to controls. Concomitant with the reduction in SCP2, a 58-kDa SCP2-immunoreactive protein, refe rred to as sterol carrier protein-X (SCPx), increased significantly (p < 0.001). The C-terminal sequence of SCPx is identical to SCP2, while its N-terminal region is homologous with 3-oxoacyl coenzyme A thiolas e, an enzyme involved in fatty acid metabolism. Increased SCPx express ion coincided with increased serum triglyceride and beta-HBA levels, s uggesting that the enhanced SCPx level may coincide with an ovarian sh ift to fatty acid metabolism. When SCPx steady-state mRNA levels were measured using an SCPx-specific riboprobe (280-60 protected fragment) in a ribonuclease protection assay, ovarian SCPx mRNA levels in the di abetic animals were increased 4.2-fold compared to control SCPx mRNA l evels. Ovarian SMR mRNA levels were increased slightly in the diabetic animals, and ovarian P450(scc) and 3 beta-HSD mRNA levels were increa sed 3-fold in the diabetic animals that aborted relative to the nondia betic animals and the +Ft diabetic animals. Results of this study conf irm that SCPx mRNA levels are elevated following diabetes onset and th at StAR, P450(scc) and 3 beta-HSD mRNA levels do not correspond with t he reduced steroid hormone profile associated with diabetes. These res ults are concordant with the possibility that reduced steroid levels i n the diabetic animals reflect a loss of SCP2-mediated cholesterol tra nsport capacity as SCPx/S-oxoacyl coenzyme A thiolase expression is en hanced.